Constellation navigation, flyby exploration, a new round of lunar exploration begins, and new trends gradually emerge

Recently, China, the United States, Russia, the European Space Agency, South Korea, India and other countries and organizations have successively released a series of lunar exploration plans, many of which have new highlights, such as building a lunar communication and navigation constellation, and using low-orbit probes, jumping probes and other means to find water ice resources. A new round of lunar exploration activities is about to begin. Compared with the classic lunar exploration missions that everyone is familiar with, what are the differences between the new missions? What new technologies and new ideas are expected to be applied in the new missions?

Building a lunar version of satellite navigation

Satellite navigation systems play an important role in ground navigation, communication, resource exploration and other activities. Having a fully autonomous satellite navigation system is the goal pursued by every major space power. In order to support more complex missions on the lunar surface and better conduct comprehensive surveys of the moon, the international competition to build a satellite navigation system has extended to the vicinity of the moon.

The National Space Administration has announced that my country is demonstrating the construction of a lunar communications and navigation satellite constellation, and the first launch may be carried out around 2024. Simply put, this will be the lunar version of the Beidou navigation system, which can provide relay communications, navigation and other services for future lunar operations, and provide information support for the next more complex lunar exploration missions.

The European Space Agency has also launched a plan to build a navigation and communication satellite network in lunar orbit, but NASA is the fastest in this regard. On June 28, 2022, the US Capstone probe was launched, marking the first successful launch of a lunar probe by the United States in nearly 10 years. As a forerunner of the "Artemis Project", this microwave-sized probe was promoted as the "world's first lunar navigation satellite", marking the substantial deployment stage of the United States' creation of a lunar version of GPS.

Schematic diagram of the US "Capstone" detector (Source: US media)

Some people may find it strange: there is no one living on the moon, no cars driving on it, and very little demand for navigation applications, so why is it necessary to build a complex satellite navigation system?

In fact, if we only want to explore the front side of the moon, then the navigation satellites operating in low-Earth orbit can meet the mission requirements. But when exploring the poles and back side of the moon, we cannot use traditional navigation satellites, so it is necessary for humans to send special "messengers" to the moon.

Today, mankind is entering a new era of lunar exploration and development, and there will be more and more lunar activities. In the future, many unmanned probes and manned spacecraft will successfully land on the moon and operate on the complex lunar surface, taking more "small steps for individuals, big steps for mankind". All of these require more accurate navigation information and smoother large-capacity communication guarantees, so the construction of a complete lunar communication and navigation constellation is essential.

Precise "portraits" of the moon

In recent years, many countries have put forward new requirements for lunar reconnaissance orbiters. As they fly around the moon in low orbit, they can provide high-precision digital elevation maps of the moon, assist in surveying possible landing sites, assess water and other resources on the moon (including sunlight conditions that can be used to generate electricity), and analyze the radiation environment that future astronauts may face.

NASA introduced the "New Space Exploration Program" in the early 21st century, and the first mission was to launch the Lunar Reconnaissance Orbiter in 2009. It operates in a 50-kilometer-high polar lunar orbit and transmits a large amount of information such as all-weather lunar temperature maps, lunar geodetic coordinates, high-resolution color images, lunar ultraviolet albedo, etc. In the future, NASA also plans to launch a nuclear-powered lunar rover to collect more samples from the far side of the moon and send them back to Earth by astronauts.

South Korea's first lunar orbiter "Wol-ho" (Source: South Korean media)

On December 27 last year, South Korea's first lunar orbiter, the "Bongwol", successfully entered the planned lunar orbit. Interestingly, the Korea Aerospace Research Institute had hoped to adjust the orbital altitude of the "Bongwol" to 300 kilometers so that it could enter orbit as soon as possible, but NASA insisted on keeping the orbital altitude at the original target of 100 kilometers. It turns out that the "Bongwol" carries NASA's shadow camera, which uses a high-resolution camera to observe the lunar surface and focus on precise imaging of the permanent shadow area at the south pole of the moon. It will help the "Artemis Project" select the landing site and water ice traces, and serve the South Korean lunar lander planned to be launched in 2032.

