In the mid-1960's the US Air Force conducted a series of classified studies on next-generation space transportation systems to support projected large military space stations, conduct manned military reconnaissance and strike missions, and reduce the cost of launching military payloads. These Air Force studies finally concluded that a partially reusable vehicle was the most attractive, along the lines of Lockheed's Starlifter, which had a large drop tank but returned the engines and avionics of the vehicle for reuse. The Air Force probably spent around $ 1 billion on 'black' technology development tests at this time, including work on linear aerospike engines and high fineness lifting body shapes that would re-emerge again 30 years later in Lockheed's X-33 space shuttle successor.
NASA also had ambitious plans - for large space stations, lunar bases, nuclear interplanetary rocket stages, and manned Mars expeditions. NASA went through a long iterative process in designing and selecting the space shuttle, leading ultimately to the same conclusion as the Air Force. Initial Phase A concepts were for two stages, both either winged or lifting bodies, both recovered at the launch site for reuse. NASA explored some alternative concepts, including Lockheed's LS200 single orbiter with drop tank, and Chrysler's SERV ballistic single stage to orbit vehicle, before proceeding to Phase B. The Phase B designs were more refined but still used the same two-stage approach. At this point the controversy were over large cross-range winged designs, medium cross-range lifting body designs, and minimal cross-range stub-wing designs. NASA's Faget strongly pushed for the stub-wing design.
Eventually the Nixon administration advised NASA that not only were there to be no flights to Mars, no nuclear interplanetary stages, no space station, no more Saturn V's, no orbital transfer vehicle - but there wouldn't be a space shuttle either if NASA couldn't get the development cost down and get the USAF to participate. A USAF requirement was a large cross-range to allow recovery of the orbiter at Vandenberg AFB from polar orbits in the case of abort-once-around scenarios. This, together with wind tunnel studies indicating that Fagetís straight wing was unstable at re-entry speeds, drove NASA to the delta wing. The reduction in development cost led NASA to throw away the concept of reusing anything but the engines and guidance systems. Instead the shuttle would be boosted by cheap solid fuel boosters and, taking a concept from the Air Force, the propellants would be put in a big expendable drop tank.
Following the usual charade of competitive bidding, NASA picked the same contractors as for X-15 and Apollo, who would build precisely the vehicle it had in mind. North American Rockwell was selected to build the orbiter, with its Rocketdyne Division making the main engines, Thiokol for the solid rocket boosters, and Martin Marietta for the External Tank, to be built at the government Saturn IC factory at Michoud.
To finance the Shuttle in the austere 1970ís, already-built Apollo hardware that would have supported a second Skylab mission was sent to museums and American manned space flight went into a long hiatus. Budget cuts and overruns reduced the number of shuttles built from five to four and delayed the first flight from 1978 to 1981 (thereby ruining the plan to save Skylab on an early shuttle mission). Although several elements were cancelled (a space tug), the project did not much overrun its original cost (development ended up costing $ 6.744 billion in 1971 dollars, versus $ 5.15 billion estimated - less than a quarter of the Apollo program cost).
The pretext for the shuttle was that it would be much cheaper than expendable launch vehicles and would replace them all. Production was accordingly terminated by the US government of Delta, Atlas, and Titan vehicles. NASA staff and contractors were under incredible pressure to justify this decision by increasing the shuttle launch rate, lowering the turn-around time, and thereby reducing the cost per launch. When the shuttle Challenger exploded and the entire US space lift program was shut down for almost a year, the fallacy of this situation was exposed. The US Air Force and commercial users returned to use of expendable launch vehicles. When the shuttle began flying again, it was only for NASA programs.
In the final analysis the shuttle came up short in two areas. First, the shuttle orbiter ended up almost 20% over its specified weight - resulting in it being unable to boost the US Air Forceís payloads into polar orbits from Vandenberg. Lighter filament-would casing Solid Rocket Boosters were being developed for use in flights from Vandenberg, but even this did not seem enough. After the Challenger explosion the USAF was able to extricate itself from the Shuttle program. The Vandenberg launch complex, built at the cost of billions, was mothballed. The Air Force started a new costly development program to design the Titan 4 expendable rocket for its large military payloads.
