posted 07-18-2005 06:00 PM               

Rosetta Overview

Rosetta is the first mission designed to orbit and land on a comet. It consists of an orbiter, carrying 11 science experiments, and a lander, called 'Philae', carrying 10 additional instruments, for the most detailed study of a comet ever attempted.

Rosetta gets its name from the famous Rosetta stone that led to the deciphering of Egyptian hieroglyphics almost 200 years ago. Similarly, scientists hope that Rosetta will unlock the mysteries of how the Solar System evolved.

Objective

To rendezvous with Comet 67P/Churyumov-Gerasimenko where it will study the nucleus of the comet and its environment for nearly two years, and land a probe on its surface.

Mission

Rosetta is en route to Comet 67P/Churyumov-Gerasimenko, where it will make the most detailed study of a comet ever attempted. It will follow the comet on its journey through the inner Solar System, measuring the increase in activity as the icy surface is warmed up by the Sun. The lander will focus on the composition and structure of the comet nucleus material. It will also drill more than 20cm into the subsurface to collect samples for inspection by the lander's onboard laboratory.

What's special?

Comets are considered the primitive building blocks of the Solar System, and likely helped 'seed' the Earth with water, and maybe even life. By studying the nature of the comet’s dust and gas, Rosetta will help scientists learn more about the role of comets in the evolution of the Solar System.

Rosetta will be the first mission ever to orbit a comet's nucleus and land a probe on its surface. It will also be the first spacecraft to fly alongside a comet as it heads towards the inner Solar System, watching how a frozen comet is transformed by the warmth of the Sun.

Rosetta is the first space mission to journey beyond the main asteroid belt and rely solely on solar cells for power generation, rather than the traditional radio-isotope thermal generators. The new solar-cell technology used on the orbiter's two giant solar panels allows it to operate over 800 million kilometers from the Sun, where sunlight levels are only 4 percent of those on Earth.

Spacecraft

The main spacecraft measures 2.8 by 2.1 by 2.0 m with two 14 meter long solar panels. It carries instruments for remote sensing and radio science, and instruments to study the composition, mass distribution and dust flux of the comet’s nucleus, as well as the comet plasma environment and its interaction with the solar wind.

The orbiter's 11 scientific instruments are accommodated on one side of the spacecraft, which will permanently face the comet during the operational phase of the mission.

Until its release, the 100kg Philae lander is carried on the opposite side of the orbiter to the large high-gain antenna dish. As Philae touches down on the comet, two harpoons will anchor it to the surface; the self-adjusting landing gear will ensure that it stays upright, even on a slope, and then the lander's feet will drill into the ground to secure it to the comet’s surface in the low gravity environment. Philae carries nine scientific instruments, including a drill to sample subsurface material.

Journey

Rosetta launched on March 2, 2004 by an Ariane 5 G+ from Europe's spaceport in Kourou, French Guiana. To place it on the required orbit to rendezvous with Comet 67P/ Churyumov-Gerasimenko it will receive four gravity assist maneuvers: three from Earth (March 4, 2005, Nov. 13, 2007 and Nov. 13, 2009) and one from Mars (Feb. 25, 2007).

Rosetta will also pass by and image two asteroids: 2867 Steins on Sept. 5, 2008 and 21 Lutetia on July 10, 2010.

The spacecraft will enter deep space hibernation in July 2011 and will be woken up in January 2014, before rendezvousing with Comet 67P/ Churyumov-Gerasimenko in May 2014. It will follow the comet around the Sun and as it moves back out towards the orbit of Jupiter.

The lander, Philae, will be delivered to the comet's surface in November 2014.

posted 06-16-2006 03:55 AM            

The spacecraft will remain in Passive Cruise Mode until 26 July 2006. During the entire period, the spacecraft will be monitored on the basis of weekly ground station passes.

Operations for the Mars swing-by (February 2007) will start in August 2006, with another payload passive checkout (PC3), an intense tracking campaign around the Trajectory Correction Manoeuvre (DSM-2) in September, and the first payload Active Checkout (PC4) in November/December.

posted 02-25-2007 09:24 AM               

Rosetta successfully swings-by Mars — next target: Earth

At 03:57 CET today, mission controllers at ESOC, ESA's Space Operations Centre in Germany, confirmed Rosetta's successful swingby of Mars, a key milestone in the 7.1-thousand-million km journey of this unique spacecraft to its target comet in 2014.

The gravitational energy of Mars helped Rosetta change direction, while the spacecraft was decelerated with respect to the Sun by an estimated 7887 km/hour. The spacecraft is now on the correct track towards Earth - its next destination planet whose gravitational energy Rosetta will exploit in November this year to gain acceleration and continue on its trek.

posted 02-25-2007 09:35 AM               

Stunning image taken by the CIVA imaging instrument on Rosetta's Philae lander just 4 minutes before closest approach at a distance of some 1000 km from Mars.

A portion of the spacecraft and one of its solar arrays are visible in nice detail. Beneath, an area close to the Syrtis region is visible on the planet's disk.

Credits: CIVA / Philae / ESA Rosetta

posted 09-04-2008 04:16 PM               

Rosetta Steins fly-by timeline

The Rosetta spacecraft control room is buzzing with anticipation as Rosetta closes in on asteroid 2867 Steins. The fly-by timeline includes a series of critical events, culminating with closest approach - expected at 20:58 CEST, 5 September 2008.

At the time of closest approach, Rosetta is planned to be 800 km from the asteroid, passing by at a speed of 8.6 km/s relative to Steins. Both Rosetta and Steins will be illuminated by the Sun, providing an excellent opportunity for science observations.

Between 40 and 20 minutes before closest approach, Rosetta will be flipped and the spacecraft will switch to a specially designed asteroid fly-by mode, an optimal configuration that supports the intensive observation and tracking activity of the on-board instruments.

Although most scientific observations will take place in the few hours around closest approach, several instruments will be switched on for a longer time around the event.

ESA's Cebreros deep space antenna (DSA 2) in Cebreros, Spain, will be used for communications with Rosetta in the two days preceding closest approach. When the spacecraft is not visible from Cebreros or New Norcia, NASA's DSN (Deep Space Network) ground stations at Goldstone, Canberra and Madrid will provide support for tracking and for science operations.

Around closest approach, Rosetta will be 2.41 Astronomical Units, or about 360 million km, from Earth. Radio signals sent to and from the spacecraft will have a 20 minute one-way travel time.

Timeline of nominal fly-by events

Note: All event times are stated in ground time, CEST.

Time	-	Event
1 September
02:20	-	Instruments switched on (except OSIRIS which was already on for the navigation campaign)
4 September
07:20-11:20	-	Slot for possible trajectory correction manoeuvre (36 hours before closest approach)
13:20-18:20	-	Last opportunity to acquire images for optical navigation campaign
5 September
07:20-10:20	-	Slot for possible trajectory correction manoeuvre (12 hours before closest approach)
10:20	-	Navigation cameras switch to tracking mode - initially both used, then use CAM 'A' only (to be decided)
11:00	-	Uplink fly-by commands for asteroid fly-by mode (AFM). Includes an update to the command profile already on board & the final updated AFM commands (only if 1 CAM at least is tracking)
20:18-20:38	-	Spacecraft flip over
20:39	-	Spacecraft switches automatically to asteroid fly-by mode
20:56	-	Sun illuminates Rosetta from the back and the asteroid fully
20:58	-	Closest approach, at a planned distance of 800 km from the asteroid
22:27	-	First post-fly-by acquisition of signal (AOS) - telemetry received via NASA's Goldstone ground station
22:30	-	Start of science data download via Goldstone
6 September
12:00	-	Live streaming of Rosetta Steins fly-by press conference from the European Space Operations Centre begins
13:00	-	Images from fly-by published on ESA web
15:00	-	End of press conference streaming
16:01	-	End of reception of first set of science data

posted 09-05-2008 04:59 PM               

Rosetta Steins fly-by confirmed

The Rosetta control room at ESA's European Space Operations Centre, ESOC, received the first radio signal after closest approach to asteroid (2867) Steins at 22:14 CEST, confirming a smooth fly-by.

Closest approach took place at 20:58 CEST ground time, 20:38 CEST spacecraft time, at a distance of 800 km. Rosetta's relative speed with respect to Steins was 8.6 km/sec, or about 31 000 km/h. The exact time of closest approach will be confirmed over the next few days after a detailed analysis of telemetry data.

To optimise the science return from this historic encounter, a series of critical operations were executed before closest approach, some of which required the spacecraft flip over and change its orientation rapidly, pushing it to its design limits.

After the flip, at 20:39 CEST (ground time), Rosetta switched to the asteroid fly-by mode, during which its orientation was automatically controlled by the on-board navigation cameras. The asteroid was tracked continuously and kept it in the field of view of the imaging instruments.

At 20:48 CEST (ground time), while still in asteroid fly-by mode, Rosetta's high gain antenna was turned away from Earth and the science observations were carried out. Radio contact established again at 22:14 CEST and the first bit of telemetry was received through NASA's Goldstone antenna.

Science data download will start tomorrow morning, 6 September at about 02:00 CEST and continue through the night. Images and the preliminary results from the fly-by will be presented tomorrow at a press conference which be held at ESOC starting at 12:00 CEST. The press conference will be streamed on the web.

posted 09-06-2008 12:28 PM               

Steins: A diamond in the sky

Asteroid Steins seen from a distance of 800 km, taken by the OSIRIS imaging system from two different perspectives. The effective diameter of the asteroid is 5 km, approximately as predicted. At the top of the asteroid (as shown in this image), a large crater, approximately 1.5-km in size, can be seen. Scientists were amazed that the asteroid survived the impact that was responsible for the crater.

The first images from Rosetta's OSIRIS imaging system and VIRTIS infrared spectrometer were derived from raw data this morning and have delivered spectacular results.

"Steins looks like a diamond in the sky," said Uwe Keller, Principal Investigator for the OSIRIS imaging system from the Max Planck Institut Fuer Sonnensystemforschung, Lindau.

Visible in the image are several small craters on the asteroid, and two huge ones, one of which is 2 km in diameter, indicating that the asteroid must be very old.

The images are 50 to 60 pixels in diameter, enough to characterise the shape and other characteristics of the body of the asteroid.

Rita Schulz, Rosetta Project Scientist, said, "In the images is a chain of impact craters, which must have formed from recurring impact as the asteroid rotated. The impact may have been caused by a meteoroid stream, or fragments from a shattered small body."

The chain is composed of about 7 craters. To determine the age of the asteroid, a count of the craters on the asteroid's surface has been started (the more the number of craters, the older the asteroid). So far, 23 craters have been spotted.

From the images, scientists will try and understand why the asteroid is unusually bright, and how fine grains of the surface regolith are. This will tell them more about how the asteroid formed.

Gerhard Schwehm, Mission Manager for Rosetta said, "It looks like a typical asteroid, but it is really fascinating how much we can learn from just the images. This is our first science highlight; we certainly have a lot of promising science ahead of us. I'm already looking forward to encountering our next diamond in the sky, the much bigger Lutetia."

The OSIRIS imaging system's Wide Angle Camera (WAC) worked perfectly through the fly-by.

The OSIRIS team expects that the images that they will retrieve from the Narrow Angle Camera (NAC) will be of comparable resolution. This will add to the detailed colour information and hence to knowledge of the surface composition.

Science team members noted that the Narrow Angle Camera (NAC) appears to have switched to safe mode a few minutes before closest approach, but switched back on after a few hours. The software is programmed to switch to safe mode when certain parameter thresholds are crossed to protect the camera. The team will concentrate investigating the reasons for this anomaly once the science data has been analysed.

After analysis of the Rosetta data, Steins will be one of the best-characterised asteroids so far.

posted 11-13-2009 12:49 AM               

First view of Earth as Rosetta approaches home

This spectacular image of our home planet was captured by the OSIRIS instrument on ESA's Rosetta comet chaser on November 12 as the spacecraft approached Earth for the third and final swingby. Closest approach is due at 08:45 CET, 13 November 2009. Follow Rosetta's progress at ESA's dedicated Rosetta site and via the Rosetta Blog.

Credits: ESA MPS/UPD/LAM/IAA/RSSD/INTA/UPM/DASP/IDA

The image was acquired with the OSIRIS narrow-angle camera from a distance of 633 000 km on 12 November 2009 at 13:28 CET. The resolution is 12 km/pixel.

