The RS-88 engine was capable of 50,000 pounds of thrust. It was designed and built by The Boeing Company's former Rocketdyne Propulsion & Power unit for use on Lockheed Martin's Pad Abort Demonstration vehicle. In 2003, NASA tested the RS-88 in a series of 14 hot-fire tests, resulting in 55 seconds of successful engine operation. Lockheed Martin's Pad Abort Demonstration (PAD) vehicle was originally scheduled for launch in late 2005 and would have carried four RS-88 engines. The engine had originally been designed by Rocketdyne under NASA's BANTAM program and was modified for application to the Lockheed-Martin PAD vehicle. Critical Design Review of the PAD propulsion module occurred in mid-2004 but use of the vehicle in CEV development was evidently abandoned.
In January 2006 it was announced that NASA was loaning the rocket engine to Rocketplane, of Oklahoma City, as part of an innovative industry partnership program. NASA's Johnson Space Center, Houston, and the company signed a Space Act Agreement for use of an RS-88 engine in tests of its Rocketplane XP vehicle for three years. The company will provide NASA with design, test and operational information from the development. The Rocketplane XP was a four-seat, modified Lear executive jet. It would incorporate a rocket engine for acceleration to achieve a planned peak altitude of almost 300,000 feet.
"With NASA, the Federal Aviation Administration, and the support of local, state and federal governments, we hope to develop a safe, affordable and reusable spaceplane by integrating established technologies, such as the RS-88 engine," said Bob Seto, Rocketplane's vice president of engineering systems and analysis. According to Seto, the craft completed a preliminary design review in March 2005, and it was in the detail design phase.