The Space Truck™

This is yet another refueling vessel for large spacecrafts that makes use of a completely detachable fuel tank. The Space Truck™ is stationed in Low Earth orbit and when a craft in Earth's SOI needs refueling, it goes to it, and does some refueling. Then, it turns to LEO.

When the attached fuel tank is empty, the space truck will detach it. Leaving just enough fuel in it for it to de-orbit itself using the onboard RCS. It then crashes into the Earth's surface and a new fuel tank is sent up and docks with the vessel.