The DC-X, short for Delta Clipper or Delta Clipper Experimental, was an uncrewed prototype of a
reusable single-stage-to-orbit
A single-stage-to-orbit (SSTO) vehicle reaches orbit from the surface of a body using only propellants and fluids and without expending tanks, engines, or other major hardware. The term usually, but not exclusively, refers to reusable vehicles ...
launch vehicle
A launch vehicle or carrier rocket is a rocket designed to carry a payload ( spacecraft or satellites) from the Earth's surface to outer space. Most launch vehicles operate from a launch pads, supported by a launch control center and sys ...
built by
McDonnell Douglas
McDonnell Douglas was a major American aerospace manufacturing corporation and defense contractor, formed by the merger of McDonnell Aircraft and the Douglas Aircraft Company in 1967. Between then and its own merger with Boeing in 1997, it ...
in conjunction with the
United States Department of Defense
The United States Department of Defense (DoD, USDOD or DOD) is an executive branch department of the federal government charged with coordinating and supervising all agencies and functions of the government directly related to national sec ...
's
Strategic Defense Initiative Organization
The Strategic Defense Initiative (SDI), derisively nicknamed the "''Star Wars'' program", was a proposed missile defense system intended to protect the United States from attack by ballistic strategic nuclear weapons (intercontinental ballistic ...
(SDIO) from 1991 to 1993. Starting 1994 until 1995, testing continued through funding of the US civil space agency
NASA
The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research.
NASA was established in 1958, succeedin ...
.
In 1996, the DC-X technology was completely transferred to NASA, which upgraded the design for improved performance to create the DC-XA.
Background
According to writer
Jerry Pournelle
Jerry Eugene Pournelle (; August 7, 1933 – September 8, 2017) was an American scientist in the area of operations research and human factors research, a science fiction writer, essayist, journalist, and one of the first bloggers. In the 1960s ...
: "DC-X was conceived in my living room and sold to
National Space Council Chairman
Dan Quayle
James Danforth Quayle (; born February 4, 1947) is an American politician who served as the 44th vice president of the United States from 1989 to 1993 under President George H. W. Bush. A member of the Republican Party, Quayle served as a U.S. ...
by General
Graham
Graham and Graeme may refer to:
People
* Graham (given name), an English-language given name
* Graham (surname), an English-language surname
* Graeme (surname), an English-language surname
* Graham (musician) (born 1979), Burmese singer
* Clan ...
,
Max Hunter
Max Franklin Hunter (July 2, 1921November 6, 1999) was an American folklorist who, while working as a travelling salesman, compiled an archive of nearly 1,600 folk songs from the Ozarks region of the southern United States between 1956 and 1 ...
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 then 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 successfully "sold" the idea to SDIO by noting that any
space-based weapon
Space weapons are weapons used in space warfare. They include weapons that can attack space systems in orbit (i.e. anti-satellite weapons), attack targets on the earth from space or disable missiles travelling through space. In the course of the ...
s system would need to be serviced by a spacecraft that was far more reliable than the
Space Shuttle
The Space Shuttle is a retired, partially reusable low Earth orbital spacecraft system operated from 1981 to 2011 by the U.S. National Aeronautics and Space Administration (NASA) as part of the Space Shuttle program. Its official program n ...
, and offer lower
launch cost
Space launch market competition is the manifestation of market forces in the launch service provider business. In particular it is the trend of competitive dynamics among payload transport capabilities at diverse prices having a greater influe ...
s 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 first for
sub-orbital
A sub-orbital spaceflight is a spaceflight in which the spacecraft reaches outer space, but its trajectory intersects the atmosphere or surface of the gravitating body from which it was launched, so that it will not complete one orbital re ...
and then 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'' being the US Air Force designation for "experimental". This would be followed by the "DC-Y", with ''Y'' being the USAF designation for pre-production test aircraft and prototypes (e.g.
YF-16). Finally the production version would be known as the "DC-1". The name "Delta Clipper" was chosen to result in the acronym "DC" to draw a connection with the Douglas "DC Series" of airliners, beginning with the
Douglas DC-1
The Douglas DC-1 was the first model of the famous American DC (Douglas Commercial) commercial transport aircraft series. Although only one example of the DC-1 was produced, the design was the basis for the DC-2 and DC-3, the latter of which b ...
