On the lasting importance of SpaceX.

Discussion in 'General Science & Technology' started by Exoscientist, Jun 2, 2012.

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  1. Exoscientist Mathematician Registered Senior Member

    They are due congratulations because of their successful launch of the Dragon, docking it to the ISS, and its successfully recovery after reentry.

    However, their most important accomplishment might be they showed how spaceflight can become routine:

    On the lasting importance of the SpaceX accomplishment.

    Bob Clark
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  3. Buddha12 Valued Senior Member

    Only time will tell and what about safety? :shrug:

    Unless there's a place to go in space, a space hotel, there's only going to be orbiting of the planet for some time to come.
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  5. sigurdV Registered Senior Member

    Maybe a combined hotel and factory would be even better.

    If we think hard about it, it may be possible to finance the project!

    How about space whisky?
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  7. billvon Valued Senior Member

    Why would it be any better than earth whiskey - and who would pay $100,000 for a bottle of whiskey?
  8. Stoniphi obscurely fossiliferous Valued Senior Member

    As I recall, a very wealthy hotel magnate plans to have an "inflatable hotel" in stable earth obit by 2015. It is currently under construction on-planet.
  9. Exoscientist Mathematician Registered Senior Member

    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.
    Posted: July 9, 2012

    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:

    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.
    Posted: May 18, 2012

    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.

    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:


    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:

    Please Register or Log in to view the hidden image!

    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
  10. Exoscientist Mathematician Registered Senior Member

    Experimental Private Rocket Makes Highest Test Hop Yet.
    by Miriam Kramer, SPACE.com Staff WriterDate: 26 December 2012 Time:
    11:04 AM ET
    "In the latest test at SpaceX's proving grounds in MacGregor, Texas,
    the Grasshopper rocket flew for 29 seconds and reached a height of
    more than 130 feet (40 meters). A video of the Grasshopper test flight
    shows the rocket soaring up into the Texas sky, then smoothly
    descending to land on four spindly legs."

    With reduced weight of the Merlin 1D engine while at increased efficiency, the Falcon 9 v1.1 first stage will have SSTO capability. Then ironically Elon is emulating the original purpose of the DC-X program in testing the Grasshopper VTVL stage, without realizing it.

    Bob Clark
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