Engineering topics

Banks, P. M.

Publications and source records attributed to Banks, P. M..

At least 19 records

NASA NTRS1993

TSS-1 - Orbiter current and voltage experiments

Although the deployment distance of the TSS-1 tethered satellite was only about 1 percent of nominal, experiments to study the current collection and vehicle charging effects at low voltages were performed. We present measurements of Orbiter charging resulting from electron beam emission from the Orbiter, currents in the TSS system with and without electron beam emissions, and the effects of Orbiter thrusters on charging and currents. Generally, charging induced by beam emission was limited to a few volts, though during times with low ambient plasma density the Orbiter was charged up to 80 V. Thrusters are seen to enhance Orbiter charging during beam emission, and reduce ion current collection at other times.

Thompson, D. C.↗

NASA NTRS1992

Recent experimental measurements of space platform charging at LEO altitudes

The paper discusses some of the results of vehicle electrical potential from recent sounding rocket experiments involving charging of a space platform by both electron beam emission and by the application of differential bias between elements of the platform. Conclusions are presented that are applicable to the experimental parameters of the CHARGE-2 and SPEAR-1 payloads. The currents collected by HV biased collectors in the sphere show strong magnetic limiting and are close to the values predicted by Parker and Murphy (1967). No volume breakdown was observed above 100 km altitude by exposing voltages up to 45 kV to the ionosphere in the SPEAR-1 payload. The release of gas at flow rates typical of ACS systems can provide sufficient plasma to electronically neutralize space platforms biased at either positive or negative potentials.

Raitt, W. J.↗

NASA NTRS1991

Estimating radiated power from a conducting tethered satellite system

In anticipation of the upcoming TSS-1 experiment, theoretical calculations are made of radiated power from a conducting tethered satellite system. The radiation results from the steady motion of the system through the ionospheric plasma and it is stimulated by collection and emission of charge by the noninsulated surfaces of the tethered end connectors. A model of the current system is developed which incorporates the tether wire, satellite surfaces, and sheath currents. The radiation impedance of the current model is calculated using the previously developed theory of Barnett and Olbert (1986). The results confirm the low-frequency Alfven wave description with a predicted radiation impedance of a few tenths of an ohm in the Alven wave limit. Calculations are also made in the lower hybrid and whistler wave band. A larger impedance of about 13 ohm is found for the frequency range 5-50 kHz. By estimating the passive ion current drawn by the system a prediction of the total radiated power is also made. The result of 0.38 mW raises the question of whether or not wave emissions from a passive current collecting system may be detectable by either ground- or space-based platforms.

Donohue, D. J.↗

NASA NTRS1990

Effects of neutral gas release on current collection during the CHARGE-2 rocket experiment

Observations of current collection enhancements due to cold nitrogen gas control jet emissions from a highly charged rocket payload in the ionosphere are reported. These observations were made during the second cooperative high altitude rocket gun experiment (CHARGE-2) which was an electrically tethered mother/daughter payload system. The current collection enhancement was observed at the daughter payload located 100 to 400 m away from the mother which was firing an energetic electron beam. The authors interpret these results in terms of an electrical discharge forming in close proximity to the daughter during the short periods of gas emission. The results indicate that it is possible to enhance the electron current collection capability of positively charged vehicles by means of deliberate neutral gas releases into an otherwise undisturbed space plasma. These results can also be compared with recent laboratory observations of hollow cathode plasma contactors operating in the ignited mode. Experimental observations of current collection enhancements due to cold nitrogen gas control jet emissions from a highly charged, isolated daughter payload in the nighttime ionosphere were made. These observations were derived from the second cooperative high altitude rocket gun experiment (CHARGE-2) which was an electrically tethered mother-daughter payload system. The rocket flew from White Sands Missile Range (WSMR) in December, 1985. The rocket achieved an altitude of 261 km and carried a 1 keV electron beam emitting up to 48 mA of current (Myers, et al., 1989a). The mother payload, carried the electron beam source, while the daughter acted as a remote current collection and observation platform and reached a distance of 426 m away from the main payload. Gas emissions at the daughter were due to periodic thruster jet firings to maintain separation velocity between the two payloads.

Gilchrist, B. E.↗

NASA NTRS1990

The interaction of an artificial electron beam with the earth's upper atmosphere - Effects on spacecraft charging and the near-plasma evironment

The ionization created in the earth's upper atmosphere by an electron beam emitted from a low altitude spacecraft is described by two coupled nonlinear differential electron transport equations for the up-going and down-going differential energy flux. The equations are solved numerically, yielding estimates of the differential electron energy flux density at the spacecraft location. At altitudes below 200-250 km and for beam energies around 1 keV, it is shown that secondary electrons supply a significant contribution to the return current to the spacecraft and thereby reduce the spacecraft potential. The numerical results are in good agreement with observations from the Charge 2 sounding rocket experiment.

