China's Relay Satellite is in Lunar Orbit

On March 20th, China’s Queqiao-2 (“Magpie Bridge-2”) satellite launched from the Wenchang Space Launch Site LC-2 on the island of Hainan (in southern China) atop a Long March-8 Y3 carrier rocket. This mission is the second in a series of communications relay and radio astronomy satellites designed to support the fourth phase of the Chinese Lunar Exploration Program (Chang’e). On March 24th, after 119 hours in transit, the satellite reached the Moon and began a perilune braking maneuver at a distance of 440 km (~270 mi) from the lunar surface.

The maneuver lasted 19 minutes, after which the satellite entered lunar orbit, where it will soon relay communications from missions on the far side of the Moon around the South Pole region. This includes the Chang’e-4 lander and rover and will extend to the Chang’e-6 sample-return mission, which is scheduled to launch in May. It will also assist Chang’e-7 and -8 (scheduled for 2026 and 2028, respectively), consisting of an orbiter, rover, and lander mission, and a platform that will test technologies necessary for the construction of the International Lunar Research Station (ILRS).

A perilune braking maneuver is vital to establishing a lunar orbit and consists of a thruster firing as the spacecraft approaches the Moon. This reduces the spacecraft’s relative velocity to less than the lunar escape velocity (2.38 km/s; 1.74 mps) so that it can be captured by the Moon’s gravity. Two experimental satellites that will test navigation and communication technology (Tiandu-1 and -2), which accompanied the Queqiao-2 satellite to the Moon, also performed a perilune braking maneuver and entered lunar orbit on Monday.

These two satellites will remain in formation in an elliptical lunar orbit and will conduct communication and navigation tests, including laser ranging with the Moon and microwave ranging between satellites. According to the CNSA, Queqiao-2 will enter a 24-hour elliptical orbit around the Moon at a distance of 200 km (125 mi) at its closest point (perigee) and 100,000 km (62,000 mi) at its farthest point (apogee). Mission controllers will further alter Queqiao-2’s orbit and inclination to bring it into a “200 by 16,000-km, highly-elliptical ‘frozen’ orbit.”

Within this highly stable orbit, Queqiao-2 will have a direct line of sight with ground stations on Earth and the far side of the Moon and will conduct communication tests with Chang’e-4 and Chang’e-6 using its 4.2-m (13.8-ft) parabolic antenna. The mission could also support other countries in their lunar exploration efforts, many of whom are also interested in scouting the Moon’s far side and southern polar region. The satellite also carries scientific instruments, including extreme ultraviolet cameras, array-neutral atom imagers, and lunar orbit Very Long Baseline Interferometry (VLBI) test subsystems.

According to state-owned media company CCTV, the CNSA chose the Queqiao-2 satellite’s present orbit for a multitude of reasons:

“Experts told me that this is an ideal location on the Moon to observe the separation of the Queqiao-2 star arrow, and it also has a deep connection with China’s lunar exploration project. This is the Moon’s rich maria region… Fifteen years ago, on March 1, 2009, it was here that the Chang’e-1 probe of China’s lunar exploration project completed a controlled collision with the Moon… The location of the Sea of Abundance on the moon is also very eye-catching. The next time the moon is full, you look up at the moon and find this dark black patch in the southeast of the moon. This is the Sea of Abundance!”

Visualization of the ILRS from the CNSA Guide to Partnership (June 2021). Credit: CNSA

The satellite will support China’s upcoming Chang’e-6 mission, China’s second attempt to return lunar samples to Earth. Mission controllers will adjust its orbit into a 12-hour period to support the Chang’e-7 and -8 missions. These missions aim to map the terrain and scout resources (particularly water ice) around the South Pole-Aitken Basin. These missions will ultimately support the creation of the ILRS, a joint project between CNSA and Roscomos to create a lunar base that will enable research and development on the Moon.

This program is intended to rival NASA’s Artemis Program, which will send astronauts on a circumlunar flight next year – the Artemis II mission. The program will culminate in 2026 with the first crewed mission to the lunar surface (Artemis III) in over 50 years. NASA also plans to deploy the core elements of the Lunar Gateway next year, an orbital habitat that will facilitate the deployment of the Artemis Base Camp. Along with its international and commercial partners, these elements will support the creation of “a sustained program of lunar exploration and development.”

Further Reading: CGTN