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NASA NTRS1984

A historical overview of the electrical power systems in the US manned and some US unmanned spacecraft

A historical overview of electrical power systems used in the U.S. manned spacecraft and some of the U.S. unmanned spacecraft is presented in this investigation. A time frame of approximately 25 years, the period for 1959 to 1984, is covered in this report. Results indicate that the nominal bus voltage was 28 volts dc in most spacecraft and all other voltage levels were derived from this voltage through such techniques as voltage inversion or rectification, or a combination. Most spacecraft used solar arrays for the main source of power except for those spacecraft that had a relatively short flight duration, or deep spaceprobes that were designed for very long flight duration. Fuel cells were used on Gemini, Apollo, and Space Shuttle (short duration flights) while radioisotope thermoelectric generators were employed on the Pioneer, Jupiter/Saturn, Viking Lander, and Voyager spacecraft (long duration flights). The main dc bus voltage was unregulated on the manned spacecraft with voltage regulation provided at the user loads. A combination of regulated, semiregulated, and unregulated buses were used on the unmanned spacecraft depending on the type of load. For example, scientific instruments were usually connected to regulated buses while fans, relays, etc. were energized from an unregulated bus. Different forms of voltage regulation, such as shunt, buck/boot, and pulse-width modulated regulators, were used. This report includes a comprehensive bibliography on spacecraft electrical power systems for the space programs investigated.

Maisel, J. E.↗

NASA NTRS1985

Shuttle electrical environment

Part of an AFGL payload flown on the STS-4 mission consisted of experiments to measure in-situ electric fields, electron densities, and vehicle charging. During this flight some 11 hours of data were acquired ranging from 5 minute snapshots up to continuous half-orbits. These experiments are described and results presented for such vehicle induced events as a main engine burn, thruster firings and water dumps in addition to undisturbed periods. The main characteristic of all the vehicle induced events is shown to be an enhancement in the low frequency noise (less than 2 kHz), in both the electrostatic and electron irregularity (delta N/N) spectra. The non-event results indicate that the electrostatic broadband emissions show a white noise characteristic in the low frequency range up to 2 kHz at an amplitude of 10 db above the shuttle design specification limit, falling below that limit above 10 kHz. The vehicle potential remained within the range of -3 to +1 volt throughout the flight which exhibits normal behavior for a satellite in a low equatorial orbit.

Smiddy, M.↗

NASA NTRS1985

Charging of DMSP/F6 spacecraft in aurora on 10 January 1983

Spacecraft charging has been widely observed in geosynchronous orbit on the ATS-5 and ATS-6 pair and on the SCATHA spacecraft. An adequate theory for explaining the observations exist. Neither the data or theory can be exported to low polar orbit and its drastically different environment. Evidence of charging on the DMSP F6 spacecraft is presented. A simple model is set up explaining the observations. Two independent instruments on the spacecraft showed charging to a moderate (44 volts) negative potential. The selection spectrometer showed a flux of 2 billion electrons per sq. cm. sec. ster. peaked at 9.5 keV. This was marginally sufficient to overcome the flux of cold ambient ions. Charging calculations are presented showing where simplications are justified and where serious uncertainties exist. More serious charging is predicted for the Shuttle in polar orbit.

Besse, A. L.↗

NASA NTRS1985

Average and worst-case specifications of precipitating auroral electron environment

The precipitation electrons in the auroral environment are highly variable in their energy and intensity in both space and time. As such they are a source of potential hazard to the operation of the Space Shuttle and other large spacecraft operating in polar orbit. In order to assess these hazards both the average and extreme states of the precipitating electrons must be determined. Work aimed at such a specification is presented. First results of a global study of the average characteristics are presented. In this study the high latitude region was divided into spatial elements in magnetic local time and corrected geomagnetic latitude. The average electron spectrum was then determined in each spatial element for seven different levels of activity as measured by K sub p using an extremely large data set of auroral observations. Second a case study of an extreme auroral electron environment is presented, in which the electrons are accelerated through field aligned potential as high as 30,000 volts and in which the spacecraft is seen to charge negatively to a potential approaching .5 kilovolts.

Hardy, D. A.↗

NASA NTRS1985

Polar orbit electrostatic charging of objects in shuttle wake

A survey of DMSP data has uncovered several cases where precipitating auroral electron fluxes are both sufficiently intense and energetic to charge spacecraft materials such as teflon to very large potentials in the absence of ambient ion currents. Analytical bounds are provided which show that these measured environments can cause surface potentials in excess of several hundred volts to develop on objects in the orbiter wake for particular vehicle orientations.

