It has been almost 12 years since China launched Chang’e 1, their unmanned spacecraft which orbits the moon. After 2007, they later launched Chang’e 2 in 2010, Chang’e 3 in 2013, and now Chang’e 4 is set to probe the dark side of the moon. According to reports, the Chang’e-4 lander and rover are scheduled to launch in December this year to perform the first-ever soft-landing on the far side of the Moon.
Even though the moon rotates, the same side always faces the Earth since the amount of time it takes for the moon to rotate on its axis is the same amount of time it takes to make a full orbit around the Earth.
This latest launch is part of China’s growing ambitions for lunar exploration, which has already achieved numerous successes. The previous mission involved the Chang’e-3 probe and Yutu lunar rover.
How Queqiao Works
This is the first communications relay satellite in orbit around the moon and the orbiter’s name, Queqiao literally means “Magpie Bridge. The name has been derived from a 2,000-year-old fairy tale originating from the Han Dynasty.
Queqiao, the 450-kilo satellite also carries a Netherlands-China Low-Frequency Explorer (NCLE) instrument to carry out low-frequency astronomy which is not possible on Earth due to its atmosphere, and provide a window into the cosmic ‘dark ages’.
The Queqiao orbiter will act as a link between the Chang’e-4, which is set to go to the far side of the moon later this year, and communications stations on Earth. However, experts say that the moon does not have a dark side. But given the way it orbits the Earth, our current satellites shows us only one side of the moon.
The far side of the moon is essentially the hemisphere that faces away from Earth. The far side’s terrain is rugged with a multitude of impact craters and flat lunar maria. It also has one of the largest craters in the Solar System, the South Pole–Aitken basin.
One of two microsatellites launched along with a required communications relay satellite in May has quietly been allowing radio operators to download images from the spacecraft taken along its elliptical lunar orbit.
After a 24-day journey, Queqiao entered the Earth-Moon L2 halo orbit. While a normal mission to lunar orbit takes up to four or five days, Queqiao took much longer due to its special orbit.
In Stage 1 from Earth to the vicinity of the Moon, the launch took place on 21 May 2018 at 5:28 AM Beijing time and the satellite was sent directly into an Earth-Moon transfer orbit without an Earth parking orbit phase. There are two kinds of transfer orbits from Earth to the vicinity of Earth-Moon L2. One is a direct transfer, which is directly from the Earth parking orbit to L2.
The relay satellite used a lunar swing-by transfer orbit with an apogee of about 400,000 kilometres from Earth. According to reports, the transfer orbit requires 2 or 3 trajectory correction manoeuvres and takes about four or five days to arrive at the Moon.
On May 25, Queqiao performed another burn when it flew past the Moon at a distance of just 100 kilometres. This successfully put it on a Moon-L2 transfer orbit.