Despite the failure of Chandrayaan-2, India has not given up its ambition to explore the moon. Earlier this year, the Indian Space Organization announced that India's third lunar exploration mission will be launched at the end of this year or early next year. In February this year, the Indian Chandrayaan-3 lander passed the electromagnetic interference and electromagnetic compatibility tests, and in March completed the key vibration and acoustic environment tests, and added more safeguards. In the future, the Chandrayaan-3 propulsion module will mainly undertake the relay communication mission, cooperate with the Chandrayaan-2 propulsion module that performs the circumlunar remote sensing mission, and jointly support the lunar rover weighing about 26 kilograms to work on the lunar surface for about half a month, thereby providing more detailed first-hand information for India's next lunar exploration mission.

More lunar exploration missions are underway in various countries, hoping to obtain rich lunar information and draw a more detailed "portrait of the moon goddess". This year, my country will fully promote the fourth phase of the lunar exploration project. In the future, Chang'e 6 will collect more samples from the back of the moon and strive to achieve the goal of 2,000 grams.

Japan's "Hakuto-R" successfully entered the lunar orbit at the end of March this year. It is expected that this commercial space lander will carry the UAE's first lunar rover and a small Japanese robot into the Atlas crater in the northern part of the front of the moon at the end of April to study the lunar soil, lunar rocks and dust movement, as well as the plasma conditions on the lunar surface.

The slightly embarrassing one is the US "Lunar Flashlight". This cubic satellite was carried by the "White Rabbit-R" and was originally planned to enter the lunar orbit about 15 kilometers from the lunar surface, using infrared lasers and new laser reflectors to search for water ice resources in the permanent shadow area of ​​the lunar south pole. Unfortunately, it encountered a malfunction when testing the "green propellant", forcing the "Lunar Flashlight" mission to be downgraded from orbiting the moon to a lunar flyby.

Flyby exploration of the lunar surface has many mysteries

According to public information, my country's Chang'e-7 is preparing to land on the lunar South Pole to conduct flyby exploration and search for water resources. In the future, Chang'e-7 and Chang'e-8 will form the basic model of the lunar South Pole scientific research station, including a lunar orbiter, lander, lunar rover, flyby and several scientific exploration instruments. In addition, many foreign commercial aerospace companies have announced plans to use jumping robots to survey the lunar surface.

So what do flyby and hopping exploration mean? What are the unique advantages of these spacecraft in carrying out missions?

At present, probes that have landed on alien planets can be divided into two categories: landers and rovers. After the lander sends the rover to the surface of the alien planet, it has preliminarily completed its mission. The rover can leave the landing point for exploration, but it is subject to greater restrictions. In addition to resting on the moonlit night, traditional lunar rovers also need to frequently avoid obstacles such as rocks, potholes, and ramps on the lunar surface. The driving process is like walking on thin ice, and it is impossible to "speed".

If the lunar probe can "jump" and repeatedly land and move on the lunar surface, it will undoubtedly significantly improve the exploration efficiency and comprehensive benefits. In addition, some areas on the lunar surface are unclear and cannot be explored by traditional lunar rovers. The lunar flyby probe will have unique advantages in observing complex terrain.

Furthermore, the lunar flyby probe can directly "fly" into the permanent shadow area, just by using the microwave imaging radar carried by the orbiter to perform high-resolution imaging of the permanent shadow area in advance, so as to plan the air and landing path in detail. It is expected that after completing a permanent shadow area exploration mission, it can return to the illuminated area to recharge in preparation for the next mission.

Of course, in order to cope with the complex lunar surface conditions, the lunar flyby probe cannot rely entirely on solar energy. It can consider storing some fuel in advance and using it at critical moments. In the future, if the lunar flyby probe is expected to use nuclear energy technology, its work continuity and efficiency will be greatly improved.

Even so, it is still not easy to make the lunar flyby probe and jumping robot operate normally on the lunar surface. After all, the moon has no dense atmosphere, and it is difficult for the probe to "take off" frequently. The lack of cushioning during landing will increase the risk. For this reason, researchers still need to make more arduous efforts.

With the advancement of aerospace technology, I believe that in the near future we will be able to see probes "adding dynamism" to the lunar surface by flying or jumping, revealing more lunar mysteries, and laying a solid foundation for lunar resource exploration and development, lunar base construction, and long-term human presence on the moon.

Looking to the future, lunar exploration activities will continue to present new highlights and attract public attention in the process of progress or setbacks. This is because it not only expands the human observation field and activity space, but also promotes the development of science and technology and the application and promotion of results. It has led the cutting-edge technology trend to a large extent and satisfied the core driving force of human progress - curiosity. (Author: Zhang Kai)