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At least 523 records · Page 29

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NASA NTRS1972

Solar electric low-thrust Mercury orbiter missions.

Results of a preliminary study of unmanned Mercury orbiter missions which might be flown in the early 1980s. Five different levels of orbiter size and complexity are considered, ranging from a small orbiter carrying 22 kg of low data-rate instruments to a dual satellite mission employing 110 kg of science instruments emphasizing regional and local scale surface imagery. An Intermediate-20 class launch vehicle is required to deliver a minimal surface-imaging science package into Mercury orbit using a ballistic mission mode. Employment of a 15 kW solar electric low-thrust stage permits delivery of the more capable dual satellite package with a Titan IIID (5)/Centaur.

Klopp, D. A.↗

NASA NTRS1972

Optical radiation from regions downstream of mercury bombardment thrusters.

Use of a 0.5-m focal length, plane grating monochromator to measure the radiance of spectral radiation emanating from regions downstream of a mercury bombardment thrustor in the wavelength range investigated was 2800 to 6000 A. This radiation was due primarily to the radiative decay of excited mercury atoms exhausted from the thrustor. Radiance values ranged from 10 to the minus 11th to 10 to the min scm/ster varying with wavelength. For resonant radiation, the spectral radiance may exceed 10 to the minus 8th W/sq cm/ster. From such radiance measurements, it was concluded that the thrustor background radiation should not interfere with the control functions of a star tracker viewing through the thrustor exhaust, provided that the tracker is designed to operate with a sufficiently small field of view. Problems may be encountered, however, during the spacecraft acquisition phase where a larger field of view may be required. Here the thrustor exhaust radiation may be comparable to the star light flux. This problem may be circumvented by locating the tracker view axis so as not to view downstream of the thrustor.

Milder, N. L.↗

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

Parametric study of mercury hollow cathode neutralizers.

A parametric investigation of mercury hollow cathode neutralizers was carried out in a bell jar over a range in bias currents up to 2 A. The parameters of particular interest were the mercury flowrate, the bias voltage, and the neutralizer cathode temperature. Three cathode orifices and several keeper geometries were tested. The bell jar tests compared well with neutralizer run with active thrusters. The effects of these parameters on the neutralizer stability and lifetime capability as well as the effects on the total thrust subsystem efficiency are discussed.

Fitzgerald, D. J.↗

NASA NTRS1972

A study of the liquid-vapor phase change of mercury based on irreversible thermodynamics.

The object of this work is to determine the transport coefficients which appear in linear irreversible-thermodynamic rate equations of a phase change. An experiment which involves the steady-state evaporation of mercury was performed to measure the principal transport coefficient appearing in the mass-rate equation and the coupling transport coefficient appearing in both the mass-rate equation and the energy-rate equation. The principal transport coefficient sigma, usually termed the 'condensation' or 'evaporation' coefficient, is found to be approximately 0.9, which is higher than that measured previously in condensation-of-mercury experiments. The experimental value of the coupling coefficient K does not agree with the value predicted from Schrage's kinetic analysis of the phase change. A modified kinetic analysis in which the Onsager reciprocal law and the conservation laws are invoked is presented which removes this discrepancy but which shows that the use of Schrage's equation for predicting mass rates of phase change is a good approximation.

Adt, R. R., Jr.↗

NASA NTRS1973

Method for treatment of water containing low concentrations of mercury

A process employing magnetic filtering techniques has been devised for treating water containing concentrations on the order of 1 microgram/cubic centimeter of atomic or ionic mercury. A laboratory-scale system has been operated and can reduce the mercury content of test solutions by as much as 90 percent.

Flood, D. J.↗

NASA NTRS1973

A 13000-hour test of a mercury hollow cathode

A mercury-fed hollow cathode was tested for 12,979 hours in a bell jar at SERT 2 neutralizer operating conditions. The net electron current drawn to a collector was 0.25 ampere at average collector voltages between 21.8 and 36.7 volts. The mercury flow rate was varied from 5.6 to 30.8 equivalent milliamperes to give stable operation at the desired electrode voltages and currents. Variations with time in the neutralizer discharge characteristics were observed and hypothesized to be related to changes in the cathode orifice dimensions and the availability of electron emissive material. A facility failure caused abnormal test conditions for the last 876 hours and led to the cathode heater failure which concluded the test.

Rawlin, V. K.↗

NASA NTRS1973

Materials technology programs in support of a mercury Rankine space power system

A large portion of the materials technology is summarized that was generated in support of the development of a mercury-rankine space power system (SNAP-8). The primary areas of investigation are: (1) the compatibility of various construction materials with the liquid metals mercury and NaK, (2) the mechanical properties of unalloyed tantalum, and (3) the development of refractory metal/austenitic stainless steel tubing and transition joints. The primary results, conclusions, and state of technology at the completion of this effort for each of these areas are summarized. Results of possible significance to other applications are highlighted.

Stone, P. L.↗

NASA NTRS1973

High voltage pulse ignition of mercury discharge hollow cathodes

A high voltage pulse generated by a capacitor discharge into a step-up transformer has been demonstrated capable of consistently igniting hollow cathode mercury discharges at propellant flows and heater power levels much below those required by conventional cathode starting. Results are presented for 3.2-mm diameter enclosed and open keeper cathodes. Starting characteristics are shown to depend on keeper voltage, mercury flow rate, heater power, keeper orifice size, emissive materials, and electrode to which the pulse is applied. This starting technique has been used to start a cathode over 10,000 times without any degradation of starting capability.

