Why did the United States choose this place as the landing site for its manned lunar landing this time?

◎ Wu Ji, Chairman of the Chinese Society of Space Science and former Director of the National Space Science Center of the Chinese Academy of Sciences

There are three reasons why Artemis plans to land at the lunar south pole:

First , there are some permanently dark craters at the South Pole of the Moon that are not exposed to sunlight all year round. There may be water ice at the bottom of these craters.

Secondly, the highlands at the lunar south pole that can be illuminated by sunlight can receive continuous sunlight and will not be troubled by long lunar nights.

Finally , due to the continuous sunlight, the temperature in the area does not vary much, which can greatly reduce the difficulty of developing manned lunar landing technology facilities.

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Today, 50 years have passed since humans last left the moon, and humans have never been to the moon again. In 2004, the US government proposed returning to the moon in its new space exploration plan, and used it as a springboard to implement the manned landing on Mars plan, announcing the restart of its return to the moon plan. In 2017, NASA officially launched the Artemis program, which aims to achieve the return of humans to the moon in 2024.

The Space Launch System (SLS) heavy rocket, which has attracted much attention recently, is a key step in the US plan to return to the moon.

Landing on the South Pole of the Moon has both advantages and disadvantages

Unlike the Apollo program, the Artemis program will land at the South Pole of the Moon. Recently, NASA announced 13 pre-selected landing areas near the South Pole of the Moon. There are three main reasons for choosing the South Pole.

First, there are some craters at the south pole of the moon that are permanently dark and cannot be illuminated by sunlight. Through radar echo detection, scientists have determined that there may be water ice at the bottom of these craters. If the scientists' inference is confirmed, this water ice can not only support the water needs of future human lunar bases, but also extract hydrogen and oxygen through electrolysis of water to provide fuel for rocket engines. It is important to know that it is much cheaper to produce fuel from the moon to refuel the spacecraft than to bring this fuel from the earth, which can greatly reduce the cost of human exploration of deep space.

Second, the highlands at the South Pole of the Moon that can be illuminated by sunlight can receive continuous sunlight, and the continuous illumination time can even reach 10 months each year. There is no lunar night as long as 14 Earth days in the low-latitude areas of the Moon.

Third, due to continuous sunlight, the temperature in the area does not change much, unlike in the low-latitude areas of the moon, where the temperature difference between day and night can exceed 250 degrees Celsius. This can greatly reduce the technical difficulty of developing manned lunar landing technical facilities, such as life support systems and space suit design.

Nevertheless, there are many disadvantages to landing on the South Pole of the Moon and establishing a human scientific research and living base there:

First of all, there are no flat lunar seas, but many mountains and canyons, making landing and takeoff very difficult. Therefore, the timing of landing is very demanding. Once you miss the original landing point, there is little possibility of finding another flat alternative landing point for the next landing.

Secondly, there is not much flat space for activities on the high ground, which is not conducive to the movement of manned lunar rovers.

In addition, the permanently dark bottom of the crater where water ice is preserved cannot see sunlight, so the energy supply for probes and excavation machinery that detect water ice must be supplied by bases located on high ground. Therefore, the energy transportation from the base to the bottom of the crater requires additional infrastructure, which must be built in advance before entering the water ice extraction and fuel production stage.

Once we overcome the cold moonlit nights, the lunar sea may be more suitable for building bases

In contrast, if the location for manned lunar landing and future base construction is chosen in the lunar seas near the zero degree longitude at the northern and mid-latitudes of the moon, except for the lack of water ice like in the Antarctic, the high energy demand on the lunar night and the large temperature difference between day and night, all other aspects are advantages. For example, the terrain in the lunar seas is flat, which is very suitable for the takeoff and landing of spacecraft, and it is also convenient for long-distance driving of manned lunar rovers, expanding the scope of personnel activities. In addition, there are a large number of oxides in the lunar soil of the lunar seas, and liquid oxygen fuel can also be extracted by reduction method, but the complexity is higher than extracting from water, and it consumes more energy. And in the near future, once the relevant technology matures, nuclear fusion fuel helium-3 can also be extracted from the lunar soil of the lunar seas.

