PUBLIC INFORMATION OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF 91109 TELEPHONE (818) 354-5011
Contact: John G. Watson
FOR IMMEDIATE RELEASEOctober 10, 1997
DEEP SPACE MISSION ION ENGINE PASSES 8,000-HOUR ENDURANCE TEST
Ion engine propulsion, a futuristic form of spacecraft
propulsion referred to in science fiction novels and films for
decades, is one step closer to becoming a reality. On September
25, JPL completed an 8,000-hour endurance test of a prototype
xenon ion engine, providing a green light for the engine's first-
ever application to a deep space mission next summer.
Ion propulsion, also known as solar electric propulsion, is
set to be used on Deep Space 1 (DS1), the first launch of the New
Millennium program, a series of missions designed to test new
technologies so that they can be confidently used on science
missions of the 21st century. DS1, which will fly by Mars, an
asteroid and a comet while validating a dozen technologies, is
scheduled to launch on July 1.
"This marks an exciting step in deep space exploration,"
explains Jack Stocky, manager of the NASA Solar Electric
Propulsion Technology Application Readiness (NSTAR) program,
which is developing ion propulsion for use on a variety of
missions. "After years of speculation about the potential of this
form of propulsion, we are finally nearing the day when we can
validate solar electric propulsion as the propulsion system of
choice for tomorrow's most distant missions."
The most extensively instrumented endurance test of an ion
engine ever performed, the test, which began on June 17, 1996,
verified the engine's life expectancy, which has proven to exceed
the needs of the DS1 mission, while demonstrating performance
levels that exceeded all expectations. Conducted in the space-
like environment of JPL's vacuum chamber, the test was designed
to run full power for several days, then shut off and restarted,
a stressing process repeated until 8,000 hours of operation were
Ion propulsion provides only the tiniest amount of thrust,
roughly equivalent to the pressure of a single sheet of paper
held in the palm of the hand - approximately 10,000 times smaller
than the thrust of the main engines on typical planetary
spacecraft. Its magic lies in its staying power, for this low
thrust slowly changes the craft's velocity from low to high
speed, making it ideal for long missions. Compared to traditional
chemical propellants, solar electric propulsion provides
tremendous savings for future deep space and Earth-orbiting
missions with great velocity-change (delta v) requirements.
Xenon, a heavy, inert gas used as fuel for the DS1
experiment, is converted into an eerie, faint, blue haze visible
from the back of the spacecraft as it catapults through space.
DS1's ion engine, which fires electrically charged xenon
atoms from its thrusters, is just 29.9 centimeters (11.8 inches)
in diameter. It is powered by another of the mission's dozen
technologies: large solar arrays generating more than 2,000
watts, provided by the Ballistic Missile Defense Organization.
The actual thrust comes from electrically accelerating and
expelling the positively charged atoms, called ions. While the
ions are fired in great numbers out the thruster at more than
100,000 kilometers (68,000 miles) per hour, their mass is so low
that the engine produces an exquisitely gentle thrust of only 90
millinewtons (20-thousandsths of a pound). Thus, it requires
patience to accumulate the great speeds which ion propulsion is
capable of achieving.
The total propellant used may be about 10 times less than
would be required for a conventional chemical propulsion system,
roughly equivalent to having one's car get 300 miles per gallon.
This efficiency in turn allows NASA to explore the solar system
with much smaller spaceraft and less expensive rockets. On DS1,
the xenon propellant will increase the spacecraft speed by about
3.6 kilometers (2.2 miles) per second, fast enough to reach a
variety of fascinating destinations in the solar system.
A few weeks after DS1 is launched by an expendable rocket
with sufficient power to escape Earth's gravity, the ion
propulsion system will be turned on to begin slowly but surely
increasing the spacecraft's speed.
In addition to the engine itself, being assembled by the
Hughes Electron Dynamics Division, Torrance, CA, NSTAR is also
delivering a power processing unit, digital control interface
unit, propellant storage and control system, and a diagnostics
system. The latter will aid in the understanding of how this
novel system performs in space.
For further details about the DS1 mission, visit
Development of the xenon ion engine is supported by NASA's
Offices of Space Science and Aeronautics, Washington, D.C. NASA's
Jet Propulsion Laboratory is a division of the California
Institute of Technology, Pasadena, CA.