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Aviation History
1984
1984 - 0078.PDF
COMMERCIAL ROCKETS radiating ability. The tiles are the first type of heat-shield to be re-usable—previous US capsules were coated with an ablative material which charred away in the heat of entry. Each SRB comprises several segments which are bolted together to form a complete booster. When each SRB has performed its task, its fall into the sea is braked by parachutes. Purpose- built tugs then right the SRBs and tow them back to shore, so that parts, including the stain less steel casings, can be re-used. So far Nasa has only re-used some parts—it has yet to re-fly a complete SRB. Space Shuttle Orbiters carried ejection seats on the first four flights, but there is now no escape system. In this respect Shuttle is unique, being the first manned launcher without means of emergency escape. The craft has three main abort modes, however, abort-to-orbit, abort- once-around, and return-to-launch site-abort. These can cope with an SSME failure at any time, but there is no way of coping with an SR& malfunction. Solid-propellant motors are tradi tionally very reliable, however, and the SRBs do have good safety margins. Lockheed Space Operations leads the team which has been awarded Nasa's Shuttle processing contract (Flight, September 24, 1983, page 818). Lockheed's team members include Grumman Services (13 per cent), Morton Thiokol (11 per cent), and Pan Ameri can World Services (1 per cent). The task of the team is to turn each Orbiter around between flights, to carry out routine maintenance, and to stack major elements together in preparation for flight. Launch record First flight on April 12, 1981. Three further test flights made, all of them successful, before Shuttle declared operational. Total of nine flights to date, including two in 1981, three in 1982, and four in 1983. Success rate of Shuttle is 100 per cent, but an IUS fail ure almost caused the loss of TDRSS A. Launch Sites — All flights to date from pad 36A at the Kennedy Space Centre, Florida. A second pad, 36B, will become available in mid- 1985. A Shuttle launch pad is also being constructed at Vandenburg AFB, California, and should be ready for use in October 1985. Development Cost Roughly $10,000 million in 1980 prices, including the first four test flights. Selling agent Nasa headquarters. Launch cost A dedicated mid-1984 Space Shuttle launch costs about $40 • 8 million in real year prices, including reflight guarantee and use fee. An average Delta-class payload would require only about 21 per cent of Shuttle's capacity, and would therefore pay only about $14-5 million (including Pam upper stage). A dedicated Shuttle launch in mid-1986 would cost $89 • 7 million in real year prices. The price is much higher because a new Nasa pricing policy comes into effect in October 1985. Comparable Delta-class launch cost is $26-1 million. Current status - Nasa has financed construc tion of four flightworthv Orbiters— Challenger (099), Columbia (102), Discovery (103), and Atlantis (104). Parts for a fifth Orbiter have also been financed. Columbia and Challenger are the only Orbiters to have flown, but Discov ery's debut is imminent. Space Shuttle's major capabilities have been successfully demonstrated, but there are many parts of the operating "envelope" still uncharted, including the first landing at the Kennedy Space Centre (KSC) runway, the use of manned manoeuvring units in space-walks, and the ability to repair and retrieve satellites. Having achieved four Shuttle flights in 1983, Nasa has scheduled ten flights in 1984—rather ambitiously, in our view. The manifest lists 12 flights in 1985, 17 in 1986, and 24 in 1987. Why an upper stage? Space Shuttle is unique in that it is designed to deliver satellites to low-Earth orbit. It simply does not make economic sense to take the 90-tonne Orbiter any higher—even if Solid Rocket Boosters and Space Shuttle main engines had the performance to do so . As a result, all Shuttle cargoes destined for a higher orbit, such as a geosta tionary path, must use an upper stage or carry their own integrated propulsion system. A I ^\ Canaveral and the Kennedy Space Centre, and 1 -Pl| [ 3U| ll confirm IUS as the most powerful upper stage 1#*;'1IMIH! w now flying. Alternatively, a Shuttle-launched IUS can place 3,185kg in a 20,200km-high circular orbit inclined at 28-5°. Technical features As its name implies, two-stage IUS comprises two solid-propellant motors (plus an interstage and guidance and control avionics). The larger unit acts as a peri gee motor, boosting IUS and its payload into geosynchronous transfer orbit. The