A computer model has been developed for the simulation of nucleation, drop growth and deposition processes during the supersonic flow of a gas mixture in a convergent-divergent nozzle and a magnetogasdynamic duct. The gas mixture is assumed to be composed of a condensable trace vapor species (e.g. uranium vapor) and a non-condensable carrier gas, flowing through a network of control volumes. Within each control volume, the physical processes of homogeneous nucleation, growth of droplets, droplet and vapor deposition onto structure walls are simulated. Nucleation and drop growth modeling is based on classical nucleation theory and heat and mass transfer to droplets. Droplet deposition is assumed to be governed by gas turbulence and thermophoresis. Magnetogasdynamic flow properties, needed to determine the rates of nucleation, growth and deposition in each control volume, are provided by a quasi-one dimensional magnetogasdynamic channel flow model. Sample calculations have been carried out for He-U and Mg-U gas mixtures. It has been found that uranium deposition on walls is insignificant. Expected thickness of the uranium film is of the order which will not cause any arcking between electrodes. Due to the large concentration of nucleation centers in the fissioning plasma the number of uranium droplets is so high that the maximum size of droplets will not exceed 0.01 μm. Therefore, the flow is essentially that of a metal vapor carrying a fine uranium mist.

A conceptual design study for a closed cycle gigawatt electric space power system has been conducted. The closed cycle static operation reduces power system interaction effects upon the space craft. This system utilizes a very high temperature (5500 K) plasma core reactor and a magnetohydrodynamic (MHD) power conversion subsystem to provide a power density of about 8 kWe/kg (0.13 kg/kWe) for several kilo-seconds. Uranium vapor is the fuel. Candidate working fluids are metal vapors such as lithium or calcium. The system is based on a Rankine cycle to minimize the electromagnetic pumping power requirement. The fission fragment induced nonequilibrium ionization in the plasma in the MHD power duct provides the plasma electric conductivity for gigawatt power generation. Waste heat is rejected utilizing lithium heat pipes at temperatures just below 2000 K, thus minimizing the radiator area requirement. Key technology issues are identified, including the containment of the 5500 K 'sun-liken plasma at 4 to 0 MPa In a reflector moderated, gas/vapor filled cavity core reactor. A promising scheme to protect the refractory metal reactor inner wall is presented, together with a heating load analysis in the wall. This scheme utilizes an ablating film of liquid lithium/calcium that evaporates into the cavity core to become the working fluid of the cycle.

The design methodology for the disk MHD generator component of a burst power (1 GWe-power level) gas core reactor (BPGCR) is presented in this paper. A disk MHD generator model is used with simple models of other important BPGCR system components, in parametric analyses to estimate BPGCR system performance levels, and to obtain disk MHD generator design parameters; implications of this analysis are addressed.

The Heterogeneous Gas Core Reactor (HGCR) departs significantly from most other gas core reactor concepts in that the majority of the system moderation occurs within the core rather than in an external reflector. This leads to significant advantages over other gas core reactor concepts operating at comparable gas temperatures and neutron flux levels. Particularly important for space nuclear power systems is the improved neutron economy which leads to very compact, high power reactors. Calculations show that cylindrical HGCR's less than one meter in diameter by one meter in height can yield power densities of 1000 w/cc and power levels of hundreds of MWt for reactor specific powers of a few hundred kWt/kg.

Pulsed Gaseous Core Nuclear Reactor Systems have undergone theoretical and experimental investigations at the University of Florida. The results of these research efforts indicate that the pulsed gaseous core reactor has attractive features for space power generation. Currently a main focus of research is a bimodal gaseous core reactor system capable of burst mode and station keeping mode operation. This bimodal reactor system consists of a large, central, cylindrical high power pulsed gaseous core surrounded by an inner beryllium moderating reflector region. This is in turn surrounded by an annular ring of small cylindrical, low power, pulsed gas core chambers which are followed by an outer beryllium moderating reflector region. Static neutronic analyses have examined the effects of variations in core gas loadings, core size and reflector thickness on neutron multiplication factor, neutron generation time, core-to-core neutron coupling coefficients and core-to-core neutron transit or delay times. Dynamic neutronic studies have also been performed using coupled core point reactor kinetics.

