What detectors do humans need to explore the universe?

there are different ways to explore the world beyond the earth, or "space exploration": one is to travel long distances and fly to a nearby place to find out; One is to deploy telescopes on the earth's surface and near-earth space to collect visible light and X-rays for analysis and research.

different targets need different detectors. The Lucy probe launched by the United States not long ago aims to go to eight asteroids; Although it takes a long journey, compared with the Mars probes launched by China and the United States last year, Lucy is more frugal and has a lower budget.

Not long ago, xi he, the first solar probe launched in China, was a small project in space exploration, although it was of the first significance to launch the "exploring the sun" in China.

it can be said that under the limited cost, it is often necessary to make a choice between detectors: either the cycle is long, the task is complex, and the scientific goal is significant; Either the cycle is short, the task is specific and the cost is low.

exploring the Trojan asteroid for the first time: 12 years of roaming in the solar system

On October 16th, the National Aeronautics and Space Administration (NASA) launched the asteroid probe Lucy. During its 12-year journey through the solar system, it will fly over eight small celestial bodies of different sizes, types and positions, which is expected to unveil the mystery of Jupiter's Trojan asteroid for the first time.

The vast majority of asteroids known in the solar system are concentrated in the asteroid belt between the orbits of Mars and Jupiter, and they are called "main belt asteroids".

And the Trojan asteroid is farther away from us. They are the floorboard of at least thousands of asteroids orbiting Jupiter. According to different positions, the Trojan asteroids can be divided into two small groups: one group is located at the L4 Lagrangian point of Jupiter-Sun (in front of Jupiter), and the other group is located at the L5 Lagrangian point of Jupiter-Sun (behind Jupiter). Together with Jupiter, these asteroids revolve around the sun in the same period and at the same speed.

According to the plan, Lucy will visit six Jupiter-Trojan asteroids, one Trojan satellite and one main belt asteroid, which will set a record for exploring the most celestial bodies in one mission.

Scientists can roughly know from long-distance observation that these detection targets are different in size and composition, and the smallest diameter is only 1km, and the largest diameter may reach 14km ...

After taking off, Lucy needs to undergo two gravitational accelerations around the earth, and it is planned to fly over the asteroid No.52246 located in the main asteroid belt in April 225. After that, Lucy will continue to fly to the outer solar system until it reaches the Lagrange point of Jupiter's orbit L4 in 227, and visit four Trojans and one asteroid's satellite respectively.

after that, Lucy will fly to the inner solar system again, and "stay inside" in Earth orbit, and then "take advantage" to fly to the Lagrange point of Jupiter's orbit L5 to explore two other asteroids. If all goes well, it will be 233.

why explore the Trojan asteroid? Scientists believe that the Trojan asteroid is probably the remains of primitive materials in the early solar system and a "time capsule" for the birth of the solar system more than 4 billion years ago. These celestial bodies contain important clues to the early history of the solar system, and may even tell us the origin of organic materials and life on earth.

It is worth mentioning that Lucy is named after the fossil of ancient human ancestor "Lucy" found in Ethiopia. This ancient human skeleton is of great significance to the study of human origin and evolution. Named after this detector, it is also the same expectation. The asteroid No.52246 that Lucy flew by in the main asteroid belt has been named "Donald Johnson Star"-he is the discoverer of the "Lucy" fossil.

classification of space missions: Lucy is a "cheap" project

If all goes well, Lucy will set a record-the farthest solar-powered spacecraft from the sun, with a maximum distance of 853 million kilometers, which is six times closer than the distance between the sun and the earth.

In the past, deep space probes flying so far, such as Voyager and Cassini, were all equipped with nuclear batteries. Lucy's use of solar windsurfing also has a last resort: the budget is limited.

in NASA's mission level, Lucy belongs to "discovery" level, which is lower than "Xinjiang boundary" level and "flagship" level.

Discovery was established in 199, with the aim of "completing many space exploration missions with low cost and public wisdom", and the budget generally does not exceed 45 million US dollars.

the most famous "discovery" mission is the Mars Pathfinder mission, which carried the rover sojourner, successfully landed on the surface of Mars in the form of airbag package, and explored on Mars for nearly three months.

higher than the "discovery" level is the "Xinjiang boundary" level. The mission objective at this level is "to be able to provide high scientific returns". At present, there are three "Xinjiang boundary" level missions, namely: the New Horizon probe launched in 26 and arrived in Pluto in 215; Juno probe launched in 211 and entered Jupiter's orbit in 216; The OSIRIS-REx probe, which was launched in 216, successfully landed on the Benu asteroid in 22 and is expected to return to Earth in 223.

