• Introduction.

The Reusable Launch Vehicle (RLV) Technology Program is a partnership between NASA and industry to design a new generation of launch vehicles expected to dramatically lower the costs of putting payloads in space. Today's launch systems are complex and costly to operate. The RLV program stresses a simple, fully reusable vehicle that will operate much like an airliner. NASA hopes to cut payload costs from $10,000 a pound, as it is today, to about $1,000 a pound. To accomplish this goal, NASA sought proposals from U. S. aerospace industries for the RLV Technology Program.

• Lockheed Martin chosen for X-33 program.

On July 2, 1996, NASA selected Lockheed Martin Skunk Works of Palmdale, Calif., to design, build, and test the X-33 experimental vehicle for the RLV program. The reusable, wedge-shaped X-33 will be about half the size of a full-scale RLV. The X-33 will not take payloads into space; it will be used only to demonstrate the vehicle's design and simulate flight characteristics of the full-scale RLV. Lockheed Martin originally planned to conduct the first flight test in June 1999 and achieve at least 15 flights by December 1999. The actual number of flights is not known, and the test flights (as well as construction of the vehicle) have been postponed indefinitely. NASA budgeted $941 million for the project through 1999 (excluding some work done by NASA civil servants). Lockheed Martin initially invested about $220 million in its X-33 design. That amount has grown since the beginning of Phase II. Upon the conclusion of the flight test program, government and industry would decide whether or not to continue with a full-scale RLV.

• RLV not a Space Shuttle replacement.

The RLV will fly much like the Space Shuttle. It will take off vertically and land on a runway. However, there are differences between the two vehicles. The RLV will be a means of transport only. It will not be used as a science platform like the current Space Shuttle.

Also, the RLV will be a single-stage-to-orbit spacecraft. It will not drop off components on its way to orbit. It will rely totally on its own built-in engines to reach orbit, omitting the need for additional boosters. Unlike the Shuttle, the RLV will use a new linear aerospike engine, which looks and runs much differently than the bell-shaped Space Shuttle Main Engine.

• The linear aerospike engine.

NASA considered the aerospike engine for the Space Shuttle 25 years ago, but opted to use the Space Shuttle Main Engine, also built by Rocketdyne. The aerospike has been revived and enhanced to power the RLV. The aerospike nozzle is shaped like an inverted bell nozzle. Where a bell nozzle begins small and widens toward the opening of the nozzle like a cone, the aerospike decreases in width toward the opening of the nozzle. The aerospike is 75 percent shorter than an equivalent bell nozzle engine. It is also lighter, and its form blends well with the RLV's lifting body airframe for lower drag during flight. The shape spreads thrust loads evenly at the base of the vehicle, causing less structural weight. The half-scale X-33 test vehicle will use two smaller test versions of the aerospike. The full-scale RLV in its current configuration will use seven aerospike engines.