The Importance of Ion Propulsion is its Great Efficiency


Ion-powered Spacecraft Sets Flight
by Richard Stenger


August 18, 2000

(CNN) -- A futuristic engine on an experimental spacecraft has racked up more operating time in space than any previous propulsion system, NASA said.

Deep Space 1, designed to test a variety of new technologies, has zoomed through space using an ion drive propulsion system for more than 200 days, mission managers said.

"The key here is the operating time. Certainly other spacecraft have been in space for a long time. But they don't run their propulsion systems very long," said John Brophy, a Deep Space 1 scientist with NASA's Jet Propulsion Laboratory.

Unlike traditional chemical rockets that blast out hot exhaust, an ion drive emits only an eerie blue glow as ions, or electrically charged atoms, exit the engine. The source of the ions is xenon, a gas found in flash tubes and lighthouse bulbs.

The hardly noticeable thrust from the ions exerts about the same amount of pressure as a sheet of paper held in the palm of one's hand. While slow to pick up speed, ion propulsion creates substantial power over great distances, delivering 10 times more thrust per pound of fuel than conventional rockets.

"It's acceleration with patience," said Deep Space 1 scientist Marc Rayan. Analogies with tortoises and hares become nearly inevitable, he said.

"The importance of ion propulsion is its great efficiency. It uses little propellant, which means the spacecraft weighs less, can use a less expensive launch vehicle and go much faster than other spacecraft," Rayan said.

A NASA rocket launched in Earth orbit in 1970 held the previous ion propulsion record in space, about 161 days. Numerous communications satellites use ion propulsion, but only to control their position, not as a primary means of propulsion.

The success of ion propulsion on Deep Space 1 could transform the future of space exploration.

"It was always considered so exotic that no one would consider relying on it unless someone showed it worked in a realistic setting. Deep Space 1 took those risks so later missions wouldn't have to," Rayan said.

Launched in 1998, Deep Space 1 completed its primary mission of testing one dozen advanced technologies by September 1999. But the ship unexpectedly lost the use of its star tracker navigation system several months later on its way to a rendezvous with a comet in 2001.

Mission engineers managed to restore its sense of direction by writing new computer programs that use an onboard camera instead of the star tracker.

"Besides that hiccup, the mission has been flawless," Rayan said.

The spacecraft is more than 206 million miles (332 million km) from Earth, according to the Deep Space 1 website.

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