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#1
August 1st 05, 07:31 PM
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STS - Then and now...... (Long article on Shuttle)
I post this article from Flight International of September 1976. It is
sad to see that so very few of the aspirations have actually been achieved. SPACE SHUTTLE DEBUT. Flight International 25 September 1976. The first Orbiter vehicle, main constituent of America's Space Shuttle, was rolled out at Palmdale in California last week. The Shuttle is a second- generation launch vehicle, and from 1980 will carry into orbit most US and European payloads. DAVID BAKER and MICHAEL WILSON here present a users' guide to the Shuttle and its growing range of "add-on" equipment. NASA has coined a new term, the Space Transportation System or STS, to more accurately reflect the capabilities of the composite launch vehicle based on the Space Shuttle as a kind of multi-purpose first stage. It comprises the Shuttle itself, Europe's Spacelab manned orbital laboratory- cum-observatory, and a series of upper stages to boost satellites into higher orbits and start deep-space or interplanetary probes on their journeys. There is also a scheme for an unmanned, heavy-lift vehicle in which the payload, taking the place of the winged Orbiter, is thrust into space by the Shuttle's main engines and boosters. The STS is therefore a building-block launch system. and will replace three of the four expendable rockets - Delta, Atlas-Centaur and Titan-Centaur - which comprise the current ffeet of Nasa/DoD launch vehicles. The smallest of the quartet is the Scout, and this is likely to co-exist inde;finitely with the Shuttle. When Nasa's search for a major project to succeed Apollo began to crystallise earlier this decade into a recoverable launch vehicle, the assumption was that it would replace all current US expendable rockets. Indeed, this was how the venture was justified to the US Government. Production rates of the two large rockets, Atlas-Centaur and Titan-Centaur, have now slowed, and their launch costs are likely to be considerably greater than those anticipated for the Shuttle. There will thus be little or no incentive for the commercial or scientific communities to use them when Shuttle operations get under way. But the smaller Delta remains attractive, and the Shuttle may be economic only if two or more payloads can be carried on one flight. This may be difficult or impossible if the desired orbital inclinations are widely different, a situation which is more likely to affect the scientific-satellite users, with their multitude of orbits, than the commercial customers requiring generally synchronous paths. The former group can often wait for a Shuttle flight going their way, however, while the latter, geared to maintaining a public or commercial service, may be able to "double-up" with another Shuttle customer. So, provided Nasa can organise its route network and schedules suitably, there is likely to be little call even for the Delta after 1980. Certainly, the continued use of expendable rockets would embarrass Nasa, though the administration would rather phase them out through the greater appeal of the Shuttle than by placing an embargo on their use. Meanwhile a new expendable, Europe's Ariane, will become operational at the same time as the STS to ensure an independent European launch capability. How far this will compete with the STS will depend on pricing policies. In order to keep costs down, the STS will be managed and operated like an airline, with scheduled flights into space leaving once a week from one or other of the two US launch sites. Nasa's chief job now is to market the Shuttle to potential users throughout the world in order to achieve the highest utilisation, particularly in the early years. To this end the agency several years ago prepared a traffic forecast or mission model covering the first 12 years of operation, 1980-1991. This is continuously revised (the latest one covers the period 1979-1992), since the costs of STS operation will be very sensitive to its utilisation. Space budgets in the US have fallen in recent years, and it seems likely that the Shuttle will be initially under- utilised despite Nasa's endeavours. Based on forecasts of eventual utilisation, Nasa plans to acquire five Orbiters (the delta-winged Orbiter, flown by a crew of four, can be regarded as the key module of the STS). Nasa has ordered one Orbiter, is negotiating for the second, and has signified its intention to buy a third. There is some doubt about who pays for the fourth and fifth Orbiters; the Shuttle is a Nasa programme, but the DoD will fly one-quarter of the missions during the first 14 years. Shuttle and its ancillaries The basic shuttle comprises the first two stages of a launch vehicle to which may be added one or more third stages to accommodate synchronous-orbit and planetary payloads. The first stage is powered by three liquid-propellant engines, supplemented by two Solid Rocket Boosters (SRBs), which provide the