19 July 2010

DC-X, the Delta Clipper

One of the holy grails of aerospace technology not yet achieved has been true reusable single stage-to-orbit (SSTO) capability- a launch vehicle that is fully reusable and completely able to reach orbit in a single structure and return to Earth for reuse. No hardware or components would be shed on the ascent (or descent, for that matter). Some approaches to SSTO have looked at air-breathing vehicles while the other approaches using rocket power face the challenge of having a high enough propellant to mass ratio to reach orbit while still carrying a useful payload.

In 1989, three diverse individuals pooled their talents to pitch a rocket-powered SSTO vehicle to Vice-President Dan Quayle. Max Hunter began his work in aerospace engineering with Douglas Aircraft, having become their chief engineer for astronautics after heading the Thor IRBM program. He later came to Lockheed to work on various aspects of the Strategic Defense Initiative (SDI). Retired Army general Daniel Graham had a background in intelligence and was one of the biggest proponents of the SDI program in the Reagan Administration. And the third individual was Jerry Pournelle, a noted science fiction author, journalist, and, like Graham, a proponent of SDI. The three men met with Quayle that year to pitch their SSTO idea as a means of lowering the cost of access to space, a necessary requirement to make SDI feasible.

With Quayle's backing and funding from the SDIO (Strategic Defense Initiative Organization), in August 1990 a request for proposals to industry was issued for an SSTO vehicle. Of the six designs submitted, four were vertical takeoff and landing designs. SDIO issued $12 million contracts to McDonnell Douglas, Rockwell, Boeing and General Dynamics for further development of their VTOL SSTO designs. The second phase of the program consisted of building an "X" subscale demonstrator to prove VTOL capability and the building of a "Y" prototype vehicle. McDonnell Douglas won this phase of the competition with their "X" subscale demonstrator being 1/3 of the size of the prototype and designated DC-X or "Delta Clipper".

Powered by four Pratt and Whitney RL10 liquid fuel rocket engines, the DC-X wasn't meant to reach orbit but to validate the technologies for VTOL, rapid prototyping, and the ability to be operated with as small a ground crew as possible to reduce costs. On 18 August 1993 at White Sands Missile Range in New Mexico, the DC-X made its maiden flight with a support crew of seven (including astronaut Pete Conrad) housed in a converted trailer. The Delta Clipper flew for 59 seconds, reaching a very modest altitude of 46 meters. Later test flights going into 1995 showed the DC-X's ability to translate side to side and land, reaching a maximum altitude of 2500 meters before a hard landing on 7 July 1995 cracked the aeroshell of the Delta Clipper.

But with the end of the Cold War, SDIO's budget had been cut and the Delta Clipper was becoming a political hot potato in Washington. The program was then transferred to NASA's Reusable Launch Vehicle program. McDonnell Douglas took the opportunity to further lighten the DC-X, including a Russian-built aluminum-lithium liquid oxygen tank from Energia. With a significant weight reduction, the vehicle was redesignated DC-XA "Clipper Graham" in honor of Daniel Graham who had passed away in 1995. The DC-XA returned to White Sands for its resumed test program and made four flights in the summer of 1996. Between the second and third flights, the rocket was turned around in only 26 hours, a first for any rocket vehicle in history. On the fourth flight, one of the landing legs failed to deploy and the DC-XA tipped over and was destroyed in a fire.

NASA refused to release money to repair the DC-XA as it preferred from the beginning its own reusable SSTO idea, the Lockheed X-33 VentureStar. However, the VentureStar program was cancelled in 2001 amidst technical difficulties, but the DC-X may yet have the last laugh. Many of the DC-X engineers are now working with commercial space startup Blue Origin, started and led by Amazon.com founder Jeff Bezos. Blue Origin's spacecraft design, New Shepard, was tested in subscale format for the first time successfully in November 2006.

Source: Air & Space Smithsonian, August 2010, Vol. 25, No. 3. "Black Day at White Sands" by Preston Lerner, p66.

No comments:

Post a Comment