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Investigation of the properties of low-energy particles measured on board ATS-5 show that the synchronous spacecraft can charge to -12,000 V in eclipse, and several hundred volts in sunlight. Differential charging can produce local fields of several thousands of volts per meter in the near vicinity of the spacecraft surface. Time constants for charging can be less than a second to tens of minutes.
The various plasma environments of the moon are described for the lunar orbit through the solar wind and geomagnetic tail. The sources of lunar surface charge, including plasma, photo, and secondary currents, are compared for their expected range of values. The electric potential is calculated from probe theory as a function of local position on the lunar surface; the theory includes plasma environments which are both stationary and flowing. In agreement with several other calculations, the potential at the subsolar point is likely to be a few volts positive. However, for the case when the moon is in the solar wind, the potential is calculated to be a few tens of volts negative at the terminator, and is expected to go to larger negative values on the dark side. If the moon traverses a significant plasma sheet in the geomagnetic tail, then the dark side potential tends toward several kilovolts negative but may be strongly limited by the secondary electron current. Associated surface electric fields are estimated.
The acceleration model for lunar ions and the resulting ionosphere dynamics are reviewed briefly. An application is made to lunar atmosphere trapped in the surface fines, and the enhancement in the Ar-40/Ar-36 ratio in samples from the Apennine Front compared to the adjacent mare is calculated to be about 2.0. The predicted lunar ion energy spectra is shown and found to agree well with Suprathermal Ion Detector measurements; from this spectra, the neutral atmosphere scale height can be studied and the neutral atmosphere number density is found to be 100,000 to 300,000 per cu cm at the sunrise and sunset terminators. The lunar surface potential is calculated and is found to be several volts positive over much of the sunlit face of the moon but to go tens of volts negative at the terminator.
Experimental observations have been made during steady state operation of a torus experiment at input powers up to 150 kilowatts in deuterium and helium gas. The steady state ion heating method utilizes a modified Penning discharge operated in a bumpy torus confinement geometry. The bumpy torus plasma is acted upon by a combination of strong electric and magnetic fields. In a deuterium plasma, electron temperatures from 14 to 140 electron volts and ion kinetic temperatures from 160 to 1785 electron volts were observed. At least two distinct operating regimes exist, each of which is associated with a characteristic range of background gas pressure and electron temperature. Experimental data show that the average ion residence time in the plasma is virtually independent of magnetic field strength.
Initial studies have been made of the sputtering and deposition phenomena in a 30-cm thruster. Sputtering rates, of the cathode baffle, one of the main sources of sputtered material in a thruster, have been measured by weight loss as a function of several thruster parameters. Sputtering rates were found to increase with both cathode flow rate and beam current when constant discharge voltage of 37 volts and power loses of 185 ev/ion were maintained. Sputtering rates were reduced 24% as discharge voltage was decreased from 37 to 33 volts while keeping discharge power constant. Qualitative agreement was found between sputtering rates obtained by the weight loss and those implied by spectroscopically observed line intensities of the excited iron sputtered atoms. After the completion of the sputtering tests, deposition and sputtering sites inside the thruster were identified.
A detailed analysis is presented of each selected equipment item, and suitability and cost analyses were documented by equipment item. Tradeoffs of alternative specification requirements are presented which include possible relaxation of vibration, material control, fungus and corrosion requirements for experiment equipment. An additional tradeoff was performed to determine whether it is cost effective to modify experiment equipment to be compatible with a 28-volt dc power source rather than the conventional 110-volt ac source. Programmatic analysis data are given which were used as the basis for the extension of results from the analyses of specific equipment items to the entire spacelab experiment program.
