Honeymoon on Mars

Andreas_Firewolf · 2018-08-18 01:43:09

Last night I have been meditating on the very long EMA proposed above for launching from Earth.
At first I was thinking about a vertical EMA like an elevator shaft.
But we can design it to rise in another angle with the horizontal plane.
If we design a very long EMA rising 2000 meters above ground with an angle of 5 degrees with the horizontal plane,
the length of the EMA would be 2000 / sin(5) meters equals 22947 meters or roughly 23 km.
(5 degrees and 2000 meters elevation are just as examples.
What is practical should be decided by costs, available land and construction limits.)

With an EMA of 23 km you can accelerate a space-vehicle to the following speed:

With an acceleration of 10 m/s2 you accelerate to 2441 km/hour
With an acceleration of 20 m/s2 you accelerate to 3456 km/hour
With an acceleration of 30 m/s2 you accelerate to 4212 km/hour
With an acceleration of 40 m/s2 you accelerate to 4867 km/hour

That is not enough speed to connect with a space-station. So the space-vehicle should carry some fuel.
But it would be significantly less. So the mass of the cargo can be much higher.

When launching a rocket from earth, you have two disadvantages.
1. You have to carry extra fuel.
2. You have to overcome the resistance of the air, which is quite thick at sea-level.
This resistance also causes a heat problem.

When you launch a space-vehicle from Earth with a very long EMA

AND

you suck out the air in the EMA before launching

your heat problem will be significantly less,
and you can launch with much less fuel.

The launch of a space-vehicle with an EMA of 23 km would take 68 seconds when you accelerate with 10 m/s2
or 34 seconds when you accelerate with 40 m/s2

Sucking out the air from the EMA would be the most time-consuming.
If you can do that in 10 minutes, you can launch 6 space-vehicle per hour.
If you have enough electricity.

The space-vehicle would be in a container.
The EMA accelerates the container.
After the container is clear from the EMA, the space-vehicle could be expelled from the container with air-pressure or electro-magnetism.
The energy and the equipment for that could be in the container.
Once the space-vehicle is clear from the container, the container could land gently with parachutes.
It would be nice if we can re-use the container again and again.

The space-vehicles should be designed in such a way, that they can land safely on earth.
More like an air-plane than like a rocket.
It is more cost-effective if we can use the same vehicles for many years.

If we can make an EMA like this, it would be possible to send large amounts of cargo into space and build very large space-stations.
And we can build a space-dock to build space-ships in space.

Andreas_Firewolf · 2018-08-18 06:22:34

Mimicking gravity
=================

I started this topic with a proposal to accelerate and decelerate with 9 m/s2 to mimic gravity.
(And to reduce the duration of a trip to Mars.)

The absence of gravity is a serious problem for the human body, when you have to travel through space for half a year of longer.
Shielding against radiation seems more or less under control, if I have understood it right.
But how about gravity?

In StarTrek you simply switch on 'artificial gravity'. Butt that does not exist in the real world.

Another way of mimicking gravity would be to create a spinning wheel.
If we have a space-dock in which we can build space-ships that never have to touch Earth or Mars,
we can create such a vehicle.
Imagine a wheel with six or eight spokes and a radius of 100 meters.
This would create a circle with a circumference of 628 meters.
That would be enough space for a few dozen people.

Perhaps it is possible to get this wheel spinning by attaching fans around the wheel and using the solar wind.
But how can we gain velocity with this ship?
We can attach jets to the wheel and burn hydrogen and oxygen.
But if we want to get real speed we have to load an enormous amount of fuel.
The mass of it would be so huge, that we would hardly move.

The solution would be to tank oxygen and hydrogen during the trip to Mars.
If we create robo tanker ships, some with hydrogen and some with oxygen
and we get them in the path of the space-ship, we can tank during the journey.

We can not use an EMA (see above) to launch a wheel-shaped space-ship with a radius of 100 meters.
But with a large EMA we can propel tanker-ships with hydrogen and oxygen.
They could use the solar wind to adjust their speed to the space-ship.
It would require a lot of calculations, but I believe we can make it happen.

If we can make this happen, a journey to Mars would become acceptable.
Putting (about) four people in s small container and keeping them there for half a year in the absence of gravity,
seems a wrong approach to me.
But putting two dozen people in a ship with mimicked gravity and a lot of space to walk,
is not much different than putting a crew in a sub-marine for half a year.
It seems doable to me.

