What problems need to be solved in building a lunar base?

To establish a long-term base on the moon, we must ensure that astronauts can live and work safely in the base, and also consider long-term sustainability, which involves many practical issues.

Bezos' lunar lander

Siting for water

If we want to establish a long-term manned base on the moon, we must first solve the problem of water supply. The surface of the moon is not a low-Earth orbit. If we rely on continuously launching cargo spacecraft from the earth to solve the water problem, it can only support the lives and exploration of a few people, and cannot support large-scale bases, nor have the ability to respond to sudden disasters. Water recycling cannot solve all problems, because there will always be losses in the process of treatment. The best way is to find a water resource on the moon that can be mined. The question is, is there such a place?

The first choice is a location on the edge of Shackleton Crater in the Aitken Basin at the lunar south pole. In a December 4, 2006 briefing, Doug Cook, associate administrator of NASA's Exploration Systems Mission Directorate, said that this area is illuminated 75% to 80% of the time and is adjacent to a permanently shadowed area. The latter will retain some volatile materials (water ice) that can be extracted and used.

NASA has announced that it intends to build an outpost at the South Pole or North Pole of the Moon, with astronauts stationed there for a long time, with shifts every six months. At that time, research believed that there was water ice in the lunar polar craters, and the outpost might be able to maintain operation with water collected locally. The outpost design includes the following elements: a living module, a solar power generator, a non-pressurized lunar rover, an on-site resource utilization (ISRU) unit, and a lunar surface transport vehicle.

The lunar lander + lunar base integration plan proposed by civilians

NASA has proposed two other candidate sites, including the rim of Pyle Crater near the moon's north pole and the Malapert Mountains on the rim of Malapert Crater.

However, in the polar regions of the moon, the blowing of the solar wind will generate electric charges on the leeward side of the edge of the crater. The resulting voltage difference may affect electrical equipment, change the surface chemical properties of materials, erode the surface of materials, and cause lunar dust to be suspended in the air. Therefore, some people advocate building a base in the equatorial region of the moon. At this location, the solar wind has a larger incident angle, so the helium-3 concentration may be higher, and a nuclear power plant can be used to power the lunar base. The equatorial position is also more conducive to taking off from the lunar surface. The lunar equator basically coincides with the earth's equatorial plane and the ecliptic plane of the moon's rotation around the earth, and the orbital correction amount for the round trip between the earth and the moon is relatively small.

It would be most convenient to place the living module directly on the lunar surface, just like the early Antarctic research stations. However, the moon does not have the protection of the Earth's ionosphere. No matter what materials are used to make it, artificial facilities exposed to cosmic rays and solar wind will quickly age and fail. Moreover, the weight and volume of artificial materials that can be sent from the Earth to the moon are limited, and cannot provide a thick enough protection for the lunar living module.

Caves and Lava Tubes

Since the conditions on the moon's surface are so harsh, is it okay to live underground? The average temperature on the moon's surface during the day (about 354 hours) is about 107°C, with a maximum of 123°C; the average temperature at night (also 354 hours) is about -153°C. However, the temperature and pressure inside the moon increase with depth. In underground facilities, the temperature during the day and at night is about -23°C, and electric heaters can be used to control the temperature to a level where humans can live comfortably.

A lunar base hidden underground

An underground lunar base can effectively avoid radiation and micrometeoroids, and will greatly reduce the risk of air leaks. However, the construction of an underground base may be more complicated. First, the excavation must be carried out by remotely controlling engineering machinery from the earth. After the excavation is completed, some kind of hardening must be carried out to avoid collapse. Such technology is relatively mature. Some concrete-like substances can be sprayed on the cave walls. After solidification, they can be guaranteed to be strong, and then porous insulating materials can be sprayed to achieve sealing. If the technology of utilizing local resources on the moon is broken through, the above materials can also be manufactured on site. Some scholars suggest using "on-demand" machines, so that the inner wall of the cave can be vitrified as the construction is completed. Others have suggested that methods such as mine rooms and pillars in mines on Earth can be used. First, a relatively large cave is dug, and then a soft inflatable sealed living cabin is set in the cave. In this way, even if there is a small amount of air leakage in the cave, the air pressure and temperature in the living cabin can be ensured to be normal. In this way, an underground city can eventually be built. Using this idea, an artificial sun can also be set on the top of the cave to provide sunlight for the underground farm.

