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I'm thinking of something akin to a space lifeboat designed to rescue crews of ships that are disabled in orbit and that would need to launch in a hurry without a lot of warning but that would also potentially have to sit for years before it was used. I'm also assuming more or less current tech but that the overall cost is not a major concern as this is only for emergency response as opposed to regular launches.

Current rockets are fueled before the crew boards, which takes a fairly long time to do. One possible idea is something based on a similar principle to ICBMs probably using SRBs.

So how would you build a rocket that was intended to launch quickly with a crew but might need to sit for years before being used?

Also, how long can RCS monopropellant be stored for orbital maneuvering?

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    $\begingroup$ It's not quite clear whether you are looking at a lifeboat (something carried on a manned ship that gets into trouble) or a rescue craft (something that travels to where a manned ship is in distress and rescues crew). Which is it? $\endgroup$ Sep 6, 2021 at 1:31
  • $\begingroup$ Hmm let's see. We have people aboard the International Space Station at all time. The ISS may be hit by a meteorite or some other accident may happen. Therefore there is a need to provide for the evacuation of the crew of the ISS at a moment's notice. What do you think, has anybody thought to provide for the evacuation of the crew of the ISS at a moment's notice? Are there regulations in place to ensure that all the crew members of the ISS have a seat available in the lifeboats? $\endgroup$
    – AlexP
    Sep 6, 2021 at 6:57
  • $\begingroup$ "Current rockets are fueled before the crew boards, which takes a fairly long time to do." Not quite true anymore. The Crew Dragon spacecraft which launches aboard the SpaceX Falcon 9 rocket is approved for what they call "load-and-go". The crew boards and then 35 minutes before launch, the rocket starts getting fueled up. $\endgroup$
    – Dragongeek
    Sep 6, 2021 at 7:59
  • $\begingroup$ @Alex Yes. The space station has 1-2 landing capsules docked at all times. Newer capsules have the capacity to hold all 7 occupants for an emergency escape. $\endgroup$
    – Redbud201
    Sep 6, 2021 at 8:22
  • $\begingroup$ @Redbud201 "The space station has 1-2 landing capsules docked at all times" - "landing capsule" is a synonym to "spaceship"? $\endgroup$
    – Alexander
    Sep 7, 2021 at 16:43

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Leave the emergency ship in orbit.

Bugs won't get in it. Heavy rains won't wash it away. Protesters won't push it over and pose on top of it. It has no crew. It just goes around and around.

There are many of the emergency ships. There are only so many useful orbits and each has some emergency ships. If a distress call goes out, the robot in the emergency ship closest adjusts its orbit to bring it along side the distressed ship. It speaks in a reassuring robotic voice.

Presumably persons on the ground also hear the distress call. They can remotely control the emergency ship if needed; for example the distressed ship is tumbling and the robot cannot match it.

Otherwise the crew of the disabled ship are expected to be able to man the emergency ship. Which will then re-enter the atmosphere. The reassuring robotic voice will sing songs on the way down, as reassurance.

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I skim read and thought you were talking about something attached to a ship or station and answered as follows: If you have a rotating module for spin gravity the easiest answer is to attach your lifeboat onto the outer rim with explosive bolts and let the spin throw it clear when you blow it loose no fuel is required at all that way. If you don't have that luxury then a highly stable solid propellant is going to be essential to keep the station safe from the lifeboat. I'd suggest something that requires specific electrical ignition rather than a heat or impact ignitable system but even then accidents happen so point the rocket exhaust tangential to the hull to prevent unexpected burn through. As for RCS fuel that will depend upon what is used, liquid air (they actually use compressed pure nitrogen) is probably the most reliable for long term storage as the tanks holding it can sit for decades without noticeable degradation.

In the case of an independent rescue craft that goes in to make pick up the same recommendations on fuel etc... apply with two notes 1. there needs to be an added emphasis on communications equipment and redundancy to try to guarantee (nothing in life is actually a sure thing of course) command and control links so these ships are useful 2. you'll use a pallet burning solid fuel rocket so that it's not an all or nothing" kick like you want in the case of an escape craft. For maximum longevity you'll want to park them strategically in orbits where they can make fast and efficient burns toward manned stations and worksites before engaging cold gas thrusters for fine tuning in light of drift etc... cause by the emergency situation.

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