• Starhip goes to 9 engines

    From JF Mezei@21:1/5 to All on Sat Dec 18 19:06:21 2021
    This week, Musk tweeted that:

    Booster will have 33 Raptor V2.0 engines
    and

    Starship will have 3 sea level gimballing engines, and 6 fixed vaccum
    engines. (so moving from 6 to 9 engines) with increased propellant load.


    For starship, would "increased propellant load" mean that that structure
    itself will grow taller? or are they growing tanks by reducing payload
    volume? If the ship itself grows taller, is that a major change in
    strcture? or did they realize that their current design/steel has the
    strength to grow taller?


    If Raptor V2.0 is much better, I can understand seeing Booster with more
    umph and thus able to lift heavier Sharship, hece ability to lift more
    fuel. But why the exra vaccuum engines in Sharship?

    I was always under the impression that once dropped by a stage 1, a
    stage 2 has luxury of time to accelerate to orbit. Does the addition of
    3 engines to Starship mean that in the end, they don't have that luxury
    and with the mass it has, it needs to finish acceleration to orbital
    speed at faster rate?

    Since Raptor 2.0 is supposed to be the "new and improved" version, once
    would have expected the need for fewer engines to achieve same thrust
    instead of need to add more.


    Since only sea level engines will gimbal, is it fair to state that they
    will be fired up after stage 1 separation to help push Starship to
    orbital speed? or will they sue differential thrust on the 6 fixed
    vaccum to achieve directional control?


    In the case of the Moon shuttle, since Starship woll operate excusively
    in vaccuum, can we expect it to have a different mix of engines with a
    sportion of vaccum engines having gimbals?

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  • From Snidely@21:1/5 to All on Mon Dec 20 01:46:52 2021
    Just this Saturday, JF Mezei explained that ...
    This week, Musk tweeted that:

    Booster will have 33 Raptor V2.0 engines
    and

    Starship will have 3 sea level gimballing engines, and 6 fixed vaccum engines. (so moving from 6 to 9 engines) with increased propellant load.


    For starship, would "increased propellant load" mean that that structure itself will grow taller? or are they growing tanks by reducing payload volume? If the ship itself grows taller, is that a major change in
    strcture? or did they realize that their current design/steel has the strength to grow taller?


    If Raptor V2.0 is much better, I can understand seeing Booster with more
    umph and thus able to lift heavier Sharship, hece ability to lift more
    fuel. But why the exra vaccuum engines in Sharship?

    I was always under the impression that once dropped by a stage 1, a
    stage 2 has luxury of time to accelerate to orbit. Does the addition of
    3 engines to Starship mean that in the end, they don't have that luxury
    and with the mass it has, it needs to finish acceleration to orbital
    speed at faster rate?

    Since Raptor 2.0 is supposed to be the "new and improved" version, once
    would have expected the need for fewer engines to achieve same thrust
    instead of need to add more.


    Since only sea level engines will gimbal, is it fair to state that they
    will be fired up after stage 1 separation to help push Starship to
    orbital speed? or will they sue differential thrust on the 6 fixed
    vaccum to achieve directional control?

    In the 3+3 configuration, it was certainly expected that all the
    engines would fire on the way to orbit. If the purpose of the engine
    count revision is to allow bigger payloads, then I would expect the sea
    level engines to be asked to contribute some kick. But it is probably
    too early for anyone not working on Starship to answer.

    In the case of the Moon shuttle, since Starship woll operate excusively
    in vaccuum, can we expect it to have a different mix of engines with a sportion of vaccum engines having gimbals?

    Lunar Lander Starship was introduced with engines that would not be
    seen on LEO Starships. There's been discussion as to whether those
    landing engines would actually be needed, of if the lunar regolith
    could stand the main engine jet blasts without becoming weaponized.

    But that's another question we don't yet have the answer for.

    /dps


    --
    "First thing in the morning, before I have coffee, I read the obits, If
    I'm not in it, I'll have breakfast." -- Carl Reiner, to CBS News in
    2015.

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  • From Alain Fournier@21:1/5 to JF Mezei on Mon Dec 20 15:27:43 2021
    On Dec/18/2021 at 19:06, JF Mezei wrote :
    This week, Musk tweeted that:

    Booster will have 33 Raptor V2.0 engines
    and

    Starship will have 3 sea level gimballing engines, and 6 fixed vaccum engines. (so moving from 6 to 9 engines) with increased propellant load.


