How do rockets in space works?

In summary, rockets work in space by ejecting mass in one direction, causing a reaction in the opposite direction due to the conservation of momentum. This is not the same as pushing against air, but rather relying on the rocket's front wall to be pushed by the pressure of the expanding gases in the combustion chamber. The center of mass of the rocket and its fuel remains constant to conserve momentum, and the Earth may play a role in the initial take-off by acting upon the total system's center of mass. There are multiple ways to understand this process, including looking at it in terms of Newton's laws of motion and considering the rocket's combustion chamber design.
  • #1
Brett13
15
0
Nasa uses chemical rockets in space right? On Earth I could understand how they work, the one reaction produces an equal and opposite reaction. So on Earth the rocket would be pushing on air to propel itself. But there's no air in space... Edit:::: I added an s to "works" in the title, my bad
 
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  • #2
Rockets on Earth don't push against the air either. It's quite simple - exhaust goes backwards, so to conserve momentum the rocket goes forward.
 
  • #3
Even then though wouldn't the exhaust have to push on something to propel the rocket? its 2:48 in the morning maybe I am just tired haha...
 
  • #4
It's not "pushing air" to propel itself, that's wrong.

Rockets just eject mass in one direction and the rocket head is pushed in the opposite direction. The center of mass of rocket + fuel cannot move since there is no net force on the system, so the rocket head must move in order to conserve momentum.

Has nothing to do with pushing air, you're thinking of a propeller.
 
  • #5
Oooooh so the ejection of the exhaust(the mass) is what propels it. OK thank you very much
 
  • #6
yes you have to lose mass. It is a very inefficient way to do it but nobody has figured out a better way.

its like standing on ice and throwing bananas... you'll start sliding a little but with much effort
 
  • #7
Curl said:
its like standing on ice and throwing bananas... you'll start sliding a little but with much effort

If you could throw bananas with a speed equal to the exhaust speed of a typical rocket engine, you would do very well! :biggrin:
 
  • #8
I believe grapes would be more efficient? :rofl:
 
  • #9
Brett13 said:
Oooooh so the ejection of the exhaust(the mass) is what propels it. OK thank you very much

It is perfectly acceptable to try to understand this in terms of Newton's 3.law of motion, as long as you do that PROPERLY:

You have then, at all times, TWO "objects":
Object 1: Ship+remaining fuel
Object 2: The fuel that is being exhausted.

Object 1 acts upon Object 2 with a force so that Object 2 is ejected.
According to Newton's 3.law, then, Object 2 acts upon Object 1 with a reaction force of equal magnitude, causing THAT to accelerate as well.

When we look, however, on the TOTAL system ship+fuel (ejected or still inside ship), there will never be any dislocation of its center of mass, under the assumption of no external forces acting upon it.

At the initial take-off, the Earth WILL act upon that total system's center of mass, by additional mechanism to, say, gravity:
Namely to push exhausted fuel hitting it.

The dislocation of the total system's center of mass must not, however, be confused by the dislocation of the SHIP's center of mass...(the latter one arguable the most important one!)
 
  • #10
There's another way to look at it, that is equally valid.

If you think about the rocket's combustion chamber, it has a front wall, side walls and no back wall.

The expanding gasses inside the chamber press against the walls.
The side walls all cancel out - there's as much pressure top as bottom and left as right. So the rocket isn't pushed sideways.
But the front wall has pressure against it that isn't balanced by the pressure against the back wall (because the IS no back wall!).
That pressure against the front of the combustion chamber pushes the rocket forward.

This isn't a different explanation - it's really the same one from a different point of view.
(You can often look at things in different ways in Physics)
 
  • #11
AJ Bentley said:
There's another way to look at it, that is equally valid.

If you think about the rocket's combustion chamber, it has a front wall, side walls and no back wall.

The expanding gasses inside the chamber press against the walls.
The side walls all cancel out - there's as much pressure top as bottom and left as right. So the rocket isn't pushed sideways.
But the front wall has pressure against it that isn't balanced by the pressure against the back wall (because the IS no back wall!).
That pressure against the front of the combustion chamber pushes the rocket forward.

This isn't a different explanation - it's really the same one from a different point of view.
(You can often look at things in different ways in Physics)

Quite so.

In an action/reaction-couple, what counts as the "action" and what is the "reaction" is largely arbitrary.

Of course, by having a chamber that can be tilted sideways, then the rocket will be pushed in a slightly different direction, along the direction indicated by the open end and the "front"
 

1. How do rockets generate enough thrust to leave Earth's atmosphere?

Rockets generate thrust through the principle of action and reaction, also known as Newton's Third Law of Motion. As the rocket's engines burn fuel and expel exhaust gases at high speeds, an equal and opposite force is created, pushing the rocket upwards.

2. How do rockets navigate and steer in space?

Rockets use a combination of thrusters and guidance systems to navigate and steer in space. Thrusters provide small bursts of thrust to change the rocket's direction, while guidance systems use sensors and computers to calculate and adjust the rocket's flight path.

3. How do rockets achieve escape velocity?

Escape velocity is the speed required for an object to break free from the gravitational pull of a planet. Rockets achieve escape velocity by continuously accelerating until they reach a speed that is faster than the planet's gravitational pull, allowing them to escape into space.

4. How do rockets generate energy and power in space?

Rockets generate energy and power through onboard power systems, such as solar panels or fuel cells. These systems convert energy from sources like sunlight or stored fuel into electricity to power the rocket's systems and equipment.

5. How do rockets return to Earth after completing their mission?

Rockets can return to Earth through a controlled descent using thrusters and parachutes, as seen in the case of reusable rockets like SpaceX's Falcon 9. Alternatively, some rockets are designed to burn up in the Earth's atmosphere, like the Space Shuttle, while others may land on a designated landing pad or in the ocean.

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