Sadly, all of the currently commonly used chemical rocket fuels that are either hypergolic or storable are horribly toxic/corrosive/explosive. RP-1 is so safe you can pour it out of a gas can, but cryogens are more problematic and hypergols are almost uniformly so dangerous that fueling spacecraft tends to involve specialized infrastructure and complex personal protective equipment.

This problem is probably one of the reasons for EVA jetpacks generally using anemic cold-gas thrusters.

But, we have 1. sophisticated self-sealing tube fittings and 2. at least in space, a handy vacuum enviroment.

Can present-day self-sealing plumbing systems make it safe to assemble, maintain, and refuel hypergol-fueled RCS systems without wearing heavy and complicated PPE? Alternatively, will hypergol spills dissipate harmlessly enough in the vacuum of space that astronauts can safely handle hypergols to refuel spacecraft on-orbit without special protective equipment or facilities beyond their EVA suits?

(To clarify: This is not really meant to be about entire docking systems, but about the manual transfer of propellant to smaller equipment.)


1 Answer 1


The ISS can be refueled with UDMH and N2O4 by visiting vehicles, initially the ATV:


The propellant transfer is done through the docking connector, through pipes that run outside the pressurized portions of the ISS.

  • $\begingroup$ Incorrect because sadly should be past tense, the ATV program has ended since 2014. en.wikipedia.org/wiki/Automated_Transfer_Vehicle ISS prop comes from Progresses now. $\endgroup$ Feb 23, 2020 at 0:20
  • $\begingroup$ Building new ATVs comes up every once in a while, it's the basis for the Orion European Service Module, and I said "visiting vehicles" because I didn't want to exhaustively list every vehicle that could or might be able to transfer propellant. $\endgroup$ Feb 23, 2020 at 1:32
  • $\begingroup$ Nice edit, looks good. $\endgroup$ Feb 23, 2020 at 4:19

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