Rockets work in a vacuum
« on: October 24, 2022, 03:28:29 PM »
I would like to make the case that rockets working in a vacuum is compatible with FE but a troubling part of some people’s FE belief.

It is conservation of momentum that propels a rocket and there’s no element of this that would require an atmosphere. If I fire a bullet out of a handgun, the force imparted on the bullet (small mass) to send it at muzzle velocity is also imparted onto my body (larger mass).

And you could argue: you’ve never been to space and can’t objectively prove a rocket works in space!
Which is, of course, a loaded argument and takes you nowhere. You can’t reasonably expect a random person to have gone to space.
The ONLY reason you would “assume” a rocket is nonfunctional in space is because it’s not pushing off air, and won’t move. However, you can prove this from home!

If I stand on a skateboard and throw a large 10 pound ball, I will move some distance. If I throw a smaller 10 pound ball with a smaller surface area, according to “rockets don’t work in vacuum theory” its lower air resistance would move me a smaller distance. But you can prove for yourself that the large 10 pound ball and the small 10 pound ball move you the same distance! This is conservation of momentum at work, and it DEMONSTRABLY does not require atmospheric conditions.

Proponents of the “rockets don’t work in a vacuum” theory like to describe the scenario of a rocket shooting off its propellant in space and “not moving” because there’s “nothing to push off”. This would violate the law of conservation of momentum, which as we established can be proven AT HOME to not require atmosphere. If you fire a 12 gauge shotgun, it is not the force of “air resistance” beating up your shoulder but the chemical force sending small pellets at muzzle velocity imparted into the shotgun sending it backwards!
The same would apply to a can full of air, or hypergolic fuels, or liquid fuel/oxygen fuel and there’s no reason to believe otherwise other than being intentionally obtuse.



If your basis in believing space is fake is because of X, once X is proven to be a null point, why continue using X as a point?

The whole “rockets don’t work in a vacuum” problem seems pretty clearly rooted in stubbornness. I’m not even saying “earth is globe because rockets work in a vacuum”. I am making the point that if you’re going to argue for the case of FE, rockets are not your winning case! I could write a book on how the earth could be flat, and still I know it’s not.


TL;DR Even FE must concede that rockets work in a vacuum, believing that they don’t is misunderstanding why.
« Last Edit: November 19, 2022, 03:50:38 AM by secretagent10 »

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Offline Tron

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Re: Rockets work in a vacuum.
« Reply #1 on: October 24, 2022, 11:40:56 PM »
I'm with you on space travel...  But to play devil's advocate consider this..

If you throw a bowling ball from a skateboard then you will move in the opposite direction.  Until of course the bowling ball drops and you lose speed because of ground resistance.

If you throw a bowling ball from a skateboard in space, you will probably move in the opposite direction but keep moving because there's no resistance.  I think that's the conservation of momentum principle.

However, whats giving you momentum in both scenarios is the initial torque generated by throwing the bowling ball or firing a bullet out of a gun.  But rockets don't "push" a spaceship for a second or two. They continually accelerate an object over time. 

If you had really long arms and pushed a bowling ball away from you on a skateboard for miles and miles the skateboard would probably stop after a few moments after the initial "push" is gone.

This principle might work in space if a ship needs to make a quick maneuver and continue slowly in one direction. I think they use quick shots of pressurized gas to move in space like in the Apollo movies.  But I'm not sure rockets can propel a spaceship continually over time in a near vacuum... Maybe thats why they loose the rocket boosters once in orbit?

I like thinking rockets are pushing against air and I don't understand other arguments.  Do they push internally against themselves?

I'm kindof new to this topic.
« Last Edit: October 24, 2022, 11:50:48 PM by Tron »
From the surface Earth looks flat.  From space Earth looks round.  Now what?

Re: Rockets work in a vacuum.
« Reply #2 on: October 25, 2022, 12:40:47 AM »

However, whats giving you momentum in both scenarios is the initial torque generated by throwing the bowling ball or firing a bullet out of a gun.  But rockets don't "push" a spaceship for a second or two. They continually accelerate an object over time. 


