QinetiQ was awarded a pound4.6 million contract by Astrium, ESA's prime contractor for the GOCE platform, in 2001 to provide the two Ion Thruster Assemblies (ITAs) for the spacecraft. By using QinetiQ's T5 ion thruster the spacecraft will be able to compensate for the drag experienced in orbit, thereby allowing highly accurate measurements of the Earth's gravity field.

Travelling at 8 kilometres per second and operating at an orbital altitude of 240 kilometres, the spacecraft will experience a small but significant disturbance in its motion from atmospheric drag. This disturbance is constantly changing so continuous and precise compensation is needed to allow the highly sensitive accelerometers on board to map the earth's gravitational field. The extreme control precision provided by the T5 ion thrusters has been likened to compensating for a snow flake landing on the deck of a super tanker.

Alex Popescu, ESA's GOCE mission manager, said: "The data collected by GOCE will be vital for the next generation of geophysical research and will contribute significantly to furthering our understanding of the impact of ocean circulation on the Earth's climate. Without the precision that is provided by the spacecraft's thrusters the mission would be impossible. Consequently, the final testing of the propulsion system is an important milestone."

Steve Morton, QinetiQ's GOCE project leader, welcomed the impending delivery of the thruster assemblies, saying: "QinetiQ's ion thrusters will play a key role in the success of GOCE as the thrust accuracy requirements of the mission demand a lot of the spacecraft's propulsion system. We have needed to push the boundaries of current knowledge and technology and are proud to be so centrally involved in this important mission."

In addition to the precision provided by the T5 thrusters, the ion engines are also exceptionally mass efficient, requiring only 40 kilogrammes of propellant for the entire 20 month duration of the mission. This is achieved by ejecting xenon gas propellant out of the thrusters at a velocity in excess of 40 thousand metres per second, which is at least 10 times faster than any other conventional rocket thruster employing volatile chemicals, such as those used on the Space Shuttle.

In addition to providing the T5 thrusters, QinetiQ has produced control software and algorithms for the GOCE propulsion system. QinetiQ is also supporting the testing of the complete propulsion sub-system, the Ion Propulsion Assembly (IPA), of which the ITA is a key component and for which Astrium has overall responsibility.

QinetiQ is currently working with partners to qualify its T6 thruster, an even more advanced electric propulsion system aimed at enabling deep space missions and capable of extending the operational life of the next generation of commercial communications satellites.

In addition to its ion engine expertise, QinetiQ has a pedigree of space research, development and operations that goes back to the early 1960s and the company is today one of Europe's foremost commercial space technology organisations, specialising in small low-cost satellites, mission design and geospatial information systems.

The GOCE (Gravity Field and Steady-State Ocean Circulation Explorer) mission is dedicated to measuring the Earth's gravity field and modelling the planet's geoid, essentially a gravitational contour map, with extremely high accuracy and spatial resolution. It is the first Earth Explorer Core mission to be developed as part of ESA's Living Planet Programme and is scheduled for launch in 2007.

A precise model of the Earth's geoid is crucial for deriving accurate measurements of ocean circulation, sea-level change and terrestrial ice dynamics - all of which are affected by climate change. The geoid is also used as a reference surface from which to map all topographical features on the planet.

An improved knowledge of gravity anomalies will contribute to a better understanding of the Earth's interior, such as the physics and dynamics associated with volcanism and earthquakes and also further our knowledge of land uplift due to post-glacial rebound.

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