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Abstract: This paper summarizes results from two postmission disposal (PMD) parametric analyses based on the high fidelity NASA orbital debris evolutionary model LEGEND. The first analysis includes a non-mitigation reference scenario and four test scenarios, where the mission lifetimes of spacecraft are set to 5, 10, 20, and 30years, respectively, before they are moved to the 25-year decay orbits. The comparison among the five scenarios quantifies how a prolonged spacecraft mission lifetime decreases the effectiveness of the 25-year decay rule in the low Earth orbit region (LEO). The second analysis includes three 25-year decay PMD scenarios where the mission lifetimes of spacecraft are set to 5years but with disposal success rates set to 50%, 70%, and 90%, respectively. It illustrates how the PMD success rate impacts the long-term debris environment. The conclusion of this paper is that a prolonged spacecraft mission lifetime and a lower PMD success rate can have noticeable negative impact on the debris environment in the long run. [Copyright &y& Elsevier]

The Skybridge system is a worldwide ATM broadband communication system based on a 80 low Earth orbit satellite constellation. The minimization of space debris generation has been taken into account very early in the frame of this program.The objectives are, first to identify the contribution of Skybridge to the space debris generation and secondly to assess the risk due to space debris for the whole system. This paper summarizes the approach of the Skybridge program for debris assessment and mitigation.As no international regulation dealing with this subject exists, the analysis is based on the existing NASA 1740 Safety Standard. The methodology and the software presented in this document were applied to demonstrate the compliance of Skybridge with the requirements. In addition the new CNES standard was used to derive additional requirements.The first point deals with the production of space debris in the various mission phases: this concerns debris released during launch, constellation deployment and mission operations. Besides these normal operations, space debris can also be generated through material ageing or in case of accidents such as explosion due to on-board stored energy or collision with other orbiting objects.In the second part the collision risk is analyzed: the probability of collision with the large cataloged objects is determined. Concerning the smaller debris, the flux models give the probability of impact per surface unit: the analysis identifies components most vulnerable to debris impact together with their shielding and gives the associated probability of failure taking into account the architecture of the satellite.The problem of the post-mission disposal procedure is then discussed in the third part. [Copyright &y& Elsevier]