Progress in Space Debris Research

During recent years, A de-orbit disposal of SinoSat 2 satellite and the depletion of the residual propellant after SC/LV separation for all LM-4 series launch vehicles were carried out. Stuffed Whipple Shields based on hypervelocity impact particles were developed. Routine observation and collision avoidance were performed. The main progress in space debris research will be introduced from three aspects: mitigation, spacecraft protection, observation and collision avoidance.


Mitigation
(1) Implementation of De-orbit and Passivation Disposal of SinoSat 2 Satellite After successful de-orbit disposal of two GEO weather satellites of FY-2B and FY-2A at the end of life on September 1, 2006 and October 7, 2006 respectively [1] , in July 2009 China carried out a deorbit disposal of failed SinoSat 2 satellite again, and in November vented and passivated residual propellant in the tank of SinoSat 2 satellite.Four times maneuverable operation were done during July 15, 2009 and July 18, making the satellite finally enter into a super-synchronous orbit with an orbital period of 25.657 h.
(2) Mitigation Disposal After SC/LV Separation Formally Into Task Flow of Missions All LM-4 series of launch vehicles were carried out depletion of the residual propellant after SC/LV separation, entirely eliminating the risk of explosion and break-up.The passivation operation after SC/LV separation has been brought into the task flow for LM-4 series of launch vehicles.After four successive launches since May 2007, in addition to disposal of residual propellant after SC/LV separation, LM-2D launch vehicle also goes through the de-orbit maneuver tests successfully, cutting the on-orbit residence time of final stage rocket greatly.
(3) China is Pioneering the Compilation of Special Technology Standards for Space Debris Mitigation China's special study plan for space debris mitigation supports specially the compilation of special technology standards for space debris mitigation.First group of special technology standards for space debris mitigation have 18 items in total, and one is space debris mitigation management standard.Presently these standards are being compiled as planned.

(4) Lawmaking of Space Debris Control in China is Advancing With Steady Steps
The experts from Chinese aerospace industry and scholars engaged in space law study carries out systematic study on the necessity, lawmaking conditions and lawmaking procedures.The task team particularly carries out study in a deep going way about how the country to realize control and management of the space debris problems in space activities through national mechanism, and puts forward related lawmaking advice to national administration authorities in order to make the laws for space debris control to be abided by Chinese aerospace activities.

Spacecraft Protection
(1) Developing of Stuffed Whipple Shields After a lot of tentative analyses and tests, two kinds of stuffed Whipple shield types are proved to be with high performances against hypervelocity impact particles, i.e.SiC/Kevlar stuffed Whipple shield and Basalt/Kevlar stuffed Whipple shield.Additional comparative tests were conducted to verify the performances of the two kinds of stuffed Whipple shield and show that both the stuffed shields are superior to a 3-sheet aluminum shield with equal areal density and equivalent with the Nextel/Kevlar stuffed shield.However, an uncertainty of the curve at low velocity region has to be pointed out due to limited test data.Aluminum foam, containing a large volume fraction of pores, was also utilized to form a shield.Large amounts of tests were conducted to investigate its protection capability.
(2) Hypervelocity Impact Tests Twenty tests were conducted to study the characteristics of secondary debris clouds by analyzing the high speed cinema images of impact processes and the numerical simulations were performed for comparison.Thermal control equipment and Solar panels were selected as target to do a series of HVI tests.A laser-driven accelerator was used to accelerate aluminum flyer plates, with diameter of 1 mm and thickness of 7 μm, to impact thermal coatings at a velocity of 3.15-5.03km/s.The coating samples consist of square OSR plates and ZKS white paints, both boned to aluminum plates.After HVI tests, the degeneration of solar absorptance α was measured in detail with the change of the thickness and diameter of flyer plates.
(3) Spacecraft Protection Design Database A spacecraft protection design database was developed and improved to facilitate the mission protection design.The database attempts to integrate all kinds of data available to provide the protection designers a useful tool.The database has strong features such as easy maintenance, easy operation, advanced structure and so on.

Observation and Collision Avoidance
(1) Routine Observatione on the Chines Non-functional Spacecraft and Upper Stage Routine observation is performed for the debris from our own space activities.For those nonfunctional spacecrafts and rocket stages, orbits of which are unexpected, we would track them as the key objects and analyze their orbits' change.At present, there are about 100 objects of these kinds involved in our daily observation plan [2−3] .Much attention is paid to the new launches in supporting mitigation measures.
(2) International Cooperation on Observation and Reentry Prediction We used 100 cm-telescope located in Xuyi of Jiangsu (see Figure 1) province to search debris in two GEO bands separately at 153.5 • and 183.5 • and obtained many images, and we found a large amount of debris which had not been cataloged.In 1995, China joined the IADC formally and began to cooperate with other space countries to take part in the international experiment of tracking upcoming reentry objects.Up to 2009, China has taken part in 11 missions [4] .Through the cooperation, the countries in IADC have exchanged their technology on reentry prediction and improved their current prediction ability. (

3) Collision Avoidance
The space debris collision avoidance method have been studied and the software have been developed.Meanwhile, a systematic avoidance standard was drafted out.We could provide the Chinese spacecraft launch mission with the service as launch window analysis and in-situ collision prediction.

Figure 1
Figure 1 Dome of the PMO's CNEOS Telescope at Xuyi Observatory.