Topic: China's Queqiao lunar communication satellites
Robert Pearlman Editor
Posts: 52106 From: Houston, TX Registered: Nov 1999
posted 05-20-2018 08:15 PM
China launched a relay satellite to set up a communication link between Earth and its planned Chang'e-4 lunar probe that will explore the far side of moon.
The satellite, named Queqiao (Magpie Bridge), was carried by a Long March-4C rocket that blasted off at 5:28 a.m. [Beijing time; 2158 GMT] from southwest China's Xichang Satellite Launch Center, according to the China National Space Administration (CNSA).
"The launch is a key step for China to realize its goal of being the first country to send a probe to soft-land on and rove the far side of the Moon," said Zhang Lihua, manager of the relay satellite project.
About 25 minutes after liftoff, the satellite separated from the rocket and entered an Earth-Moon transfer orbit with the perigee at 200 km and the apogee at about 400,000 km. The solar panels and the communication antennas were unfolded.
Queqiao is expected to enter a halo orbit around the second Lagrangian (L2) point of the Earth-Moon system, about 455,000 km from the Earth. It will be the world's first communication satellite operating in that orbit.
Blackarrow Member
Posts: 3700 From: Belfast, United Kingdom Registered: Feb 2002
posted 05-23-2018 08:33 AM
In such an orbit, will the satellite be in constant line-of-sight contact with Earth, or will it at times pass behind the Moon as seen from Earth?
Does China have a system of Earth-orbiting communications satellites capable of maintaining constant between the control centre and the lunar satellite?
Robert Pearlman Editor
Posts: 52106 From: Houston, TX Registered: Nov 1999
An Earth-Moon L2 halo orbit is ideal for Queqiao because it can 1) provide nearly continuous contact between both lunar farside and Earth ground station, 2) get continuous illumination from the Sun, avoiding eclipses, and 3) requires little energy to maintain its orbit over the long term.
As for the ground stations, gbtimes notes that Queqiao "will rely solely on Chinese facilities, thanks in part to a new, 35m-diameter parabolic antenna in Argentina."
Blackarrow Member
Posts: 3700 From: Belfast, United Kingdom Registered: Feb 2002
posted 05-23-2018 06:25 PM
That's helpful, Robert, but the diagram is clearly not to scale and the description of "nearly continuous contact between both lunar farside and Earth ground station" could mean either that the halo orbit "wobbles" enough to cause occasional occultation; or that there might be a gap in Earth station coverage.
Still, they seem to have established a pretty efficient communications link. From memory, the suggestion of an Apollo far-side landing (quickly squashed by NASA) depended on a pair of surplus communications satellites in lunar orbit. I don't remember any suggestion of placing a comsat at L2. Was that beyond NASA's capabilities at the time?
Robert Pearlman Editor
Posts: 52106 From: Houston, TX Registered: Nov 1999
posted 05-23-2018 09:39 PM
Apparently, NASA considered an L2 halo orbit to support a communications relay for a far side Apollo mission, but ultimately the concept (and, of course, the mission) never came to be.
Robert W. Farquhar first used the name "halo" for these orbits in his 1968 Ph.D. thesis. Farquhar advocated using spacecraft in a halo orbit on the far side of the Moon (Earth-Moon L2) as a communications relay station for an Apollo mission to the far side of the Moon. A spacecraft in such a halo orbit would be in continuous view of both the Earth and the far side of the Moon.
Robert Pearlman Editor
Posts: 52106 From: Houston, TX Registered: Nov 1999
posted 03-19-2024 08:53 PM
Xinhua state news agency release
China launches new relay satellite for Earth-Moon communications
China launched a new relay satellite on Wednesday (March 20) to provide Earth-Moon communications services, a key step for its future lunar exploration missions such as retrieving samples from the far side of the moon.
A Long March-8 rocket, carrying the satellite dubbed Queqiao-2, or Magpie Bridge-2, soared into the sky at 8:31 a.m. Beijing time (0031 GMT or 8:31 p.m. EDT March 19) from the Wenchang Space Launch Site in south China's Hainan Province.
After 24 minutes of flight, the satellite separated from the rocket, and entered the planned Earth-Moon transfer orbit with the perigee at 200 kilometers and the apogee at 420,000 kilometers. The satellite's solar panels and communications antennae were unfolded, according to the China National Space Administration.
Queqiao-2 will serve as a relay platform for the fourth phase of China's lunar exploration program, providing communications services for the Chang'e-4, Chang'e-6, Chang'e-7, and Chang'e-8 missions.
posted 05-20-2018 08:15 PM
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