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Can a Model Rocket reach space?

  1. Feb 4, 2015 #1
    I was wondering if there is a way to build a model rocket that has the capabilities to reach space (not go into orbit though). It would seem to be very difficult to reach space from the ground, but if you launch it from a balloon some 30 miles up, would it be possible, if not, any easier?
     
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  3. Feb 4, 2015 #2

    jfizzix

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    Getting a rocket (model or otherwise) into space is a matter of thrust and time.

    The engines most model rockets have have enough thrust, but not for enough time, and engines that do have enough thrust for enough time can't (yet) be made small and light enough to be used in model rockets.

    I'm not an aerospace engineer or a rocket scientist, though, so you may want to get a second opinion.
     
  4. Feb 4, 2015 #3
    Thanks. Though would it have enough thrust for enough time if you launched it from a balloon?
     
  5. Feb 5, 2015 #4

    boneh3ad

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    First, it depends on what your definition of "model rocket" is. You could certainly design and build a rocket yourself that could reach space, though only with a substantial investment of time and money, and at that point it would cease being a "model" rocket by most definitions.

    Second, placing it on a balloon and launching it from 30 miles up changes the escape velocity from 11.2 km/s to 11.1 km/s, so there really isn't a whole lot to be gained by placing it on the balloon.
     
  6. Feb 5, 2015 #5
    If OP doesn't want it to orbit, it doesn't need to reach escape velocity...
    The question here is, where do you define "space"? At what altitude?
     
  7. Feb 5, 2015 #6

    mheslep

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    The OP did not exclude orbit. I think getting to "space" for the layman from earth commonly means orbit.
     
  8. Feb 5, 2015 #7

    mheslep

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    Specific orbital energy might be a good place to start. To place any object in low earth orbit requires the addition of 32.8 MJ/kg to the object beyond its energy at the earth's surface, not counting any energy lost to other than the final object in orbit. Energy is either potential energy (mgh) or kinetic energy (mv2/2). As an example, the velocity for the all kinetic energy case is ~8.1 km/sec.

    Energy density of carried hydrogen and oxygen fuel is 16 MJ/kg, so some 2 kg of, say, H2-O2 fuel is required per kg of orbital mass using a perfectly efficient engine, then more fuel is required to lift the fuel and the apparatus for using the fuel, so that the compounding effect is apparent.
     
    Last edited: Feb 5, 2015
  9. Feb 5, 2015 #8

    mheslep

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    The advantage is the avoidance of lost energy to atmospheric drag on ascent. Drag power is proportional to air density, which reduces from sea level by a factor of ~1000 at 30 miles/50km.
     
  10. Feb 5, 2015 #9
    What about the reduced time it would take to get to space from 30 miles up. And the reduced drag.
     
  11. Feb 5, 2015 #10
    I would say there are two major schools of thought:
    1) Reaching orbit. Obviously a model rocket, with current technology and pricing, is out of the realm of possibility.
    2) Reaching the Karman Line, ~100 km up, which is an internationally agreed upon boundary between Earth's atmosphere and "space". This can be, and has been, done. Though, I'm not sure I'd call these guys "hobbyists" at this scale... http://www.hobbyspace.com/Rocketry/Advanced/records.html

    OP, if you are talking about orbit, 30 Miles isn't going to help you very much at all...It may help a bit with drag early on and reduce some fuel costs, but you're not very close to orbit at that point, and you still need to get your horizontal (tangent) velocity up high enough to orbit that's still a TON of delta V.
     
  12. Feb 5, 2015 #11
    Ok, so how exactly large would this rocket have to be to get into orbit with no other payload than itself? And at this point you wouldn't be using model rocket engines anymore.
     
  13. Feb 5, 2015 #12

    mheslep

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    See the hobbyspace rocket examples provide to you above. They reached space, or close to it, and appear to be ~3-5M long, maybe ~0.1M diameter
     
  14. Feb 6, 2015 #13

    cjl

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    Typically, you'd look at something more like 8-10 inch diameter (~0.25m or so), but your length seems about right (probably closer to the long end). They also contain custom made high performance solid rocket motors that put out in excess of a thousand pounds of thrust for 10-15 seconds, so they're not really what you would consider "model" rockets anymore.
     
  15. Feb 6, 2015 #14

    mheslep

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    Somebody reportedly got to space (Karman) from that hobbyist group, so somebody must have flown much longer.
     
  16. Feb 6, 2015 #15

    mheslep

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    It occurs to me that the Kerbal Space video program would much more quickly satisfy curiously about the limits of low budget rocketry than, say, traveling to Nevada for a high altitude launch. Apparently JPL engineers are obsessed with the thing, and Elon Musk is a fan.

    https://kerbalspaceprogram.com/



     
  17. Feb 6, 2015 #16
    Minimal low Earth orbital velocity is only 9.4 km/s. You don't need to achieve escape velocity to put something in LEO.
     
  18. Feb 7, 2015 #17

    Bandersnatch

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    Here you can see a bunch of undergrads launching a rocket from a balloon. You can ascertain the dimensions of the thing, and appreciate some of the issues that need to be overcome.
     
  19. Feb 10, 2015 #18

    cjl

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    Oh, the flight is much longer. The motor only burns for 10-15 seconds, and the majority of the flight is an unpowered coast.
     
  20. May 30, 2015 #19

    K41

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    You want to also launch in the direction of rotation of the Earth to get an added incremental benefit.
     
  21. Jun 3, 2015 #20

    cjl

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    Only if you want to achieve orbit. If you simply want to reach space (>100km altitude), straight up is the easiest way to do it.
     
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