Is Space Really Empty and What Does That Mean for Propulsion?

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    Compressed Space
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Discussion Overview

The discussion revolves around the nature of propulsion in space, particularly focusing on whether space can be considered empty and how this affects the mechanics of rocket propulsion. Participants explore concepts related to Newton's Third Law, the behavior of gases in a vacuum, and the implications for understanding thrust generation in space versus within an atmosphere.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant expresses confusion about how propulsion works in space if space cannot be compressed, questioning what expanding gases push against to gain momentum.
  • Another participant uses an analogy of throwing a shoe on ice to illustrate how action and reaction forces operate in propulsion, emphasizing that the rocket pushes gases out and the gases push back on the rocket.
  • Some participants argue that the concept of compressing space is a misunderstanding, asserting that rockets do not push against anything in space but rather rely on the reaction forces from expelled gases.
  • There is a discussion about the differences in propulsion mechanisms inside and outside of an atmosphere, with some suggesting that the principles remain consistent despite the absence of atmospheric pressure.
  • One participant attempts to clarify that in a vacuum, the absence of air allows for more efficient thrust generation as there is no gas blocking the exhaust.
  • Another participant highlights the importance of understanding reaction forces and the need for a proper vocabulary to discuss these concepts effectively.
  • There is a mention of how the pressure dynamics within a rocket engine work, including the necessity of maintaining pressure inside the combustion chamber to produce thrust.

Areas of Agreement / Disagreement

Participants exhibit a mix of agreement and disagreement. While some clarify and refine their understanding of propulsion mechanics, others maintain differing views on the role of space and pressure in propulsion, leading to an unresolved discussion on these concepts.

Contextual Notes

Some limitations in the discussion include varying definitions of terms related to pressure and propulsion, as well as differing levels of understanding among participants regarding the physics involved. The conversation reflects ongoing attempts to reconcile these differences without reaching a consensus.

  • #31
CaptTrey said:
. You cannot compress a vacuum but since that area is really not a vacuum. It should be compressible. By that I mean it is possible create a high pressure from a low pressure. I find it hard to believe that the area known as space is completely empty...
It isn't like we are guessing. Humans have sent thousands of objects into space and hundreds of people. We have a pretty good idea about what is out there. Yes, the vacuum of space is pretty empty. In our solar system it is on the order of 100 particles per cubic centimeter, which is sparse enough for a hydrogen atom to travel an average of 150,000 km without hitting another.
 
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  • #32
I'm sure that someday the word vacuum will find a new place. As a mechanic. I never used and was not aware of the use of absolute pressure. As far as empty well, I believe that in time we will find that it is not necessarily true either. 100 particles Per cubic centimeter. Does not sound empty to me.And that is just the particles we are aware of. Until discoveries are actually made I am willing to accept things as they are being presented.
As I wrote previously, I do understand how a rocket engine( external combustion engine) works. Can anyone tell me though, how compressed air jets are used?
 
  • #33
CaptTrey said:
I do understand how a rocket engine( external combustion engine) works. Can anyone tell me though, how compressed air jets are used?
The same way a rocket engine works, just easier to turn on and off. In both cases you accelerate a gas one way and the rest of the rocket accelerates the other way in accordance with Newton's third law.
 
  • #34
CaptTrey said:
100 particles Per cubic centimeter. Does not sound empty to me.
At sea level, it is about 30000000000000000000, so yeah, 100 is pretty empty by comparison.
 
  • #35
DaleSpam said:
The same way a rocket engine works, just easier to turn on and off. In both cases you accelerate a gas one way and the rest of the rocket accelerates the other way in accordance with Newton's third law.
Also exactly like the recoil from a gun.
 
  • #36
CaptTrey said:
As far as empty well, I believe that in time we will find that it is not necessarily true either. 100 particles Per cubic centimeter. Does not sound empty to me.And that is just the particles we are aware of.
This sounds an awful lot like a personal theory to me. What are the rules about threads with personal theories again? Aren't they supposed to be shut down?

In addition, I think we've beat this one to death. I'm closing the thread.

Chet
 
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