However, although Lucy's mission belongs to the "Discovery" level, its budget has reached 981 million US dollars, which has actually reached the level of "Xinjiang Boundary".

the highest level mission of NASA is the "flagship" level, which is also called "large-scale strategic science mission". Most of the "flagship" missions are well known, including Viking Mars exploration mission in 197s, Voyager project, Hubble Space Telescope, Chandra X-ray Observatory, Curiosity Mars rover, Magnetospheric Multi-scale Mission (MMS) and Terra Earth observation satellite. The latest "flagship" mission is the Mars exploration mission launched by NASA last year.

The book Assisting Science: NASA's Large-scale Strategic Science Mission published by four universities in the United States points out that the flagship mission "focuses on a wide range of goals", while the smaller mission "focuses on a single goal or a few closely related goals". However, "compared with large-scale strategic tasks that usually take ten years or more to develop, smaller tasks can often be completed within five years. Sometimes, this makes smaller tasks more suitable for responding to the latest findings. "

Similarly, regarding the classification model of deep space exploration missions in China, Liu Jizhong, director of the Center for Lunar Exploration and Space Engineering of the National Space Administration, pointed out that future deep space exploration missions can be divided into three categories based on the constraints of mission objectives, technical capabilities, system scale and funding requirements:

Small missions embody "short, flat and fast": for a specific celestial body, scientific objectives or aerospace technology verification, mature aerospace products are launched after adaptive transformation, and the detector size is controlled.

Medium-sized missions are cost-effective. Aiming at the objectives of joint exploration of multiple celestial bodies and combination of multiple detection methods, on the basis of existing spacecraft, rockets and other technical products, more new technologies are conquered, some new equipment is developed, and some new facilities are built. The scale of detectors is controlled at 3-1 tons, and the cost is moderate.

Large-scale tasks reflect great scientific discoveries and technology-driven, aiming at the sampling and returning of extraterrestrial celestial bodies, long-term unmanned/robot-manned catalog research stations, etc., overcoming a large number of new technologies, building a number of large-scale scientific research facilities, and developing brand-new spacecraft. The detector scale is controlled to be more than 1 tons, and it is implemented once or twice every 1 years, which is costly.

China's space exploration: there are big projects and small goals

Wu Ji, the head of the space science pilot project (Phase I) of China Academy of Sciences and a researcher at the Center for Space Science and Applied Research of Chinese Academy of Sciences, believes that almost all the "firsts" in space exploration were divided up by the United States and the Soviet Union because of the massive investment of the former Soviet Union and the United States during the Cold War. "Repeated discovery is of no scientific significance. Therefore, we must find an innovative entry point. "

Wu Ji also pointed out that at present, China's investment in space science can't be compared with that of the United States, and limited funds must be invested in the places where they are most needed.

Statistics show that among the 6, spacecrafts launched worldwide in recent decades, there are about 7 satellites and deep space probes dedicated to space science research. For a long time, China's space science has been the shortcoming of China's space industry; Space science research relies heavily on the secondary analysis of public data in other countries.

To this end, in 211, China Academy of Sciences launched the special project of strategic pilot science and technology in space science. Up to now, specially deployed dark matter satellites, such as Wukong, Shijian 1, Mozi, and the hard X-ray modulation telescope satellite, have produced or are producing a series of major scientific discoveries and original innovations, and achieved many international leading or advanced breakthroughs in space technology, greatly enhancing China's international reputation in space science.

It can be seen that in recent years, China's space missions include both the "China Planetary Exploration Project", which is a very challenging major project, and the "small target" implemented by relying on existing equipment or platforms to solve a single goal.

Take xi he, China's first scientific and technological experimental satellite for solar exploration, which was launched on October 14th as an example: xi he is a "small satellite" with a total weight of just over 5 kilograms. It has a design life of 3 years and runs in a sun-synchronous orbit with a height of 517 kilometers and an inclination of 98 degrees. Xi he is an "ultra-high pointing accuracy and ultra-high stability" satellite platform developed by the Eighth Institute of China Aerospace Science and Technology Corporation. According to Chen Jie, executive deputy director of the Science and Technology Committee of the Eighth Academy of Sciences, the platform will also be widely used in the new generation of space missions, such as high-resolution detailed earth survey, large-scale stereo mapping, solar stereo detection and exoplanet discovery.

planning: Zhang Zhichao