The X-33 was a sub-scale demonstration vehicle for a (proposed) larger single-stage-to-orbit spacecraft called the VentureStar. For the reasons I've mentioned in my previous posts, single-stage-to-orbit spacecraft are not feasible with the technology we have today. In the future it may be possible to air-launch orbital vehicles similar to the VentureStar, but we don't have that sort of air-launch capability yet. The proposed VentureStar would weigh in at 2,200,000 lbs, which is 5 times the external payload of the largest cargo aircraft in existence (the Russian AN-225).neutrino78x":3hc4pjm2 said:So could we make an X-33 type rocketplane that launched horizontally, like an airplane? Like I said, like that Lynx rocketplane, except using hydrogen and oxygen instead of hydrocarbon (for environmentally clean exhaust). Still can't believe they canceled the X-33, it was a great idea.