The second was that it failed, by most definitions, to reduce the cost of putting payloads into orbit. The shuttle program inherited from Apollo huge fixed costs - the Manned Spaceflight Center in Houston, the cadres of government and contractor workers at the Kennedy Space Center, and so on. The result was that there is a fixed base cost of around $ 2.8 billion per year, just to keep all those people and facilities in place, even if you donít conduct any flights at all (as occurred after the shuttle disaster). The marginal cost of each flight added to this base is under $ 100 million per year. Seen this way the shuttle is almost competitive expendable boosters - but doesnít come anywhere near the reductions NASA promised when development started. But if you divide the usual number of flights per year by the total costs, you come up with a figure of $ 245 million per year, significantly more than a Titan 4 or Proton launch with the same payload.
If the shuttle failed as a space truck, it succeeded in keeping the US in the manned spaceflight business in a period of low public interest and political support. With the excuse of delivering payloads to orbit, NASA got to fly up to seven astronauts and run a host of supplementary experiments and payloads with each flight.
With construction of the international space station beginning, NASA is looking forward to finally using the shuttle for its intended purpose. Due to the lower than planned flight rate, NASAís contractors are confident they can keep the existing shuttles flying through 2030. The real test will come when (inevitably) another shuttle is lost.
|Launch Vehicle: Shuttle. |
The manned reusable space system which was designed to slash the cost of space transport and replace all expendable launch vehicles. It did neither, but did keep NASA in the manned space flight business for 30 years (and counting...) Redesign of the shuttle with reliability in mind after the Challenger disaster reduced maximum payload to low earth orbit from 27,850 kg to 24,400 kg.
|Launch Vehicle: Shuttle ISS. |
Redesign of the shuttle with reliability in mind after the Challenger disaster reduced maximum payload to low earth orbit from 27,850 kg to 24,400 kg. When the decision was made to move the International Space Station to a high-inclination 51.6 degree orbit, net payload to the more challenging orbit dropped to unacceptable limits. The situation was improved by introduction of the Super Lightweight External Tank, which used 2195 Aluminium-Lithium alloy as the main structural material in place of the 2219 aluminium alloy of the original design. This saved 3,500 kg in empty mass, increasing shuttle payload by the same amount. The tank was first used on STS-91 in June 1998.
|Launch Vehicle: IHLLV. Same concept as Shuttle C. Shuttle orbiter replaced by recoverable pod with shuttle main engines and payload cannister. Quick way for US to obtain heavy payload capability and reduce shuttle cost per kg to orbit by 3 X.|
|Launch Vehicle: Shuttle C. Marshall design for replacement of shuttle orbiter with recoverable main engine pod. Same concept as Interim Heavy Lift Launch Vehicle; IHLLV. 2 SSME configuration would have a payload of 45,450 kg.|
|Launch Vehicle: Shuttle LRB. Shuttle with Liquid Rocket Boosters in place of Solid Rocket Boosters.|
|Launch Vehicle: Ares. |
The Ares launch vehicle was designed for support of Zubrin's Mars Direct expedition. It is a shuttle-derived design taking maximum advantage of existing hardware. It would use shuttle Advanced Solid Rocket Boosters, a modified shuttle external tank for handling vertically-mounted payloads, and a new Lox/LH2 third stage for trans-Mars or trans-lunar injection of the payload. Ares would put 121 tonnes into a 300 km circular orbit , boost 59 tonnes toward the moon or 47 tonnes toward Mars. Without the upper stage 75 tonnes could be placed in low earth orbit.
|Launch Vehicle: Shuttle ASRM. Shuttle using Advanced Solid Rocket Motors (development cancelled 1993).|