    For starship, would "increased propellant load" mean that that structure itself will grow taller? or are they growing tanks by reducing payload volume? If the ship itself grows taller, is that a major change in
    strcture? or did they realize that their current design/steel has the strength to grow taller?


    If Raptor V2.0 is much better, I can understand seeing Booster with more
    umph and thus able to lift heavier Sharship, hece ability to lift more
    fuel. But why the exra vaccuum engines in Sharship?

    I was always under the impression that once dropped by a stage 1, a
    stage 2 has luxury of time to accelerate to orbit. Does the addition of
    3 engines to Starship mean that in the end, they don't have that luxury
    and with the mass it has, it needs to finish acceleration to orbital
    speed at faster rate?

    Since Raptor 2.0 is supposed to be the "new and improved" version, once
    would have expected the need for fewer engines to achieve same thrust
    instead of need to add more.


    Since only sea level engines will gimbal, is it fair to state that they
    will be fired up after stage 1 separation to help push Starship to
    orbital speed? or will they sue differential thrust on the 6 fixed
    vaccum to achieve directional control?


    In the case of the Moon shuttle, since Starship woll operate excusively
    in vaccuum, can we expect it to have a different mix of engines with a sportion of vaccum engines having gimbals?

    I don't have answers to your questions. But I can give you some general information about sea level vs vacuum engines and about engine counts.

    The difference between sea level engines and vacuum engines is mainly
    the length of the nozzle. Longer nozzle make more efficient engines but
    can make the engine unstable in an atmosphere. That means that sea level engines will work fine in a vacuum but will be less efficient than
    vacuum engines. On the other hand, vacuum engines will tend to tear
    apart if used in an atmosphere.

    A higher engine count (for engines with similar power) will make you
    accelerate faster, which will save you on gravity loss. But when you
    have reached orbit you basically no longer suffer gravity loss. If you
    haven't yet reached orbital speed but you are close you will have some
    gravity loss, but it will be small. So once near orbital speed extra
    engines tend to be not very useful extra weight. Therefore the last
    stages of a multistage rocket will usually have a lower fraction of its
    mass in engines. Once you are in orbit to go higher up or to escape, it
    is more efficient to have longer burn times with less engines.

    So, a "traditional" rocket that you want to use to send stuff very high
    or escape Earth's gravity, usually has a smaller fraction of its mass
    for engines in upper stages. On the other hand if you want to optimise
    the rocket for LEO, your engines are used before reaching orbit while
    you can suffer gravity loss, and you might want to have more engines to
    avoid gravity loss.

    So why would SpaceX put extra engines on Starship which they want to use
    to go to Mars? Well Starship is not a traditional rocket. For trips to
    Mars, they want to refuel it in LEO. So when Starship is used to launch satellites in LEO, you want more power to avoid gravity loss. And when
    it is used to go to Mars, well you are really using it to go to LEO
    first and you are willing to use extra mass to avoid gravity loss. Then
    you refill, at that point, the extra engines are not very useful to goto
    Mars but you still have them because you needed them to avoid gravity
    loss at launch and they will be useful to avoid gravity loss when you
    will launch from Mars.


    Alain Fournier

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  • From Snidely@21:1/5 to Alain Fournier on Mon Dec 20 13:19:22 2021
    Remember Monday, when Alain Fournier asked plaintively:
    On Dec/18/2021 at 19:06, JF Mezei wrote†:
    This week, Musk tweeted that:

    Booster will have 33 Raptor V2.0 engines
    and

    Starship will have 3 sea level gimballing engines, and 6 fixed vaccum
    engines. (so moving from 6 to 9 engines) with increased propellant load.


    For starship, would "increased propellant load" mean that that structure
    itself will grow taller? or are they growing tanks by reducing payload
    volume? If the ship itself grows taller, is that a major change in
    strcture? or did they realize that their current design/steel has the
    strength to grow taller?


    If Raptor V2.0 is much better, I can understand seeing Booster with more
    umph and thus able to lift heavier Sharship, hece ability to lift more
    fuel. But why the exra vaccuum engines in Sharship?

