Slide 7 of 99
Notes:
NASA's 1980s space tug plans were usually based on the aerobraking concept. This NASA/Marshall concept from 1985 is equipped with a huge disc-shaped aeroshell which slows the vehicle down as it passes through the Earth's upper atmosphere. The space tug could then return heavy payloads from geostationary orbit without using any fuel to rendezvous with the low Earth orbit space station.
Another NASA/Marshall space tug concept from 1985. This design would have better maneuvrability thanks to its aerodynamic shape, but it would also weigh more.