English: Space Tug Elements Managed by Marshall Space Flight Center, the Space Tug concept was intended to be a reusable multipurpose space vehicle designed to transport payloads to different orbital inclinations. Utilizing mission-specific combinations of its three primary modules (crew, propulsion, and cargo) and a variety of supplementary kits, the Space Tug would have been capable of numerous space applications. The Tug could dock with the Space Shuttle to receive propellants and cargo, as visualized in this 1970 artist's concept. The Space Tug program was cancelled and did not become a reality.