Living Planet   


The T5 Ion Propulsion Assembly for Drag Compensation on GOCE

Dr Clive Edwards(1)and Mr Neil Wallace(1)

(1) Qinetiq Ltd, Cody Technology park, Farnborough, GU14 0lX, United Kingdom


Due to the nature of the gravity field measurements to be made by GOCE, the satellite must fly in a near-circular, sun-synchronous, dawn-dusk orbit at an altitude of around 250 km. At this altitude the residual air drag is significant, and must be actively compensated by onboard thrusters. In addition the gradiometer instrument is sensitive to linear acceleration, which must also be precisely compensated for by the thruster system.

The dominant component of the drag force is in the primary flight axis, requiring a system capable of continuous throttling between 1 and 20 mN, with a thrust resolution of 12 mN, a response rate up to 2.5 mN/s, and a thrust vector stability of better than 0.2 degrees. In addition to the drag compensation role, the thruster will also be operated at a fixed high thrust during orbit raising for the long eclipse season.

These stringent requirements can only realistically be met using a highly controllable ion thruster assembly (ITA). The QinetiQ T5 Kaufman- type thruster is ideally suited for this mission, having been designed for a nominal thrust of between 15 - 25 mN, and including solenoid magnets which allow the operating parameters to be efficiently and accurately controlled over the required thrust range. As such the T5 represents an enabling technology for the mission.

At the time of the workshop all pre-verification activities will have been completed, and formal qualification of the ITA will be well underway. This paper will present an overview of the pre-verification and qualification programmes, and is intended to provide the GOCE scientific users with an understanding of the technology, its performance, and the challenges which have been overcome to provide it. The presentation will also offer them an opportunity to clarify any issues linking the ion propulsion system to the performance of the gradiometer instrument.


Full paper

Workshop poster

Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry