Shuttle-C

The Shuttle-C was a study by NASA to turn the Space Shuttle launch stack into a dedicated uncrewed cargo launcher.

[3] With the Shuttle-C, it was thought that the lower maintenance and safety requirements for the uncrewed vehicle would allow a higher flight rate.

[4][5] The Shuttle-C would have been the main crew launch vehicle for the ILREC Piloted Lander in the International Lunar Resources Exploration Program.

[citation needed] As early as the 1970s, some iteration of the Shuttle-C had been studied (Encyclopedia Astronautica mentions it as "Class 1 SDV").

[1] It was discussed in Gerard O'Neill's 1976 book The High Frontier: Human Colonies in Space, with artwork by Don Davis.