Global Trends in Achieving Successful End-Of-Life Disposal in LEO and GEO

摘要

Guidelines for space debris mitigation have been formulated by the IADC (Inter Agency Debris Coordination Committee) in 2002. The principal mitigation actions are the passivation of space systems after the end of operations, the limitation of the remaining post-mission dwell time in the LEO and GEO protected region and the limitation of the release of debris. In the past ten years, these recommendations and associated threshold values have been included in several national and international standards and should now be applicable to numerous new missions. Verification of the implementation of mitigation measures in the design of a mission is the responsibility of each nations' or agencies' project control during design reviews. The proper implementation of the measures will be followed up by the review of procedures, mission logs and reports. The aforementioned processes are important but they are not very transparent to all space farers. Surveillance data, obtained through national sensors, shared by large surveillance networks such as USSTRATCOM's SSN, provide visibility on all trackable objects. With the help of these data the fulfillment of requirements on orbital dwell time in protected zones can be verified. This assessment, however, requires dedicated methods to determine the end-of-life of a mission. Methods as used for the current paper allow the detection of orbit maintenance manoeuvres in LEO and GEO by processing historic, publicly available surveillance data. This first assessment needs to be followed by an estimation of the area-to-mass ratio of the decommissioned objects to allow a subsequent orbit propagation with the aim to estimate the remaining orbit dwell time in a protected region. An independent cross-check using surveillance data provides a very important layer of visibility on the implementation of mitigation measures. It offers a unique global transparence and it even provides additional information as, e.g., the unintentional release of debris during operations, or an off-nominal orbit evolution of an object (e.g. due to non-nominal thruster performance, non-nominal attitude,...). The basic underlining guidelines have been formulated more than 10 years ago and global trends in the application of the guidelines would need to monitored to assess future in-orbit risk levels. In this paper we present multi-year trends on the level of application of guidelines for the clearance of protected zones after the end of mission. The results are presented in statistical form, separating the behaviour of upper-stages from spacecraft with and without orbit control system. The trends are presented for the GEO and LEO protected zones. The mass involved in the space hardware (which is a critical factor for the future environment) is taken into account. The underlying methods used by ESA in order to arrive at this data, based on publicly available surveillance data, are presented.