Facing complex road conditions, how does a manned lunar rover master all its skills?

Recently, the design of my country's manned lunar rover has entered a new stage. At the same time, some novel and unique manned lunar rover plans have been exposed at home and abroad. So what challenges does the manned lunar rover need to deal with in the lunar environment? How can it be designed in the future with the help of new technologies to complete complex and diverse tasks?

The lunar environment presents many challenges

The lunar rover is a special vehicle that can travel on the lunar surface and complete complex tasks such as detection, investigation, collection and analysis of samples. Its scientific name is "lunar rover". In particular, the manned lunar rover can greatly expand the scope of astronauts' activities on the moon, reduce physical exertion, and facilitate the storage of lunar samples collected by astronauts. Even though it seems simple, it still has to overcome many challenges.

The US Apollo 16 crew trained in driving the manned lunar rover

First, it is necessary to adapt to the unique gravity environment. As we all know, the gravity on the lunar surface is only 1/6 of that on Earth. A larger and heavier manned lunar rover will experience a greater "weight loss", which will in turn face the risk of weakening its grip. If the vehicle uses common rubber tires, the tires are likely to experience pressure drops, abnormal shapes, and other problems, and will not work properly, significantly affecting driving efficiency and safety.

Secondly, the complex road conditions cannot be ignored. The lunar surface is covered with thick lunar soil, which is mainly composed of debris produced by celestial bodies after long-term grinding and mixing. There is no atmosphere and water cycle on the moon, so there is no wind and rain erosion to level the lunar surface, resulting in a rugged lunar surface. The terrain changes are more irregular than the surface of the earth. In addition, the lunar soil is very small, sharp, and sticky, which is likely to pierce, scratch, and block the wheels and other driving mechanisms. The manned lunar rover must overcome many obstacles to ensure that it can move forward, backward, turn, and climb. The selected materials, structures, and testing processes must withstand the intense "torment", and the driving must also be in line with the principles of ergonomics.

Third, it is difficult to avoid a strong radiation environment. The type, energy, and intensity of radiation in the cis-lunar space and on the lunar surface are very different from those near the Earth. For example, the moon has no protective layer to block solar radiation. The Chang'e-4 probe once found that the particle radiation dose in the landing area on the far side of the moon was 300 times that of the surface. Therefore, the mechanical parts of the manned lunar rover and the highly integrated microelectronic components that are extremely sensitive to radiation must adopt strict radiation resistance, corrosion resistance, and aging resistance measures. Compared with the unmanned lunar rover, astronauts are the "weak link" and focus of radiation protection for the manned lunar rover.

Fourth, the drastic temperature difference needs to be overcome. The lack of air and water, coupled with the extremely low thermal conductivity of the lunar soil, leads to drastic temperature changes on the lunar surface. It is not uncommon for the temperature difference between day and night at the same location to exceed 300 degrees Celsius. Rubber and other materials are easy to age, harden, crack, and fall off, so they are basically not used for manned lunar rovers. In the "Apollo" mission, the manned lunar rover was a "simple convertible frame". In order to avoid extreme temperature and radiation damage, astronauts actually hid in the cabin for most of their "moon landing time". The materials used for the new generation of manned lunar rovers must have good heat and cold resistance, and will not lose elasticity and strength due to temperature changes. They must also have their own "air conditioning" to continuously adjust the temperature at any time, so that the astronauts' time on the moon is more "real".

In addition, the manned lunar rover must adapt to the special mechanical environment of space launch and the test of the space environment. For example, during the rocket launch and the lunar landing, the manned lunar rover must overcome the test of impact, vibration, overload and noise.

Strict demands for food, clothing, housing and transportation

In the foreseeable future, the manned lunar rover will be the only means of transportation for astronauts to conduct scientific research and stay on the moon. Based on human needs, the manned lunar rover must meet the astronauts' "clothing", "food", "housing" and "transportation" needs on the moon.

Imaginary picture of Japan's large enclosed manned lunar rover

"Clothes" - lunar rovers need "armor". After landing on the moon, astronauts and the manned lunar rover are completely exposed to strong cosmic rays. They cannot rely solely on space suits to protect their health, and it is difficult to ensure that the electronic remote control system is foolproof. It also places very high demands on many indicators of the communication system. In addition, the thickness of the lunar soil in relatively flat areas of the moon can reach 5 to 6 meters. When the manned lunar rover is driving, it is easier to bring up a large number of fine particles, covering instruments and equipment, affecting work efficiency and data analysis accuracy, and even threatening personnel safety. Therefore, the "armor" must have good protection strength and be "meticulous".

"Food" - Lunar rovers cannot do without stable and abundant energy. Currently, unmanned lunar rovers mostly use a combination of solar cells and isotope heat sources for energy supply. Manned lunar rovers consume more energy and have higher requirements for the continuity and stability of energy supply.

