0191-9067/83 $3.00 + .00 Copyright ® 1984 SUNSAT Energy Council UNLIMITED POWER FOR OUR SPACE VEHICLES LARRY G. CHIDESTER Electrical Power Systems, 0/62-16 Lockheed Missiles & Space Company, Inc. 1111 Lockheed Way Sunnyvale, California, USA 94086 Abstract — Photovoltaic solar arrays, deriving their energy from the sun, have provided the electrical power needed on all of our long life space vehicles. Solar arrays were first used as satellite power sources in 1958 and many new developments have occurred over the past 20 years in these high technology solid-state energy conversion devices. Present spacecraft solar arrays provide in the range of 1-5 kW; however, new lightweight flexible arrays, now in the developmental stage, will provide several hundred kilowatts of power at much less cost and lighter weight than present arrays. This paper describes the state of the art of solar cell technology, Lockheed’s development efforts on new solar arrays, and the upcoming NASA Solar Array Flight Experiment (SAFE). This flight experiment will demonstrate orbital operation of a huge 4 x 32 m flexible solar array which is described in detail. Demonstration of this technology will allow mission planners to initiate new spacecraft programs which need 50-100 kW. Beyond the SAFE technology, concepts are on the drawing boards at Lockheed which will take advantage of highly advanced solar cell technology, sunlight concentrators, and lightweight structures to provide multi-100 kW of power at a specific power of 200-300 W/kg, instead of present values of 20-30 W/kg. Three concepts are described which are specifically tailored to using single shuttle launches to establish a power source in orbit providing hundreds of kilowatts. 1. INTRODUCTION Our sun is the one nuclear energy source that no one objects to or worries about. It is a giant thermonuclear reactor producing electromagnetic waves which travel through space at 186,000 mi/sec. In electrical power terms the sun, an eternal, unchanging power source, generates 1 x 1024 kW (one septillion kilowatts) of energy constantly, and, as Leonardo daVinci noted, “It heats the universe.” As shown in Fig. 1, the Earth intercepts only a tiny fraction of that radiated energy — only 18 x 1012 kW (180 trillion kilowatts). That equates to about 130 W for every square foot of Earth area facing the sun. Taking into account atmospheric absorption, hours of darkness, cloud cover, and geographical location, the average amount of energy falling on a square foot of ground in the United States is only 13% of this, or 17 W. Even so, the amount of energy falling on the U.S. each year exceeds the total fossil fuel energy we could ever take out of the ground. One way of converting this sunlight directly to usable power is by using photovoltaic solar cells. In fact, with the present state-of-the art of solar cells, a photovoltaic array field covering an area only 70 mi on a side, in the Arizona desert, would generate enough electricity for the entire United States. As important as that information is concerning the potential generation of power on Earth, there is an even greater challenge in providing power for our space vehicles, which is my responsibility at Lockheed and the subject of this paper. Our earliest spacecraft were powered by batteries and lasted only a few days, whereas
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