Tuesday, March 28, 2006

Testing New Rockets

Now that a respectful period for SpaceX's loss has passed, it's time to begin the enthusiastic but uninformed Monday morning quarterbacking. Don't be shy. Here, I'll go first.

First, I don't see why people are at all sad the thing blew up. It was a test article, and test articles break, generally with tons of instrumentation to tell you how. If you want to feel sad, feel sad for the upper stage testing guy, who won't see a video of his machine airstarting for another six to nine months. And that's what motivates the rest of this post.

Why does the vehicle have to be tested all-up? Testing all-up is gutsy and smart when your expectation of failure is very low, but wasteful if you are pretty sure you have multiple problems to find and fix. Dwayne Day has pointed out that about half of all new rockets succeed on their first launch, but this launch was not like the first launches of most of those other rockets. Those rockets had very expensive Big Government testing programs behind them. This rocket did not. That's good (because it can be more efficient), but it means that an all-up launch is not likely to yield a lot of testing data for the amount of money and time invested.

At this point, SpaceX has already paid for plenty of expensive lessons at Kwaj, so incremental flight testing might not seem necessary anymore. I'd do it anyway: they'll need it for the Falcon 9 too, and nobody knows how many gremlins remain to be flushed out of the Falcon 1 design, because they didn't get to test much of the vehicle.

If each stage carries a full load of LOX but only enough kerosene for about 100 m/s delta-V, we should get a short, locally recoverable hop, without the need for an intercontinental missile range. A set of large floats attached to the tail of the rocket might keep the engine from a complete dunking on splashdown, if that is perceived to be a problem. The lack of a range is a huge deal -- they could have done quite a bit of flight testing in parallel with getting onto Kwaj, and my guess is they're going to need plenty of launch experience before Vandenberg will let them launch there.

So the test plan, then, would be to launch two or three rockets perhaps a dozen or more times from a small island in the middle of a small uninhabited lake in the continental United States. Start by launching single stages by themselves (first and second), and then move on to two stage launches. I've read that Wisconsin wants to have a spaceport, perhaps they'd be willing to cough up the necessary permits.

While short hops are not going to test the vacuum and high-speed portions of the flight, they will test all sorts of other good stuff, many of which were tested for the first time at Kwaj (where it was more expensive):

  • Launch procedures, except those relating to the interface with the range and the recovery vessel. This would include things like discovering how many shitloads of LOX it takes to load the thing up.

  • Launch in high winds, heat, etc, by picking the time of year and using ballast. Granted, this takes time, but expanding the launch envelope is only needed once you are trying to support a high flight rate.

  • First and second stage structure under some but not all flight loads. Again, ballast necessary.

  • Payload environment in the lower atmosphere.

  • The staging event -- shutdown, seperation, propellant settling, ignition, interstage seperation. This is huge.

  • Fairing seperation, unfortunately with an aerodynamic load. The load could be mitigated by blowing the fairing at the top of an almost vertical flight, perhaps by adding enough delay between first stage engine stop and seperation that the vehicle coasts to a stop.

  • Some of the first stage recovery hardware, obviously not including the re-entry sequence.

  • Recovery of first stages -- water handling, floatation, etc.

  • The flight termination system in various stages of flight. Note that since flight termination is nondestructive, they can really test the hell out of it by using FTS to shut down half the time.

  • Reuse of first stages. This could be really big, since some lessons that might otherwise be learned might be erased by reentry.

  • Recovery and reuse of second stages. Yes! They are going to try to do this with Falcon 9, so why not start now? Testing this out with moneymaking operational launches sounds cheap, but you'll never get the same instrumentation or number of tests as you can have with low-altitude test flights.

  • I'll stop here, the list is endless. The point is that a lot of confidence can be built doing cheap flight tests away from the U.S. Government's test range.


    1. For Microlaunchers (google it) I plan just such an incremental approach. Both for the engineering/testing aspects but for licensing. At first, just an atmospheric flight version of the full weight firat stage will be flown to 500 to 50,000 ft and the landing process and some abort modes will be worked out. This will be less expensive. See the site.

    2. Your test ideas sound great, and they would give all the systems a workout before integrating them, but they don't bring in any money. If you can get someone who's willing to give you your per launch cost to fly on the first flight, refusing the opportunity would not make much business sense.


    3. Many a person suggested to Mr Musk that
      Incremental Flight test would be a good idea.
      A very reasonable suggestion was made to fly
      the first stage with a dummy second stage
      out of Kwaj and to cut down the second stage
      nozzle and fly it off a rail at White Sands.
      As SpaceX is a private firm, it is their right
      to ignore advice. We will see what the future

    4. The cheapness depends on the recoverability, which is a big assumption to make here. It's still not at all clear whether they will be able to recover the rocket without major damage. I suspect they rather risk a multi-million dollar rocket on a flight that potentially gives them a-heck-of-a-lot-of-data instead of on one that gives them data-about-this-one-thing-they-are-testing.
      Sure, recoverability is a thing on your list of things to test, but it might be really expensive to test it early on. You need the whole refurbishing infrastructure basically on the test-site in order to be able to start such a test-campaign. And that needs to be build. It's something they don't have any experience with this yet. Who knows what happens to a Merlin engine when it has been in the water for a while? What do you need to do to get it working?
      I get what you're saying and I agree that it would be *really nice* if they were able to do it. I just don't think it will be as easy as you portrait it to be.

    5. Your testing plan is a good one. It is the same sort of practive we have been using at Beyond-Earth. A lot of people have been critical of this apporach, but it does work. Slow steady progress, testing everything you can on the ground, low altitude flights, followed by higher altitudes and then suddenly, you are all set for Space.