The biggest difficulty in landing in the mid-latitude lunar sea is to overcome the cold lunar night that lasts for 14 Earth days. However, there are many related research works underway to provide feasible solutions to the lunar night problem. For example, when the temperature is high on the moon and the sun, a large amount of heat energy on the lunar surface can be stored and slowly released during the lunar night; there is also the use of silicon in the lunar soil to build large-scale, highly sensitive solar panels on site, so that during the lunar night, it can also use the reflected light of the earth to generate a certain amount of electricity; there is also the layout of lunar satellites with solar reflectors in the lunar orbit to reflect sunlight to the large-area solar panels at the base for power generation. Of course, if a small and safe nuclear power plant can break through its key technology as soon as possible, it will be easier to solve the problem of lunar night energy demand at the mid-latitude lunar base.

As for the astronauts' daily water needs, it does not seem to be a big problem. Because according to the recycling technology developed by the Earth orbit space station, the recycling rate of water can reach about 90%, and coupled with the continuous small amount of water supply from the Earth to the Moon, the astronauts' daily water needs can be met.

To sum up, in addition to the landing plan at the South Pole of the Moon that NASA is paying attention to, the establishment of a manned lunar base in the lunar seas in the northern and mid-latitude regions of the Moon has also attracted the attention of more and more relevant institutions, and a number of research projects have begun to be deployed.

With the implementation of various lunar landing plans, the goal of returning to the moon will surely become a reality in the near future. As an indispensable measure in the great rejuvenation of the Chinese nation, it is also an inevitable choice for the development of my country's manned space program. With the completion of the construction of China's Earth orbital space station mission and entering the application stage, China has also begun to demonstrate the next stage of manned space missions, one of the important goals of which is manned lunar landing. The dream of the Chinese people to land on the moon will also become a reality in the near future.

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Technological innovation reduces costs and promotes the return of manned lunar landing program

Why haven't humans landed on the moon since the Apollo program? In fact, the main problem is funding. During the era of the US-Soviet "space race", the US government invested a lot of money in the Apollo program for political reasons. At its peak, 6.5% of the government budget was invested in the Apollo program. But after that, the political demand was no longer so urgent, and the political significance of continuing to land on the moon was greatly reduced, so the US government would no longer invest so much money in space exploration projects.

People can't help but ask, with the technological capabilities of the 1960s, it might cost a huge amount of money for humans to land on the moon. Today's technology is many times more advanced than that time. Is it still necessary to spend so much money? This is to talk about the characteristics of government space missions. Because government space missions spend taxpayers' money, they always have to ensure that everything is foolproof, especially manned space missions, which cannot make any mistakes. Although so many years have passed, this characteristic of government space missions has not changed. Therefore, although technology has improved, the cost of the mission has not decreased, and it is even higher than before. This is why 50 years have passed, and humans have not returned to the moon again. Even the Saturn 5, the most powerful rocket ever used by humans to land on the moon at that time, no longer exists.

However, this situation has changed in recent years. On the one hand, commercial spaceflight has gradually emerged. Due to different funding sources and the driving force of the market, the cost of human entry into space has been reduced again and again through technological innovation and the development of recycling and reuse technology. It has now dropped to 1/10 of the government's spaceflight cost. On the other hand, Europe, Japan, China, and India have all launched moon exploration programs with moderate funding. In particular, China's "Chang'e Project" has been successfully implemented several times in a row, including three successful landings and one successful return of moon samples to Earth. These programs have broken the monopoly of the United States and the Soviet Union on moon exploration in the 1960s and 1970s to varying degrees. The pressure of the "space race" has also forced countries to accelerate the testing and development of related technologies, indirectly promoting the implementation of the manned moon landing program.

Source: Science and Technology Daily

Editor: Wang Yu

Review: Yue Liang

Final judge: Wang Tingting

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