Andreas_Firewolf · 2018-08-18 06:38:00

Building a very large EMA in space
===========================

In post 26 of this topic I proposed a very long EMA on Earth to launch vehicles to get to a space-station.
Suppose we design a modular EMA with modules of about 10 meters length.
We launch them into space and put them together.
With 100 of these modules we could get an EMA of 1000 meters.
We could use this EMA to launch robo tanker ships.
If we use an acceleration of 40 m/s2 and a length of 1000 meters, the tankers would get a speed of 1000 km per hour.
If we launch them before we launch the wheel-shaped space-ship, they could use the solar wind to gain speed.
And they could use jets and burn some fuel, when necessary.

If we want more much more speed, we could use a higher acceleration or make the EMA longer.

kbd512 · 2018-08-18 08:53:15

louis wrote:

Hmmm... If it's sucked into the condenser unit at a speed slightly at or above the speed of the exhaust stream, I don't see how you get that effect. Put it another way, as I did to GW: why don't rockets fall out of the sky when you walk under their exhaust stream? There must be some limit to disruptive effects...my suspicion is the limit is what experts refer to as the plume boundary.

The reaction mass expelled from the rocket nozzle is pushing on the nozzle and whatever is connected to the nozzle, not something below the nozzle. That'd be why a rocket still works in the absence of any external body to push away from. If you could somehow survive walking under a rocket nozzle to collect the exhaust products, the exhaust from the rocket is still pushing on the rocket nozzle. Sucking up the combustion products at a higher velocity than their exhaust velocity behind the rocket nozzle would not change the basic physics of how that works. This is much like using a fan mounted to the deck of a sailboat to move the boat by blowing on the sail. It doesn't work that way in real life and no amount of magical thinking will change that. That'd probably be why we don't see any hovercraft with sails mounted ahead of the fans to improve their efficiency.

louis wrote:

The material collected in the condenser unit isn't held there - it's immediately pumped back into the boiler system. I could accept that you might be reducing the rocket's efficiency by some small percentage, but that doesn't affect the great merit of the theoretical PV/nuclear-steam-condenser rocket, which would be that you don't have to seek out new propellant, it's being recycled all the time...of course you can't achieve 100% recycling but even if you are getting 95%, it's a huge advantage in the vaccuum of space, allowing you 20 cycles of acceleration.

The "small percentage" that you're reducing the rocket's efficiency by is 100%. I guess that's a minor detail in the world of hypothetical propulsion systems that have never worked when tried in the past. If you stick to using electric propulsion systems with substantially higher Isp, then you don't have to invoke any of these fantasy rocket concepts that don't actually work and never will unless basic physics is repealed.

Using existing chemical rockets to attain orbital velocity, followed by electric propulsion for orbital transfers, are more than efficient enough to go to Mars affordably and reliably without the need for multiple gas tanker flights. The two propulsion problems are very different and require different solutions. Fortunately for us, both solutions are nearly in hand.

GW Johnson · 2018-08-18 09:02:49

Louis:

I don't understand why you reject 3 centuries of consensus on Newton's Laws and their application to rocketry, in favor of an isolated article that backs your notion.

Spacenut and I (and now Kbd512, too) have tried various ways to tell you that you cannot recycle rocket exhaust and still thrust, and that Newton says so, not us. You seem determined to ignore Newton in favor of your pet idea. That is insane, given those 3 centuries of confirmation for Newton.

Sorry, your exhaust-recycling idea just won't work. Go re-read a high-school physics book, particularly the chapter on impulse and momentum, which in nearly every version out there shows the application to rocketry. Many of them even derive the rocket equation, if calculus is allowed for the math.

For a rocket isolated in space, with the coordinate system pinned to the rocket, it takes a certain amount of force upon the expelled mass for that expelled mass to reach a certain velocity with respect to the rocket. The equal and opposite reaction to that force, acts upon the rocket to push it the other way.