Studies are being performed on burst power mode gas core reactors that employ closed cycle disk MHD generators for energy conversion. The disk MHD generator is configured to be an integral part of the reactor. Consequently, significant fissioning occurs throughout the MHD duct and fission fragment induced ionization of the uranium bearing fuel gas/ working fluid is anticipated to yield the required nonequilibrium electrical conductivity (> 100 mho/m) despite the relatively low gas temperatures. Calculations performed to date have shown that the Burst Power Gas Core Reactor-Disk. MHD Generator system can achieve overall efficiencies of 25 percent effective radiator temperatures of 1200 K, reactor specific powers of 100 to 200 kWt/kg and system specific powers of 5 kWe/kg.

Fundamental physics and engineering limitations on gas core reactors (GCR) have been found from coupled effects of reactor neutronics with oscillatory core fuel gas flows and with overall gas dynamics. These show allowable regimes for system operation as natural re-sults of the basiciphysics of the system. Cylindrical BeO-moderated systems, such as the acoustic GCR (AGCR ), are found to be well-suited for pressure wave oscillation at 100-Hz frequencies. These result in stable oscillations of core gas electrical conductivity which may be used for direct alternating current electric power production in magnetohydrodynamic (MHD) convertors. In contrast, single-cavity axial-flow spherical GCR (SGCR²) systems are inherently limited by core flow and fission energy-generation fluctuation phenomena (to continuous wave operation with mixed flows that cannot sustain high internal core gas tempera-ture gradients. Resulting low mixed-mean temperatures place upper limits on system MHD electrical performance.

Two phenomenologically-based computer programs have been developed to study nuclear power systems for strategic defense. One code models total system mass-in-orbit requirements derived from detailed orbit track and coverage computations. This showed that power plant specific mass dominates systems application assessments. The other code models technical features of a variety of nuclear systems, to show performance in terms of technology level and variability. Together they can help define optimal paths for fruitful research on advanced concepts.

The Alkali Metal Thermoelectric Converter (AMTEC) is a direct energy conversion device, utilizing a high sodium vapor pressure or activity ratio across a beta"-alumina solid electrolyte (BASE). It has been operated at a device efficiency of 19% and at power densities near 1.0 W/cm². This paper describes progress on the remaining scien-tific issue which must be resolved to demonstrate AMTEC feasibility for space power systems: a stable, high power density electrode. Two electrode systems have recently been discovered at JPL that now have the potential to meet space power requirements. One of these is a very thin sputtered molybdenum film, less than 0.5 micron thick, with over-lying current collection grids. This electrode has experimentally demonstrated stable performance at 0.4-0.5 W/cm² for hundreds of hours. Recent modeling results show that at least 0.7 W/cm² can be achieved. The model of electrode performance now includes all loss mechanisms, including charge transfer resistances at the electrode/electrolyte interface. A second electrode composition, co-sputtered platinum/tungsten, has demon-strated 0.8 W/cm² for 160 hours. Systems studies show that a stable electrode performance of 0.6 W/cm² will enable high efficiency (near 20%) space power systems.

