China launches Chang'e-4, in attempt to be first in landing on far side of the Moon
By Wu Lei, Chen Weikui
China successfully launched the Chang'e-4 lunar probe aboard a Long March 3B rocket at 2:23 a.m. BJT on December 8. With a lander and rover, its key mission is to explore the far side of the Moon, a side not visible from the Earth.
People have been admiring the Moon for thousands of years, but the mysteries there are about to get a lot closer. Blasting off from Xichang Satellite Launch Center, China's Chang'e-4 lunar probe could be the first ever to soft-land on the far side of the Moon.
The Moon's far side, or dark side, is not visible from the Earth due to a phenomenon called tidal locking.
To explore this uncharted area, the first key challenge was to guarantee communication with controllers on Earth. On May 21, China launched Chang'e-4's relay satellite, Queqiao or Magpie Bridge. It has since entered the Halo orbit, where it serves as a perfect communication link.
In addition to carrying out three scientific pilot projects developed by three Chinese universities, the rover will serve as a platform for global cooperation.
The rover will be equipped with four major scientific payloads, which were jointly developed by scientists from the Netherlands, Germany, Sweden, Saudi Arabia and China.
Why does the lunar probe have to be launched in the early morning?
Both of China's Chang'e-3 and Chang'e-4 lunar probes were lifted off in the early morning.
According to Sun Zezhou, chief designer of Chang'e-4, the window for the probe to touch and land on the Moon is strictly limited. The probe has first to become the Moon's satellite and then, land on the Moon. After exact calculating, they set the launch time at 2:23 a.m.
Why does the probe have to orbit the Moon for over two weeks?
The lunar probe has to be landed on the Moon in the morning so that they can get enough solar energy to work.
Sun explained that since the rotation period of the Moon is 28 days, that is to say, the "one day" on the Moon is equivalent to a month on Earth, so the lunar probe Chang'e-4, which began to orbit the Moon at night, will have to wait for about half a month before it can catch up with the Moon in the daytime to land.
Over the next few weeks, Chang'e-4's journey through space will bring it to the Aitken Basin in the lunar south pole region. It's expected to touch down there sometime in January.