PUBLIC INFORMATION OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109. TELEPHONE (818) 354-5011
http://www.jpl.nasa.gov

CONTACT: Jim Doyle

FOR IMMEDIATE RELEASE                                                            
July 16, 1996

ENGINE BUILT TO CATCH A COMET BEGINS ENDURANCE TEST

	A new NASA spacecraft engine that begins flight at less than 
a snail's pace but builds up enough speed to catch a comet will 
soon be used to push exploring spacecraft to the far reaches of 
the solar system.

	A prototype of a xenon ion engine, which fires electrically 
charged atoms from its thruster, began a nearly year-long 
endurance test April 30 at NASA's Jet Propulsion Laboratory, 
Pasadena, CA.

	Once validated by the test, a similar engine will power the 
first New Millennium mission, called Deep Space-1, to an asteroid 
and a comet in 1998.  The comet will be West-Kohoutek-Ikemura and 
the asteroid will be McAuliffe, named after the school teacher 
Christa McAuliffe who died in the Challenger accident.

	"NASA has been experimenting with ion drive engines for 30 
years," said Jack Stocky, manager of the ion propulsion system 
project at JPL.  "However, this test will be the most extensively 
instrumented endurance test of an ion engine ever performed."

	In space, the 30-centimeter-diameter (11.8-inch) engine will 
use the heavy but inert xenon gas as fuel and be powered by more 
than 2,000 watts from large solar arrays provided by the 
Ballistic Missile Defense Organization.  The actual thrust comes 
from accelerating and expelling the positively charged atoms, 
called ions.  The thrusting action is similar to that of chemical 
propellant engines which expel burning gases, except that such 
engines can produce up to millions of pounds of thrust.  The 
engines in rockets that lift the Space Shuttle, for instance, 
combine metal-warping heat with an earthshaking roar and quickly 
lift the shuttle to more than 7.6 kilometers per second (17,000 
miles per hour).

	An ion engine, however, starts with only about 20-
thousandths of a pound of thrust.  There's no roar, just an eerie 
blue glow.  While the atoms, charged by an electric arc which 
removes one of the 54 electrons around its nucleus, are fired in 
great numbers out the thruster at more than 31 kilometers per 
second (70,000 miles an hour), their accumulative mass is so low, 
the spacecraft moves only millimeters per second in its early 
stages of flight.

	Still, ion propulsion is more propellant efficient than 
chemical propulsion because it expels molecules from the engine 
at a much higher speed, Stocky said.  A chemical propulsion 
engine has an exhaust velocity of 4.6 kilometers per second 
(10,400 miles per hour), while ion propulsion exhaust is 31.5 
kilometers per second (70,200 miles per hour).

	Built at NASA's Lewis Research Center, Cleveland, OH, the 
engine will be tested for 8,000 hours (330 days) in the space-
like environment of JPL's vacuum chamber.  "Ion engines have such 
low thrust they cannot operate in an atmosphere and have to be 
tested in a vacuum," said Dr. John Brophy, user validation 
assessment manager  for the project.  "JPL has the technical 
expertise and the cost-effective facility for the test."  The 
test is designed to run full power for two days and then shut off 
for one hour and restart.  This stressing process will be 
repeated until 8,000 hours of operation have been accumulated.

	After Deep Space-1 is launched by an expendable rocket with 
sufficient power to escape Earth's gravity, it will be in orbit 
around the Sun moving at the same speed the Earth moves in its 
orbit.  That means that relative to Earth, the spacecraft will 
not be moving at all.  But, slowly, the low-thrust ion engine 
will increase and the spacecraft's velocity over time to greet 
its celestial target at more than 22,000 miles per hour, fast 
enough to rendezvous with a comet or asteroid.  The prototype ion 
engine carries 80 kilograms (176 pounds) of xenon in a tank, 
which in flight would last from one to two years, depending on 
its destination and the amount of total thrusting required, 
Brophy said.  Deep Space-1 will consume only 45 kilograms (99 
pounds) of xenon during its mission.

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7-10-96 JJD
#9653