Space nuclear reactors adapt admirably to compact maneuverable multimegawatt power generation. The compactness, maneuverability and productive weight utilization benefit from the use of thermionic converters at high temperatures. These modular static generators reduce waste-heat-radiator weights which loom large in high-power space systems. But greater space-power levels test even thermionic conversion because of its high current densities at low voltages: Relatively low-temperature power conditioning also contributes to large waste-heat-radiator weights. Therefore electromagnetic-wave outputs from thermionic conversion offer important advantages over its traditional direct-current power. In this advantageous operating mode thermionic-conversion lasing yet occupies a theoretic niche. Pulsing and switching with triode thermionic converters appear ready for development guided by continuing applied research. And power-producing thermionic-diode oscillators are excellent prospects for United States research exploitation. This direct thermal power oscillator continues to receive intense experimental and theoretical attention in the USSR--under the aegis of the State Committee for Utilization of Atomic Energy. Now the SDIO through AFWAL has funded a three-year program at Arizona State University to investigate high-temperature oscillatory thermionic conversion. Ascending toward its thermal limits enables thermionic conversion to produce more power at higher voltages and lower currents with greater efficiencies. These gains accrue with minimal collisional damping afforded by surface ionization and Knudsen-arc-mode operation. Here at high neutralization ratios p actual ionization JEXP greatly outstrips the equilibrium ion currents JISL predicted by Saha and Langmuir. In fact for large values of p the value of EXP can exceed JSL by 100-150 times" (Babanin, Ender et alii). And here high neutralization ratios with low collisional damping at reduced cesium pressures favor strong oscillatory thermionic-conversion outputs. Optimization of these effects appears possible through coefficient utilization of cesium for neutralizing ionization and barium for emitter work-function hence emission-current control. These and other related phenomena as well as important material interactions are subjects of the research on oscillating thermionic conversion recently initiated at ASU. This presentation covers some aspects of that SDIO, AFWAL, ASU program.

A ThermoElectroMagnetic Pump (TEMP) is the integration of a thermoelectric generator (TEG) and an electromagnetic pump (EMP) into a single component. TEMPs are ideally suited for space nuclear power systems (SNPSs) currently being developed to provide sustained power sources for the Stategic Defense Initiative (SDI). They are unique safety devices used in the removal of decay heat after reactor shutdown because the decay heat itself is used as the source of energy for pumping power to circulate the coolant. TEMPs may also be used as pumps in the main coolant loops. This paper is a status report on an on-going systematic study of TEMPs for the sustained SDI NSPSs and technolgies being developed, namely thermoelectric, thermionic, and Stirling cycle conversion. TEMPs for power systems ranging from 100ekW to 10eMW are being considered with temperatures ranging up to 1500 K. Permanent magnet, electromagnet, and coreless magnet TEMPs are included. Current and advanced thermoelectric, permanent magnet, electromagnet, and high temperature electrical conductors materials are being evaluated and selected for TEMP designs. The characteristic of TEMP specific mass, i.e., their mass as a function of their hydraulic power output, is the prime criterion of performance. Configuration changes required as a function of pump power and the identity of critical development issues to be resolved in Phase II will be presented in a future report.

Space nuclear power systems require materials with low density, high thermal conductivity, and high electrical conductivity at elevated temperatures. Vapor grown carbon fiber (VGCF) is a novel material which is a good candidate for these structures. VGCF has been shown to have combined characteristics of thermal conductivity, strength and modulus which exceed values for PAN and pitch-based fibers, and has an electrical conductivity comparable to single crystal graphite. Major thrusts of the current research are to explore growth and processing of vapor grown fibers, and to study the effect of boron doping on the electrical properties of VGCF. Doping of graphite is known to change the distribution of electrons between energy levels in carbon, to enhance graphitization, and to modify the chemical composition of the surface of carbon fibers. Measurements of electrical resistivity as a function of temperature from 4 K to 2700 K have been obtained. The product of resistivity times density of annealed VGCF has been observed to be substantially lower than that of refractory metals at temperatures exceeding 1000 K, suggesting the utility of this unique material as an electrical conductor in space nuclear power thermionic conversion and other high temperature applications.

An innovative concept for space power systems utilizes an electrochemical-loop, which comprises a high temperature electrolytic cell and a low temperature fuel cell. In the electrolytic cell, the working fluid is electrolyzed using combined thermal and electrical input. The products of the electrolysis are recombined in a lower temperature fuel cell, generating more voltage output than required to operate the electrolytic cell. The excess electricity from the loop is available for external loads. The thermal energy can be made available from a nuclear reactor. The zirconia cells of solid oxide electrolyte under development by Ztek would serve as the high temperature electrolytic cell. The low temperature fuel cells, which are under development in various space programs, can be adapted for this system. Studies suggest that this system is a desirable light-weight option in meeting future space power needs. Recent technical advances in zirconia cell development have brought the hardware loop integration close to realization.

