Venturestar

VentureStar was a proposed design for a single-stage-to-orbit reusable launch system. Lockheed Martin's Venturestar was to be the full scale commercial version of the X-33. Unfortunately the X-33 was cancelled in 2001. Venturestar was seen as a possible successor to the Space Shutle.

Venturestar was going to use Aerospike Engines.

The VentureStar vehicle was designed to place up to 50,000 lb of payload in a LEO orbit and 15,000 lb in a GTO orbit. 

Specs:

Reference:

Picture from 
http://www.abcnews.go.com/sections/science/DailyNews/nasa_x33_990826.html