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Hall, D. F.

Publications and source records attributed to Hall, D. F..

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Aerospace spacecraft-charging guidelines document

A short summary document on spacecraft charging was prepared for use by engineers in the various Aerospace Corporation program offices that support Air Force Space Division programs. The magnetospheric charging environment at near-geosynchronous altitudes is outlined and the mechanisms of charging and discharging are discussed. Statistical results from the P78-2 (SCATHA) satellite engineering experiments are given. The document is intended to be a layman's source for charging information and for design guidance and criteria.

Fennell, J. F.↗
NASA NTRS1980

Flight evidence of spacecraft surface contamination rate enhancement by spacecraft charging obtained with a quartz crystal microbalance

The significance of the fraction of the mass outgassed by a negatively charged space vehicle which is ionized within the vehicle plasma sheath and electrostatically reattracted to the space vehicle was determined. The ML-12 retarding potential analyzer/temperature controlled quartz crystal microbalances (RPA/TQCMs) distinguishes between charged and neutral molecules and investigates contamination mass transport mechanism. Two long term, quick look flight data sets indicate that on the average a significant fraction of mass arriving at one RPA/TQCM is ionized. It is assumed that vehicle frame charging during these periods was approximately uniformly distributed in degree and frequency. It is shown that electrostatic reattraction of ionized molecules is an important contamination mechanism at and near geosynchronous altitudes.

Clark, D. M.↗
NASA NTRS1975

Experiment to measure enhancement of spacecraft contamination by spacecraft charging

An ambitious effort to measure contamination on a highly instrumental spacecraft is being carried out. Spacecraft contamination enhancement by spacecraft charging is described. A brief summary of the motivation for and the capabilities of the Spacecraft Charging at High Altitudes (SCATHA) Spacecraft is given. The experimental approach is described and summaries are given of previous spaceflight experiments in which similar instrumentation has been used. A description of the experimental flight hardware planned for SCATHA is included.

Hall, D. F.↗
NASA NTRS1973

Ion time-of-flight determinations of doubly to singly ionized mercury ion ratios from a mercury electron bombardment discharge

Doubly to singly charged mercury ion ratios in electron bombardment ion thruster exhaust beams have been determined as functions of bombardment discharge potential, thrust beam current, thrust beam radial position, acceleration-deceleration voltage ratio, and propellant utilization fraction. A mathematical model for two-step ionization processes has been derived, and calculated ion ratios are compared to observed ratios. Production of Hg(++) appears to result primarily from sequential ionization of Hg(+) in the discharge. Experimental and analytical results are presented, and design, construction, and operation features of an electrostatic deflection ion time-of-flight analyzer for the determination of the above-mentioned ratios are reviewed.

Sellen, J. M., Jr.↗
NASA NTRS1973

Effects of cesium ions and cesium vapor on selected ATS-F samples

Thermal control coating samples were subjected to cesium ion beam and vapor exposures. Degradation of solar absorptance and infrared emittance were measured. Solar cells and samples selected from surfaces on the ATS-F spacecraft likely to experience ion or vapor impingement were bombarded by 10-volt cesium ions. Other samples were subjected to high levels of cesium vapor. Aluminum and white paint were backsputtered by 550-volt cesium ions onto selected samples. For direct bombardment, the threshold for ion-induced property changes was above five-thousand trillion ions/sq cm. With material sputtered from a 450-sq cm target onto samples 36 cm distant, the threshold for noticeable effects was above 5 times 10 to the 17-th power ions/sq cm.

Kemp, R. F.↗
NASA NTRS1973

Electrostatic propulsion beam divergence effects on spacecraft surfaces, volume 3

Tests were conducted to determine the effects of electrostatic propulsion beam divergence effects on spacecraft surfaces. The subjects discussed are: (1) sensitive surfaces on the ATS 6 spacecraft, (2) the cesium ion source and testing facility, (3) cesium ion effects on thermophysical properties, and (4) simulated charge-exchange ion exposure. The compatibility of the ATS 6 ion engine experiment with the engineering subsystems and other experiments aboard the ATS 6 spacecraft was analyzed.

