Electric impulse engines propel spacecraft to Mercury

BepiColombo, Europe’s first mission to Mercury, is blazing a trail for futuristic Star-Trek style space propulsion.

The four-tonne spacecraft is the biggest ever built to be fitted with electric “impulse engines” instead of chemical rocket motors.

It will pave the way for future long distance missions to Mars and beyond that use the same advanced technology, according to Justin Byrne, head of science at aerospace company Airbus.

The Mercury Transfer Module (MTM) that will carry BepiColombo’s two orbiters on their five-billion mile journey was built at the company’s Defence and Space division assembly plant in Stevenage.

Key elements of the European Space Agency’s Mercury Planet Orbiter (MPO) were also constructed at the UK facility.

The MTM has four ion plasma engines, supplied by UK defence technology company QinetiQ, which generate thrust by expelling beams of electrically charged or “ionised” xenon gas atoms.

The “plasma” of gas particles are accelerated by electrostatic forces and ejected at 90,000mph.

During the seven-year journey to Mercury they will operate cyclically, two at a time, to preserve their lifespan.

Two thrusters produce just 290 millinewtons of force – the equivalent of an ounce.

Mr Byrne said: “It’s about as much force as you’d get from a canary flapping its wings, but the thrusters can keep firing for long periods of time.

“Chemical engines are cheaper and quicker, but nowhere near as efficient.

“The ion engines have a fuel economy equivalent to 17 million kilometres. to the gallon.”

For most of the voyage to Mercury, the engines will be firing in the direction of travel to brake rather than accelerate the spacecraft.

As it falls into the sun’s powerful gravity “well”, BepiCololombo’s velocity has to be reduced by about 7km per second to prevent it overshooting its target.

At top speed after launch, the spacecraft will be travelling at about 60km (37 miles) per second.

Both the ion thrusters and a complex series of fly-bys past the Earth, Venus and Mercury will be used to slow the craft down.

“You could get to Mercury in a few months but you’d shoot straight past it,” said Mr Byrne.

“The challenge is to get to Mercury and be captured into its orbit and to do that you have to brake, brake, brake for years and years.”

To generate the 10,000 volts of electricity needed to power the ion engines, BepiColombo has a pair of giant solar panels spanning 30 metres that unfold after launch.

Ion thrusters are already routinely used by the latest geostationary Earth orbit satellites.

Other small robotic missions have employed the technology on trips to asteroids and the moon. But BepiColombo  is the first ion-drive spacecraft to fly to another planet.

Mr Byrne said: “BepiColombo is paving the way for other interplanetary missions. The next generation of missions to Mars and beyond will all be ion based.

“It’s the biggest change in space engine technology to have happened in the last 50 years.”

- Press Association

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