posted 10-25-2006 09:23 PM               

NASA's First 3-D Solar Imaging Mission Soars Into Space

NASA's twin Solar Terrestrial Relations Observatories mission, known as STEREO, successfully launched Wednesday at 8:52 p.m. EDT from Cape Canaveral Air Force Station, Fla.

STEREO's nearly identical twin, golf cart-sized spacecraft will make observations to help researchers construct the first-ever three-dimensional views of the sun. The images will show the star's stormy environment and its effects on the inner solar system, vital data for understanding how the sun creates space weather.

"The stunning solar views the two observatories will send back to Earth will help scientists get a better understanding of the sun and its activity than we've ever been able to obtain from the ground or any of our other missions," said Nick Chrissotimos, STEREO project manager at NASA's Goddard Space Flight Center, Greenbelt, Md.

The two observatories were launched on a Delta II rocket in a stacked configuration and separated from the launch vehicle approximately 25 minutes after lift-off. After receiving the first signal from the spacecraft approximately 63 minutes after launch, mission control personnel at the Johns Hopkins University Applied Physics Laboratory (APL), Laurel, Md., confirmed each observatory's solar arrays successfully deployed and were providing power. NASA's Deep Space Network antennas in Canberra, Australia received the initial radio signals.

During the next two weeks, mission managers at APL will ensure all systems are properly working. For the next three months, the observatories will fly from a point close to Earth to one that extends just beyond the moon's orbit.

After about two months, STEREO's orbits will be synchronized to encounter the moon. The "A" observatory will use the moon's gravity to redirect it to an orbit "ahead" of Earth. The "B" observatory will encounter the moon again for a second swing-by about one month later to redirect its position "behind" Earth. STEREO is the first NASA mission to use separate lunar swing-bys to place two observatories into vastly different orbits around the sun.

Just as the slight offset between human eyes provides depth perception, this placement will allow the STEREO observatories to obtain 3-D images of the sun. The arrangement also allows the two spacecraft to take local particle and magnetic field measurements of the solar wind as it flows by.

During the observatories' two-year mission, they will explore the origin, evolution and interplanetary consequences of coronal mass ejections, some of the most violent explosions in our solar system. These billion-ton eruptions can produce spectacular aurora, disrupt satellites, radio communications and Earth's power systems. Energetic particles associated with these solar eruptions permeate the entire solar system and can be hazardous to spacecraft and astronauts.

Better prediction of solar eruptions provides more warning time for satellite and power grid operators to put their assets into a safe mode to weather the storm. A better understanding of the nature of these events will help engineers build better and more resilient systems.

"We're becoming more and more reliant on space technologies in our everyday lives and are hatching ambitious plans to explore our outer space surroundings," said Michael Kaiser, STEREO Project Scientist at Goddard. "But nature has a mind of its own and STEREO is going to help us figure out how to avoid those surprises the sun tends to throw at us and our best-laid plans."

Goddard manages the STEREO mission. The APL designed and built the spacecraft. The laboratory will maintain command and control of the observatories throughout the mission, while NASA tracks and receives the data, determines the orbit of the satellites, and coordinates the science results. Each observatory has 16 instruments, including imaging telescopes and equipment to measure solar wind particles and to perform radio astronomy.

The STEREO mission includes significant international cooperation with European partners in instrument development, data sharing and analysis.

posted 02-06-2011 11:52 PM               

First Ever STEREO Images of the Entire Sun

It's official: The sun is a sphere.

On Feb. 6th, NASA's twin STEREO probes moved into position on opposite sides of the sun, and they are now beaming back uninterrupted images of the entire star -- front and back.

"For the first time ever, we can watch solar activity in its full 3-dimensional glory," says Angelos Vourlidas, a member of the STEREO science team at the Naval Research Lab in Washington, DC.

NASA released a 'first light' 3D movie on, naturally, Super Bowl Sunday:

"This is a big moment in solar physics," says Vourlidas. "STEREO has revealed the sun as it really is — a sphere of hot plasma and intricately woven magnetic fields."

Each STEREO probe photographs half of the star and beams the images to Earth. Researchers combine the two views to create a sphere. These aren't just regular pictures, however. STEREO's telescopes are tuned to four wavelengths of extreme ultraviolet radiation selected to trace key aspects of solar activity such as flares, tsunamis and magnetic filaments. Nothing escapes their attention.

"With data like these, we can fly around the sun to see what's happening over the horizon — without ever leaving our desks," says STEREO program scientist Lika Guhathakurta at NASA headquarters. "I expect great advances in theoretical solar physics and space weather forecasting."

Consider the following: In the past, an active sunspot could emerge on the far side of the sun completely hidden from Earth. Then, the sun's rotation could turn that region toward our planet, spitting flares and clouds of plasma, with little warning.

"Not anymore," says Bill Murtagh, a senior forecaster at NOAA's Space Weather Prediction Center in Boulder, Colorado. "Farside active regions can no longer take us by surprise. Thanks to STEREO, we know they're coming."

