This is SpaceX's plan for Starship (and one of the reasons I think it will take longer than expected[1]). ULA posited an orbital tanker for cryogenic fuels[2] w

This is SpaceX's plan for Starship (and one of the reasons I think it will take longer than expected[1]). ULA posited an orbital tanker for cryogenic fuels[2] which was most notable for having an internal combustion engine that ran off the fuel it would hold to keep the fuel chilled. [1] If NASA were to plan a mission that needed on orbit refueling they would not even start building a spacecraft until they had tested out all of the elements of on orbit refueling before hand. SpaceX is "assuming" they can make it work and proceeding with Starship. To date NASA has awarded some contracts (https://spaceflightnow.com/2020/10/16/nasa-selects-companies-to-demonstrate-in-space-refueling-and-propellant-depot-tech/ https://spaceflightnow.com/2020/10/16/nasa-selects-companies...) [2] https://sciences.ucf.edu/class/wp-content/uploads/sites/23/2017/04/ULA-UCF.pdf https://sciences.ucf.edu/class/wp-content/uploads/sites/23/2...