The ion propulsion system on NASA's Deep Space 1 spacecraft came to life Tuesday, November 24, and has continued running smoothly since. Metallic grit or other contamination between the two high-voltage grids at the rear of the advanced engine is believed to have caused the engine to just down during it's first test Nov 10.

The engine started up at 2:53 p.m. Pacific Standard Time in

response to commands sent to the spacecraft. After running

overnight in low-thrust mode, engineers commanded the engine to

switch to higher-thrust modes today. The mission team plans to

leave the engine running over the four-day Thanksgiving weekend.

The team originally powered up the engine November 10, but

the system shut itself off after running for 4-1/2 minutes. When

controllers sent commands to the engine to turn itself on

Tuesday, they planned to collect more data on the status of the

system but believed it was unlikely the engine would keep

running.

"We are very pleased that the engine started and continued

to thrust," said Dr. Marc Rayman, Deep Space 1's chief mission

engineer and deputy mission manager at NASA's Jet Propulsion

Laboratory, Pasadena, CA. "In fact, it has been running very

smoothly over the first day of its operation."

Engineers believe that the engine probably shut itself off

when it was started two weeks ago because of metallic grit or

other contamination between the two high-voltage grids at the

rear of the advanced engine. It is likely that changes in

temperature as the spacecraft conducted other technology

validation activities affected the flakes, and powering-up the

thruster may have vaporized the remains.

"It's common for new ion engines on the ground or on Earth-

orbiting spacecraft to shut themselves off a few times when they

are first exercised," said Rayman. "We would not be surprised if

the engine shut itself off again over the first few days or weeks

that it runs.

"Deep Space 1's charter is to test new, advanced

technologies," Rayman added. "If everything worked perfectly on

the first try, it would be an indication we had not been

sufficiently aggressive in selecting the technologies.

Diagnosing the behavior we have seen is a very valuable part of

Deep Space 1's objective of enabling future space science

missions."

The fuel used in Deep Space 1's ion engine is xenon, a

colorless, odorless and tasteless gas more than 4-1/2 times

heavier than air. When the ion engine is running, electrons are

emitted from a hollow bar called a cathode into a chamber ringed

by magnets, much like the cathode in a TV picture tube or

computer monitor. The electrons strike atoms of xenon, knocking

away one of the 54 electrons orbiting each atom's nucleus. This

leaves each atom one electron short, giving it a net positive

charge — making the atom what is known as an ion.

At the rear of the chamber is a pair of metal grids which

are charged positive and negative, respectively, with up to 1,280

volts of electric potential. The force of this electric charge

exerts a strong "electrostatic" pull on the xenon ions — much

like the way that bits of lint are pulled to a pocket comb that

has been given a static electricity charge by rubbing it on wool

on a dry day. The electrostatic force in the ion engine's

chamber, however, is much more powerful, causing the xenon ions

to shoot past at a speed of more than 100,000 kilometers per hour

(60,000 miles per hour), continuing right on out the back of the

engine and into space.

At full throttle, the ion engine would consume about 2,500

watts of electrical power and put out 90 millinewtons (1/50th of

a pound) of thrust. This is comparable to the force exerted by a

single sheet of paper resting on the palm of a hand.

When the engine was started Tuesday, it ran overnight

thrusting at a power level of 500 watts. This morning engineers

commanded it to thrust at a level of 885 watts, then at 1,300

watts. Engineers may decide to have the engine thrust at a lower

level while it runs over the next few days.

The ion propulsion system flight hardware was built for Deep

Space 1 by Hughes Electron Dynamics Division, Torrance, CA;

Spectrum Astro Inc., Gilbert, AZ; Moog Inc., East Aurora, NY; and

Physical Science Inc., Andover, MA. Development of the ion

propulsion system was supported by NASA's Office of Space Science

and Office of Aeronautics and Space Transportation Technology,

Washington, DC. JPL is managed for NASA by the California

Institute of Technology.