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First stage reusability questions

Discussion in 'SpaceX' started by PeterW, Nov 5, 2014.

  1. PeterW

    PeterW Member

    Feb 20, 2009
    Palmerston North, New Zealand
    I have a question about first stage reusability.

    How many missions would SpaceX expect from a reusable first stage rocket?

    Are we talking the same sort of reusability as a commercial jet?

    What are the limiting factors?
  2. ElSupreme

    ElSupreme Model S 03182

    Jan 13, 2012
    Atlanta, GA
    I think most of the limiting factors boil down to material science. How many thermal/physical stress cycles can the rocket engines survive and still be reliable.

    I would think getting reuseability up to more than 2 cycles will take lots of iteration and trialing. After that I think 100 or more cycles could be possible. I don't think aircraft number of cycles will happen in our lifetimes. The thermal and physical stresses on a rocket are so much more demanding than conventional aircraft.
  3. ItsNotAboutTheMoney

    ItsNotAboutTheMoney Well-Known Member

    Jul 12, 2012
    The aim is to maximize re-use to lower costs. So the limit is repair costs and repair quality v risk of failure and cost of failure on the next mission, with the long term goal of airplane-like reusability.

    Whether to re-use would depend on the cost of the satellite being launched.

    Say a new rocket is $100M to launch and has a 1% kaboom rate.
    Say cost to relaunch with an re-used first stage is $50M. (Target is exponentially lower than that, of course, but it's early days).
    Say the kaboom rate increases 5% with each mission.

    A company wants to launch a small $100M satellite. Each 1% chance of failure costs $1M.
    Given that they'd save $50M on the launch, they'll readily opt for reusability, maybe into the 9th or 10th mission.

    A company wants to launch a $1B satellite. Each 1% chance of failure costs $10M.
    A re-used first stage would have a 6% failure rate, costing them at least $50M in extra risk, rendering re-use pointless.

    Corollary: successful re-use will lead to the construction of cheaper, less-reliable satellites.
  4. TEG

    TEG TMC Moderator

    Aug 20, 2006
    Compare to re-usability of the old space shuttle...

    At some point you want an improved design, so it doesn't need to be reusable forever.
  5. Grendal

    Grendal SpaceX Moderator

    Jan 31, 2012
    Santa Fe, New Mexico
    I think the sweet spot is to reuse a rocket 10 times or more. On the later reuse runs you can take less valuable material. Spare fuel, oxygen, foodstuffs, and basic construction materials should be at the top of the list. That way if you lose the material in a "kaboom" you can replace it easily and with little cost. Though it does come down to what SpaceX learns from their reused rockets.

    I'm thinking that creating a orbital storage depot for excess material would be useful.

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