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