Three images with an orange, green, and blue filter were combined to create this one. The illuminated crescent is centered roughly around the South Pole (South at the bottom of the image). The outline of Antarctica is visible under the clouds that form the striking south-polar vortex. Pack ice in front of the coastline with its strong spectacular reflection is the cause for the very bright spots on the image.

The OSIRIS (Optical, Spectroscopic, and Infrared Remote Imaging System) is a wide-angle camera and a narrow-angle camera to obtain high-resolution images of the comet's nucleus and the asteroids that Rosetta passes on its voyage to Comet 67P/Churyumov-Gerasimenko. It will help in identifying the best landing sites.

posted 07-09-2010 06:45 PM               

Rosetta lines up for spectacular asteroid flyby

On 10 July, ESA's Rosetta will fly past 21 Lutetia, the largest asteroid ever visited by a satellite. After weeks of manoeuvres and a challenging optical navigation campaign, Rosetta is perfectly lined up to skim by at 3162 km at 18:10 CEST.

Rosetta is expected to pass Lutetia at a relative speed of 54 000 km/hr, when both are located some 454 million km from Earth. As Lutetia is a major scientific target of Rosetta's mission, most of the orbiter and lander instruments will be on for flyby, studying the asteroid's surface, dust environment, exosphere, magnetic field, mass and density.

The OSIRIS (Optical, Spectroscopic, and Infrared Remote Imaging System) camera system is expected to obtain visible-spectrum images before and at closest approach. The powerful imaging system is operated by the Max Planck Institute for Solar System Research, Germany. Although most scientific observations will be performed in the few hours around closest approach, several instruments will be on several days before or after.

Challenging optical navigation technique

Since 31 May, the navigation cameras and the OSIRIS scientific imaging system have been used in a challenging optical navigation campaign aimed at visually tracking Lutetia and determining its orbit with more accuracy.

Initially, images were taken twice a week; since late June, images have been taken daily and this will continue until 9 July.

The results of the optical navigation campaign have been used to programme a series of Trajectory Correction Manoeuvres (TCM), or thruster burns, to nudge Rosetta onto the optimum trajectory. After the last TCM on 18 June, analysis of the spacecraft's orbit indicated that remaining manoeuvre slots (one week, three days, 40 hours and 12 hours before flyby) will most likely not be used.

Intense preparations for a deep-space encounter

Preparations for Lutetia flyby have been underway for a number of months by scientists and engineers at ESA, the German Aerospace Center (DLR) and two dozen institutes and universities in Europe and the USA. In the past weeks, activities at the Agency, and especially within the mission's science and operations teams, have intensified.

"There are several special configurations for Rosetta, including a special 'Asteroid Fly-by Mode' in which the spacecraft can operate autonomously and use its cameras to guide its attitude. It's been a challenge, but we are looking forward to an excellent flyby," said Andrea Accomazzo, Rosetta Spacecraft Operations Manager at ESOC, ESA's European Space Operations Centre, Darmstadt, Germany.

Scientists at ESAC, ESA's European Space Astronomy Centre, in Spain, have generated a series of coordinated commands for individual instruments so that observations can be conducted autonomously as Rosetta passes the asteroid. These will be radioed up to Rosetta in advance of the flyby, which will be conducted without ground station contact.

About four hours before closest approach, mission controllers at ESOC will issue commands that will flip Rosetta over and ready the spacecraft to enter Asteroid Fly-by Mode. During this mode, the orientation of the spacecraft is automatically driven by the navigation cameras to continuously keep the asteroid in the field of view of the imaging instruments.

ESA-NASA cooperation for tracking Rosetta

Increased ground tracking support has been scheduled throughout the fly-by period. In addition to ESA's 35m deep-space stations at New Norcia, Australia, and Cebreros, Spain, NASA's 70m Deep Space Network (DSN) stations at Goldstone, California, Canberra, Australia, and Madrid, Spain, will assist in relaying commands and data. The two agencies often work together and regularly share tracking station resources.

Time-line of critical events 10 July

Note: Times shown are ground event times in Central European Summer Time (CEST = UTC/GMT + 2 hours). Spacecraft event time is 25 mins and 21 secs earlier. All times are estimates and may change.

Watch the live fly-by webcast from ESA/ESOC, 10 July 2010, starting 18:00 CEST.

Time	Event
00:00:00	Start of tracking - NASA/DSN Goldstone (GDS)
00:25:05	Start - Rosetta's NAVCAM asteroid tracking
05:30:00	End of tracking - NASA /DSN Goldstone (GDS)
05:33:00	Start of tracking - ESA/ESTRACK New Norcia station (NNO)
08:00:00	Final telecommands for flyby ready from ESA Flight Dynamics team
10:00:00	Uplink of updated final fly-by commands
10:20:00	Start of tracking - NASA/DSN Canberra (CAN)
12:20:00	End of tracking - NASA/DSN Canberra (CAN)
13:05:00	Start of tracking - ESA/ESTRACK Cebreros (CEB) & NASA/DSN Madrid (MAD)
14:30:00	End of tracking - ESA/ESTRACK Cebreros station (CEB)
15:26:00	End of tracking - ESA/ESTRACK New Norcia station (NNO)
13:50:07	Start Rosetta flip manoeuvre
14:30:07	End Rosetta flip manoeuvre
15:10:07	Start asteroid closed-loop tracking - Rosetta on self-navigation
18:00:00	Start media event live from ESA/ESOC
18:05:07	Stop - radio communications via high-gain antenna - Loss of signal (earliest)
18:10:07	Closest approach to Lutetia
18:20:07	End asteroid closed-loop tracking
18:45:07	Resume radio communications via high-gain antenna - Acquisition of signal (latest)
18:47:00	Media event pause
20:05:35	Start science data downlink
23:00:00	Resume media event - Science team presents data
23:45:00	End media event
23:55:00	End of tracking - NASA/DSN Madrid (MAD)

posted 07-10-2010 11:58 AM               

First pre-flyby images now available

Largest view of Lutetia shows asteroid at a distance of 80,000 km.

Credit: ESA

posted 07-10-2010 05:14 PM               

Rosetta triumphs at asteroid Lutetia

Asteroid Lutetia has been revealed as a battered world of many craters. ESA's Rosetta mission has returned the first close-up images of the asteroid showing it is most probably a primitive survivor from the violent birth of the Solar System.

Credit: ESA

Lutetia at Closest approach.

The flyby has been a spectacular success with Rosetta performing faultlessly. Closest approach took place at 18:10 CEST, at a distance of 3162 km.

The images show that Lutetia is heavily cratered, having suffered many impacts during its 4.5 billion years of existence. As Rosetta drew close, a giant bowl-shaped depression stretching across much of the asteroid rotated into view. The images confirm that Lutetia is an elongated body, with its longest side around 130km.

The images come from OSIRIS instrument, which combines a wide angle and a narrow angle camera. At closest approach, details down to a scale of 60 metres can be seen over the entire surface of Lutetia.

Credit: ESA

At a distance of 36000km the OSIRIS Narrow Angle Camera (NAC) took this image catching the planet Saturn in the background.

"I think this is a very old object. Tonight we have seen a remnant of the Solar System's creation," says Holger Sierks, OSIRIS principal investigator, Max Planck Institute for Solar System Research, Lindau.

Rosetta raced past the asteroid at 15 km/s completing the flyby in just a minute. But the cameras and other instruments had been working for hours and in some cases days beforehand, and will continue afterwards. Shortly after closest approach, Rosetta began transmitting data to Earth for processing.

Lutetia has been a mystery for many years. Ground-based telescopes have shown that the asteroid presents confusing characteristics. In some respects it resembles a C-type asteroid, a primitive body left over from the formation of the Solar System. In others, it looks like an M-type asteroid. These have been associated with iron meteorites, are usually reddish in colour and thought to be fragments of the cores of much larger objects.

The new images and the data from Rosetta's other instruments will help to decide but not tonight. Compositional information will be needed for that.

Credit: ESA

Zoom in on a possible landslide and boulders at the highest resolution.

Rosetta operated a full suite of instruments at the encounter, including remote sensing and in-situ measurements. Some of the payload of its Philae lander were also switched on. Together they looked for evidence of a highly tenuous atmosphere, magnetic effects, and studied the surface composition as well as the asteroid's density. They also attempted to catch any dust grains that may have been floating in space near the asteroid for on-board analysis. The results from these instruments will come in time.

The flyby marks the attainment of one of Rosetta's main scientific objectives. The spacecraft will now continue to its primary target, comet Churyumov-Gerasimenko. It will rendezvous with the comet in 2014, mapping it and studying it. It will then accompany the comet for months, from near the orbit of Jupiter down to its closest approach to the Sun. In November 2014, Rosetta will deploy Philae to land on the comet nucleus. "Wunderbar!" says David Southwood, ESA Director of Science and Robotic Exploration, "It has been a great day for exploration, a great day for European science. The clockwork precision is a great tribute to the scientists and engineers in our Member States in our industry and, not least, in ESA itself. Roll on 2014 and our comet rendezvous."

But for now, analysing the Lutetia data will now become the focus for the Rosetta instrument teams. Just twenty-four hours ago, Lutetia was a distant stranger. Now, thanks to Rosetta, it has become a close friend.

posted 01-19-2014 04:19 PM               

The most important alarm clock in the Solar System

At 10:00 GMT (4 a.m. CST) on Monday (Jan. 20), the most important alarm clock in the Solar System will wake up ESA's sleeping Rosetta spacecraft.

Rosetta is chasing comet 67P/Churyumov Gerasimenko and, since its launch in 2004, has made three flybys of Earth and one of Mars to build up enough speed and get on a trajectory towards the comet. It has also encountered asteroids Steins and Lutetia along the way.

Operating on solar energy alone, the spacecraft was placed into a deep space slumber in mid-2011 as it cruised far from the Sun and out towards the orbit of Jupiter. To prepare for its long sleep, Rosetta was oriented so that its solar arrays faced the Sun and put into a once per minute spin for stability.

The only devices left running were its computer and several heaters.

Thirty-one months later, Rosetta's orbit has brought it back to within 'only' 673 million kilometres of the Sun, and there is finally enough solar energy to power the spacecraft fully again. It is time to wake up.

Rosetta's computer is programmed to carry out a sequence of events to re-establish contact with Earth on 20 January, starting with an 'alarm clock' at 10:00 GMT.

Immediately after, the spacecraft's startrackers will begin to warm up, taking around six hours.

Then its thrusters will fire to stop the slow rotation. A slight adjustment will be made to Rosetta's orientation to ensure that the solar arrays are still facing directly towards the Sun, before the startrackers are switched on to determine the spacecraft's attitude.

Once that has been established, Rosetta will turn directly towards Earth, switch on its transmitter and point its high-gain antenna to send its signal to announce that it is awake.

Because of Rosetta's vast distance — just over 807 million kilometres from Earth — it will take 45 minutes for the signal to reach the ground stations. The first opportunity for receiving a signal on Earth is expected between 17:30 GMT and 18:30 GMT (1:30 p.m. and 2:30 p.m. CST).

Deep space tracking dishes will be listening out for the signal, starting with NASA's 'big ears' — the 70 m-diameter station at Goldstone, California, followed by, as the Earth rotates, the Canberra station in eastern Australia. ESA's New Norcia 35 m antenna, in Western Australia, would be next in line to await the signal's arrival.

Whenever the signal is received, it will be relayed immediately to ESOC, ESA's Operations Centre in Darmstadt, Germany.

This exciting moment will be announced to the world straightaway via the @ESA_Rosetta twitter account.

Once mission controllers have verified Rosetta's health, each of its scientific instruments will be switched back on and checked out, an effort that will take several months as the spacecraft continues to eat up the remaining 9 million kilometres separating it from the comet.

In May, Rosetta will make a major manoeuvre to line up for arriving at its target comet in August. If all goes well, it will become the first space mission to rendezvous with a comet, the first to attempt a landing, and the first to follow a comet as it swings around the Sun.

Comets are considered to be the primitive building blocks of the Solar System and likely helped to 'seed' Earth with water, and perhaps even the ingredients for life. But many fundamental questions about these enigmatic objects remain, and through its comprehensive, close-up study of comet 67P/Churyumov-Gerasimenko, Rosetta aims to unlock the secrets within.

posted 01-20-2014 12:25 PM               

ESA's 'sleeping beauty' wakes up from deep space hibernation

It was a fairy-tale ending to a tense chapter in the story of the Rosetta space mission this evening as ESA heard from its distant spacecraft for the first time in 31 months.

