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Abstract: When Ariane 5 ECA development has been decided by Europe to increase Ariane 5 performance, the rule of 25 years in GTO orbit for the upper stage has been anticipated. This was 14 years ago and this rule was known to be satisfied with a perigee lower than 250km. Even when lowering slightly Ariane 5 ECA performance, this maximum perigee altitude has been held and the whole Launch System has been developed under CNES responsibility with this GTO perigee. In the meantime, more precise calculations demonstrated that such a GTO perigee was giving for the ESCA a mean lifetime higher than 25 years. So studies are in progress inside CNES to decrease the perigee and re-enter inside the 25 years lifetime domain. This paper presents a CNES study to reduce the orbital lifetime of Ariane 5''s upper stage that last in GTO after each commercial mission. Usually the aimed orbit has a perigee altitude of 250km, an apogee altitude near to the geostationary position and an inclination between 2° and 7°. These conditions make stage''s mean lifetime superior to 90 years. The CNES study is to expose the possibility to decrease this lifetime by reducing the perigee altitude of the final upper stage orbit through a passivation process optimised to produce orbit modification. It is shown that taking into account material and functional stage constraints the optimised passivation process is able to decrease the perigee by a few tenths of kilometres. [Copyright &y& Elsevier]

Abstract: The French Space Agency (CNES) is currently operating thirteen satellites among which five remote sensing satellites. This fleet is composed of two civilian (SPOT) and three military (HELIOS) satellites and it has been recently completed by the first PLEIADES satellite which is devoted to both civil and military purposes. The CNES operation board decided to appoint a Working Group (WG) in order to anticipate and tackle issues related to the emergency End Of Life (EOL) operations due to unexpected on-board events affecting the satellite. This is of particular interest in the context of the French Law on Space Operations (LSO), entered in force on Dec. 2010, which states that any satellite operator must demonstrate its capability to control the space vehicle whatever the mission phase from the launch up to the EOL. Indeed, after several years in orbit the satellites may be affected by on-board anomalies which could damage the implementation of EOL operations, i.e. orbital manoeuvres or platform disposal. Even if automatic recovery actions ensure autonomous reconfigurations on redundant equipment, i.e. setting for instance the satellite into a safe mode, it is crucial to anticipate the consequences of failures of every equipment and functions necessary for the EOL operations. For this purpose, the WG has focused on each potential anomaly by analysing: its emergency level, as well as the EOL operations potentially inhibited by the failure and the needs of on-board software workarounds… The main contribution of the WG consisted in identifying a particular satellite configuration called “minimal Withdrawal From Service (WFS) configuration”. This configuration corresponds to an operational status which involves a redundancy necessary for the EOL operations. Therefore as soon as a satellite reaches this state, a dedicated steering committee is activated and decides of the future of the satellite with respect to three options: a/. the satellite is considered safe and can continue its mission using the redundancy, b/. the EOL operations must be planned within a mid-term period, or c/. the EOL operations must be implemented as soon as possible by the operational teams. The paper describes this management and operational process illustrated with study cases of failures on SPOT and PLEIADES satellites corresponding to various emergency situations. [Copyright &y& Elsevier]