How does Tiangong-1 enter the atmosphere accurately?

In March 30th, the official website of China's manned space flight project announced that the average height of the Tiangong-1 target aircraft had dropped to 189.5 km, about 181.8 kilometers, about 197.2 kilometers and 42.68 degrees in the apogee. China Science Daily reporter has verified that since March 13, 2017, the website has released Tiangong-1 flight status data every week, and it will be released every March 14th this year.
According to orbit prediction, Tiangong-1 will re-enter the atmosphere on the day before April 1st and March 31st, April 1st. The acquisition of these data is inseparable from the support of laser track technology.
Influence of complex factors on orbit calculation
Orbit calculation is one of the ways to obtain the orbit of celestial bodies. In theory, in the simplest model, only the velocity and mass of the celestial body are known, and the orbit of the celestial motion can be obtained by using the Kepler's second law and the law of universal gravitation.
The history of orbital computing can be traced back to seventeenth Century. The most classic example is Neptune's discovery. In 1846, a French astronomer found a bias in the actual observation of the operation of Uranus. After calculation, he found the orbit, mass and position of a new planet behind Uranus. This new planet is Neptune. Through the calculation of motion orbit, scientists will be able to predict the precise location of celestial bodies at a certain time. Qian hang, a space designer of China Aerospace Science and technology group, and Ph. D. of the National Center for space science of the Chinese Academy of Sciences, told the Chinese science newspaper reporter that considering the friction resistance of the atmosphere, the calculation and position prediction of the satellite orbit were more complex.
When Tiangong-1 is in orbit attenuation, the closer it is to the ground, the thicker the atmosphere is, the greater the frictional resistance of the spacecraft will be. "In theory, the prediction of the Tiangong-1 movement track must take into account its quality, the atmospheric friction resistance and the ratio of its area to the mass," said Qian.
Laser rangefinder: monitoring new weapon
When the theoretical prediction is not able to track the trajectory accurately, we must track closely and accurately locate the spacecraft accurately.
Liu Chengzhi, stationmaster Liu Chengzhi of the National Observatory of the National Astronomical Observatory of the Chinese Academy of Sciences (hereinafter referred to as "Changchun man station"), introduced to the Chinese science newspaper reporter that the satellite laser ranging is a technology of obtaining space target distance information by measuring the round-trip time of laser signals from the ground station to the space target, and the precision is far higher than that of the satellite. Photoelectric observation and radar technology, but it is greatly influenced by weather.
The corner reflector on Tiangong-1 provides a good experimental platform for laser ranging. In March 2016, the track height of Tiangong-1 was about 400 kilometers. Since then, the Changchun Wei station has actively carried out the tracking and monitoring of Tiangong-1. A total of more than 100 cycles of high precision laser ranging data have been obtained, which plays an important role for its precision orbit determination.
At present, laser ranging technology in Changchun Observatory has entered the international advanced level. According to the "scientific bulletin" published in the twenty-fourth period of 2017, the experiment analysis of laser ranging after the failure of Tiangong-1 aircraft, from 3 to May 2016, the laser ranging experiment of the Sheshan Observatory of Shanghai Observatory and the Zijin Observatory of the Zijin Observatory of the Shanghai Observatory showed that the precision could reach 10 centimeters. Moreover, the orbit prediction error based on laser ranging is less than 100 meters.
Liu Chengzhi introduced the latest data in Changchun Observatory Tiangong-1 laser ranging in March 8th this year to obtain. "But in recent days, because of the bad weather in Changchun, the track is low, and the station has been passed by the day." He said.
Scientific research is fruitful
In September 2011, Tiangong-1 launched successfully, and its design life is two years. Actually, it has been in orbit for four and a half years.
In 1630 days in orbit, Tiangong-1 has carried out a number of expansion technology tests and scientific research, which has accumulated important experience for the construction and operation of space stations and the application and promotion of human space achievements.
Tiangong-1 completed the three rendezvous and docking missions of Shenzhou eight, No. nine and ten, breaking through many key technologies, including combination control technology and on - orbit flight life support technology. Six astronauts participated in many space medical experiment tasks in Tiangong-1.
According to the official website of China's manned space program, Tiangong-1 has also completed tasks such as earth environment monitoring and space environment detection, and composite colloid crystal growth experiment. Zhang Shan, deputy general designer of the space station engineering space application system, introduced the data obtained by the hyperspectral imager loaded by Tiangong-1 in an interview with the media. In the first time, the mineral mapping and oil and gas exploration in Gansu, Xinjiang, Inner Mongolia and Qinghai were used in China for the first time, and the data was first used to detect the sea water pollution. . The experiment of composite colloidal crystals has laid a good foundation for the preparation of future space materials and new materials on the ground. Zhang Shancong said.
The first space instruction in China was carried out on Tiangong-1, and Qian airlines, as the CCTV live guest for this space lesson, made a ground contrast experiment for Wang Yaping's course in space. Qian said, "many researchers have deep feelings for Tiangong-1. In a day or so, Tiangong-1 will burn into the atmosphere again. It will make a great contribution to the development of China's manned spaceflight.