Well for one, torque is a twisting force unrelated to gas leaving a nozzle or bowling balls being thrown.
As for the bowling ball/rocket analogy, imagine instead of just throwing the bowling ball I have 1000 bowling balls and I’m throwing them at a very fast rate. Now imagine instead of bowling balls and throwing force, it’s just gas and chemical energy!
If you like the pushing off air idea, you could say that the rocket is “pushing off” its own gases. Or if you’re throwing a bowling ball, you’re “pushing off” the bowling ball’s mass. You can see how atmosphere isn’t involved in this process!

And for the people (not you) that say “show me a repeatable experiment where rockets work in a vacuum”, I would say just look at the the thousands of rockets that have been to space. It is, in fact, repeatable if you have millions of dollars. What FE’ers are really saying is “it’s not repeatable without having millions of dollars”, which is an easy trap to fall into.
« Last Edit: October 25, 2022, 12:44:57 AM by secretagent10 »

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Re: Rockets work in a vacuum.
« Reply #3 on: October 25, 2022, 12:51:11 AM »
That's a good analogy.  It's like firing a gun continually in space and being kicked backed over and over, faster and faster.

I knew Torque wasn't the word but it sounded legit.   ;D
From the surface Earth looks flat.  From space Earth looks round.  Now what?

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Re: Rockets work in a vacuum.
« Reply #4 on: October 26, 2022, 09:17:11 AM »
I've been digging into this topic and I'm sort of on the fence still. If you launched an unbreakable balloon into space filled with highly pressurized air and released it out of the tip, I think it would probably stand still and just lose air. 

Rockets are built in a similar way.  Highly pressurized gas is released from a nozzle. 

If space is not a complete vacuum, which I don't believe it is, then the two above mechanisms should have propulsion from the exhaust.

Anyway, here's a fun picture of a metallic space balloon called Echo which was  the first satellite America sent into orbit.


https://en.wikipedia.org/wiki/Project_Echo
From the surface Earth looks flat.  From space Earth looks round.  Now what?

Offline SteelyBob

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Re: Rockets work in a vacuum.
« Reply #5 on: October 26, 2022, 10:04:35 AM »
I've been digging into this topic and I'm sort of on the fence still. If you launched an unbreakable balloon into space filled with highly pressurized air and released it out of the tip, I think it would probably stand still and just lose air.

No, that’s not right, as that would violate conservation of momentum. If the air is leaving the balloon in one direction, then the balloon has to move in the other direction to balance out the momentum. In simple terms, the mass times the velocity of the air on one direction will equal the mass times the velocity of the balloon.

If you want to really get into it, you’ll see that the rocket thrust equation has both a momentum term (the mass flow rate x velocity) and a pressure term (the net pressure across the rocket / balloon etc) so the ambient static pressure does make a difference - you actually get higher thrust in a vacuum all things being equal.

There’s nothing in the wiki that I can see about this, so can we conclude that the general tfes consensus is that rockets can work in a vacuum?


Re: Rockets work in a vacuum.
« Reply #6 on: November 18, 2022, 12:45:36 AM »
There’s nothing in the wiki that I can see about this, so can we conclude that the general tfes consensus is that rockets can work in a vacuum?

I believe so, but I’m ready to hear any possible responses to this. It doesn’t inherently disprove flat earth, so it may not be a problem.

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Offline Tumeni

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Re: Rockets work in a vacuum.
« Reply #7 on: November 18, 2022, 05:11:07 PM »
If you throw a bowling ball from a skateboard then you will move in the opposite direction.  Until of course the bowling ball drops and you lose speed because of ground resistance.

Whether the ball drops or not is immaterial, since you are now separated from it. All that determines whether you keep going or not is air resistance and wheel friction, along with slope of the ground.


I'm not sure rockets can propel a spaceship continually over time in a near vacuum... Maybe thats why they loose the rocket boosters once in orbit?