Orbiter with 99 per cent of the impulse required to impart low Earth orbit velocity. Fuel for the Orbiter's liquid- propellant engines is carried in the external tank, mounted under the vehicle's belly. Shortly after the tank has been jettisoned, two Orbital Manoeuvring System (OMS) engines at the rear of the Orbiter ignite briefly to impart the, additional impulse needed for a 50 n.m. x100 n.m. ellipse. This is transformed into a 100 n.m. circular orbit by re-igniting the OMS propulsion unit at first apogee. The Shuttle's load-carrying capacity reflects a preference for this two-stage configuration, which will be used when the altitude required is less than 650 n.m. for a 10,000lb payload. The maximum lifting capacity of 65000lb limits altitude to a 220 n.m. circular orbit. If payload/ height requirements fall outside these limits a third stage is carried in the cargo bay. The Shuttle then becomes a platform from whicha supplementary expendable propulsion system known as the Interim Upper Stage (IUS) and its payload can be separated and put into its own trajectory. The IUS is a DoD- sponsored vehicle to deliver at least 4,500lb to synchronous orbit and several such stages can be assembled to cater for high-energy planetary or heavy synchronous-orbit payloads which exceed this limit. In this three-stage configuration the Shuttle promises to accommodate all anticipated Earth-orbit and interplanetary unmanned payloads for the remainder of the century. IUS costs The IUS will cost the Dod about $1 million a unit, but launch costs to the user will work out at about $5 million, including development amortisation and launch services. In preparation for introducing the IUS in 1980, the USAF's Space and Missile Systems Organisation (SAMSO) proposes a definition phase from September 1976 to February 1978 (mainly to settle the payload rrquirement), followed by full-scale development From February 1978 to June 1980. The two-stage solid-propellant IUS will employ low- cost, off-the-shelf equipment and SAMSO anticipates placing a production order for about 270 units in 1980. The USAF intends to retain its Titan III launch vehicle as an insurance against Shuttle non-availability or technical failure, and requires IUS to be compatible with the Titan family so that it could replace the existing Burner II upper stage if necessary. The IUS will be uneconomic for small synchronous-orbit satellites, and for payloads in the 2,000lb class (equivalent to the lifting capacity of a Delta 3914) Nasa hopes to introduce a cheap, spin-stabilised, small boost stage. Definition begins next February, with detailed design getting under way by the end of 1977, leading to first flight in December 1979 on one of the six Shuttle development missions. If development of this supplementary propulsion system is approved, Nasa will have two third-stage boost elements (albeit expendable ones) tailored to synchronous-orbit payloads. Planners consider it likely that by the mid-1980s some customers will be calling for payloads to be retrieved from synchronous orbit for refurbishment and subsequent re-use. With this requirement in mind, Nasa proposes to develop a Space Tug for service In 1985-87. The current basic design is a single-stage liquid oxygen/liquid hydrogen-powered vehicle 30ft long, 15ft in diameter and with a propellant capacity of 50000lb. Carried to a low Earth orbit by the Shuttle, the Tug would boost its payload to synchronous orbit following separation from the Orbiter cargo bay, just like the IUS and the small boost stage. After circularising its orbit and placing the payload on station the rocket would return to a low Earth orbit for retrieval by the Shuttle. The Tug will be lifed for up to 100 flights and will be able to carry 8000lb to synchronous height, retrieve 3400lb or deliver and retrieve 2,400lb. Its synchronous-orbit delivery capability is twice that of the expendable IUS, and retrieval and delivery/ retrieval (or so-called round-trip) missions would provide a new level of flexibility for payload planners. Emphasising simplicity and reliability, the Tug will be powered by the RL- 10 rocket motor designed for the Centaur upper stage. With a minimum development time of six years a decision to proceed will have to be taken within the next three years if it is to be introduced by 1986. Although designed primarily for synchronous-orbit activities, the Tug's generous performance opens up the possibility of larger versions capable of supporting construction of the space station that will supercede Spacelab. A two-stage development of the Tug would deliver 34,500lb to synchronous orbit or perform a round trip with 8,800lb. Another version, the Aeromanoeuvring Tug designed to use Earth's atmosphere for braking, would deliver 12,800lb to synchronous orbit or take 6,700lb on a round-trip fight. It would "skip" through the outer layers of the atmosphere to lower apogee and reduce the propellant required to set up a low orbit after returning from synchronous altitude. Yet another scheme, the two-stage Growth