Space Tug - Mission and program planning
An additional propulsive stage, carried in the payload bay, will be necessary for delivery of payloads to orbits beyond those which can be reached by the Shuttle alone. The concept of a reusable third stage, or Space Tug, has been under study for several years. Aspects of space tug operations planning are discussed together with payload studies, shuttle third stage program options, expendable stage studies, growth stage studies, and engine studies. Studies concerning reusable space tugs are considered, giving attention to a minimum development cost tug, a direct developed tug for 1983 operational capability, and a phased developed tug. Payload requirements are examined along with shuttle interface requirements, ground operations, and program options.