Farm at the Moon Base

In addition to man-made underground facilities, people also expect to find some naturally formed caves on the moon. The moon was originally a large piece of magma, which solidified to form the moon today. Therefore, these caves are generally formed during the solidification process because the volume of magma gradually decreases. Lunar research professionals call them lava tubes. People believe that such lava tubes may also exist on Mars.

So far, no probe launched by humans to the moon has discovered or investigated a real lava tube, and astronauts did not look for such terrain during the Apollo moon landing. Some probes orbiting the moon have photographed landforms that appear to be lava tubes, which shows that there is hope for finding natural caves to build a lunar base.

If a suitable lava tube can be found, it will bring great benefits to the construction of a lunar base. Lava tubes can allow base facilities and astronauts to avoid the harsh environment on the lunar surface, and they will not be attacked by frequent meteorite impacts, high-energy ultraviolet radiation and high-energy particles. The workload of air conditioning equipment will not be as heavy as on the lunar surface. Of course, it can also save the huge amount of earthwork work of digging artificial caves.

Artificial Mountain

So, can we build an artificial mountain on the moon? To this end, many researchers have proposed the so-called double dome plan, which is to first build an artificial facility and then cover it with lunar soil. According to American research, the main components of the lunar dome are silicon dioxide and iron-containing compounds. If they can be heated by powerful microwave beams, they can be melted and condensed to form a glassy solid. A scientist named Balacock believes that this "lunar glass" may have quite good mechanical properties and is a promising material for making rigid structures. The lunar soil can also be fired into "lunar bricks" and laid on a metal frame.

After the emergence of 3D printing technology, it has naturally become one of the most concerned construction technologies for lunar scientists. In addition to NASA, some private companies are also designing lunar 3D printing technology. According to a company called "Foster + Partners", if the lunar regolith is used to make building materials and covered on the inflatable living cabin, only 10% of the structural materials for the entire construction project need to be transported from the earth. Specifically, this technology mixes lunar regolith with magnesium oxide and then uses an adhesive to "convert this material into a stone-like solid." It is said that the capacity of this 3D printing prototype is enough to build a house within a week.

NASA plans to use 3D printing to build houses on the moon

The floor of the lunar base is also 3D printed

Power supply

Whether it is construction or living, people need to provide enough electricity for the lunar base. So far, three means of power supply have been used in lunar exploration - chemical batteries, solar cells and radioisotope power sources. Chemical batteries were used by lunar rovers and drilling tools during the Apollo moon landing. Because the activity time of each Apollo mission on the moon was very limited, chemical batteries were sufficient, which of course could not be used as a source of energy for long-term lunar activities.

There is no atmosphere on the moon, and the sun shines directly on the surface, with strong energy. Therefore, as long as it is during the lunar day, solar power generation is not a problem. Moreover, the silicon materials needed for the production of solar panels and the iron and aluminum materials needed for the solar panel brackets can be mined on the lunar surface, which has great advantages for the subsequent gradual expansion of the lunar base. Some people also proposed that solar energy can be used for heating, and then Stirling engines can be used to drive electric motors. However, although the lunar day is long, the lunar night is also long. In order to obtain continuous electricity, solar power stations must be set up at the poles, or large-capacity fuel cells must be set up at the lunar base. Fuel cell technology has been successfully applied on the space shuttle and can operate for up to 17 Earth days, which exceeds the demand for power generation on the lunar night. Today's proton exchange membrane (PEM) fuel cells are far more advanced than the technology on the space shuttle, but the proton exchange membrane has not yet been implemented in space flight. In any case, combining fuel cells with solar power generation has the hope of providing a sustainable power supply. Some people even proposed that power generation satellites can be deployed in the lunar geostationary orbit, so there is no need to worry about the lunar night. However, the lunar geostationary orbit is very far from the lunar surface, and the beam divergence problem is relatively serious.