Each lunar night is equivalent to 14 days on Earth, which has become the energy supply duration indicator for some foreign manned lunar rovers and lunar habitat designs. So for nearly half a month, the manned lunar rover cannot rely on solar power and must innovate the technical design model of "increasing revenue and reducing expenditure".

"Living" - If astronauts frequently enter the space capsule to avoid radiation and extreme temperatures, it will inevitably affect work efficiency and accelerate the consumption of energy in the manned lunar rover. Therefore, the development of the manned lunar rover into a "lunar RV" is likely to be the general trend.

This not only puts higher demands on the "armor" and energy of the manned lunar rover, but also challenges its temperature control system: it must sensitively measure temperature changes, quickly transfer heat, and maintain internal temperature balance. Obviously, the material selection of different parts of the manned lunar rover must be carefully planned.

"Travel" - The manned lunar rover driving on the moon not only relies on special wheels to overcome the harsh terrain. On the one hand, there will be a delay in the transmission of commands from the Earth team, and the manned lunar rover needs to process road condition information in a timely manner, which emphasizes autonomy. It requires the driver to pay attention to road conditions and cannot do without artificial intelligence support. On the other hand, if you want to find your way on the moon, the detection equipment of the manned lunar rover is indispensable. If it is supported by aerial remote sensing, it will be twice the result with half the effort.

New technology helps you to run faster

If a manned lunar rover wants to carry out activities safely on the moon, the most basic preparation is to "wear the right clothes". In response to the threat of radiation, in addition to using traditional electromagnetic protection materials, some researchers have proposed a new idea: cleverly deploy a series of magnets at the right time to generate a stable magnetic field around the manned lunar rover, which is equivalent to "putting on invisible electromagnetic protection armor" for it. This is not only expected to shield and offset the adverse effects of electromagnetic radiation, but also to absorb lunar dust particles, solving the "unspeakable secret" of the manned lunar rover.

Concept image of the "Wangshu Chariot" manned lunar rover designed by a team led by Tsinghua University in my country

What should we do when solar cells are out of service on cold moonlit nights? Many manned lunar rover plans use isotope heat sources. Obviously, isotope heat sources make energy supply devices smaller and lighter, helping manned lunar rovers store enough "rations".

Of course, if the requirements for volume and weight are not so stringent, and the problem of in-situ utilization of lunar resources is further solved, fuel cells may also have the opportunity to be used in manned lunar rovers.

In addition, advanced thermal control technologies such as high-efficiency heat pipes, phase change energy storage, and variable emissivity thermal control devices are also expected to help keep the manned lunar rover warm: during the day, sufficient heat is collected and stored in phase change materials; at night, the heat is released through phase change and passes through an efficient fluid heat pipe loop to create a comfortable environment.

Mesh tires that use "piano wire" to maintain elasticity are gradually becoming the choice of extraterrestrial rovers, and manned lunar rovers are no exception. In view of the complex terrain of the moon, the independently driven multi-wheeled rocker-arm walking system has a considerable advantage. Each wheel can adjust its height by itself, just like the joints of the human body, helping and cooperating with each other, making the lunar rover a "climbing expert" when necessary. Considering the special characteristics of lunar gravity and lunar soil, the manned lunar rover may be able to try rocket-powered jumping and sled-like sliding forward, provided that it fully understands the lunar terrain information.

In order to understand the lunar terrain, the manned lunar rover needs to be equipped with autonomous navigation and intelligent driving systems, implement autonomous obstacle avoidance and path planning, or provide the driver with an expert assistance mode. For example, the 360-degree rotating navigation camera can observe the terrain in advance, and the system automatically edits the map and plans the route. When encountering a slope greater than 30 degrees, a stone higher than 25 cm, or a lunar impact crater with a diameter of more than 2 meters, the manned lunar rover can receive an early warning in time and make an emergency detour, reducing manual intervention, helping astronauts concentrate, and completing the task more scientifically and efficiently.

Recently, the China Manned Space Engineering Office announced the preliminary results of the manned lunar rover development plan, and there are many novel and cool elements. For example, the human-machine intelligent hybrid enhanced driving technology, the adjustable body tilt design, the creeping driving function, etc. help astronauts drive more easily and safely, the seat position design helps astronauts save energy and broaden their horizons, and the ingenious folding and unfolding structure also alleviates the difficulties of power supply, temperature control, space, etc.

In short, the manned lunar rover program fully demonstrates the strength and creativity of scientific researchers, and will surely help astronauts further uncover the mysteries of the moon. (Author: Zhang Kai Image source: NASA, Japan Aerospace Exploration Agency, Tsinghua University Review expert: Jiang Fan, deputy director of the Science and Technology Committee of China Aerospace Science and Technology Corporation)