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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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Quantitative degradation rates of power subsystems of nineteen initial defense satellite communication system spacecraft and their solar array activity
Solar sensor with coarse and fine sensing elements for matching preirradiated cells on degradation rates
The testing of 30 practical size, experimental 25 ampere hour cells constructed as part of an earlier negative limited cell development program is discussed. The test results showed that the negative limited cell is a possible means of developing a long-lived secondary cell. The cells were tested for 500 cycles using an accelerated regime approximating a 90-minute orbit period. Three groups of ten cells were tested at 0,25, and 40 C. The cycle data showed that the negative limited cells had higher degradation rates at the higher operating temperatures. At the conclusion of 500 cycles, the three groups had average capacities of 16.83, 12.74, and 5.71 ampere hours for testing at 0, 25, 40 C, respectively. The conditioning capacities of these cells was in the 25 ampere hours range. The internal cell pressures of the three groups was also temperature dependent and was, in general, in the 2 psig range during the course of the test program. No periodic variation of the internal pressure with the state-of-charge was observed except with some cells tested at 40 C.
Results of experimental work to evaluate the degradation rate of a parasol that was used as a means of alleviating thermal problems encountered soon after the launch of the Skylab 1 space vehicle are presented. Material selection criteria are discussed; the material chosen is described, and results of tests performed after environmental exposure at five facilities are given. The facilities used for exposure to ultraviolet radiation/thermal-vacuum environments and the equipment used for testing physical properties before and after exposure are described. Comparisons of ground test and flight test data are included.
A facility was constructed to evaluate solar collector performance outdoors for conditions that would be encountered by collectors if they were incorporated in a solar heating/cooling system. In addition to obtaining initial collector performance data, the outdoor facility will enable collector durability and degradation rates to be evaluated for operating periods of several months. The data obtained from the outdoor tests were compared to collector performance predicted on the basis of results obtained with a solar simulator. The performance measured outdoors was less than the predicted performance.
The physical and electrical characteristics of the Apollo Telescope Mount (ATM) solar array are described and in-flight performance data are analyzed and compared with predicted results. Two solar cell module configurations were used. Type I module consists of 228 2 x 6 cm solar cells with two cells in parallel and 114 cells in series. Type II modules contain 684 2 x 2 cm cells with six cells in parallel and 114 cells in series. A different interconnection scheme was used for each type. Panels using type II modules with mesh interconnect system performed marginally better than those using type I module with loop interconnect system. The average degradation rate for the ATM array was 8.2% for a 271-day mission.
The use of negative-limited nickel-cadmium cells with adequate charge control is shown to provide an effective means for controlling internal pressure. Cycle test data show that negative-limited cells have somewhat higher ampere-hour degradation rates at higher operating temperatures. The most important advantages of these cells are: (1) lesser heat generation during operation; (2) longer separator life, as a result of operation at lower temperatures; (3) decreased stresses on cell seals due to lower operating pressures; and (4) significant weight savings.
The establishment of the absolute age range for the unmodified crater class is considered in an attempt to estimate the change of crater degradation rates as a function of time. It is assumed that both the Moon and Mars have had similar time rate of changes in impacting rates. This means that both were subjected to intense bombardment in early history. The rate rapidly declined to low rates around 3.5 b.y. ago.
A facility was constructed to evaluate solar collector performance outdoors for conditions that would be encountered by collectors if they were incorporated in a solar heating/cooling system. In addition to obtaining initial collector performance data, the outdoor facility will enable collector durability and degradation rates to be evaluated for operating periods of several months. The data obtained from the outdoor tests were compared to collector performance predicted on the basis of results obtained with a solar simulator. The performance measured outdoors was less than the predicted performance.
Results of experimental work to evaluate the degradation rate of a parasol that was used to alleviate thermal problems encountered soon after the launch of the Skylab 1 space vehicle are presented.
A multiple-task research and development program was performed to improve the weight, life, and performance characteristics of hydrogen-oxygen alkaline fuel cells for advanced power systems. During Phase 4, the lowest stabilized degradation rate observed in all the testing completed during four phases of the program, 1 microvolt/hour, was demonstrated. This test continues after 5,000 hours of operation. The cell incorporates a PPf anode, a 90Au/10Pt cathode, a hybrid frame, and a Fybex matrix. These elements were developed under this program to extend cell life. The result demonstrated that the 80Au/20Pt cathode is as stable as a 90Au/10Pt cathode of twice the precious metal loading, was confirmed in full-scale cells. A hybrid frame two-cell plaque with dedicated flow fields and manifolds for all fluids was demonstrated to prevent the cell-to cell electrolyte transfer that limited the endurance of multicell plaques. At the conclusion of Phase 4, more than 90,900 hours of testing had been completed and twelve different cell designs had been evaluated. A technology base has been established which is ready for evaluation at the powerplant level.
