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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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The applicability of frame imaging from a spinning spacecraft. Volume 1: Summary report
A detailed study was made of frame-type imaging systems for use on board a spin stabilized spacecraft for outer planets applications. All types of frame imagers capable of performing this mission were considered, regardless of the current state of the art. Detailed sensor models of these systems were developed at the component level and used in the subsequent analyses. An overall assessment was then made of the various systems based upon results of a worst-case performance analysis, foreseeable technology problems, and the relative reliability and radiation tolerance of the systems. Special attention was directed at restraints imposed by image motion and the limited data transmission and storage capability of the spacecraft. Based upon this overall assessment, the most promising systems were selected and then examined in detail for a specified Jupiter orbiter mission. The relative merits of each selected system were then analyzed, and the system design characteristics were demonstrated using preliminary configurations, block diagrams, and tables of estimated weights, volumes and power consumption.
The status of defect studies pertinent to radiation damage in silicon solar cells
The status of radiation defects in silicon is briefly reviewed and discussed in relation to the problem of radiation tolerance of silicon solar cells in space.
Thin silicon solar cell performance characteristics
Refined techniques for surface texturizing, back surface field and back surface reflector formation were evaluated for use with shallow junction, single-crystal silicon solar cells. Each process was characterized individually and collectively as a function of device thickness and bulk resistivity. Among the variables measured and reported are open circuit voltage, short circuit current and spectral response. Substantial improvements were obtained by the utilization of a low cost aluminum paste process to simultaneously remove the unwanted n(+) diffused region, form the back surface field and produce an ohmic contact metallization. The highly effective BSF which results from applying this process has allowed fabrication of cells 0.05 mm thick with initial outputs as high as 79.5 mW/4 sq cm (28 C, AM0) and superior electron radiation tolerance. Cells of 0.02 mm to 0.04 mm thickness have been fabricated with power to mass ratios well in excess of 2 watts per gram.
Photovoltaic technology development for synchronous orbit
Accomplishments and expected benefits are summarized for the following efforts: (1) achieving silicon solar cell efficiency of 18% at 200 micron m to 250 micron m thickness; (2) reducing silicon cell radiation damage in geosynchronous orbit after 10 years to less than 15%; (3) demonstrating coplanar back contact 50 micron m thick silicon solar cells with efficiency of 14%; (4) demonstrating the feasibility of a radiation tolerant GaAs concentrator cell; (5) achieving 30% efficient photo conversion in the laboratory; (6) defining candidate concepts for 50% efficient electromagnetic conversion; and (7) demonstrating the technology for protecting arrays capable of 300W/kg after 10 years in geosynchronous orbit.
Theoretical results on the tandem junction solar cell based on its Ebers-Moll transistor model
A one-dimensional theoretical model of the tandem junction solar cell (TJC) with base resistivity greater than about 1 ohm-cm and under low level injection has been derived. This model extends a previously published conceptual model which treats the TJC as an npn transistor. The model gives theoretical expressions for each of the Ebers-Moll type currents of the illuminated TJC and allows for the calculation of the spectral response, I(sc), V(oc), FF and eta under variation of one or more of the geometrical and material parameters and 1MeV electron fluence. Results of computer calculations based on this model are presented and discussed. These results indicate that for space applications, both a high beginning of life efficiency, greater than 15% AM0, and a high radiation tolerance can be achieved only with thin (less than 50 microns) TJC's with high base resistivity (greater than 10 ohm-cm).
Radiation-Hardness Data For Semiconductor Devices
Document presents data on and analysis of radiation hardness of various semiconductor devices. Data specifies total-dose radiation tolerance of devices. Volume 1 of report covers diodes, bipolar transistors, field effect transistors, silicon controlled rectifiers and optical devices. Volume 2 covers integrated circuits. Volume 3 provides detailed analysis of data in volumes 1 and 2.