First stages or boosters are discarded after a few minutes simply because they run out of fuel. After that point, there is no value in carrying the weight of the stage or booster. In SpaceX's case, they bring them back down and re-use them. In the recent Artemis launch, the solid fuel boosters were discarded totally. Shuttle boosters were recovered in some instances, but not re-used, as far as I know

Most all spacecraft do not use rockets continuously. In Apollo, a 2 or 3 minute exit burn sent the craft toward the Moon, and it coasted the rest of the way, with nothing to slow it down. SpaceX runs the second stage for a few minutes in order to get the craft to its intended orbital height, then it too, coasts along.
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Re: Rockets work in a vacuum
« Reply #8 on: November 18, 2022, 05:27:48 PM »
I think I said the skater had long arms, but either way I agree with you.  Lol.

That's interesting info you provided about rocket burns with SoaceX and NASA.  I didn't know they generally coasted once they reach a Target attitude.

This sort of lends evidence to the idea that rockets work best in an atmosphere...Or they need an atmosphere. 

  Why not keep firing rockets in the middle of there trip to the moon if it gets them there sooner? 
From the surface Earth looks flat.  From space Earth looks round.  Now what?

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Offline Tumeni

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Re: Rockets work in a vacuum
« Reply #9 on: November 18, 2022, 05:33:31 PM »
This sort of lends evidence to the idea that rockets work best in an atmosphere...Or they need an atmosphere.

Why?

 
Why not keep firing rockets in the middle of there trip to the moon if it gets them there sooner?

For a manned mission such as Apollo, you need to carry enough fuel in the first and second stages to get to the velocity where you can leave orbit. The third stage is used to leave Earth orbit, but ... the faster you go, the more fuel you need in order to stop at the other end of the journey. The only brakes you have are the fuelled engines, and lunar gravity. So there's a fine balancing act between all the stuff you need to carry for survival of the crew, the duration of the mission, and your fuel capacity.
 

« Last Edit: November 18, 2022, 05:43:09 PM by Tumeni »
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Offline markjo

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Re: Rockets work in a vacuum
« Reply #10 on: November 18, 2022, 06:01:28 PM »
That's interesting info you provided about rocket burns with SoaceX and NASA.  I didn't know they generally coasted once they reach a Target attitude.
That can happen when you rely on science fiction to teach you astrodynamics.

This sort of lends evidence to the idea that rockets work best in an atmosphere...Or they need an atmosphere. 
Actually, rocket engines are more efficient in a vacuum.
https://www.uu.edu/dept/physics/scienceguys/2002Sept.cfm

Why not keep firing rockets in the middle of there trip to the moon if it gets them there sooner?
Because that requires more propellant, which in turn requires a bigger rocket.  It's known as the tyranny of the rocket equation.
https://www.nasa.gov/mission_pages/station/expeditions/expedition30/tryanny.html
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Re: Rockets work in a vacuum
« Reply #11 on: November 18, 2022, 08:23:03 PM »
I'll be honest, Markjo, Tumeni - I've considered your arguments and read your literature...

Nobody, and I mean nobody, really goes into detail about how rockets behave in a vacuum.  They try, but nobody, not even the rocket builders go into detail about how "newton's" law of momentum explains everything...  It stills leaves a big question mark about the simple question of - how do you push against nothing?  A gun explodes against a bullet.  A rocket explodes against nothing.. A vacuum, which by definition pulls things away from an object; not remain stationary to cause an opposite reaction which is needed to propel another object the opposite way (like Newton said). 

That being said, I don't discredit the argument that rockets push off their own fumes.  It seems silly, but I might be missing something here..

But here's the problem...    I have two ideas for how Rockets work.  The first is that Rockets do propel themselves.  Rockets take off, enter earth's orbit - and if they don't stay there = they use rockets again to leave orbit and point themselves at another target like the moon or mars, etc... 

Why do they shut off?  Possible cost restraints but I find this hard to believe.  The earth's gravity is what slows the Lunar spacecraft before approaching the moon (to about 2,500mph) before they use thrusters again..

So, it seems like most of their speed and braking power were gained by orbiting earth and later by possibly orbiting the moon or just using earth's gravity to gradually accelerate the spacecraft back to earth.

