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Keefer, D.

Publications and source records attributed to Keefer, D..

8 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

Electric Propulsion: Experimental Research

This paper describes experimental electric propulsion research which was carried out at the University of Tennessee Space Institute with support from the Center for Space Transportation and Applied Research. Specifically, a multiplexed LIF technique for obtaining vector velocities, Doppler temperatures, and relative number densities in the exhaust plumes form electric propulsion devices is described, and results are presented that were obtained on a low power argon arcjet. Also, preliminary Langmuir probe measurements on an ion source are described, and an update on the vacuum facility is presented.

Ruyten, W. M.↗
NASA NTRS1993

Spectroscopic investigation of a low-power arcjet plume

We report the results of spectroscopic measurements on the exhaust plume from a 1 kW NASA Lewis arcjet operated on simulated ammonia. In particular, we analyze emissions from the Balmer lines of atomic hydrogen and from one of the rotational bands of the NH radical. We find that exit plane temperatures are in the range 2000 to 3500 K, depending on the measurement method, and that the electron density upstream of the exit plane is on the order of 1.5 x 10 exp 14/cu cm as determined by the Stark width of the Balmer-alpha line. Also, we have determined that the average velocity of atomic hydrogen at the exit plane is about 4 km/sec, and that strong acceleration (to 5.5 km/sec) of the flow occurs just beyond the exit plane.

Ruyten, W. M.↗
NASA NTRS1993

Spectroscopic investigations of beam-plasma interactions in an ion plume

We report the results of spectroscopic investigations of beam-plasma interactions in the plume from a 3 cm ion source operated on argon. Ion-electron, ion-neutral, and electron-neutral scattering are identified by studying the dependence of neutral and ion emission intensities on chamber pressure and mass flow rate, and by analyzing the emission lineshapes at a non-orthogonal angle to the plume axis. Through the Doppler shift, we are able to separate contributions from fast beam ions and fast charge-exchange neutrals on the one hand, and of slow neutrals and slow ions on the other. We discuss the application of this new technique to the characterization of beam plasma interactions in the downstream region of ion thruster engines, and its potential for identifying the processes which lead to grid erosion.

Ruyten, W. M.↗
NASA NTRS1992

Characterization of electric thruster plumes using multiplexed laser induced fluorescence measurements

The use of laser-induced fluorescence to obtain spatially resolved measurements of propellant velocities and temperatures in electric thruster plumes is discussed, with emphasis on two innovations of the technique, namely simultaneous recording of the optogalvanic signal in a hollow cathode lamp for the purpose of calibrating Doppler shifts, and two-beam multiplexing to allow the measurement of two velocity components at once. It is also shown how information on plume fluctuations can be obtained from the multiplxed LIF data. The techniques are demonstrated on the plume from a low power arcjet, operated on argon, and its extension to the measurement of ion velocities in electrostatic ion thrusters and stationary plasma thrusters is discussed.

Ruyten, W. M.↗
NASA NTRS1984

Laser thermal propulsion

Laser thermal propulsion (LTP) is studied for the case in which laser power is absorbed by a small very high-temperature plasma (about 20,000 K) and transferred to the remainder of the pure hydrogen propellant by radiation and mixing. This concept could lead to the realization of a lightweight orbital transfer vehicle propulsion system having a specific impulse in the range 1000-2000 s. Approximately 12 percent of the input power may be radiated to the thruster walls, and 15 percent of the total propellant flow must be heated to 20,000 K to provide a bulk temperature of 5000 K prior to expansion. Three principal research issues identified are: (1) conditions for hydrogen plasma ignition, (2) control of the plasma position within the laser beam, plasma stability, and plasma absorption efficiency, and (3) characterization of the mixing of the plasma and buffer flows.

Keefer, D.↗
NASA NTRS1983

A reexamination of the laser supported combustion wave

Kantrowitz (1972) and Minovitch (1972) have proposed the use of laser sustained plasmas as a means to heat a rocket propellant. Recent studies of laser-powered propulsion have been directed toward the application of high-specific-impulse space propulsion systems for orbital transfer missions. Analyses of rocket performance relied heavily on the concept of the laser-supported combustion (LSC) wave. Raizer (1971) first drew the analogy between laser-sustained plasmas and combustion waves in an analysis. The Raizer model was later applied to hydrogen by Kemp and Root (1979). In connection with certain problems arising with the approach considered by Kemp and Root, the present investigation is concerned with a reexamination of the Raizer model. Attention is given to a numerical approach for the entire LSC wave in hydrogen, taking into account the incorporation of the proper boundary conditions far downstream of the wave.

Keefer, D.↗
NASA NTRS1982

A two-dimensional model of the hydrogen plasma for a laser powered rocket

A two-dimensional, closed-form model originally developed by Batteh and Keefer (1974) is modified and applied to the absorption of laser radiation by a hydrogen plasma. The model is used to predict the power absorbed by plasmas at one- and ten-atmosphere pressure as a function of laser beam radius. Predicted isotherms are given for one- and ten-atmosphere plasmas, together with thermal loading of the absorption chamber wall. The model is also used in predicting the laser power required to sustain a hydrogen plasma as a function of the absorption coefficient.

Keefer, D.↗