Galileo 1986 on Centaur
The mission, flight profile, instrumentation, and developmental program for the Galileo Jupiter probe, scheduled for Shuttle launch in 1986, are discussed. Gravity assists from each Galilean satellite at spacecraft periapsis will be used in order to configure for approaching the next satellite after a swingby past Jupiter. The process will continue for twenty months, and will yield data on the Jovian magnetosphere and tail, as well as on the satellites. A probe will be released 150 days from Jupiter orbit, followed by a course adjustment for the main instrumentation payload. The dual-spin spacecraft will proceed on its mission and act as a relay for the atmospheric entry probe, which is expected to broadcast data for one hour. Instrumentation on the Galileo will perform imaging, IR and UV spectrometry, radiometry, magnetometry, particle and dust detection, as well as plasma measurements, and celestial mechanics and radio propagation experiments. The direct trajectory to Jupiter, including a plane change maneuver, will be powered by a Centaur upper stage, and will encompass a journey taking over two years. The key constraints on the satellite tour are propellant and radiation tolerance.
Space solar cell technology development - A perspective
The developmental history of photovoltaics is examined as a basis for predicting further advances to the year 2000. Transistor technology was the precursor of solar cell development. Terrestrial cells were modified for space through changes in geometry and size, as well as the use of Ag-Ti contacts and manufacture of a p-type base. The violet cell was produced for Comsat, and involved shallow junctions, new contacts, and an enhanced antireflection coating for better radiation tolerance. The driving force was the desire by private companies to reduce cost and weight for commercial satellite power supplies. Liquid phase epitaxial (LPE) GaAs cells are the latest advancement, having a 4 sq cm area and increased efficiency. GaAs cells are expected to be flight ready in the 1980s. Testing is still necessary to verify production techniques and the resistance to electron and photon damage. Research will continue in CVD cell technology, new panel technology, and ultrathin Si cells.
The NASA photovoltaic technology program
The NASA Office of Aeronautical and Space Technology OAST Program in space photovoltaics is reviewed. From the perspective of national landmark mission requirements and five year and 25-year long range plans, the texture of the program is revealed. Planar silicon and concentrator GaAs array technology advances are discussed. Advances in lightweight (50 micro cell) arrays and radiation tolerance research are presented. Recent progress in cascade cells and ultralightweight GaAs planar cells is noted. Progress in raising silicon cell voltage to its theoretical maximum is detailed. Advanced concepts such as plasmon converters and the Long Duration Exposure Facility LDEF flight experiments pertaining to solar cell and array technology are also shown.
Ultrasonic seam welding on thin silicon solar cells
The ultrathin silicon solar cell has progressed to where it is a serious candidate for future light weight or radiation tolerant spacecraft. The ultrasonic method of producing welds was found to be satisfactory. These ultrathin cells could be handled without breakage in a semiautomated welding machine. This is a prototype of a machine capable of production rates sufficiently large to support spacecraft array assembly needs. For comparative purposes, this project also welded a variety of cells with thicknesses up to 0.23 mm as well as the 0.07 mm ultrathin cells. There was no electrical degradation in any cells. The mechanical pull strength of welds on the thick cells was excellent when using a large welding force. The mechanical strength of welds on thin cells was less since only a small welding force could be used without cracking these cells. Even so, the strength of welds on thin cells appears adequate for array application. The ability of such welds to survive multiyear, near Earth orbit thermal cycles needs to be demonstrated.
The NASA photovoltaic technology program
The NASA Office of Aeronautical and Space Technology OAST Program in space photovoltaics is reviewed. From the perspective of national landmark mission requirements and five year and 25-year long range plans, the texture of the program is revealed. Planar silicon and concentrator GaAs array technology advances are discussed. Advances in lightweight (50 micro cell) arrays and radiation tolerance research are presented. Recent progress in cascade cells and ultralightweight GaAs planar cells is noted. Progress in raising silicon cell voltage to its theoretical maximum is detailed. Advanced concepts such as plasmon converters and the Long Duration Exposure Facility LDEF flight experiments pertaining to solar cell and array technology are also shown.
