China is preparing for a new ambitious mission to land on the side of the moon

In December, China will attempt the first ever soft landing of a spacecraft on dark side of the moon. The official start date of the mission have not been announced, but according to the latest rumors, the launch should take place on December 8th and landing on the satellite at the end of the month, according to the magazine IEEE Spectrum. According to the mission team, the possibility of accurate landing at a specific point of the satellite, as well as scientific work in offline mode, could form the basis for future programmes to explore deep space, as well as give scientists the experience that will prove useful in future missions to study the poles of the moon, scheduled for early 2020-ies.

At the same time the first landing of a spacecraft on the back side of the satellite promises to be a stern test new communications and navigational techniques, and planting methods.

The unit “Chang’e-4”, consisting of a stationary lunar station and Rover, which landed on the side of the moon, was originally developed as a stand-in “Chang’e-3” — the first Chinese unit landed on the lunar surface in 2013. But after the spacecraft successfully landed in a place called the Sea of Rains, the scientists decided to use the “Chang’e-4” in a separate mission, the purpose of which is the study of the back side of the moon.

Interestingly, the lunar Rover “WiTu”, which “Chang’e-3” landed on the surface in 2013, managed over two lunar day after landing (by earthly standards about a month) to move only 114 meters, then went out. Li Ming, Vice President of the China Academy of space technology meeting International Astronautical Congress, held in October of this year in Germany, without technical details said that the main cause of breakage of steel “small machine components”. A new 140-kilogram lunar Rover “Chang’e-4,” said Mines, must be more reliable and will be able to operate much longer than originally structurally prepared for a 3-month work Rover “WiTu”.

As a repeater to transmit data to Earth from the new Rover “Chang’e-4” will make Chinese artificial satellite “, Zhuazao” (marked orange) which orbit (marked in green) will be over the Moon

One of the toughest tests for the team involved in the preparation of the mission “Chang’e-4” is the fact that the reverse side of the moon cannot be seen from Earth. With time the gravitational forces of the planet slowed its rotation, so the satellite is now in the permanent tidal capture. In other words, the Moon is always turned to us only on one side. Unfortunately, the inability to see the opposite side of the satellite makes it difficult for communications with the Rover and the lander.

To solve the problem, China will send in may next year to the back side of the moon artificial satellite repeater “, Zhuazao”, which is a so-called Lissajous orbit. While in this orbit, the probe will rotate around 60-80 thousand kilometers behind the Moon in the so-called point of Lagrange L2. From this position he can see the other side of the moon, and the Earth, which will be relayed signals from the Rover and the lander.

To communicate with the Rover and lander satellite”, Zhuazao” will use the three-centimeter range (frequency 5200-11000 MHz). In turn, the devices on the surface will transmit messages to each other using ultra high frequency radio waves. For transmitting messages between “Cacao” and ground stations will use the S band (frequencies 1550-5200 MHz). China has recently increased the number of its ground stations, adding to what is already defined in Jiamusi and Kashi, is a new installation in Argentina and Namibia – they are going to use for the transmission of telemetry devices, tracking and sending commands to new scientific problems.

During landing of the combined spacecraft weight 3780 pounds, you should consider the topography of the back side of the moon, which is substantially different from the one that is nearest to us side. The surface on the reverse side is very uneven, with only several relatively flat areas of dark, basaltic plains, which is on the near side much more. In addition, on the reverse side there is a very big difference of heights and a more generous coating of craters. All this complicates the search spacious enough and flat landing pad. For the same lander “Chang’e-3,” choosing seats was carried out on an area of hundreds of square kilometers. “Chang’e-4” will have to choose on the basis of only a few tens of square kilometers of suitable area.

Because of these limitations it was decided to hold the landing of the spacecraft “Chang’e-4” in the Pocket crater diameter of 180 kilometers, which is near the pool South pole — Aitken. This place is the oldest and largest impact crater in the Solar system (diameter of 2500 km) and enjoys a great interest from scientists because it may contain the exposed areas of the lunar mantle, which could open up new details about the evolutionary processes in the system Earth-Moon. According to Ping Zingana responsible for nizkochastotnoi spectrometer new Rover, crater Pocket was chosen not only for this reason. In fact, this is the only place in the basin South pole— Aitken, having at least some flat surface suitable for planting.

This photograph of the lander “Chang’e-3” was made by the lunar Rover mission in 2013

The algorithms used by the subsystems for navigation and control of spacecraft, “Chang’e-4”, responsible for the movement of the lander, its orientation in space and the laying of the course has been significantly modified and tailored to the topography of the back side of the moon.

The descent of the apparatus to the surface will be carried out in six steps. The first three or deceleration, rapid adjustment of rate and orientation, as well as convergence with the surface – will be monitored by the control center from Earth. The remaining three hang-up, security check of the descent and, in fact, slow landing on the moon – will be carried out lander offline. The radius of the area of the lower unit will be around 450 kilometers, but compared to the “Chang’e-3” new lander and Rover will sit at a more direct angle.

It should also be noted that the new lander and the Rover are more adapted to work on the lunar surface, compared with the previous devices. Both come with power supplies on the basis of radioisotope thermoelectric generators, which allow them to conduct temperature measurements of the surface. For example, during the lunar night the ambient temperature may fall here to almost -180 degrees Celsius. The Chinese space Agency expects that due to more careful preparation of new lunar mission will be longer and more successful.

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