Rosetta is chasing down Comet 67P/Churyumov-Gerasimenko, where it will become the first space mission to rendezvous with a comet, the first to attempt a landing on a comet's surface, and the first to follow a comet as it swings around the Sun.

Since its launch in 2004, Rosetta has made three flybys of Earth and one of Mars to help it on course to its rendezvous with 67P/Churyumov-Gerasimenko, encountering asteroids Steins and Lutetia along the way.

Operating on solar energy alone, Rosetta was placed into a deep space slumber in June 2011 as it cruised out to a distance of nearly 800 million km from the warmth of the Sun, beyond the orbit of Jupiter.

Now, as Rosetta's orbit has brought it back to within 'only' 673 million km from the Sun, there is enough solar energy to power the spacecraft fully again.

Thus today (Jan. 20), still about 6 million miles (9 million km) from the comet, Rosetta's pre-programmed internal 'alarm clock' woke up the spacecraft. After warming up its key navigation instruments, coming out of a stabilising spin, and aiming its main radio antenna at Earth, Rosetta sent a signal to let mission operators know it had survived the most distant part of its journey.

The signal was received by NASA's Goldstone ground station in California at (12:18 p.m. CST) 18:18 GMT, during the first window of opportunity the spacecraft had to communicate with Earth.

It was immediately confirmed in ESA's space operations centre in Darmstadt and the successful wake-up announced via the @ESA_Rosetta twitter account, which tweeted: "Hello, World!"

"We have our comet-chaser back," says Alvaro Giménez, ESA's Director of Science and Robotic Exploration. "With Rosetta, we will take comet exploration to a new level. This incredible mission continues our history of 'firsts' at comets, building on the technological and scientific achievements of our first deep space mission Giotto, which returned the first close-up images of a comet nucleus as it flew past Halley in 1986."

"This was one alarm clock not to hit snooze on, and after a tense day we are absolutely delighted to have our spacecraft awake and back online," adds Fred Jansen, ESA's Rosetta mission manager.

Comets are considered the primitive building blocks of the Solar System and likely helped to 'seed' Earth with water, perhaps even the ingredients for life. But many fundamental questions about these enigmatic objects remain, and through its comprehensive, in situ study of Comet 67P/Churyumov-Gerasimenko, Rosetta aims to unlock the secrets contained within.

"All other comet missions have been flybys, capturing fleeting moments in the life of these icy treasure chests," says Matt Taylor, ESA's Rosetta project scientist. "With Rosetta, we will track the evolution of a comet on a daily basis and for over a year, giving us a unique insight into a comet's behaviour and ultimately helping us to decipher their role in the formation of the Solar System."

But first, essential health checks on the spacecraft must be completed. Then the eleven instruments on the orbiter and ten on the lander will be turned on and prepared for studying Comet 67P/Churyumov-Gerasimenko.

"We have a busy few months ahead preparing the spacecraft and its instruments for the operational challenges demanded by a lengthy, close-up study of a comet that, until we get there, we know very little about," says Andrea Accomazzo, ESA's Rosetta operations manager.

Rosetta's first images of 67P/Churyumov-Gerasimenko are expected in May, when the spacecraft is still 2 million km from its target. Towards the end of May, the spacecraft will execute a major manoeuvre to line up for its critical rendezvous with the comet in August.

After rendezvous, Rosetta will start with two months of extensive mapping of the comet's surface, and will also make important measurements of the comet's gravity, mass and shape, and assess its gaseous, dust-laden atmosphere, or coma. The orbiter will also probe the plasma environment and analyse how it interacts with the Sun's outer atmosphere, the solar wind.

Using these data, scientists will choose a landing site for the mission's 100 kg Philae probe. The landing is currently scheduled for 11 November and will be the first time that a landing on a comet has ever been attempted.

In fact, given the almost negligible gravity of the comet's 4 km-wide nucleus, Philae will have to use ice screws and harpoons to stop it from rebounding back into space after touchdown.

Among its wide range of scientific measurements, Philae will send back a panorama of its surroundings, as well as very high-resolution pictures of the surface. It will also perform an on-the-spot analysis of the composition of the ices and organic material, including drilling down to 23 cm below the surface and feeding samples to Philae's on-board laboratory for analysis.

The focus of the mission will then move to the 'escort' phase, during which Rosetta will stay alongside the comet as it moves closer to the Sun, monitoring the ever-changing conditions on the surface as the comet warms up and its ices sublimate.

The comet will reach its closest distance to the Sun on 13 August 2015 at about 185 million km, roughly between the orbits of Earth and Mars. Rosetta will follow the comet throughout the remainder of 2015, as it heads away from the Sun and activity begins to subside.

"We will face many challenges this year as we explore the unknown territory of comet 67P/Churyumov-Gerasimenko and I'm sure there will be plenty of surprises, but today we are just extremely happy to be back on speaking terms with our spacecraft," adds Matt Taylor.

posted 06-10-2014 04:08 PM               

NASA Instruments Begin Science on European Spacecraft Set to Land on Comet

Three NASA science instruments aboard the European Space Agency's (ESA) Rosetta spacecraft, which is set to become the first to orbit a comet and land a probe on its nucleus, are beginning observations and sending science data back to Earth.

Launched in March 2004, Rosetta was reactivated January 2014 after a record 957 days in hibernation. Composed of an orbiter and lander, Rosetta's objective is to arrive at comet 67P/Churyumov-Gerasimenko in August to study the celestial object up close in unprecedented detail and prepare for landing a probe on the comet's nucleus in November.

Rosetta's lander will obtain the first images taken from a comet's surface and will provide the first analysis of a comet's composition by drilling into the surface. Rosetta also will be the first spacecraft to witness at close proximity how a comet changes as it is subjected to the increasing intensity of the sun's radiation. Observations will help scientists learn more about the origin and evolution of our solar system and the role comets may have played in seeding Earth with water, and perhaps even life.

"We are happy to be seeing some real zeroes and ones coming down from our instruments, and cannot wait to figure out what they are telling us," said Claudia Alexander, Rosetta's U.S. project scientist at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California. "Never before has a spacecraft pulled up and parked next to a comet. That is what Rosetta will do, and we are delighted to play a part in such a historic mission of exploration."

Rosetta currently is approaching the main asteroid belt located between Jupiter and Mars,. The spacecraft is still about 300,000 miles (500,000 kilometers) from the comet, but in August the instruments will begin to map its surface.

The three U.S. instruments aboard the spacecraft are the Microwave Instrument for Rosetta Orbiter (MIRO), an ultraviolet spectrometer called Alice, and the Ion and Electron Sensor (IES). They are part of a suite of 11 science instruments aboard the Rosetta orbiter.

MIRO is designed to provide data on how gas and dust leave the surface of the nucleus to form the coma and tail that gives comets their intrinsic beauty. Studying the surface temperature and evolution of the coma and tail provides information on how the comet evolves as it approaches and leaves the vicinity of the sun.

Alice will analyze gases in the comet's coma, which is the bright envelope of gas around the nucleus of the comet developed as a comet approaches the sun. Alice also will measure the rate at which the comet produces water, carbon monoxide and carbon dioxide. These measurements will provide valuable information about the surface composition of the nucleus.

The instrument also will measure the amount of argon present, an important clue about the temperature of the solar system at the time the comet's nucleus originally formed more than 4.6 billion years ago.

IES is part of a suite of five instruments to analyze the plasma environment of the comet, particularly the coma. The instrument will measure the charged particles in the sun's outer atmosphere, or solar wind, as they interact with the gas flowing out from the comet while Rosetta is drawing nearer to the comet's nucleus.

NASA also provided part of the electronics package for the Double Focusing Mass Spectrometer, which is part of the Swiss-built Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) instrument. ROSINA will be the first instrument in space with sufficient resolution to be able to distinguish between molecular nitrogen and carbon monoxide, two molecules with approximately the same mass. Clear identification of nitrogen will help scientists understand conditions at the time the solar system was formed.

U.S. scientists are partnering on several non-U.S. instruments and are involved in seven of the mission's 21 instrument collaborations. NASA's Deep Space Network (DSN) is supporting ESA's Ground Station Network for spacecraft tracking and navigation.

posted 07-17-2014 11:18 AM               

The dual personality of comet 67P/C-G

This week's images of comet 67P/Churyumov-Gerasimenko reveal an extraordinarily irregular shape. We had hints of that in last week's images and in the unscheduled previews that were seen a few days ago, and in that short time it has become clear that this is no ordinary comet. Like its name, it seems that comet 67P/C-G is in two parts.

What the spacecraft is actually seeing is the pixelated image shown below, which was taken by Rosetta's OSIRIS narrow angle camera on 14 July from a distance of 12 000 km.

A second image and a movie show the comet after the image has been processed. The technique used, called "sub-sampling by interpolation", only acts to remove the pixelisation and make a smoother image, and it is important to note that the comet's surface features won't be as smooth as the processing implies. The surface texture has yet to be resolved simply because we are still too far away; any apparent brighter or darker regions may turn out to be false interpretations at this early stage.

But the movie, which uses a sequence of 36 interpolated images each separated by 20 minutes, certainly provides a truly stunning 360-degree preview of the overall complex shape of the comet. Regardless of surface texture, we can certainly see an irregular shaped world shining through. Indeed, some people have already likened the shape to a duck, with a distinct body and head.

Although less obvious in the 'real' image, the movie of interpolated images supports the presence of two definite components. One segment seems to be rather elongated, while the other appears more bulbous.

Dual objects like this – known as 'contact binaries' in comet and asteroid terminology – are not uncommon.

Indeed, comet 8P/Tuttle is thought to be such a contact binary; radio imaging by the ground-based Arecibo telescope in Puerto Rico in 2008 suggested that it comprises two sphere-like objects. Meanwhile, the bone-shaped comet 103P/Hartley 2, imaged during NASA's EPOXI flyby in 2011, revealed a comet with two distinct halves separated by a smooth region. In addition, observations of asteroid 25143 Itokawa by JAXA's Hayabusa mission, combined with ground-based data, suggest an asteroid comprising two sections of highly contrasting densities.

Is Rosetta en-route to rendezvous with a similar breed of comet? The scientific rewards of studying such a comet would be high, as a number of possibilities exist as to how they form.

One popular theory is that such an object could arise when two comets – even two compositionally distinct comets – melded together under a low velocity collision during the Solar System's formation billions of years ago, when small building blocks of rocky and icy debris coalesced to eventually create planets. Perhaps comet 67P/C-G will provide a unique record of the physical processes of accretion.

Or maybe it is the other way around – that is, a single comet could be tugged into a curious shape by the strong gravitational pull of a large object like Jupiter or the Sun; after all, comets are rubble piles with weak internal strength as directly witnessed in the fragmentation of comet Shoemaker-Levy 9 and the subsequent impacts into Jupiter, 20 years ago this week. Perhaps the two parts of comet 67P/C-G will one day separate completely.

On the other hand, perhaps comet 67P/C-G may have once been a much rounder object that became highly asymmetric thanks to ice evaporation. This could have happened when the comet first entered the Solar System from the Kuiper Belt, or on subsequent orbits around the Sun.

One could also speculate that the striking dichotomy of the comet's morphology is the result of a near catastrophic impact event that ripped out one side of the comet. Similarly, it is not unreasonable to think that a large outburst event may have weakened one side of the comet so much that it simply gave away, crumbling into space.

But, while the interpolated images are certainly brilliant, we need to be closer still to see a better three-dimensional view – not to mention to perform a spectroscopic analysis to determine the comet's composition – in order to draw robust scientific conclusions about this exciting comet.

Rosetta Mission Manager Fred Jansen comments: "We currently see images that suggest a rather complex cometary shape, but there is still a lot that we need to learn before jumping to conclusions. Not only in terms of what this means for comet science in general, but also regarding our planning for science observations, and the operational aspects of the mission such as orbiting and landing.

"We will need to perform detailed analyses and modelling of the shape of the comet to determine how best we can fly around such a uniquely shaped body, taking into account flight control and astrodynamics, the science requirements of the mission, and the landing-related elements like landing site analysis and lander-to-orbiter visibility. But, with fewer than 10 000 km to go before the 6 August rendezvous, our open questions will soon be answered."

posted 07-31-2014 09:46 AM               

Comet on 29 July 2014

The nucleus of Rosetta's target comet seen from a distance of 1,212 miles (1,950 km) on July 29, 2014.