Tug, would require an improved Shuttle capability but promises to deliver 48,700lb to synchronous orbit or send 12,600lb on a round trip. A follow-on Tug, called the Orbital Transport Vehicle (OTV), would be able to deliver 45,000lb to synchronous orbit and, following refuelling from an orbital propellant dump, could return with the same payload mass. Spacelab is the manned laboratory which, carried aboard the Shuttle Orbiter, will enable experimenters to carry out a wide variety of scientific, technological and biological activities for civil and military customers. Though considerably smaller than America's Skylab, it will - like the Shuttle itself - be reusable and, with specially designed modular experiments and equipment, be capable of rapid turnround on the ground to suit it for different missions. It comprises a pressurised habitable laboratory, known as a module, in which up to four payload specialists or experiment operators may work, and a number of unpressurised pallets on which are mounted those experiments or payloads calling for direct exposure to space. The configuration can be tailored to the needs of the flight. Some missions may call simply for a module, others for a combination of module and pallets, and yet others will require any number of pallets up to five, but no module. The basic module itself is a cylinder 4.5m in diameter and 2.7m long, but two such units can be joined together, increasing the length to about 5.93m to provide additional space for experiments. Fokker-VFW of Germany was signed up as prime contractor on September 30, 1975, for the six-year design and development task. The initial contract calls for the delivery to Nasa free of charge of a single flight unit, two engineering models and three sets of ground-support equipment and initial spares. Nasa and ESA are negotiating a second Spacelab, but in this case the US agency would pay the cost. At one time Germany was considering a purpose-built Spacelab to fly its own equipment, but this scheme has been abandoned owing to the high cost of the unit and the sharply increased levels of national expenditure required for regular Shuttle launches and the experiments needed to justify the acquisition. There is a possibility that Europe may buy a Spacelab of its own, though similar arguments appear to make it unlikely. In February 1975 Austria, though not an ESA member, officially joined the programme, relieving Germany of 0.8 per cent of its agreed commitment. Programme costs at mid-1976 prices for the single flight vehicle were estimated at 396 million accounting units, $515 million. The engineering models are to be delivered in August 1978. followed by the flight unit in August of the following year. Spacelab will go into orbit for the first time during the fifth Shuttle development flight, in 1980, and its first operation mission is scheduled for 1981. Germany is the main supporter, with 53 per cent of the programme, and Hawker Siddeley Dynamics, building the pallets, accounts for Britain's 6.5 per cent. The design lifetime is ten years or 50 flights, and a European will be one of the four payload experimenters on the initial flight. In terms of economy, Spacelab should be one of the most efficient payloads, since it makes use of a relatively large proportion of the facilities offered by the Shuttle. Maximum allowable Spacelab weight is 32,000lb, limited by the Orbiter's design landing weight. Between 12,000lb and 20,000lb of this figure, depending on the Spacelab configuration chosen, can be assigned to it. Spacelab will be the platform for the Western world's manned space activities up to about 1985, when the United States plans to bring along a "Mk 2" Spacelab. This at present appears likely to be an all-American design master-minded by the DoD, in the absence of a more pronounced European commitment in the present Spacelab. Predicting the market. The Space Transportation System will be capable of accommodating a wide range of missions. The Shuttle, spin-stabilised small boost stage and IUS offer a payload/ height performance better than that of current expendable launch vehicles. For the first three years of Shuttle operations (1980-82) payload planners will be cramped by the limited orbital capability from Kennedy. Not until the Vandenberg facility becomes operational will missions be possible with orbital inclinations greater than 55 degrees. Nevertheless, the initial performance envelope will include low Earth orbit, synchronous orbit and escape trajectories. With this restriction in mind, Nasa has prepared a preliminary schedule of missions, or traffic model, on the assumption that US Government, commercial and foreign users will call for a maximum of 60 flights a year by 1985. A single launch-pad at Kennedy will be available in 1979, followed by a second in June 1982; the first Vandenberg pad will not be ready before early 1983, with the second reaching completion by December 1986. Mission opportunities will be tailored to this schedule and to the Orbiter procurement plan. On present