Lockheed Martin X-33
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The X-33 was a subscale technology demonstrator for a next-generation, commercially operated reusable launch vehicle. The X-33 was to flight test a range of technologies 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 (unmanned) flight control, rapid flight turn-around times through streamlined operations, and its lifting body aerodynamics.
Function and Design
Most importantly, through the use of the lifting body shape, composite 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. An SSTO craft 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 (currently thought to be 0.9999999999 reliable), 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 system.
The unmanned craft would have been launched vertically (from a specially designed facility constructed on Edwards Air Force Base, Calif.), and have landed horizontally on a runway at the end of its mission. Initial sub-orbital test flights were planned from Edwards AFB to Dugway Proving Ground southwest of Salt Lake City, Utah. Once those test flights were completed, further flight tests would be conducted from Edwards AFB to Malmstrom AFB in Great Falls, Mont., to gather more complete data on aircraft heating and engine performance at higher speeds and altitudes.
On July 2, 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 designs from Boeing and McDonnell Douglas. Boeing featured a Space Shuttle-derived design, and McDonnell Douglas featured a design based on its vertical takeoff and landing DC-XA test vehicle.
Commercial Spaceflight
Based on the X-33 experience shared with NASA, Lockheed Martin hoped to make the business case for a full-scale SSTO RLV, called VentureStar, that would be developed and operated through commercial means. The intention was that rather than operate space transport systems as it has with the Space Shuttle, NASA would instead look to private industry to operate the reusable launch vehicle and NASA would purchase launch services from the commercial launch provider. Thus, the X-33 was not only about honing space flight technologies, but also about successfully demonstrating the technology required to make a commercial reusable launch vehicle possible.
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.
Project Cancellation
Construction of the prototype was some 85% complete when the program was cancelled 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 be light enough in order for the craft to demonstrate necessary technologies for single-stage-to-orbit operations. A hydrogen fuelled SSTO craft must reach what is called a "mass fraction" where the vehicle weight unfueled is 10% of the weight of the craft when fully fueled. This would allow for a vehicle to fly to low earth orbit without the need for external boosters and fuel tanks, as currently used with the Space Shuttle. But, after the composite tank's failure 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.
NASA had invested $912m in the project before cancellation and Lockheed Martin a further $357m. 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 number of anticipated commercial satellite launches per year -- Lockheed Martin deemed that the business case to continue development privately without government support was unviable.
After the cancellation, engineers were able to make a working Oxygen tank out of Carbon Fiber Composite.
The X-33 in Fiction
- A Boeing X-33 [sic] is mentioned in Dan Brown's Angels & Demons as owned by CERN, a nuclear physics research laboratory in Switzerland, and is able to go at Mach 15, although the CERN does not actually own an X-33 in real life.
- The PC game Nexus: the Jupiter Incident depicts an X-33 in orbital flight during the opening movie.
- During the opening credits of the television series "", an X-33 is shown in orbit during a sequence showing the advancing engineering progress of launch vehicles. It is sandwiched between the space shuttle, and the fictional first flight to achieve warp speed.
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