(word processor parameters LM=8, RM=78, TM=2, BM=2) Taken from KeelyNet BBS (214) 324-3501 Sponsored by Vangard Sciences PO BOX 1031 Mesquite, TX 75150 August 3, 1990 Courtesy of NASA BBS at 205 895-0028 -------------------------------------------------------------------- ION-THRUSTER OPERATION The first electron-bombardment thruster was conceived and tested by Dr. Harold R. Kaufman in 1959 at the NASA Lewis Research Center (ref. 1). The thruster operates by flowing a gaseous propellant into a discharge chamber. The propellant may be any gas, but mercury, cesium, and the noble gases are the most efficient for propulsion applications. Propellant atoms are ionized in the discharge chamber by electron bombardment in a process similar to that in a mercury arc sunlamp. This ionization occurs when an atom in the discharge loses an electron after bombardment by an energetic (40-eV) discharge electron. The electrons and the ions form a plasma in the ionization chamber. The electric field between the screen and the accelerator draws ions from the plasma. These ions are then accelerated out through many small holes in the screen and accelerator electrode to form an ion beam. A neutralizer injects an equal number of electrons into the ion beam. This beam of electrons allows the spacecraft to remain electrically neutral and is a requirement for successful thruster operation. A more complete description of the mercury-bombardment ion thruster is given in the appendix. Laboratory testing of thrusters must be done in a moderately large vacuum facility in order to simulate the environment of space. Facilities are thus required for laboratory testing. Typically, these facilities are capable of simulating altitudes of more than 300 kilometers, where the background air pressure is less than 1/100 000 000 of sea-level pressure. The development of the mercury-bombardment thruster has continued through the 1960's to the present time. Thrusters 2.5 to 150 centimeters in diameter have been successfully tested. These thrusters require power of 50 watts to 200 kilowatts and produce thrust of 0.4x10(-3) to 4 newtons (0.1x10(-3) to 1 lb). Two of the most advanced bombardment thrusters, the 8-and 30- centimeter-diameter thrusters, are described in the sections AUXILIARY PROPULSION and PRIMARY PROPULSION, respectively. Thrusters of these two sizes fulfill the requirements of present-day missions. Many laboratories in this country, Europe, and Japan have worked on a wide variety of electric thrusters. These include colloid thrusters using a doped-glycerine propellant, a pulsed-plasma thruster using ablation of a Teflon propellant block (ref. 2), and a bombardment thruster using cesium propellant. In Germany, France, and England, numerous laboratories and universities are at work on electric thrusters for both auxiliary and primary propulsion. The electric propulsion effort by the Soviet Union includes flights of Zond, Meteor, and Yantar spacecraft with ion thruster experiments onboard. The mercury-bombardment thruster technology developed at the NASA Lewis Research Center has been used worldwide. England has developed the T-4 thruster based on this technology (ref. 3). The T-4 thruster is a 10-millinewton (2.2mlb) thruster proposed as one of two possible ion thrusters to be flight tested by the European Space Agency in late 1980. The other thruster, the RIT-10, is a radiofrequency mercury-bombardment ion thruster developed by Germany. It has a similar thrust level of 10 millinewtons (2.2 mlb) (ref. 4). The Lewis technology has also been used by Japan. That country has built and tested a 5-centimeter-diameter, 5-millinewton-thrust, mercury-bombardment thruster for possible flight qualification in 1982 (ref. 5). Both the European and Japanese ion thrusters are proposed for auxiliary electric propulsion applications. Two spacecraft have been flown by the United States specifically for the purpose of testing ion thrusters in space. These tests, SERT I and SERT II, are described in the next two sections. -------------------------------------------------------------------- If you have comments or other information relating to such topics as this paper covers, please upload to KeelyNet or send to the Vangard Sciences address as listed on the first page. Thank you for your consideration, interest and support. Jerry W. Decker.........Ron Barker...........Chuck Henderson Vangard Sciences/KeelyNet -------------------------------------------------------------------- If we can be of service, you may contact Jerry at (214) 324-8741 or Ron at (214) 484-3189 --------------------------------------------------------------------