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30-centimeter-diameter thruster accelerator grids accomplished achievable additional allows anode applications auxiliary bombardment thruster cathode centimeter-diameter thruster characteristics chronous orbit components continuous cycles decrease density described developed diameter discharge chamber dished Earth efficient electric propulsion electric thrusters electrons excess exhaust figure 17 flight Force geosynchronous gimbal given ground increase indicated ion beam ion thruster ionization isolate kilograms Lewis Research Center lifetime magnetic maintained mass measure ment mercury missions mounted NASA needs neutralizer north-south orbit passed payload performance periods permit plasma potential power processor powerplant pressure primary produce propellant propellant flow propulsion system provides quirement range result rocket screen separate SERT II shown in figure shows similar space spacecraft specific impulse stationkeeping successfully supply tests thrust thrust level thruster operation thruster system tion Typically values vapor voltage weight wheel
Page 3 - 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.
Page 3 - 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, as shown in figure 5.
Page 7 - They had tested small pulsed-plasma thrusters as well. Thus, they established that electric thrusters would work in space and that they could predict the thrusters' performance in space from ground-based tests in vacuum facilities. The next step was to determine how durable the thrusters were. As mentioned previously, electric thrusters produce only a small amount of thrust; therefore, they must be capable of operating for long periods — several months to years in most applications. SERT II.
Page 12 - A primary electric propulsion stage could offer large payload advantages as a commercial tug in conjunction with the space shuttle. The interest in electric propulsion derives mainly from the reduction in propellant requirements relative to chemical propulsion due to operation at increased specific impulse. One way to compare the capability of an electric propulsion spacecraft with that of a chemical system is to consider the total impulse delivered by two such systems. A...
Page 5 - Teflon propellant block, and a combardment thruster using cesium propellant. In England, France, and Germany 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.
Page 11 - Figure 87 shows how the thrusters can help despin the momentum wheel for one of the three axes of a spacecraft. Auxiliary electric propulsion can present a profit when used in place of other types of auxiliary propulsion for geosynchronous spacecraft. Figure...
Page 6 - I were to demonstrate neutralization in space and to measure any differences between ground and space operation. The direct evidence of incorrect neutralization would be a decrease in thrust from the predicted values. The SERT I flight was a partial success.
Page 3 - ... 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. Then, these ions are accelerated out through many small holes in the screen and accelerator electrode to form an ion beam. Figure 8 1 shows this.
Page 15 - Two-axis gimbaling system. The propellant supply and distribution system proposed for all missions is quite similar to that successfully flown on the SERT II mission. A common propellant supply, in one or more tanks, provides the propellant to all thrusters. The engine turns each thruster on or off as required during the mission. A blowdown system provides the required pressure. Use of appropriate internal liners allows multiple-mission use for a single qualified tank design. Fusion propulsion.
Page 11 - North-South thruster alignment on three-axis stable platform spacecraft. at specific times throughout the orbit. Station walking, or changing the east-west location of the geosynchronous spacecraft can also be accomplished. Because the center of solar pressure and the center of mass of the spacecraft are rarely the same point, the thrusters must increase gradually the speed of fly wheels to hold the spacecraft in proper orientation.