Sigh--I'm talking about dealing with liquids in zero gravity
and how very hard they are to deal with. Ever heard of ullage rockets? Guess why they are used--to help seat propellants because, when not underway, they tend to form blobs:
Michael Gazarik, NASA’s space technology program director, says that CPST and the Space Launch System (SLS) heavy-lift rocket currently under development are complementary technologies. “To explore deep space we need a heavy-lift vehicle — SLS...
Patrick R. Chai and Alan W. Wilhite of the Georgia Institute of Technology presented a study earlier this year estimating that depot tanks would lose about $12 million worth of propellant per month in low Earth orbit ...
Now I don't mind cryoogenics like some do--but I'd prefer to deal with them in as few large segments as possible to eliminate boil off. As it stands, it is expected for SLS itself to launch a depot with enough active cooling an volume to make LH2 handling worthwhile--something Musk has not demonstrated.