A new concept for accelerating projectiles to ultra high velocities is described. The concept, termed BASH, rapidly (milliseconds) heats a hydrogen U235 mix-ture in a pulsed nuclear reactor. The hot high pressure propellant, which has a sound speed of .'20 km/sec, then accelerates a 2 kilogram projectile in a conventional gas-gun type barrel to a very high velocity, 30 km/sec or more. The BASH gun can fire at a rate of several Hertz, if desired. Features of the BASH gun are described, along with trade studies of performance and a 30 km/sec baseline design. Technical issues are discussed, including protection against high convective and radiative heat transfer rates.

Current increase induced by laser photodetachment of negative ions and current decrease due to laser modification of gas property were observed. This current switching could be applied for the development of discharge switches. Basic data (such as electron drift velocity, photodetachment cross section, electron attachment rate, and electron-impact ionization cross section) are being measured for such applications.

This paper analyzes a switch design utilizing a static magnetic field to displace the electron-hole plasma to surfaces having high recombination velocities. This mechanism can markedly speed up the opening of the switch without decreasing its conductance in the illuminated steady state.

A high power closing and opening bulk semiconductor switch is discussed where a high energy electron- beam (e- beam) is used to control the switch conductivity. The electrons are injected through a contact into the cathode region of a direct semiconductor switch. They generate a high concentration of electron-hole pairs over a distance of several micrometers to several hundred micrometers, depending on the electron energy. Ionization of the bulk of the semiconductor is provided by recombination radiation and X-ray Bremsstrahlung. The optical generation of an electron-hole plasma in the bulk region of the semiconductor switch overcomes the space charge limitation on the switch current and therefore allows external control of high current densities. Current and voltage measurements of e-beam irradiated semi-insulating GaAs samples were performed. A change of resistance of more than three orders of magnitude was obtained with e- beam current densities of some tens of mA/cm², corresponding to current gains (switch current/e-beam current) of up to 600. Closing and opening times of less than 50 ns seem to be achievable with these GaAs switches. An improvement in current gain by more than an order of magnitude can be obtained by proper doping of the cathode region of the semiconductor switch.

Optically controlled bulk semiconductor switches have the potential to replace plasma switches in applications where fast (nanosecond) response, remote control and fast recovery are important. A concept for an optically controlled closing and opening switch is presented, where laser radiation is not used to sustain the switch conductance, but to drive the switch into and out of the conductive state. The concept is based on photoexcitation of electrons and holes, respectively from deep centers. Photoconductance measurements on cadmium sulfide doped with copper (CdS:Cu) have proved the feasibility of using stimulated electron-hole recombination as mechanism for opening a semiconductor switch. Besides CdS:Cu, gallium arsenide (GaAs) doped with copper (Cu) and silicon (Si) is used as a switch material. The steady state and transient behavior of such a GaAs:Cu:Si switch has been modeled using a system of rate equations. From the calculations it is seen that an increase or decrease in conductivity by several orders of magnitude can be achieved with laser power in the range of MW/cm². The theoretical results are compared with the actual performance of optically controlled GaAs:Cu:Si switches.

A novel electronic material, a Si-TaSi₂ semiconductor-metal eutectic composite, offers promise in high-power switching applications. In this paper, the basic electronic properties of the material are briefly described. It is shown that the in situ Schottky junctions inherent to the material can be used to fabricate transistors. The advantages of these devices are their volumetric current transport and their unusual resistance to avalanche breakdown.

When subjected to modest levels of illumination (1W/cm²) of green light, the fast-Lon conductor Ag₁₃I₉W₂0₈ exhibits an order of magnitude decrease in conductivity. This effect is fast and repetitive, but experiments reveal problems with the material in the form of serious aging (shelf-life) effects that are accelerated in the presence of strong illumination.

A novel technique is presented for the characterization of surface electric fields. The technique uses the electro-optic Pockels effect. An electro-optic crystal is placed in the fringing field above the surface to be monitored and is probed with a short optical pulse. The modulated optical pulse is imaged onto a detector array to produce a map of the surface field. This technique can be exploited to study surface breakdown.