Katz, I.↗

NASA NTRS1985

An investigation of arc discharging on negatively biased dielectric conductor samples in a plasma

Proposals are now being developed for the construction of high-power photovoltaic systems for operation in low Earth orbit, where the plasma number density is about 1,000 to 1,000,000 per cubic cm. Existing data indicate that interactions between the plasma and high-voltage surfaces of an orbiting power system will occur. In ground tests, where the applied voltage is increased negatively from ground, the array current collection shows an approximately linear rise until it terminates in arcing at greater than several hundred volts negative. This arcing may reduce the power generation efficiency and could possibly affect the low-level logic circuits of the spacecraft. Therefore it is important that the arcing phenomenon be well understood. This study is a survey of the behavior of different dielectric-conductor samples, including a solar cell module, that were biased negatively in a low-density plasma environment with the intent of defining arc discharge conditions and characteristics. Procedures and results are discussed.

Miller, W. L.↗

NASA NTRS1985

Discharges on a negatively biased solar cell array in a charged-particle environment

The charging behavior of a negatively biased solar cell array when subjected to a charged particle environment is studied in the ion density range from 200 to 12,000 ions/sq cm with the applied bias range of -500 to -1400 V. The profile of the surface potentials across the array is related to the presence of discharges. At the low end of the ion density range the solar cell cover slides charge to from 0 to +5 volts independent of the applied voltage. No discharges are seen at bias voltages as large as -1400 V. At the higher ion densities the cover slide potential begins to fluctuate, and becomes significantly negative. Under these conditions discharges can occur. The threshold bias voltage for discharges decreases with increasing ion density. A condition for discharges emerging from the experimental observations is that the average coverslide potential must be more negative than -4 V. The observations presented suggest that the plasma potential near the array becomes negative before a discharge occurs. This suggests that discharges are driven by an instability in the plasma.

Snyder, D. B.↗

NASA NTRS1985

Life cycle test results of a bipolar nickel hydrogen battery

A history is given of low Earth orbit (LEO) laboratory test data on a 6.5 ampere-hour bipolar nickel hydrogen battery designed and built at the NASA Lewis Research Center. The bipolar concept is a means of achieving the goal of producing an acceptable battery, of higher energy density, able to withstand the demands of low-Earth-orbit regimes. Over 4100 LEO cycles were established on a ten cell battery. It seems that any perturbation on normal cycling effects the cells performance. Explanations and theories of the battery's behavior are varied and widespread among those closely associated with it. Deep discharging does provide a reconditioning effect and further experimentation is planned in this area. The battery watt-hour efficiency is about 75 percent and the time averaged, discharge voltage is about 1.26 volts for all cells at both the C/4 and LEO rate. Since a significant portion of the electrode capacity has degraded, the LEO cycle discharges are approaching depths of 90 to 100 percent of the high rate capacity. Therefore, the low end-of-discharge voltages occur precipitously after the knee of the discharge curve and is more an indication of electrode capacity and is a lesser indicator of overall cell performance.

Cataldo, R. L.↗

NASA NTRS1984

T/R switch design for short-range measurements, part 6.1A

The positive intrinsic negative (PIN) diode switch which is designed to protect the receiver from burnout or damage on transmission and channel the echo signal to the receiver on reception is outlined. The receiver must be protected firmly. A schematic diagram of a transformer rectifier (TR-ATR) switch for the Urbana Radar is shown. The T/R switch consists of a half wavelength coaxial cavity with tuning condenser and PIN diodes. Two UM4300 PIN diodes were mounted between the inner and outer conductor. The dc biasing voltage required for the PIN diodes is supplied by a control circuit. On transmission, the PIN diodes are forward biased to about 0.5 amperes. On reception, about 10 volts reverse voltage is applied to the diodes, which produces an initial reverse current to speed the recovery time. The T/R switch characteristics are estimated and the result of testing at different peak transmitter powers from 410 kW to 1500 kW is shown.

Yu, B.↗

NASA NTRS1985

Vehicle Charging And Potential (VCAP)

The vehicle charging and potential (VCAP) payload includes a small electron accelerator capable of operating in a pulsed mode with firing pulses ranging from 600 nanoseconds to 107 seconds (100 milliamps at 1000 volts), a spherical retarding potential analyzer - Langmuir probe, and charge current probes. This instrumentation will support studies of beam plasma interactions and the electrical charging of the spacecraft. Active experiments may also be performed to investigate the fundamental processes of artificial aurora and ionospheric perturbations. In addition, by firing the beam up the geomagnetic field lines of force (away from the Earth) investigations of parallel electric field may be performed.

Roberts, W. T.↗

NASA NTRS1984

A fast Fermi process - Energetic electrons accelerated by a nearly perpendicular bow shock

A fast Fermi process which may explain how solar wind electrons are energized in the vicinity of the point of tangency of the IMF to the earth's bow shock is discussed. In the solar wind frame, the nearly perpendicular bow shock behaves as a rapidly moving magnetic mirror in such a manner that electrons with sufficiently large pitch angles can be reflected and accelerated. If the seed electrons have energies of several hundred electron volts, they can attain energies of several keV through the acceleration process.

