Space Debris Mitigation Status of China s Launch Vehicle

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1 Space Debris Mitigation Status of China s Launch Vehicle SONG Qiang (Beijing Institute of Aerospace Systems Engineering) Abstract: China s launch vehicle has being developed for more than 40 years. Various payloads can be sent to orbits by China s Long March series. On the aspect of space debris mitigation, China paid more attention to its launch vehicles design and operation in recent decades. Modifications had been applied to present launch vehicles, while space debris mitigation is considered in the preliminary design of the newly-developed ones. This paper presents introductions to studies and engineering application on China s launch vehicle, such as de-orbit, passivation, launch collision avoidance, etc.. Coupled with the tendency abroad, the advice is summarized for the future. KEY words: China, Launch Vehicle, Space debris mitigation. Introduction At present, the expendable launch vehicle still takes charge of sending payloads into space. The end-stage will be left in the orbit, becoming space debris, unless direct re-entry is operated. That s why a launch vehicle is a huge source of space debris generation. And related mitigation is paid more and more attention. The space agencies and launch service providers worldwide had devoted to the space debris mitigation, since the last century. Different organizations are involved in mitigation activities. Since the space debris problem has become more and more severe in recent years, more guidelines and policies are implemented. Some organizations, such as IADC (Inter-Agency Space Debris Coordination Committee), ISO, etc., are involved and keep being active in recent years. This paper presents introductions to studies and engineering practice on China s launch vehicle, such as de-orbit, passivation, launch collision avoidance, etc.. Coupled with the tendency abroad, the advice is summarized for the future. 1. China s launch vehicle family On the history of China s launch vehicle, there are 3 milestones, listed in Table 1 and demonstrated in Fig.1 as below. China developed its 1 st launch vehicle in the 1960s, and carried out the first launch on 24 th April 1970, sending DFH-1 into LEO. The 1 st GTO mission succeeded on 28 th April 1984 by LM-3, with a failure that occurred 3 months previously. The 1 st launch vehicle with strap-on boosters did its maiden flight on 16 th July 1990.

2 Table.1 Three milestones of China s launch vehicle No. Launch Vehicle Orbit Payload Date 1 LM-1 LEO DFH LM-3 GTO DFH (Failure) LM-2E LEO BARD-1/DP Fig.1 Three milestones of China s launch vehicle At present, China has developed more than 10 types of launch vehicles, covering the destination orbits from LEO to LTO,taking both unmanned and manned missions, forming the launch vehicle family as demonstrated in Fig. 2. Fig. 2 China s launch vehicle family On the other hand, the new generation launch vehicle is being studied and developed. New techniques and materials will be applied, while launch vehicles will be environmental friendly. 2. IADC questionnaire survey IADC used to send questionnaire to survey the community (among major launch service providers and space agencies) on mitigation practice worldwide. In this chapter, these questionnaire surveys shall be answered according to status of China s launch vehicles. Generally speaking, mitigation practice includes: 1) Assessment of effects of space debris on planned space systems and effects of the planned system on the environment; 2) Design measures not to generate debris and to avoid damage caused by debris; 3) Operational efforts to avoid collision and to perform adequate disposal operation after the end of mission to avoid breakups and collision.

3 The survey taken by IADC focuses on the following items as below: 1) Practice and procedures to assess the effects of debris 2) Analysis tools to assess risk of debris 3) Efforts for debris mitigation during system design and manufacturing phase 4) Efforts during ascent and early orbit operation phase 5) Efforts during system design operation phase 6) Mitigation practice after the end of mission IADC questionnaire survey is consisted of 24 items, including 3 general ones, and the other 20 divided in to 4 parts (System Design & Manufacturing, Ascent, System Operation, End of Life). All the questions are listed in Table.2. N o. 1 Categories Table. 2 IADC questionnaire survey Effects of space debris on LV Items 2 General Debris effects of LV on the environment Questions Analysis tools and techniques (predict collision hazards, debris footprints 3 from breakup upon launch). 4 5 System Design & Manufactu ring Operational debris of Launch Vehicles Passivation of Launch Vehicles(Fuel depletion, Pressure vessels, Batteries) 6 Redundancy and Shielding for launch vehicles 7 Final orbit selection for launch vehicles 8 Program or project review for launch vehicles 9 Launch and Early operation phase Ascent 10 Collision between LV and SC during the operations 11 Consideration in case of planning special test which will generate debris? 12 Consideration for prevention of on-orbit explosion? 13 Identification of released objects and assessment of collision hazard? Information on-orbit breakups and analysis for collision hazard with the 14 System fragments 15 Operation Consideration for collision hazards from background environment 16 Consideration for system survivability (shielding of critical units, etc) 17 Consideration for collision hazards from maneuvers 18 Constellation planning and consideration on failure of members 19 Collision hazard from other program s debris 20 Removal of mission terminated objects from operational orbit 21 End of Considerations for uncontrolled reentry risk 22 Life Sending to graveyard region and study for its long term effects 23 Passivation after sending graveyard orbital region

