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Report presents basic engineering concepts of trash-disposal module for Space Station. Module conserves valuable cargo volume and reduces both launching and returning weights of Space Shuttle or other spacecraft carrying materials to and from Space Station. Module relatively cheap and simple to operate.
Conceptual device combines resonant reflection and photovoltaic action to enable one light beam to impose spatial and temporal modulation on another light beam. Such spatial light modulator, with high speed and multiplicity of parallel signal channels, used in image processing or similar computation requiring high data-throughput rates. Microstructures of GaAs and InAs with multiple quantum wells and compositional superlattices grown by molecular-beam epitaxy. Enhanced electro-optical properties of arrangement of alternating layers enables writing light beam to modulate reading light beam.
The effect of different module configurations on the performance of multijunction (MJ) solar cells in a radiation environment was investigated. Module configuration refers to the electrical circuit in which the subcells of the multijunction cell are wired. Experimental data for AlCaAs, GaAs, InGaAs, and silicon single-junction concentrator cells subjected to 1 MeV electron irradiation was used to calculate the expected performance of AlGaAs/InGaAs, AlGa/silicon, GaAs/InGaAs, and GaAs/silicon Mj concentrator cells. These calculations included independent, series, and voltage-matched configurations. The module configuration was found to have a significant impact on the radiation tolerance characteristic of the MJ cells.
A concept is described for the assembly of the outboard PV modules for Space Station Freedom. Analysis of the on-orbit assembly operations was performed using CADAM design graphics software. A scenario for assembly using the various assembly equipment, as currently defined, is described in words, tables and illustrations. This work is part of ongoing studies in the area of space station assembly. The outboard PV module and the assembly equipment programs are all in definition and preliminary design phases. An input is provided to the design process of assembly equipment programs. It is established that the outboard PV module assembly operations can be performed using the assembly equipment currently planned in the Space Station Freedom Program.
Electric power generation for Space Station Freedom will be provided by four photovoltaic (PV) power modules using silicon solar cells during Phase 1 operation. Each PV power module requires two solar arrays with 32,800 solar cells generating 18.75 kW of dc power for a total of 75 kW. A portion of this power will be stored in nickel-hydrogen batteries for use during eclipse, and the balance will be processed and converted to 20 kHz ac power for distribution to end users through the power management and distribution system. The design incorporates an optimized thermal control system, pointing and tracking provision with the application of gimbals, and the use of orbital replacement units (ORU's) to achieve modularization. Design status of the PV power module, as derived from major trade studies, is discussed at hardware levels ranging from component to system. Details of the design are presented where appropriate.
A technique which can provide frequency doubling, with high efficiency, while cavity dumping a laser for pulse position M-ary modulation while being used for an optical communication link is discussed. This approach uses a secondary cavity that provides feedback of the undoubled fundamental light, which is normally lost, into the primary cavity to be recirculated and frequency doubled. Specific operations of the electrooptic modulator and frequency-doubling crystal are described along with the overall modulation scheme and experimental setup.
The first demonstration of an optically controlled absorption modulator based on state filling in a periodically doped In(x)Ga(1-x)As/GaAs multiple quantum well structure is reported. Differential absorption of approximately 10,000/cm is observed in the quantum wells of the test structure at saturation pump powers. Photoluminescence and time-resolved modulation measurements confirm the predicted behavior of carrier recombination and give a measure of enhanced carrier lifetime of approximately 1 ms. These initial results show the potential for developing these structures into optically addressed spatial light modulators.
An optically controlled reflection modulator has been demonstrated that consists of a combination of a GaAs-AlGaAs n-i-p-i doping structure with a multiple-quantum-well structures on top of a distributed Bragg reflector, all grown by MBE. A modulation of approximately 60 percent is obtained on the test structure, corresponding to a differential change of absorption coefficient in the quantum wells of approximately 7500/cm. Changes in reflectance can be observed with a control beam power as low as 1.5 microW. This device structure has the potential of being developed as an optically addressed spatial light modulator for optical information processing.
The influence of periodically-modulated planar stagnation-point flow on the morphological stability of a directionally-solidifying interface is presently considered with a view to the effect of unsteady nonparallel flows on single-crystal growth. The modeling of the system assumes that the viscous boundary layer thickness is much greater than that of the solute boundary layer, and that the modulation frequency is much smaller than the strength of plane stagnation-point flow. The solidifying interface is either stabilized or destabilized depending on the ratio of the period of modulation to the solute-diffusion time.
This paper presents results of development testing of various solar thermal parabolic dish modules and assemblies. Most of the tests were at modules and assemblies that used a dish-mounted, organic Rankine cycle turbine for production of electric power. Some tests were also run on equipment for production of process steam or for production of electricity using dish-mounted reciprocating steam engines. These tests indicate that early modules achieve efficiencies of about 18 percent in converting sunlight to electricity (excluding the inverter but including parasitics). A number of malfunctions occurred. The performance measurements, as well as the malfunctions and other operating experience, provided information that should be of value in developing systems with improved performance and reduced maintenance.
The describing function method is employed for the nonlinear control analysis and design of a flexible spacecraft equipped with pulse modulated reaction jets. The method provides a means of characterizing the pulse modulator in terms of its gain and phase for structural mode limit cycle analysis. Although the describing function method is inherently inexact and is not widely used in practice, a new way of utilizing it for practical control design problems is presented. It is shown that the approximations inherent in the method can be accounted as a modeling uncertainty for the nonlinear control robustness analysis. The pulse modulated control system of the Intelsat 5 spacecraft is used as an example to illustrate the concept and methodology developed in the paper. The nonlinear stability margins predicted by the describing function analysis are verified from nonlinear simulations.
