Prometheus was a proposed manned vertical-takeoff, horizontal-landing (VTHL) spaceplane concept put forward by Orbital Sciences Corporation in late 2010 as part of the second phase of NASA's Commercial Crew Development (CCDev) program.
The Prometheus design was based on an earlier NASA design, the HL-20 Personnel Launch System. Prometheus also included other NASA-funded design improvements to HL-20 by Orbital Sciences that were done some years ago as part of NASA's Orbital Space Plane program. Whereas the HL-20 was a pure lifting body, the Prometheus design was for a Blended Lifting Body (BLB). This design combines volumetric efficiency with superior aerodynamic qualities. Prometheus could have initially carried four astronauts to the International Space Station or future but further development could have increased the seating capacity to six. The baselined launch vehicle was the Atlas V, but the design could have accommodated other launch vehicles. The cost of the development of the Prometheus spacecraft and of upgrading the Atlas V would be between $3.5 and $4 billion.
Failing to be selected in NASA's CCDev phase 2 program, Orbital Sciences announced in April 2011 that they will likely wind down their efforts to develop a commercial crew vehicle.