Douglas Isbell 
Headquarters, Washington, DC                 November 25, 1998
(Phone:  202/358-1753)

Frank O'Donnell
Jet Propulsion Laboratory, Pasadena, CA
(Phone:  818/354-5011)

RELEASE:  98-215

DEEP SPACE 1 ION PROPULSION SYSTEM STARTS UP 

     The ion propulsion system on NASA's Deep Space 1 spacecraft 
came to life Tuesday, Nov. 24, and has continued running smoothly 
since. 

     The engine started up at 5:53 p.m. EST, 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 Nov. 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 60,000 miles per hour (100,000 
kilometers 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 puts out 1/50th of a pound (90 
millinewtons) 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.