NOAA is already using 3D STEREO models of CMEs (billion-ton clouds of plasma ejected by the sun) to improve space weather forecasts for airlines, power companies, satellite operators, and other customers. The full sun view should improve those forecasts even more.

The forecasting benefits aren't limited to Earth.

"With this nice global model, we can now track solar storms heading toward other planets, too," points out Guhathakurta. "This is important for NASA missions to Mercury, Mars, asteroids... you name it."

NASA has been building toward this moment since Oct. 2006 when the STEREO probes left Earth, split up, and headed for positions on opposite sides of the sun (movie). Feb. 6, 2011, was the date of "opposition" -- i.e., when STEREO-A and -B were 180 degrees apart, each looking down on a different hemisphere. NASA's Earth-orbiting Solar Dynamics Observatory is also monitoring the sun 24/7. Working together, the STEREO-SDO fleet should be able to image the entire globe for the next 8 years.

Above: Latest image of the far side of the Sun based on high resolution STEREO data, taken on February 2, 2011 at 23:56 UT when there was still a small gap between the STEREO Ahead and Behind data. This gap will start to close on February 6, 2011, when the spacecraft achieve 180 degree separation, and will completely close over the next several days.

The new view could reveal connections previously overlooked. For instance, researchers have long suspected that solar activity can "go global," with eruptions on opposite sides of the sun triggering and feeding off of one another. Now they can actually study the phenomenon. The Great Eruption of August 2010 engulfed about 2/3rd of the stellar surface with dozens of mutually interacting flares, shock waves, and reverberating filaments. Much of the action was hidden from Earth, but plainly visible to the STEREO-SDO fleet.

"There are many fundamental puzzles underlying solar activity," says Vourlidas. "By monitoring the whole sun, we can find missing pieces."

Researchers say these first-look whole sun images are just a hint of what's to come. Movies with even higher resolution and more action will be released in the days and weeks ahead as more data are processed. Stay tuned!

posted 08-23-2016 07:26 AM               

NASA Establishes Contact With STEREO Mission

On Aug. 21, 2016, contact was reestablished with one of NASA's Solar Terrestrial Relations Observatories, known as the STEREO-B spacecraft, after communications were lost on Oct. 1, 2014. Over 22 months, the STEREO team has worked to attempt contact with the spacecraft. Most recently, they have attempted a monthly recovery operation using NASA's Deep Space Network, or DSN, which tracks and communicates with missions throughout space.

Above: This graphic shows the positions of the two STEREO spacecraft and their orbits in relation to Earth, Venus, Mercury and the sun.

The DSN established a lock on the STEREO-B downlink carrier at 6:27 p.m. EDT. The downlink signal was monitored by the Mission Operations team over several hours to characterize the attitude of the spacecraft and then transmitter high voltage was powered down to save battery power. The STEREO Missions Operations team plans further recovery processes to assess observatory health, re-establish attitude control, and evaluate all subsystems and instruments.

Communications with STEREO-B were lost during a test of the spacecraft’s command loss timer, a hard reset that is triggered after the spacecraft goes without communications from Earth for 72 hours. The STEREO team was testing this function in preparation for something known as solar conjunction, when STEREO-B’s line of sight to Earth – and therefore all communication – was blocked by the sun.

STEREO-A continues to work normally.

posted 08-11-2023 12:49 PM               

After Seventeen Years, A Spacecraft Makes Its First Visit Home

On Aug. 12, 2023, NASA's STEREO-A spacecraft will pass between the Sun and Earth, marking the first Earth flyby of the nearly 17-year-old mission. The visit home brings a special chance for the spacecraft to collaborate with NASA missions near Earth and reveal new insights into our closest star.

Above: NASA's STEREO-A spacecraft will cross the Sun-Earth line on Aug. 12, 2023. The crossing comes one day before Venus passes between the Sun and Earth, though the planet will appear 10 degrees below the Sun from Earth's view and outside of STEREO-A's field of view. (NASA's Goddard Space Flight Center/Scientific Visualization Studio/Tom Bridgman)

The twin STEREO (Solar TErrestrial RElations Observatory) spacecraft launched on Oct. 25, 2006, from the Cape Canaveral Air Force Station in Florida. STEREO-A (for "Ahead") advanced its lead on Earth as STEREO-B (for "Behind") lagged behind, both charting Earth-like orbits around the Sun.

During the first years after launch, the dual-spacecraft mission achieved its landmark goal: providing the first stereoscopic, or multiple-perspective, view of our closest star. On Feb. 6, 2011, the mission achieved another landmark: STEREO-A and -B reached a 180-degree separation in their orbits. For the first time, humanity saw our Sun as a complete sphere.

"Prior to that we were 'tethered' to the Sun-Earth line – we only saw one side of the Sun at a time," said Lika Guhathakurta, STEREO program scientist at NASA Headquarters in Washington, D.C. "STEREO broke that tether and gave us a view of the Sun as a three-dimensional object."

