The Guanghan Palace is full of distinguished guests. How did the moon become a popular check-in spot step by step?

Time flies, and in a blink of an eye, it has been 20 years since the State Council approved the lunar exploration project, the "Chang'e Project", on January 23, 2004. We are delighted to see that lunar exploration is becoming a hot spot in human space activities. Especially this year, Guanghan Palace will welcome many guests.

Lunar Exploration: Mankind's First Step Out of the Cradle of the Earth

It is human nature to explore the unknown world. The moon, the largest celestial body seen from the ground, has carried mankind's infinite yearning for the vast universe since ancient times, and has produced countless legends and stories about the moon.

With the advancement of science and technology, humans have learned more and more about the moon. The moon is the only natural satellite of the earth. The average distance between the earth and the moon is about 380,000 kilometers. The diameter of the moon is about one-fourth of the earth. The gravity on the moon's surface is one-sixth of the earth's. A day and night on the moon is equivalent to 27.3 earth days. The surface temperature of the moon is about 130 to -180 degrees Celsius. These common senses that have gradually become familiar to us have made humans realize that the moon is not the paradise they imagined, but a barren land that is not suitable for human survival.

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" The Earth is the cradle of mankind, but mankind cannot be bound to the cradle forever ." This famous quote by Tsiolkovsky reveals the code of continuous reproduction and expansion that exists at the bottom of life. Compared with the vast space of the universe, tangible planets are as hard to find as dust in the clear sky, and there are even fewer planets for humans to stay. The long distance between planets has become the most difficult barrier for humans to cross when they leave the cradle of the Earth.

The moon, which is closest to the earth, has become the first testing ground for humans to set foot in outer space. Because the short distance means low technical difficulty, risk and cost, humans can practice and explore relatively easily. As soon as the curtain of the human space age opened, the exploration of the moon ushered in the first wave of enthusiasm.

The climax of the first round of lunar exploration mainly revolved around the space race between the two space powers, the United States and the Soviet Union.

On January 3, 1959, the Soviet Union successfully launched the Luna 1 probe. Luna 1 was originally planned to impact the moon, but due to a malfunction in the ground control system, it failed to complete the planned plan. Instead, it flew by the moon at a distance of 6,000 kilometers on January 4, becoming the first probe to fly by the moon. Subsequently, on September 12, 1959, the Soviet Union successfully launched the Luna 2 probe, which successfully impacted the front of the moon on September 14, 1959 as planned, making it the first man-made object to reach the lunar surface. Then on October 7, 1959, Luna 3 successfully obtained an image of the back of the moon, which was the first time that humans had witnessed a photo of the back of the moon.

The Luna 3 probe sent back the first photo of the far side of the moon, giving humans their first glimpse of what the far side of the moon looks like from a distance.

Image source: Russian State Archives of Scientific and Technological Documents

Although it fell behind in the early stages, the United States quickly caught up and conceived a grand manned lunar landing plan, trying to rely on its own strong scientific and technological strength to win the space race in one fell swoop. The United States successively launched lunar probes such as "Pioneer", "Ranger" and "Surveyor", achieved a hard landing on the lunar surface , carried out environmental detection of the Earth-Moon space, and obtained more accurate lunar astronomical parameters, laying the foundation for subsequent manned lunar landing missions. On July 20, 1969, Apollo 11 finally sent Armstrong and Aldrin to the moon, achieving the great feat of manned lunar landing. After landing on the moon, Armstrong left a sentence that is still remembered by the world today: "This is a small step for a man, but a giant step for mankind."

Magnificent Desolation: The Apollo 11 Moonwalk Pictures (NASA)

From July 1969 to December 1972, American astronauts successfully completed six manned lunar landings, sending a total of 12 people to the moon and bringing back a total of 381.7 kilograms of lunar samples. At the same time, the Soviet Union successfully implemented lunar rovers and unmanned sample return missions. From September 1970 to August 1976, the Soviet Union's Luna 16, 20 and 24 successfully landed on the moon three times and sent hundreds of grams of lunar soil collected back to Earth.

When the moon gradually opens its arms to ordinary people

After the Soviet Union's "Luna 24" mission ended in 1976, global lunar exploration activities entered a stage of calm reflection. From 1976 to 1994, the world only conducted one successful lunar exploration activity, that is, Japan launched the "Hiten" lunar probe in January 1990, becoming the third country to explore the moon. The reasons are: with the easing of the Cold War situation, the competition for space hegemony has eased; it is necessary to summarize the experience and lessons of exploration activities that are costly, inefficient, and low in detection level, and propose new exploration ideas and strategies; it is necessary to transform, promote and apply lunar exploration technology to various fields; it is necessary to accelerate the development of new space round-trip transportation systems and efficient detection equipment; it takes a long time to digest, analyze and synthesize the detection data, and raise lunar scientific research to a higher level of rational understanding.

The Clementine lunar probe launched by the United States on January 25, 1994 truly set off the world's second round of lunar exploration . Clementine entered lunar orbit on February 6 of that year and eventually moved into lunar polar orbit, mapping the entire moon. The probe sent back a total of 1.8 million (some reports say 1.6 million) images, and the detection data showed that there was water ice on the moon. This discovery caused the value of the moon to rise sharply.

In the subsequent journey to the moon, in addition to the traditional countries such as the United States, Russia, China, India, Japan, ESA, South Korea and others have achieved remarkable results, and countries such as Israel and the United Arab Emirates are also constantly trying and joining the race. The moon has become a hot spot for countries to explore first.

