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McDonnell Douglas DC-X

McDonnell Douglas DC-X

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The DC-X, short for Delta Clipper or Delta Clipper Experimental, was an unmanned prototype of a reusable single stage to orbit launch vehicle built by McDonnell Douglas
McDonnell Douglas
McDonnell Douglas was a major American aerospace manufacturer and defense contractor, producing a number of famous commercial and military aircraft. It formed from a merger of McDonnell Aircraft and Douglas Aircraft in 1967. McDonnell Douglas was based at Lambert-St. Louis International Airport...

 in conjunction with the United States Department of Defense
United States Department of Defense
The United States Department of Defense is the U.S...

's Strategic Defense Initiative Organization (SDIO) from 1991 to 1993. After that period the DC-X technology was transferred to the US civil space agency NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...

, which upgraded the design for improved performance to create the DC-XA.


According to writer Jerry Pournelle
Jerry Pournelle
Jerry Eugene Pournelle is an American science fiction writer, essayist and journalist who contributed for many years to the computer magazine Byte and has since 1998 been maintaining his own website/blog....

: "DC-X was conceived in my living room and sold to National Space Council
National Space Council
The National Space Council was a body within the Executive Office of the President of the United States, which existed from 1989 to 1993 during the administration of George H.W. Bush...

 Chairman Dan Quayle
Dan Quayle
James Danforth "Dan" Quayle served as the 44th Vice President of the United States, serving with President George H. W. Bush . He served as a U.S. Representative and U.S. Senator from the state of Indiana....

 by General Graham
Daniel O. Graham
Daniel O. Graham was a U.S. Army officer. Graham was born in Portland, Oregon and grew up in Medford. He attended college at the United States Military Academy at West Point, the Army's Command and General Staff College, and graduated in 1946. He also attended the U.S...

, Max Hunter
Maxwell Hunter
Maxwell White Hunter II was a prominent American aerospace engineer. He worked on the design of the Douglas B-42 and B-43 bombers, the Honest John, Nike-Ajax, and Nike-Zeus missiles, the Thor IRBM, and on parts of the Strategic Defense Initiative.In later years he worked on space-launch vehicles...

 and me." According to Max Hunter, however, he had tried hard to convince Lockheed-Martin of the concept's value for several years before he retired. Hunter had written a paper in 1985 entitled "The Opportunity", detailing the concept of a Single-Stage-To-Orbit spacecraft built with low-cost "off-the-shelf" commercial parts and currently-available technology, but Lockheed-Martin was not interested enough to fund such a program themselves.

On February 15, 1989, Pournelle, Graham and Hunter were able to procure a meeting with Vice-President Dan Quayle. They "sold" the idea to SDIO by noting that any space-based weapons system would need to be serviced by a spacecraft that was far more reliable than the Space Shuttle
Space Shuttle
The Space Shuttle was a manned orbital rocket and spacecraft system operated by NASA on 135 missions from 1981 to 2011. The system combined rocket launch, orbital spacecraft, and re-entry spaceplane with modular add-ons...

, and offer lower launch costs and have much better turnaround times.

Given the uncertainties of the design, the basic plan was to produce a deliberately simple test vehicle and to "fly a little, break a little" in order to gain experience with fully reusable quick-turnaround spacecraft. As experience was gained with the vehicle, a larger prototype would be built for sub-orbital and orbital tests. Finally a commercially acceptable vehicle would be developed from these prototypes. In keeping with general aircraft terminology, they proposed the small prototype should be called the DC-X, X for "experimental". This would be followed by the "DC-Y", Y referring to pre-run prototypes of otherwise service-ready aircraft. Finally the production version would be known as the "DC-1". The name "Delta Clipper" was chosen deliberately to result in the "DC" acronym, an homage to the famous DC-3 aircraft, which many credit for making passenger air travel affordable.


The DC-X was never designed to achieve orbital altitudes or velocity, but instead to demonstrate the concept of vertical take off and landing. The vertical take off and landing concept was popular in science fiction films from the 1950s (Rocketship X-M
Rocketship X-M
Rocketship X-M was the second of the American science fiction feature films of the space adventure genre begun in the post-war era, in 1950...