planning the Department of Defence will fly 27 per cent of all Shuttle flights proposed by the traffic model. Of the 578 fights envisaged in the 1979-1992 period, 70 per cent will be launched from Kennedy, 39 per cent will require seven-dlay Spacelab operations, and 6 per cent call for 30- day missions with the manned laboratory. About 34 per cent of the fights will involve the use of an IUS or Space Tug for synchronous-orbit delivery or delivery/retrieval missions. Spacelab and IUS/Tug missions account for 79 per cent of all launches tabulated in the 14-year traffic model, leaving 21 per cent for solo Shuttle missions or low-orbit delivery and retrieval work. The new traffic prediction shows a build-up to 60 flights a year from 1985 to 1991, with 40 launches a gear from Kennedy and 20 a year from Vandenberg, and replaces the original 1973 traffic model, which envisaged a total of 725 missions. Cost to the customer of a Shuttle launch is expected to be $20 million at 1976 prices, with Interim Upper Stages charged at 1.8 times the nominal $5 million rate for those users who want a launch at less than three years' notice. It is unlikely, however, that foreign participation will justify specific Shuttle flights, and most STS missions will accommodate a mixture of US and foreign payloads. In this case the cost to the user will be based on the proportional weight and volume requirements of the payload. Benefits to payload designers Introduction of the Space Transportation System in 1980 will greatly influence payload planners. To begin with the Shuttle will provide a comparatively comfortable environment for the payload, permitting designers many new freedoms. Payloads of up to 65,000lb can be carried to orbit within a volume of 10,500 cu ft, and satellites weighing up to 32,000lb can be returned. It is impossible to predict with accuracy the impact of the Shuttle's more favourable acceleration, temperature and vibration environment on payload design, but several technology studies have indicated cost-savings of up to 25 per cent. Nasa has already discovered that costs arising from the use of an expendable rocket with expensive excess lifting ability can be more than offset by a cheaper payload-development phase. The time-consuming process of designing to stringent weight, volume and reliability constraints imposed by expendable rockets can add significantly to the cost of payload development. The Shuttle also provides an "intact abort capability" which permits the Orbiter to return with its payload to a safe landing if the fight is terminated early after a mechanical or "software" failure. All of these features will serve to reduce space transportation costs beyond the current level. Organisations providing commercial services such as weather forecasting or communication are at present required to have back-up satellites in orbit ready to take over in the event of the primary spacecraft becoming unserviceable. The Shuttle will remove the need for orbital spares by quickly flying modularised repair packages to ailing or dead satellites in low orbit. A similar service for synchronous satellites will of course have to await the introduction of the Space Tug. On a typical repair mission, part of a scheduled Orbiter flight would be dedicated to carrying a Tug and an equipment dispenser. The combination would fly under remote control from low Earth orbit to a synchronous satellite. Once on station the dispenser would dock with the satellite, remove the faulty module and replace it with a new unit. The Tug, still attached to the dispenser, would then return to the Shuttle for capture and return to Earth. There could foreseeably be some opposition from the satellite builders, whose production rates might fall if the replacement market became slack as a result of extensive satellite refurbishment. But this objection might be offset by an increase in the market for satellites as launch costs fall. Again, refurbishment of a satellite will become progressively more uneconomic as it ages. Development of a standardised modular satellite would be essential for the effetive use of orbital-repair techniques, as would be equipment and experiment packages tailored to specific missions. Low-Earth-orbit satellites could also be built to a common design, with a rotary equipment or experiment dispenser carried within this Orbiter cargo bay. The modularised approach to satellite engineering would, again, reduce payload design costs by permitting a potential user to procure a standard, proven spaceframe and simply install his own experiments, sensors and other equipment. Modular sensors on an Earth-resources satellite could. for instance, permit adjustments to be made to the choice of spectral surveillance bands from time to time, so increasing the useful life of the satellite and circumventing the need for a costly replacement every few years. This approach would permit the more immediate application of even minor technological improvements. At present, advances in technology have to accumulate over a number