Half a century in the making

The concept of electric propulsion has been around for 50 years or more, but was deemed too experimental to commit to major projects. Only now is it beginning to find real applications. For example, keeping geostationary satellites in their correct orbit, to counteract the aerodynamic drag from the very tenuous atmosphere 200 km above the Earth. Or interplanetary missions such as Deep Space 1—the first experimental mission to use ion engines, it was originally intended as a technology demonstrator but performed a successful fly-past of the asteroid 9969 Braille and the comet Borrelly 15 years ago.

Another very successful mission using ion engines was the ESA Gravity field and steady-state Ocean Circulation Explorer (GOCE) satellite which for four years until 2013 was able to map in unprecedented detail the Earth’s gravity field.

dawn spacecraft
The Dawn spacecraft, equipped with large solar panels to power its electrical engine.
Image: NASA

Future designs

Now that electric spacecraft engines have entered mainstream use, they look set to reduce the cost of deploying satellites. With compact ion engines onboard, satellites can raise themselves from low Earth orbit to their final geostationary orbit under their own power. This will save enormous amounts of fuel required to lift the satellite through conventional chemical rockets, and allow the use of much smaller launch vehicles which will save a lot of money. Boeing was the first off the blocks in 2012 with an all-electric version of their 702 platform satellite fitted with xenon-powered gridded ion engines, and other satellite manufacturers are following suit.

Currently all electric power designs use xenon gas as the propellant, but the search is on for alternative propellants since xenon is enormously expensive and in limited supply. But electrical power is here to stay, and over the longer term, space tugs and even manned missions to Mars based on nuclear electric propulsion will be the next on the drawing board.

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