What's the context?
If this is from 1971, I suspect it is an early artist concept of a potential European space tug for the NASA space shuttle. Europe was initially offered the tug job until the USAF objected, noting (correctly) that this would be making Europe responsible for building a piece of hardware that was essential to launching US military and intelligence satellites. So the offer was rescinded and the USAF began looking at potential space tug ideas. They didn't get very far because of costs. The idea of a reusable vehicle was abandoned, and USAF and NASA decided to settle for the Interim Upper Stage (IUS) and later the Centaur. IUS became the Inertial Upper Stage after it was clear that it was more than just "interim." Centaur got built, but canceled after the Challenger accident.