Among them , China's three-step lunar exploration project of "orbiting", "landing" and "returning" has undoubtedly achieved the most outstanding results . In December 2013, with the successful soft landing of "Chang'e 3" on the lunar surface, China became the third country in the world to achieve a soft landing on the moon after the United States and the Soviet Union. The Chang'e 4 probe autonomously landed in the designated area on the back of the moon, achieving the first soft landing of a human probe on the back of the moon, which has never been done abroad. On December 17, 2020, Chang'e 5 returned safely to the Earth landing site with lunar soil, marking the complete success of the three-step strategy.

The Chang'e-5 lunar rover lands on the lunar surface.

Image source: China Lunar Exploration

The discovery of water ice on the moon has inspired the United States to return to the moon. The United States has launched lunar orbiters such as the Lunar Prospector, the Lunar Reconnaissance Orbiter, the Lunar Crater Observation and Sensing Satellite, the Lunar Gravity Recovery and Interior Laboratory, and the Lunar Atmosphere and Dust Environment Explorer, which have further confirmed the existence of a large amount of water ice on the moon through remote sensing. At the same time, they have accurately measured the lunar gravity field, analyzed the composition of the moon's thin atmosphere, studied the role of lunar dust, and studied the possible impact of future exploration activities on the lunar environment.

The bright prospects of lunar exploration have not only inspired the enthusiasm of governments of various countries, but also attracted many commercial aerospace companies to join the effort, making the moon gradually open to ordinary people and lunar landing probes becoming increasingly popular. Israel's "Genesis", Japan's "White Rabbit-R" and "Lunar Exploration Intelligent Lander", India's Chandrayaan-2 and Chandrayaan-3, Russia's Luna 25, and the United States' "Peregrine" and other lunar landers have successively gone to the moon and tried to land on the lunar surface.

As a result of the US Commercial Lunar Payload Services (CLPS) program, private companies plan to carry out five launch and lunar landing missions in 2024, including Intuitive Machines 1 and 2 preparing to land at the South Pole of the Moon, Intuitive Machines 3 landing in the Lenaga crater in the Ocean of Storms, the Blue Ghost lander landing in the Sea of ​​Crisis, and the Griffin 1 lander landing in the Nobile crater at the South Pole of the Moon.

A forward base for deep space expeditions

The moon is rich in resources, such as rare earths, iron, titanium, etc., but due to the high cost of mining, people are currently focusing on the moon's solar energy and helium-3 resources. The moon is not covered by an atmosphere, and the solar radiation energy that reaches the moon each year is equivalent to 25,000 times the energy consumed by the earth each year. In addition to solar energy, there are 1.03 million to 1.29 million tons of helium-3 resources in the lunar soil. If these helium-3 are used as nuclear fusion raw materials for nuclear fusion power generation, they can solve the energy needs of human society for the next 10,000 years.

At the same time, as the only natural platform closest to the Earth, the Moon's high space location, special space environment, and unique natural resources have irreplaceable value to the development of the Earth and human society, and may become a transit station for Mars or deep space exploration . Since the Moon's gravity is only one-sixth of that of the Earth, the energy consumed in launching a rocket on the Moon is much lower than on Earth. In addition, the presence of water ice makes it possible to manufacture and replenish rocket propellants on the Moon, and the prospects for a lunar transit station are even more promising.

The optimization and secondary development of lunar exploration engineering technology can drive and promote the development of basic science and high technology, such as space astronomy, space physics; new energy technology, new material technology, robotics technology, telemetry technology, etc., drive multidisciplinary cross-infiltration, and promote the sustainable development of the national economy.

Lunar exploration is a complex scientific and technological project, and an important symbol of a country's national will, scientific and technological development level, and modern civilization. The lunar exploration project can not only improve human cognition of the universe and its own living environment, but also greatly stimulate scientific and technological innovation and drive the leapfrog development of a large number of high-tech technologies. Looking at the international community, a new round of manned lunar missions is about to begin. The United States has launched the Artemis program and is preparing to build a lunar space station and return to the moon. China's manned lunar exploration project has also started its lunar landing phase mission, and plans to achieve the first Chinese landing on the moon before 2030 .

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In order to achieve long-term human presence on the moon, my country also plans to establish a lunar scientific research station to conduct comprehensive and large-scale scientific exploration, technical experiments, lunar resource development and lunar environment utilization. Among them, the Chang'e-6 mission is planned to be implemented in 2024, with the main task of sampling the back of the moon and returning to Earth with lunar samples. Chang'e-7 is planned to go to the South Pole of the Moon in 2026 to look for evidence of the existence of water on the moon. Chang'e-8 is planned to cooperate with Chang'e-7 to establish a basic model of the International Lunar Scientific Research Station at the South Pole of the Moon in 2028, and conduct a series of experiments on lunar resource exploration and utilization.

In the future, an international lunar research station with the participation of multiple countries will appear at the South Pole of the Moon, and human footprints will once again set foot on the Moon. The Moon, with its rich resources, will become a new frontier for human beings to explore space and move toward deep space.

Author: Yu Yuanhang, Senior Engineer, Beijing Institute of Aerospace Systems Engineering

Reviewer: Pang Zhihao, Chief Scientific Communication Expert of National Space Exploration Technology, Chief Scientific Communication Expert of China Space Science Communication Expert Studio

Produced by: Science Popularization China

Produced by: China Science and Technology Press Co., Ltd., China Science and Technology Publishing House (Beijing) Digital Media Co., Ltd.