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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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Silicone coatings applied to polyimide sheeting for variety of space-related applications. Coatings intended to protect flexible substrates of solar-cell blankets from degradation by oxygen atoms, electrons, plasmas, and ultraviolet light in low Earth orbit and outer space. Since coatings are flexible, generally useful in forming flexible laminates or protective layers on polyimide-sheet products.
A progress report, starting with November 1973, is given in the design, development, and performance of lightweight flexible FET (Fluorinated Ethylene Propylene) encapsulated solar cell modules intended to form standardized building blocks for large roll-up or fold-up solar cell blankets with performances on the order of 100 W/sq m and 80 W/kg in near space. It is shown that interconnected FEP encapsulated modules of advanced design can withstand all typical ground handling, assembly, storage, and launch conditions, and are well suited for high-power space applications.
The National Aeronautics and Space Administration (NASA) is interested in developing low-cost highly efficient solar cells on light-weight flexible substrates, which will ultimately lower the mass-specific power (W/kg) of the cell allowing extra payload for missions in space as well as cost reduction. In addition, thin film cells are anticipated to have greater resistance to radiation damage in space, prolonging their lifetime. The flexibility of the substrate has the added benefit of enabling roll-to-roll processing. The first major thin film solar cell was the "CdS solar cell" - a heterojunction between p-type CuxS and n-type CdS. The research on CdS cells started in the late 1950s and the efficiency in the laboratory was up to about 10 % in the 1980s. Today, three different thin film materials are leading the field. They include amorphous Si, CdTe, and Cu(In,Ga)Se2 (CIGS). The best thin film solar cell efficiency of 19.2 % was recently set by CIGS on glass. Typical module efficiencies, however, remain below 15 %.
Solar cell array deployment systems applied to spinning satellites based on flexible substrates and chemical rigidization
A plasma interaction analysis in support of the solar electric propulsion subsystem examined the effects of a large high voltage solar array interacting with an ion thruster produced plasma. Two solar array test modules consisting of 36 large area wraparound contact solar cells welded to a flexible Kapton integrated circuit substrate were abricated. The modules contained certain features of the effects of insulation, din-holes, and bonding of the cell to the substrate and a ground plane. The possibility of a significant power loss occurring due to the collection of charged particles on the solar array interconnects was the focus of the research.
Space Station Freedom will feature six large solar arrays, called solar array wings, built by Lockheed Missiles & Space Company under contract to Rockwell International, Rocketdyne Division. Solar cells are mounted on flexible substrate panels which are hinged together to form a 'blanket.' Each wing is comprised of two blankets supported by a central mast, producing approximately 32 kW of power at beginning-of-life. During launch, the blankets are fan-folded and compressed to 1.5 percent of their deployed length into containment boxes. This paper describes the main containment box mechanisms designed to protect, deploy, and retract the solar array blankets: the latch, blanket restraint, tension, and guidewire mechanisms.
This work is directed toward a low-cost approach to the fabrication of silicon solar cells and combines the advantages and flexibility of the epitaxial technique with the use of potentially low-cost silicon substrates. Epitaxial graded base n/p/p+ solar cell structures were grown and evaluated on various forms of polycrystalline and metallurgical grade silicon as well as single crystal substrates. X-ray topographic techniques have shown improvements in the crystallographic quality of the layer grown on polycrystalline material.