4 2.1 General questions Three general questions and relevant answers are listed as below: Q: Effects of space debris on LV A: The effect of debris on the launch vehicle during ascent and the initial operation phase is thought to be far smaller than that on operating spacecraft because of its limited time of mission duration. So the practices and procedures to assess the effects of the space debris are not considered by most of launch missions. In other space faring nations, the collision risk with catalogued objects during ascent phase is analyzed by certain software, such as COLA (Collision Avoidance for new launch) of US. China had done some efforts in this field, but it is not widely applied at present. The cooperation had been performed between CAS (China Academy of Science), CASC (China Aerospace Science and Technology Corporation). Q: Debris effects of LV on the environment. A: The assessment for debris effects of the planned systems on the environment is taken into consideration, including operational debris and explosion risk (certain missions that have not performed passivation process yet). Q: Analysis tools and techniques which are used to predict collision hazards, debris footprints from breakup upon launch. A: About the assessment tools for the ground footprint, it is thought that the footprint means those that will be caused by accidental breakup during ascent phases, and should be performed by the range safety organizations. For the boosters that do not get into the orbits, their reentry will be controlled in a certain area with safety criteria; while the end stage always stays in the orbits for quite a long time, even with the de-orbit process. 2.2 Specific questions System Design & Manufacturing Q: Operational debris of Launch Vehicles A: China has done efforts and carried out studies on limitation of operational debris, such as multi-sc SEPARATION STRUCTURE STUDY, retro-rocket ejection pollution control, and separation device debris mitigation. Q: Passivation of Launch Vehicles(Fuel depletion, Pressure vessels, Batteries) A: We have carried out study and practice in the following ways: Batteries passivation, safety analysis on self-destructive device, pressure vessel disposal (pressured gas released), the leaving propellant venting, Q: Redundancy and Shielding for launch vehicles A: Debris shielding and components redundancy will require significant weight, design modification and so additional cost. Because of limited mission duration, neither shielding nor redundancy for debris collision risk are considered.

5 Q: Final orbit selection for launch vehicles A: Final orbit selection has nothing to do with the LV without engine re-ignition ability or propellant venting. A series of maneuvers to eliminate the possibility of re-contact with the deployed spacecraft is conducted as usual procedure, but more active maneuvers to remove end-stage to lower orbit by using remaining propellant and electric power is without guarantee. Whether the final orbit can be reached, depends on the amount of remaining propellant. The problem is that it will require significant amount of propellant. For GTO mission, to protect GEO environment, low enough perigee altitude has been selected so the apogee altitude will be decreased faster. Q: Program or project review for launch vehicles A: Newly developed ones are planned for mitigation practice in the very beginning, according to the requirements and space environment conditions. For existing ones, mitigation process verification and assessment are included in every mission cycle Ascent Q: Launch and Early operation phase A: Few missions carried out launch collision avoidance, while for most missions, relative motion analysis after SC/LV separation had been done to verify the safety at the design phase. Q: Collision between LV and SC during the operations A: Relative motion analysis after SC/LV separation had been done System Operation Q: Consideration in case of planning special test which will generate debris? A: Some special test and simulations had been done in certain studies, such as Eliminate operational debris. Q: Consideration for prevention of on-orbit explosion? A: Yes, passivations have been considered in certain types of launch vehicles. Q: Identification of released objects and assessment of collision hazard? A: Yes, the common released objects include the cover of retro-rocket, support frame of SC (in some multi-satellite launch). The relative motion relations will be predicted in mission design phase to estimate the collision possibility and hazard. Q: Information on-orbit breakups and analysis for collision hazard with the fragments A: It seems that there is no official route of getting such information and for common launch missions (excluding special ones, such as manned space missions) no such analysis will be performed. Q: Consideration for collision hazards from background environment A: Only some missions carried out the launch collision avoidance.