The mission accomplished many other scientific feats over the years, and researchers studied both spacecraft views until 2014, when mission control lost contact with STEREO-B after a planned reset. However, STEREO-A continues its journey, capturing solar views unavailable from Earth.

On Aug. 12, 2023, STEREO-A's lead on Earth has grown to one full revolution as the spacecraft "laps" us in our orbit around the Sun. In the few weeks before and after STEREO-A's flyby, scientists are seizing the opportunity to ask questions normally beyond the mission's reach.

A 3D View of the Sun

During the Earth flyby, STEREO-A will once again do something it used to do with its twin in the early years: combine views to achieve stereoscopic vision.

Above: Stereoscopic vision is what's behind 3D movies, as two slightly offset images are overlaid, and red-blue 3D glasses ensure each eye perceives only one of the images. Readers with such glasses will perceive this view of the Sun, created from combining views of the Sun captured by STEREO-A and NASA's Solar Dynamics Observatory (SDO) on July 6, 2023. (NASA's Goddard Space Flight Center/Scientific Visualization Studio/Tom Bridgman)

Stereoscopic vision allows us to extract 3D information from two-dimensional, or flat, images. It's how two eyeballs, looking out at the world from offset locations, create depth perception. Your brain compares the images from each eye, and the slight differences between those images reveal which objects are closer or farther away.

STEREO-A will enable such 3D viewing by synthesizing its views with NASA's and the European Space Agency's Solar and Heliospheric Observatory (SOHO) and NASA's Solar Dynamics Observatory (SDO). Better yet, STEREO-A's distance from Earth changes throughout the flyby, optimizing its stereo vision for different sized solar features at different times. It's as if scientists were adjusting the focus on a several million-mile-wide telescope.

STEREO scientists are using the opportunity to make much-needed measurements. They are identifying active regions, the magnetically complex regions underlying sunspots, hoping to uncover 3D information about their structure usually lost in 2D images. They'll also test a new theory that coronal loops – giant arches often seen in close-up images of the Sun – aren't what they appear to be.

"There is a recent idea that coronal loops might just be optical illusions," said Terry Kucera, STEREO project scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland. Some scientists have suggested that our limited viewing angles make them appear to have shapes they may not truly have. "If you look at them from multiple points of view, that should become more apparent," Kucera added.

Inside a Solar Eruption

It's not just what STEREO-A will see as it flies by Earth, but also what it will "feel," that could lead to major discoveries.

Above: This coronagraph image shows a coronal mass ejection escaping the Sun, which is occluded behind the black circle at the center of the image. STEREO-A imaged this Earth-directed CME eruption on July 17, 2023. The CME was captured by the COR2 instrument on STEREO-A at the highest cadence (2.5 mins) ever achieved by a coronagraph. (NASA/STEREO-A/SECCHI)

When a plume of solar material known as a coronal mass ejection, or CME, arrives at Earth, it can disrupt satellite and radio signals, or even cause surges in our power grids. Or, it may have hardly any effect at all. It all depends on the magnetic field embedded within it, which can change dramatically in the 93 million miles between the Sun and Earth.

To understand how a CME's magnetic field evolves on the way to Earth, scientists build computer models of these solar eruptions, updating them with each new spacecraft observation. But a single spacecraft's data can only tell us so much.

"It's like the parable about the blind men and the elephant – the one who feels the legs says 'it's like a tree trunk,' and the one who feels the tail says 'it's like a snake,'" said said Toni Galvin, a professor at the University of New Hampshire and principal investigator for one of STEREO-A's instruments. "That's what we're stuck with right now with CMEs, because we typically only have one or two spacecraft right next to each other measuring it."

During the months before and after STEREO-A's Earth flyby, any Earth-directed CMEs will pass over STEREO-A and other near-Earth spacecraft, giving scientists much-needed multipoint measurements from inside a CME.

A Fundamentally Different Sun

STEREO-A was also close to Earth in 2006, shortly after launch. That was during "solar minimum," the low-point in the Sun's roughly 11-year cycle of high and low activity.

Above: Images from NASA's Solar Dynamics Observatory show the Sun at solar minimum in October 2019 (left) and the last solar maximum in April 2014 (right). Dark coronal holes cover the Sun during solar minimum, while bright active regions—indicating more solar activity—cover the Sun during solar maximum. (NASA's Solar Dynamics Observatory/Joy Ng)

"The Sun was so quiet at that point! I was looking back at the data and I said 'Oh yeah, I recognize that active region' – there was one, and we studied it," Kucera said, laughing. "OK, it wasn't quite that bad – but it was close."

Now, as we approach solar maximum predicted for 2025, the Sun isn't quite so sleepy.

"In this phase of the solar cycle, STEREO-A is going to experience a fundamentally different Sun," Guhathakurta said. "There is so much knowledge to be gained from that."