Neubert, T.↗

NASA NTRS1990

The excitation of plasma waves by a current source moving in a magnetized plasma - Two-dimensional propagation

The steady motion of a large conducting body in a magnetized plasma has been shown to create a spatial structure of charges and currents in the plasma which propagate without attenuation along the magnetic field direction (the label 'Alfven wings' has been given to this structure because of its resemblance to the wings of a biplane). It has been found that the Alfven wing structure breaks up into individual Fourier components which propagate away from the source at an angle slightly greater with respect to the magnetic field than the alignment of the original structure. This process depends on wave frequency. A given frequency is lost from the Alfven wing structure at a distance which varies as 1/omega-cubed. The amplitude of these traveling waves decreases at a rate which is inversely proportional to the square root of the distance from the source.

Rasmussen, Craig E.↗

NASA NTRS1990

Spacelab 2 electron beam wave stimulation - Studies of important parameters

Experimental results from Spacelab 2 experiments on the production of waves in ionospheric plasma by the injection of pulsed electron beams are reported. The wave environments which exist in the orbiter payload bay and at several hundred meters away are compared both during ambient conditions and during electron beam injections. The duty cycle of the beam is found to be one of the most important parameters affecting the amplitude and the harmonic structure of the waves. Maximum amplitudes are produced by 50 percent duty cycles and amplitudes are proportional to instantaneous, rather than average, beam current. The dependence of the harmonic structure on pulsing frequency shows good agreement with theory for whistler mode waves produced by the Cerenkov resonance.

Reeves, G. D.↗

NASA NTRS1990

The sheath structure around a negatively charged rocket payload

The sheath structure around a rocket payload charged up to 460 V negative relative to the ambient ionospheric plasma is investigated experimentally and by computer simulations. The experimental results come from the Charge 2 sounding rocket experiment in which the payload was split into two separate sections (mother and daughter) connected with a conducting, insulated tether. In one of the experimental modes, the voltage between the payloads was increased linearly from 0 to 460 V in 2.5 s. A floating probe array was mounted on the mother with probes located 25, 50, 75, and 100 cm from the rocket surface. The internal impedance of the array was smaller than the probe/plasma impedance, which influenced the potential measurements. The measurements contain signatures, resulting from the outward expansion of the ion sheath with increasing negative mother potential. This conclusion is substantiated by computer simulations of space charge limited flow.

Neubert, T.↗

NASA NTRS1990

VLF wave emissions by pulsed and dc electron beams in space. II - Analysis of Spacelab 2 results

Results are presented from experiments on the generation of radio frequency waves in space plasmas by the injection of artificial electron beams into ionospheric plasmas that were conducted on the Spacelab 2 Space Shuttle mission. The observations of narrow-band radiation (Reeves et al., 1988) are compared with the prediction of a theory of wave generation by pulsed electron beams (Harker and Banks, 1987). Good agreement is found between the observations and predictions for the s = 0, root 2 solutions representing Cerenkov radiation with wave normal angles less than the Gendrin angle. Also, for broadband emissions, predictions using a single-ion cold plasma theory are compared with the observed features. The broadband dc and pulsed electron beam emissions also have features that can be explained in terms of the characteristics of whistler mode waves produced by Cerenkov resonance.

Reeves, G. D.↗

NASA NTRS1988

VLF wave emissions by pulsed and dc electron beams in space. I - Spacelab 2 observations

The properties of radio waves generated by electron beams in space were investigated using data from the wideband wave receiver on the Spacelab 2. The VLF observations were found to confirm the results of the STS 3/OSS-1 mission. It was found that a 1-keV electron beam injected from the orbiter produced copious broadband electromagnetic emissions. When the electron beam was square-wave modulated, narrow-band emissions at the pulsing frequency and harmonics of that frequency were produced along with the broadband emissions. The observations indicated that dc 50-mA electron beams and pulsed 50-percent duty-cycle 100-mA beams produce broadband radiation which is comparable in intensity and spectral shape at all points for which the wave field was sampled.

Reeves, G. D.↗

NASA NTRS1988

Double-probe potential measurements near the Spacelab 2 electron beam

As part of the Spacelab 2 mission the plasma diagnostics package (PDP) was released from the shuttle as a free-flying satellite. The PDP carried a quasi-static electric field instrument which made differential voltage measurements between two floating probes. At various times during the free flight, an electron beam was ejected from the shuttle. Large differential voltages between the double probes were recorded in association with the electron beam. However, analysis indicates that these large signals are probably not caused by ambient electric fields. Instead, they can be explained by considering three effects: shadowing of the probes from streaming electrons by the PDP chassis, crossing of the PDP wake by the probes, and spatial gradients in the fluxes of energetic electrons reaching the probes. Plasma measurements on the PDP show that energetic electrons exist in a region 20 m wide and up to at least 170 m downstream from the electron beam. At 80 or more meters downstream from the beam, the double probe measurements show that the energetic electron flux is opposite to the injection direction, as would be expected for a secondary returning electron beam produced by scattering of the primary electron beam.