.
The vehicle is inspired by the designs of McDonnell Douglas engineer
Philip Bono
Philip Bono (13 January 1921 – 23 May 1993) was a Douglas Aircraft Company engineer. He was a pioneer of reusable vertical landing single-stage to orbit launch vehicles. As a visionary designer, he is credited with inventing the first vers ...
, who saw single stage to orbit VTOL lifters as the future of space travel. The Delta Clipper was very similar to Bono's
SASSTO vehicle from 1967. Bono died less than three months before the DC-X's first test flight.
SDIO requirement
SDIO wanted a "suborbital, recoverable rocket (SRR) capable of lifting up to 3,000 pounds (1361 kg) of payload to an altitude of 1.5 million feet (457 km); returning to the launch site for a precise soft landing; with the capability to launch for another mission within three to seven days".
Specification
DC-X Specifications:
*12 m high, 4.1 m diameter at base, conical shape
*Empty mass: 9100 kg. Fuelled mass: With full load of propellants:18,900 kg
*Propellants: Liquid oxygen and liquid hydrogen
*Propulsion: Four
RL10
The RL10 is a liquid-fuel cryogenic rocket engine built in the United States by Aerojet Rocketdyne that burns cryogenic liquid hydrogen and liquid oxygen propellants. Modern versions produce up to of thrust per engine in vacuum. Three RL ...
A5 rocket engines, each generating 6,100 kgf thrust. Each engine throttleable from 30% to 100%. 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
The McDonnell Douglas F-15 Eagle is an American twin-engine, all-weather tactical fighter aircraft designed by McDonnell Douglas (now part of Boeing). Following reviews of proposals, the United States Air Force selected McDonnell Douglas's ...
Navigation System with
ring laser gyros.
F/A-18
The McDonnell Douglas F/A-18 Hornet is an all-weather, twin-engine, supersonic, carrier-capable, multirole combat aircraft, designed as both a fighter and attack aircraft (hence the F/A designation). Designed by McDonnell Douglas (now part ...
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 five aerodynamic flaps and eight engine gimbal actuators (two per engine).
*Construction Materials: Aeroshell and base heat shield: graphite epoxy composite with special silicon-based thermal protection coating; Main propellant tanks: 2219 alloy aluminium; Main structural supports: aluminium; Landing gear: steel and titanium
Design
Built as a one-third-size scale prototype, the DC-X was never designed to achieve orbital altitudes or velocity, but instead to demonstrate the concept of
vertical take off and landing
A vertical take-off and landing (VTOL) aircraft is one that can take off and land vertically without relying on a runway. This classification can include a variety of types of aircraft including helicopters as well as thrust-vectoring fixed-win ...
. The vertical take off and landing concept was popular in science fiction films from the 1950s (''
Rocketship X-M
''Rocketship X-M'' (a.k.a. ''Expedition Moon'' and originally ''Rocketship Expedition Moon'') is a 1950 American black-and-white science fiction film from Lippert Pictures, the first outer space adventure of the post-World War II era. The film wa ...
'', ''
Destination Moon'', and others), but not seen in real world designs of space vehicles. It would take off vertically like standard
rocket
A rocket (from it, rocchetto, , bobbin/spool) is a vehicle that uses jet propulsion to accelerate without using the surrounding air. A rocket engine produces thrust by reaction to exhaust expelled at high speed. Rocket engines work entirely fr ...
s, but also land vertically with the nose up. This design used
attitude control
Attitude control is the process of controlling the orientation of an aerospace vehicle with respect to an inertial frame of reference or another entity such as the celestial sphere, certain fields, and nearby objects, etc.
Controlling vehicle ...
thrusters and
retro rocket
A retrorocket (short for ''retrograde rocket'') is a rocket engine providing thrust opposing the motion of a vehicle, thereby causing it to decelerate. They have mostly been used in spacecraft, with more limited use in short-runway aircraft land ...
s to control the descent, allowing the craft to begin
atmospheric entry
Atmospheric entry is the movement of an object from outer space into and through the gases of an atmosphere of a planet, dwarf planet, or natural satellite. There are two main types of atmospheric entry: ''uncontrolled entry'', such as the en ...