One pixel corresponds to about 120 feet (37 m) in this narrow-angle camera view. The bright neck between the two lobes of the nucleus is becoming more and more distinct.

posted 08-02-2014 12:20 PM               

Comet at 1000 km

Rosetta sees the comet just five days before arrival.

This image was acquired Aug. 1 at 04:48 CEST (02:48 UTC) by the OSIRIS Narrow Angle Camera on board ESA's Rosetta spacecraft. The distance was approximately 1000 km. Note that the dark spot is an artifact from the onboard CCD.

posted 08-04-2014 06:00 PM               

Comet at 300 km

Rosetta navigation camera (NAVCAM) image taken on Aug. 3, 2014 at about 300 km from comet 67P/C-G. The Sun is towards the bottom of the image in the depicted orientation.

posted 08-06-2014 05:24 AM               

Rosetta arrives at comet destination

After a decade-long journey chasing its target, ESA's Rosetta has today (Aug. 6) become the first spacecraft to rendezvous with a comet, opening a new chapter in Solar System exploration.

Comet 67P/Churyumov–Gerasimenko and Rosetta now lie 405 million kilometers from Earth, about half way between the orbits of Jupiter and Mars, rushing towards the inner Solar System at nearly 55 000 kilometers per hour.

The comet is in an elliptical 6.5-year orbit that takes it from beyond Jupiter at its furthest point, to between the orbits of Mars and Earth at its closest to the Sun. Rosetta will accompany it for over a year as they swing around the Sun and back out towards Jupiter again.

Above: This animation comprises 101 images acquired by the Navigation Camera on board ESA's Rosetta spacecraft as it approached comet 67P/C-G in August 2014. The first image was taken on 1 August at 11:07 UTC (12:07 CEST), at a distance of 832 km. The last image was taken 6 August at 06:07 UTC (08:07 CEST) at a distance of 110 km.

Comets are considered to be primitive building blocks of the Solar System and may have helped to 'seed' Earth with water, perhaps even the ingredients for life. But many fundamental questions about these enigmatic objects remain, and through a comprehensive,in situstudy of the comet, Rosetta aims to unlock the secrets within.

The journey to the comet was not straightforward, however. Since its launch in 2004, Rosetta had to make three gravity-assist flybys of Earth and one of Mars to help it on course to its rendezvous with the comet. This complex course also allowed Rosetta to pass by asteroids Šteins and Lutetia, obtaining unprecedented views and scientific data on these two objects.

"After ten years, five months and four days traveling towards our destination, looping around the Sun five times and clocking up 6.4 billion kilometers, we are delighted to announce finally 'we are here'," says Jean-Jacques Dordain, ESA's Director General.

"Europe's Rosetta is now the first spacecraft in history to rendezvous with a comet, a major highlight in exploring our origins. Discoveries can start."

Today saw the last of a series of ten rendezvous maneuvers that began in May to adjust Rosetta's speed and trajectory gradually to match those of the comet. If any of these maneuvers had failed, the mission would have been lost, and the spacecraft would simply have flown by the comet.

"Today's achievement is a result of a huge international endeavor spanning several decades," says Alvaro Giménez, ESA's Director of Science and Robotic Exploration.

"We have come an extraordinarily long way since the mission concept was first discussed in the late 1970s and approved in 1993, and now we are ready to open a treasure chest of scientific discovery that is destined to rewrite the textbooks on comets for even more decades to come."

The comet began to reveal its personality while Rosetta was on its approach. Images taken by the OSIRIS camera between late April and early June showed that its activity was variable. The comet's 'coma' — an extended envelope of gas and dust — became rapidly brighter and then died down again over the course of those six weeks.

In the same period, first measurements from the Microwave Instrument for the Rosetta Orbiter, MIRO, suggested that the comet was emitting water vapor into space at about 300 milliliters per second.

Meanwhile, the Visible and Infrared Thermal Imaging Spectrometer, VIRTIS, measured the comet's average temperature to be about –70ºC, indicating that the surface is predominantly dark and dusty rather than clean and icy.

Then, stunning images taken from a distance of about 12,000 km began to reveal that the nucleus comprises two distinct segments joined by a 'neck,' giving it a duck-like appearance. Subsequent images showed more and more detail — the most recent, highest-resolution image was downloaded from the spacecraft earlier today and will be available this afternoon.

"Our first clear views of the comet have given us plenty to think about," says Matt Taylor, ESA's Rosetta project scientist.

"Is this double-lobed structure built from two separate comets that came together in the Solar System's history, or is it one comet that has eroded dramatically and asymmetrically over time? Rosetta, by design, is in the best place to study one of these unique objects."

Today, Rosetta is just 100 km from the comet's surface, but it will edge closer still. Over the next six weeks, it will describe two triangular-shaped trajectories in front of the comet, first at a distance of 100 km and then at 50 km.

At the same time, more of the suite of instruments will provide a detailed scientific study of the comet, scrutinizing the surface for a target site for the Philae lander.

Eventually, Rosetta will attempt a close, near-circular orbit at 30 km and, depending on the activity of the comet, perhaps come even closer.

"Arriving at the comet is really only just the beginning of an even bigger adventure, with greater challenges still to come as we learn how to operate in this unchartered environment, start to orbit and, eventually, land," says Sylvain Lodiot, ESA's Rosetta spacecraft operations manager.

As many as five possible landing sites will be identified by late August, before the primary site is identified in mid-September. The final timeline for the sequence of events for deploying Philae – currently expected for 11 November – will be confirmed by the middle of October.

"Over the next few months, in addition to characterizing the comet nucleus and setting the bar for the rest of the mission, we will begin final preparations for another space history first: landing on a comet," says Matt.

"After landing, Rosetta will continue to accompany the comet until its closest approach to the Sun in August 2015 and beyond, watching its behavior from close quarters to give us a unique insight and realtime experience of how a comet works as it hurtles around the Sun."

posted 08-06-2014 10:10 AM               

Postcards from Rosetta

Stunning close up detail focusing on a smooth region on the 'base' of the 'body' section of comet 67P/Churyumov-Gerasimenko.

The image was taken by Rosetta's OSIRIS narrow-angle camera and downloaded today, 6 August. The image clearly shows a range of features, including boulders, craters and steep cliffs.

The image was taken from a distance of 130 km and the image resolution is 2.4 metres per pixel.

Close-up detail of comet 67P/Churyumov-Gerasimenko.

The image was taken by Rosetta's OSIRIS narrow-angle camera and downloaded today, 6 August. The image shows the comet's 'head' at the left of the frame, which is casting shadow onto the 'neck' and 'body' to the right.

The image was taken from a distance of 120 km and the image resolution is 2.2 metres per pixel.

posted 08-26-2014 09:36 AM               

Rosetta: Landing site search narrows

Using detailed information collected by ESA's Rosetta spacecraft during its first two weeks at Comet 67P/Churyumov-Gerasimenko, five locations have been identified as candidate sites to set down the Philae lander in November – the first time a landing on a comet has ever been attempted.

Before arrival, Comet 67P/Churyumov-Gerasimenko had never been seen close up and so the race to find a suitable landing site for the 100 kg lander could only begin when Rosetta rendezvoused with the comet on 6 August.

The landing is expected to take place in mid-November when the comet is about 450 million km from the Sun, before activity on the comet reaches levels that might jeopardise the safe and accurate deployment of Philae to the comet's surface, and before surface material is modified by this activity.

The comet is on a 6.5-year orbit around the Sun and today is 522 million km from it. At their closest approach on 13 August 2015, just under a year from now, the comet and Rosetta will be 185 million km from the Sun, meaning an eightfold increase in the light received from the Sun.

While Rosetta and its scientific instruments will watch how the comet evolves as heating by the Sun increases, observing how its coma develops and how the surface changes over time, the lander Philae and its instruments will be tasked with making complementary in situ measurements at the comet's surface. The lander and orbiter will also work together using the CONSERT experiment to send and detect radio waves through the comet's interior, in order to characterise its internal structure.

Choosing the right landing site is a complex process. That site must balance the technical needs of the orbiter and lander during all phases of the separation, descent, and landing, and during operations on the surface with the scientific requirements of the 10 instruments on board Philae.

A key issue is that uncertainties in the navigation of the orbiter close to the comet mean that it is only possible to specify any given landing zone in terms of an ellipse – covering up to one square kilometre – within which Philae might land.

For each possible zone, important questions must be asked: Will the lander be able to maintain regular communications with Rosetta? How common are surface hazards such as large boulders, deep crevasses or steep slopes? Is there sufficient illumination for scientific operations and enough sunlight to recharge the lander's batteries beyond its initial 64-hour lifetime, while not so much as to cause overheating?

To answer these questions, data acquired by Rosetta from about 100 km distance have been used, including high-resolution images of the surface, measurements of the comet's surface temperature, and the pressure and density of gas around the nucleus. In addition, measurements of the comet's orientation with respect to the Sun, its rotation, mass and surface gravity have been determined. All of these factors influence the technical feasibility of landing at any specific location on the comet.

This weekend, the Landing Site Selection Group (comprising engineers and scientists from Philae's Science, Operations and Navigation Centre at CNES, the Lander Control Centre at DLR, scientists representing the Philae Lander instruments and ESA's Rosetta team) met at CNES, Toulouse, to consider the available data and determine a shortlist of five candidate sites.

"This is the first time landing sites on a comet have been considered," says Stephan Ulamec, Lander Manager at DLR.

"Based on the particular shape and the global topography of Comet 67P/ Churyumov-Gerasimenko, it is probably no surprise that many locations had to be ruled out. The candidate sites that we want to follow up for further analysis are thought to be technically feasible on the basis of a preliminary analysis of flight dynamics and other key issues – for example they all provide at least six hours of daylight per comet rotation and offer some flat terrain. Of course, every site has the potential for unique scientific discoveries."

"The comet is very different to anything we've seen before, and exhibits spectacular features still to be understood," says Jean-Pierre Bibring, a lead lander scientist and principal investigator of the CIVA instrument.

"The five chosen sites offer us the best chance to land and study the composition, internal structure and activity of the comet with the ten lander experiments."

The sites were assigned a letter from an original pre-selection of 10 possible sites, which does not signify any ranking. Three sites (B, I and J) are located on the smaller of the two lobes of the comet and two sites (A and C) are located on the larger lobe.

Summary of the five candidate sites

• Site A
  Site A is an interesting region located on the larger lobe, but with a good view of the smaller lobe. The terrain between the two lobes is likely the source of some outgassing. Higher-resolution imaging is needed to study potential surface hazards such as small depressions and slopes, while the illumination conditions also need to be considered further.

• Site B
  Site B, within the crater-like structure on the smaller lobe, has a flat terrain and is thus considered relatively safe for landing, but illumination conditions may pose a problem when considering the longer-term science planning of Philae. Higher-resolution imaging will be needed to assess the boulder hazards in more detail. In addition, the boulders are also thought to represent more recently processed material and therefore this site may not be as pristine as some of the others.

• Site C
  Site C is located on the larger lobe and hosts a range of surface features including some brighter material, depressions, cliffs, hills and smooth plains, but higher-resolution imaging is needed to assess the risk of some of these features. It is also well illuminated, which would benefit the long-term scientific planning for Philae.

• Site I
  Site I is a relatively flat area on the smaller lobe that may contain some fresh material, but higher-resolution imaging is needed to assess the extent of the rough terrain. The illumination conditions should also allow for longer-term science planning.

• Site J
  Site J is similar to site I, and also on the smaller lobe, offering interesting surface features and good illumination. It offers advantages for the CONSERT experiment compared with Site I, but higher-resolution imaging is needed to determine the details of the terrain, which shows some boulders and terracing.

The next step is a comprehensive analysis of each of the candidate sites, to determine possible orbital and operational strategies that could be used for Rosetta to deliver the lander to any of them. At the same time, Rosetta will move to within 50 km of the comet, allowing a more detailed study of the proposed landing sites.

By 14 September, the five candidate sites will have been assessed and ranked, leading to the selection of a primary landing site, for which a fully detailed strategy for the landing operations will be developed, along with a backup.

