The Chang'e-4 mission - the results of the fifth lunar day: problems with the Yutu-2 rover and a new scientific discovery

The apparatuses of the Chang'e-4 mission (descent module and rover) successfully completed scientific research during their fifth lunar day on the far side of the moon, sending more than 6.6 GB of scientific data to Earth, and an analysis of some of them obtained using a spectrometer rover "Yutu-2" on the composition of the mantle of the moon, has become a new scientific discovery.

But the operators of the Yut-2 rover had to make some efforts to compensate for the negative impact of the problem that arose in the autonomous driving system.


Data on the project and modules of the Chang'e-4 lunar mission:

May 21, 2018: the Tseyuqiao relay satellite (fortieth bridge) was launched from the Sichang Chinese spaceport, it is necessary for organizing communication between the Earth and the far side of the Moon.

June 14, 2018: Tseyuqiao satellite relay entered orbit around the Lagrange point L2 of the Earth-Moon system, approximately 65,000 km from the Moon, becoming the first communication satellite in this orbit in the world.

December 8, 2018: The Changzheng-3B booster rocket with the Chang'e-4 station was successfully launched from the Sichan space center in China.

January 3, 2019: Chang'e-4 lander makes landing in the Karman crater on the far side of the moon. The Chang'e-4 lander contains the second Chinese lunar rover Yutu-2, a modernized analogue of the Yutu rover. The devices of the Chang'e-4 mission are now continuing to operate normally and send data to Earth for the fifth month.


The Chang'e-4 Descent Module:

• 4.4 meters between opposite landing supports, weight 1200 kg .;
• Duration of work: one earth year.

The following devices are installed on the Chang'e-4 descent module:

• LFS - Low Frequency Spectrometer;
• LND - Lunar Lander Neutrons and Dosimetry (neutron dosimeter);
• TCAM - Terrain Camera (landscape camera);
• LCAM - Landing Camera (landing camera).

Rover "Yutu-2":

• height 1 meter, width 1 meter (without solar panels), 1.5 meters in length, two folding solar panels, six wheels;
• total rover weight is about 140 kg (310 lbs);
• load capacity of about 20 kg (44 lbs);
• can move on slopes and has automatic sensors to prevent collision with other objects;
• The rover is supplied with electricity by means of two solar panels, allowing the rover to work during a lunar day;
• maximum speed of 200 meters per hour (this speed on the Moon can still not be reached, since the elements on the surface will not allow to accelerate and damage the rover earlier);
• the maximum research area is 3 square meters. km;
• the estimated operating time is 3 months (2160 hours), the rover has already exceeded its service life by two months;
• the maximum estimated distance is 10 km, now 190.66 meters have been passed along the lunar surface in five months (1 place among rovers on the far side of the moon, sixth place among all lunar rovers), a table of the distance of rovers is given here ;
• control mode: automatic (detour of small obstacles), manual (main) - the operator controls from the Earth.

The following devices are installed on the Yutu-2 rover:

• LPR - Lunar Penetrating Radar (lunar ground penetrating radar);
• ASAN - Advanced Small Analyzer for Neutrals (small analyzer of neutral particles);
• VNIS - Visible and Near-Infrared Imaging Spectrometer (infrared spectrometer);
• PCAM - Panoramic Camera (dual panoramic camera).

The fifth lunar working day is over, these are the new photos from the far side of the moon that the devices sent to Earth.

A beautiful shadow from the just awakened Yutu-2 rover:





An interesting surface of the back of the moon:





Traces of the Yutu-2 rover and the small stones that it goes around:







But what stones remain away from the Yutu-2 rover route:



Linking the panorama from the descent module to the real relief of the far side of the moon in the landing zone:



Very distant mountains, magnification from the camera of the landing module:



And the most lonely photo - the Chang'e-4 descent vehicle is now more than 100 meters from the Yutu-2 rover (and the likelihood that the rover will return to the descent the device is very small):





Here's how far (its total distance for five lunar days - 190.66 meters) the Yutu-2 rover went from the landing site and the Chang'e-4 descent vehicle:



By the way, based on the discovery, which will be discussed later in the publication, to the rover operators Yut-2 was given the command to take the rover from the landing site to a distance of at least two kilometers so that it was possible to conduct scientific research and compare the results with data obtained near the landing site.

