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  1. #31
    Tim K's Avatar
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    Default Re: SSTO's would have made possible Arthur C. Clarke's vision of 2001.



    Bob,

    Going from 1% to 3% is a major accomplishment, but the resulting SSTO is still an ungainly beast. The recent (and cancelled) X-projects involving exotic composite structures and odd fuels like slush hydrogen certainly added to the knowledge base. Is any of it practical in a commercial context? Imagine if the Wright brothers had attempted to power their flyer with a steam engine -- IMO that's where we're at with current SSTO engine technology.

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    Default Re: SSTO's would have made possible Arthur C. Clarke's vision of 2001.

    Elon Musk to Address Mars Society Convention in Pasadena.
    posted Jul 20, 2012 10:05 AM by Mars Society - PR [ updated Jul 21,
    2012 1:13 PM ]
    The Mars Society is very pleased to announce that SpaceX Founder and
    CEO Elon Musk will address the 15th Annual International Mars Society
    Convention in Pasadena, California, on Saturday, August 4th during the
    organization's evening banquet.
    Elon Musk to Address Mars Society Convention in Pasadena - The Mars Society


    Bob Clark
    If you use both the most weight efficient structures and the best sea level-to-vacuum efficient engines at the same time,
    then what you will wind up with will be a SSTO whether you intend it to or not.
    Blog: http://exoscientist.blogspot.com

  3. #33
    RGClark's Avatar
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    Default Re: SSTO's would have made possible Arthur C. Clarke's vision of 2001.

    I've been arguing that SSTO's are actually easy because how to achieve
    them is perfectly obvious: use the most weight optimized stages and
    most Isp efficient engines at the same time, i.e., optimize both
    components of the rocket equation. But I've recently found it's even
    easier than that! It turns out you don't even need the engines to be
    of particularly high efficiency.
    SpaceX is moving rapidly towards testing its Grasshopper scaled-down
    version of a reusable Falcon 9 first stage:

    Reusable rocket prototype almost ready for first liftoff.
    BY STEPHEN CLARK
    SPACEFLIGHT NOW
    Posted: July 9, 2012
    Spaceflight Now | Breaking News | Reusable rocket prototype almost ready for first liftoff

    SpaceX deserves kudos for achieving a highly weight optimized Falcon 9
    first stage at a 20 to 1 mass ratio. However, the Merlin 1C engine has
    an Isp no better than the engines we had in the early sixties at 304
    s, and the Merlin 1D is only slightly better on the Isp scale at 311 s.
    This is well below the highest efficiency kerosene engines (Russian)
    we have now whose Isp's are in the 330's. So I thought that closed
    the door on the Falcon 9 first stage being SSTO.

    However, I was surprised when I did the calculation that because of
    the Merlin 1D's lower weight, the Falcon 9 first stage could indeed be
    SSTO. For the calculation we'll need the F9 dry mass and propellant
    mass. I'll use the Falcon 9 specifications estimated by GW Johnson, a
    former rocket engineer, now math professor:

    WEDNESDAY, DECEMBER 14, 2011
    Reusability in Launch Rockets.
    An Ex Rocket Man's Take On It: Reusability in Launch Rockets

    The first stage propellant load is given as 553,000 lbs, 250,000 kg,
    and the dry weight as 30,000 lbs, 13,600 kg.

    I'll actually calculate the payload for the first stage of the new version of
    the Falcon 9, version 1.1. The Falcon Heavy will use this version's first stage
    for its core stage and side boosters. SpaceX expects the Falcon 9 v1.1
    to be ready by the end of the year.

    Elon Musk has said version 1.1 will be about 50% longer:

    Q&A with SpaceX founder and chief designer Elon Musk.
    BY STEPHEN CLARK
    SPACEFLIGHT NOW
    Posted: May 18, 2012
    Spaceflight Now | Dragon Mission Report | Q&A with SpaceX founder and chief designer Elon Musk

    I'll assume this is coming from 50% larger tanks. This puts the
    propellant load now at 375,000 kg. Interestingly SpaceX says the side
    boosters on the Falcon Heavy will have a 30 to 1 mass ratio. This
    improvement is probably coming from the fact it is using the lighter
    Merlin 1D engines, and because scaling up a rocket actually improves
    your mass ratio, and also not having to support the weight of an upper
    stage and heavy payload means it can be made lighter.

    So I'll assume for this SSTO version of the Falcon 9 v1.1 the mass
    ratio is 30 to 1, which makes the dry mass 13 mT.

    To estimate the payload I'll use the payload estimation program of
    Dr. John Schilling:

    Launch Vehicle Performance Calculator.
    Launch Vehicle Performance Calculator

    It actually gives a range of likely values of the payload. But I've found
    the midpoint of the range it specifies is a reasonably accurate estimate
    to the actual payload for known rockets.

    Input the vacuum values for the thrust in kilonewtons and Isp in
    seconds. The program takes into account the sea level loss. SpaceX
    gives the Merlin 1D vacuum thrust as 161,000 lbs and vacuum Isp
    as 311 s:

    FALCON 9 OVERVIEW.
    Space Exploration Technologies Corporation - Falcon 9

    For the 9 Merlins this is a thrust of 9*161,000lb*4.46N/lb = 6,460
    kN. Use the default altitude of 185 km and select the Cape Canaveral
    launch site, with a 28.5 degree orbital inclination to match the
    Cape's latitude.

    Input the dry mass of 13,000 kg and propellant mass of 375,000 kg.
    The other options I selected are indicated here:



    Then it gives an estimated 7,564 kg payload mass:

    =====================================
    Launch Vehicle: User-Defined Launch Vehicle
    Launch Site: Cape Canaveral / KSC
    Destination Orbit: 185 x 185 km, 28 deg
    Estimated Payload: 7564 kg
    95% Confidence Interval: 3766 - 12191 kg
    =====================================

    This may be enough to launch the Dragon capsule, depending on the mas
    of the Launch Abort System(LAS).


    Bob Clark
    If you use both the most weight efficient structures and the best sea level-to-vacuum efficient engines at the same time,
    then what you will wind up with will be a SSTO whether you intend it to or not.
    Blog: http://exoscientist.blogspot.com

  4. #34
    Tim K's Avatar
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    Default Re: SSTO's would have made possible Arthur C. Clarke's vision of 2001.

    Bob,

    Aren't you forgetting a minor detail called "man-rated"? It will add considerable weight and margins.

    That Dragon capsule won't always be hauling watermelons.

 

 
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