Electrical Power Subsystem Research Articles

Electrical power subsystem initial sizing

The basics of performing the initial electrical power subsystem (EPS) sizing for a spacecraft using solar cells for an energy source and batteries for energy storage are covered. The basic engineering inputs are described. The outputs are the first estimate of the number of solar cells, the solar array area, and the number of batteries required. A spreadsheet program to keep track of the inputs, perform the calculations, and document the inputs and outputs was written. >

A system with two subsystems working in alternating periods

We come across in daily life systems consisting of two subsystems which work alternatively. One of the subsystems works for a period which has a probability distribution. Then the other subsystem begins to work for a further period, having a different probability distribution. The system after this period swings back to the previous subsystem and the process goes on. We have the striking example of a power system which has a hydroelectric power subsystem and a thermal electric power subsystem. The hydro-subsystem works for a period when water is let out for irrigation. Then, when the irrigation is stopped, the thermal subsystem works. Again, when irrigation shutters are open, the hydro-subsystem resumes working. In the problem under consideration the system consists of two independent subsystems desigfiated as subsystem 1 and subsystem 2. The subsystem 1 has two i.i.d units, one of which is a cold standby. This subsystem works for a period which has a general probability distribution. In the subsequent period of working the subsystem 2 (consisting of units in series) works for a period which has another general probability distribution. The system again alternates to the 2-unit standby subsystem. In this way the process continues. Thus, we have two alternating periods: working period 1 and working period 2. During the working period 1, the subsystem 1 works and during the working period 2, the subsystem 2 works. Working period I and working period 2 alternate. In model I we have assumed that if in a period a subsystem fails, the other is not switched on. In model II, if the subsystem 1 (2-unit standby system) fails the subsystem 2 (units in series) is immediately switched on. On the other hand, if the subsystem 2 fails during its operation period, the subsystem 1 is not switched on, and the whole system is considered as failed. In both the models, the i.i.d units and the subsystem 2 have exponential failure time distributions. There is a repair facility, the repair (hazard) rate being also a constant. The reliability of the system and the mean time to the first system failure in each of the models are derived. For model I, Markov renewal technique is applied and for model II, supplementary variable technique. In model I, the two subsystems can be considered to be similar to a single system which has a working period as well as a rest period, which has been discussed by the authors Eli. The working period is the period when the subsystem 1 of the original system works and the rest period coincides with the working period of subsystem 2.

ATS-6 Description and Performance

The Applications Technology Satellite-6 (ATS-6) uses a 9l1-r parabolic antenna with high gain to enable communications with simple, low-cost ground stations with 3-m-diameter antennas. The structural system met all of its requirements, deployed properly, and preserved sensor alignment within 0.1 degree. The thermal control system has kept all temperatures within specified limits. The communications subsystem in-orbit performance has also exceeded specifications with high receiver gain-to-temperature ratios and high transmitter El RP. The spacecraft propulsion system performance has been within specifications. The near-perfect geosynchronous orbit achieved by the Titan IIIC resulted in a 8-kg fuel saving which should extend mission life. The attitude and control subsystem is providing the necessary stabilization and accurate slewing control. The electrical power subsystem provided 40 W more than the specified value at the last summer solstice. The telemetry and command subsystem performance has also been nominal.

Computer Simulation of Satellite Electric Power Systems

A computer program concept is described for performing an electrical analysis and a transient thermal analysis of a satellite electric power subsystem consisting of a solar array, battery, and power controls. The program "flies" the power subsystem and certain thermally sensitive portions of the spacecraft through one or more complete orbits, and plots curves of voltages, currents, temperatures, and energy balance in critical parts of the power and thermal subsystems.