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Part of Delta Clipper Family
American SSTO VTOVL orbital launch vehicle. Proposed intermediate 1/2 scale test vehicle between DC-X and DC-Y orbital version. No government agency was willing to fund the $450 million development cost -- and neither were any private investors.

AKA: Delta Clipper-Prototype;SX-2. Status: Study 1993. Thrust: 1,051.20 kN (236,319 lbf). Gross mass: 84,000 kg (185,000 lb). Unfuelled mass: 6,000 kg (13,200 lb). Specific impulse: 373 s. Specific impulse sea level: 316 s. Burn time: 271 s. Height: 24.00 m (78.00 ft). Diameter: 5.00 m (16.40 ft). Span: 5.00 m (16.40 ft).

The DC-X2/SX-2 was a proposed risk-reduction 1/2 scale demonstrator for the DC-Y. The Single Stage Rocket Technology (SSRT) program was to begin flight testing the DC-X vehicle in the summer of 1993. SDIO did not budget funds for any other effort other than $5 million in FY94 to complete the DC-X flight testing. SDIO encouraged other DOD agencies (ARPA and USAF), the Department of Energy (Sandia and Los Alamos National Laboratories), NASA, or a combination of the above to support a joint follow-on ATD program run from SDIO or another agency. The SX-2 was proposed as a Fast Track ATD program that was well defined and for which independent government cost and schedule estimates exist.

SX-2 Program Definition

The follow-on program would build and fly the SX-2 (Spaceplane Experimental) ATD by 1997. The SX-2 would use the same RL-10A5 engines as the DC-X with performance enhancements provided by subcontracts with the Russian rocket engine company Energomash. The vehicle would operate out of the same basic facilities and use the same ground-based crew and control center used to fly the DC-X. Airframe construction was to demonstrate the identical composites and unit weights needed for follow-on suborbital and Single Stage to Orbit (SSTO) vehicles. Maximum altitude for the SX-2 would be 180 km, providing four to five minutes of microgravity time in space.

Like its predecessor, the DC-X, the SX-2 was to push even further toward demonstrating the feasibility of rocket powered 'aircraft-like' operations, support, reliability and associated recurring flight costs in the only credible way -- by doing it. The SX-2, like the DC-X, used oxygen and hydrogen to support all propulsion and power needs, and offered an environmentally benign exhaust product -- water. With clean exhaust, manageable noise levels and no staging debris, the SX-2 was an environmentally friendly system that could help set the standard for all 21st century launch systems.

The rationale for funding the SX-2 program centered around five military/commercial 'dual use' points

  • enabling the construction of follow-on suborbital and orbital vehicles providing vastly less expensive commercial spacelift services and fundamentally new strategic and tactical military capabilities,
  • assuring that the American aerospace industry is the first to commercially exploit low cost, highly reliable space access,
  • providing dual use technology spin-offs to the commercial and military sectors,
  • bolstering the aerospace industrial base by opening profitable new commercial opportunities, and
  • developing American-Russian co-operative ventures.
Funding Requirements

The SX-2 program was envisioned as a competitive procurement in which three prime airframe contractors expressed an interest: Lockheed, McDonnell Douglas and Rockwell International. Total program cost as estimated by both the government and the McDonnell Douglas industry team was $450 million. The fiscal year breakout was $75, $185, $180 and $10 million through FY94 through FY97 respectively. The first year of design was to focus on reducing the program cost as far as possible towards a self-imposed $300 million Design-to-Cost goal. Just as completing the DC-X significantly reduced the cost and uncertainty of proceeding with the SX-2, the SX-2 program was to provide accurate, low risk estimates of the cost of proceeding with follow-on suborbital and orbital vehicles.

A successful SX-2 program was to directly enable a family of military, civil and commercial derived vehicles. From cheap suborbital rockets identical to the SX-2 for university and commercial research, to intercontinental ballistic transport vehicles able to deliver cargo globally within minutes, to future SSTO launch vehicles, a successful SX-2 program was to conclusively show that such vehicles could be built and allow credible estimates of their operating costs and reliability. Moreover, if the SX-2 flew as cheaply as the DC-X, by the turn of the century follow-on vehicles could begin reducing operating costs by up to an order of magnitude over the $10 billion the U.S. spends annually on space launch.

The SX-2 would have provided a focus for high technology American-Russian co-operation and was to bolster the declining American aerospace industry with contracted work in many of the 50 states, but focused in Alabama, California, Colorado, Florida, Missouri and New Mexico. With Russian provided propulsion enhancements it was likely the SX-2 could eventually break the X-15 speed record of Mach 6.7. Once its initial flight test objectives were achieved, the SX-2 could be used for many experiments and high speed technology development for the next century. Low cost, routine access to the hypersonic flight regime could expedite high speed technology development. Experiments flown on the SX-2 could benefit many key technologies including base burning, actively cooled structures, heat pipes, high temperature materials, durable flight controls, hot structures, advanced cryogenic tanks, slush hydrogen, triple point oxygen, advanced avionics and rocket augmented flight.

Launch Price $: 10.000 million in 1991 dollars.

Family: orbital launch vehicle, SSTO. Country: USA. Agency: Douglas. Bibliography: 282.

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