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  • Re: Starship engine tests

    From Snidely@21:1/5 to All on Sat Dec 17 18:47:12 2022
    JF Mezei speculated:

    This past week, SpaceX had another SN24 engie test.
    But just a startup and shutdown.


    Considering that during the "iterative" testing early on, one of the
    problems was the restart of the engine(s) for landing, shouldn't engine
    tests at this point in time test the ability to start and restart
    engines to emulate a flight ?

    In a previous inteview, the PR person had explained that the engine
    start is the most challenging part with a serious challenge to spin up
    the turbo pumps at the right time/sync etc. (so that would explain why previous tests had been for short burns, since they were only testing
    engine start, not actual engine performance).

    But as engine start remains a challenge, shouldn't restarts be tested?

    Restarts are tested, at SpaceX's McGregor site.

    Note that with Falcon 9s, SpaceX doesn't test relight during a static
    fire test.

    [...]
    And without the ability to target an "X" on a landing site
    (since neither booster now Starship have landing legs),
    how can they test the ship's ability to land precisely at a tower?

    With the water landings, they will have a chance to assess the
    performance of the landing guidance, although they already have some information from the belly-flop tests. Plus all the experience with
    the F9 landings.

    /dps

    --
    And the Raiders and the Broncos have life now in the West. I thought
    they were both nearly dead if not quite really most sincerely dead. --
    Mike Salfino, fivethirtyeight.com

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  • From JF Mezei@21:1/5 to All on Sat Dec 17 21:19:57 2022
    This past week, SpaceX had another SN24 engie test.
    But just a startup and shutdown.


    Considering that during the "iterative" testing early on, one of the
    problems was the restart of the engine(s) for landing, shouldn't engine
    tests at this point in time test the ability to start and restart
    engines to emulate a flight ?

    In a previous inteview, the PR person had explained that the engine
    start is the most challenging part with a serious challenge to spin up
    the turbo pumps at the right time/sync etc. (so that would explain why
    previous tests had been for short burns, since they were only testing
    engine start, not actual engine performance).

    But as engine start remains a challenge, shouldn't restarts be tested?

    I know it is totally diferrent, but when thgey built the Ottawa LRT, I
    could see they knew of problems in advance because they were avoiding
    testing stuff. Big snow storm? testing cancelled (when it should have
    been done to test behaviour). Didn't test doors while trains were
    traveling in empty/closed stations. By NOT finding problems during
    testing, they were able to get paid by the city for meeting various
    steps in the building of the system, so there was incentive to not find problems (and later hide them under a carpet).




    So it is in this context where I note how it seems to me that SpaceX
    isnt REALLY testing its ships to the full extend that is possible on
    ground to really debug. Looks to me like their goal is just to launch
    and no care about landing, but that would mean that once they have done
    their first orbital flight, they will have to restart testing to get the landing to work and suspect that will take quite a biut of time before
    they have the trust needed to let a landing happen at the tower.

    And without the ability to target an "X" on a landing site (since
    neither booster now Starship have landing legs), how can they test the
    ship's ability to land precisely at a tower?

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  • From JF Mezei@21:1/5 to Snidely on Sun Dec 18 15:33:18 2022
    On 2022-12-17 21:47, Snidely wrote:

    Restarts are tested, at SpaceX's McGregor site.

    And that didn't prevent engine problesm for re-ignition during actual
    flights since the problems were more of a system integration between
    tanks and engines.


    With the water landings, they will have a chance to assess the
    performance of the landing guidance, although they already have some information from the belly-flop tests. Plus all the experience with
    the F9 landings.

    F9 experience will be of help to the "static" booster that always comes
    back empty and uses the similar "grid fins" for guidance and staying
    upright. On the other hand, I have to wonder if they will have enough
    data on G-force at time of landing which is something that would matter
    when doinging on the "chopsticks" and which would be measured if it had
    landing legs landing on hard surface.

    But for Starship itself, the couple fo tests flights they had so far
    resulted in them moving weight to the nose (the landing tanks), but what happens when they start to fit the rocket with real payloads that are
    returned (humans etc) ? The variability in how Starship will return will
    change a lot in how the falling upject turns to vertical at last second
    to land.

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  • From Snidely@21:1/5 to All on Sun Dec 18 23:27:03 2022
    Remember when JF Mezei bragged outrageously? That was Sunday:
    On 2022-12-17 21:47, Snidely wrote:

    Restarts are tested, at SpaceX's McGregor site.

    And that didn't prevent engine problesm for re-ignition during actual
    flights since the problems were more of a system integration between
    tanks and engines.

    And now they have the data from those flights, and IIRC the re-ignition problems were on SN8 and SN9, with SN10 and SN15 not having issues.
    SN11 was probably Raptor 1 issues, since 2 engines were not at full
    performance on the way up.

    Also, there is some evidence that one or more headers tanks were filled
    for SN24's latest static fire.

    But keep those worry beads handy.

    With the water landings, they will have a chance to assess the
    performance of the landing guidance, although they already have some
    information from the belly-flop tests. Plus all the experience with
    the F9 landings.

    F9 experience will be of help to the "static" booster that always comes
    back empty and uses the similar "grid fins" for guidance and staying
    upright. On the other hand, I have to wonder if they will have enough
    data on G-force at time of landing which is something that would matter
    when doinging on the "chopsticks" and which would be measured if it had landing legs landing on hard surface.

    But for Starship itself, the couple fo tests flights they had so far
    resulted in them moving weight to the nose (the landing tanks), but what happens when they start to fit the rocket with real payloads that are returned (humans etc) ? The variability in how Starship will return will change a lot in how the falling upject turns to vertical at last second
    to land.

    They already have some evidence as to how good their models worked.
    (All 5 flown starships have belly flopped just fine, turned upright
    just fine.) Elon has said the forward flaps are too big.

    Turning upright is a relatively small part of the accuracy issue.
    Getting the braking force right is crucial, of course, but remember
    that Raptors have deeper throttling than Merlins, and Starship has some
    slight ability to hover, unlike a Falcon 9 which has a hot slam
    landing.

    /dps


    --
    Maybe C282Y is simply one of the hangers-on, a groupie following a
    future guitar god of the human genome: an allele with undiscovered
    virtuosity, currently soloing in obscurity in Mom's garage.
    Bradley Wertheim, theAtlantic.com, Jan 10 2013

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