smaller unit acts as an apogee boost motor, circularising the orbit into a geosynchronous one. Launch record lUS first flew aboard Titan 34D on October 30, 1982, when it successfully boosted a DSCS II and DSCS III into geosyn chronous orbit. The stage made its Shuttle debut on April 4, 1983. All went well until part wav through the burn of the smaller motor, when a seal failed. This set the TDRS A payload tumbling, and also left it short of geosynchrous orbit. Fortunately Nasa was able to stabilise TDRS A and use its thrusters to raise the orbit. Development cost This was estimated at $350 million in August 1980, including five flight-standard IUSs. Selling agent USAF. Launch cost Estimated to be more than $40 million. Current status Boeing Aerospace and the USAF have yet to implement and qualify a fix for the seal failure which nearly caused the loss of TDRS A. Three further craft, TDRS B, C, and D, are to be launched by Shuttle using IUS—once the stage gets a clean bill of health. Boeing has so far received orders to build a total of 14 IUSs. The contract for the last six of these was awarded by the USAF in January 1983. It was worth $277 million, and called for delivery between November 1983 and April 1985. Nasa became seriously interested in Centaur G for shuttle work in April 1981, because of IUS cost overruns and delays. The liquid hydrogen and oxygen-fuelled Centaur G, a derivative of the Centaur upper stage used on Atlas, offered much greater performance. It could also be ready in time to launch the Galileo and ISPM interplanetary probes in May 1986. In October 1982 the USAF agreed to finance half the development of Centaur G, mainly to carry large payloads to higher earth orbits, leaving Nasa to fund the other half and the more powerful Centaur G-prime. Centaur G is able to place 4,800kg in geosyn chronous orbit, or 5,260kg into a l,670km-high polar orbit (after launch from KSC). Corre sponding values for Centaur G-prime are 6,350kg (GEO) and 5,350kg. Technical features Centaur G differs from the current Centaur in having a fatter hydro gen tank and more powerful engines (operating on a mixture ratio of 6:1). Centaur G prime differs from the G version in having a stretched hydrogen tank, a lengthened oxygen tank, and engines running on a 5:1 mixture ratio. As with the original Centaur, General Dynamics is the prime contractor. Launch record Two Centaur G-primes are due to fly in May 1986, making it necessary for Nasa to modify two Orbiters for the upper stage Flight, November 13, 1982, page 1432). The cargoes are ISPM and Jupiter probe, Galileo. Development cost Centaur G was expected to cost $270 million in real-year dollars in late 1982, while Centaur G-prime adds a further $88 million. Other costs are; modifications of two Orbiters (S80 million), KSC launch pad changes ($80 million), and production start-up and the ISPM and Galileo Centaur G-primes ($190 million). Selling agent Nasa or USAF. Current status In addition to building two test vehicles, there are plans to build two Centaur G-primes in 1985 (Galileo and ISPM) and two Centaur Gs in 1986. IUS Boeing Aerospace was originally contracted to develop three versions of Inertial Upper Stage (IUS)—two-stage, twin-stage, and three-stage. Two-stage is financed by the US Department of Defence and is the only version which survives today, cost overruns and delays having forced Nasa to withdraw from the other two ventures. An IUS flying aboard Titan 34D can place 1,870kg in geosynchronous orbit, while one flying Shuttle can transport 2,270kg into the same path. These figures allow for a 28 • 5° plane change, necessary for launches from Cape Pam McDonnell Douglas Astronautics developed its payload assist module (Pam) as a private venture, after Nasa agreed that it would not finance development of a competing upper stage. Three versions are now being offered—Pam D (1,250kg to a geosynchronous transfer orbit inclined at 27°), Pam D-II (1,590kg), and Pam A (1,995kg). Of these, only Pam D may be used as the third stage of a Delta 3910 or 3920 series rocket. Note that Nasa refers to Pam as a solid spinning upper stage (SSUS). Technical features Each marque uses a single solid-propellant motor. In the Shuttle role, Pam sits on a spin-table, which is in turn mounted on a framework. Pam relies on Space Shuttle Orbiter to deploy it in correct attitude. Firing of the motor occurs automatically 45min after ejection from Orbiter. Launch record Pam D first flew on Novem ber 15, 1980, aboard Delta, with SBS 1 as the ' payload. It first flew aboard Shuttle on STS 5, 104 FLIGHT International, 14 January 1984
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