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
A low Earth orbit (LEO) is an orbit around Earth with a period of 128 minutes or less (making at least 11.25 orbits per day) and an eccentricity less than 0.25. Most of the artificial objects in outer space are in LEO, with an altitude never mor ...
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 . If the spacecraft is launched to the east this does not present a problem, but for the
polar orbit
A polar orbit is one in which a satellite passes above or nearly above both poles of the body being orbited (usually a planet such as the Earth, but possibly another body such as the Moon or Sun) on each revolution. It has an inclination of about ...
s 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 in its control center (two for flight operations and one for ground support).
Flight testing
![DC-XA first landing](https://upload.wikimedia.org/wikipedia/commons/7/70/DC-XA_first_landing.jpg)
Construction of the DC-X started in 1991 at McDonnell Douglas' Huntington Beach facility.
The aeroshell was custom-constructed by
Scaled Composites
Scaled Composites (often called simply Scaled) is an American aerospace company founded by Burt Rutan and currently owned by Northrop Grumman. It is located at the Mojave Air and Space Port in Mojave, California, United States. Founded to deve ...
, but the majority of the spacecraft was built from
commercial off-the-shelf parts, including the engines and flight control systems.
The DC-X first flew, for 59 seconds, on 18 August 1993;
[ it was claimed that it was the first time a rocket had landed vertically on Earth. 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; in addition the program was considered far-fetched by detractors. Apollo astronaut ]Pete Conrad
Charles "Pete" Conrad Jr. (June 2, 1930 – July 8, 1999) was an American NASA astronaut, aeronautical engineer, naval officer and aviator, and test pilot, and commanded the Apollo 12 space mission, on which he became the third person to ...
was at the ground-based controls for some flights. These tests were conducted at the White Sands Missile Range in New Mexico.
Further funding was provided by NASA and the Advanced Research Projects Agency (ARPA) however, and the test program restarted on 20 June 1994 with a 136-second flight. The next flight, 27 June 1994, suffered a minor inflight explosion, but the craft successfully executed an abort and autoland. Testing restarted 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, and there were no funds for the needed repairs. The altitude record for the DC-X was 2,500 m, set during its last flight before being upgrading to the DC-XA, on 7 July 1995.
DC-XA
NASA agreed to take on the program after the last DC-X flight in 1995. 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) aluminium-lithium alloy tank from Russia, and the hydrogen tank by a graphite-epoxy composite design. 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, and 142 seconds of flight time. Also, during the 8 June flight, the vehicle executed the first planned rotation maneuver for a rocket, where it transitioned from nose first forward flight to controlled backwards flight. At the apex of this rotation maneuver, DC-XA slowed itself by rotating to a backwards orientation, and flew backwards, base first, with its nose 10 degrees below the horizon, under control of the main engines. It then exercised a controlled rotation to a nose up attitude, and executed a powered soft landing. This maneuver showed that a single stage to orbit vehicle could efficiently return from orbit using aerodynamic braking in a forward attitude, and then rotate to a base first powered landing at a spaceport.
Its next flight, on 31 July 1996, proved to be its last. The launch and flight portion of the this mission was flawless, however, after slowing to a perfect touchdown, only 3 of the 4 landing struts extended. The vehicle could not balance on 3 struts, and slowly fell sideways on the landing pad. When the side of the vehicle struck the concrete pad, the main liquid oxygen tank cracked open and leaked LOX onto the pad. This LOX contacted a small amount of glowing material on the base heat shield, and started a fire. Post flight inspection of the landing struts revealed that the pneumatic nitrogen actuation line to the failed strut was disconnected. This line was normally disconnected from the strut during pre-flight testing, when each strut was extended and retracted by a ground cart. 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
The Lockheed Martin X-33 was a proposed uncrewed, sub-scale technology demonstrator suborbital spaceplane that was developed for a period in the 1990s. The X-33 was a technology demonstrator for the VentureStar orbital spaceplane, which was plan ...