Now here's the second theory:  What if the rockets performed well within earth's atmosphere, then entered earth orbit - which in my opinion is solar winds going around earth consisting of some matter - then rockets are used briefly to exit the solar winds, at which time the spacecraft has enough momentum in a "limited vacuum" to go to there destination with course corrections on the way.   

What about rockets working better in a vacuum?  Why?  Because the gas can exit the "thrusters" at a higher speed.

Okay, but rarely mentioned is that rockets also are freer from gravity and atmospheric friction which allows it to travel faster.... 

But, more importantly, rockets will work just as well in a "semi-vacuum" using a little bit of matter to "push off of" as I'm suggesting...

I'm gonna be mad when the final answer to "do rockets work in a vacuum" is - well, it depends on what you mean by a vacuum... An absolute vacuum or a semi-vacuum?

Either way it's an impasse...  NASA builds the rockets and they say they work in a vacuum...   I believe it's probably a combination of both "gas pushing on gas" and "gas pushing on matter" like jets do. 
From the surface Earth looks flat.  From space Earth looks round.  Now what?

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Offline Tumeni

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Re: Rockets work in a vacuum
« Reply #12 on: November 18, 2022, 09:47:41 PM »
Vacuums don't "pull". Vacuums cannot "do" anything to influence matter.

Let's indulge you on the "rockets push off air" line. Consider this; in order for the rocket to push off the air, wouldn't the air need to, generally speaking, stay in the vicinity of the rocket? Have you ever seen air do this? Have you ever seen a rocket launch where there has NOT been considerable movement of air, exhaust product, etc. AWAY from the rocket?

Also, consider this; exhaust product leaves the rocket, where it contacts air. How does this transfer back to the rocket in order to generate forward motion? The exhaust and the air are both detached from the rocket now, and the exhaust product is moving away from the rocket, and taking the air with it.

You can bleat about "nobody going into detail about how they work" all you like, but I'll wager that you haven't looked at any real textbooks or peer-reviewed papers on the topic, and I'll wager that you don't actually work in an industry involved in rocketry, and so wouldn't encounter anyone who knows this stuff on a day-to-day basis.
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Re: Rockets work in a vacuum
« Reply #13 on: November 18, 2022, 09:52:22 PM »
Nobody, and I mean nobody, really goes into detail about how rockets behave in a vacuum.  They try, but nobody, not even the rocket builders go into detail about how "newton's" law of momentum explains everything...  It stills leaves a big question mark about the simple question of - how do you push against nothing?  A gun explodes against a bullet.  A rocket explodes against nothing..

The engines shut off because they’re only used to accelerate, not maintain velocity. If you burn outwards from earth, you could burn for a short period then coast out of its gravitational pull - most of that trip the engines are off.

And it’s not “pushing against nothing”, that’s a misunderstanding. That’s like saying it’s air resistance pushing you back when you fire a
shotgun, when it’s not. It’s an extremely powerful chemical reaction. The pellets go forwards, you go backwards.

No part of that process involved atmosphere - so why would it be any different in a vacuum?

And to say that nobody goes into detail about the matter is untrue, there’s thousands of books and explanations to read, and experiments that can be done by anyone.

Offline SteelyBob

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Re: Rockets work in a vacuum
« Reply #14 on: November 18, 2022, 10:38:47 PM »
.. A vacuum, which by definition pulls things away from an object; 

It’s hard to know where to start when you’re so all over the place. It’s ok to ask questions, but when people show you the answers, you need to actually listen and learn. I mentioned, and another poster actually linked to detailed information about the rocket equation. This isn’t fiction - it is extensively used and tested.

Your ‘definition’ of a vacuum simply isn’t even close to being the definition of a vacuum.

If you look at the equation for thrust from a rocket:

Thrust = F = dm/dt Ve+ (Pe-Po)Ae

you can see that part of the thrust depends on the static pressure, Po, around the rocket. That means less thrust at sea level, for example, than at 40,000 feet - all other things being equal, of course. Extend that logic and, as you go further away from earth and the static pressure reduces, the thrust will actually increase. In a vacuum, that term disappears from the equation - but the rocket is still developing thrust.

