How does propulsion in space work

[anonymous-user]

Space is a vacuum, so when rocket propulsion is used, what is it "pushing" against to propel the space craft?

Surely the jet would be firing into a vacuum which wouldn't give any thrust, and simply get consumed into the vacuum.

[tmk2]

I may be wrong but isn't it just Newton's third law.
For every action, there is an equal and opposite reaction

[anonymous-user]

Conservation of momentum!

[Lefty]

tmk2 said:

I may be wrong but isn't it just Newton's third law.
For every action, there is an equal and opposite reaction

Nope, don't think you're wrong.

[CubanPete]

It's pushing against the fuel it expels.

[CubanPete]

(M1+M2)V = M1V1 + M2V2

[Sylvaforever]

Hamsters. Thousands of them in fact.#



















#this may not be accurate.

[stuartmmcfc]

Fake news.
Space travel is a hoax.

[xRIEx]

As above - reaction engines.

https://en.wikipedia.org/wiki/Reaction_engine

[Eric Mc]

Thunderhead said:

Space is a vacuum, so when rocket propulsion is used, what is it "pushing" against to propel the space craft?

Surely the jet would be firing into a vacuum which wouldn't give any thrust, and simply get consumed into the vacuum.

One of the most common misconceptions as to how reaction motor work.

A rocket engine - or a jet engine - moves forward simply because of the thrust it is pushing in the opposite direction.

It doesn't need anything to push against, except itself.

Therefore, whether the engine is operating in a medium, that contains are or in a vacuum matters not one jot.

The only limit for air breathing jet engines is that they need to be immersed in an atmosphere so they can feed off the oxygen in the atmosphere.

A rocket engine continues to work in a vacuum because it carries its own oxygen with it, either in the form of liquid oxygen or in the form of a chemical which contains oxygen (an oxidiser)

[Simpo Two]

Sooo... if you used molten lead as a fuel you'd go much faster due to the mass of the stuff coming out of the back...

[jmorgan]

Always found this helpful.
http://www.braeunig.us/space/index.htm

From here.
http://www.braeunig.us/space/index.htm

OK, got actual maths n stuff but its there.

[eldar]

Simpo Two said:

Sooo... if you used molten lead as a fuel you'd go much faster due to the mass of the stuff coming out of the back...

You would if you were throwing it. Needn't even melt it.

[Eric Mc]

You can chuck what you like out the back but rocket fuel tends to work better.

[xRIEx]

Simpo Two said:

Sooo... if you used molten lead as a fuel you'd go much faster due to the mass of the stuff coming out of the back...

P = mv

If the mass of lead was greater than the mass of the exhaust gases in current rocket engines and the velocity was the same, then sure.

[Moonhawk]

Simpo Two said:

Sooo... if you used molten lead as a fuel you'd go much faster due to the mass of the stuff coming out of the back...

The amount of thrust is a function of the mass of the propellant and the speed at which it is chucked out the back.

That's why ion engines are so good - they only use a small amount of fuel - but they chuck it out at very high speed.

[Buzz84]

Spacecraft in orbit are not necessarily manouvered using rocket engines carrying out burns. For more precise manouvering they simply use a release of a compressed gas.

Almost like the bloke on an office chair with a CO2 fire extinguisher!

[Beati Dogu]

Cold gas thrusters they're called. Nitrogen gas mostly.

Sylvaforever said:

Hamsters. Thousands of them in fact.#


#this may not be accurate.

There were 40 mice on the most recent SpaceX resupply capsule to the ISS.

[talksthetorque]

Got to have something for Space Cat to chase

[Eric Mc]

Buzz84 said:

Spacecraft in orbit are not necessarily manouvered using rocket engines carrying out burns. For more precise manouvering they simply use a release of a compressed gas.

Almost like the bloke on an office chair with a CO2 fire extinguisher!

They do work on the same principle as a rocket i.e. they are reaction thrusters. They tend to be used for low mass objects, like small satellites and even astronaut manoeuvering units.





Another technique used to manoeuver an object in space are reaction control wheels. These have the advantage of not needing any sort of rocket fuel or gas so, in theory, can be used for as long as they have an electricity supply or don't physically break. The Hubble Space Telescope uses this method because they didn't want the area around the telescope polluted by particles of gas or spent fuel, for obvious reasons.