Speaker
Saika Aida
(DLR/GSOC)
Description
The ever increasing number of objects in the near Earth region has been causing growing concerns about the space environment and accordingly about the safety of future space missions. Since most of orbital debris stay in the orbit for years, even a single collision between space objects could seriously increase the debris population, making further collisions more likely.
The German Space Operations Center (GSOC) has been performing collision avoidance operation since 2009. Additional to the operational satellites currently 5 in LEO and 2 in GEO, conjunction monitoring and mitigation for several satellites are supported, which are operated by other organizations or ended the operation phase. The Conjunction Data Message (CDM) provided by the Joint Space Operations Center (JSpOC) is currently the main source for the orbital information of the space objects due to the quality and timeliness of the available information. Conjunction prediction, risk assessment, and avoidance maneuver planning are performed automatically in the operational process.
In the collision avoidance operation, numerous conjunctions are reported daily, which were detected within certain thresholds. Early detection of possible critical conjunctions among all predicted events is therefore important to handle critical situations promptly and efficiently. Additionally, earlier estimation of a possible avoidance maneuver strategy is also important, because the decision of the avoidance maneuver execution is mostly done within one day before the closest approach based on the latest prediction. Especially, the operational satellites TerraSAR-X and TanDEM-X are flying in a very close formation with a minimum distance of ~300 m, therefore the avoidance maneuver for both satellites shall be taken into account to handle close approaches of each encountering object. The avoidance strategies to meet the control requirements and to optimize the maneuver shall be investigated in the limited time.
The important factors for the criticality assessment are the conjunction geometry and the collision probability. In addition to the geometry and probability analysis at the latest and in the historical prediction, estimation of the future prediction is also necessary to detect the high risk conjunction. Even after a detection of the high probability event, the conjunction shall be carefully analyzed due to the large variety of the orbit prediction accuracy depending on the encountering objects. In case of very large orbit uncertainties, the probability density is spread widely, therefore the cumulative probability that the object comes near the target could become lower as a result. For the avoidance maneuver planning, it is useful for operators to be able to estimate the effect of the different maneuver strategies to the conjunction geometry as well as the collision probability. The maneuver size and epoch shall be then adjusted depending on the desired safety criteria, the time constraints, and the orbit control requirements.
In the paper, algorithms for the conjunction risk assessment and the avoidance maneuver planning are described, followed by a presentation of their application in the automated collision avoidance process in the user-friendly way to facilitate the handling of the critical conjunctions. Finally, the lessons learned through the operation are presented.
| Applicant type | First author |
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Primary author
Saika Aida
(DLR/GSOC)