Liquid metal ion sources (LMIS) of the type used for ion beam lithography can also be used to produce large pulses of electrons via field emission. These sources typically consist of a small capillary through which a liquid metal is forced. The application of a voltage between this capillary and an extraction anode causes the liquid metal to form a sharp cone. When the intense field at the tip exceeds the threshold for field emission, a large electron current flows from the tip to the anode. The production of this electron pulse results in the rapid heating of the liquid-metal tip, leading to an explosive pressure increase, and a collapse of the tip. As the field is restored, the tip reforms, with a resultant self-pulsing mode of operation. The pulse repetition rate, the average current, and the current per pulse are all functions of the metal composition, emitter geometry, and applied diode voltage. These characteristics are reported for a variety of conditions, and show that a single emitter tip can produce current pulses in excess of 50 amperes, with a rise time of a few nsec, and a width of 5-50 nsec. Repetition rates vary between 10 Hz and 20 kHz. In addition to the observed electron emission, optical radiation is also produced. The dispersed visible spectrum shows predominantly emission from neutral, atomic species presumably excited by electron impact in the gas phase.

This article reports measurements of the characteristic parameters of a pseudo-spark switch designed for operation voltages up to 40 kV and peak currents of 20 kA for a pulse length of 90 ns. In all experiments the switch was operated with permanent external gas flow. There was no gas reservoir. Part of the investigations were performed on a water-filled matched pulse line. The repetition rate was limited to 40 Hz at full power. The switch parameters are comparable or superior to thyratrons, with respect to rate of current rise or current reversal. The tests with the .(Ω.-pulse line delivered dI/dt values between 8 and 9 x 10¹¹ A/sec. The prototype switches were triggered by a pulsed low current D.C. discharge. Two switch configurations were used, one partly the other totally derived from metal-ceramic technology. The electrode degradation seems to be small and lifetimes of more than 108 discharges can be expected. Aside from this, some more fundamental investigations of the switch plasma are presented. The overall inductance is about 10 nH, the resistance during the con-ductive phase is less than 10 mdΩ.

This paper discusses the need for and the requirements of high voltage insulation systems that operate in the space environment. The space environment is characterized and the environmental limitations of common earth insulation systems are discussed. Several alternative high voltage insulation systems are presented and the results of space high voltage experiments discussed. A high voltage space system design approach is presented based on contained field designs using controlled vacuum insulation. The limitation of alternate insulation systems in long-lived space high voltage power systems will require the development of alternate methods of capacitive energy storage at high energy densities.

This paper presents a modular state variable approach for the simulation of large and complex spacecraft power systems. Each component in the spacecraft power system is treated as a multi-port network, and a state model is written with the port voltages as the inputs. The state model of a component is solved independently of the other component state models using the state transition matrix method. The port voltages of each component are assumed to be clamped during the solution of the state models. Network analysis principles are then employed to calculate the new value of all port voltages.

A self-contained, disposable cartridge serves both as prime power source and electrical energy store. The energy initially stored in chemical form is transformed into kinetic form and stored in a hydromagnetic capacitor. The capacitor discharges through a closing switch into the electrical input of the weapon system. There are no structural rotating parts and no effluent. A comparative assessment with existing systems shows that the cartridge has the potential for increasing the achievable energy density by two orders of magnitude and the power density by four orders of magnitude.

In this paper the vibration research being conducted at Auburn in regard to both the vibration prediction and the vibration control of large flexible structures is discussed. This research work has been carried out in the following areas each of which is reviewed briefly. A finite element model of the vibratory response of large flexible spacecraft truss structures to systems of applied forces representing machinery forces and maneuvers has been developed. Predictions on the pointing accuracy and tip displacement of such structures to assumed maneuvering and machinery force inputs is presented. A study of the response of structures to traveling loads is also underway. An analytical model using spatial/temporal Finite Element method is di cussed. The motivation of this study is the determination and minimization of the response of a structure such as an electromagnetic launcher system to the traveling loads imposed by the projectiles. Another area of study has been the optimization of space structures to minimize dynamic response. The goal of this study is to optimize the location of the masses (such as power generating equipment and other systems that would be positioned on the space structure) in order to obtain minimum dynamic response. The vibration response of structures can be minimized by the use of passive damping techniques. One area of study is the modeling of interfacial passive damping in composite materials. Because of lack of passive energy dissipation mechanisms in space, even small disturbances can lead to motions sufficiently large to be detrimental to the performance requirements (of the structures) such as precision pointing in a micro-gravity environment. In such cases an active vibration control system can be added to the passive damping devices to enhance system performance. Hence work in the area of active vibration control is in progress. A new approach to active vibration control based on wave cancellation techniques is also presented.