, Destination Moon
Destination Moon (film)
Destination Moon is an American science fiction feature film produced by George Pal, who later produced When Worlds Collide, The War of the Worlds, and The Time Machine. Pal commissioned the script by James O'Hanlon and Rip Van Ronkel...

, and others), but not seen in real world designs. It would take off vertically like standard rocket
A rocket is a missile, spacecraft, aircraft or other vehicle which obtains thrust from a rocket engine. In all rockets, the exhaust is formed entirely from propellants carried within the rocket before use. Rocket engines work by action and reaction...

s, but also land vertically with the nose up. This design used attitude control thrusters and retro rockets to control the descent, allowing the craft to begin reentry nose-first, but then roll around and touch down on landing struts at its base. The craft could be refueled where it landed, and take off again from exactly the same position — a trait that allowed unprecedented turnaround times.

In theory a base-first re-entry profile would be easier to arrange. The base of the craft would already need some level of heat protection to survive the engine exhaust, so adding more protection would be easy enough. More importantly, the base of the craft is much larger than the nose area, leading to lower peak temperatures as the heat load is spread out over a larger area. Finally, this profile would not require the spacecraft to "flip around" for landing.

The military role made this infeasible, however. One desired safety requirement for any spacecraft is the ability to "abort once around", that is, to return for a landing after a single orbit. Since a typical low earth orbit
Low Earth orbit
A low Earth orbit is generally defined as an orbit within the locus extending from the Earth’s surface up to an altitude of 2,000 km...

 takes about 90 to 120 minutes, the Earth will rotate to the east about 20 to 30 degrees in that time; or for a launch from the southern United States, about 1500 miles (2,414 km). If the spacecraft is launched to the east this does not present a problem, but for the polar orbits required of military spacecraft, when the orbit is complete the spacecraft overflies a point far to the west of the launch site. In order to land back at the launch site, the craft needs to have considerable cross-range maneuverability, something that is difficult to arrange with a large smooth surface. The Delta Clipper design thus used a nose-first re-entry with flat sides on the fuselage and large control flaps to provide the needed cross range capability. Experiments with the control of such a re-entry profile had never been tried, and were a major focus of the project.

Another focus of the DC-X project was minimized maintenance and ground support. To this end, the craft was highly automated and required only three people to man its control center (two for flight operations and one for ground support). In some ways the DC-X project was less about technology research than operations.

Flight testing

Construction of the DC-X started in 1991 at McDonnell Douglas' Huntington Beach facility. The aeroshell was custom-constructed by Scaled Composites
Scaled Composites
Scaled Composites is an aerospace company founded by Burt Rutan and currently owned by Northrop Grumman that is located at the Mojave Spaceport, Mojave, California, United States...

, but the majority of the spacecraft was built from "off the shelf" parts, including the engines and flight control systems.

The DC-X first flew, for 59 seconds, on 18 August 1993. It flew two more flights 11 September and 30 September, when funding ran out as a side effect of the winding down of the SDIO program. Apollo astronaut Pete Conrad
Pete Conrad
Charles "Pete" Conrad, Jr. was an American naval officer, astronaut and engineer, and the third person to walk on the Moon during the Apollo 12 mission. He set an eight-day space endurance record along with command pilot Gordon Cooper on the Gemini 5 mission, and commanded the Gemini 11 mission...

 was at the ground-based controls for some flights.

Further funding was forthcoming, however, and the test program re-started on 20 June 1994 with a 136 second flight. The next flight, 27 June 1994, suffered an inflight (minor) explosion, but the craft successfully executed an abort and autoland. Testing re-started after this damage was fixed, and three more flights were carried out on 16 May 1995, 12 June, and 7 July. On the last flight a hard landing cracked the aeroshell. By this point funding for the program had already been cut, as a side effect of the winding down of the SDIO program, and there were no funds for the needed repairs.