Steinberg, J. T.↗

NASA NTRS1988

An analysis of whistler mode radiation from the Spacelab 2 electron beam

During the Spacelab 2 mission the plasma diagnostics package (PDP) was released from the Shuttle to free fly. At times during this free flight, when the PDP was magnetically connected to the Shuttle, Stanford's fast-pulsed electron generator, located in the Shuttle cargo bay, ejected a 1-keV 50-mA electron beam. The PDP plasma-wave instrument detected intense whistler-mode radiation during these beam ejections. This paper presents a study of a whistler mode emission detected during one particular continuous electron beam firing. Calculations indicate that the beam radiated approximately 1.6 mW in the whistler mode as the beam traversed the 200 m from the Shuttle to the PDP. The emissivity also decreased by about a factor of 10 over this same distance. The measured wave powers are 10 to the 7th greater than wave powers expected from incoherent Cerenkov radiation, verifying that the radiation is generated by a coherent process. Estimates of the emissivity based on measured electric field intensities in the beam indicate that the whistler-mode noise is produced by radiation from electron bunches created by an electrostatic beam-plasma instability.

Farrell, W. M.↗

NASA NTRS1988

VLF wave stimulation by pulsed electron beams injected from the Space Shuttle

Among the investigations conducted on the Space Shuttle flight STS-3 of March 1982 was an experiment in which a 1-keV, 100-mA electron gun was pulsed at 3.25 and 4.87 kHz. The resultant waves were measured with a broadband plasma wave receiver. At the time of flight the experimental setup was unique in that the electron beam was square wave modulated and that the Shuttle offered relatively long times for in situ measurements of the ionospheric plasma response to the VLF pulsing sequences. In addition to electromagnetic response at the pulsing frequencies the wave exhibited various spectral harmonics as well as the unexpected occurrence of 'satellite lines' around those harmonics. Both phenomena occurred with a variety of different characteristics for different pulsing sequences.

Reeves, G. D.↗

NASA NTRS1988

Pulsed electron beam emission in space

During the Spacelab-2 mission of July 1985, electron beams (1 keV, 50-150 mA) pulsed at ELF and VLF frequencies were emitted from the Space Shuttle Orbiter. The wave fields generated by the beam were monitored by a Plasma Diagnostics Package which was released as a free-flying subsatellite during a six hour period. Measurements of the Orbiter potential and the return current during beam emissions were obtained from a Charge and Current Probe mounted in the payload bay.

Neubert, T.↗

NASA NTRS1988

Shuttle electrodynamic tether system

The Shuttle Electrodynamic Tether System (SETS), an investigation of the interaction of a tethered satellite, a conducting tether, and the Orbiter with each other and with their environments is discussed. The historical development of SETS and its objectives are reviewed. The SETS instrumentation is described, including the Tether Current and Voltage Monitor, Fast Pulse Electron Gun, Spherical Retarding Potential Analyzer and Langmuir Probe, Charge Current Probe, Digital Control and Interface Unit, and Dedicated Experiment Processor. The measurements to be made by SETS are examined, and its operations are briefly addressed.

Williamson, P. R.↗

NASA NTRS1987

ELF oscillations associated with electron beam injections from the Space Shuttle

ELF oscillations (f less than 500 Hz) were observed during the electron beam emissions of the space experiments with particle accelerators (SEPAC) flown on the Spacelab 1 Shuttle mission. The beams had energies up to 5 keV and currents up to 300 mA, and the oscillations were present in the data from a Langmuir probe, a floating probe, an electron energy analyzer, and a photometer. The power density and frequency of the fundamental increased with the Shuttle charge-up potential. The emission level observed during the beam sequences increased with the charge-up potential of the Orbiter, which largely depended on the wake structure. It is most likely that the ELF oscillations are expressions of fluctuations in the return current and the Shuttle potential and that these fluctuations are caused by processes involving charge imbalances in the near environment of the Shuttle, possibly in a comoving plasma cloud.

Cai, D.↗

NASA NTRS1987

Electromagnetic fields from pulsed electron beam experiments in space - Spacelab-2 results

During the Spacelab-2 mission a small satellite carrying various plasma diagnostic instruments was released from the Shuttle to coorbit at distances up to 300 m. During a magnetic conjunction of the Shuttle and the satellite an electron beam modulated at 1.22 kHz was emitted from the Shuttle during a 7 min period. The spatial structure of the electromagnetic fields generated by the beam was observed from the satellite out to a distance of 153 m perpendicular to the beam. The magnetic field amplitude of the strongest harmonics were comparable to the amplitude of simultaneously observed whistlers, while the electric field amplitudes were estimated to 1-10 mV/m.

Bush, R. I.↗

NASA NTRS1987

Active vehicle charging measurements in sounding rocket and space shuttle orbiter environments at Low Earth Orbit (LEO) altitude

It was concluded that for electron beam emission up to 100mA, vehicle charging is not a significant problem with the Space Shuttle Orbiter. Similarly, sounding rocket payloads have no serious charging problems up to this level of beam current, provided that the maximum amount of the rocket skin is available to collect ionospheric electrons from the LEO altitude range. However, sounding rockets are marginal in their collecting area capability and other effects may occur to balance the beam current when operated at lower altitudes during the night.

Raitt, W. J.↗