An experimental facility at the new campus of the University of Buffalo, which is capable of generating impulse voltages up to 260 kV at 170 J, is described in this paper. The values of circuit components can he chosen and arranged to provide varying risetimes and pulsewidths of the output transient voltage. Depending on the circuit components, an output voltage pulse with risetime from 50 ns to 35 us and pulsewidth from 40 us to 200 us can be obtained. These parameters, which cover a wide range of voltage surges, allow actual high voltage simulation of insulating materials, used in high voltage energy storage and transport devices, being stressed under impulse voltages in a laboratory environment. This paper describes the circuitry and damping unit, the double isolated screen room, the sealtite tubings and cable connections that were all installed in this new facility to make the impulse generator operational in a noise-free and safe laboratory environment. Other facilities which can perform a variety of material characterization tests are also described.

An Extended Proximate Time-Optimal Servomechanism (XPTOS) is developed for the control of a flexible structure with a single structural mode. The resulting control system is closed-loop , and embodies in its structure the characteristics of a time-optimal control law and the fine tracking properties of a properly tuned linear regulator. Simulation results demonstrate the performance of the XPTOS, and its robustness in the face of uncertain plant parameters.

Based on a recent survey of Large Space System concepts and the identified characteristics of ground-based experiments needed to demonstrate capability for future systems, a sequence of vibration control experiments have been designed and are being carried out at Harris Corporation. This paper reviews the concepts and status of these experimental activities. The experiments involve a progression of structural configurations ranging from relatively simple one and two-dimensional structures to a large aperture, multi-segment optical structure.

Space exploration and other exotic applications of space have recently drawn attention to the need for multimegawatt power producing systems and other systems that could deliver gigawatts of power for short periods of time. Several nuclear fission schemes have been proposed but power to weight ratios and other considerations may open the door to other innovative approaches that may develop in the not too distant future. One such scheme is the "Magnetically Insulated Inertial Confinement Fusion" (MICF) reactor which combines the favorable aspects of both inertial and magnetic fusions in that physical containment of the burning plasma is provided by a metallic shell while thermal insulation is provided by a strong, self-generated magnetic field. Because of these unique properties the lifetime of the plasma is sufficiently longer than conventional, implosion type inertial fusion that very attractive energy gains can be achieved. In this paper we utilize a quasi one-dimensional, time-dependent set of appropriate equations to investigate the dynamic and reactor properties of this system and apply the results to a space-based power reactor, and to an advanced space propulsion device. In both instances we find that MICF can meet the space needs of the next century.

A new interconnect structure formed by the selective anodization of aluminum thin films is examined. Interconnect lines of aluminum embedded in anodic aluminum oxide dielectric were fabricated. Resistivity of the lines was determined to be - 3.1 μΩcm. This value compares well to the bulk value of 2.8 μΩ.cm Crosstalk is expected to be < 10%.

Repetitively pulsed (rep-rate) power systems are currently found in a diverse range of technologies. One particular aspect of interest within rep-rate system development is the characterization of the electrical breakdown of dielectric and insulating materials in the power components for these applications. Very little information exists in the literature concerning the effects of rep-rate stresses on these materials. A facility to simulate the high voltage stresses which occur in rep-rate systems has been developed at the University at Buffalo. These unique high voltage and instrumentation equipment are described with insulation breakdown results.