/VentureStar
VentureStar was a single-stage-to-orbit reusable launch system proposed by Lockheed Martin and funded by the U.S. government. The goal was to replace the Space Shuttle by developing a re-usable spaceplane that could launch satellites into orbit ...
project. Pete Conrad priced a new DC-X at $50 million, cheap by NASA standards, but NASA decided not to rebuild the craft in light of budget constraints. Instead, NASA focused development on the Lockheed Martin VentureStar
VentureStar was a single-stage-to-orbit reusable launch system proposed by Lockheed Martin and funded by the U.S. government. The goal was to replace the Space Shuttle by developing a re-usable spaceplane that could launch satellites into orbit ...
which it felt answered some criticisms of the DC-X, specifically the airplane-like landing of the VentureStar, which many NASA engineers preferred over the vertical landing of the DC-X. Just a few years later, the repeated failure of the Venturestar project, especially the composite LH2 (liquid hydrogen
Liquid hydrogen (LH2 or LH2) is the liquid state of the element hydrogen. Hydrogen is found naturally in the molecular H2 form.
To exist as a liquid, H2 must be cooled below its critical point of 33 K. However, for it to be in a fully l ...
) tank, led to program cancellation.
Program cost
The original DC-X was built in 21 months for a cost of $60 million. This is equivalent to $ in present-day terms.
Future
Several engineers who worked on the DC-X were hired by Blue Origin, and their New Shepard
New Shepard is a fully reusable suborbital launch vehicle developed by Blue Origin for space tourism. The vehicle is named after Alan Shepard, the first American astronaut in space. The vehicle is capable of vertical takeoff and vertical lan ...
vehicle was inspired by the DC-X design. The DC-X provided inspiration for many elements of Armadillo Aerospace
Armadillo Aerospace was an aerospace startup company based in Mesquite, Texas. Its initial goal was to build a crewed suborbital spacecraft capable of space tourism, and it had also stated long-term ambitions of orbital spaceflight. The company ...
's,[ ]Masten Space Systems
Masten Space Systems was an aerospace manufacturer startup company in Mojave, California (formerly in Santa Clara, California) that was developing a line of vertical takeoff, vertical landing (VTVL) rockets, initially for uncrewed research sub- ...
's,[ and TGV Rockets's spacecraft designs.
Some NASA engineers have noted that the DC-X could provide a solution for a crewed ]Mars
Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury. In the English language, Mars is named for the Roman god of war. Mars is a terrestrial planet with a thin at ...
lander. Had a DC-type craft been developed that operated as an SSTO in Earth's gravity well
The Hill sphere of an astronomical body is the region in which it dominates the attraction of satellites. To be retained by a planet, a moon must have an orbit that lies within the planet's Hill sphere. That moon would, in turn, have a Hil ...
, 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 people proposed design changes include using an oxidizer/fuel combination that does not require the relatively extensive ground support required for the liquid hydrogen
Liquid hydrogen (LH2 or LH2) is the liquid state of the element hydrogen. Hydrogen is found naturally in the molecular H2 form.
To exist as a liquid, H2 must be cooled below its critical point of 33 K. However, for it to be in a fully l ...
and liquid oxygen
Liquid oxygen—abbreviated LOx, LOX or Lox in the aerospace, submarine and gas industries—is the liquid form of molecular oxygen. It was used as the oxidizer in the first liquid-fueled rocket invented in 1926 by Robert H. Goddard, an app ...
that DC-X utilized, and adding a fifth leg for increased stability during and after landing.
See also
*
*
*
*
* SpaceX reusable launch system development program
SpaceX is privately funding the development of orbital launch systems that can be reused many times, in a manner similar to the reusability of aircraft. SpaceX has been developing the technologies over several years to facilitate full and ...
*
* to continue developing ALHAT and Quad landers
*
*
References
External links
DC-X page on Astronautix.com
an
About the DCX
– includes a first-person account and video
– explains X programs and SSTO
– selling the DC-X to Dan Quayle
from hobbyspace.com
Environmental Assessment (for) Single Stage Rocket Technology DC-X Test Program
June 1992 147 pages
{{DEFAULTSORT:Mcdonnell Douglas Dc-X
DC-X
Single-stage-to-orbit
Former proposed space launch system concepts
VTVL rockets
Scaled Composites
DC-X
Cancelled spacecraft
Cancelled space launch vehicles
Aircraft first flown in 1993