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Multi-stage rockets

  1. Nov 25, 2016 #1
    • Poster has been reminded that they need to show their best efforts to answer the question
    1. The problem statement, all variables and given/known data
    Assess why there can advantageously be used multistage rockets, with a calculation example.

    2. Relevant equations - 3. The attempt at a solution

    Hello all,
    i need to show why it is an advantage to use multistage rockets, with some mathematical proof, and im a bit lost. I have done calculations on single-stage rockets, but im not sure where to start with multistage rockets.
    So it would be great if somebody could suggest some formulars to use to proof this.

    (sorry for my english)
    thanks
     
  2. jcsd
  3. Nov 25, 2016 #2

    BvU

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    Hi,

    PF culture insists you make the first move by proposing something. But to get you under way: Suppose you have a backpack full of bottles of water. Would you get further if you carried the empty ones with you on your trip through the desert ? Or would it be better to make use of the many recycle points they have on the way to the next oasis :smile: ?

    And your english is just fine (said the dutchman)
     
  4. Nov 25, 2016 #3
    1. The problem statement, all variables and given/known data
    Assess why there can advantageously be used multistage rockets, with a calculation example.

    2. Relevant equations - 3. The attempt at a solution

    Hello all,
    i need to show why it is an advantage to use multistage rockets, with some mathematical proof, and im a bit lost. I have done calculations on single-stage rockets, but im not sure where to start with multistage rockets.
    So it would be great if somebody could suggest some formulars to use to proof this.

    I dont know if this is right but:

    If i have tried to do some calculations on multi-stage rocket with the rocket equation,
    dv=u*ln(m0/mf)+u*ln(m0-dm/mf-mr-dm) where dm is the propellant used, mr is the stage there are droped off, m0 is total mass, including propellant, i find the sum of the total delta V, in the first step i use the tsiolkovsky rocket equation, and i add it with again the tsiolkovsky rocket equation just with the new mass for the next stage.
    i have tryed looking at det difference in delta V, ( the maximum change of velocity of the vehicle) but when i
    comparer the numbers, the dV is a lot smaller with a 2-stage-rocket - can that be true?

    thanks @BvU

    (sorry for my english)
    thanks
     
  5. Nov 25, 2016 #4

    haruspex

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    I've not gone through what you wrote in detail, but it sounds like you have not done the right comparison. You need to compare a two stage rocket and a one stage rocket with the same payload and same total fuel.
     
  6. Nov 25, 2016 #5
    Thanks- i see my mistake now, in my calculations for the masse i accidently changed the size of the payload's mass
     
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