Microwave signals modulate optical signals in unit integrable with GaAs and GaAIAs devices. Experimental GaAIAs electro-optical modulators designed and built for operation at wavelength of 0.82 micrometers. Easily integrable with GaAs monolithic microwave integrated circuits. Integrated optical and microwave waveguides in electro-optical materials constitute traveling-wave electro-optical modulator in configuration of Mach-Zehnder interferometer. Because characteristic impedance of waveguide 50 ohms - standard value - no impedance-matching network required.
The fourth year progress is described on a program to develop a 27.5 to 30 GHz GaAs monolithic receive module for spaceborne-communication antenna feed array applications, and to deliver submodules for experimental evaluation. Program goals include an overall receive module noise figure of 5 dB, a 30 dB RF to IF gain with six levels of intermediate gain control, a five bit phase shifter, and a maximum power consumption of 250 mW. Submicron gate length single and dual gate FETs are described and applied in the development of monolithic gain control amplifiers and low noise amplifiers. A two-stage monolithic gain control amplifier based on ion implanted dual gate MESFETs was designed and fabricated. The gain control amplifier has a gain of 12 dB at 29 GHz with a gain control range of over 13 dB. A two-stage monolithic low noise amplifier based on ion implanted MESFETs which provides 7 dB gain with 6.2 dB noise figure at 29 GHz was also developed. An interconnected receive module containing LNA, gain control, and phase shifter submodules was built using the LNA and gain control ICs as well as a monolithic phase shifter developed previously under this program. The design, fabrication, and evaluation of this interconnected receiver is presented. Progress in the development of an RF/IF submodule containing a unique ion implanted diode mixer diode and a broadband balanced mixer monolithic IC with on-chip IF amplifier and the initial design of circuits for the RF portion of a two submodule receiver are also discussed.
The Space Station Module Power Management and Distribution (SSM/PMAD) Breadboard, located at NASA's Marshall Space Flight Center (MSFC) in Huntsville, Alabama, models the power distribution within a Space Station Freedom Habitation or Laboratory module. Originally designed for 20 kHz ac power, the system is now being converted to high voltage dc power with power levels on a par with those expected for a space station module. In addition to the power distribution hardware, the system includes computer control through a hierarchy of processes. The lowest level process consists of fast, simple (from a computing standpoint) switchgear, capable of quickly safing the system. The next level consists of local load center processors called Lowest Level Processors (LLP's). These LLP's execute load scheduling, perform redundant switching, and shed loads which use more than scheduled power. The level above the LLP's contains a Communication and Algorithmic Controller (CAC) which coordinates communications with the highest level. Finally, at this highest level, three cooperating Artificial Intelligence (AI) systems manage load prioritization, load scheduling, load shedding, and fault recovery and management. The system provides an excellent venue for developing and examining advanced automation techniques. The current system and the plans for its future are examined.
The creation of a computer module used to calculate the size of the horizontal control surfaces of a conceptual aircraft design is discussed. The control surface size is determined by first calculating the size needed to rotate the aircraft during takeoff, and, second, by determining if the calculated size is large enough to maintain stability of the aircraft throughout any specified mission. The tail size needed to rotate during takeoff is calculated from a summation of forces about the main landing gear of the aircraft. The stability of the aircraft is determined from a summation of forces about the center of gravity during different phases of the aircraft's flight. Included in the horizontal control surface analysis are: downwash effects on an aft tail, upwash effects on a forward canard, and effects due to flight in close proximity to the ground. Comparisons of production aircraft with numerical models show good accuracy for control surface sizing. A modified canard design verified the accuracy of the module for canard configurations. Added to this stability and control module is a subroutine that determines one of the three design variables, for a stable vectored thrust aircraft. These include forward thrust nozzle position, aft thrust nozzle angle, and forward thrust split.
A waveguide Mach-Zehnder electro-optic modulator and an interdigitated photoconductive detector designed to operate at 820 nm, fabricated on different GaAlAs/GaAs heterostructure materials, are being investigated for use in optical interconnects in phased array antenna systems. Measured optical attenuation effects in the modulator are discussed and the observed modulation performance up to 1 GHz is presented. Measurements of detector frequency response are described and results presented.
Details of a proposed test program for PV thin-film modules which the Department of Energy has directed the Solar Energy Research Institute (SERI) to prepare are presented. Results of one of the characterization tests that SERI has performed are also presented. The objective is to establish a common approach to testing modules that will be acceptable to both users and manufacturers. The tests include acceptance, qualification, and characterization tests. Acceptance tests verify that randomly selected modules have similar characteristics. Qualification tests are based on accelerated test methods designed to simulate adverse conditions. Characterization tests provide data on performance in a predefined environment.
The Arecibo HF heater is normally composed of two separate sets of antenna array, transmitting waves vertically at the same frequency and polarization. However, when these two sets of antenna array radiate at slightly different frequencies, the intensities of HF heater-induced plasma lines (HFPLs) can be drastically modulated. In recent Duncan et al.'s (1989) experiments the 100 percent intensity modulation of HFPLs was seen to persist even when the secondary set of antenna array radiated at a few percent of the power transmitted by the primary set of antenna array. An explanation is offered, and it is shown that there exists a minimum power, Pmin, and if the secondary set of antenna array radiates at a power lower than Pmin, the 100-percent intensity modulation of HFPLs will not be observed. The functional dependence of Pmin on the difference frequency of the two sets of antenna array is also predicted for future experiments to corroborate.