Esa Bulletin May 2002 [antikvár]

Artemis- 'A Lost Mission' on Course for a Full RecoveryG. Oppenhaeuser, A.G. Bird L. van HoltzArtemis Programme Office, ESA Directorate of Telecommunications, ESTEC, Noordwijk, The NetherlandsIntroductionArtemis is ESA's latest and most complex geostationary communication satellite. It carries a number of advanced communication payloads to support new communication services for mobile communication, data-relay and navigation services. In particular its L-band land mobile payload will be used to complement and augment the European Mobile System operated by Eutelsat, its data-relay payloads will provide operational support to Envisat and SPOT-4, and its navigation payload will form an element of the European Global Navigation Overlay Service (EGNOS).Artemis was launched on Ariane flight 142 from Kourou in French Guiana on 12 July 2001. Unfortunately, the second stage of the launcher did not perform to the full, resulting in an abnormal transfer orbit with an apogee of only 17 000 km instead of the nominal 36 000 km. For any other standard communication satellite this would have been the end of the mission. Indeed, for insurance purposes, Artemis has been declared a 'total loss'. However, thanks to the combination of technologies onboard Artemis, a recovery of the mission is possible. At the time of publication, the final phase of recovery has achieved 1100 of the 5000 km needed to reach geostationary orbit.The satellite will also demonstrate the flight-worthiness of a number of new technologies, the most significant being the electrical propulsion system for full north-south station-keeping and the SILEX optical inter-satellite data-transmission system.The Artemis prime contractor is Alenia Spazio, responsible under contract to ESA for the development, assembly, integration and test, launch operations, and in-orbit operations of the spacecraft. Spacecraft operations from injection until end-of-life are managed by Telespazio from the Fucino Space Centre in Italy.The choice of a launch vehicle for Artemis was a long and involved process. Initially it was planned to launch on an Ariane-4, but for funding reasons it was later slated for launch onthe first, and then the second Ariane-5 APEX flights. When delays in the Artemis Programme made an APEX launch untenable, an agreement was reached between ESA and NASDA for a launch on the new Japanese H-IIA rocket. Following the failure of two H-ll launch vehicles, NASDA announced significant delays in the H-IIA programme. In order to launch Artemis in time for its main customers, new funds were made available for a commercial Ariane-5 launch.From injection to parking orbitFollowing launch around midnight on 12 July, the operations team managed to establish TTC (telemetry, tracking and command) contact with the satellite, despite the non-nominal orbit. The malfunction of the launcher was quickly reported and the first ranging results confirmed the orbit to be non-nominal. In particular, the apogee altitude was 17 487 instead of 35 853 km, the perigee was 590 instead of 858 km, and the inclination was 2.94 instead of 2.0 deg.The satellite was placed in a safe Sun-pointing mode with its arrays partially deployed, and its systems were checked out. The battery charge cycle was adequate, but due to the relatively long and frequent exposure to the radiation belts in this orbit, a limit of 6 days was set for implementing a recovery.The first meeting to assess recovery strategies took place on 13 July. The launch vehicle had shown a shortfall of some 500 m/s in injection velocity and it was apparent that, taking uncertainties into account, there was insufficient chemical propellant to reach geostationary orbit (GEO) and provide a useful station-keeping function. Therefore, three mission options were considered, based on making the most of the available chemical propellant, and included the use of non-geostationary orbits. Allowing for uncertainties and residuals, as a first approximation it was considered necessary to retain some 100 kg of