of years before they justify a costly new project. Flight operations Shuttle launches and recoveries will be confined to the Kennedy Space Centre in Florida and Vandenberg AFB in California. By US regulation, no part of a launch vehicle's ground-track may intersect a major land-mass during the ascent to Earth orbit, and this limitation will be particularly important in the case of the Shuttle. The Eastern seaboard of the United States is so shaped that Shuttle operations from Kennedy will be limited to orbits not-exceeding an inclination of 55 degrees. Missions with orbital inclinations greater than this will have to use the USAF launch site at Vandenberg. Three elements of the Shuttle will return to Earth through the atmosphere during the Orbiter's ascent. The two boosters separate at an altitude of about 25 n.m., with the Shuttle 24 n.m. down-range from the launch site and moving at 4,600ft/sec. The resulting trajectory carries them to a height of 54 n.m. before they fall back towards the sea 210 n.m. from the launch site. Their descent through the atmosphere is slowed by a single drogue and three main parachutes, which lower the 147ft long units into the sea at 85 ft/sec. The external tank, the only expendable part of the Shuttle vehicle. separates at an altitude. of 70 n.m. and breaks up in the atmosphere 2,200 n.m. down-range of the launch site. Boosters from Kennedy fall into the Atlantic, those from Vandenberg into the Pacific. Each booster is designed for 20 flights and each recovery unit (attachment points, transponders and locator beacon) is expected to survive ten cycles. Shuttle launch costs are assessed on these utilisation rates and on the assumption that each Orbiter can fly at least 100 missions, with the main engines being replaced after 55 launches. Nasa assumes that the thermal- insulation tiles will survive 100 flights, with the reinforced carbon-carbon segments (fitted to 3.5 per cent of the exterior surface area, mainly the wing leading edges) replaced after 60 flights. External tank elements will be shipped from the Martin Marietta plant to Kennedy or Vandenberg as required. The tank costs about $2 million a unit at 1971 prices, or 22 per cent of the total Shuttle launch cost, with the boosters contributing $3.3 million per flight, 31 per cent of each launch. Shuttle services from the Kennedy Space Centre with Orbiter 102 (the second vehicle) will use the converted Saturn V launch pad (LC-39A) from the first flight in April 1979 until the second pad (LC-39B) becomes available in June 1982. Nasa expects to introduce Orbiter 101, refurbished from its drop-test configuration, in March 1981. It will be followed by Orbiter 103 in March 1982. Operations from Vandenberg will begin in March 1983 with delivery of Orbiter 104, followed a year later by Orbiter 105. Tentative plans envisage the introduction of a second Shuttle launch pad at Vandenberg by December 1986. Orbiter landings at Vandenberg call for a 7,000ft extension to an existing 8,000ft runway, but emergency landings can be made on the Edwards AFB runway 150 miles east of the launch site. Edwards was ruled out as the prime west-coast landing site because it would require a 747 to return the Orbiters to Vandenberg--with attendant delays in turnround time and expense--and an emergency landing following an aborted launch would necessitate an approach over Los Angeles. Emergency landing sites will be provided at Guam and Hawaii to accommodate east or west-coast flights aborted at an early stage. Nasa expects to provide opportunities for non-astronauts to fly in the Orbiter. The two pilots responsible for flying the Orbiter and controlling it in orbit will be supplemented by up to four payload specialists and a mission specialist. The latter will oversee the programme on each flight and ensure that each experiment operates for its allotted period. Payload specialists will be recruited from the scientific community and will require only a minimum of pre-flight training since they will not be involved in piloting or managing Shuttle systems. Flight crews will be recruited from the astronaut corps. Initial flight tests An important part of the Shuttle flight-qualification programme involves Orbiter 101, the initial vehicle, in a series of air-launched approach and landing tests. It will be carried to 24,000ft atop a modified Boeing 747 and released for a glide return to the Dryden Flight Research Centre at Edwards AFB, California. Test objectives are verification of Orbiter airworthiness and equipment operation; verification of the glide approach and landing techniques; qualification of the automatic landing system; and verificaticun of Orbiter performance and handling qualities over the weight and centre-of-gravity envelopes. The tests will also qualify the Shuttle carrier aircraft for ferrying Orbiters between the manufacturer's plant and the launch sites. Orbiter 101 will fly without main ascent engines, orbital manoeuvring engines or reaction-control equipment. Nor will it carry fuel-cell cryogenic tanks, cargo-bay