page_title: Lockheed Martin X-33
section_title: Design and development
hierarchical_section_title: Lockheed Martin X-33 / Design and development
caption_attribution_description: English: The F-15B in flight with the X-33 Thermal protection System (TPS) fixture mounted under its fuselage.
context_page_description: The Lockheed Martin X-33 was an uncrewed, 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 next-generation, commercially operated reusable launch vehicle. The X-33 would flight-test a range of technologies that NASA believed it needed for single-stage-to-orbit reusable launch vehicles, such as metallic thermal protection systems, composite cryogenic fuel tanks for liquid hydrogen, the aerospike engine, autonomous flight control, rapid flight turn-around times through streamlined operations, and its lifting body aerodynamics.
  Failures of its 21-meter wingspan and multi-lobed, composite-material fuel tank during pressure testing ultimately led to the withdrawal of federal support for the program in early 2001. Lockheed Martin has conducted unrelated testing, and has had a single success after a string of failures as recently as 2009 using a 2-meter scale model.
context_section_description: Through the use of the lifting body shape, composite multi-lobed liquid fuel tanks, and the aerospike engine, NASA and Lockheed Martin hoped to test fly a craft that would demonstrate the viability of a single-stage-to-orbit (SSTO) design.  A spacecraft capable of reaching orbit in a single stage would not require external fuel tanks or boosters to reach low Earth orbit. Doing away with the need for "staging" with launch vehicles, such as with the Shuttle and the Apollo rockets, would lead to an inherently more reliable and safer space launch vehicle.  While the X-33 would not approach airplane-like safety, the X-33 would attempt to demonstrate 0.997 reliability, or 3 mishaps out of 1,000 launches, which would be an order of magnitude more reliable than the Space Shuttle.  The 15 planned experimental X-33 flights could only begin this statistical evaluation. 
  The uncrewed craft would have been launched vertically from a specially designed facility constructed on Edwards Air Force Base, and landed horizontally (VTHL) on a runway at the end of its mission. Initial sub-orbital test flights were planned from Edwards AFB to Dugway Proving Grounds southwest of Salt Lake City, Utah.
  Once those test flights were completed, further flight tests were to be conducted from Edwards AFB to Malmstrom AFB in Great Falls, Montana, to gather more complete data on aircraft heating and engine performance at higher speeds and altitudes.
  On 2 July 1996, NASA selected Lockheed Martin Skunk Works of Palmdale, California, to design, build, and test the X-33 experimental vehicle for the RLV program.  Lockheed Martin's design concept for the X-33 was selected over competing concepts from Boeing and McDonnell Douglas. Boeing proposed a Space Shuttle-derived design, and McDonnell Douglas proposed a design based on its vertical takeoff and landing (VTVL) DC-XA test vehicle.
  The uncrewed X-33 was slated to fly 15 suborbital hops to near 75.8 km altitude. It was to be launched upright like a rocket and rather than having a straight flight path it would fly diagonally up for half the flight, reaching extremely high altitudes, and then for the rest of the flight glide back down to a runway.
  The X-33 was never intended to fly higher than an altitude of 100 km, nor faster than one-half of orbital velocity.  Had any successful tests occurred, extrapolation would have been necessary to apply the results to a proposed orbital vehicle.
  The decision to design and build the X-33 grew out of an internal NASA study titled "Access to Space". Unlike other space transport studies, "Access to Space" was to result in the design and construction of a vehicle.
caption: Test of the X-33's thermal protection system, 1998
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