PAGE CONTENTS
Objectives
ARTEMIS (Advanced Relay and Technology MISsion) is a geo-stationary telecommunication satellite developed by Alenia Spazio as prime contractor for the European Space Agency, as part of the Data Relay Technology Mission (DRTM).
Due to a malfunction in the launcher’s upper stage, on 12 July 2001 ARTEMIS was injected into an abnormally low transfer orbit. Thanks to the satellite’s novel experimental ion-propulsion system, and to an innovative attitude-control strategy, the satellite could still be slowly and carefully coaxed, over a period of 18 months, into its intended operating position in geo-stationary orbit.
Since the goal to allow a 5 year mission at nominal orbit was more than achieved, as a life time of 7 to 10 years could be predicted, the ARTEMIS Ion Propulsion capabilities proved to be the key to the rescue of an otherwise lost mission.
The objective of this study is to formally capture the history and lessons learnt from the ARTEMIS electric propulsion experience, from the Platform Prime and Spacecraft Operator perspective.
Challenges
The experience gained during the ARTEMIS mission shows the value of such a flexible propulsion architecture using bi-propellant and ion propulsion, which allows reacting even on nearly mission catastrophic launcher failures. It shows also the value of the flexible AOCS system using a combination of chemical propulsion with a high specific impulse system.
The very successful adaptation of the AOCS software, designed for a GEO telecommunication satellite – earth pointed – application, with respect to orbit raising purposes proves that an orbit raising with ion propulsion can be performed cost effective by applying a nearly autonomous strategy.
Plan
The Study had a duration of one year and was organised in four main tasks.
The first task was focused on the description of the ARTEMIS spacecraft, including definition of the mission, payload capability, final platform configuration and detailed description of the IPP system.
The second tasks documented the options considered and the trade-off activities performed that resulted in the selection of the successful recovery strategies adopted to bring the satellite in the final orbital position.
The third task reported the operational aspects of the electric propulsion system observed after the launch with emphasis on ion thruster performances, observed anomalies, critical evaluation of IPP existing documentation (operation handbook, FMECA documents, etc).
Finally the fourth task resumed the lessons learned in order to derive recommendations useful for current and future exploitations of electric propulsion technologies.
A fifth task was also included, having as target the transfer of EIDP’s for IPP Equipment and the IPP TM/TC data from ARTEMIS archives to the Agency.
Current Status
Study Outputs
Tasks 1 to 4 have been completed with the publication of the related Technical Notes describing the Artemis Platform and IPP architecture, the adopted recovery strategy, the operational aspects of IPP and the lessons learnt during the Development and Operational phases of the ARTEMIS program that are related to the use of the electric propulsion. These last two tasks were conducted by Alcatel Alenia Space with the co-operation of the Vega Company, who were actively involved during the recovery phase.
The Study has been completed with the publication of a comprehensive Final Report, whose conclusions are critical in discussing key issues raised during the development and flight operations related to IPP, and an Executive Summary that summarizes the main tasks and gives "Recommendations for future Exploitations".
On 04 July 2007, at the ESTEC site, Thales Alenia Space with the cooperation of VEGA LTD carried out the "Final Presentation", consisting of about 150 slides showing the Purpose, the Contents and the final Conclusions and Recommendations of the Study.
Major Conclusions
The ARTEMIS mission was supported by ESA with the main objective to promote advanced telecommunication technology and to demonstrate the innovation of ion propulsion for station keeping of geo-synchronous satellites during a real mission.
Finally the possibility of using electric propulsion for any kind of manoeuvre has been verified in orbit. This result is not only very useful, but in some case quite mandatory for large satellites where the demand of chemical propellant could be prohibitive.
The recovery operation following the launcher failure resulted in a certain number of unusual activities, in particular the Attitude Control System for which a new operational mode has been designed.
This new operational mode has been introduced to the satellite through a patch of the AOCS software that was designed to allow the satellite to be controlled in the attitudes needed to permit the ion thrusters to be used for orbit raising.
The ARTEMIS rescue operations proved very demanding in terms of ground operations due to the complexity of the operations and to the stringent times for their accomplishment. This resulted in the need for staffing of both the space controllers and the operations engineers, the development of automatic sequences for the satellite control and the preparation of new flight procedures and telecommands.
With regard to the IPP performance, the data collected during the initial inclination reduction phase and the orbit raising to date are in good compliance with the ground test results and no degradations caused by the use of ion propulsion were observed (except for the unavoidable erosion effects of the ion thrusters on the acceleration grid). The failures occurred on the Ion Thrusters during the rescue mission (three of four out of service), provided the indication that a careful system integration, testing and qualification policy shall be adopted for the IPP System. Also, on board software reprogramming should be allowed, as well as the autonomy of the IPP operations should be increased to reduce the operators workload.
Having reached its final orbital position on the 31st of January 2003, ARTEMIS is now working exactly as originally planned having a predicted lifetime of about 10 years (as in the original requirements) though the main consequence of the launcher failure is in the loosing of the Inclination Control Capability. In fact no inclination correction manoeuvres will be performed with chemical Thrusters due to the limited chemical fuel available on board and no effective inclination correction manoeuvres will be possible with the only one functioning IPP thruster.
ARTEMIS is the first European satellite to fly with operational electric propulsion technology and the mission has become the longest to sustain itself on ion propulsion.
Even though the intended use of the Ion Propulsion Package was to perform North-South station keeping manoeuvres, ARTEMIS’s propulsion capabilities proved to be the key for the rescue of an otherwise lost mission. This demonstrates the high level of flexibility of the IPP and opens new perspectives for its use in future missions.