A comparison of two potential conversion methods, the series inverter and the inductive energy transfer (IET) conversion technique, is presented. The investigations showed that a characteristic of the series inverter circuit (high equalizing current values in each half cycle) could not be accomplished with available components, and the investigations continued with the IET circuit only. An IET circuit system was built with the use of computer-aided design in a 2, 4, and 8 stage configuration, and these stages were staggered 180, 90, and 45 degrees, respectively. All stages were pulsewidth modulated to regulate over an input voltage range from 200 to 400 volts dc at a regulated output voltage of 56 volts. The output power capability was 100 to 500 watts for the 2 and 8 stage configuration and 50 to 250 watts for the 4 stage configuration. Equal control of up to eight 45 degree staggered stages was accomplished through the use of a digital-to-analog control circuit. Equal power sharing of all stages was achieved through a new technique using an inductively coupled balancing circuit. Conclusions are listed.
Experimental observations have been made during steady-state operation of the NASA Lewis Bumpy Torus experiment at input powers up to 150 kilowatts in deuterium and helium gas. A steady-state ion heating method utilizes a Modified Penning discharge operated in a bumpy torus confinement geometry. The bumpy torus plasma is acted upon by a combination of strong electric and magnetic fields. In a deuterium plasma, electron temperatures from 14 to 140 electron volts and ion kinetic temperatures from 160 to 1785 electron volts were observed. At least two distinct operating regimes exist, each of which is associated with a characteristic range of background gas pressure and electron temperature. Experimental data show that the average ion residence time (ionization time) in the plasma is virtually independent of the magnetic field strength.
Calculations of the low frequency rectification efficiency of power Schottky diodes show that silicon Schottky rectifiers have lower losses than silicon p-n junctions for all voltage applications up to approximately 150 volts. These calculations are presented. Large area Schottky diodes have been fabricated which exhibit near ideal reverse leakage at 100 C out to approximately 100 volts and which have current capability of 100 A. Fabrication details and performance data are presented.
Initial studies have been made of the sputtering and deposition phenomena in a 30-cm thruster. Sputtering rates, of the cathode baffle, one of the main sources of sputtered material in a thruster, have beem measured by weight loss as a function of several thruster parameters. Sputtering rates were found to increase with both cathode flow rate and beam current when constant discharge voltage of 37 volts and power losses of 185 ev/ion were maintained. Sputtering rates were reduced 24% as discharge voltage was decreased from 37 to 33 volts while keeping discharge power constant. Qualitative agreement was found between sputtering rates obtained by the weight loss and those implied by spectroscopically observed line intensities of the excited iron sputtered atoms. After the completion of the sputtering tests, deposition and sputtering sites inside the thruster were identified.
Balanced symmetrical y-axis amplifier uses zener-diode level shifting to interface operational amplifiers to high voltage bipolar output stages. Nominal voltage transfer characteristic is 40 differential output volts per input volt; bandwidth, between -3-dB points, is approximately 8 kHz; loop gain is nominally 89 dB with closed loop gain of 26 dB.
Recent developments at JPL have demonstrated that high conversion efficiencies are found with GaAs metal semiconductor solar cells when a particular heat treatment processing step is used to introduce an interfacial layer between the metal and the semiconductor. The new cell, called AMOS (Antireflection-Coated Metal-Oxide-Semiconductor), has open circuit voltages of 0.68-0.72 volts and efficiencies of 15% under terrestrial sunlight, as compared to values of 0.45-0.48 volts and 10%, respectively, for similar cells without an interfacial layer. Potentially higher efficiencies are feasible as further improvements are made in optimizing the interfacial layer effect and in increasing the blue response of the cells. A thin film AMOS cell is proposed that uses a thin recrystallized germanium (Ge) layer between a low cost metal substrate and the vapor phase epitaxially (VPE)-grown GaAs.
Contaminated oxide cells have been fabricated with efficiencies of 8.6% with values of I sub sc = 120 ma, V sub oc = .54 volts, and curve factor of .73. Attempts to optimize the fabrication step to yield a higher output have not been successful. The fundamental limitation is the inadequate antireflection coating afforded by the silicon dioxide coating used to hold the contaminating ions. Coatings of SiO, therefore, were used to obtain a good antireflection coating, but the thinness of the coatings prevented a large concentration of the contaminating ions, and the cells was weak. Data of the best cell were .52 volts V sub oc, 110 ma I sub sc, .66 CFF and 6.7% efficiency.
