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Superheavy prototype #7 and Starship prototype #24 undergo static fire tests

Superheavy #7's first launchpad engine test
Click for original photo.

Capitalism in space: SpaceX engineers yesterday performed static fire tests of both its Superheavy prototype #7 and its Starship prototype #24.

The Superheavy prototype fired one engine, and did so only a few weeks after that prototype experienced an explosive event the launchpad during earlier fueling/engine tests. Yesterday’s engine test was the first time any Superheavy prototype had fired its engines on the launchpad.

The Starship prototype meanwhile fired two engines on a nearby vertical test stand.

SpaceX’s plan is to stack #24 on top of #7 and attempt an orbital launch test that will have the Superheavy prototype land in the Gulf of Mexico while the Starship prototype reaches orbit and then returns to Earth in the Pacific northeast of Hawaii. Based on the company’s normal pace of operations, that flight is probably only weeks away. However, before that flight engineers will have to do a full static fire test of all 33 of #7 engines, and then like do it again with Starship #24 stacked on top.

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  • Ray Van Dune

    I wonder if there is true value in test firing all 33 booster engines simultaneously, as opposed to incrementally, perhaps in groups. There is no doubt that a firing of all 33 at once would create a greater amount of blast and sonic forces that doing so piecemeal, but depending on the firing duration, it could perhaps do more damage than an actual launch.

    This concern comes from the fact that the Starship has a relatively high thrust / weight ratio, meaning it will accelerate upward off the pad at a fairly high climb rate for a large rocket, faster than the Saturn 5 for instance. In turn this means that forces directed down onto the launch platform will also reduce faster than the Saturn 5.

    So a (say) 5-second all-engine static fire could generate significantly more pressure and damage than an actual blastoff, where the rocket would have nearly cleared the tower after 5 seconds.

    For this reason I believe any all-engine static fire will be extremely brief if it occurs at all, and that a full-duration all-engine static fire would be essentially impossible.

  • Ray Van Dune: Excellent points. Based on your analysis, it seems more likely that SpaceX will do staggered static fire tests, and reserve the full firing for the launch itself.

  • Ray Van Dune

    And what would make sense as a “staggered” testing principle?

    So looking up from the bottom in the famous 33-nozzle picture, as I recall we see 20, 10, and finally 3 engines from the outer rim to the center. Think of it as a giant pie containing 33 huge berries!

    Remember that all engines have been individually tested at McGregor, so what we primarily want to test is that we have mitigated the impact of adjacent engines on each other, and on adjacent vehicle structure. The best way to do that (without lighting everything off) might be to test the engines in each “slice” of the berry pie! This looks at a population of engines and their close mates both radially and laterally. About 4-6 slices should do it.

    Of course this assumes we re-verified all engines after the recent explosive anomaly, and replaced any damaged ones with fresh fruit!! Looked at this way, it could be a month of testing, even doing the Ship in parallel.

  • sippin_bourbon


    SpaceX has lost its bid for nearly $900 million in rural broadband subsidies for its Starlink broadband service.

  • Ray Van Dune: It is my understanding that when launched, the engines on Superheavy will not all fire at the same exact second, but their ignition will be staged in groups several microseconds apart, for numerous reasons.

    I don’t remember the breakdown of that staging, but I would expect if they stagger the static fires, they will do it to match that launch staging.

  • sippin_bourbon: This deserves a post on the main page. Thank you.

  • Ray Van Dune

    Bob Zimmerman, yes I understand that such engine start phasing is used even on the Falcon 9 and Heavy, to reduce instantaneous startup shocks.

    It might indeed make sense to follow the same pattern. But OTOH the purpose of the hypothetical testing we are speculating about could be best served by amplifying any problem interactions, not reduce them, could it not? Just a guess.

  • Trent Castanaveras

    It also appears that SpaceX has ambitiously reserved the possibility for a Super Heavy catch on the debut launch to orbit, at least in a recent FCC filing:

  • Ray Van Dune

    Well, it occurs to me that with the huge thrust that these Raptors can generate, any off-center group firing alone would probably destroy the whole vehicle… I feel pretty stupid!

  • Diane E Wilson

    Launch license granted; launch window open September 1.

    My understanding is that they can’t do a full 33 engine static fire with anything less than a fully fueled booster with a fully fueled Starship with cargo, mounted on top of the booster. Too much thrust with just the booster alone; the launch mount can’t hold it down.

  • ” . . .the launch mount can’t hold it down.”

    Just send in some White people.

  • Diane E Wilson: Do you have a link to this info?

  • Star Bird

    When you bring Matter and Anti-Matter together you get a big time Explosion

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