The X-33 is one of NASA's new technology demonstrator programs which will pave the way to lower launch costs.  The X-33 vehicle is being built by Lockheed Martin Skunk Works in Palmdale, CA.  The X-33 will be a vertical take-off / horizontal landing lifting body vehicle employing the Boeing Linear Aerospike XRS-2200 engine.  The vehicle has two aft composite hydrogen tanks and a single aluminum liquid oxygen tank located forward in the nose of the vehicle.

Program Objectives (as described by NASA)

• Implementation of technology demonstrations (flight and ground) so as to reduce the business and technical risks which will enable privately financed development and operation of a low cost next generation space transportation system. The goal is to lower the cost from $10,000 per pound of payload to low earth orbit to $1,000 per pound to low earth orbit.
  
• The X-33 flight system, subsystems, and major components shall be designed and tested (in flight and ground) so as to ensure their traceability (technology and general design similarity) and scaleability (directly scaleable weights, margins, loads, design, fabrication methods, and testing approaches) to a full scale SSTO rocket system. Technical objectives also include improved mass fraction for vehicle structures and improved thrust to weight for rocket propulsion systems.
  
• The X-33 system will demonstrate key "aircraft like" operational attributes required for a cost effective SSTO rocket system. At a minimum, key demonstrations will include: operability (e.g., increased Thermal Protection System (TPS) robustness, weather, etc.), reusability, affordability, and safe abort.