Engineering topics

Jones, R. M.

Publications and source records attributed to Jones, R. M..

31 records · Page 2

NASA NTRS1982

Comparison of evolving photovoltaic and nuclear power systems for earth orbital applications

Photovoltaic and fission reactor orbital power systems are compared in terms of the end-to-end system power-to-mass ratios. Three PV systems are examined, i.e., a solid substrate with a cell array and a NiCd battery, a modified SEP array and an NiH2 battery, and a 62-micron Si cell array and a fuel cell. All arrays were modeled to be 13.5% efficient and to produce 25 kW dc. The SP-100 reactor consists of the heat source, radiation shield, heat pipes to transfer thermal energy from the reactor to thermoelectric elements, and a waste heat radiator. Consideration is given to system applications in orbits ranging from LEO to GEO, and to mission durations of 1, 5, and 10 yr. PV systems are concluded to be flight-proven, useful out of radiation belts, and best for low to moderate power levels. Limitations exist for operations where atmospheric drag may become a factor and due to the size of a large PV power supply. Space nuclear reactors will continue under development and uses at high power levels and in low altitude orbits are foreseen.

Rockey, D. E.↗

NASA NTRS1980

The applicability of MFD thrusters to satellite power systems

The high power self field MPD thruster uses electromagnetic forces rather than electrostatic to accelerate a neutral plasma. The most attractive application of MPD thrusters to satellite power systems is in the area of electric propulsion for a cargo orbit transfer vehicle (COTV). Calculations were performed in order to compare the performance of a COTV using an ion or MPD propulsion system. Results show that the MPD propulsion system gives a shorter trip time with the same power and payload when compared to the ion thruster propulsion system at either value of specific impulse. More important than the trip time benefit may be the advantage a MPD propulsion system provides in system simplicity. Another interesting COTV concept using MPD thrusters is the use of a remote power supply located on the Earth, at GEO, or somewhere in between to transmit power to the COTV in a microwave transmission. The specific impulse at thrust levels of tens of newtons makes a MPD propulsion system a candidate for stationkeeping and attitude control of large space structures such as a SPS.

Jones, R. M.↗

NASA NTRS1980

Applications of an MPD propulsion system

Recent studies of the self-field magnetoplasmadynamic (MPD) thruster indicate that the attainable value of thrust efficiency can be over 50% with argon propellant at 5000 sec. Projections for hydrogen propellant show that the specific impulse may exceed 10,000 sec. Improving performance projections such as these create a need for systems and applications studies to be updated. This paper reviews the configurations for an MPD propulsion system and those missions on which such a system might find application. An MPD propulsion system could be used for: (1) attitude control and stationkeeping of large space structures, (2) interorbit transportation, and (3) interplanetary propulsion. A trajectory analysis of a Saturn Orbiter using a nuclear power supply and an MPD propulsion system is presented. A LEO to GEO MPD-OTV concept is presented that uses a remote source transmitting power to the OTV in the form of microwaves. Trajectory analysis of this latter concept indicates that a payload of 20,000 kg can be delivered to GEO in about 20 days if the MPD propulsion system receives 20 MW of input power.

Jones, R. M.↗

NASA NTRS1979

Propellant injection for MPD thrusters

The propellant gas for a pulsed self-field MPD thruster must be supplied by a valve which will necessarily be separated from the thruster injectors by some ullage volume. A model and experimental data are presented showing the effect of the ullage volume on the propellant pulse shape, along with a discussion of the proper location for the propellant flow choke point(s). Prospective MPD pulse valves are surveyed and the performance of two solenoid valves, one with a pulse length less than 2 milliseconds, is included. Pulse shape data is presented for a thruster specially modified to reduce the ullage volume.

Jones, R. M.↗

NASA NTRS1979

Pulsed plasma thruster contamination studies

The exhaust plume of the one millipound pulsed plasma thruster has a measurable backflow upstream of the nozzle exit plane which may deposit on and degrade the performance of exposed spacecraft surfaces. High speed photographs and Faraday cup measurements suggest that this backflow is predominantly an electrically neutral, relatively low energy vapor. Articulated collimator quartz crystal microbalance measurements of this backflow were made for a thruster with a radically modified nozzle and a flat plate backflow shield, to determine the backflow sensitivity to nozzle design changes. The results are compared with the original nozzle backflow and show a measurable reduction in the backflow directly upstream of the shield.

Rudolph, L. K.↗

NASA NTRS1979

Plume Characterization of a One-Millipound Solid Teflon Pulsed Plasma Thruster, Phase 2

Measurements of the pulsed plasma thruster (PPT) plume upstream mass flux were made in the Molecular Sink (MOLSINK) vacuum facility in order to minimize the plume-tank wall reflected mass flux. Using specially designed collimators on 4 rows of Quartz Crystal Microbalanced (QCMs) mounted on a support extending radially away from the plume axis, measurements were made of the mass flux originating in a thin slice of the PPT primary plume at an arbitrary dip angle with respect to the thruster axis. The measured and analytically corrected mass flux from particles reflected from the MOLSINK walls was substracted from the collimated QCM measurements to improve their accuracy. These data were then analytically summed over dip angle to estimate the total plume backflow upstream of the thruster nozzle. The results indicate that the PPT backflow is of order 10 to the minus 10th power g/square cm/pulse in the region from 38 to 86 cm from the PPT axis in the nozzle exit plane. This flux drops with the square of the radial distance from the PPT axis and is comparable to the backflow of an 8 cm ion thruster, which has performance characteristics similar to those of the PPT.

Rudolph, L. K.↗

NASA NTRS1979

Inductive energy storage for MPD thrusters

The high thrust density of the self-field magnetoplasmadynamic (MPD) thruster makes it a promising candidate for many advanced space missions. The high power requirements of this thruster lead to its operation in a pulsed mode from an energy storage device. The system characteristics of an inductive energy storage circuit with a solar array power from 25 kwe to 400 kwe are considered, by solving the circuit equations for the inductor charge and discharge phases. Using simple analytic models of the circuit components, the total system efficiency and inductance are determined as functions of the array output power and circuit resistance. The total system efficiency increases with array power and is acceptable only for low values of circuit resistance, indicating that superconducting circuitry may be desirable. The optimum charge-discharge cycle changes fundamentally as the circuit resistance is decreased through a critical value dependent on the thruster operating characteristics.

Rudolph, L. K.↗

NASA NTRS1967