Revolutionary GOCE spacecraft benefits from QinetiQ precision

16 Mar 2009
Ion thrusters provide cruise control for ESA gravity mission to be launched today

QinetiQ's electric engines are playing a crucial role on a revolutionary spacecraft to be launched today (14.21 GMT Monday) from the Plesetsk cosmodrome in Northern Russia.

The electric engines, known as T5 ion thrusters, are providing high-precision drag compensation for the dart-shaped GOCE spacecraft being launched by the European Space Agency (ESA) to map the Earth's gravitational field.

GOCE is the first spacecraft to be launched as part of ESA's living planet programme which is investigating the impact that human activity is having on the Earth. By measuring the Earth's gravity, GOCE will contribute significantly to our understanding of the Earth's structure, ocean circulation and climate change.

The strength of the Earth's gravitational field diminishes with altitude, so GOCE's orbit skirts the outer reaches of the atmosphere at just 200-300 kms (125-185 miles) above the Earth. As a result the spacecraft experiences small but significant disturbances in its motion from atmospheric drag. QinetiQ's electric engines act as cruise control for the spacecraft, continuously compensating for this atmospheric drag and quite literally preventing the spacecraft from falling out of the sky.

"In order to achieve its very challenging mission objectives, the GOCE spacecraft is based on cutting-edge technology, making it a jewel of innovations," commented Volker Liebig, Director of Earth Observation Programmes at ESA. "It has been designed to fly at an extremely low orbital altitude, just 250km (155 miles) above Earth. For this reason it has an eye-catching aerodynamic shape and will actively compensate for the air drag by using the finely controlled thrust of QinetiQ's ion engine."

QinetiQ's T5 ion thrusters are around ten times more efficient than rocket thrusters that have traditionally been used to propel spacecraft, requiring only 40kgs of propellant for the whole 30-month GOCE mission. The thrusters use the inert gas xenon as their propellant ensuring they are also more environmentally friendly than conventional thrusters that use volatile chemical propellant.

"This important space mission would not be possible without the precision provided by the QinetiQ's electric engines," commented Mary Carver, Managing Director of QinetiQ's Integrated Systems business. "Our space engineers have overcome a challenge that has been likened to compensating for the impact of an insect landing on the windscreen of a car travelling at 100mph."

Mary Carver added: "In the next few years electric propulsion could make previously impossible missions into deep space a reality and extend the operational life of commercial communications satellites, reducing costs."

QinetiQ is currently working with partners to qualify its T6 thruster, an even more advanced electric propulsion system that has been designed for use on the ESA BepiColombo mission to Mercury.
ENDS

About the GOCE mission

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.

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.

The prime contractor for the mission is Thales Alenia Space Italy, with Astrium Friedrichshafen responsible for the spacecraft.

About the Ion Propulsion Assembly

The electric propulsion system is responsible for controlling and maintaining the spacecraft’s orbit and as such is a vital GOCE subsystem. Uniquely it also ensures the drag free attitude control in the flight direction essential to allow the scientific objectives of the mission to be achieved.

At the heart of the system is QinetiQ's T5 ion thruster, mounted on an adjustable alignment bracket to direct the thrust vector through the spacecraft centre of mass. The thruster is extremely efficient requiring dramatically less propellant than conventional rocket thrusters, allowing the 30-month mission to be achieved using only 40 kg of propellant. For redundancy, two ion thrusters are mounted externally on the rear panel of the satellite.

The propellant is the inert xenon gas which is continuously fed into the 10 cm diameter cylindrical discharge chamber. The xenon is then ionised by electrons emitted by an internal cathode which both ignites and subsequently sustains the plasma inside the thruster chamber. A weak variable magnetic field is also applied which enhances the ionisation efficiency and also allows the number of ions created, and therefore the thrust produced, to be rapidly varied to precisely match the drag level.

In addition to providing the T5 thrusters, QinetiQ has produced control software and algorithms for the GOCE propulsion system. QinetiQ has also supported the testing of the Ion Propulsion Assembly.
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Revolutionary GOCE spacecraft benefits from QinetiQ precision