6 Q: Consideration for system survivability (shielding of critical units, etc) A: No shielding is considered for system survivability when facing space debris, because that will require significant weight, design modifications and extra cost. Q: Consideration for collision hazards from maneuvers A: No collision hazards with space debris on orbit are considered. But it is considered to avoid collision with the mission payload. The relative motion analysis covers this issue. Q: Constellation planning and consideration on failure of members A: No. Q: Collision hazard from other program s debris A: Only some missions carried out the launch collision avoidance End of Life Q: Removal of mission terminated objects from operational orbit A: Some launch vehicles perform de-orbit action. For uncontrolled ones, they cannot be removed, including retro-rocket, support frame of SC, etc.. Q: Considerations for uncontrolled reentry risk A: No. Q: Sending to graveyard region and study for its long term effects A: GEO/MEO upper stage will be sent into graveyard region, and China s GEO/MEO upper stage will take the 1st flight test in recent years. It will be the 1st time to check out the mitigation practice on such a high altitude orbit for launch vehicles. Q: Passivation after sending graveyard orbital region A: Graveyard region is always referred to GEO satellites or GEO upper-stages. There is no Chinese GEO upper-stage at present, but at the development phase, this factor is considered. 3. Mitigation practice taken by LONG MARCH Series 3.1 Mitigation appliance The most typical mitigation appliance is carried out on LM-2C, a two-stage launch vehicle which takes a SSO mission. After the separation of the satellite, the end stage will do the attitude adjustment according to the scheduled program, when the relative distance is large enough, the valve of main engine will be opened and the remaining propellant vented while the thrust is generated. That is the process of de-orbit. As mentioned before, the effect of de-orbit depends on how much propellant is left, whether the attitude control is normal, whether the thrust generated is as we expected. The main engine is without swing ability, 4 small engines can be swung. In the future, we plan to re-start 4 small engines to realize more stable de-orbit process.

7 LM-2C/Upper stage, which is famous for dual-satellite mission [Motorola Iridium] and High eccentricity mission [ESA double star], does the end-stage disposal powered by RCS(Reaction Control System). LM-3A Series which take GTO/LTO missions, carried out an end-stage disposal experiment in recent years and plans to do disposal in the following missions. End Stage propellant venting system is added to LM-4B/4C to avoid the danger of explosion on-orbit. The end stages of former LM-4A used to be exploded in early 1990s, and then the space debris problem brought by launch vehicles started to be paid more attention by Chinese. The new generation LV of China includes LM-5, LM-6, and LM-7 which considers the debris mitigation problem in the R&D phase, and carried out many studies. In the meanwhile, several modification studies are also performed. 3.2 Mitigation study Mitigation studies are performed in several aspects, such as multi-sc separation structure design, retro-rocket ejection pollution, separation structure debris mitigation design, separation structure debris mitigation design, passivation of battery and self-destructive device, PMD (propellant management design) in de-orbit phase and passive de-orbit study. For the launch avoidance study, several missions are performed coupled with a related process. CAS (China Academy of Science), which takes charge of many observatories, is involved and offered observation data support. SHENZHOU manned spaceship and LM-2C/upperstage launch mission are two typical examples in this study. Besides, launch site work process was also taken into account. 3.3 Conclusion From all the above, three conclusions can be achieved as below: -The generation of operational debris can be limited without so much cost, and seems to be accomplished already by the production process of China s LVs. -Prevention of on-orbit breakups is technically and financially feasible, and already applied in some China s LVs. -Disposal of end stage to reduce orbit lifetime is widely applied but the effect depends. 4. Advice for the future Three advices are drawn for future: -With more and more severe space environment, the reliability requirements and realization for mitigation measures should be paid more attention. -There is still a long way for China to go in the field of mitigation design and flight verification. -The necessary international communications are important for China s space program.