NASA agreed to take on the program at this point. In contrast to the original concept of the DC-X demonstrator, NASA applied a series of major upgrades to test new technologies. In particular, the oxygen tank was replaced by a lightweight (alloy 1460 equivalent of alloy 2219) Al-Li tank from Russia
Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...

, and the fuel tank by a newer composite design. According to Bob Hartunian (former McDonnell Douglas and Boeing cryo-tank specialist), the Russian-made tank was poor quality, had "16-inch/40.6-cm long weld defects, and there were other issues that, according to U.S. standards, would prevent it from flying."

The control system was likewise improved. The upgraded vehicle was called the DC-XA, renamed the Clipper Advanced/Clipper Graham, and resumed flight in 1996.

The first flight of the DC-XA test vehicle was made on 18 May 1996 and resulted in a minor fire when the deliberate "slow landing" resulted in overheating of the aeroshell. The damage was quickly repaired and the vehicle flew two more times on 7 and 8 June, a 26-hour turnaround. On the second of these flights the vehicle set its altitude and duration records, 3,140 meters and 142 seconds of flight time. Its next flight, on 7 July, proved to be its last. During testing, one of the LOX
Lox is salmon fillet that has been cured. In its most popular form, it is thinly sliced—less than in thickness—and, typically, served on a bagel, often with cream cheese, onion, tomato, cucumber and capers...

 tanks had been cracked. When a landing strut failed to extend due to a disconnected hydraulic line, the DC-XA fell over and the tank leaked. Normally the structural damage from such a fall would constitute only a setback, but the LOX from the leaking tank fed a fire which severely burned the DC-XA, causing such extensive damage that repairs were impractical.

In a post-accident report, NASA's Brand Commission blamed the accident on a burnt-out field crew who had been operating under on-again/off-again funding and constant threats of outright cancellation. The crew, many of them originally from the SDIO program, were also highly critical of NASA's "chilling" effect on the program, and the masses of paperwork NASA demanded as part of the testing regimen.

NASA had taken on the project grudgingly after having been "shamed" by its very public success under the direction of the SDIO. Its continued success was cause for considerable political in-fighting within NASA due to it competing with their "home grown" Lockheed Martin X-33
Lockheed Martin X-33
The Lockheed Martin X-33 was an unmanned, sub-scale technology demonstrator suborbital spaceplane developed in the 1990s under the U.S. government-funded Space Launch Initiative program. The X-33 was a technology demonstrator for the VentureStar orbital spaceplane, which was planned to be a...

VentureStar was a proposed spaceplane design for a single-stage-to-orbit reusable launch system by Lockheed Martin. The program's primary goal as a United States federally funded program was to develop a reusable unmanned spaceplane for launching satellites into orbit at a fraction of the cost of...

 project. Pete Conrad priced a new DC-X at 50 million dollars, but NASA decided not to rebuild the craft in light of the budget constraints.

Rather, NASA focused development on the Lockheed Martin
Lockheed Martin
Lockheed Martin is an American global aerospace, defense, security, and advanced technology company with worldwide interests. It was formed by the merger of Lockheed Corporation with Martin Marietta in March 1995. It is headquartered in Bethesda, Maryland, in the Washington Metropolitan Area....

VentureStar was a proposed spaceplane design for a single-stage-to-orbit reusable launch system by Lockheed Martin. The program's primary goal as a United States federally funded program was to develop a reusable unmanned spaceplane for launching satellites into orbit at a fraction of the cost of...

 which it felt answered some criticisms of the DC-X; specifically the requirement that many NASA engineers preferred the airplane-like landing of the VentureStar over the vertical landing of the DC-X.

The future of the DC-X

Several engineers who worked on the DC-X have since been hired by Blue Origin
Blue Origin
Blue Origin is a privately funded aerospace company set up by Amazon.com founder Jeff Bezos. The company was awarded $3.7 million in funding in 2009 by NASA via a Space Act Agreement under the Commercial Crew Development program for development of concepts and technologies to support future human...

