In December, China will attempt the first ever soft landing of a spacecraft on the back of the moon. The official start date of the mission has not yet been announced, but according to the latest rumors, the launch should take place on December 8, and landing on the satellite – at the end of the month, according to IEEE Spectrum magazine. According to the mission team, the possibility of precise landing at a certain point of the satellite, as well as scientific work in offline mode can lay the Foundation for future programs for the exploration of deep space, as well as provide scientists with experience that will be useful in future missions to study the poles of the moon, planned for the early
At the same time, the first landing of the spacecraft on the back of the satellite promises to be a severe test of new communication and navigation technologies, as well as landing technologies.
The device “Chang’e-4″, consisting of a stationary lunar station and lunar Rover, which will land on the reverse side of the moon, was originally developed as a backup” Chang’e-3 ” — the first Chinese device landed on the lunar surface in 2013. But after the device successfully landed in a place called the sea of Rains, the scientists decided to use “Chang’e-4” in a separate mission, the purpose of which is to study the reverse side of the moon.
Interestingly, the lunar Rover “Yutu”, which “Chang’e-3” landed on the surface in 2013, was able to two lunar days from the date of landing (by earth standards about a month) to move only 114 meters, and then out of order. Li Ming, Vice-President of the Chinese Academy of space technology at the meeting of the international Congress of Astronautics, held in October this year in Germany, without technical details said that the main cause of the failure was “small components of the machine”. The new 140-kilogram lunar Rover “Chang’e-4”, Min added, should be more reliable and will be able to function much longer than the initially structurally prepared for 3-month operation of the Rover “Yutu”.
One of the most difficult tests for the team involved in the preparation of the mission “Chang’e-4” is the fact that the reverse side of the moon can not be seen from the Earth. Over time, the gravitational forces of our planet slowed its rotation, so the satellite is now in constant tidal capture. In other words, the Moon is always turned to us only one side. Unfortunately, the inability to see the back of the satellite makes it difficult to communicate 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 about 60-80 thousand kilometers behind the Moon at the so-called Langrange point L2. From this position, he will be able to see the reverse side of the moon, and the Earth, which will be retransmitted 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 microwave 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 installed in jiamus and Kashi, new installations in Argentina and Namibia – they are going to be used to transmit telemetry from vehicles, tracking, and transmitting commands for new scientific tasks.
When landing a combined spacecraft weighing 3780 kilograms, it is necessary to take into account the topography of the back side of the moon, which is significantly different from the one on the side closest to us. The surface on the reverse side is very uneven, with only a few relatively flat areas – dark basalt plains, which are much larger on the near side. In addition, on the reverse side there is a very large difference in height and more abundant coverage of craters. All this complicates the search for a sufficiently spacious and flat landing site. For the same landing module “Chang’e-3” the choice of a landing place was carried out on the area of hundreds square kilometers. Place for “Chang’e-4” will have to choose based on 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. The site is the oldest and largest impact crater in the Solar system (2,500 km in diameter) and is of great interest to scientists, as it may contain open areas of the lunar mantle that may reveal new details about the evolutionary processes in the Earth-Moon system. According to Ping Jinsun, who is responsible for the operation of the low-frequency spectrometer of the new lunar Rover, the Pocket crater was chosen not only for this reason. In fact, this is the only place in the South pole basin— Aitken, which has at least some flat surface suitable for planting.
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 device to the surface will be carried out in six steps. The first three – deceleration, rapid course and orientation adjustment, as well as approach to the surface – will be controlled by the control center from the Ground. 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 descent of the device will be about 450 kilometers, but compared to the” Chang’e-3 ” the new landing module and the lunar Rover will land at a more right angle.
It should also be noted that the new lander and lunar Rover are more adapted to work on the lunar surface, compared to previous devices. Both are equipped with power supplies based on radioisotope thermoelectric generators, which will allow them to carry out temperature measurements of the surface. For example, during the lunar night the ambient temperature can drop here to almost -180 degrees Celsius. The Chinese space Agency expects that, with more careful preparation, the new lunar mission will be longer and more successful.
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