The thermal loading of high current, high energy opening and closing switches require electrode materials which have superior high temperature strength and thermal conductivi-ty. A recently developed class of copper alloys, called in-situ materials', such as Cu-Nb, Cu-Ta, and Cu-W, provide these char-acteristics. In addition, our recent tests have verified that the addition of LaB6 to Cu and CuW composite materials improved their performance. Results are given for several of these material combinations in both stationary and moving arc closing switches. Performance is evaluated using figures of merit derived from thermal considerations.

Many applications of high current switches require operation in the burst mode or at high repetition rates. Under these conditions, it has been observed that electrode erosion rates increase signifi-cantly. An analytical solution to the heat conduction equation is discussed which determines the onset of the bulk surface erosion mode as a function of peak current, pulse width, rep-rate and material properties. The solution indicates that materials with lower thermal diffusivities can operate at higher rep-rates before gross melting of the electrode surface occurs. The overall effect of increasing rep-rate is to shift the point of transition on the standard electrode erosion graph to lower values of peak current or charge transfer.

A capability developed to study the dynamics and control of space platforms in connection with the generation, conversion and utilization of power in space is described. It is based on the use of both rigid and flexible models of platform configurations which may be rather arbitrary. The principal part of the capability is a digital simulation code which uses the results of analyses of finite element models of platforms to account for their flexibilities. By using the code, the general motion of fairly complex configurations including rotating components may be simulated. The control of gross attitude motion is accomplished via a minimum impulse limit cycle controller. Examples of gross attitude motion and "fine" motion due to flexibility are presented. Also, to illustrate the versatility of the code, results are presented of simulations of the motion of a small, suborbital, experimental payload which has deployable booms. Another aspect of the overall capability is spotlighted through an example of the attitude dynamics of the experiment carrying suborbital vehicle during boom deployment.

Silicon photoconductive switches have the potential to replace such plasma discharge switches as sparkgaps and thyratrons that are commonly found in pulsed laser drive circuits. This offers the possibility of developing advanced modulators that are all solid-state, and which enjoy the advantages of improved efficiency, compactness, and life expectancy. Silicon operating at liquid nitrogen temperature is especially attractive as a power switch because at 77K it displays an extremely low coefficient of thermal expansion, a large optical absorption depth for 1.06um light, and a large thermal conductivity. These factors allow low temperature silicon to switch power levels an order of magnitude greater than at 300K, and an experimental cyrogenic silicon switch has been made to switch pulses of 15kV, 1.2kA, 0.5uS duration at 100Hz recurrent frequency. It is shown that silicon switches compare favorably with thyratrons in terms of electrical ratings and energy transfer efficiency, and should be considered in advanced pulser designs for both terrestrial and space applications.

The dielectric properties of DLC films formed by bias plasma enhanced CVD of methane are examined. Capacitors with nickel, copper, aluminum, silicon and carbon film electrodes to the PLC film were formed. Resistivity and dielectric strength were determined, in relation to substrate and plasma energy and bias. PLC films with breakdown over 10 Volts/cm a, d CF (Dissipation Factor) less than .01 were used in capacitor structures. Five layer structures were evaluated.

A system for the production of ground state atomic oxygen, 0(3P), has been constructed and tested. Prime importance has been given to the use of a generation method in which the 0-atom flux could be accurately characterized with respect to both the exact identity and the absolute flux of the 0-atom species produced. Additionally, the system has been designed to permit multi-factor stress studies of test samples while they are being exposed to the 0-atom flux. A modular system of construction has been used for maximum flexibility in order to facilitate rapid changes in the experimental setup. 0(3P), atoms are produced by the well-known reaction of nitrogen atoms with nitric oxide to yield 0(³P) and N₂. The reactions occurring are chemiluminescent and the reaction of N-atoms with NO is 'titrated' so that the number of oxygen atoms produced can be calculated from the measured flow rate of NO at the stoichio-metric end-point of the reaction. With all of the NO exactly consumed, the gas stream contains only helium carrier gas, a known concentration of oxygen atoms, and chemically unreactive N2. By means of a suitable excitation and detection system, the resonance fluorescence of O(³P) is monitored. This continuous but relative measure of 0-atom concentration is then calibrated from the absolute value of the 0-atom concentra-tion, as previously described, to provide a continuous measure of the absolute concentration of atomic oxygen at any desired location in the system. Stress factors which can be applied include UV light (4000-2000 A at 50 suns intensity), temperature (ambient to 700 K), and electrical potential (0-5) kV).