Wu, C. S.↗

NASA NTRS1984

Unusual structures of high-latitude stratospheric electric fields

A possible explanation is given for three unusual stratospheric electric field structures reported by Madsen et al. (1983). It is suggested that stratospheric vertical electric-current structures may arise as extensions into the stratosphere of tropospheric currents generated by convective charge transport. A convective tropospheric current generator is presented which is capable of producing, at altitudes of about 30 km, the vertical electric field intensities of several volts per meter that are sometimes (although very rarely) observed by balloon-borne sensors (Madsen et al., 1983).

Dangelo, N.↗

NASA NTRS1984

Superthermal ionospheric outflows

In recent years observations have shown that the terrestrial ionosphere serves as a significant source of the hot plasma in the magnetosphere. These findings imply that cold plasma flows upward to great altitudes and at some point along the way gains energies much larger than typical ionospheric values. The present investigation is mainly concerned with observations of ionospheric outflows at energies higher than those predicted by ambipolar wind models but lower than those associated with keV auroral ion acceleration, giving particular attention to the energy range from a few to a few hundred electron volts. The ion flows in the energy range intermediate between polar wind and keV auroral ion beams are called superthermal ion outflows. It is shown that recent observations of superthermal ion outflows from the terrestrial ionosphere are related to theoretical models of the topside ionosphere.

Moore, T. E.↗

NASA NTRS1984

Middle atmospheric electrodynamics - Status and future

Recent theoretical and observational studies of middle atmosphere electrodynamics are reviewed. Attention is given to observations of large electric fields in the mesosphere and stratosphere which suggest magnitudes of about one volt per sq m. Recommendations are offered with respect to areas of future study, with emphasis on studies of the morphology of large electric fields, and their relationship with external influences such as magnetospheric electric fields and tropospheric thunderstorms.

Goldberg, R. A.↗

NASA NTRS1985

Trapping of ion conics by downward parallel electric fields

Energetic particle data from electrostatic analyzers aboard the S3-3 satellite indicative of a downward parallel electric field at low altitudes are presented to argue for a causal connection between downward parallel electric fields and ion heating. The data include observations of upward field-aligned electron beams in regions where precipitating electron fluxes are suppressed. Evidence of downward acceleration of ions and locally mirroring ion conics is also presented. It is argued that the presence of a downward electric field may have important consequences for ion conic heating and might in fact be required for the observed heating of ions to several hundred electron volts.

Gorney, D. J.↗

NASA NTRS1985

Thin film module development

The design of ARCO Solar, Inc.'s Genesis G100 photovoltaic module was driven by several criteria, including environmental stability (both electrical and mechanical), consumer aesthetics, low materials costs, and manufacturing ease. The module circuitry is designed as a 12 volt battery charger, using monolithic patterning techniques on a glass superstrate. This patterning and interconnect method proves amenable to high volume, low cost production throughput, and the use of glass serves the dual role of handling ease and availability. The mechanical design of the module centers on environmental stability. Packaging of the glass superstrate circuit must provide good resistance to thermal and humidity exposure along with hi-pot insulation and hailstone impact resistance. The options considered are given. Ethylene vinyl acetate (EVA) is chosen as the pottant material for its excellent weatherability.

Jester, T.↗

NASA NTRS1985

Thin film module electrical configuration versus electrical performance

The as made and degraded states of thin film silicon (TFS) based modules have been modelled in terms of series resistance losses. The origins of these losses lie in interface and bulk regions of the devices. When modules degrade under light exposure, increases occur in both the interface and bulk components of the loss based on series resistance. Actual module performance can thus be simulated by use of only one unknown parameter, shunt losses. Use of the simulation to optimize module design indicates that the current design of 25 cells per linear foot is near optimum. Degradation performance suggests a shift to approx. 35 cells to effect maximum output for applications not constrained to 12 volts. Earlier studies of energy based performance and tandem structures should be updated to include stability factors, not only the initial loss factor tested here, but also appropriate annealing factors.

Morel, D. L.↗

NASA NTRS1985

PASP: A high voltage array experiment

In the near future, Air Force mission payloads will require significant increases in power. Sophisticated sensing systems such as infrared focal plane detector arrays and radar will be employed by the Air Force to fulfill its strategic objectives. These payloads will demand that the power subsystem provide up to 50 kW at the end of mission life, more than an order of magnitude greater than is currently required. Some of these payloads must be flown in low-Earth polar orbits to satisfy mission objectives, and it is likely that large (500 to 600 sq m) solar photovoltaic arrays will operate in the low-Earth polar environment. The standard 28 volt power subsystem is not weight efficient for the array power levels being considered. The impact of the solar array operating voltage on the total weight of the array and the subsystem power conditioning and distribution components is illustrated. In the interest of reducing power subsystem weight, higher array operating voltages are considered. The problems which the higher array voltage present to the array designer are discussed. In order to provide a maximum return on the tremendous investment of resources required to develop and place these assets in orbit, they must be designed to operate effectively for extended periods of time. To achieve this, the system must be able to function in the threat-induced and natural space environment.

Scott-Monck, J.↗