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Graph of multi-stage rockets

  1. Nov 26, 2016 #1
    1. The problem statement, all variables and given/known data
    Show why it is advantageous to use multistage rockets

    2. Relevant equations - 3. The attempt at a solution
    Hello there
    I have to show why using multi stage rockets are an advantage, i have done som calculations for a 2. stage rocket and a singel stage, with the same payload mass, and the same total fuel, i took 80% of the stage
    was fuel, and in total 800, i think this is right, (plis correct me if i'm wrong, the math is shown in the pic) - so to my question, can i make a plot like a graph, to show the multistage rocket is superior, i have tryed to plot v as a funktion to t v(t), but i cant seem to get a t into the equation.
    sorry if it sounds a bit silly, but hope someone can help, rocket physics is difficult :/ - thanks
    upload_2016-11-26_22-10-55.png
     
    Last edited: Nov 26, 2016
  2. jcsd
  3. Nov 26, 2016 #2

    haruspex

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    Typically you do not care how long the rocket takes, so time is not that interesting. What you care about is how much fuel it needs to lift a given payload into a given orbit. Relate that to the velocity achieved.
     
  4. Nov 26, 2016 #3
    Okay, yes i see your point - can you give me a hint to what equations i can use for this. Im a bit unsure on how to calculate, how much fuel there are used at a specific velocity.
    But Thanks :)
     
  5. Nov 26, 2016 #4

    haruspex

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    You did not define all your mass variables, but I assume some of them refer to fuel masses in the stages. You ended up with an equation for velocity achieved. So you could just plot velocity achieved in the two cases (1 v. 2 stages) against total fuel.
    Before you do that, it would be handy to figure out the optimal distribution of fuel between two stages for a given total.
     
  6. Nov 26, 2016 #5
    Hello thank you for your help, i will try that. I have read that a 2. stage rocket with the same exhaust velocity, should be ½ and ½. Sorry for being a bit slow - if i take the single stage again, i take u*ln( total mass / total mass - fuel) upload_2016-11-27_0-15-2.png
    so how can i plot velocity achieved against total fuel?

    again thank you for helping
     
  7. Nov 26, 2016 #6

    haruspex

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    Rewrite the equation in terms of payload and fuel mass, instead of using total mass. Vary the fuel mass an plot the result.
     
  8. Nov 26, 2016 #7
    Okay i understand now :) thanks
     
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