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Posts posted by RCgothic

  1. Gateway's core elements are going up on Falcon Heavy.

    And there is no large surface element that isn't going to have to go down on HLS, which will be commercially launched.

    So which large elements would SLS be pre-positioning exactly, at maybe one flight a year and an unreasonable cost per flight?

    From where we are now there's no sensible use case. Falcon Heavy and Commercial Crew changed everything.

  2. 21 hours ago, RCgothic said:

    They do like to milk the "SLS is the most powerful rocket ever" propaganda. It's not.

    SLS will, assuming Superheavy doesn't fly with at least 14 engines before next February, briefly hold the title of most thrust at liftoff of any rocket ever.

    Haha, wait, N1 had massively more thrust than SLS at liftoff!

    Nope, genuinely can't think of a metric under which SLS is most powerful without some sort of qualification.

  3. Well Wikipedia also defines Saturn V as "most powerful (total impulse)", so I'm being a little generous to SLS by considering a definition of total impulse to be "total mass accelerated to final velocity, multiplied by velocity", thus including its heavier final stage and saying "arguably", because stages without fuel don't count as useful payload, as rightly pointed out.

    But if block 5 can only manage 45t payload to TLI and EUS weighs around ~15.6t at burnout, that's just 60.6t.

    Saturn V managed 48.5t to TLI and S-IVB weighs 13.5t, then that's about 62t, so SLS won't win even on this metric unless it finds some extra payload somewhere.


    Bottom lines:

    Thrust on the pad is not power.

    SLS will probably not have the highest instantaneous power.

    SLS probably won't have most payload to TLI.

    SLS probably won't have highest total mass (total impulse) to TLI.

    SLS will not have most mass/payload to LEO.

  4. 11 minutes ago, tater said:

    Do they claim 60t to TLI on Block 2? With Orion? (cargo TLI mass is better than with Orion presumably because of LES mass combined with a different trajectory compatible with safe crew abort)

    Heck, that's almost useful... not sure what the cutoff is for a lander that also gets stuck with the LOI burn in LLO. I want to say I figured it was closer to 65-70t for the whole stack at TLI.

    That'd be SLS ~48t payload to TLI plus ~15t EUS after burnout ~=63t total.

    Saturn V was ~60t to TLI including S-IVB.


    Of course Saturn V sent over 48t payload to TLI as well, so in terms of useful work done it'd still be a tossup. It's just that S-IVB is lighter. Hence the argument.

  5. They do like to milk the "SLS is the most powerful rocket ever" propaganda. It's not.

    SLS will, assuming Superheavy doesn't fly with at least 14 engines before next February, briefly hold the title of most thrust at liftoff of any rocket ever.

    Most powerful (total impulse) is still Saturn V.  60t total to TLI can't be argued with until Block 2, if that ever happens.

    Most powerful (instantaneous power) is probably also Saturn V.  Thrust times velocity, I'm pretty sure S-IC is producing more power at centre engine cut off and outboard-engine cutoff than SLS is at BECO. SRBs have a vaguely decaying thrust profile.

    And Superheavy is rapidly arriving to take all of these titles for itself if SLS doesn't hurry up.

  6. 13t including payload and propellant seems very light compared to FH's expendable or semi-expendable capability. Both configurations could easily send the heaviest payload either falcon has ever lofted - 15.6t - to TLI. With a payload attachment upgrade it could easily manage 13t of spacecraft NOT INCLUDING 5t of cargo, 18t total.

    But at the same time 13t is way too heavy for a fully reusable configuration. That'd be more like 8.5t.

    Not sure why they're reserving semi-expendable performance TBH.

  7. Having finished the video, I'd agree that seems like a fair assessment.

    I do think it would be mad not to try and keep Starship in the mix just because it has *so* much capability. But it's probably going to the moon at some point whether or not NASA funds it.

  8. Based on 100t payload to LEO, 30t landing propellant, a regular Starship mass of 80t, and an ISP of 370s, Starship can push ~88t total to TLI.

    An expendable starship can ditch all the unnecessary weight, heat shield, fins, fairing. Falcon9 upper stage has a dry weight to propellant ratio of 4%. The square cube law is friendly to Starship. If expendable Starship weighs 4% of 1250t of propellant dry, that's 50t.

    So Starship Expendable can send ~38t to TLI without considering expending Superheavy.





    But that's not the best use of a Starship. Raptors are super-cheap by engine standards. Put a 3t Raptor powered kick stage on top of Starship, and send 38t to TLI without even expending Starship.





    ... And whilst we're at it, 370s ISP and a Methalox mass fraction trump 465s ISP on an EUS. An RVac kick stage weighing 99t wet can put a 1t payload through over an extra 1km/s compared to EUS weighing 130t in LEO.

    Assuming the 1t payload could get there on an SLS without being shaken to pieces.

  9. 2 hours ago, Spaceman.Spiff said:

    oh geez....

    i read my units wrong..... 

    Do you want to crash a spacecraft? Because that's how you crash a spacecraft. ;-p

    1 hour ago, sevenperforce said:

    Aiming for an orbital flight with SN20 and BN3 by July 1?


    But the good kind.

    Gives them six months' float to beat SLS to orbit. It'll be so so funny if SLS is never the world's most powerful rocket.

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