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> The timeline for the first propellant-transfer test is three to four weeks. 14 launches over 30 days comes to a launch every other day. Not sure I understand

by avmich 2y ago

> The timeline for the first propellant-transfer test is three to four weeks. 14 launches over 30 days comes to a launch every other day. Not sure I understand your numbers here in relation to the quoted part?

JumpCrisscross 2y ago
> Not sure I understand your numbers here in relation to the quoted part The unknown variable is in-orbit propellant boil-off. How much propellant will poof away for each day in orbit, and during the propellant transfer. The test next month will observe this for 3 to 4 weeks. So for the actual mission, we will presumably have 3 to 4 weeks to put all the fuel in orbit. Assuming it takes 14 launches to launch that fuel (we won't know the final number until we do the tests), that gives us a required average launch cadence of about 2 days.
- avmich 2y ago
  Thanks. I'd assume the boil-off should be insignificant, in a sense, or - alternatively - some active cooling systems can be used, they don't need to be big or complex.
  - JumpCrisscross 2y ago
    > I'd assume the boil-off should be insignificant 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_lift_versus_depot-centric_architectures https://en.wikipedia.org/wiki/Orbital_propellant_depot#Heavy...
    - avmich 2y ago
      > It should be, but we haven't done it yet [1]. Yes, but there were some calculations for this - http://astronautix.com/n/n1blocksr.html http://astronautix.com/n/n1blocksr.html - which hints on boiling off to be manageable for large stages.
  - withinboredom 2y ago
    You’ve got to put that heat somewhere… and space being a vacuum means there’s no where to put it.
    - avmich 2y ago
      Space radiators, I believe, are still having some space to evolve, particularly liquid droplet radiators.
      - withinboredom 2y ago
        And, where, pray, does that liquid come from ... in space? It also seems like a terrible idea to leave little ice particles flying around at hundreds of km/h...
        avmich 2y ago
        You'd think that, but on Mir space station that kind of radiator showed some good results, and the liquid was gathered back with negligible losses.

by avmich 2y ago

JumpCrisscross 2y ago

> Not sure I understand your numbers here in relation to the quoted part The unknown variable is in-orbit propellant boil-off. How much propellant will poof away for each day in orbit, and during the propellant transfer. The test next month will observe this for 3 to 4 weeks. So for the actual mission, we will presumably have 3 to 4 weeks to put all the fuel in orbit. Assuming it takes 14 launches to launch that fuel (we won't know the final number until we do the tests), that gives us a required average launch cadence of about 2 days.

avmich 2y ago
Thanks. I'd assume the boil-off should be insignificant, in a sense, or - alternatively - some active cooling systems can be used, they don't need to be big or complex.
- JumpCrisscross 2y ago
  > I'd assume the boil-off should be insignificant 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_lift_versus_depot-centric_architectures https://en.wikipedia.org/wiki/Orbital_propellant_depot#Heavy...
  - avmich 2y ago
    > It should be, but we haven't done it yet [1]. Yes, but there were some calculations for this - http://astronautix.com/n/n1blocksr.html http://astronautix.com/n/n1blocksr.html - which hints on boiling off to be manageable for large stages.
- withinboredom 2y ago
  You’ve got to put that heat somewhere… and space being a vacuum means there’s no where to put it.
  - avmich 2y ago
    Space radiators, I believe, are still having some space to evolve, particularly liquid droplet radiators.
    - withinboredom 2y ago
      And, where, pray, does that liquid come from ... in space? It also seems like a terrible idea to leave little ice particles flying around at hundreds of km/h...
      - avmich 2y ago
        You'd think that, but on Mir space station that kind of radiator showed some good results, and the liquid was gathered back with negligible losses.