Experts on why Tianzhou-2 deorbited and re-entered: Fulfilling the responsibility of a major country
Recently, the China Manned Space Engineering Office announced that the Tianzhou-2 cargo spacecraft was controlled to re-enter the atmosphere at 18:40 on March 31, Beijing time.
Most of the spacecraft's components were ablated and destroyed, and a small amount of debris fell into the predetermined safe waters of the South Pacific.
Why did Tianzhou-2 implement deorbit reentry?
How is it controlled to deorbit?
Yang Sheng, the chief designer of the Tianzhou-2 cargo spacecraft of the Fifth Academy of Aerospace Science and Technology Group, explained this in an interview with the media.
Controlled de-orbit to avoid occupying orbital resources
Yang Sheng told reporters that Tianzhou-2 has successfully completed various technical tests and verifications in the construction phase of the space station, as well as on-orbit expansion tests. After completing the mission, the on-orbit spacecraft will perform de-orbit operations, which is an inevitable choice for China Aerospace to fulfill its responsibility as a major country.
"Generally speaking, space debris larger than 10 centimeters is a disaster for an orbiting spacecraft once it collides." Yang Sheng explained that these space debris often force the speeding spacecraft to take measures to change orbits. Collision avoidance to ensure one's own safety can sometimes severely impact on-orbit missions and even lead to mission failure.
The management of space debris is very difficult. In low-Earth orbit at an altitude of 400 kilometers, it takes several years or even decades for space debris to gradually deorbit and disappear.
Yang Sheng analyzed that after the expiry of the Tianzhou-2 mission, the de-orbit operation will be implemented in accordance with international practice, which can not only reduce the amount of space debris and avoid harm to on-orbit spacecraft and the ground, but also play a role in global space debris environmental governance. important role to avoid occupying orbital resources.
Gradual control, precise control of fall
So, how was Tianzhou-2 controlled to deorbit?
Yang Sheng introduced that at the end of the life of satellites or other spacecraft in low orbits, their orbits gradually decrease under the action of atmospheric resistance or control systems. When it decreases, the aerodynamic action intensifies, and it can be considered that the spacecraft re-enters the atmosphere at this time.
"When a low-orbit spacecraft re-enters the atmosphere, it will fly at a speed of 8 kilometers per second. At this time, under the dual action of aerothermal and aerodynamic forces, the spacecraft will gradually disintegrate, disintegrate and ablate again." Yang Sheng Say.
He told reporters that in order to reduce risks, the common practice for deorbiting large near-Earth spacecraft is to conduct controlled re-entry. way to successfully deorbit and fall into a safe area.
The safe area is generally chosen in the uninhabited area of the South Pacific, where few planes and ships pass by, and it is an internationally common low-orbit spacecraft re-entry "grave".
"my country also implemented the controlled re-entry missions of Tianzhou-1 and Tiangong-2 in 2017 and 2019. In order to reduce ground risks, orbit and attitude maneuvers were adopted to control the re-entry point." Yang Sheng introduced.
"The controlled re-entry process of the Tianzhou-2 cargo spacecraft adopts a step-by-step control method to accurately control the fall." Yang Sheng said that the first time was from a circular orbit at an altitude of 400 kilometers to a perigee elliptical orbit of 200 kilometers. The second time is to change its perigee to below the atmospheric height of 90 kilometers, so that it can enter the atmosphere to burn up, and those that do not burn up enter the intended drop zone, and finally complete the mission successfully.