# The Naked Scientists Forum

### Author Topic: What pushes spacecraft along?  (Read 3391 times)

#### Don_1

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##### What pushes spacecraft along?
« on: 17/09/2008 10:05:28 »
Not being a rocket scientist, well not being a scientist of any sort, nor a rocket for that matter, I was wondering how space propulsion works.

I can understand that a rocket is pushed along by the thrust from it's engines. On the launch pad it is pushing against the pad and once airborne it is pushing against the gases in the atmosphere, but once it has left Earth's atmosphere, what is it pushing against for the thrust to make the rocket move? Why does the thrust not simply dissipate into space?
« Last Edit: 18/09/2008 18:11:03 by chris »

#### Pumblechook

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##### Re: What pushes spacecraft along?
« Reply #1 on: 17/09/2008 11:23:14 »
Have to think about firing a gun  and the recoil backwards.

#### Pumblechook

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##### Re: What pushes spacecraft along?
« Reply #2 on: 17/09/2008 11:29:06 »
http://www.sciencebyjones.com/momentum1.htm

""The operation of a rocket illustrates conservation of linear momentum.  When the rocket stands stationary on its launching platform, its momentum is zero.  When it is fired, the momentum of the gases rushing out downward is balanced by the momentum in the other direction of the rocket body moving upward; the total momentum of all constituents of the rocket, gases, and body, remains zero, because momentum is a vector quantity and the upward and downward momenta cancel outs.   Thus a rocket does not operate by ‘pushing’ against anything and functions best in the near vacuum of space, where friction is virtually absent. ""

#### Don_1

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##### Re: What pushes spacecraft along?
« Reply #3 on: 17/09/2008 14:07:30 »
So I was wrong in assuming that the thrust was pushing against anything. Thank you.

I shall now hotfoot to the garage, nail a few bits of wood together, stick on some old diner plates (for the heat shield), eat a huge bowl full of Heinz baked beans & Planters peanuts vindaloo, with a side dish of Brussel Sprout Jalfreze all washed down with a few pints of Guinness and in no time I shall pose a serious threat to NASA and my underwear.

#### Pumblechook

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##### Re: What pushes spacecraft along?
« Reply #4 on: 17/09/2008 21:10:51 »
A jet engine might work both by pulling itself through the air like a propeller aircraft or a ship in water and by the principle of the conservation of linear momemtum.??

#### DoctorBeaver

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##### Re: What pushes spacecraft along?
« Reply #5 on: 18/09/2008 08:05:34 »
So I was wrong in assuming that the thrust was pushing against anything. Thank you.

I shall now hotfoot to the garage, nail a few bits of wood together, stick on some old diner plates (for the heat shield), eat a huge bowl full of Heinz baked beans & Planters peanuts vindaloo, with a side dish of Brussel Sprout Jalfreze all washed down with a few pints of Guinness and in no time I shall pose a serious threat to NASA and my underwear.

If you wish to achieve warp speed, add a couple of hard boiled eggs to your baked bean curry

#### Don_1

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##### Re: What pushes spacecraft along?
« Reply #6 on: 18/09/2008 08:12:55 »
Good stinking thinking Doc

#### The Naked Scientists Forum

##### Re: What pushes spacecraft along?
« Reply #6 on: 18/09/2008 08:12:55 »