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X-33 and Reusable Launch Vehicle (RLV) The X-33 is a half-scale prototype of the RLV Lockheed Martin calls the "VentureStar." What are the differences? X-33 Length - 69 ft Width - 77 ft Takeoff weight - 285,000 lbs Fuel - LH2/LO2 Main Propulsion - 2 J-2S Linear Aerospikes Take-off thrust - 410,000 lbs Maximum speed - Mach 13+ VentureStar Length - 151 ft Width - 159 ft Takeoff weight - 2,628,900 lbs Fuel - LH2/LO2 Main Propulsion - 8 RS2200 Linear Aerospikes Take-off thrust - 3,537,000 lbs Maximum speed - Mach 25 to orbital Payload to Low Earth Orbit - 56,000 lbs