Kemp, R. F.↗
NASA NTRS1973

Electrostatic Propulsion Beam Divergence Effects on Spacecraft Surfaces. Volume 2, Addendum 1: Ion Time-of-flight Determinations of Doubly to Singly Ionized Mercury Ion Ratios from a Mercury Electron Bombardment Discharge

The analysis of ion exhaust beam current flow for multiply charged ion species and the application to propellant utilization for the thruster are discussed. The ion engine in use in the experiments is a twenty centimeter diameter electromagnet electron bombardment engine. The experimental technique to determine the multiply charged ion abundance ratios using ion time of flight is described. An analytical treatment of the discharge action in producing various ion species has been carried out.

Sellen, J. M., Jr.↗
NASA NTRS1973

Solar electric propulsion/instrument/subsystems interaction study

The interactive effects between a solar electric propulsion system and an electrically propelled scientific spacecraft were examined. The operation of the ion thrusters may impact upon the acquisition and interpretation of data by the science payload of the spacecraft. The effluents from the operation of the electric propulsion unit may also impact upon the operation of the various subsystems of the vehicle. Specific interactive effects were isolated where meaningful levels of interaction may occur. The level of impact upon elements of the science payload and other affected subsystems is examined, and avenues for the reduction or elimination of impact are defined.

Sellen, J. M., Jr.↗
NASA NTRS1973

Electrostatic propulsion beam divergence effects on spacecraft surfaces, volume 2

The third phase of a program to develop understanding of and tolerance-level criteria for the deleterious effects of electrostatic rocket exhaust (Cs, Cs(+), Hg, Hg(+)) and materials of rocket construction impinging on typical classes of spacecraft (S/C) surfaces was completed. Models of ion engine effluents and models describing the degradation of S/C surfaces by these effluents are presented. Experimental data from previous phases are summarized and Phase 2 data and analysis are presented in detail. The spacecraft design implications of ion engine contaminants are discussed.

Hall, D. F.↗
NASA NTRS1972

Damage of thermal control coating properties by energetic mercury ion bombardment.

The thermophysical properties (absorptance and emittance) of five commonly used spacecraft thermal control coatings have been measured in situ after exposure to 1.5 and 3 KeV mercury ions. Sample temperature was varied from 20 to 150 C. The results showed negligible change in emittance but significant degradation of the solar absorptance at fluences of 10 to the 17th power ions/sq cm. Plots of absorptance as a function of ion fluence are presented, along with pre- and post-exposure ex situ spectral absorptance measurements. The widely used Z93 white paint exhibited quantitative degradation from mercury ions similar to that reported by other experimenters for hydrogen and helium ions.

Kelley, L. R.↗
NASA NTRS1972

Effects of electrostatic rocket material deposited on solar cells.

If solar arrays on solar-electric spacecraft protrude into the exhaust hemisphere of the electric thrusters, they will receive fluxes (usually small) of both propellant and accelerator grid atoms. Unlike propellants, grid materials have low vapor pressures and will not reevaporate. An analysis is presented of degradation in the optical, thermal, and electrical performance of solar cells resulting from thin deposits of grid material (aluminum and molybdenum) on various array surfaces. The classical optical theory of thin films, heat balance equations, and a typical relationship for solar cell efficiency vs temperature are used to compute curves showing optical properties, temperature, and power output as functions of film thickness. The results compare favorably with available experimental data. It is shown that a few monolayers of metal deposition on the illuminated surface will seriously degrade cell performance. A means of estimating the arrival rate of these materials is provided.

Kemp, R. F.↗
NASA NTRS1972

Low thrust propulsion system effects on communication satellites.

Choice of type and placement of thrusters on spacecraft (s/c) should include consideration of their effects on other subsystems. Models are presented of the exhaust plumes of mercury, cesium, colloid, hydrazine, ammonia, and Teflon rockets. Effects arising from plume impingement on s/c surfaces, radio frequency interference, optical interference, and earth environmental contamination are discussed. Some constraints arise in the placement of mercury, cesium, and Teflon thrusters. Few problems exist with other thruster types, nor is earth contamination a problem.

Hall, D. F.↗