• Super Heavy landing in arms

    From JF Mezei@21:1/5 to All on Sat Jun 26 20:41:13 2021
    The animations I have seen show superheavy landing between cradle arms
    and the stack rotated such that the extended grid fins are caught by
    those arms.

    Considering that the grid fins should be very agile and able to move
    quickly to manage attitude during the descent phase, is it possible to
    have both this agility AND the structural strength needed not not only
    support full weight of the Super Heavy but also the G-force at time of
    landing?


    Also, while the multiple Starship landing attempts showed good software
    ability to manage attitude down to near vertical when engines are
    supposed to do the final bit to the ground, do we know if this included
    control of rotation (roll?) of the stack once vertical?

    Since such a cradle landing requires not only that the fuselage drop at
    right place, speed, but also rotated so its grid fins are oriented to be
    caught by the arms and not touch the tower itself, has there been any indication that this has been tested with the startship flights? (even
    though starship won't use that, just curious of the software for
    rotation control was tested on it).

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  • From Jeff Findley@21:1/5 to All on Sun Jun 27 17:02:15 2021
    In article <KOPBI.457$al1.203@fx26.iad>, jfmezei.spamnot@vaxination.ca
    says...

    The animations I have seen show superheavy landing between cradle arms
    and the stack rotated such that the extended grid fins are caught by
    those arms.

    Any of those animations "official" SpaceX videos? If not, I'd take them
    with a huge grain of salt.

    Considering that the grid fins should be very agile and able to move
    quickly to manage attitude during the descent phase, is it possible to
    have both this agility AND the structural strength needed not not only support full weight of the Super Heavy but also the G-force at time of landing?

    Yes.

    Also, while the multiple Starship landing attempts showed good
    software
    ability to manage attitude down to near vertical when engines are
    supposed to do the final bit to the ground, do we know if this included control of rotation (roll?) of the stack once vertical?

    Heavy will go up and down like a Falcon 9 booster. Starship is an
    entirely different beast.

    Since such a cradle landing requires not only that the fuselage drop
    at
    right place, speed, but also rotated so its grid fins are oriented to be caught by the arms and not touch the tower itself, has there been any indication that this has been tested with the startship flights? (even
    though starship won't use that, just curious of the software for
    rotation control was tested on it).

    No, Starship has no grid fins.

    Jeff
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  • From JF Mezei@21:1/5 to Jeff Findley on Sun Jun 27 19:48:53 2021
    On 2021-06-27 17:02, Jeff Findley wrote:

    Heavy will go up and down like a Falcon 9 booster. Starship is an
    entirely different beast.

    However, I was wondering if SpaceX has experience in precicely
    controlling roll (is it roll?) so that "arms" would be aligned correctly
    to fall on the cradle. Has it mentioned wherher Falcon 9 not only lands
    on the X but also with the correct roll?

    Thinking about it, there is probably little in common between starship
    and super heavy landings in terms of software so probably no attempt at evaluating roll.

    The latest I saw was 4 grid fins, but at 2 groups of finds 60° apart,
    and then 120" between groups. So this definitely requires precise "roll"
    when landing to have these grid fins aligned with the cradle so that the
    2 grid fins from each side end up on the cradle.


    I take it final roll alignement would be done by thrusters on fuselage?

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  • From Snidely@21:1/5 to All on Sun Jun 27 23:01:14 2021
    Jeff Findley scribbled something on Sunday the 6/27/2021:
    In article <KOPBI.457$al1.203@fx26.iad>, jfmezei.spamnot@vaxination.ca says...

    Considering that the grid fins should be very agile and able to move
    quickly to manage attitude during the descent phase, is it possible to
    have both this agility AND the structural strength needed not not only
    support full weight of the Super Heavy but also the G-force at time of
    landing?

    Yes.

    Acceleration relative to the tower should be very close to 0 at the
    time of capture, so what G-force are you imagining besides the
    no-longer-full weight of the Super Heavy?

    [That's a pun, son, since the tanks should be very close to empty at
    the time of capture]

    That said, Elon has apparently allowed as how some additional hard
    points might be needed.

    /dps

    --
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    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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  • From JF Mezei@21:1/5 to Snidely on Mon Jun 28 11:34:14 2021
    On 2021-06-28 02:01, Snidely wrote:

    Acceleration relative to the tower should be very close to 0 at the
    time of capture, so what G-force are you imagining besides the
    no-longer-full weight of the Super Heavy?

    Falcon9 still has crush zone in landing gear because some landings are
    harder than others. Shouldn't one assume that some Super Heavy landings
    might not be perfectly smooth ?

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  • From Jeff Findley@21:1/5 to All on Mon Jun 28 14:07:27 2021
    In article <XZlCI.49215$8f1.5015@fx23.iad>,
    jfmezei.spamnot@vaxination.ca says...

