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 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 (SSTO RLVs), such as metallic thermal protection systems, composite cryogenic fuel tanks for liquid hydrogen, the aerospike engine, autonomous (uncrewed) 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 had a single success after a string of failures using a 2-meter scale model.
History In 1994 NASA initiated the Reusable Launch Vehicle (RLV) program. After a Phase I programme developing proposals from Rockwell International, McDonnell Douglas, and Lockheed Martin, a Phase II contract to develop the X-33 as a demonstrator vehicle was awarded to Lockheed Martin in 1996. At the same time Orbital Sciences was awarded a contract to develop the X-34, an air-launched hypersonic research vehicle. The goals of the RLV program were:
To "demonstrate technologies leading to a new generation of space boosters capable of delivering payloads at significantly lower cost" To "provide a technology base for development of advanced commercial launch systems that will make U.S. aerospace manufacturers more competitive in the global market." $1 billion was spent through 1999 with about 80 percent coming from NASA and additional money contributed by the industry partners. The goal was to have a first flight by March 1999, and to have the VentureStar, the operational reusable space vehicle, flying in 2006.
.. to build a vehicle that takes days, not months, to turn around; dozens, not thousands, of people to operate; with launch costs that are a tenth of what they are now. Our goal is a reusable launch vehicle that will cut the cost of getting a pound of payload to orbit from $10,000 to $1,000.
Cancellation The program was cancelled in February 2001. Construction of the prototype was some 85% assembled with 96% of the parts and the launch facility 100% complete when the program was canceled by NASA in 2001, after a long series of technical difficulties including flight instability and excess weight. In particular, the composite liquid hydrogen fuel tank failed during testing in November 1999. The tank was constructed of honeycomb composite walls and internal structures to reduce its weight. A lighter tank was needed for the craft to demonstrate necessary technologies for single-stage-to-orbit operations. A hydrogen fueled SSTO craft's mass fraction requires that the weight of the vehicle without fuel be 10% of the fully fueled weight. This would allow a vehicle to fly to low Earth orbit without the need for the sort of external boosters and fuel tanks used by the Space Shuttle. But, after the composite tank failed on the test stand during fueling and pressure tests, NASA came to the conclusion that the technology of the time was simply not advanced enough for such a design. While the composite tank walls themselves were lighter, the hydrogen tank shape necessary to fit inside the aerodynamic mouldline resulted in complex joints increasing the total mass of the composite tank to above that of an aluminum-based tank, and too heavy for an SSTO vehicle.
NASA had invested $922 million in the project before cancellation, and Lockheed Martin a further $357 million. Due to changes in the space launch business—including the challenges faced by companies such as Globalstar, Teledesic, and Iridium and the resulting drop in the anticipated number of commercial satellite launches per year, Lockheed Martin concluded that continuing development of the X-33 privately without government support would not be profitable. In 2004 Northrop Grumman successfully built and tested a simple cylindrical composite cryogenic hydrogen tank as part of early work for the Constellation program.
Design and development
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.
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