    I was always under the impression that once dropped by a stage 1, a
    stage 2 has luxury of time to accelerate to orbit. Does the addition of
    3 engines to Starship mean that in the end, they don't have that luxury
    and with the mass it has, it needs to finish acceleration to orbital
    speed at faster rate?

    Since Raptor 2.0 is supposed to be the "new and improved" version, once
    would have expected the need for fewer engines to achieve same thrust
    instead of need to add more.


    Since only sea level engines will gimbal, is it fair to state that they
    will be fired up after stage 1 separation to help push Starship to
    orbital speed? or will they sue differential thrust on the 6 fixed
    vaccum to achieve directional control?


    In the case of the Moon shuttle, since Starship woll operate excusively
    in vaccuum, can we expect it to have a different mix of engines with a
    sportion of vaccum engines having gimbals?

    I don't have answers to your questions. But I can give you some general information about sea level vs vacuum engines and about engine counts.

    The difference between sea level engines and vacuum engines is mainly the length of the nozzle. Longer nozzle make more efficient engines but can make the engine unstable in an atmosphere. That means that sea level engines will work fine in a vacuum but will be less efficient than vacuum engines. On the other hand, vacuum engines will tend to tear apart if used in an atmosphere.

    The RVACs are known (by design and test results so far) to not tear
    when used in the atmosphere. They can be used at sea level. This is,
    of course, made possible by trade-offs ... some vacuum efficiency is
    sacraficed to provide more stability down low. I believe this was
    discussed during Tim Dodd's tour, as well as being mentioned in other
    places.

    A higher engine count (for engines with similar power) will make you accelerate faster, which will save you on gravity loss. But when you have reached orbit you basically no longer suffer gravity loss. If you haven't yet reached orbital speed but you are close you will have some gravity loss, but it will be small. So once near orbital speed extra engines tend to be not very useful extra weight. Therefore the last stages of a multistage rocket will usually have a lower fraction of its mass in engines. Once you are in orbit to go higher up or to escape, it is more efficient to have longer burn times with less engines.

    So, a "traditional" rocket that you want to use to send stuff very high or escape Earth's gravity, usually has a smaller fraction of its mass for engines in upper stages. On the other hand if you want to optimise the rocket for LEO, your engines are used before reaching orbit while you can suffer gravity loss, and you might want to have more engines to avoid gravity loss.

    So why would SpaceX put extra engines on Starship which they want to use to go to Mars? Well Starship is not a traditional rocket. For trips to Mars, they want to refuel it in LEO. So when Starship is used to launch satellites in LEO, you want more power to avoid gravity loss. And when it is used to go to Mars, well you are really using it to go to LEO first and you are willing to use extra mass to avoid gravity loss. Then you refill, at that point, the extra engines are not very useful to goto Mars but you still have them because you needed them to avoid gravity loss at launch and they will be useful to avoid gravity loss when you will launch from Mars.

    The extra engines are not the sea level engines, they are the 3
    additional vacuum engines (RVACs). You don't need sea level engines
    in LEO, you only need them during launch and landing. But they are
    still useful in orbit, despite reduced efficiency.

    /dps

    --
    Who, me? And what lacuna?

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  • From JF Mezei@21:1/5 to Snidely on Mon Dec 20 17:31:24 2021
    On 2021-12-20 16:19, Snidely wrote:

    The extra engines are not the sea level engines, they are the 3
    additional vacuum engines (RVACs). You don't need sea level engines
    in LEO, you only need them during launch and landing. But they are
    still useful in orbit, despite reduced efficiency.


    Does adding mass for 3 additional engines matter much in the grand
    scheme of things? I recall criticism of Space Shuttle having to
    accelerate its SSMEs to orbital speed as dead weight since it was OMS
    that did the work.

    I gather this is some fancy equation of accelerating with lighter mass
    (6 engines) vs accelerating with higher mass ( 9 engines) but greater
    thrust. But those extra 3 engines still have to be lifted from ground
    before they kick in.

    Do second stages typically have to throttle back to maintain comfortable
    3G when there are humans on-board? Curious to see if the existing 6
    engiunes can reach that 3G easily after being dropped off in semi orbit
    bu the booster, or whether they really need those extra 3 to reach 3G.


    In terms of lunar lander, I was under the impression that the "main"
    engines would be used for orbital ops, and the "side mounted" thrusters
    would be used in proximity of lunar ground (last stage of landingk first
    stage of taking off).


