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Space Shuttle SRB Operation Question.

  1. Jul 25, 2005 #1
    Have an interesting (and hopefully easy) question for you.

    Does the Shuttle require the Earth (and any resulting force/element) for Launch?

    Such as, Atmosphere. Does the main engines, or SRB's utilize the atmosphere to aid in the ignition or combustion?

    Does the Shuttle utilize the magnetic pull of the Earth, the rotational velocity, anything?



    My 'research' suggests that the atmosphere may be required for the SRB ignition.

    So, the small rocket motor... is its reaction self contained, or does it use the elements (O2?) in the atmosphere to generate the 'Flames'?

    Do you think the SRB's could ignite and be used in space? If not, then the shuttle does use the Earth (ok, the atmosphere) to launch..

    Input?
     
  2. jcsd
  3. Jul 25, 2005 #2

    Clausius2

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    I think it SRB's cannot be used without atmosphere, or another oxydizer ambient. Although as you have pointed the first ignition can be made by an external liquid propellant engine (which is completely autonomous and doesn't need any atmosphere), the fire and flame propagation inside SRB's needs an oxydizer. I think this oxydizer is the air contained inside of each engine, which are open to atmosphere. But I am not sure at all. Maybe they have another oxydizing substance. I want to know it too!
     
  4. Jul 25, 2005 #3

    Clausius2

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    Ok. I've got it:

    "The propellant mixture in each SRB motor consists of an ammonium perchlorate (oxidizer, 69.6 percent by weight), aluminum (fuel, 16 percent), iron oxide (a catalyst, 0.4 percent), a polymer (a binder that holds the mixture together, 12.04 percent), and an epoxy curing agent (1.96 percent). The propellant is an 11-point star- shaped perforation in the forward motor segment and a double- truncated- cone perforation in each of the aft segments and aft closure. This configuration provides high thrust at ignition and then reduces the thrust by approximately a third 50 seconds after lift-off to prevent overstressing the vehicle during maximum dynamic pressure."
    Nasa internet resource.

    The main problem boosting without an atmosphere could be pressure. But once the flow is supersonic just at the nozzle exit, it doesn't matter, because there would be an independent hot atmosphere inside each engine. SRB's have oxydizer on board, so they don't need any atmosphere. Anyway, as Aerospace engineers know, the default of atmosphere can cause a variation in the engine performance, because power and thrust are also dependant on external pressure.
     
  5. Jul 25, 2005 #4

    FredGarvin

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    From here: http://www.csar.uiuc.edu/F_info/space_shuttle_srb.htm

    EDIT: Clausius beat me to it.
     
  6. Jul 25, 2005 #5

    Clausius2

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  7. Jul 25, 2005 #6
    Thanks for the responses.

    I did encounter the statement that the SRB's include an oxidizing agent. So I am still hung up on the 'traditional rocket motor' part.

    The traditional rocket motor does not require the earths atmosphere as I'm led to believe, so the last question is the output of the traditional motor. If the flames are a result of the atmosphere, and their ignition of the SRB's are a result of the flame, and not the heat or resulting reaction of the traditional motor, then I have to conclude the Earth is required to launch the shuttle.

    If however, the gasses expelled from the traditional motor are sufficient to ignite the SRB's regardless of the light or heat (flames) then the earth is not required.
     
  8. Jul 26, 2005 #7

    Clausius2

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    I) it is not neccessary flames are a result of the atmosphere. Inside the engine could be flames by means of ammonia perchlorate + aluminium reaction. Flames outside the engine can be seen due to a postcombustion by ambient oxygen.

    II) thrust doesn't understand if you are expelling flames or gases. In order to have thrust it is interesting to gather a high mass flow and high exhaust velocity. The multiplication of this two quantities has dimensions of force, and gives you an idea about what will influence thrust. Thrust is not reached via hot flames, but speed of expelled gases. The more temperature and pressure is reached in combustion chamber, the more stagnation enthalpy will be there, and so the more potential exhaust kinetic energy will be. Maybe SRB's are a great example of postcombustion due to the violence of the process, which is not present in Main engines outlet. I keep on thinking it couldn't be neccesary an atmosphere, but I also think that without atmosphere it could there be problems in flame propagation inside engines due to low pressure just at the boosting instant. It could case a premature failure of flame, because the solid fuel will be exposed to a low atmosphere.
     
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