    On 2021-06-28 02:01, Snidely wrote:

    Acceleration relative to the tower should be very close to 0 at the
    time of capture, so what G-force are you imagining besides the no-longer-full weight of the Super Heavy?

    Falcon9 still has crush zone in landing gear because some landings are
    harder than others. Shouldn't one assume that some Super Heavy landings
    might not be perfectly smooth ?

    Any necessary "cushioning" of a Super Heavy booster would be done by the catching mechanism attached to the launch/landing tower.

    Jeff

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  • From Jeff Findley@21:1/5 to All on Mon Jun 28 14:06:06 2021
    In article <F78CI.863359$nn2.491117@fx48.iad>,
    jfmezei.spamnot@vaxination.ca says...

    On 2021-06-27 17:02, Jeff Findley wrote:

    Heavy will go up and down like a Falcon 9 booster. Starship is an
    entirely different beast.

    However, I was wondering if SpaceX has experience in precicely
    controlling roll (is it roll?) so that "arms" would be aligned correctly
    to fall on the cradle. Has it mentioned wherher Falcon 9 not only lands
    on the X but also with the correct roll?

    Engine gimabling provides roll control.

    Thinking about it, there is probably little in common between starship
    and super heavy landings in terms of software so probably no attempt at evaluating roll.

    The latest I saw was 4 grid fins, but at 2 groups of finds 60 apart,
    and then 120" between groups. So this definitely requires precise "roll"
    when landing to have these grid fins aligned with the cradle so that the
    2 grid fins from each side end up on the cradle.


    I take it final roll alignement would be done by thrusters on fuselage?

    Possibly.

    Jeff
    --
    All opinions posted by me on Usenet News are mine, and mine alone.
    These posts do not reflect the opinions of my family, friends,
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  • From Niklas Holsti@21:1/5 to Jeff Findley on Mon Jun 28 22:34:51 2021
    On 2021-06-28 21:06, Jeff Findley wrote:
    In article <F78CI.863359$nn2.491117@fx48.iad>,
    jfmezei.spamnot@vaxination.ca says...

    On 2021-06-27 17:02, Jeff Findley wrote:

    Heavy will go up and down like a Falcon 9 booster. Starship is an
    entirely different beast.

    However, I was wondering if SpaceX has experience in precicely
    controlling roll (is it roll?) so that "arms" would be aligned correctly
    to fall on the cradle. Has it mentioned wherher Falcon 9 not only lands
    on the X but also with the correct roll?

    Engine gimabling provides roll control.


    Not during the Falcon 9 landing burn -- only the center engine is used,
    so gimballing can control only pitch and yaw.

    During Falcon 9 landing, roll must be controlled by the grid fins and/or
    by thrusters. Judging from the rolling during the landing that failed
    (and was "sent to sea") because the grid fins were stuck, both methods
    can be used for roll control.

    If the Super Heavy uses multiple engines for landing, it can control
    roll by gimballing.


    Thinking about it, there is probably little in common between starship
    and super heavy landings in terms of software so probably no attempt at
    evaluating roll.


    ISTR that SpaceX will try to avoid using entry burns for the Super
    Heavy. If so, roll during the entry phase cannot be controlled by
    enginge gimballing. They will probably want to have a certain roll
    position before the grid fins can get a grip on the atmosphere, so
    thrusters will probably be used there.

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  • From JF Mezei@21:1/5 to Niklas Holsti on Mon Jun 28 16:47:08 2021
    On 2021-06-28 15:34, Niklas Holsti wrote:

    During Falcon 9 landing, roll must be controlled by the grid fins and/or
    by thrusters.


    In final stage, is there sufficient vertical speed for grid fins to have
    any aerodynamic control? Or is that something that MUST be done before
    it slows down and hope the roll doesn't change in the last seconds of
    flight?

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  • From Niklas Holsti@21:1/5 to JF Mezei on Tue Jun 29 00:47:36 2021
    On 2021-06-28 23:47, JF Mezei wrote:
    On 2021-06-28 15:34, Niklas Holsti wrote:

    During Falcon 9 landing, roll must be controlled by the grid fins and/or
    by thrusters.


    In final stage, is there sufficient vertical speed for grid fins to have
    any aerodynamic control?


    Obviously the grid fins stop working when the vertical speed goes to zero.


    Or is that something that MUST be done before it slows down and hope
    the roll doesn't change in the last seconds of flight?


    On the Falcon 9 booster where the grid fins locked into a position that
    caused a rapid roll, when the booster slowed down for its ocean landing,
    the torque from the grid fins also decreased, and I believe the
    thrusters were increasingly able to overcome that torque, and thus the roll-rate decreased before the "landing".

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