It should be, but we haven't done it yet [1].
> active cooling systems can be used, they don't need to be big or complex
Cooling in space is always complicated given the only way to dump heat is radiating (or dumping into ejected mass, i.e. boil off).
[1] https://en.wikipedia.org/wiki/Orbital_propellant_depot#Heavy...
Yes, but there were some calculations for this - http://astronautix.com/n/n1blocksr.html - which hints on boiling off to be manageable for large stages.
It should be, but we haven't done it yet [1].
> active cooling systems can be used, they don't need to be big or complex
Cooling in space is always complicated given the only way to dump heat is radiating (or dumping into ejected mass, i.e. boil off).
[1] https://en.wikipedia.org/wiki/Orbital_propellant_depot#Heavy...