The SPEAR I and SPEAR II sounding rocket flights, will carry the highest exposed voltage systems yet flown in space. SPEAR I was launched December 13, 1987, to investigate the electrical current drain to highly charged objects in the ionosphere. SPEAR I results, augmented with laboratory and theoretical studies, will be used to determine the ambient conditions that would cause discharging and arcing of high power systems in space. These results will then be used for the design, test and flight of high power systems. SPEAR II, scheduled for launch in early 1989, will involve the innovative operations of high voltage and high current systems in the ionosphere. These flight programs utilize theoretical research efforts of several groups, as well as vacuum and plasma chamber testing of high power systems. Innovative aspects will include the exposure of uninsu-lated transmission and pulse forming systems to the ambient plasma, the charging and use of high energy storage systems during flight, and the use of high voltage and high current loads not previously used in space. Unique problems include outgassing, mitigation of electrical breakdown, loading, and the use of innovative spacecraft integration techniques for commands and telemetry to high voltage systems.

Aging and degradation of high voltage insulation due to applied and environmental stresses are being studied in order to predict the performance of high voltage equipment in space. Results will be presented on surface flashover measurements on commercially available polymers which have been stressed by exposure to vacuum, d.c. electric fields, and pulsed electric fields. A newly developed analysis technique using laser excited fluorescence (LEF) has been applied to analyze damage caused by flashover and aging. LEE allows analysis, on a molecular scale, of chemical and structural changes with a sensitivity much greater than previously possible. Data will be presented on the degradation due to aging before flashover occurs, as well as damage caused by flashover events.

The C-Mo and C-Zr alloy systems were investigated as possible candidates for high temperature applications in extraterrestrial power systems. Alloys containing 0 to 6 weight percent carbon were produced using induction melting techniques. The Zr-C alloys produced were found to be composed of alpha-Zr and gamma (ZrC), while the Mo-C alloys were composed of theta (Mo₂C) and the eutectic mixture of Mo plus theta. The volume fraction of carbide increased as the carbon content was increased. Half of all alloys produced were annealed. The Mo-C alloys were heat treated in a vacuum furnace at 1370°C / 1 hr. / FC while the Zr-C alloys were annealed at 1000°C / 1 hr. / FC> Room temperature compression tests were performed on both the as-cast and annealed material. The results of these tests are described as a function of the volume fraction of the primary carbide phase present. The indicated a decrease in strength and a decrease in ductility as the volume fraction of carbide increased. Annealing was found to improve the properties over those of the as-cast materials. Microhardness of ZrC increased but all other phases seemed to be relatively independent of the carbide or C-content.

The influence of magnetic fields on dielectric surface breakdown voltages for space conditions (pressure in the range of 10^-7 to 10^-2 Torr, background plasma, and UV illumination) is investigated, both for DC and pulsed voltages as well as DC and pulsed magnetic fields, including conditions for magnetic self insulation. DC conditions are susceptible to corona-type discharges with major influences of magnetic fields on discharge paths and geometry. For pulsed volt-ages, insulation effects dependent on the polarity of the magnetic field (with respect to the electric field and the surface) are starting at field amplitudes of 0.2 T.

Power conversion units for the proposed Strategic Defence Initiative (SDI) objectives must be capable of supplying very high power for short periods, must start (and restart) rapidly, and must be as compact and lightweight as possible. Open cycle gas turbines offer attractive potential for such applications. Typical proposed turbine designs are of the axial throughflow type, utilizing combinations of hydrogen (H₂) and oxygen (0₂) as the working fluid. As an alternative, an analytical model of a multistage radial outflow Ljungstrom turbine utilizing H₂-0₂ (combinations) as the working fluid is presented. Families of such turbines are generated, using design constraints consistent with SDI objectives and modern turbine design. Comparisons are made with multistage axial throughflow machines. It is shown that Ljungstrom type configurations indeed offer an attractive design alternative for SDI missions.