If you disagree with this, you aren’t just arguing with the fact that rockets work in space, you’re arguing with the variation in thrust at different pressures in the atmosphere, which is widely tested and understood.

Maybe it’s time to rethink and admit that you’re wrong?

Re: Rockets work in a vacuum
« Reply #15 on: November 18, 2022, 11:24:03 PM »
I believe it's probably a combination of both "gas pushing on gas" and "gas pushing on matter" like jets do.

Jets don't "push on" anything; they eject gas (which has mass) at high velocity in a particular direction, and the reactive force accelerates the engine in the opposite direction, just like Isaac Newton, Bob, Tumeni, SA10 and the jet engine books have been telling you.  And rockets work on exactly the same principal except that they don't have to collect the gas through an intake; they create it by a chemical reaction between fuel and oxidiser.  I'm a retired jet engine engineer.  it was my job. 

Your posts are littered with phrases like "I think", "it seems like" and "I believe".   With the greatest respect, rather than argue from ignorance, you really need to just take some time out to do some proper education about physics.  Don't even sweat the numbers and formulas, just get your head around the principals.  It really isn't difficult. 

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Offline markjo

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Re: Rockets work in a vacuum
« Reply #16 on: November 19, 2022, 01:27:54 AM »
I'll be honest, Markjo, Tumeni - I've considered your arguments and read your literature...

Nobody, and I mean nobody, really goes into detail about how rockets behave in a vacuum.  They try, but nobody, not even the rocket builders go into detail about how "newton's" law of momentum explains everything... 
Well, it helps if you understand Newton's laws of motion.
http://www.physics4kids.com/files/motion_laws.html

It stills leaves a big question mark about the simple question of - how do you push against nothing?  A gun explodes against a bullet.  A rocket explodes against nothing..
It might also help if you used the right terms.  The rocket is the system as a whole.  It's the rocket's exhaust gasses that do the work and the action/reaction happens in the the expanding gasses push against the engine bell as they exit.  The conservation of momentum comes in when you look at the mass and velocity of the exhaust gasses going in one direction and the mass and velocity of the rocket moving in the other.
Abandon hope all ye who press enter here.

Science is what happens when preconception meets verification.

Ignorance more frequently begets confidence than does knowledge. -- Charles Darwin

If you can't demonstrate it, then you shouldn't believe it.

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Offline Tron

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Re: Rockets work in a vacuum
« Reply #17 on: November 19, 2022, 01:47:52 AM »
Thank you everyone for your responses.  Please give me a day to adaquetly respond.
From the surface Earth looks flat.  From space Earth looks round.  Now what?

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Offline stack

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Re: Rockets work in a vacuum
« Reply #18 on: November 19, 2022, 05:40:42 AM »
Thank you everyone for your responses.  Please give me a day to adaquetly respond.

Just a quick and dirty visual for you whilst you ponder...



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Offline Tron

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Re: Rockets work in a vacuum
« Reply #19 on: November 19, 2022, 08:12:31 PM »


Hi Guys,

Please consider the picture above.  I am unsure where the "thrust" is generated in a rocket.  More importantly, where does the friction occur between the Gas and another object to get an Action/Reaction.  Hot Gas is hitting what exactly to propel the rocket in the opposite way? 

MarkJo says the Gas is hitting the Bell/Thruster.   Another says it's Gas on Gas.  I think it's Gas on Air.   I've labeled each possibility in the picture above. 

Once the gas hits a medium, it generates back pressure which propels a rocket forward.   The circular flat injection plate is the location where gas pressure pushes against the Saturn V rocket to propel it forward. 

Naturally this is a confusing subject.  I'd like to conclude by asking why a rocket should behave any differently than an afterburner on a jet.  It uses very hot gas to push against air in the exhaust "bell".  Assuming space isn't a "complete" zero vacuum, then why shouldn't it work the same?

And stack, Newton made it clear that MASS is important in the action/reaction equation.  The greater the mass of one object compared to another, the less it will move. 
From the surface Earth looks flat.  From space Earth looks round.  Now what?