X-33 was the sub-scale prototype version of the Single Stage to Orbit Venture Star. It was wedge shaped X-33. It was developed jointly between NASA and Lockheed Martin Skunk Works of Palmdale, California. X-33 was cancelled in 2001.

X-33 - Single Stage to Orbit

The X-33 was designed to take off vertically like a rocket, reaching an altitude of up to 60 miles and speeds faster than Mach 13 (13 times the speed of sound), and landing horizontally like an airplane. The X-33 was to be launched at Edwards Air Force Base, Edwards, California.

The X-33 design was chosen in the X-33 competion in 1986. The competitors were the DC-X Vertical take-off and Vertical landing vehicle and Rockwell X-33. Lockheed Martin’s version won the competion. In hindsight, perhaps two competing vehicles should have been built.


Length 69 ft
Width 77 ft
Take-off weight 285,000 lbs
Fuel LH2/LO2
Fuel weight 210,000 lbs
Main Propulsion (2) J-2S Linear Aerospikes
Take-off Thrust 410,000 lbs
Maximum Speed Mach 13+

The X-33s was to use: 

–  Linear aerospike rocket engines : The novel, highly efficient design had undergone numerous component-level tests. The first aerospike test engine had completed 14 planned hot fire tests. It accumulated more than 1,460 seconds of total operating time, including a demonstration of the ability to vary the thrust from top to bottom that will be used to steer the X-33. This engine was developed at a fraction of the cost of normal standard efforts.

–  Thermal Protection System (TPS) certification: The rugged, metallic thermal-protection system panels designed for the X-33 had passed an intensive test series that included sessions in high-speed, high-temperature tests in laboratories, wind tunnels and NASA research aircraft to duplicate flight conditions. Industry partner BF Goodrich had delivered more than 95 percent of the X-33’s TPS panels. NASA expected the panels could reduce maintenance time and costs associated with more fragile thermal tile systems. The panels also made up the lower surfaces of the rocket plane’s aerodynamic structural shell, resulting in significant weight savings over traditional thermal systems while being more durable and waterproof.

–  Internal Structures: Lightweight graphite composite trusses and supports that serve as the backbone of the X-33’s aeroshell have been assembled. They also support the three large propellant tanks that comprise most of its interior. The X-33 is pioneering extensive use of composite materials for RLVs.

–  The X-33 was based on a lifting body shape. The lightweight components and fuel tanks were built to conform to the vehicle’s outer shape.

X-33 Status

Construction of the X-33 was more than 85 percent complete, with the liquid oxygen tank, avionics bay, flight umbilicals, reaction control system thruster controller and landing gear installed. However, the X-33 was cancelled in 2001.

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