During this phase, Rosetta will move to within 20–30 km of the comet, allowing even more detailed maps of the boulder distributions at the primary and backup landing sites to be made. This information could be important in deciding whether to switch from primary to backup.

The Rosetta mission team are working towards a nominal landing date of 11 November, but confirmation of the primary landing site and the date will likely only come on 12 October. This will be followed by a formal Go/No Go from ESA, in agreement with the lander team, after a comprehensive readiness review on 14 October.

"The process of selecting a landing site is extremely complex and dynamic; as we get closer to the comet, we will see more and more details, which will influence the final decision on where and when we can land," says Fred Jansen, ESA Rosetta mission manager.

"We had to complete our preliminary analysis on candidate sites very quickly after arriving at the comet, and now we have just a few more weeks to determine the primary site. The clock is ticking and we now have to meet the challenge to pick the best possible landing site."

posted 09-15-2014 07:56 AM               

'J' marks the spot for Rosetta's lander

Rosetta's lander Philae will target Site J, an intriguing region on Comet 67P/Churyumov–Gerasimenko that offers unique scientific potential, with hints of activity nearby, and minimum risk to the lander compared to the other candidate sites.

Site J is on the 'head' of the comet, an irregular shaped world that is just over 4 km across at its widest point. The decision to select Site J as the primary site was unanimous. The backup, Site C, is located on the 'body' of the comet.

Above: Philae's primary landing site will target Site J, the centre of which is indicated by the cross in this OSIRIS narrow-angle image. (ESA)

The 100 kg lander is planned to reach the surface on 11 November, where it will perform indepth measurements to characterise the nucleus in situ, in a totally unprecedented way.

But choosing a suitable landing site has not been an easy task.

"As we have seen from recent close-up images, the comet is a beautiful but dramatic world – it is scientifically exciting, but its shape makes it operationally challenging," says Stephan Ulamec, Philae Lander Manager at the DLR German Aerospace Center.

"None of the candidate landing sites met all of the operational criteria at the 100% level, but Site J is clearly the best solution."

"We will make the first ever in situ analysis of a comet at this site, giving us an unparalleled insight into the composition, structure and evolution of a comet," says Jean-Pierre Bibring, a lead lander scientist and principal investigator of the CIVA instrument at the IAS in Orsay, France.

"Site J in particular offers us the chance to analyse pristine material, characterise the properties of the nucleus, and study the processes that drive its activity."

Above: Context image showing the location of the primary landing site for Rosetta's lander Philae. (ESA)

The race to find the landing site could only begin once Rosetta arrived at the comet on 6 August, when the comet was seen close-up for the first time. By 24 August, using data collected when Rosetta was still about 100 km from the comet five candidate regions had been identified for further analysis.

Since then, the spacecraft has moved to within 30 km of the comet, affording more detailed scientific measurements of the candidate sites. In parallel, the operations and flight dynamics teams have been exploring options for delivering the lander to all five candidate landing sites.

Over the weekend, the Landing Site Selection Group of engineers and scientists from Philae's Science, Operations and Navigation Centre at France's CNES space agency, the Lander Control Centre at DLR, scientists representing the Philae Lander instruments and ESA's Rosetta team met at CNES, Toulouse, France, to consider the available data and to choose the primary and backup sites.

A number of critical aspects had to be considered, not least that it had to be possible to identify a safe trajectory for deploying Philae to the surface and that the density of visible hazards in the landing zone should be minimal. Once on the surface, other factors come into play, including the balance of daylight and nighttime hours, and the frequency of communications passes with the orbiter.

The descent to the comet is passive and it is only possible to predict that the landing point will place within a 'landing ellipse' typically a few hundred metres in size.

A one square kilometre area was assessed for each candidate site. At Site J, the majority of slopes are less than 30º relative to the local vertical, reducing the chances of Philae toppling over during touchdown. Site J also appears to have relatively few boulders, and receives sufficient daily illumination to recharge Philae and continue science operations on the surface beyond the initial battery-powered phase.

Provisional assessment of the trajectory to Site J found that the descent time of Philae to the surface would be about seven hours, a length that does not compromise the on-comet observations by using up too much of the battery during the descent.

Above: Close-up of Philae's primary landing site J, which is located on the 'head' of Comet 67P/Churyumov–Gerasimenko. The image was taken by Rosetta's OSIRIS narrow-angle camera on 20 August 2014 from a distance of about 67 km. The image scale is 1.2 metres/pixel. (ESA)

Both Sites B and C were considered as the backup, but C was preferred because of a higher illumination profile and fewer boulders. Sites A and I had seemed attractive during first rounds of discussion, but were dismissed at the second round because they did not satisfy a number of the key criteria.

A detailed operational timeline will now be prepared to determine the precise approach trajectory of Rosetta in order to deliver Philae to Site J. The landing must take place before mid-November, as the comet is predicted to grow more active as it moves closer to the Sun.

"There's no time to lose, but now that we're closer to the comet, continued science and mapping operations will help us improve the analysis of the primary and backup landing sites," says ESA Rosetta flight director Andrea Accomazzo.

"Of course, we cannot predict the activity of the comet between now and landing, and on landing day itself. A sudden increase in activity could affect the position of Rosetta in its orbit at the moment of deployment and in turn the exact location where Philae will land, and that's what makes this a risky operation."

Once deployed from Rosetta, Philae's descent will be autonomous, with commands having been prepared by the Lander Control Centre at DLR, and uploaded via Rosetta mission control before separation.

During the descent, images will be taken and other observations of the comet's environment will be made.

Once the lander touches down, at the equivalent of walking pace, it will use harpoons and ice screws to fix it onto the surface. It will then make a 360° panoramic image of the landing site to help determine where and in what orientation it has landed.

The initial science phase will then begin, with other instruments analysing the plasma and magnetic environment, and the surface and subsurface temperature. The lander will also drill and collect samples from beneath the surface, delivering them to the onboard laboratory for analysis. The interior structure of the comet will also be explored by sending radio waves through the surface towards Rosetta.

"No one has ever attempted to land on a comet before, so it is a real challenge," says Fred Jansen, ESA Rosetta mission manager. "The complicated 'double' structure of the comet has had a considerable impact on the overall risks related to landing, but they are risks worth taking to have the chance of making the first ever soft landing on a comet."

The landing date should be confirmed on 26 September after further trajectory analysis and the final Go/No Go for a landing at the primary site will follow a comprehensive readiness review on 14 October.

posted 10-01-2014 08:29 AM               

Rosetta to deploy lander on November 12

The European Space Agency's Rosetta mission will deploy its lander, Philae, to the surface of Comet 67P/Churyumov–Gerasimenko on Nov. 12.

Philae's landing site, currently known as Site J, is located on the smaller of the comet's two 'lobes', with a backup site on the larger lobe. The sites were selected just six weeks after Rosetta arrived at the comet on Aug. 6, following its 10-year journey through the Solar System.

In that time, the Rosetta mission has been conducting an unprecedented scientific analysis of the comet, a remnant of the Solar System's 4.6 billion-year history. The latest results from Rosetta will be presented on the occasion of the landing, during dedicated press briefings.

The main focus to date has been to survey 67P/Churyumov–Gerasimenko in order to prepare for the first ever attempt to soft-land on a comet.

Site J was chosen unanimously over four other candidate sites as the primary landing site because the majority of terrain within a square kilometre area has slopes of less than 30º relative to the local vertical and because there are relatively few large boulders. The area also receives sufficient daily illumination to recharge Philae and continue surface science operations beyond the initial 64-hour battery-powered phase.

Over the last two weeks, the flight dynamics and operations teams at ESA have been making a detailed analysis of flight trajectories and timings for Rosetta to deliver the lander at the earliest possible opportunity.

Two robust landing scenarios have been identified, one for the primary site and one for the backup. Both anticipate separation and landing on Nov. 12.

For the primary landing scenario, targeting Site J, Rosetta will release Philae at 08:35 GMT/09:35 CET at a distance of 22.5 km from the centre of the comet, landing about seven hours later. The one-way signal travel time between Rosetta and Earth on Nov. 12 is 28 minutes 20 seconds, meaning that confirmation of the landing will arrive at Earth ground stations at around 16:00 GMT/17:00 CET.

If a decision is made to use the backup Site C, separation will occur at 13:04 GMT/14:04 CET, 12.5 km from the centre of the comet. Landing will occur about four hours later, with confirmation on Earth at around 17:30 GMT/18:30 CET. The timings are subject to uncertainties of several minutes.

Final confirmation of the primary landing site and its landing scenario will be made on Oct. 14 after a formal Lander Operations Readiness Review, which will include the results of additional high-resolution analysis of the landing sites conducted in the meantime. Should the backup site be chosen at this stage, landing can still occur on Nov. 12.

A competition for the public to name the primary landing site will also be announced during the week of Oct. 14.

The Rosetta orbiter will continue to study the comet and its environment using its 11 science instruments as they orbit the Sun together. The comet is on an elliptical 6.5-year orbit that takes it from beyond Jupiter at its furthest point, to between the orbits of Mars and Earth at its closest to the Sun. Rosetta will accompany the comet for more than a year as they swing around the Sun and back to the outer Solar System again.

The analyses made by the Rosetta orbiter will be complemented by the in situ measurements performed by Philae's 10 instruments.

posted 11-06-2014 06:53 AM               

Farewell 'J', hello Agilkia

The site where Rosetta's Philae lander is scheduled to touch down on Comet 67P/Churyumov–Gerasimenko on 12 November now has a name: Agilkia.

The landing site, previously known as 'Site J', is named for Agilkia Island, an island on the Nile River in the south of Egypt. A complex of Ancient Egyptian buildings, including the famous Temple of Isis, was moved to Agilkia from the island of Philae when the latter was flooded during the building of the Aswan dams last century.

The name was selected by a jury comprising members of the Philae Lander Steering Committee as part of a public competition run 16–22 October by ESA and the German, French and Italian space agencies.

Agilkia was one of the most popular entries – it was proposed by over 150 participants. The committee selected Alexandre Brouste from France as the overall winner. As a prize, Mr Brouste will be invited to ESA's Space Operations Control Centre in Darmstadt, Germany, to follow the landing live.

Although perhaps not quite as complicated as navigating Rosetta and Philae towards the comet, the task of choosing a name was by no means simple. More than 8000 entries from 135 countries were received in one week, showing great creativity and cultural diversity.

"The decision was very tough," says Prof. Felix Huber of the DLR German Aerospace Center, chair of the Steering Committee.

"We received so many good suggestions on how to name Site J, and we were delighted with such an enthusiastic response from all over the world. We wish to thank all participants for sharing their great ideas with us."

Participants proposed names in a variety of languages, both ancient and modern; some were even in Esperanto. There were also some interesting acronyms, curious sequences of digits, and onomatopoeiac words.

The entries covered a tremendous range of themes, from abstract concepts to the names of places on Earth. As with the winning entry, many suggestions echoed the Egyptian origins of Rosetta and Philae, named in recognition of milestones in decoding hieroglyphics, the sacred writing system of ancient Egypt.

Many names dated back to the history of our planet's exploration, as those journeys into the unknown are the natural forebears of Rosetta and Philae. Mythological names from all over the globe were also proposed, including gods and goddesses of water, fertility, life and creation, relating closely to the fundamental themes investigated by the mission.

Other names were drawn from ancient history and prehistory, while others recalled milestones in the history of science, particularly the history of our understanding of comets.

The progress of the Space Age was also honoured by many entries. There were many references to science fiction, celebrating the work of Jules Verne, Arthur C. Clarke and Douglas Adams, among others.

Fictional characters from films, television shows, literary and musical works were also proposed. Some even referred to the virtual astronauts of the Kerbal Space Program, a popular online space exploration game.

Several entries acknowledged the Rosetta mission as an endeavour achieved through the cooperation of many European countries, while others referred to its groundbreaking technical and scientific achievements.

And, of course, there was no shortage of more humorous entries, many referring to the resemblance of the comet's nucleus to a rubber duck, a potato or even the cartoon dog, Snoopy.

But the final choice is Agilkia, which is how the landing site on the comet will be referred to by ESA and its mission partners.

"And it couldn't be a more appropriate name," comments Fred Jansen, ESA Rosetta mission manager. "The relocation of the temples of Philae Island to Agilkia Island was an ambitious technical endeavour performed in the 1960s and 1970s to preserve an archaeological record of our ancient history.

