
Image credit: NASA
Image source: NASA MSFC

Image credit: NASA
Image source: NASA MSFC

Image credit: NASA
Image source: National Archives

Image credit: NASA
Image source: Numbers Station

Image credit: NASA
Image source: National Archives

Image credit: NASA
Image credit: Mike Acs

Image credit: NASA
Image source: Cradle of Aviation Museum

Image credit: Grumman
Image source: Cradle of Aviation Museum

Shown on this chart is an artist’s rendition of a tug configuration which is made up of individual propellant modules and thus provides extreme operational flexibility. The stage is designed to be compatible with a variable number of propellant modules which contain oxidizer, fuel and pressurants. The basic propulsion platform includes engines, control, avionics and primary structure. In concept, the configuration has the option of staging tanks for extremely high performance.
Although this modular concept is extremely versatile, it has a lower mass fraction than one which is designed for a single performance capability.
Image credit: NASA
File source: NASA NTRS