Electrical power on a 30 kW space-based radar satellite
An electrical power system for a space-based radar satellite is described. When the radar is on, its transmitter needs an average DC power of 30 kW. The problem of distributing the power efficiently in pulses to many transmit/receive modules is addressed. System requirements include a high-voltage battery and transmission line, load-sharing between the solar array, and the battery during sunlit periods, and a 25-kW solar array. A scaled-down version of the power system for a proof-of-concept demonstration is described.<<ETX>>
Five-year update: nickel hydrogen industry survey
A 1984 survey of the nickel hydrogen (NiH/sub 2/) battery industry is updated. Late 1980s and early 1990s issues are identified, and usage and testing results of the survey are summarized. NiH/sub 2/ is the system of choice for new geosynchronous-earth-orbit (GEO) satellites and is being seriously considered for low-earth-orbit (LEO) applications. In five years, the annual cell production rate has doubled from approximately 1000 to 2000 cells. A number of cells under test have exceeded 20000 cycles at 40% DOD in LEO regimes, while other cells have achieved over 35 seasons in accelerated GEO regimes. The LEO database clearly indicates that NiH/sub 2/ performance is at least as good as the best conventional nickel-cadmium performance demonstrated under test.<<ETX>>
Effects of reservoir volume on performance of pulse tube cooler.
A pulse tube cooler has the advantages of long-life and low-vibration over conventional cryocoolers such as G-M and Stirling coolers because of the absence of moving parts at low temperature. On the other hand, the combination of a reservoir and orifice is indispensable to optimize the performance of pulse tube coolers. In order to make the pulse tube cooler compact for practical applications, the volume of reservoir should be minimized. This paper analyzes the effects of the reservoir volume on the thermodynamic performance of various components in a simple orifice and a double-inlet pulse tube cooler by combining a linearized model with a thermodynamic analysis. Expressions of entropy production for those components are presented. The results show that the reservoir volume has a significant influence on the entropy production in the various components when the reservoir to pulse tube volume ratio is smaller than about 5. The ratio is important to determine the minimum reservoir volume for a pulse tube cooler. Optimum settings for a double-inlet pulse tube cooler are also discussed.