Firing up QinetiQ’s ion engines

All systems on the dart-shaped GOCE were activated by early April, providing the first real, in-orbit qualification for the QinetiQ space team’s ion engines.

QinetiQ's electric engines, known as T5 ion thrusters, are providing high-precision drag compensation for the GOCE (Gravity and steady-state Ocean Circulation Explorer) spacecraft launched in March by the European Space Agency (ESA).

GOCE is the first spacecraft to be launched as part of ESA's Living Planet program, which is investigating the impact that human activity is having on the Earth.

The strength of the Earth's gravitational field diminishes with altitude, so GOCE's orbit skirts the outer reaches of the atmosphere at about 260-280 km above the Earth. Because of that, the spacecraft experiences small but significant disturbances in its motion from atmospheric drag. GOCE's ultra-sensitive measurements of the Earth's gravitational field depend on the ability of QinetiQ's engines to maintain the spacecraft's orbit by finely controlling its altitude and speed.

QinetiQ's electric engines act as cruise control for the spacecraft, providing tiny but continuous levels of thrust to actively compensate for atmospheric drag without disturbing the sensitive payload.

"This mission would not be possible without QinetiQ's electric engines," said 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 100 mph."

The T5 ion thruster is mounted on an adjustable alignment bracket to direct the thrust vector through the spacecraft center of mass. For redundancy, two thrusters are mounted externally on the rear panel of the satellite.

QinetiQ says the thrusters are around ten times more efficient than rocket thrusters that have traditionally been used to propel spacecraft, requiring only 40 kg of propellant for the entire 30-month GOCE mission. The propellant is inert xenon gas, which is continuously fed into the 100-mm diameter cylindrical discharge chamber. The xenon is then ionized by electrons emitted by an internal cathode that both ignites and subsequently sustains the plasma inside the thruster chamber. A weak variable magnetic field is also applied that enhances the ionization efficiency and also allows the number of ions created, and therefore the thrust produced, to be rapidly varied to precisely match the drag level.

Work is currently underway with QinetiQ and its partners to qualify its T6 thruster, an even more advanced electric propulsion system that is being designed for use on the next generation of deep space and interplanetary science missions, such as the ESA BepiColombo mission to Mercury scheduled for August 2013.

“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,” said Carver.

In addition to providing the T5 thrusters, QinetiQ produced control software and algorithms for the GOCE propulsion system.