DC-X (Delta Clipper-Experimental)

The Ballistic Missile Defense Organization's Single Stage Rocket Technology (SSRT) program is chartered to demonstrate the practicality, reliability, operability and cost efficiency of a fully reusable, rapid turnaround single stage rocket, with the ultimate goal of aircraft-like operations of reusable launch vehicles (RLVs).

The program is focused on using existing technologies and systems to demonstrate the feasibility of building both suborbital and orbital RLVs which are able to fly into space, return to the launch site, and be serviced and ready for the next mission within three days. Such a suborbital RLV could potentially support many of BMDO's planned suborbital system tests and experiments.

As part of the program, BMDO has built an experimental suborbital launch vehicle, officially designated the SX-1 (Spaceplane Experimental), but known as the DC-X (Delta Clipper-Experimental). Flight testing was conducted in mid 1993 at White Sands Missile Range (WSMR) in New Mexico. The DC-X is designed to take off vertically and return to land in the same attitude. The DC-X is not designed as an operational vehicle capable of achieving orbital flight. Its purpose is to test the feasibility of both suborbital and orbital RLVs.

The SSRT program consisted of three phases. Phase I began in August 1990 and consisted of a $12 million design and risk reduction competition. At that time, the program was focused on multiple single stage-to-orbit concepts which were found to be potentially viable, including vertical take off and landing (VTOL), horizontal takeoff and landing (HTOL) and vertical takeoff and horizontal landing (VTHL) configurations.

Following completion of Phase I, a two-year $60 million Phase II contract was competitively awarded to McDonnell Douglas Aerospace, Huntington Beach, Calif., in August 1991.

The program was subsequently restructured and focused on building the DC-X and enabling suborbital RLVs for potential use by BMDO. The DC-X design emphasizes simplified ground and flight operations, vehicle maintenance, rapid turnaround, and operational characteristics that are also relevant to future orbital vehicles. For example, the highly automated control center for this system is manned by only three people: two for flight operations and one for ground operations and servicing.

Successful completion of the DC-X testing in mid 1993 was to form the basis for a Phase III "go/no go" decision by the Department of Defense to develop a follow-on Advanced Technology Demonstrator for support of flight tests and experiments. If a decision was made to proceed with Phase III, the program would have been transferred to another agency.

Since August 1991, BMDO and McDonnell Douglas proceeded with the design and fabrication of the DC-X as well as the planning activities for the vehicle system and subsystem ground and flight tests.

A systems ground test facility was activated at NASA's White Sands Test Facility (WSTF), and a launch and recovery site at WSMR. The completed DC-X vehicle is undergoing testing on a modified propulsion test stand at the WSTF prior to flight testing at WSMR. Maintenance and ground support techniques required for the flight test phase of the program will be tested, evaluated and refined at WSTF.

The aircraft-like flight test program, planned to start in mid 1993, will begin with low altitude hover flights, gradually increasing in altitude and duration, and lead to suborbital flights to approximately 18,000 feet.

Throughout the DC-X ground and flight test series, demonstration of low cost operations, vehicle operability, reliability, supportability and maintainability directly linked to follow-on operational vehicles are the prime factors for determining program success.

It first flew in August 1993 and had completed three flights when SDIO terminated the Delta Clipper program. After additional funding was procured, the vehicle flew five more flights before being returned to Huntington Beach for conversion into the DC-XA.

The Delta Clipper Experimental Advanced was a modified version of the DC-X. It had a lightweight 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. After the fourth flight, however, the DC-XA suffered severe damage and the program ended due to lack of funding.

During flight 4 on July 31, 1997, 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." Like any good experimental vehicle, the DC-XA flew until it was destroyed.

The prime contractor is McDonnell Douglas Aerospace, Huntington Beach, Calif. Subcontractors include the following: Douglas Aircraft, Long Beach, Calif.; McDonnell Douglas Aerospace East and McDonnell Douglas Research Laboratories, St. Louis, Mo.; Aerojet Propulsion Division, Sacramento, Calif.; Allied Signal Aerospace Co., Torrance, Calif.; Chicago Bridge and Iron Services, Inc., Oak Brook, Ill.; Deutsche Aerospace, Munich, Germany; General Connector, San Fernando, Calif; Harris Corp., Rockledge, Fla.; Honeywell Clearwater, Fla.; Integrated Systems, Santa Clara, Calif.; Martin Marietta, Denver, Colo.; Pratt and Whitney Government Engines and Space Division, West Palm Beach, Fla.; Process Fabrication, Inc., Santa Fe Springs, Calif.; Scaled Composites, Mojave, Calif.; and SpaceGuild, San Carlos, Calif. (Current as of April 1993)

DC-X Specifications

• Size 40 feet high, 13 1/3feet at base, conical shape.
• Weight Empty: 20,000lbs.
• With full load of propellants: 41,600 lbs.
• Propellants Liquid oxygen and liquid hydrogen.
• Propulsion Four RL-lOA5 rocket engines, each generating 13,500 lbs thrust. Each engine throttleable from 30% to lOO%. Each gimbals +/-8 degrees.
• Reaction Controls Four 440-lb thrust gaseous oxygen, gaseous hydrogen thrusters.
• Guidance, Navigation and Control Avionics
• Advanced 32 bit, 4.5 mips computer.
• F-15 Navigation System with ring laser gyros.
• F/A-18 accelerometer and rate gyro package.
• Global Positioning Satellite P(Y) code receiver.
• Digital data telemetry system.
• Radar altimeter.
• Hydraulic System
• Standard hydraulic aircraft-type system to drive vehicle's four aerodynamic flaps and eight engine gimbal actuators (two per engine).
• Construction MaterialsAeroshell and base heat shield: Graphite Epoxy composite with special silicone-based thermal protection coating.
• Main propellant tanks: 2219 alloy aluminum
• Main structural supports: aluminum
• Landing gear: steel and titanium