• Support PF! Buy your school textbooks, materials and every day products Here!

Minimum thrust of engines at lift-off

  • Thread starter zebra1707
  • Start date
  • #1
107
0

Homework Statement



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?

Homework Equations





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
 
Last edited:

Answers and Replies

  • #2
107
0
Any thoughts?

Cheers
 
  • #3
77
0
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.
 

Related Threads for: Minimum thrust of engines at lift-off

  • Last Post
Replies
2
Views
1K
Replies
4
Views
3K
  • Last Post
Replies
1
Views
2K
  • Last Post
Replies
6
Views
10K
Replies
4
Views
822
  • Last Post
Replies
21
Views
1K
Replies
7
Views
1K
  • Last Post
Replies
4
Views
3K
Top