|Volume 4,||Number 1||March/April 1996|
The goal of the NASA Office of Space Access and Technology's On-Board Propulsion Program is to provide advanced propulsion technology that will benefit both government and commercial missions. Under the Russian Hall Electric Thruster Technology (RHETT) program, NASA, the Ballistic Missile Defense Organization (BMDO), U.S. industry and two Russian space institutes have formed a partnership to bring advanced propulsion technology from Russia into Western markets.
Because spacecraft are limited to one fuel tank, NASA engineers are always examining ways to use the propellant on a spacecraft more efficiently. For nearly all spacecraft, the propulsion system, including the propellant, is a major fraction of the spacecraft. On a typical communications satellite, the propulsion system, which inserts and maintains the satellite in the correct orbit, can be two-thirds of the mass of the satellite.
The NASA program is centering on a category of rockets called electric propulsion. Unlike conventional rockets, which use combustion to add heat to the propellant, electric rockets use electrical power to add energy to the propellant. This allows a much greater amount of energy to be added to the gas than could ever be accomplished using conventional combustion, resulting in a very fuel-efficient system. Millions of dollars per spacecraft can be saved by either reducing the launch vehicle size through smaller on-board propulsion systems or by reducing the replacement costs of communications or remote sensing satellites through an increase in spacecraft life.
The Russian Hall effect thruster is one type of electric propulsion system particularly suited for near-Earth missions. The Hall effect thruster uses xenon gas as the propellant. Using combined electric and magnetic fields, the gas is ionized. The xenon ions are then accelerated through 300 volts of electric field to a velocity of 16,000 meters per second, providing thrust to the spacecraft. Russian Hall thrusters have been extensively developed and space tested in the former Soviet Union over the past 30 years.
RHETT is entirely self-contained. The structure, flow control, power conditioning and thermal control are packaged in one compact system. Through the RHETT program, BMDO and NASA will provide commercial and government satellites with a highly fuel-efficient, long-life propulsion system that can be easily integrated with future small satellites. The performance of the system is ideally suited for orbit raising, stationkeeping and orbit repositioning. Furthermore, RHETT can be coupled with advanced solar concentrator arrays for missions through the Earth's radiation belts. RHETT is moving advanced propulsion technology out of the laboratory and into space, allowing low-cost, small satellites to do a job that previously would be too expensive to undertake.
The RHETT I propulsion system receiving final inspection at NASA's Lewis Research Center in Cleveland prior to system testing in January 1996. Flight hardware built under the second phase of the program, RHETT II, will be space-tested in November 1996.
For more information, contact John Sankovic at the Lewis Research Center. Phone: 216/977-7429, E-Mail email@example.com Please mention that you read about it in Innovation.