Present satellite communications systems normally use separate solar cells and antennas. Since solar cells generally account for the largest surface area of the spacecraft, co-locating the antenna and solar cells on the same substrate opens the possibility for a number of data-rate-enhancing communications link architecture that would have minimal impact on spacecraft weight and size. The idea of integrating printed planar antenna and solar array cells on the same surface has been reported in the literature. The early work merely attempted to demonstrate the feasibility by placing commercial solar cells besides a patch antenna. Recently, Integrating multiple antenna elements and solar cell arrays on the same surface was reported for both space and terrestrial applications. The application of photovoltaic solar cell in a planar antenna structure where the radiating patch antenna is replaced by a Si solar cell has been demonstrated in wireless communication systems (C. Bendel, J. Kirchhof and N. Henze, 3rd Would Photovotaic Congress, Osaka, Japan, May 2003). Based on a hybrid approach, a 6x1 slot array with circularly polarized crossdipole elements co-located on the same surface of the solar cells array has been demonstrated (S. Vaccaro, J. R. Mosig and P. de Maagt, IEEE Trans. Ant. and Propag., Vol. 5 1, No. 8, Aug. 2003). Amorphous silicon solar cells with about 5-10% efficiency were used in these demonstrations. This paper describes recent effort to integrate advanced solar cells with printed planar antennas. Compared to prior art, the proposed WSAC concept is unique in the following ways: 1) Active antenna element will be used to achieve dynamic beam steering; 2) High efficiency (30%) GaAs multi-junction solar cells will be used instead of Si, which has an efficiency of about 15%; 3) Antenna and solar cells are integrated on a common GaAs substrate; and 4) Higher data rate capability. The IA/SAC is designed to operate at X-band (8-12 GH) and higher frequencies Higher operating frequencies enable greater bandwidth and thus higher data transfer rates. The first phase of the effort involves the development of GaAs solar cell MIMs (Monolithically Integrated Module) with a single patch antenna on the opposite side of the substrate. Subsequent work will involve the integration of MIMs and antennas on the same side of the substrate. Results from the phase one efforts will be presented.
The results of the ATS-5 solar cell experiment after one year in synchronous orbit are reported. A partial failure in the experimental electronics package has caused a loss of data from half the 80 experimental solar cells. Procedures for extracting data due to a partial spacecraft failure are described and discussed. Data from the remaining 40 solar cells, including 15 mounted on a thin flexible structure are analyzed. Data are corrected to a solar intensity of 140 mW/sq cm and a temperature of 25 C. It was found that after one year in synchronous orbit: (1) cells with 1.52-mm-thick coverslides did not show a clear-cut advantage over those with 0.15-mm coverslides, (2) cells with solderless grid lines are degrading at the same rate as are cells with solder-dipped grid lines, (3) cells not quite completely covered with coverslides suffered a large power loss in comparison to cells fully covered, (4) no clear-cut advantage of 10-cm cells over 2-cm cells has yet been observed, (5) cells mounted on the flexible panel with relatively little backshielding did not degrade any faster than those with substantial backshielding, and (6) the flight data in large part confirms the adequacy of the ground-based techniques used in our preflight radiation test program.
A heat sealable transparent plastic film, such as a flourinated ethylene propylene copolymer, is used both as a cover material and as an adhesive for mounting a solar cell array to a flexible substrate.
Report and detailed appendix describe protective coat of SiOx (where x is 1.9 - 2.0) on Kapton H(R) polyimide sheet. Surface film protects substrate from bombardment by atomic oxygen. Intended for use as blanket substrate material of flexible array of solar photovoltaic cells on Space Station Freedom.
The Aerospace Corporation, NASA Glenn Research Center, Lockheed-Martin, and ILC Dover over the past two years have been engaged in developing a Multifunctional Inflatable Structure for the Powersphere Concept under contract with NASA (NAS3-01115). The Powersphere concept consists of a relatively large spherical solar array, which would be deployed from a microsatellite. The Powersphere structure and the deployment method was patented by the Aerospace Corporation (U.S. Patent Numbers 6,284,966 B 1 and 6,3 18,675). The work on this project has resulted in a number of technological innovations in the state of the art for integrating flexible thin-film solar cells with flex circuit harness technology and inflatable ultraviolet-light-rigidizable structures. The specific power, specific volume, for the Powersphere are presented in Figures 1 and 2 as a function of solar cell technology and efficiency. The Powersphere will enable microsatellite missions across NASA enterprises and DoD missions by providing ample electric power at an affordable cost. The Powersphere design provides attitude-independent electric power and thermal control for an enclosed microsatellite payload. The design is scalable, robust in high radiation environments and provides sufficient electric power to allow the use of electric propulsion. Electric propulsion enables precise positioning of microsatellites which is required for inspectors that would be deployed to inspect the International Space Station, Space Shuttle or large unmanned spacecraft. The Powersphere allows for efficient launch packaging versus deployed volume as shown in Figure 3.
