5 thoughts on “Low-Cost Propellant Depots Habitats”

  1. Rand,

    While I did link to my 2009 propellant depot paper, most of the discussion was about a low-cost, low-development-risk alternative to expandable/inflatable habitats, not depots per se…


    1. I’ll expand on your concept with an idea I just had while making a cup of coffee, which involves one of several possible reconfigurations of a Falcon 9/Falcon 9 Heavy.

      Falcon 9 upside-down: Take a Falcon 9 first stage tank and build it as your habitat, then put it on top of a Falcon 9 second stage. Launch the structure purely with the thrust from 2 Falcon 9 Heavy strap on boosters, with the bottom-positioned second stage firing after booster separation. If the empty first stage tank is light enough, the boosters alone might be sufficient to orbit it. Another possibility is to use a pair of two-stage Falcon v1.1’s as the strap on boosters, dropping the first stages as normally done but leaving the pair of second stages attached to the top of the empty core stage (the habitat). This of course assumes that exhaust impingement along the length of the core isn’t a serious problem.

      Building the habitat would then just require the structure from a Falcon 9 first stage tank combined with expanded versions of the Dragon Rider’s solar array system and life support, along with their existing docking collar.

      I’m thinking that having high-performance liquid strap-ons brings up new possibilities. if you can end-wise mate two or more habitats the length of a Falcon 9 v1.1 (225 feet), you get into the range where spinning the station can produce a useful amount of artificial gravity. I would allow the cost saved on the engineless core to go toward internal facilities and estimate that each station segment would cost approximately the same as a Falcon 9 Heavy launch, or perhaps a bit more depending on how fancy you got with the facilities.

      If you can launch it with a pair of all-up Falcon v1.1’s as boosters, so that the entire central core is habitable, you’d get 700 cubic meters of internal volume, almost as much as the 930 cubic meters of pressurized volume on the ISS.

  2. Obviously there are a lot of options but the common theme is eliminating by integrating the fairing.

    We’re also talking habitats and space ships since keeping the upper stage (or better integrating it) essentially turns a habitat into a space ship (that needs more fuel storage for any meaningful mission.)

    One difference is the rocket equation. Once a habitat is in orbit it’s not really much of a concern but for a ship it certainly is. That rocket equation dominates the operational costs of a space ship. Considering how much that cost is and how much it’s focused on (ignoring the profit side of the equation since imagining that seems a bridge too far) we need to keep the mass of our space ship as low as possible (meaning the Orion is already obsolete before ever seeing space because it’s too fat by mass and too thin by volume relative to almost any other option.) Meaning we shouldn’t even be considering anything larger than existing launch vehicles (I’d make some exception for the FH which seems like a done deal by next year.)

    Why do some think we need bigger payloads than we can already launch? Because they want to throw everything to a destination without refueling. But when you throw operational costs back in it makes no sense. There is not a single reason why you would not want your space ship to be a fully reusable fuel and go vehicle. At some point no launch vehicle is large enough so we might want to look harder at that other option.

    Don’t we want an aftermarket for used but still operational vehicles?

  3. This whole discussion comes to an even larger point. Mass (of anything!) in orbit is crushingly expensive; why throw it away?

    There was a semi-serious proposal, IIRC, to accept a small payload penalty (which was acceptable for most missions) in Shuttle launches in order to take the external tank with them. Not because the thing was immediately usable, but because it would be simply a large, sealed volume in orbit which could be used later.

    It is possible that once there is some industry in space – and may it happen soon – most habitats or factory areas will have a junkyard of assorted spare parts such as upper-stage boosters and external tanks close to them. That’s until the capacity for getting materials from celestial bodies swings into gear of course – but the habit might persist.

Comments are closed.