Just 11 days ago, in the early morning of December 6, Japan’s JAXA falcon-2 probe sent samples from the asteroid “Dragon Palace” back to earth after six years of trekking. < / P > < p > taking the initiative to go to space to collect samples is rare in human history. In a short period of half a month, two “local products” from space are undoubtedly a great gift to give back human wisdom and tenacity in the rough year of 2020. < / P > < p > in addition to bringing back interstellar dust and solar wind particles, only nine moon sampling returns, one comet sampling return and two asteroid sampling returns have been completed in the short history of more than 60 years of deep space exploration. Every time, it is accompanied by the unknown, difficulties and challenges. Every time, it is a historic feat. On July 20, 1969, NASA’s Apollo 11 lunar module with two astronauts, Neil & middot; Armstrong and buzz & middot; aldrin, successfully set foot on the Jinghai base in the front of the moon. < / P > < p > during a total of 2.5 hours of lunar extravehicular activities, the two astronauts completed three lunar surface sampling, collecting 21.6 kg of lunar rock and soil samples and bringing them back to earth. < / P > < p > today, we will still marvel that the first space sampling of human beings has such a “high standard”. Not only human beings came out, but also tens of kilograms of goods were brought back to us. Later, we only collected dozens of grams or even several milligrams of unmanned sampling mission and cried in the toilet. < / P > < p > since then, Apollo 12, 14, 15, 16 and 17 have successfully achieved manned lunar landing, lunar rock and soil sampling and return, and more and more samples have been collected each time. < p > < p > in 1972, Apollo 17 was even more powerful. The astronauts of this mission not only spent 22 hours outside the lunar module, but also collected 110.5 kg of lunar samples. What’s more, this mission was to send living geologists directly to the moon. Before becoming a NASA astronaut, Harrison Schmidt, one of the Apollo 17 astronauts, was a geologist with a bachelor’s degree in geology. Geologists’ on-the-spot investigation and sampling made the Apollo mission truly realize where there is scientific value in digging, and make the professional digging to the extreme. In fact, Harrison Schmidt is also the only scientist among the 12 astronauts on the moon. < / P > < p > in addition to collecting samples, the Apollo mission also made full use of the advantages of human beings to complete a series of on-the-spot lunar explorations, including seismic experiments, heat flow detection, gravimeter and laser reflection array installation, which are still beyond today. This has little to do with this article, so I won’t say much about it. One year after Apollo 11 landed on the moon, the late Soviet moon 16 landed in the rich sea on September 20, 1970, and collected 101 grams of lunar samples. The Soviet Union’s three lunar sampling missions: Lunar 16, lunar 20, and lunar 24 were all returned by unmanned sampling, which was the only unmanned lunar sampling mission before chang’e-5. Limited by the rocket transport capacity and return mode, the samples collected in the three lunar missions are only tens to 100 grams, which is not much compared with the Apollo mission. < / P > < p > the samples collected from Apollo and lunar missions have been assiduously studied by planetary scientists over the next 40 years, helping people to solve many lunar mysteries. Unfortunately, with the success of Apollo’s manned landing on the moon, the space race between the United States and the Soviet Union quickly came to an end, and the upsurge of lunar sampling stopped abruptly in its heyday. After the Soviet Union’s lunar 24 mission in 1976, lunar sampling was silent for 44 years. < p > < p > in 2013, chang’e-3 successfully landed in the northwest of Yuhai in front of the moon and released the lunar rover Yutu. This is 37 years after the Apollo missions of the United States and the lunar missions of the Soviet Union, the human probe has successfully stepped on the surface of the moon again. In 2019, chang’e-4 will be the first time for a human probe to set foot on the back of the moon. < / P > < p > chang’e-5, China’s most complex lunar exploration mission to date, started in the early morning of November 24, 2020 and returned in the early morning of December 17, 2020. It has completed a series of complex operations such as going to the moon, sampling the lunar surface, taking off the lunar surface, docking the lunar orbit and returning to the earth, realizing many “first time” in the history of China’s deep space exploration. < p > < p > chang’e-5 successfully landed on Mount rumke in the northern part of the lunar frontal storm ocean, and collected at least 2 kg of lunar samples. This is the largest number of samples collected in the unmanned lunar sampling return mission so far, leaving the second place far behind. < / P > < p > after chang’e-5, China’s chang’e-6 will go to the south pole of the moon for sampling, reaching more moon surfaces that have not been reached by previous explorers, and accomplishing more feats that have not been accomplished by previous explorers. < / P > < p > compared with the “near” moon, the way to sample comets and asteroids is bound to be more full of accidents and dangers. But human beings have never stopped exploring the unknown. On February 7, 1999, NASA’s Stardust probe was launched. One of its goals is to collect the dust and interstellar dust samples from the coma of comet Verde 2 and bring them back to earth. < / P > < p > this is a kilometer sized comet that orbits the sun every 6.4 years. Compared with the small objects that humans tried to sample later, comet Verde 2 is a giant. < / P > < p > how to collect things as small as dust, let alone comet dust? Stardust, which has no previous experience to copy, can only do its best to think and work on its own.
