|First Commercial Satellite to Use Triple Junction Photovoltaics.|
The Cover photo is the DIRECTTV-4S, a Boeing 601P satellite, which is the fifth satellite to be built by Boeing Satellite Systems (BBS) for DIRECTVR, a unit of Hughes Electronics Corp. The satellite as launched aboard an Ariane 4 rocket at the Guiana Space Center on the Northeast coast of South America . Once deployed and in service at 1010 West longitude, the more than 85-foot-long, 24.5 foot-wide DIRECTV-4S will provide the capacity to deliver additional local channels and strengthen the redundancy of the DIRECTV in-orbit fleet.
|Being checked out with the solar panels removed is the DIRECTV Boeing satellite which weighs 9,400 pounds fully fueled at launch. The launch vehicle will put it into a geosynchronous orbit approximately 22,500 miles above the earth. Because the shadow of the earth only affects the collection of solar power during two eclipses each year, the satellite operates from the PV panels most of the time. During the growing eclipse cycles, the PVs must generate enough power for satellite operations and recharge current for the 30 cell Nickel-hydrogen batteries which provide anything form partial to full power in full eclipse. At present, the proven performance of Nickel-hydrogen in both cycle life and long term reliability makes it the superior battery chemistry. While a terrestrial team controls the satellites TV operations, its navigation and health, a special group responsible for spacecraft power will be focusing on the management of the PV panels and the batteries . +|
The DIRECTV-4S will be the first worlds commercial satellite to employ high efficiency solar arrays with triple junction gallium arsenide solar cells built by Spectrolab, Inc., a BSS subsidiary. These solar cells employ a three-layered structure, with each layer able to capture and convert a different portion of the solar spectrum. Arranged in two solar arrays, the panel is 85.8 feet long when deployed. Its photovoltaic solar cells will be able to convert 24.5 percent of the suns energy into electricity, the highest efficiency of any commercial satellite to date. This will equate to 8.3 kiloWatts of power at the end of its 15-year design life.
This Boeing-built satellite deployed by DIRECTV is the first spacecraft in the DIRECTV fleet to employ spot beams. This technology reuses the same frequencies on multiple spot beams to reach the major television markets where DIRECTV delivers the signals of local network affiliates.