"In eight days' time, Philae will be deployed from the orbiter onto Agilkia. On 12 November, we'll be attempting a unique comet landing, an even more ambitious endeavour to unlock secrets of our most remote origins."

About the landing

Rosetta will release Philae at 08:35 GMT/09:35 CET on 12 November at a distance of 22.5 km from the centre of the comet, with a scheduled landing about seven hours later at Agilkia.

Taking into account the signal travel time from Rosetta on 12 November, confirmation of landing is expected on Earth at around 16:00 GMT/17:00 CET.

posted 11-12-2014 04:07 AM               

Rosetta and Philae separation confirmed

The Philae lander has separated from the Rosetta orbiter, and is now on its way to becoming the first spacecraft to touch down on a comet.

Separation was confirmed at ESA's Space Operation Centre, ESOC, in Darmstadt, Germany at 3:03 a.m. CST (0903 GMT) on Wednesday (Nov. 12). It takes the radio signals from the transmitter on Rosetta 28 minutes and 20 seconds to reach Earth, so separation actually occurred in space at 2:35 a.m. CST (0835 GMT).

The first signal from Philae is expected in around two hours, when the lander establishes a communication link with Rosetta. Philae cannot send its data to Earth directly — it must do it via Rosetta.

Once the link has been established, the lander will relay via Rosetta a status report of its health, along with the first science data. This will include images taken of the orbiter shortly after separation.

The descent to the surface of Comet 67P/Churyumov–Gerasimenko will take around seven hours, during which the lander will take measurements of the environment around the comet. It will also take images of the final moments of descent.

Confirmation of a successful touchdown is expected in a one-hour window centred on 11:02 a.m. CST (1702 GMT). The first image from the surface is expected some two hours later.

posted 11-12-2014 05:44 PM               

'Philae is on the comet!' ESA probe makes historic first touchdown on comet

A small European space probe has become the first manmade object in history to touch down on the surface of a comet

And it may have done it twice.

Philae, the European Space Agency's three-legged lander, successfully fell to the surface of Comet 67P/Churyumov-Gerasimenko after a seven-hour, suspenseful descent on Wednesday (Nov. 12). The unprecedented touchdown was confirmed at 11:03 a.m. EST (1603 GMT), 28 minutes and 20 seconds after it occurred, given the time needed for the lander's signal to reach Earth.

"We're there and Philae is talking to us," Stephan Ulamec, the director of the Philae landing team at the DLR German Aerospace Center, said just moments after cheers erupted in the control room. "We are sitting on the surface. We are on the comet."

posted 11-13-2014 06:24 AM               

Welcome to a comet

Rosetta's lander Philae is safely on the surface of Comet 67P/Churyumov-Gerasimenko, as these first two CIVA images confirm. One of the lander's three feet can be seen in the foreground. The image is a two-image mosaic.

posted 11-13-2014 02:38 PM               

ESA's Philae probe 'bounced' twice during historic comet landing

The first space probe to touch down on the surface of a comet did so three times before it finally came to rest in the shadow of a cliff.

The European Space Agency (ESA) on Thursday (Nov 13) released photos captured by the Rosetta mission's Philae lander showing the three-legged probe was on the surface of Comet 67P/Churyumov-Gerasimenko. The probe, which on Wednesday separated from the Rosetta spacecraft and descended for seven hours to the comet's surface, did, in fact, land, but where exactly is still not known.

"We understood that we... bounced two times and finally stopped at a place we haven't entirely located," said Jean-Pierre Bibring, the Philae lander's lead scientist. "We sort of got close to the place that we are, where we think we are, which is not very close to [where] we wanted to [be], but not very far away."

posted 11-14-2014 11:52 PM               

Philae falls silent: European comet lander goes to sleep as its power runs out

"I'm feeling a bit tired, did you get all my data? I might take a nap..."

And with that, the European Space Agency's (ESA) Philae lander, the first probe to land on a comet, went to sleep.

The status update, posted on Twitter by its mission team on Friday evening (Nov. 14), signaled the likely end for the probe. With its batteries depleted and not enough sunlight reaching its solar panels to recharge, the Philae lander fell into an "idle mode," with all of its science instruments and most of its systems shut down.

"[It] performed magnificently under tough conditions, and we can be fully proud of the incredible scientific success Philae has delivered," said Stephan Ulamec, the lander's manager, from the European Space Operations Center in Darmstadt, Germany.

posted 06-14-2015 09:16 AM               

'I'm awake!' Philae comet lander wakes up after seven-month hibernation

Seven months after falling silent on the side of a comet, a European probe "woke up" on Saturday (June 13) and began sending data back to Earth.

"Hello Rosetta!" the Philae lander exclaimed on Twitter to its parent orbiter and communications relay. "I'm awake!"

The first-ever spacecraft to land on a comet, the European Space Agency's (ESA) Philae probe bounced twice before touching down on comet 67P/Churyumov-Gerasimenko on Nov. 12, 2014. Designed to search for water and organics of the type that could have given rise to life on Earth, the probe operated for just about 60 hours before running out of power and entering a hibernation mode as a result of its solar panels being in the shadow of a cliff.

Mission managers held out hope that as the comet moved closer to the sun, that Philae would receive more light and be able to resume operations — which apparently is what led to the probe making contact now...

posted 06-15-2015 02:34 PM               

Philae wake-up triggers intense planning

The receipt of signals from Rosetta's Philae lander on June 13 after 211 days of hibernation marked the start of intense activity. In coordination with its mission partners, ESA teams are working to juggle Rosetta's flight plan to help with renewed lander science investigations.

Philae has woken up after seven months in hibernation on Comet 67P/Churyumov–Gerasimenko. Hidden by shadows, Philae shut down on November 15, 2014 at 00:36 GMT after completing its main science operations sequence on the comet when the primary battery expired as expected after about 60 hours.

Since March 2015, when Philae's environmental conditions started to improve with higher surface temperatures and better illumination, the orbiter's receiver had been turned on periodically to listen for signals from the lander when the orbital geometry was thought to be optimum.

On the evening of June 13, a weak but solid radio link between Rosetta and the lander was finally established for 85 seconds. More than 300 'packets' – 663 kbits – of lander housekeeping telemetry were received. This information had been stored on board at an as-yet-to-be determined time in the past, as much as several days to a few weeks, so does not necessarily reflect the lander's current status.

Rosetta then relayed the signal to ESA's European Space Operations Center, ESOC, in Darmstadt, Germany, at 20:28 GMT.

Lander subsystems working nominally

"We are still examining the housekeeping information at the Lander Control Center in the DLR German Aerospace Center's establishment in Cologne, but we can already tell that all lander subsystems are working nominally, with no apparent degradation after more than half a year hiding out on the comet's frozen surface," says DLR's Stephan Ulamec, Philae Lander Project Manager.

A second, smaller burst of lander data was received on Sunday, 14 June, at about 21:26 GMT, lasting just a few seconds. These data were confirmed to give the current status, showing the lander's internal temperature had already risen to –5ºC.

Philae's memory has stored over 8000 packets of additional status data, but it is unclear from when in recent days they were recorded.

Here comes the Sun

Engineers at the Lander Control Center have determined that Philae is already being exposed to sufficient sunlight to heat it to an acceptable operating temperature and to generate electricity.

"Power levels increase during the local 'comet day' – the part of the about-12 hour comet rotation when Philae is in sunlight – from 13 W at comet sunrise to above 24 W," notes ESA's Patrick Martin, Rosetta Mission Manager. "It needs at least 19 W to switch on the transmitter."

The telemetry downloaded covered the lander's status for a full night-day cycle of the comet, which is helping ground teams to understand how the Sun is shining on the lander. The solar panels appear to be receiving power for over 135 minutes in each illumination period.

"While the information we have is very preliminary, it appears that the lander is in as good a condition as we could have hoped," says Dr Ulamec.

The task at hand

The main task now for all the mission partners – ESA for Rosetta operations and DLR and France's CNES space agency for lander operations and science, respectively – is to determine how to optimize Rosetta's orbit so as to facilitate contact and enable new science investigations.

It is believed that there is sufficient power now being generated to allow some science measurements during the time Philae is illuminated, with initial activities focusing on low-power measurements. This first phase would also likely include measurements that did not previously generate science in November.

However, the mission teams first must establish a more robust link between Rosetta and Philae before uploading the first batch of science operations commands.

The quality of the communication link is also possibly related to the trajectory Rosetta is flying and the orientation it adopts.

Optimizing an orbit 305 million km away

Currently, Rosetta experiences two possible communication slots per 24 hours – once per 12-hour comet rotation.

Until 23:35 GMT on Tuesday, June 16, Rosetta will be flying an orbit set by already-uploaded commands on the terminator – the plane between comet day and night – moving out from about 200 km to 235 km altitude.

This orbit is not optimized for lander communication, so longer periods of contact may not be possible until the trajectory has been changed.

"With work done by the flight dynamics and operations team at ESOC and based on intense planning being conducted with the mission partners today, a new orbit will be devised that ensures optimum lander communications beginning with the next command upload later tonight," says Paolo Ferri, ESA's Head of Mission Operations.

This new orbit will include an already-planned reduction of distance from the nucleus, down to 180 km versus 200 km, and 'nadir pointing' – continuously pointing Rosetta's communications unit at the comet. In the coming days, the orbiter may also be moved closer to the comet, without compromising the safety of the spacecraft, to help communications.

The new orbit will be flown by Rosetta starting after 23:25 GMT on 16 June until 19 June, aiming to enable more and longer contacts with Philae, especially towards the end of this period.

Ready to react quickly

Establishing a regular and predictable pattern of contacts is a prerequisite for performing a complete assessment of the lander's status and for planning science operations.

"If we manage to achieve and maintain a predictable contact pattern," continues Paolo Ferri, "the lander teams can devise a strategy for a new sequence of scientific operations."

"Regardless, we will stay very flexible and be ready to react quickly. It's clear this incredible mission continues to stimulate and challenge us, developing in ways we could never have predicted."

As a bonus, any operation of Philae's instruments up to or through perihelion on 13 August – the comet's closest point to the Sun along its orbit – will allow in-situ study of a comet during its peak activity.

Had Philae landed at the planned site, at Agilkia in November 2014, its mission would likely have ended in March because of the higher temperatures of that location as solar illumination increased.

Philae was contributed by a consortium led by DLR, the Max Planck Institute for Solar System Research (MPS), CNES and Italy's ASI space agency. It made the first-ever soft landing on a comet on November 12, 2014.

posted 06-19-2015 12:35 PM               

Rosetta and Philae in contact again

ESA and its Rosetta mission partners have confirmed that another communication link has been made between Rosetta and Philae today.

The signal was transmitted from Rosetta to ESA's space operations center in Darmstadt and received at 15:37 CEST on June 19, and confirmed by the Lander Control Center at the German Space Center, DLR. A second signal was received at 15:54 CEST.

The downlink was stable; the two contacts received by Rosetta lasted two minutes each. Both delivered numerous packets of lander housekeeping and status data, 185 in total, which are still being analyzed at the time of this writing. No science data were anticipated or received.

"We are very happy to have received signals from the lander again, and we are all working hard towards establishing a robust link between Rosetta and Philae," comments Patrick Martin, ESA Rosetta mission manager.

This was the first signal received from Philae since June 14. This was not unexpected, however, due to the pre-planned science operations of the orbiter, and its location around 180 km above the comet's surface today.

In the meantime, new commands have been uploaded to Rosetta to further adjust its trajectory and distance from the comet to improve the radio visibility between the two spacecraft, with the first sets of thruster burns taking place on Wednesday morning. The goal is to bring Rosetta to about 177 km from the comet nucleus and keep it in a range of latitudes that maximize opportunities for lander communication.

The Rosetta and Philae teams will be closely monitoring subsequent transmissions between the spacecraft, not only to better determine the health of the lander, but also to understand the length and frequency of available communication timeslots. This information is needed to determine when to upload new commands in order to restart science operations and, similarly, when the data can be downloaded.

posted 06-23-2015 04:58 PM               

Rosetta Mission Extended

The adventure continues: ESA today confirmed that its Rosetta mission will be extended until the end of September 2016, at which point the spacecraft will most likely be landed on the surface of Comet 67P/Churyumov-Gerasimenko.

