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Aviation History
1979
1979 - 0871.PDF
fUCHTInternational, 17 March 1979 HEAVY-LIFT LAUNCHERS CLASSIFIED 837 Class Payload (tonnes) Annual payload (tonnes) 60-90 90-135 135-200 200-300 300-450 500-2,500 500-2,500 500-2,500 125,000 125,000 the ground by teams of engineers in control rooms. Nasa envisages two different annual payload levels. The first is 500-2,500 tonnes orbited per year in support of a space programme embracing manned orbital stations, laboratories in geosynchronous orbit, automated inter planetary flights and a demonstration solar power satellite. The second model calls for the annual uplift of the 125,000 tonnes needed for a full-scale solar power satellite pro gramme. The Shuttle is puny in comparison, with an expected annual average of 40 flights a year at 60 per cent load factor resulting in an annual level of about 700 tonnes. Nasa has studied five different classes of heavy-lift launcher (see table). A Class 1 (60-90 tonnes payload) un manned launcher could be developed from the Space Shuttle by modification of the Orbiter. The Orbiter replace ment would consist of an expendable cylindrical container 7m in diameter and nearly 24m long, and capable of housing 65 tonnes of payload. Three Space Shuttle Main Engines (SSME) housed in a separate recoverable pod would be fed from the ET, and two standard SRBs would complete the combination. The cost per flight, discounting development, is estimated at about $19 million. This promises a payload cost of less than $300/kg, about a third of the present Shuttle rate. One Boeing estimate puts the development cost of the SSME pod at about $860 million spread over five years. This compares with a development cost for the present Space Shuttle of nearly $7,300 million over eight years. A further development of the Class 1 launcher, using liquid-fuelled boosters instead of the SRBs, has also been proposed by Rockwell and Boeing. This would raise Earth-orbit payload capacity to nearly 90 tonnes. The new boosters would be recoverable, with clamshell doors to protect the rocket nozzles. Launch cost is likely to be as low as $195/kg. The drawback of liquid reusable boosters is their high development cost. One estimate puts development of this Shuttle derivative at $2,250 million over &2 years. Development of the liquid-powered booster would account for about $1,400 million of the total. Once developed, the new booster could also be applied to the present Shuttle. The proposed booster would be fuelled with a combina tion of kerosene and liquid hydrogen, with liquid oxygen as the oxidiser. The advantage of this approach is a reduc tion in propellant volume, as much as 20 per cent com pared with a liquid hydrogen/liquid oxygen system. The resulting saving in structural weight is even higher at about 35 per cent. The clamshell doors are necessary to protect the four engines of each booster from damage during splashdown in the sea. Unlike the SRB, the pro posed booster would thus be sealed against sea water, making refurbishment easier. The Class 2 (90-135 tonnes payload) unmanned Shuttle derivative would have an expendable cylindrical container nearly 8m in diameter, and a pod containing three SSMEs. The External Tank would be conventional, but there would be four SRBs instead of two. Payload is 108 tonnes, but the relatively high launch cost of $36 million means that users would have to pay about $340/kg. This is more expensive than the Class 1 launcher with SRBs, and far more costly than the version with liquid-propellant reusable boosters. An obvious solution would be to use four liquid- propellant boosters instead of the SRBs, thereby reducing launch costs. Development costs are likely to be high, however, and the potential for further improvement is limited. It may therefore make more sense to go for a completely new heavy-lift launcher. The Class 3 (135-200 This artist's impression shows a Shuttle derivative designed to carry more than a hundred tonnes of cargo to low Earth orbit. The Orbiter has been replaced by a cylindrical container and an engine pod. Four liquid-propellant reusable boosters have replaced the existing pair of Solid Rocket Boosters tonnes payload) launcher does not come into this category, offering more performance than Shuttle derivatives but less than the largest vehicles envisaged. Nasa may eventually be able to afford a Shuttle deriva tive and a new heavy-lift launcher, but is not likely to have funds for two completely new spacecraft. In this event it would be best to develop a Shuttle derivative to handle the smaller payloads and an all-new heavy-lifter for the upper end of the scale. Boeing and Rockwell have both proposed new, Class 4 (200-300 tonnes payload), launcher concepts with payloads of 230-270 tonnes. Unlike the Shuttle Orbiter, which returns to Earth like an aeroplane, these launchers have a completely ballistic trajectory. Each has two stages, both of which are recovered at the end of their ballistic flight. The external appearance of the launchers is unimpressive, the shape being rather squat in comparison with the arrow-like outline of most rockets. The first stage is fuelled with liquid hydrogen and kerosene and the propellants, separated by a bulkhead, share a single tank. The nine main engines which operate on a gas generator cycle, are set into the base of the stage, which also doubles as a heat shield. The nozzles are blanked off by doors during the re-entry phase. Unlike the Shuttle, which is protected by ablative surface insula tion, the heat shield of the Class 4 craft consists of a double skin cooled by the passage of water between the surfaces. The steam generated in this way is vented over board. The total thrust generated by the first stage is over 8,700 tonnes. After the first stage has done its job, the casing costs downrange to a rocket-braked splashdown in the sea.
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