    BTW, if the Raptors can't be used to land on the Moon where regolith
    obeys laws of physics (pushed sideways) could they be used to land on
    Mars where the atmosphere causes the dust/rocks to behave more
    unpredictably?

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  • From Snidely@21:1/5 to All on Mon Dec 20 15:37:54 2021
    JF Mezei pounded on thar keyboard to tell us
    On 2021-12-20 16:19, Snidely wrote:

    The extra engines are not the sea level engines, they are the 3
    additional vacuum engines (RVACs). You don't need sea level engines
    in LEO, you only need them during launch and landing. But they are
    still useful in orbit, despite reduced efficiency.


    Does adding mass for 3 additional engines matter much in the grand
    scheme of things? I recall criticism of Space Shuttle having to
    accelerate its SSMEs to orbital speed as dead weight since it was OMS
    that did the work.

    I gather this is some fancy equation of accelerating with lighter mass
    (6 engines) vs accelerating with higher mass ( 9 engines) but greater
    thrust. But those extra 3 engines still have to be lifted from ground
    before they kick in.

    Do second stages typically have to throttle back to maintain comfortable
    3G when there are humans on-board?

    Yes.

    Curious to see if the existing 6
    engiunes can reach that 3G easily after being dropped off in semi orbit
    bu the booster, or whether they really need those extra 3 to reach 3G.

    It depends on the payload, no doubt. We'll know more about the 3+3 configuration early in the New Year, it seems.

    In terms of lunar lander, I was under the impression that the "main"
    engines would be used for orbital ops, and the "side mounted" thrusters
    would be used in proximity of lunar ground (last stage of landingk first stage of taking off).

    It appears you acquired an accurate impression. However, that design
    may still be in play, or it may have been dropped.

    BTW, if the Raptors can't be used to land on the Moon where regolith
    obeys laws of physics (pushed sideways) could they be used to land on

    Pushed sideways is an oversimplification even in vacuum.

    Mars where the atmosphere causes the dust/rocks to behave more
    unpredictably?

    The dust and rocks on Mars still obey the laws of physics. Details of
    how to land a large rocket on Mars are still under investigation. Some
    of the possibilities have already been discussed here, such as adding
    aluminum [compounds?] to the exhaust as way to make the landing site
    less loose.

    /dps

    --
    Rule #0: Don't be on fire.
    In case of fire, exit the building before tweeting about it.
    (Sighting reported by Adam F)

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  • From Snidely@21:1/5 to All on Fri Dec 31 05:01:28 2021
    Snidely asserted that:
    Just this Saturday, JF Mezei explained that ...
    This week, Musk tweeted that:

    Booster will have 33 Raptor V2.0 engines
    and

    Starship will have 3 sea level gimballing engines, and 6 fixed vaccum
    engines. (so moving from 6 to 9 engines) with increased propellant load.


    For starship, would "increased propellant load" mean that that structure
    itself will grow taller? or are they growing tanks by reducing payload
    volume? If the ship itself grows taller, is that a major change in
    strcture? or did they realize that their current design/steel has the
    strength to grow taller?


    If Raptor V2.0 is much better, I can understand seeing Booster with more
    umph and thus able to lift heavier Sharship, hece ability to lift more
    fuel. But why the exra vaccuum engines in Sharship?

    I was always under the impression that once dropped by a stage 1, a
    stage 2 has luxury of time to accelerate to orbit. Does the addition of
    3 engines to Starship mean that in the end, they don't have that luxury
    and with the mass it has, it needs to finish acceleration to orbital
    speed at faster rate?

    Since Raptor 2.0 is supposed to be the "new and improved" version, once
    would have expected the need for fewer engines to achieve same thrust
    instead of need to add more.


    Since only sea level engines will gimbal, is it fair to state that they
    will be fired up after stage 1 separation to help push Starship to
    orbital speed? or will they sue differential thrust on the 6 fixed
    vaccum to achieve directional control?

    In the 3+3 configuration, it was certainly expected that all the engines would fire on the way to orbit. If the purpose of the engine count revision is to allow bigger payloads, then I would expect the sea level engines to be asked to contribute some kick. But it is probably too early for anyone not working on Starship to answer.

    Somewhat more informed speculation: <URL:https://www.teslarati.com/spacex-starship-upgrade-plans-elon-musk-2021/>

    /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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