MEDIA RELATIONS OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109 TELEPHONE (818) 354-5011
Contact: Franklin O'Donnell
FOR IMMEDIATE RELEASENovember 25, 1998
DEEP SPACE 1 ION PROPULSION SYSTEM STARTS UP
The ion propulsion system on NASA's Deep Space 1 spacecraft
came to life Tuesday, November 24, and has continued running
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
"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
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.