Stardust uses silica aerogel material to make a tennis racket size collection device, which is porous and porous like sponge. 99.8% of the space is filled with air, so the density is very low, though solid, it is extremely light. When the detector flew through the comet’s comet, the Stardust approached the collector and gently collected the dust trapped by the aerogel. This method of aerogel collecting particles was tested at Mir space station in 1996-1997 years, and NASA’s origin probe also collected solar wind particles in a similar way. < p > < p > the Stardust capsule was opened in a temporary clean room at Michael army airport in Utah, and the sample collection device was then repackaged and transported to the Johnson Space Center in Houston. NASA < / P > < p > in 2003, JAXA’s Falcon probe was launched to explore the near Earth Asteroid Ishikawa and bring back samples. < / P > < p > the asteroid Ishikawa is an Apollo type near Earth Asteroid. Its spectral composition is classified as S-type, with a size of 535m × 294m × 209 M. it orbits the sun once every 1.5 years. < p > < p > the Falcon’s journey is not smooth. It has been malfunctioning before reaching its target. After arriving at the asteroid Ishikawa, the lander was released and landing sampling failed to proceed as expected. Fuel leakage, injuries, and even long-term loss of contact and near death However, it overcame all kinds of difficulties and difficulties and miraculously sent the samples from Sichuan back to earth in June 2010. < p > < p > for such a small asteroid with a diameter of less than 1 km, there are new problems in sampling. The vast majority of asteroids do not erupt “local products”, and do not allow the probe to complete the sampling without contacting the surface like Stardust; the gravity of small objects is too small, so it is difficult for the probe to land safely and steadily without repeatedly bouncing; on the other hand, the probe to small stars is usually much lighter than that to the moon and Mars, so it does not have the ability to travel in asteroids Conditions for landing and takeoff. < p > < p > Falcon first tried the “contact and leave” method: the probe controlled landing until the sampling rod touched the surface of the small object, completed the sampling within a few seconds of contact, and then ignited and left. < / P > < p > once the probe detects that the long sampling rod touches the surface of the asteroid, a tantalum bullet is immediately launched from the sampling rod at a speed of 300 m / s, and the debris from the bullet is ejected into the sampling rod, which is collected by multiple reflection detectors. < / P > < p > although the sampling work of Falcon was not carried out smoothly, the “contact and leave” sampling method itself was recognized and used by the later JAXA Falcon 2 and NASA’s Hades probe. And fortunately, Falcon’s return capsule still brought back some asteroid dust particles that flew in during the sampling process. < p > < p > about 1500 dust samples were collected by falcon, with a total mass of less than 1 mg. Although the weight is not much, and some samples may be contaminated , it still provides planetary scientists with a lot of “first-hand” information from asteroid Ishikawa. More importantly, as the first attempt to sample asteroids, Falcon’s “undead bird” spirit still inspires future generations to continue to explore the universe. < p > < p > based on the experience of Stardust and falcon, JAXA and NASA began to sample small objects again more than ten years later. Falcon 2 and Hades were born. < / P > < p > the tantalum bullet sampling method of Falcon 2 was adopted. Falcon 2 completed two sampling in 2019, and collected two samples from the surface and underground of the asteroid dragon palace. However, the actual “out of the box” weighing results show that a total of 5.4G of the asteroid Dragon Palace samples were collected, which is more than 50 times of the planned sampling amount, and the gas material of the asteroid Dragon Palace may have been collected. < / P > < p > on the other hand, NASA’s Pluto has successfully completed the sample collection and packaging in October 2020. In the contact sampling stage, Pluto chose to launch compressed nitrogen to excite the asteroid surface material. Compared with the “ejection bullet type”, this “dust suction type” sampling may collect more samples. If all goes well, it will leave in March 2021 and return the sample to earth on September 24, 2023. < / P > < p > China’s first asteroid sampling and comet exploration mission is also under close planning. It plans to launch in 2024, orbit and detect the near Earth Asteroid 2016ho3, collect samples and send them back to earth. The asteroid is estimated to be only 40-100 meters in diameter, which will be the smallest asteroid detected by humans. < / P > < p > as China’s first small object exploration mission, this mission can definitely be regarded as a big goal. After completing the close range detection and sampling of asteroid 2016ho3 and sending the “local products” back to earth by express, it will continue to go to the main belt comet 133p / EST Pizarro for close range detection. < / P > < p > in addition to asteroid sampling, Mars sampling return is also in China’s deep space exploration planning. On the other hand, NASA’s willpower rover, which is about to arrive on Mars, will begin sampling and packaging Mars in the next few years. However, these samples will not be able to return to earth in a short time – they will have to be recovered and brought back by future Mars return missions. < / P > < p > after the great success of falcon-2, JAXA plans to continue to play the experience and advantages of small object exploration, which is under planning