Rosetta was launched in 2004 and arrived at the comet in August 2014, where it has been studying the nucleus and its environment as the comet moves along its 6.5-year orbit closer to the Sun. After a detailed survey, Rosetta deployed the lander, Philae, to the surface on 12 November. Philae fell into hibernation after 57 hours of initial scientific operations, but recently awoke and made contact with Rosetta again.

Rosetta's nominal mission was originally funded until the end of December 2015, but at a meeting today, ESA's Science Programme Committee has given formal approval to continue the mission for an additional nine months. At that point, as the comet moves far away from the Sun again, there will no longer be enough solar power to run Rosetta's set of scientific instrumentation efficiently.

"This is fantastic news for science," says Matt Taylor, ESA's Rosetta Project Scientist. "We'll be able to monitor the decline in the comet's activity as we move away from the Sun again, and we'll have the opportunity to fly closer to the comet to continue collecting more unique data. By comparing detailed 'before and after' data, we'll have a much better understanding of how comets evolve during their lifetimes."

Comet 67P/Churyumov-Gerasimenko will make its closest approach to the Sun on 13 August and Rosetta has been watching its activity increase over the last year. Continuing its study of the comet in the year following perihelion will give scientists a fuller picture of how a comet's activity waxes and wanes along its orbit.

The extra observations collected by Rosetta will also provide additional context for complementary Earth-based observations of the comet. At present, the comet is close to the line-of-sight to the Sun, making ground-based observations difficult.

As the activity diminishes post-perihelion, it should be possible to move the orbiter much closer to the comet's nucleus again, to make a detailed survey of changes in the comet's properties during its brief 'summer'.

In addition, there may be an opportunity to make a definitive visual identification of Philae. Although candidates have been seen in images acquired from a distance of 20 km, images taken from 10 km or less after perihelion could provide the most compelling confirmation.

During the extended mission, the team will use the experience gained in operating Rosetta in the challenging cometary environment to carry out some new and potentially slightly riskier investigations, including flights across the night-side of the comet to observe the plasma, dust, and gas interactions in this region, and to collect dust samples ejected close to the nucleus.

As the comet recedes from the Sun, the solar-powered spacecraft will no longer receive enough sunlight to operate efficiently and safely, equivalent to the situation in June 2011 when the spacecraft was put into hibernation for 31 months for the most distant leg of its journey out towards the orbit of Jupiter.

In addition, Rosetta and the comet will again be close to the Sun as seen from the Earth in October 2016, making operations difficult by then.

However, with Rosetta's propellant largely depleted by that time, it makes little sense to place the spacecraft in hibernation again.

"This time, as we're riding along next to the comet, the most logical way to end the mission is to set Rosetta down on the surface," says Patrick Martin, Rosetta Mission Manager.

"But there is still a lot to do to confirm that this end-of-mission scenario is possible. We'll first have to see what the status of the spacecraft is after perihelion and how well it is performing close to the comet, and later we will have to try and determine where on the surface we can have a touchdown."

If this proposed scenario were played out, then the spacecraft would be commanded to spiral down to the comet over a period of about three months.

It is expected that science operations would continue throughout this period and be feasible up to very close to the end of mission, allowing Rosetta's instruments to gather unique data at unprecedentedly close distances.

Once the orbiter lands on the surface, however, it is highly unlikely to be able to continue operations and relay data back to Earth, bringing to an end one of the most successful space exploration missions of all time.

posted 07-11-2015 01:29 PM               

New communication with Philae – commands executed successfully

The Philae lander communicated with the Rosetta orbiter again between 19:45 and 20:07 CEST on 9 July 2015 and transmitted measurement data from the COmet Nucleus Sounding Experiment by Radiowave Transmission (CONSERT) instrument. Although the connection failed repeatedly after that, it remained completely stable for those 12 minutes.

"This sign of life from Philae proves to us that at least one the lander's communication units remains operational and receives out commands," said German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) engineer Koen Geurts, a member of the lander control team at DLR Cologne.

The mood had been mixed over the last few days; Philae had not communicated with the team in the DLR Lander Control Center (LCC) since 24 June 2015. After an initial test command to turn on the power to CONSERT on 5 July 2015, the lander did not respond. Philae's team began to wonder if the lander had survived on Comet 67P/Churyumov-Gerasimenko.

Commanded from the ground successfully

"We never gave up on Philae and remained optimistic," said Geurts.

There was great excitement when Philae 'reported in' on 13 June 2015 after seven months of hibernation and sent data about its health. The lander was ready to perform its tasks, 300 million kilometres away from Earth.

However, Philae has to communicate with the ground stations through Rosetta, which acts as a radio relay. Restrictions on the orbiter's approach to and orbit around the comet have not permitted regular communication with the lander. The data sent on 24 June did not suggest that the lander had experienced technical difficulties.

Now, Philae's internal temperature of zero degrees Celsius gives the team hope that the lander can charge its batteries; this would make scientific work possible regardless of the 'time of day' on the comet.

Currently, DLR's team is evaluating the data that were received.

"We can already see that the CONSERT instrument was successfully activated by the command we sent on 9 July," explained Geurts.

Even now, Philae is causing the team some puzzlement: "We do not yet have an explanation for why the lander has communicated now, but not over the past few days." The trajectory of the orbiter, for example, has not changed over the last three weeks. However, one thing is certain; Philae has survived the harsh conditions on the comet and is responding to commands from the LCC team.

"This is extremely good news for us," said Geurts.

posted 08-13-2015 11:01 AM               

Rosetta's big day in the Sun

ESA's Rosetta today (Aug. 13) witnessed Comet 67P/Churyumov–Gerasimenko making its closest approach to the Sun. The exact moment of perihelion occurred at 02:03 GMT this morning when the comet came within 186 million km of the Sun.

Above: This series of images of Comet 67P/Churyumov–Gerasimenko was captured by Rosetta’s OSIRIS narrow-angle camera on 12 August 2015, just a few hours before the comet reached the closest point to the Sun along its 6.5-year orbit, or perihelion.

In the year that has passed since Rosetta arrived, the comet has traveled some 750 million kilometers along its orbit towards the Sun, the increasing solar radiation heating up the nucleus and causing its frozen ices to escape as gas and stream out into space at an ever greater rate. These gases, and the dust particles that they drag along, build up the comet's atmosphere – coma – and tail.

The activity reaches its peak intensity around perihelion and in the weeks that follow – and is clearly visible in the spectacular images returned by the spacecraft in the last months. One image taken by Rosetta's navigation camera was acquired at 01:04 GMT, just an hour before the moment of perihelion, from a distance of around 327 km.

The scientific camera is also taking images today – the most recent available image was taken at 23:31 GMT on 12 August, just a few hours before perihelion. The comet's activity is clearly seen in the images, with a multitude of jets stemming from the nucleus, including one outburst captured in an image taken at 17:35 GMT yesterday.

"Activity will remain high like this for many weeks, and we're certainly looking forward to seeing how many more jets and outburst events we catch in the act, as we have already witnessed in the last few weeks," says Nicolas Altobelli, acting Rosetta project scientist.

Above: This single frame Rosetta navigation camera image was acquired at 01:04 GMT on 13 August 2015, just one hour before Comet 67P/Churyumov–Gerasimenko reached perihelion – the closest point to the Sun along its 6.5-year orbit. The image was taken around 327 km from the comet.

Rosetta's measurements suggest the comet is spewing up to 300 kg of water vapor – roughly the equivalent of two bathtubs – every second. This is a thousand times more than was observed this time last year when Rosetta first approached the comet. Then, it recorded an outflow rate of just 300 g per second, equivalent to two small glasses of water.

Along with gas, the nucleus is also estimated to be shedding up to 1000 kg of dust per second, creating dangerous working conditions for Rosetta.

"In recent days, we have been forced to move even further away from the comet. We're currently at a distance of between 325 km and 340 km this week, in a region where Rosetta's startrackers can operate without being confused by excessive dust levels – without them working properly, Rosetta can't position itself in space," comments Sylvain Lodiot, ESA's spacecraft operations manager.

Monitoring the comet's changing environment in the lead up to, during and after perihelion is one of the primary long-term science goals of the mission.

Over the last few months, seasons on the comet have changed, throwing its southern hemisphere into a short – about 10 month – summer after more than five-and-a-half years in darkness. This has revealed parts of the surface that have previously been cast in shadow during Rosetta's sojourn at the comet, allowing scientists to fill in some of the missing pieces of its regional map.

They have now identified four new geological regions on the southern hemisphere, which includes parts of both comet lobes, bringing the total number of regions to 23. The names of the new regions follow the naming convention of Egyptian gods and goddesses adopted for the comet: Anhur, Khonsu, Sobek and Wosret.

The comet's average temperature has also been on the increase. Not long after arriving, surface temperatures of around –70ºC were recorded. By April–May 2015, this had risen to only a few degrees below zero celsius, and now highs of a few tens of degrees above zero are forecast for the next month.

Meanwhile, astronomers back on Earth have been following the comet's evolution from afar. Rosetta is far too close to the comet to see its growing tail, but images collected over the past few months with telescopes across the world show that it already extends more than 120 000 km.

A lop-sided coma, with a notable high-density region away from the main tail, was revealed in various images, including some taken last week from the Gemini-North telescope on Mauna Kea, Hawaii.

"Combining these big-picture views from ground-based telescopes with Rosetta's close-up study of individual jets and outbursts will help us to understand the processes at work on the comet's surface as it approaches the Sun," adds Nicolas.

"We aim to go back in much closer again after the activity subsides and make a survey of how the comet has changed. We also continue to hope that Philae will be able to resume its scientific operations on the surface and give us a detailed look at changes which may be occurring immediately surrounding its landing site."

Finally, Patrick Martin, ESA's Rosetta mission manager remarks: "It's exciting to reach the milestone of perihelion, and we look forward to seeing how this amazing comet behaves as we move away from the Sun with it over the coming year."

posted 02-12-2016 09:54 AM               

Rosetta's lander faces eternal hibernation

Silent since its last call to mothership Rosetta seven months ago, the Philae lander is facing conditions on Comet 67P/Churyumov–Gerasimenko from which it is unlikely to recover.

Rosetta, which continues its scientific investigations at the comet until September before its own comet-landing finale, has in recent months been balancing science observations with flying dedicated trajectories optimized to listen out for Philae. But the lander has remained silent since July 9, 2015.

"The chances for Philae to contact our team at our lander control center are unfortunately getting close to zero," says Stephan Ulamec, Philae project manager at the German Aerospace Center, DLR. "We are not sending commands any more and it would be very surprising if we were to receive a signal again."

Philae's team of expert engineers and scientists at the German, French and Italian space centers and across Europe have carried out extensive investigations to try to understand the status of the lander, piecing together clues since it completed its first set of scientific activities after its historic landing on Nov. 12, 2014.

A story with incredible twists and turns unfolded on that day. In addition to a faulty thruster, Philae also failed to fire its harpoons and lock itself onto the surface of the comet after its seven-hour descent, bouncing from its initial touchdown point at Agilkia, to a new landing site, Abydos, over 1 km away. The precise location of the lander has yet to be confirmed in high-resolution images.

A reconstruction of the flight of the lander suggested that it made contact with the comet four times during its two-hour additional flight across the small comet lobe. After bouncing from Agilkia it grazed the rim of the Hatmehit depression, bounced again, and then finally settled on the surface at Abydos.

Even after this unplanned excursion, the lander was still able to make an impressive array of science measurements, with some even as it was flying above the surface after the first bounce.

Once the lander had made its final touchdown, science and operations teams worked around the clock to adapt the experiments to make the most of the unanticipated situation. About 80% of its initial planned scientific activities were completed.

In the 64 hours following its separation from Rosetta, Philae took detailed images of the comet from above and on the surface, sniffed out organic compounds, and profiled the local environment and surface properties of the comet, providing revolutionary insights into this fascinating world.

But with insufficient sunlight falling on Philae's new home to charge its secondary batteries, the race was on to collect and transmit the data to Rosetta and across 510 million kilometers of space back to Earth before the lander's primary battery was exhausted as expected. Thus, on the evening of Nov. 14-15, 2014, Philae fell into hibernation.

As the comet and the spacecraft moved closer to the Sun ahead of perihelion on Aug. 13, 2015 – the closest point to the Sun along its orbit – there were hopes that Philae would wake up again.

Estimates of the thermal conditions at the landing site suggested that the lander might receive enough sunlight to start warming up to the minimum -45°C required for it to operate on the surface even by the end of March 2015.