Thus, the Yutu-2 rover awaits a large and complex journey to the center of the Karman crater.



What problems arose with the Yutu-2 rover on the fifth lunar day of its operation?

In fact, the estimated operating time of the Yutu-2 rover is three Earth months, and almost two times have already passed, so breakdowns and problems with the elements of the Yutu-2 rover should begin.

Why was he able to exceed his working time? Because the operators on Earth tried as much as possible to secure its movement on the far side of the moon, minimizing the possibility of damage.

During the first two lunar days, the Yutu-2 rover traveled 120 meters (this is reconnaissance of the landing site and studying the surface of the back of the moon), on the third lunar day the rover traveled 43 meters (the operators started the research phase of the project, in which the rover needs a long time to linger in one place, so that places for research were identified and studied that day), on the fourth lunar day the rover traveled 16 meters, on the fifth lunar day it was already 12 meters, measuring the distance equal to 190.66 meters on its odometer that was covered them about brotherly side of the moon.

Why, on the fifth lunar day, the Yutu-2 rover drove very little?

It turns out that he had a breakdown in the automatic obstacle avoidance system.

Using this system, the Yutu-2 rover can automatically bypass small obstacles that will be fixed by its on-board cameras and sensors.

If there is a large rock or crater in front of him, then he can stop on his own and plan a new route bypassing this place, in this case, the operator at the MCC can register this situation and rebuild the planned route to a new one already after the rover maneuvers automatically and stop. 

So, on the fifth lunar day, the sensors of the automatic obstacle avoidance system, which activate alarms when obstacles occur before the rover, began to work abnormally at the Yutu-2 rover. Because of this, the Yutu-2 rover froze several times, and at that moment control was not transferred to operators on Earth.

The reason for the failure of the rover obstacle avoidance system was established quite quickly - the sensors of the system were exposed due to the reflection of sunlight from elements of the rover body.



Operators in the MCC on Earth were able to compensate for this situation by adjusting the software for the obstacle avoidance system and rebooting this system on the rover. Only after performing all these remote manipulations from the Earth, the Yutu-2 rover was able to continue its studies of the far side of the moon in normal mode.

What new discovery did the Yutu-2 rover make with its VNIS scientific instrument, the Visible and Near-Infrared Imaging Spectrometer (infrared spectrometer)?

What kind of scientific device is VNIS, which is installed on the Yutu-2 rover.

The VNIS lunar infrared spectrometer (The Visible and Near-Infrared Imaging Spectrometer) was developed at the Shanghai Institute of Technical Physics of the Chinese Academy of Sciences.

The spectrometer uses non-collinear acousto-optic tunable filters, it consists of a VIS / NIR video spectrometer (0.45–0.95 μm) and a short-wave infrared spectrometer (0.9–2.4 μm), and it also includes a calibration unit with protection from dust and pollution.

The spectrometer is installed in front on board the Yutu-2 rover, has the following restrictions on positioning and working with lunar material (an operator on Earth needs to literally catch interesting surface areas in a small window in front of the rover):





Minerals, such as pyroxene, plagioclase, olivine and ilmenite, which make up most of the lunar surface rocks, have distinctive spectral characteristics:



The structure of the spectrometer:



The main technical characteristics of the spectrometer:




Appearance of the spectrometer:



Geometric dimensions of the detection window:



Data obtained by the spectrometer:



The most difficult task for the Yutu-2 rover is to obtain scientific data using the VNIS onboard stationary spectrometer (Visible and Near-Infrared Imaging Spectrometer), whose sensor field of view is only a few centimeters, therefore it is necessary to accurately position the rover "Yut-2" so that you can bring the "eye" of the spectrometer to the desired area of ​​the lunar surface to receive the correct data from the optimal distance.



After a short walk along the moon, the Yut-2 rover reached an interesting stone glade, in the center of which a large stone with a diameter of 20 centimeters was discovered. Scientists were immediately interested in this find, its origin (meteorite, lunar formation) and the process of education.

General view of the surface panorama during the search for stones:



The rocky surface, to a large rock (its diameter is 20 centimeters) is a distance of 120 centimeters:



An enlarged image of a large rock:





Work with a spectrometer:





Further, data from the Yutu-2 rover spectrometer is transmitted to the aerospace control center of the Chinese Academy of Space Technologies, where they are analyzed, stored and part of them finally became open to the scientific community and the world .

