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Aviation History
1985
1985 - 3320.PDF
SPACEFLIGHT Vandenberg launch schedule date slips VANDENBERG Propellant loading and other problems at the new Shuttle launch complex at Vanden berg Air Force Base, Califor nia, have pushed the maiden military flight from the complex back from March 20 to mid-July 1986 at the earliest. This will put pressure on some commercial satellite deployment flights, the first of which is mission 61H, sched uled for June 1986 (in which the UK's Skynet IVA military satellite, and the first UK astronaut, are due to be carried). The planned second flight from Vandenberg will almost certainly now be pushed into 1987, reducing the number of flights planned in 1986 to 14 at the most. Other missions threatened with delays during 1986 are 61E, 61F, 61G, and 61 J, carrying Astro 1, Ulysses, Galileo, and the Hubble Space Telescope respectively. The latest Shuttle mission, STS 61B, flown by Atlantis, came after a 50-day turn around—the fastest to date. Since November 1983 all Shuttle turnarounds have been handled by the Lockheed-managed process ing team. The average interval between the 23 Shuttle flights so far is 72 days, with an aver age of 32 days being achieved this year. This figure is eight days over the average interval target Nasa had set itself in 1986, before the Vandenberg delay. The new target for next year is 35 days. The longest interval between two Shuttle flights was, predictably, the 212 days between STS 1 and STS 2— Columbia in 1981. The best Discovery turnaround was the 59 days between missions STS 51D and STS 51G this year, the best by Challenger 56 days between STS 41B and STS 41C in 1984, and the best by Columbia 89 days between STS 3 and STS 4 in 1982. The average of the best turn around figures is 63 days. The US Air Force's Aeronautical Systems Division materials laboratory will use a GTE module similar to this to carry out the Shuttle-borne gallium arsenide experiment. The module will be built by GTE and flown • in late 1986 or early 1987 Shuttle GaAs study funded WRIGHT-PATTERSON AFB The growth of gallium arsen ide crystals in the micro- gravity of space is to be stud ied by GTE, the US Air Force, and Nasa under a $750,000 cash-sharing contract. Gallium arsenide (GaAs) is a crystal similar to silicon, but having certain advantages. Digital circuits produced on GaAs chips operate six times faster than circuits produced on silicon, and consume only one fortieth of the power. In addition, GaAs is more radiation-resistant than sili con and can operate at much higher temperatures, making it much more reliable for use in space. The material is formed by heating gallium and arsenic, which react chemically to produce liquid GaAs. This forms a crystal when cooled. Terrestrially produced GaAs, however, has defects caused by uneven temperatures in the growth furnace, causing convection currents in the liquid and destroying its uniformity. GTE has constructed a heater in a Space Shuttle getaway special which will melt a pre-grown crystal to within one inch of becoming entirely liquid. The one-inch crystal will form the core of a crystal to be regrown in space, where weightlessness will simplify the heating and growth process. Research scientists from the US Air Force Aero nautical Systems Division's materials laboratory will compare Shuttle-grown and terrestrially-produced crys tals. The comparison will help to assess the importance of gravity currents in defect formation. Nasa faces Space Station power question CLEVELAND Nasa is due to decide in March on the power gener ation system it wants for the US Space Station. The choice is between photovoltaic solar arrays and a solar dynamics technique. Photovoltaic solar arrays, which convert the sun's energy directly into elec tricity, have been used on spacecraft for more than 25 years. Although they are reliable, they are expensive and suffer from gradual degradation. Large arrays are also needed to provide adequate power. The US Space Station's baseline requirement for 75kW would, for example, need around 6,000m2 of panels. This could substantially affect orbital stability, requiring the storage of a large amount of pro pellant to maintain orbital altitude. The panels could also obstruct the field of view. Solar dynamics uses mirrors to concentrate sun light to heat a fluid, which drives a turbine. This is not yet a space-proven system, although it has been tested successfully on the ground. The technique would require only one-third the panel area of the photovoltaic system, and would be easier to grow to meet future power demands of up to 300kW. Lead contractors Rocket- dyne and TRW are each working on $6 million contracts as part of the Work Package 4, Phase B, study being managed by the Lewis Research Centre. It is likely that Nasa will decide on a compromise between the two power generation methods, involving either a dual system using both techniques, or a photovoltaic system that would eventually evolve into a solar dynamics system as experience is gained in the latter technology. Arianespace signs up ECS 4 and Hipparcos PARIS Arianespace and the Euro pean Space Agency have signed the launch contracts for two more satellites, ECS 4 and Hipparcos. Launch of the ECS 4 communications satellite has been bought forward from 1987 to late 1986, to fill the gap left by the demise of ECS 3 when Ariane V15 failed last September. The prime con tractor for ECS 4 is British Aerospace. Hipparcos, due to be launched in mid-1988 aboard Ariane 4, is being built by the Mesh consortium. Hipparcos is an astrometric satellite that will produce an extremely accurate map of 100,000 stars. The recent orders bring the Arianespace order backlog to FFr7,600 million ($950 million). 12 FLIGHT INTERNATIONAL, 21/28 December 1985
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