, and their Blue Origin New Shepard
Blue Origin New Shepard
The Blue Origin New Shepard reusable launch vehicle is a vertical-takeoff, vertical-landing , suborbital manned rocket that is being developed by Blue Origin, a company owned by Amazon.com founder and businessman Jeff Bezos, as a commercial system for suborbital space tourism.The New Shepard makes...

 vehicle is based on the DC-X design. Blue Origin does not require the high cross range capabilities, and therefore uses a base-first re-entry profile. Also, the DC-X provided inspiration for many elements of Armadillo Aerospace
Armadillo Aerospace
Armadillo Aerospace is an aerospace startup company based in Mesquite, Texas. Its initial goal is to build a manned suborbital spacecraft capable of space tourism, but it has stated long-term ambitions of orbital spaceflight. The company was founded by John Carmack.On October 24, 2008, Armadillo...

's, Masten Space Systems
Masten Space Systems
Masten Space Systems is an aerospace startup company in Mojave, California that is developing a line of vertical takeoff, vertical landing spacecraft, initially for unmanned suborbital research flights and eventually intended to support unmanned orbital launches.- Overview :Masten Space Systems...

's, and TGV Rockets's spacecraft designs.

Returning the DC-X design to NASA's active research portfolio has been considered for some time now. Some NASA engineers believe that the DC-X could provide a solution for a manned Mars
Mars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance...

 lander. Had a DC-type craft been developed that operated as an SSTO in Earth's gravity well
Gravity well
A gravity well or gravitational well is a conceptual model of the gravitational field surrounding a body in space. The more massive the body the deeper and more extensive the gravity well associated with it. The Sun has a far-reaching and deep gravity well. Asteroids and small moons have much...

, even if with only a minimum 4-6 crew capacity, variants of it might prove extremely capable for both Mars and Moon missions. Such a variant's basic operation would have to be "reversed"; from taking off and then landing, to landing first then taking off. Yet, if this could be accomplished on Earth, the weaker gravity found at both Mars and the Moon would make for dramatically greater payload capabilities, particularly at the latter destination.

Some proposed design changes include using an oxidizer/fuel combination that does not require the relatively extensive ground support required for the liquid hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...

 and liquid oxygen
Liquid oxygen
Liquid oxygen — abbreviated LOx, LOX or Lox in the aerospace, submarine and gas industries — is one of the physical forms of elemental oxygen.-Physical properties:...

 that DC-X utilized, and adding a fifth leg for increased stability during and after landing. Recently, NASA's Centennial Challenges program has announced a suborbital Lunar Lander Challenge which is a prize for the first team to build a VTVL
Vertical takeoff, vertical landing is a form of takeoff and landing using rockets . Multiple VTVL craft have flown. , at least five VTVL rocket vehicles are currently under development at four different aerospace companies...

 rocket that has the same delta-v
In astrodynamics a Δv or delta-v is a scalar which takes units of speed. It is a measure of the amount of "effort" that is needed to change from one trajectory to another by making an orbital maneuver....

 as a vehicle capable of landing on the moon and operate it under competition conditions.

See also

  • Lockheed Martin X-33
    Lockheed Martin X-33
    The Lockheed Martin X-33 was an unmanned, sub-scale technology demonstrator suborbital spaceplane developed in the 1990s under the U.S. government-funded Space Launch Initiative program. The X-33 was a technology demonstrator for the VentureStar orbital spaceplane, which was planned to be a...

  • Rockwell X-30
    Rockwell X-30
    -See also:-References: 2. -External links:*...

    HOTOL, for Horizontal Take-Off and Landing, was a British air-breathing space shuttle effort by Rolls Royce and British Aerospace.Designed as a single-stage-to-orbit reusable winged launch vehicle, it was to be fitted with a unique air-breathing engine, the RB545 called the Swallow, to be...

  • VTVL
    Vertical takeoff, vertical landing is a form of takeoff and landing using rockets . Multiple VTVL craft have flown. , at least five VTVL rocket vehicles are currently under development at four different aerospace companies...

  • Quad (rocket)
    Quad (rocket)
    In rocketry, the Armadillo aerospace Quad vehicle is a computer controlled VTVL rocket that is used to compete in the Lunar Lander Challenge.-General description:...

  • Zarya

External links