Wintucky, E. G.↗

NASA NTRS1973

Investigation of mercury thruster isolators

Mercury ion thruster isolator lifetime tests were performed using different isolator materials and geometries. Tests were performed with and without the flow of mercury through the isolators in an oil diffusion pumped vacuum facility and cryogenically pumped bell jar. The onset of leakage current in isolators occurred in time intervals ranging from a few hours to many hundreds of hours. In all cases, surface contamination was responsible for the onset of leakage current and subsequent isolator failure. Rate of increase of leakage current and the leakage current level increased approximately exponentially with isolator temperature. Careful attention to shielding techniques and the elimination of sources of metal oxides appear to have eliminated isolator failures as a thruster life limiting mechanism.

Mantenieks, M. A.↗

NASA NTRS1973

Ballistic mode Mercury orbiter mission opportunity handbook

Significant payloads in Mercury orbit can be achieved through use of high-thrust, chemical propulsion systems on ballistic trajectories. Interplanetary trajectory characteristics are presented, for Venus swingbys to Mercury, were multiple revolutions about the sun are allowed on each leg to provide low energy mission in 1977, 1980, 1985 and 1988. Guidance and navigation results are shown for each opportunity. Additionally, the use of midcourse maneuvers and multiple Venus swingbys are explored as means of further reducing the energy requirements.

Hollenbeck, G. R.↗

NASA NTRS1972

Mercury - Surface composition from the reflection spectrum.

The reflection spectrum for the integral disk of the planet Mercury was measured and was found to have a constant positive slope from 0.32 to 1.05 micrometers, except for absorption features in the infrared. The reflectivity curve matches closely the curve for the lunar upland and mare regions. Thus, the surface of Mercury is probably covered with a lunar-like soil rich in dark glasses of high iron and titanium content. Pyroxene is probably the dominant mafic mineral.

Mccord, T. B.↗

NASA NTRS1972

Thermal elastic deformations of the planet Mercury.

The variation in solar heating due to the resonance rotation of Mercury produces periodic elastic deformations on the surface of the planet. The thermal stress and strain fields under Mercury's surface are calculated after certain simplifications. It is found that deformations penetrate to a greater depth than the variation of solar heating, and that the thermal strain on the surface of the planet pulsates with an amplitude of .004 and a period of 176 days.

Liu, H.-S.↗

NASA NTRS1972

Microwave dual frequency propagation experiment using the Mariner Venus Mercury probe.

The Mariner Venus Mercury spacecraft (MVM) will be launched in a multiple planet flyby orbit. A coherent dual frequency down link operating at 2.3 and 8.4 GHz will be used to measure the dispersive nature of the transmission medium. Radio tracking will produce Doppler and range information at both 2.3 and 8.4 GHz so that the dispersive group and phase velocity perturbations of the medium can be measured. Interpretation of the dispersive results will yield information about the neutral and ionized atmospheres of Venus and Mercury, the interplanetary media, the solar wind, and corona.

Levy, G. S.↗

NASA NTRS1972

Orbital eccentricity of Mercury and the origin of the moon.

The results of some recent work conducted by Anderson (1972) are considered. If Anderson is correct in his conclusion that the bulk composition of the moon resembles that of the Allende inclusions, then the natural place for the formation of the moon in the solar system is inside the orbit of Mercury, through planetary accumulation from the condensed material to be found there. This explains the anomalous large eccentricity of the orbit of Mercury.

Cameron, A. G. W.↗

NASA NTRS1972

Mercury - Interpretation of optical observations.

The spectral reflectivity of Mercury has constant positive slope from 0.32 to 1.05 microns, except for the possibility of an absorption feature in the infrared. The reflectivity curve matches closely the curve for lunar upland and mare regions. Thus, the surface of Mercury is probably covered with lunar-like soil rich in dark glasses of high iron and titanium content. If the absorption band is real, pyroxene is the dominant mafic mineral.

Mccord, T. B.↗

NASA NTRS1973

Icelandic geothermal activity and the mercury of the Greenland icecap.

Aerometric studies concerning the level of atmospheric mercury were conducted at a number of sites in Iceland during June and July 1972. Samples from widely separated locations yielded Hg concentrations well above the range commonly cited for unpolluted air. Atmospheric mercury may be introduced in part by degassing fluid magmas. However, the release from fine ash could also serve as a vehicle. It is pointed out that from the mid-17th century to the present, Iceland has recorded nearly 50 volcanic eruptions.

Siegel, B. Z.↗

NASA NTRS1974

Development of a mercury electromagnetic centrifugal pump for the SNAP-8 refractory boiler development program

An electromagnetic pump, in which pressure is developed in mercury because of the interaction of the magnetic field and current which flows as a result of the voltage induced in the mercury contained in the pump duct, was developed for the SNAP-8 refractory boiler test facility. Pump performance results are presented for ten duct configurations and two stator sizes. These test results were used to design and fabricate a pump which met the SNAP-8 criteria of 530 psi developed pressure at 12,500 lb/hr. The pump operated continuously for over 13,000 hours without failure or performance degradation. Included in this report are descriptions of the experimental equipment, measurement techniques, all experimental data, and an analysis of the electrical losses in the pump.

Fuller, R. A.↗