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Minimum thrust of engines at lift-off

by zebra1707
Tags: engines, liftoff, minimum, thrust
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zebra1707
#1
Feb28-10, 02:18 AM
P: 107
1. The problem statement, all variables and given/known data

Hi there

Rocket has a total mass of 3.4 x 10^6 kg at lift-off. The first stage contains 2.0 x 10^6 kg of propellants which is consumed at a rate of 1.4 x 10^4 kg s

Find the minimum thrust of the engines at lift-off?

I would have thought that you needed one more variable to be able to solve this?

2. Relevant equations



3. The attempt at a solution

I used the mass flow x escape velocity and ended up with 15.7 x 10^6 N. It takes 142 sec for the first stage to finish its burn.

I just dont think that this is right - as the next part states that if this thrust is sustained - find the time over which the first stage operates and the acceleration of the vehicle at that time. (Neglect air friction - and suume whole flight is vertical.

Help needed please. Cheers
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zebra1707
#2
Mar1-10, 06:43 PM
P: 107
Any thoughts?

Cheers
thehacker3
#3
Sep15-10, 12:29 PM
P: 69
Wouldn't the minimum thrust just be m*g? In order to get the rocket moving, you would need at least 3.3*10^7 N of force.


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