This paper discusses both state-of-the-art and advanced development cell and array technology. Present technology includes rigid, roll-out, and foldout flexible substrate designs, with silicon and GaAs solar cells. The use of concentrator array systems is discussed based on both DOD efforts and NASA work. The benefits of advanced lightweight array technology, for both near term and far term utilization, and of advanced high efficiency thin radiation resistant cells is examined. This includes gallium arsenide/germanium, indium phosphide, and thin film devices such as copper indium disclenide.
The Power Extension Package (PEP), a 32-kilowatt, flexible-substrate, retrievable solar array system for use on the Space Shuttle, is described. It is noted that solar cell costs will be reduced by increasing cell area and simplifying cell and coverglass fabrication processes and specifications. The tests that have been carried out on the cells are described, among them a unique radiation damage test and a side-by-side comparison of candidate cell types with pre- and post-irradiation airplane calibration of outer space short-circuit current
The innovation targets small satellites or CubeSats for which conventional deployable arrays are not feasible due to their size, weight and complexity. This novel solar cell array includes a thin and flexible photovoltaic cell applied to an inflatable structure to create a high surface area array for collecting solar energy in a lightweight, simple and deployable structure. The inflatable array, with its high functional surface area, eliminates the need and the mechanisms required to point the system toward the sun. The power density achievable in these small arrays is similar to that of conventional high-power deployable/pointable arrays used on large satellites or space vehicles. Although inflatable solar arrays have been previously considered by others, the arrays involved the use of traditional rigid solar cells. Researchers are currently working with thin film photovoltaics from various suppliers so that the NASA innovation is not limited to any particular solar cell technology. NASA has built prototypes and tested functionality before and after inflation. As shown in the current-voltage currents below, deployment does not damage the cell performance.
Silicon dendritic web, a single crystal ribbon shaped during growth by crystallographic forces and surface tension (rather than dies), is a highly promising base material for efficient low cost solar cells. The form of the product smooth, flexible strips 100 to 200 microns thick, conserves expensive silicon and facilitates automation of crystal growth and the subsequent manufacturing of solar cells. These characteristics, coupled with the highest demonstrated ribbon solar cell efficiency-15.5%-make silicon web a leading candidate to achieve, or better, the 1986 Low Cost Solar Array (LSA) Project cost objective of 50 cents per peak watt of photovoltaic output power. The main objective of the Web Program, technology development to significantly increase web output rate, and to show the feasibility for simultaneous melt replenishment and growth, have largely been accomplished. Recently, web output rates of 23.6 sq cm/min, nearly three times the 8 sq cm/min maximum rate of a year ago, were achieved. Webs 4 cm wide or greater were grown on a number of occassions.
This paper describes recent efforts to integrate advanced solar cells with printed planar antennas. Several previous attempts have been reported in the literature, but this effort is unique in several ways. It uses Gallium Arsenide (GaAs) multi-junction solar cell technology. The solar cells and antennas will be integrated onto a common GaAs substrate. When fully implemented, IA/SAC will be capable of dynamic beam steering. In addition, this program targets the X-band (8 - 12 GHz) and higher frequencies, as compared to the 2.2 - 2.9 GHz arrays targeted by other organizations. These higher operating frequencies enable a greater bandwidth and thus higher data transfer rates. The first phase of the effort involves the development of 2 x 2 cm GaAs Monolithically Integrated Modules (MIM) with integrated patch antennas on the opposite side of the substrate. Subsequent work will involve the design and development of devices having the GaAs MIMs and the antennas on the same side of the substrate. Results from the phase one efforts will be presented.
Highly reproducible, very thin (40-80 microns thick) silicon solar cells are examined. These cells are the product of silicon thinning techniques that produce very flexible, resilient slices as compared to other techniques. Measurements on solar cells 2 cm by 2 cm by 50 microns thick producing 60 mW or more at AM0 are described. These cells have fine-line metallizations, tantalum oxide antireflection coatings and back-surface aluminum alloy.