Space tug.

The reusable space tug is a major system being planned for use with the space shuttle to augment its capability to deliver, retrieve, and support automated payloads. The reusable space tug will be designed to support all the planned missions beyond low earth orbit including geosynchronous orbit. Tug missions and requirements are discussed together with tug options, giving attention to existing transfer stages and growth stages. System studies for an interim tug concept are planned to begin in February 1973. Three independent studies will be conducted: two on cryogenic tugs and one on storable propellant tugs.-