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Rocket propulsion

  1. Dec 30, 2011 #1
    Did a question about this a few weeks ago, but I thought I might do another, as I don't quite get, what is going on.
    The relationship:
    v=vex * log(m0/m(t))
    tells us that a rocket will attain greater and greater acceleration as time goes. However, when I try to simulate this in Matlab I get the curve attached (time versus velocity). Anyone got an idea, what could be wrong? It looks similar to that of a ln-curve, but shouldnt it look differently. If someone is into Matlab programming, can they please look at what I've failed in my (short!) script (attached).
     

    Attached Files:

  2. jcsd
  3. Dec 30, 2011 #2

    Filip Larsen

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    Gold Member

    If you want something to compare with you can look at plot of the normalized rocket equation on WolframAlpha: http://www.wolframalpha.com/input/?i=plot+-ln(1-x)+from+0+to+1 where x-axis is the mass ratio (relative to initial mass) spend as fuel and y-axis is the change in velocity relative in unit of the exhaust speed.
     
  4. Dec 30, 2011 #3

    D H

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    aaaa202: Typically the independent variable (time in this case) is on the horizontal axis and the dependent variable (velocity in this case) is on the vertical axis. You are plotting time on the vertical axis, velocity on the horizontal.

    Switch the arguments to the plot function and all will be well.
     
  5. Dec 31, 2011 #4
    OMG! I can't believe that solved it! Thank you so much!
     
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