Japan's lunar base concept

The environment on the moon's surface is harsh. Even if it is covered with thick lunar soil, it may not be able to completely block cosmic rays, especially high-energy particles. Therefore, some people have proposed that an artificial magnetic field needs to be built to provide radiation shielding. This requires a strong power supply for the lunar base, and whether the solar power plant can meet the requirements is somewhat doubtful. Therefore, it seems reasonable to build a nuclear power plant on the moon. However, the investment required and the technical difficulties to be overcome are also imaginable.

According to the Fission Surface Power (FSP) project proposed by NASA in 2000, low-temperature stainless steel, liquid metal cooling reactor technology and Stirling generators can be used to generate electricity on the moon. By 2010, the testing of important components of FSP had been completed, and non-nuclear system demonstration tests were being carried out intermittently. FSP can generate a stable 40 kilowatts of electricity, which is equivalent to the power consumption of about 8 single-family houses on Earth. This reactor is buried below the surface of the moon to avoid radiation to astronauts. The tower-shaped generator part extends above the reactor surface, and the umbrella-shaped radiator extends out of the moon surface, radiating waste heat directly into space.

We mentioned radioisotope thermal batteries earlier. Russia is currently in the lead in nuclear batteries. This type of battery is characterized by a simple structure and no moving parts, but has a relatively low power generation capacity. It can be used as a backup power source and emergency power source for the lunar base.

Bases and transportation

From the above discussion, we can find a problem. It seems that no base site is absolutely perfect. So, can humans build a base in different locations on the moon to undertake different tasks? If the exploration of lunar minerals is successful and some important rich mines are discovered, then the necessity of opening multiple bases will be even more significant. Therefore, scientists have begun to discuss the issue of lunar transportation. Obviously, using lunar rovers for commuting or transportation is too slow, so can railways work? There is no air resistance on the moon, the gravity is relatively small, and there is no need to consider troublesome things such as land acquisition and demolition. The high-speed rail that the Chinese are good at has better conditions to be carried forward, and even freight trains can run at the speed of airplanes! Of course, if passengers do not want to wear space suits and ride open-top trains, they need to set up life support systems in railway passenger cars.

If you want to conduct an investigation far from the base and the lunar rover is too slow, you can also consider flying there. There is no air on the moon, so airplanes that use the pneumatic flight principle are of course useless. Therefore, scientists have long imagined jet-jumping aircraft, and Bell Aerosystems of the United States has proposed such an idea. Of course, if Musk's stainless steel rocket "Starship" can really be successfully developed and enter the universe, it can also undertake this kind of work.

Musk's "Starship" can be used as a means of transportation for long-distance transportation on the moon

Earth-Moon Transit

Although the focus of this article is the lunar base, it is still necessary to discuss the prerequisite for building a lunar base, that is, the lunar spacecraft. Strictly speaking, China, the United States, and Russia have not yet developed a lunar spacecraft. The Apollo spacecraft of the United States has long been lost, and the lunar spacecraft of the Soviet Union is just a PPT. China, the United States, and Russia are developing manned spacecraft that travels between the earth and the lunar orbit. The most advanced is the Orion spacecraft. This model proposed in 2004 has already carried out a space flight. Whether it can really fly to the moon actually depends on the development progress of the SLS rocket.

China's new generation of manned spacecraft also carried out a flight in early 2020. Its subsequent development progress also needs to wait for the successful development of higher-performance rockets. In contrast, the progress of Russia's new generation of spacecraft "Eagle" is worrying. What people have seen so far is just a model, and the engineering prototype has not yet been unveiled. Russia publicly announced in 2020 that it would achieve its first flight in 2024. Whether it can really be achieved remains to be seen.