The coldest places on Earth and nearby do not stand close to the temperature of the moonlit night - and it is very difficult to create a base that will be able to protect settlers from such a temperature. For many decades, the thought of colonizing the moon has worried scientists and far-sighted people. Various concepts of lunar colonies have appeared on TV screens and monitors.
Perhaps a lunar colony will be the next logical step for humanity. This is our closest neighbor in the stars, which is some 383,000 kilometers from us, which simplifies resource support. In addition, there is an excess of helium-3 on the moon, an ideal fuel for thermonuclear reactors, which is very scarce on Earth.
The route for the permanent lunar colony was theoretically sketched by various space programs. China has expressed interest in locating a base on the far side of the moon. In October 2015, it became known that the European Space Agency and Roscosmos are planning a number of missions to the Moon in order to assess the possibilities for placing permanent settlements.
Nevertheless, our satellite has a number of problems. The Moon makes one revolution in 28 Earth days, and the lunar night lasts 354 hours - more than 14 Earth days. A long night cycle means a significant drop in temperatures. Temperatures at the equator range from 116 degrees Celsius during the day to -173 degrees at night.
Moonlit nights will be shorter if the base is located at the North or South Pole. “There are many reasons to build such a base at the poles, but there are other factors to consider besides the hours of sunlight,” says Edmond Trollope, space operations engineer at Telespazio VEGA Deutschland. As on Earth, it can be very cold at the poles.
At the lunar poles, the Sun will move along the horizon, not across the sky, so you will have to build side panels (in the form of walls), which will complicate construction. A large flat base at the equator would collect a lot of heat, but to get to the heat at the pole, you have to build upwards, which is not easy. “With a sensible location, temperature differences can be easily controlled,” says Volcker Meiwald, a scientist at the DLR German Aerospace Center.
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The wide variability of temperatures in the cycle of day and night means that lunar bases will have to be provided not only with sufficient insulation from the freezing cold and searing heat, but also to cope with thermal stresses and thermal expansion.
Thermal protection
The first robotic missions to the moon, like the Soviet Moon missions, were designed to live one lunar day (two Earth weeks). The lander of NASA Surveyor missions could resume work on the next lunar day. But the damage done to components during the night often prevented scientific data from being obtained.
The lunar rovers of the Soviet space program of the same name, which was carried out in the late 60s and 70s, included elements of radioactive heating with an ingenious ventilation system, which allowed the vehicles to live up to 11 months. Lunar rovers would hibernate at night and launch with the sun when solar energy became available.
One option to avoid high thermal fluctuations is to bury the building in lunar regolith. This powdery material, which covers the surface of the Moon, has low thermal conductivity and high resistance to solar radiation. This means that it has strong insulating properties, and the deeper the colony, the higher the thermal protection. In addition, since the base will heat up and the heat on the moon is poorly transferred due to the lack of atmosphere, this will reduce further thermal stress.
However, while the idea of "burying" the colony was, in principle, accepted successfully, in practice it will be an incredibly difficult task. “I haven't seen a project yet that could handle this,” says Volcker. "They are supposed to be robotic construction vehicles that can be controlled remotely."
Embed or cover?
Another method by which it was possible to achieve the desired result lies in the ground itself. Penetrators capable of penetrating the surface during impact have already been proposed (but on a smaller scale) for several lunar missions, such as Japan's Lunar-A and Britain's MoonLite (the project is currently delayed, although the idea of penetration landing was so convincing that ESA decided to use for a mechanism for the rapid delivery of samples for analysis from the surface and subsurface of a planet or moon). The advantage of this concept is that the base is buried on impact, which means it will be exposed to relatively moderate thermal conditions before being protected.
However, there will remain a problem with energy provision, as a typical penetration project offers only very limited solar energy options. There are also the problems of high collision acceleration loads and high accuracy required for guidance. “The collision force required to burrow the structure will be very difficult to match with the required functions of the manned base,” says Trollope.
An alternative to this would be to pour lunar regolith on top of the colony, possibly using machines such as hydraulic excavators. But to do this effectively, you have to work quickly.
If the lunar regolith cannot be poured over the colony, then a hat of multilayer insulation (MLI) can be deployed over it, which will prevent heat dissipation. MLI thermal insulation materials are widely used on spacecraft, protecting them from the cold of space.
The advantage of this method is that it allows solar arrays to be used to collect and store energy over a two-week lunar day. But if not enough energy is collected, alternative energy generation methods will have to be considered.
Thermoelectric generators could provide the colony with energy during the night cycle: although they are low in efficiency, they, however, have no problems with maintenance, since they have no moving parts. Radioisotope Thermoelectric Generators (RTGs) offer great efficiency and have a very compact fuel source. But the base will have to be shielded from radiation, while allowing it to transfer heat. The logistics of installing a removable radioactive isotope generator is fraught with problems: risks will be all the way, from takeoff from Earth to landing on the moon, along with political and security concerns.
Fission reactors could be used, but there will be even more problems with them, including those listed above.
And if thermonuclear reactors are developed, they can also be used on the Moon, given the excess of helium-3. Batteries - such as lithium-ion batteries - can also come in handy, provided sufficient solar power is generated in a two-week night cycle.
There is an idea to provide power to the station on the surface during the night cycle using an orbiting satellite that will transmit energy through microwaves or a laser. This idea was investigated 10 years ago. The study found that for a large lunar base, requiring hundreds of kilowatts of energy supplied from orbit by a 50-kilowatt laser, a rectenna (a type of antenna that converts electromagnetic energy into direct electric current) will be 400 meters in diameter, and on a satellite - 5 square meters kilometers of solar panels. The International Space Station is about 3.3 sq. km of solar panels.
Despite significant difficulties in building a colony that will have to withstand the harsh nocturnal lunar cycle, they are not insurmountable. With the right thermal protection and the proper power generation system during a long two-week night, we could have a lunar colony in the next twenty years. And then we can turn our gaze farther.