The landing of China’s Chang’e-4 on the far side of the moon represented one small step for a Chinese probe and one giant leap for mankind’s space exploration.
Separation of the Rocket and the Probe
On December 8, 2018, a Long March 3B rocket was launched from Xichang Satellite Launch Center in Sichuan Province, carrying the Chang’e-4 probe into Earth-moon transfer orbit. After a flight of about 1,133 seconds, the two separated.
The Chang’e-4 probe consists of a lander and a rover. Chang’e-4 was born as the backup to Chang’e-3. The first spacecraft to soft-land on the far side of the moon, Chang’e-4 focuses on carrying out comprehensive research on the moon’s geology and resources to enrich studies about the celestial body.
Solar wings unfolded to collect solar energy to power the Chang’e-4 probe.
Queqiao Relay Satellite
Queqiao is operating on the halo orbit around the L2 point, providing communications relay for the lander and rover.
Lagrangian Point 2
Lagrangian Point 2 (L2) is one point near Earth and the moon where a smaller object will maintain its position relative to the two orbiting bodies. At this point, both the far side of the moon and Earth can be “seen” and the Queqiao relay satellite can maintain stable condition.
On December 9, 2018, Chang’e-4 made one trajectory correction before entering its designed orbit for landing. According the original plan, the probe would need three trajectory corrections. One-time trajectory correction could save incredible amounts of fuel for the probe, thus creating good conditions for its later performance and prolonging the lifespan of the device.
Elliptical Lunar Polar Orbit with a Perilune of 100 Kilometers
On December 12, 2018, after space braking, the probe entered an elliptical lunar polar orbit with a perilune of 100 kilometers in which it would stay for 18 days.
On December 30, 2018, after an orbital transfer, the Chang’e-4 probe entered a preset orbit with a perilune of 15 kilometers and an apolune of 100 kilometers, where it would stay for four days.
The braking was a crucial orbital maneuver for the Chang’e-4 probe, through which the probe slowed down below escape velocity, enabling it to be pulled by the gravity of the moon and enter lunar orbit.
On the morning of January 3, 2019, the Chang’e-4 probe began its descent from an orbit 15 kilometers above the surface of the moon. Using an engine thrust, the probe lowered its power and slowed down. Eventually, Chang’e-4 soft-landed on the far side of the moon, the first-ever contact for mankind.
Illustration designed by Xinhua News Agency
Information sourced from China National Space Administration