Development of a radiation-hard CMOS process
It is recommended that various techniques be investigated which appear to have the potential for improving the radiation hardness of CMOS devices for prolonged space flight mission. The three key recommended processing techniques are: (1) making the gate oxide thin. It has been shown that radiation degradation is proportional to the cube of oxide thickness so that a relatively small reduction in thickness can greatly improve radiation resistance; (2) cleanliness and contamination control; and (3) to investigate different oxide growth (low temperature dry, TCE and HCL). All three produce high quality clean oxides, which are more radiation tolerant. Technique 2 addresses the reduction of metallic contamination. Technique 3 will produce a higher quality oxide by using slow growth rate conditions, and will minimize the effects of any residual sodium contamination through the introduction of hydrogen and chlorine into the oxide during growth.
Superlattices and multilayer structures for high efficiency solar cells
Possible applications of superlattices to photovoltaic structures are discussed. A new concept based on doping superstructures (NIPI) can be exploited to significantly reduce recombination losses in III-V compound solar cells. A novel multijunction structure with lateral current transport is proposed. A computer simulation has been performed which shows that by optimizing the multilayer structure, short circuit current is substantially increased with minimum drop in open circuit voltage. An additional advantage of the structure is enhanced radiation tolerance. It is anticipated that this multilayer structure can be incorporated in multibandgap cells to achieve high efficiencies.
A possible radiation-resistant solar cell geometry using superlattices
A solar cell structure is proposed which uses a GaAs nipi doping superlattice. An important feature of this structure is that photogenerated minority carriers are very quickly collected in a time shorter than bulk lifetime in the fairly heavily doped n and p layers and these carriers are then transported parallel to the superlattice layers to selective ohmic contacts. Assuming that these already-separated carriers have very long recombination lifetimes, due to their across an indirect bandgap in real space, it is argued that the proposed structure may exhibit superior radiation tolerance along with reasonably high beginning-of-life efficiency.
Superstructure high efficiency photovoltaics
A novel class of photovoltaic cascade structures is introduced which features multijunction upper subcells. These superstructure high efficiency photovoltaics (SHEP's) exhibit enhanced upper subcell spectral response because of the additional junctions which serve to reduce bulk recombination losses by decreasing the mean collection distance for photogenerated minority carriers. Two possible electrical configurations were studied and compared: a three-terminal scheme that allows both subcells to be operated at their individual maximum power points and a two-terminal configuration with an intercell ohmic contact for series interconnection. The three-terminal devices were found to be superior both in terms of beginning-of-life expectancy and radiation tolerance. Realistic simulations of three-terminal AlGaAs/GaAs SHEP's show that one sun AMO efficiencies in excess of 26 percent are possible.
Proposal for superstructure based high efficiency photovoltaics
A novel class of cascade structures is proposed which features multijunction upper subcells, referred to as superstructure high-efficiency photovoltaics (SHEPs). The additional junctions enhance spectral response and improve radiation tolerance by reducing bulk recombination losses. This is important because ternary III-V alloys, which tend to have short minority-carrier diffusion lengths, are the only viable materials for the high-bandgap upper subcells required for cascade solar cells. Realistic simulations of AlGaAs SHEPs show that one-sun AM0 efficiencies in excess of 26 percent are possible.
Multijunction upper subcell cascade photovoltaics for space applications
A new class of cascade high-efficiency photovoltaics designed for space-based applications is proposed. The design improves upper subcell performance and avoids electrical and optical losses associated with an intercell ohmic contact. Multijunction upper subcells reduce bulk recombination of photogenerated minority carriers by decreasing the average collection distance, yielding improved spectral response and radiation tolerance. A three-terminal design is employed which circumvents the need for a monolithic intercell contact and, thus, the losses associated with such a contact. Problems related to array interconnection of three-terminal devices may be solved by creating a two-terminal cell from complementary pairs (n-p-n and p-n-p) of three-terminal cells. Simulations of lattice-matched AlGaAs-GaAs and lattice-mismatched AlGaAs-InGaAs cascade cells show that one-sun AM0 efficiencies in excess of 26 and 28 percent, respectively, are possible.