The planetary feature of the deep structure of the Moon is its division into a powerful rigid, cold outer sphere and a heated, partially molten and plastic inner region.

The thickness of the Moon's crust averages 68 km, varying from 0 km under the lunar sea of ​​Crisis to 107 km in the northern part of Korolev Crater on the reverse side.

Under the crust is a mantle and a small core of sulphurous iron (with a radius of approximately 340 km and a mass of 2% of the mass of the moon).



However, on the far side of the moon, the crust is thinner and easier to explore the mantle of the moon.



Scientists from the Chinese Academy of Sciences presented in the journal Nature the primary results of analysis from the surface of the far side of the moon using a VNIS spectrometer - the first data on the composition of the mantle of the moon were obtained, it turns out that it contains iron-rich minerals.

The composition of the elements located on the lunar surface in the two studied regions with the Yutu-2 rover using a VNIS spectrometer revealed the presence of pyroxenes and olivines - minerals with a high iron content.



These rocks were originally part of the upper mantle and were on the surface of the moon due to the fall of meteorites and asteroids.

Moreover, the moon’s crust consists of lighter minerals of the plagioclase class.

Of course, this discovery requires additional confirmation and a detailed study of the samples. But many scientists already claim that, in general, the new data "were obtained in the framework of the correct and accurate application of spectroscopic methods, and the mineral composition was determined fairly reliably."

The landing site of the Chang'e-4 mission is located in the Karman crater, in the South Pole-Aitken basin, the depth of which reaches 8 km.









Topographic photo of the landing zone in the crater Pocket of the far side of the moon of the Chang'e-4 descent module (made by LRO probe, NASA):



The age of the South Pole-Aitken Basin is 4.2–4.3 billion years. It was formed as a result of a blow of enormous power.

Simulation of the impact along a close to vertical trajectory shows that a considerable amount of the Moon’s substance should have been thrown to the surface from depths of up to 200 kilometers - from the mantle (the lunar crust was pierced to the lower layer).



Thus, with the help of the VNIS spectrometer in the Karman crater, the Yutu-2 rover detected stones and rocks falling there from great depths, presumably from the mantle, on the surface of the back of the Moon.

How the studies were conducted.

After analyzing the photographs and obtaining the primary spectrograms of different places of the lunar surface on the rover route, the operators and scientists at the MCC on Earth chose two places (between them a distance of about 50 meters) to conduct a full cycle of scientific research there (it takes several earth days).

The Yutu-2 rover using the VNIS spectrometer performed extensive studies of the lunar surface at two points on the route (CE4_0015 and CE4_0016): The



data of these measurements, after analysis and processing on Earth:











Here are the test calibration samples for comparison:





Here is such an interesting scientific discovery made by the Yutu-2 rover with the VNIS spectrometer - the soil in the area of ​​the Chang'e-4 mission’s landing area contains olivine and pyroxene - high-density minerals with low calcium and high iron content that hit the surface from the top mantle of the moon under the South Pole – Aitken basin after the shock event that created the nearby Finsen Crater.

Lunar basalts and plagioclases, which became the material for the formation of a regolith layer covering the surface of the Moon, were discovered earlier, and they were brought to Earth in large quantities from the Moon for research.

And in this discovery, on the surface of the moon, elements were found that are contained in the mantle of the moon (very deep), and not on the surface. But they found it in a scientific way - they did not drill hundreds of kilometers in depth, but investigated the area on the far side of the moon, on which particles of the upper mantle were thrown out from the bowels of the moon as a result of a meteorite / asteroid impact into a nearby crater.

The first discovery, which was made back in January 2019: analysis of data from the temperature sensors of the Chang'e-4 apparatus showed that on the surface during a moonlit night on the far side of the moon, the temperature drops to -190 ° C.

By the way, the special Chinese Internet portal “The System of Publication and Collection of Scientific Data and Research of the Moon and Deep Space”, which has already begun to publish and process the data and images from Chang'e-4 (and there are already gigabytes of data), is currently operating from earlier missions).

→ The path to the portal



So lunar exploration continues, and new discoveries await us: