6 thoughts on “Rockets”

  1. And once SpaceX has reusability of it’s first stage [and possibly second stage] the next thing we
    need is reusability of spacecraft. So need depots.

    If SpaceX can reuse it’s first stage, a question related to it is how many times can the first stage be re-used. Airplane are reusable, but designed to be reused a finite amount of times.
    So obviously one does start re-using rockets say 1000 times. Before designing for 100 times, you want to reuse a rocket say, 5 to 10 times.
    And it seems a way to test the number of times one can re-use a rocket is by delivering rocket fuel
    to orbit.
    So you you recover the rocket the first time, and test the engine and refurnish them. Then one might use it to deliver cargo to ISS [maybe] or a test payload and land it again. But how times can you do this and fly something like crew or expensive satellite?
    ISS cargo is pretty good for test purposes, but rocket fuel would be better- if it fails you lose some rocket fuel, whereas ISS cargo can include things worth millions of dollars- and are needed in timely fashion. So rocket fuel fuel delivery can used pushing the limit of number of times one reuses the rocket engines [and reusing the entire stage].

    And when SpaceX successfully lands a first stage, it’s not going to be start of using stages, it’s going to be start of learning how to re-use stages so it possible in future to safely use a stage say 100 times, then work towards a 1000 times.
    So in the future one have a stage being used 10 times for expensive payload, and used 90 times to lift non expensive payload. So this a step towards using depots.

    1. No one who designs an airplane has ever thought of the number of flights it could do. In other words, airplanes are not designed for N uses. They are designed to fly, and get back. Making them fly again is usually not difficult, but once in a while one comes up with big, nasty surprises. The earliest one in Western aviation history was that of metal fatigue in B-17 wings and wing spars. Metal fatigue as such had not been known before that. The Comet stress riser problem was another big surprise.

      Generally, though, the problem of “reusing” airplanes has been one of developing a maintenance schedule. There are a few DC-3s in commercial operation today, the oldest one having been built 78 years ago. Douglas probably never gave a thought to how long the planes would last. But the people who operate them love them, and keep them flying through maintenance. The Shuttle never had enough spare parts for a similar maintenance regime to develop. They scavenged parts from the last flying orbiter to keep the next one flying. That was never sustainable.

      Similarly, the Minuteman ICBM was not designed to a specific lifetime, because no one knew how to do such a thing. They designed it instead to a 3 to 5 year “goal.” They have been in service for more than 40 years, and are supposed to remain there until 2030.

      Yes, they have been “upgraded” from time to time. Stages and guidance systems have been replaced, but not all of them. It’s amazing how much of the original hardware is still on alert. That, too, came at the price of a substantial Aging and Surveillance Test Program, where deterioration was identified, and fixes proposed.

      It’s better to just design something that flies and gets back, then figure out how to make it last longer. All of the real-world data we have points to that as the route to success.

    1. Elon will only make a BFR when it has profit potential. The Raptor has value w/o the BFR. His satellite venture is more concerning, but like solar city may not be a focus of his time.

      1. The Raptor has value w/o the BFR.

        Only if he builds a new booster to accomidate it a BFR or a MFR or something. To retrofit the Falcon would end up as a new booster in the same way the Blue Origin engine will end up making the Atlas a new booster. Going from Keralox to CH4 requires an extensive change in tanking.

  2. > No one who designs an airplane has ever thought of the number of flights it could do. In other words, airplanes are not designed for N uses.

    This is grossly inaccurate. Everything on an airplane has a designed cycle life and flight hours rating. That is not set by a wild guess, and it’s sure as hell not set by selling a bunch of them and seeing when it breaks. Not only do engineers think about this stuff, but it drives a large part of the cost because you have to qualify parts for flightlike durations before you fly them.

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