Type: lightweight Single Stage to Orbit (SSTO) demonstrator
Powerplant: 4 x United Technology/P&W RL10A-5 rocket engines,
Reaction controls: 4 x 440-lb thrust gaseous oxygen thrusters
First launch: 18 August 1993
In 1991 Scaled Composites was selected by McDonnell Douglas Aerospace for the SDIO Single Stage to Orbit (SSTO) demonstrator program. MDA proposed a lightweight one-third scale proof of concept (POC) demonstrator vehicle known as the Delta Clipper- Experimental, or DC-X Delta Clipper, conceived as a reuseable flight test vehicle to validate the rocket-powered vertical take-off and landing (VTOL) concept as well as "airplane like" serviceability, small ground crew, rapid turn-around, etc. It was initially funded by the Ballistic Missile Defense Organization (a.k.a. SDIO), and was built by Scaled Composites, working as a sub-contractor for McDonnell Douglas.
Scaled was tasked with building the structural aeroshell and aerodynamic control surfaces. The DC-X aeroshell has a height of 62 feet and a maximum width of 15 feet at the base. Four large hydraulically-actuated flap sections are incorporated into the aeroshell for aerodynamic control during reentry and landing. A removable nose cone houses the emergency parachute recovery system. Also incorporated into the aeroshell was a "finger ring" used to restrain and stabilize the fuel tanks during temperature induced expansion and contraction cycles. The retractable landing gear are mounted to the aeroshell structure and all landing gear loads are reacted through the aeroshell. This structural philosophy would benefit the overall vehicle both in weight and complexity.
Scaled employed low cost tooling methods for fabrication of the DC-X structure. A 1/4 fuselage section male plug was fabricated from the loft lines supplied by MDA. A single female tool was fabricated from the male plug, and the four graphite/epoxy sandwich panel sections were fabricated in the female tool. The sections were installed in an assembly fixture and bonded together using in-place graphite/epoxy laminates. The landing gear receptacles, flap mechanisms and servos were then added. The materials and structural design of the sandwich panel proved to be capable of maintaining structural integrity under the extreme conditions of the operating environment.
In order to deliver the aeroshell structure in a timely fashion, Scaled did not delay the aeroshell fabrication schedule while waiting for the resolution of sub-systems integration issues. Scaled sent a structures team to MDA's facility to support the final installation of the subsystems, which were often performed as minor repairs to the aeroshell structure. This was made possible because the vehicle was not an autoclaved or high-temperature-cured structure; the low-temperature curing and simple manufacturing process allowed this prototype flexibility. Despite all the post fabrication modifications, Scaled was able to build the complete aeroshell structure for 300 lb (10%) less than the weight goal. This weight reduction was instrumental in helping the DC-X vehicle stay within its weight budget.
Scaled was responsible for the emergency parachute recovery system. Scaled selected a parachute vendor and worked closely with that vendor to insure a timely and cost effective response to the program schedule. Scaled fabricated the necessary parachute test/qualification components and supervised all the qualification testing for the recovery system. Scaled's team was also dispatched to the White Sands launch facility to support additional modifications and repairs to the aeroshell structure during the test program.
The single DC-X had eight test flights spanning August 1993 to July 1995, two of which, taking place in June 12 and July 7, were for the U.S. Air Force. The prototype was then transferred to NASA for refurbishment using NASA funding, and renamed the Delta Clipper-Experimental Advanced, also known as the DC-XA Clipper Graham (after an early proponent of the program). The DC-XA demonstrated new light weight components such as a graphite-epoxy liquid hydrogen tank and an advanced graphite/aluminum honeycomb intertank built by McDonnell Douglas; an aluminum-lithium liquid oxygen tank built by Energia; and an improved reaction control system from Aerojet. These improvements reduced dry vehicle mass by 620 kilograms.
The DC-XA was operated by NASA and the Department of Defense under the Reusable Launch Vehicle program. The flight vehicle was tested at White Sands during the summer of 1996, and demonstrated a 26-hour turnaround between its second and third flights, a first for any rocket. During flight 4 on July 31, 1996, however, the DC-XA suffered severe damage when landing strut #2 failed to extend, causing the unbalanced vehicle to tip over on its landing pad. The LOX tank exploded and there were indications of secondary explosions in the LH2 tank as well. The ensuing fire damaged large sections of the DC-XA. An investigation board was convened to determine the cause of the accident, which was later determined to be an unconnected helium pressurant line that supplied hydraulic pressure to extend the landing strut.
The conclusion of the program was summed up well by the Reusable Launch Vehicle program director, Gary Payton. He stated, "The way the budget is now, we cannot afford to rebuild the Clipper Graham and will not be able to continue with that takeoff and landing technique, so we will declare victory with the DC-XA." And so the program ended due to lack of funding. Like any good experimental vehicle, the DC-XA flew until it was destroyed, but this little rocket taught a lot about the right way to travel to the heavens. Many of the technologies tested in the DC-X program were to be applied to the X-33 project to demonstrate "single stage-to-orbit" launch capability, but this too was canceled.
Crew/passengers: none (unmanned)