It is worth noting that if Philae had remained at its original landing site of Agilkia, it would have likely overheated by March, ending any further operations.

On June 13, 2015, the lander finally hailed the orbiting Rosetta and subsequently transmitted housekeeping telemetry, including information from its thermal, power and computer subsystems.

Subsequent analysis of the data indicated that the lander had in fact already woken up on April 26, 2015, but had been unable to send any signals until June 13.

The fact that the lander had survived the multiple impacts on Nov. 12 and then unfavorable environmental conditions, greatly exceeding the specifications of its various electronic components, was quite remarkable.

After June 13, Philae made a further seven intermittent contacts with Rosetta in the following weeks, with the last coming on July 9. However, the communications links that were established were too short and unstable to enable any scientific measurements to be commanded.

Despite the improved thermal conditions, with temperatures inside Philae reaching 0°C, no further contacts were made as the comet approached perihelion in August.

However, the months around perihelion are also the comet's most active. With increased levels of outflowing gas and dust, conditions were too challenging for Rosetta to operate safely close enough to the comet and within the 200 km where the signals had previously been detected from Philae.

In more recent months, the comet's activity has subsided enough to make it possible to approach the nucleus again safely – this week the spacecraft reached around 45 km – and Rosetta has made repeated passes over Abydos.

No signal has been received, however. Attempts to send commands 'in the blind' to trigger a response from Philae have also not produced any results.

The mission engineers think that failures of Philae's transmitters and receivers are the most likely explanation for the irregular contacts last year, followed by continued silence into this year.

Another difficulty that Philae may be facing is dust covering its solar panels, ejected by the comet during the active perihelion months, preventing the lander from powering up.

Also, the attitude and even location of Philae may have changed since November 2014 owing to cometary activity, meaning that the direction in which its antenna is sending signals to Rosetta is not as predicted, affecting the expected communication window.

"The comet's level of activity is now decreasing, allowing Rosetta to safely and gradually reduce its distance to the comet again," says Sylvain Lodiot, ESA's Rosetta spacecraft operations manager.

"Eventually we will be able to fly in 'bound orbits' again, approaching to within 10-20 km – and even closer in the final stages of the mission – putting us in a position to fly above Abydos close enough to obtain dedicated high-resolution images to finally locate Philae and understand its attitude and orientation."

"Determining Philae's location would also allow us to better understand the context of the incredible in situ measurements already collected, enabling us to extract even more valuable science from the data," says Matt Taylor, ESA's Rosetta project scientist.

"Philae is the cherry on the cake of the Rosetta mission, and we are eager to see just where the cherry really is!"

At the same time, Rosetta, Philae and the comet are heading back out towards the outer Solar System again. They have crossed the orbit of Mars and are now some 350 million km from the Sun. According to predictions, the temperatures should be falling far below those at which Philae is expected to be able to operate.

Nevertheless, while hopes of making contact again with Philae dwindle, Rosetta will continue to listen for signals from the lander as it flies alongside the comet ahead of its own comet landing in September.

"We would be very surprised to hear from Philae again after so long, but we will keep Rosetta's listening channel on until it is no longer possible due to power constraints as we move ever further from the Sun towards the end of the mission," says Patrick Martin, ESA's Rosetta mission manager.

"Philae has been a tremendous challenge and for the lander teams to have achieved the science results that they have in the unexpected and difficult circumstances is something we can all be proud of.

"The combined achievements of Rosetta and Philae, rendezvousing with and landing on a comet, are historic high points in space exploration."

posted 07-26-2016 05:46 PM               

Farewell, silent Philae

Tomorrow, 27 July 2016 at 09:00 UTC / 11:00 CEST [5 a.m. EDT], the Electrical Support System Processor Unit (ESS) on Rosetta will be switched off. The ESS is the interface used for communications between Rosetta and the lander, Philae, which has remained silent since 9 July 2015.

Switching off the ESS is part of the preparations for Rosetta's end of mission. By the end of July 2016, the spacecraft will be some 520 million km from the Sun, and will start facing a significant loss of power – about 4W per day. In order to continue scientific operations over the next two months and to maximize their return, it became necessary to start reducing the power consumed by the non-essential payload components on board.

No signal has been received by Rosetta from Philae since last July and earlier this year the lander was considered to be in a state of eternal hibernation. In spite of this, the ESS was kept on until now in the unlikely chance that Philae would re-gain contact. Although Rosetta has reached altitudes well below 10 km over the surface of Comet 67P/Churyumov-Gerasimenko, however, no signal from the lander was received since July 2015.

The decision was taken by the mission manager and will be implemented by the Rosetta Mission Operations Center, in coordination with the DLR Lander Control Center and the Rosetta Science Ground Segment.

posted 09-05-2016 11:10 AM               

Philae found!

Less than a month before the end of the mission, Rosetta's high-resolution camera has revealed the Philae lander wedged into a dark crack on Comet 67P/Churyumov-Gerasimenko.

The images were taken on 2 September by the OSIRIS narrow-angle camera as the orbiter came within 2.7 km of the surface and clearly show the main body of the lander, along with two of its three legs.

The images also provide proof of Philae's orientation, making it clear why establishing communications was so difficult following its landing on 12 November 2014.

"With only a month left of the Rosetta mission, we are so happy to have finally imaged Philae, and to see it in such amazing detail," says Cecilia Tubiana of the OSIRIS camera team, the first person to see the images when they were downlinked from Rosetta yesterday.

"After months of work, with the focus and the evidence pointing more and more to this lander candidate, I'm very excited and thrilled that we finally have this all-important picture of Philae sitting in Abydos," says ESA's Laurence O'Rourke, who has been coordinating the search efforts over the last months at ESA, with the OSIRIS and SONC/CNES teams.

Philae was last seen when it first touched down at Agilkia, bounced and then flew for another two hours before ending up at a location later named Abydos, on the comet's smaller lobe.

After three days, Philae's primary battery was exhausted and the lander went into hibernation, only to wake up again and communicate briefly with Rosetta in June and July 2015 as the comet came closer to the Sun and more power was available.

However, until today, the precise location was not known. Radio ranging data tied its location down to an area spanning a few tens of metres, but a number of potential candidate objects identified in relatively low-resolution images taken from larger distances could not be analysed in detail until recently.

While most candidates could be discarded from analysis of the imagery and other techniques, evidence continued to build towards one particular target, which is now confirmed in images taken unprecedentedly close to the surface of the comet.

At 2.7 km, the resolution of the OSIRIS narrow-angle camera is about 5 cm/pixel, sufficient to reveal characteristic features of Philae's 1 m-sized body and its legs, as seen in these definitive pictures.

"This remarkable discovery comes at the end of a long, painstaking search," says Patrick Martin, ESA's Rosetta Mission Manager. "We were beginning to think that Philae would remain lost forever. It is incredible we have captured this at the final hour."

"This wonderful news means that we now have the missing 'ground-truth' information needed to put Philae's three days of science into proper context, now that we know where that ground actually is!" says Matt Taylor, ESA's Rosetta project scientist.

"Now that the lander search is finished we feel ready for Rosetta's landing, and look forward to capturing even closer images of Rosetta's touchdown site," adds Holger Sierks, principal investigator of the OSIRIS camera.

The discovery comes less than a month before Rosetta descends to the comet's surface. On 30 September, the orbiter will be sent on a final one-way mission to investigate the comet from close up, including the open pits in the Ma'at region, where it is hoped that critical observations will help to reveal secrets of the body's interior structure.

Further information on the search that led to the discovery of Philae, along with additional images, will be made available soon.

posted 09-11-2016 10:50 AM               

Rosetta's descent towards region of active pits

Squeezing out unique scientific observations until the very end, Rosetta's thrilling mission will culminate with a descent on 30 September towards a region of active pits on the comet's 'head'.

The region, known as Ma'at, lies on the smaller of the two lobes of Comet 67P/Churyumov–Gerasimenko. It is home to several active pits more than 100 m in diameter and 50–60 m in depth – where a number of the comet's dust jets originate.

The walls of the pits also exhibit intriguing metre-sized lumpy structures called 'goosebumps', which scientists believe could be the signatures of early 'cometesimals' that assembled to create the comet in the early phases of Solar System formation.

Rosetta will get its closest look yet at these fascinating structures on 30 September: the spacecraft will target a point adjacent to a 130 m-wide, well-defined pit that the mission team has informally named Deir el-Medina, after a structure with a similar appearance in an ancient Egyptian town of the same name.

Like the archaeological artefacts found inside the Egyptian pit that tell historians about life in that town, the comet's pit contains clues to the geological history of the region.

Rosetta will target a point very close to Deir el-Medina, within an ellipse about 700 x 500 m.

Since 9 August, Rosetta has been flying elliptical orbits that bring it progressively closer to the comet – on its closest flyby, it may come within 1 km of the surface, closer than ever before.

"Although we've been flying Rosetta around the comet for two years now, keeping it operating safely for the final weeks of the mission in the unpredictable environment of this comet and so far from the Sun and Earth, will be our biggest challenge yet," says Sylvain Lodiot, ESA's spacecraft operations manager.

"We are already feeling the difference in gravitational pull of the comet as we fly closer and closer: it is increasing the spacecraft's orbital period, which has to be corrected by small manoeuvres. But this is why we have these flyovers, stepping down in small increments to be robust against these issues when we make the final approach."

The final flyover will be complete on 24 September. Then a short series of manoeuvres needed to line Rosetta up with the target impact site will be executed over the following days as it transfers from flying elliptical orbits around the comet onto a trajectory that will eventually take it to the comet's surface on 30 September.

The collision manoeuvre will take place in the evening of 29 September, initiating the descent from an altitude of about 20 km. Rosetta will essentially free-fall slowly towards the comet in order to maximise the number of scientific measurements that can be collected and returned to Earth before its impact.

A number of Rosetta's scientific instruments will collect data during the descent, providing unique images and other data on the gas, dust and plasma very close to the comet. The exact complement of instruments and their operational timeline remains to be fixed, because it depends on constraints of the final planned trajectory and the data rate available on the day.

The impact is predicted to occur within 20 minutes of 10:40 GMT, with uncertainties linked to the exact trajectory of Rosetta on the day, and the influence of gravity close to the comet. Taking into account the additional 40 minute signal travel time between Rosetta and Earth on 30 September, this means that the confirmation of impact is expected at ESA's mission control in Darmstadt, Germany, within 20 minutes of 11:20 GMT (13:20 CEST). The times will be updated as the trajectory is refined.

Mirroring Rosetta's wake-up from deep space hibernation in January 2014, where a rising peak at the right frequency confirmed that the spacecraft was alive and transmitting its carrier signal, mission controllers will see that peak disappear for a final time once Rosetta impacts. It will not be possible to retrieve any data after this time.

"Last month we celebrated two thrilling years since arriving at the comet, and also a year since the comet's closest approach to the Sun along its orbit," says Matt Taylor, ESA's Rosetta project scientist.

"It's hard to believe that Rosetta's incredible 12.5 year odyssey is almost over, and we're planning the final set of science operations, but we are certainly looking forward to focusing on analysing the reams of data for many decades to come."

"This pioneering mission may be coming to an end, but it has certainly left its mark in the technical, scientific and public spheres as being one of outstanding success, with incredible achievements contributing to the current and future understanding of our Solar System," adds Patrick Martin, ESA's Rosetta mission manager.

More information

All times and details regarding the end of mission are preliminary and subject to change as Rosetta's final trajectory is refined. Even on the day, timings will have uncertainties owing to circumstances at the comet beyond the control of the mission team.

For further information, you can consult the end-of-mission FAQ.

posted 09-30-2016 07:15 AM               

End of mission: ESA's Rosetta spacecraft collides with comet

The first spacecraft to orbit a comet and deploy a lander to its surface came to its end Friday (Sept. 30) with its own controlled impact on the dusty-icy body.

The European Space Agency's Rosetta probe descended to a pitted region of Comet 67P/Churyumov-Gerasimenko, bringing its 12.5-year journey to a finish. The mission was ended due to the spacecraft's increasing distance from the sun, reducing the available solar power needed to operate it and its instruments.

Confirmation of the mission's end came from the European Space Agency (ESA) control room at 7:19 a.m. EDT (1119 GMT). It took 40 minutes for the last signal from the probe to reach Earth.