Preliminary data indicating thermionic-conversion potentialities for a 111-iridium emitter and collector spaced 0.2 mm apart are presented. These results comprise output densities of current and of power as functions of voltage for three sets of emitter, collector, and reservoir temperatures: 1553, 944, 561 K; 1605, 898, 533 K; and 1656, 1028, 586 K. For the 1605 K evaluation, estimates produced work-function values of 2.22 eV for the emitter and 1.63 eV for the collector with a 2.0-eV barrier index (collector work function plus interelectrode voltage drop) corresponding to the maximum output of 5.5 W/sq cm at 0.24 volt. The current, voltage curve for the 1656 K 111-iridium diminiode yields a 6.2 W/sq cm maximum at 0.25 volt and is comparable with the 1700 K envelope for a diode with an etched-rhenium emitter and a 0.025-mm electrode gap made by TECO and evaluated by NASA.
Rocket observations of auroral electrons are compared with the predictions of a number of theoretical acceleration mechanisms that involve an electric field parallel to the earth's magnetic field. The theoretical models are discussed in terms of required plasma sources, the location of the acceleration region, and properties of necessary wave-particle scattering mechanisms. We have been unable to find any steady state scatter-free electric field configuration that predicts electron flux distributions in agreement with the observations. The addition of a fluctuating electric field or wave-particle scattering several thousand kilometers above the rocket can modify the theoretical flux distributions so that they agree with measurements. The presence of very narrow energy peaks in the flux contours implies a characteristic temperature of several tens of electron volts or less for the source of field-aligned auroral electrons and a temperature of several hundred electron volts or less for the relatively isotropic 'monoenergetic' auroral electrons. The temperature of the field-aligned electrons is more representative of the magnetosheath or possibly the ionosphere as a source region than of the plasma sheet.
Results are presented of several 30 cm diameter mercury ion thruster isolator life tests that show that the onset and exponential increase of leakage current problems observed in earlier thruster operations and isolator tests have been solved. A 10,006 hour life test of a main isolator vaporizer operated with no mercury flow at 320 C and 1500 volts was found to have no onset of leakage current during the test. A cathode-isolator vaporizer operated with a mercury discharge at 340 to 360 C and 1200 volts for 18,000 hours, was found to have a small increase of leakage current with time. A 10,000 hour thruster life test exhibited no increase of leakage current during the life test. Isolators have been developed which will satisfy 30 cm mercury ion thruster mission requirements.
A 40 watt experimental solar array was directly regulated by shorting out appropriate combinations of series and parallel segments of a solar array. Regulation switches were employed to control the array at various set-point voltages between 25 and 40 volts. Regulation to within + or - 0.5 volt was obtained over a range of solar array temperatures and illumination levels as an active load was varied from open circuit to maximum available power. A fourfold reduction in regulation switch power dissipation was achieved with series-parallel regulation as compared to the usual series-only switching for direct solar array regulation.
Results are presented for several 30-cm-diameter mercury-ion-thruster isolator life tests which show that the onset and exponential increase of leakage-current problems observed in earlier thruster operations and isolator tests have been solved. A 10,006-hour life test of a main isolator-vaporizer operated with no mercury flow at 320 C and 1500 volts was found to have no onset of leakage current during the test. A cathode-isolator-vaporizer (CIV) operated with a mercury discharge at 340 to 360 C and 1200 volts for 18,000 hours was found to have a small increase (0.004 micro A/hr) in leakage current with time. A 10,000-hour thruster life test exhibited no increase in leakage current during the life test. It is concluded that isolators have been developed which will satisfy 30-cm mercury-ion-thruster mission requirements.