payload, radiators, star-trackers or S-band and rendezvous radar. No water, waste-management equipment or food will be carried, and the thermal-protection tiles will be simulated by plastic plates to duplicate the mass characteristics of an operational Orbiter. The leading edges of the wings will be clad with glass-fibre and an instrumentation boom will be mounted on the nose. Fuel-cell reactants will be high- pressure gaseous hydrogen and oxygen (operational flights will use liquid hydrogen and oxygen), and simulated rocket nozzles will ensure realistic airflow characteristics across the boat-tail rear end. Standard aircraft-type ejection seats will be fitted for these drop tests, with blow-out panels in the roof of the flight deck providing an escape path if the vehicle has to be abandoned in the air. The first of a number of captive flights will take place in February next year, with a gradual progression from simple take-off and landing to long-duration handling trials of the 747/0rbiter combination. The Orbiter will be unmanned for the first 15 flights, but by May 1977 the first of six "captive-active" tests will provide an opportunity for manning, powering up the equipment and testing the flying controls while remaining anchored to the 747. During these tests the crew will be able to check their procedures in preparation for the first of eight manned drop-tests, which Nasa hopes to begin next year. A typical flight profile begins with a climb to 24,000ft, followed by a turn on to the desired heading relative to the runway selected for the landing. When the checks are completed the combination resumes its climb, to 28,000ft. From this altitude, about 31 n.m. from the runway, the carrier aircraft pitches 9 degrees nose-down and releases the Orbiter at 260kt, 22,000ft. Carried on a single attachment point under the nose and two latches under the rear fuselage, the Orbiter pitches up 6 degrees relative to the 747 and flies off the carrier aircraft. After separation the two vehicles bank in opposite directions to avoid a collision, and the Orbiter glides back to the Dryden Research Centre. On early flights a tailcone will shroud the simulated main engines, but on later drop-tests the cone will be jettisoned so that the flow across the inert rocket engines of a Shuttle returning from space may be simulated. The tailcone is carried at all times during mated flight to prevent turbulence set up by the aerodynamically dirty boat-tail from impinging on the 747's tail. The Orbiter will normally be released about 55min after take-off and will take about 5min to reach the ground. Follow-on Shuttle Believing that requirements may emerge for payloads in excess of 65,000lb to be launched on single flights, Nasa proposes a Heavy Lift Launch Vehicle (HLLV) using standard Shuttle elements. In this configuration the Orbiter would be replaced by a cylindrical payload shroud mounted on top of a normal Orbiter boat-tail structure carrying the three main-propulsion and the two orbit-insertion engines. The flight profile would closely follow that of a conventional manned Shuttle, with all propulsive elements being retained, but the automated control mode would call for a substantially revised guidance system. Based on present manned Shuttle performance, payloads of up to 230,000lb could be delivered into a due-east 200 n.m. orbit. Excluding development, the HLLV would thus offer a launch cost of $65/lb of payload at 1976 prices. Future American space-transportation systems will build on Shuttle-derived technology. This includes high-pressure/high-energy rocket engines, re- usable thermal insulation, large-diameter/high-thrust solid-propellant rockets, composite materials for structures, and better performance simulation and environmental-prediction techniques. Decision on a go-ahead with any one of several proposed Shuttle follow-on configurations obviously depends on the traffic achieved during the early 1980s. If Nasa is correct in its assumptions about initial traffic demands. the present Orbiter will need to be replaced bv a second-generation re- usable transporter by the early 1990s. -- End -- All OCR errors mine! Eugene Griessel 
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#3
August 2nd 05, 12:20 PM
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On Mon, 01 Aug 2005 15:16:38 -0400, John Steinberg
wrote: posts this article from Flight International of September 1976. It is sad to see that so very few of the aspirations have actually been achieved. SPACE SHUTTLE DEBUT. Flight International 25 September 1976. The first Orbiter vehicle, main constituent of America's Space Shuttle, was rolled out at Palmdale in California last week. The Shuttle is a second- generation launch vehicle, and from 1980 will carry into orbit most US and European payloads. DAVID BAKER and MICHAEL WILSON here present a users' guide to the Shuttle and its growing range of "add-on" equipment. --- snip! --- Don't you guys know how to post links, FFS!
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