Modeling for Electric Propulsion Effects: Lessons Learnt on ARTEMIS

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.

 


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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.

Benefits

The aim of this project is reviewing the available experiences and data involved in ARTEMIS mission and in its innovative Ion Propulsion System, in order to derive recommendations useful for current and future exploitation of electric propulsion technologies.
Since lessons learnt could be derived for each stage of the ARTEMIS life cycle, worth is the innovative recovery procedures devised by the spacecraft control team. In fact, thanks to the re-programmable onboard control concept, modifications could be made by up linking "software patches" to the satellite. These software patches amounted to a total of 15 000 words, making it the largest reprogramming of flight software ever attempted for a telecommunications satellite.
Alenia Spazio (now Thales Alenia Space) and Astrium, in close cooperation, redesigned all control and data handling software modules affected, since the original spacecraft configuration was designed for inclination control only and not to generate thrust with the ion engines in a direction tangential to the orbit.
The ion propulsion thrusters on ARTEMIS provide an excellent heritage for a new generation of advanced low mass and moderate power satellites. Although this thrust level is not sufficient for large commercial applications or deep space missions, it is a sound basis for larger thrusters models.

Features

The ARTEMIS satellite has been selected to demonstrate the advantages of ion propulsion for north-south station keeping of geo-synchronous satellites during a real mission, so it has been equipped with an ion propulsion package. The main advantage deriving from the IPP is the saving of large amount of propellant because of the performance increase. This resulted in a reduction of the on-orbit propellant equivalent to about 15% of the BOL satellite mass.

 

After the ARIANE failure on 12 July 2001, ESA and industry specialists selected the only mission rescue scenario that has offered the possibility to bring the satellite from the useless degraded injection orbit to the nominal geostationary position in a short time and using less propellant than possible.

Although the satellite was launched with a surplus of 200 kg bi-propellant fuel and oxidizer, this would have been just sufficient to achieve GEO using the bi-propellant system, but as nearly all propellant would have been used up, no meaningful mission would be possible. It was decided to bring ARTEMIS into a safe circular orbit and to use the ion propulsion for orbit raising up to the geostationary height.

At first the liquid apogee engine using chemical propulsion has been used to bring
ARTEMIS into a near circular parking orbit.

Thanks to the various and very complex strategies utilized, the satellite has been at first "spiralled" from the circular parking position to an intermediate orbit using alternatively both south and north IPP thrusters, effecting also a partial inclination correction.


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Finally on 31 January 2003, due to the ion thrusters successive breaking, a continuous firing of only one thruster has brought the satellite into the target geostationary orbit, leaving sufficient propellant necessary for the operational life.

Since then, ARTEMIS is playing its part in the development of new telecommunications services, delivering its planned data relay, land-mobile and navigation services: its L-band land mobile payload is being used to complement and augment the European Mobile System, its data-relay payloads are being prepared to provide operational services to Envisat and SPOT-4, and its navigation payload will form an operational element of the European Geostationary Navigation Overlay Service (EGNOS).

It is planned that in the future Artemis will also support the major institutional users of the ISS. The Automated Transfer Vehicle and the Columbus Orbital Facility will also be able to use Artemis to complement existing capacity for communicating with the ISS, resulting in greater reliability, flexibility and autonomy, and also delivering potential cost savings.

Plan


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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.

Status date

Saturday, August 9, 2008 - 09:14