Centaur Interim Upper Stage (IUS) system study. Volume 2: Technical

The IUS programs defined in the study incorporate a primary propulsive stage based on the existing D-1 Centaur vehicle used by NASA for Viking and by DoD for FleetSatComm. The study concludes that lowest development costs are incurred with an expendable Centaur IUS which is 89 percent existing hardware. The principal development tasks for this program would be modifications for compatibility with the Orbiter and SGLS/STDN communications. Lowest life cycle costs can be achieved with a reusable Centaur IUS where added development is required for a wide hydrogen tank and a fuel cell power supply. Trade studies and options including shorter length vehicles and compatibility with NASA planned Tracking and Data Relay Satellite (TDRSS) system are also defined. The inherent high performance of cryogenic propellants assures comfortable accommodation of current and future IUS program requirements.