The adequacy of the signal design approach chosen for the TDRSS/orbiter uplink was evaluated. Critical functions and/or components associated with the baseline design were identified, and design alternatives were developed for those areas considered high risk. A detailed set of RF and signal processing performance specifications for the orbiter hardware associated with the TDRSS/orbiter Ku band uplink was analyzed. Performances of a detailed design of the PN despreader, the PSK carrier synchronization loop, and the symbol synchronizer are identified. The performance of the downlink signal by means of computer simulation to obtain a realistic determination of bit error rate degradations was studied. The three channel PM downlink signal was detailed by means of analysis and computer simulation.
A program has been underway to evaluate materials for advanced solar arrays which are required to provide power to weight ratios up to 100 W/kg. Severe mission environments together with the lack of knowledge of space environmental materials degradation rates require the generation of irradiation and outgassing engineering data for use in the initial design phase of the flight solar arrays. Therefore, approximately 25 candidate array materials were subjected to selected mission environments of vacuum, UV, and particle irradiation, and their mechanical and/or optical properties were determined where appropriate.
A candidate pre-Analog to Digital filter bandwidth versus data rate design is presented for the multimegabit telemetry demodulator/detector. The design is based on considerations of Analog to Digital bias, quantization errors, and automatic gain control effects, as well as the deleterious effects of filtering. Two methods of gain control of the input level to the analog to Digital converter are considered. The first method uses a particular value of gain, according to which bandwidth is selected. The second method uses a second narrowband noncoherent Automatic Gain Controls (in the LPF bandwidth) to attempt to keep the Analog to Digital input level constant. This second method reduces the bit error rate degradation slightly but appears to be more difficult to implement.
Various aspects of glass encapsulation that are important for the designer of photovoltaic systems are discussed. Candidate glasses and available information defining the state of the art of glass encapsulation materials and processes for automated, high volume production of terrestrial photovoltaic devices and related applications are presented. The criteria for consideration of the glass encapsulation systems were based on the low-cost solar array project goals for arrays: (1) a low degradation rate, (2) high reliability, (3) an efficiency greater than 10 percent, (4) a total array price less than $500/kW, and (5) a production capacity of 500,000 kW/yr. The glass design areas discussed include the types of glass, sources and costs, physical properties, and glass modifications, such as antireflection coatings.
Cosmochemical considerations suggest various potential sources for the accumulation of organic matter on Mars. However the Viking Molecular Analysis did not indicate any indigenous organic compounds on the surface of Mars. Their disappearance from the top layer is most likely caused by the combined action of the high solar radiation flux and various oxidizing species in the Martian atmosphere and regolith. In this study the stability of several organic substances and a sample of the Murchison meteorite was tested under simulated Martian conditions. After adsorption on powdered quartz, samples of adenine, glycine and naphthalene were irradiated with UV light at various oxygen concentrations and exposure times. In the absence of oxygen, adenine and glycine appeared stable over the given irradiation period, whereas a definite loss was observed in the case of naphthalene, as well as in the volatilizable and pyrolizable content of the Murchison meteorite. The presence of oxygen during UV exposure caused a significant increase in the degradation rate of all samples. It is likely that similar processes have led to the destruction of organic materials on the surface of Mars.
Experiments performed to determine the effects of temperature and creep strain on the fatigue life of a graphite/epoxy composite laminate show that (1) sustained periods of static loading have significant retardation effects on the fatigue degradation rate of the laminated composite, and (2) cyclic loading with a lower frequency preceding higher frequency loading also prolongs the fatigue life. A creep crack hypothesis is proposed that can provide reasonable interpretations for these experimental results.
In photovoltaic systems, the encapsulant material that protects the solar cells should be highly transparent and very durable. Glass satisfies these two criteria and is considered a primary candidate for low-cost, photovoltaic encapsulation systems. In this paper, various aspects of glass encapsulation are treated that are important for the designer of photovoltaic systems. Candidate glasses and available information defining the state of the art of glass encapsulation materials and processes for automated, high volume production of terrestrial photovoltaic devices and related applications are presented. The desired characteristics of glass encapsulation are (1) low degradation rates, (2) high transmittance, (3) high reliability, (4) low-cost, and (5) high annual production capacity. The glass design areas treated herein include the types of glass, sources, prices, physical properties and glass modifications, such as antireflection coatings.