The McDonnell Douglas DC-X, better known as the Delta Clipper or Delta Clipper Experimental, was an unmanned prototype of a reusable single stage to orbit launch vehicle developed in conjunction with NASA and the DOD SDIO from 1991 to 1993. The DC-X flew a series of flight tests successfully, with Apollo astronaut Pete Conrad at the ground-based controls for some flights. However, on the eighth flight in July 1995, a hard landing cracked the aeroshell.