That reaction pushing the rocket we call "thrust", the velocity of the expelled mass we call the "exhaust velocity", the force upon the expelled mass is created by the thermochemistry and compressible fluid dynamics of the engine's chamber and nozzle (acting together), and the point of measure for exhaust velocity is the physical exit plane of the rocket nozzle. All of that is well-established and perfectly understandable with a high-school physics background, even without calculus and the final rocket equation.

Now, imagine a catcher's mitt somewhere out in space in the path of that plume of expelled mass, and big enough to intercept all of it. The same conservation of momentum that created the thrust on the rocket by expelling that exhaust still applies. The catcher's mitt forces that plume to cease moving, relative to a coordinate system pinned to the mitt. For that plume to cease its motion, the mitt exerts a force upon the plume. The equal and opposite reaction is a thrust force upon the mitt, in the direction that the plume was formerly moving (which is opposite to the direction of the rocket's thrust and motion).

If the nozzle expansion were perfect, all of the thrust on the rocket would be exhaust momentum without a pressure-area term. That is a bit beyond high school physics, coming from compressible fluid mechanics as it does. But this is a small effect. So, we'll ignore that, and say expansion was perfect. Since plume momentum is conserved (no friction out in space), when you stop that exhaust plume with the big catcher's mitt, the force upon the mitt is equal to the thrust upon the rocket, just oppositely-directed.

Now, if the mitt is physically attached to the rocket (which is EXACTLY what you are trying to do by recycling your exhaust), the rocket now feels the force upon the mitt as well as the original plume thrust upon itself. Since the two forces are of equal magnitude but oppositely directed, you have zero net force acting upon the rocket. It will go nowhere! Nowhere at all! QED.

Now, as a corollary to this description, put the rocket down here in the atmosphere. The atmosphere itself is now a catcher's mitt that eventually stops the motion of the exhaust plume, by fluid friction forces that actually dissipate momentum, and mixing phenomena that dilute the undissipated momentum over ever-larger mass.

But the atmosphere IS NOT attached to the rocket! The forces exerted by the atmosphere upon the plume are not transmitted to the rocket. That is why the rocket still thrusts and moves, and you cannot perceive its jet blast, if you are far enough away. (Get too close, and you WILL feel it, which is where the concept of "plume boundary" comes from.)

Sorry, but you are barking up the wrong tree. Newton wins. As he has for 3 centuries. And specifically with rocketry for those 3 centuries, starting with the design calculations for Mr. Congreve's rocket weapons.

GW

Last edited by GW Johnson (2018-08-18 09:12:05)

Terraformer · 2018-08-18 09:06:13

louis,

Try pulling yourself up by your bootstraps. Literally, try it. If you pull hard enough, you should be able to start flying. You need about 10 newtons of force for every kilogram you mass to do that, though.

GW Johnson · 2018-08-18 09:18:55

Andreas_Firewolf likes the notion of electromagnetic accelerators. The science is good, the engineering technology still not so much. It's good enough now to build a railgun that throws a small artillery round. It was, until very recently, not good enough to launch even a small airplane or rocket, although the latest aircraft carrier has replaced the steam catapult with an electromagnetic one for trials.

This electromagnetic launch technology was first looked at about 1950, for flinging overweight bombers off the runway. Auxiliary rockets called JATO bottles proved to be far more practical for that application back then, and still are today. That is also exactly why some launch rockets add solid boosters. It's the same problem, just made worse by accelerating vertically upward directly against gravity.

GW

Last edited by GW Johnson (2018-08-18 09:21:00)

kbd512 · 2018-08-18 09:54:01

In the Navy, we went to using electromagnetic launch because the nuclear reactor power output levels and the volume occupied by the super capacitor systems for launch and arresting gear finally became much more compact than the labyrinth of steam pipes. We've had a number of sailors who were severely injured or killed maintaining the steam catapult launch and arresting systems. However, it took many billions of dollars to produce a system that was as usable as the old steam system and it's still not completely ready for prime time.

In combat, the utility of an aircraft carrier is all about how fast you can get every jet in multiple squadrons off the deck and into the air, fully laden with fuel and weapons. The EMALS system held the promise of increasing the launch rate over a steam-powered system with less maintenance. The faster launch repetition rate has been well-proven at this point, but maintenance requirements actually increased. That just proves the old adage, "there ain't no such thing as a free lunch".

I can't even imagine how much a space EMALS system will cost, but it'll be a very pretty penny and that's for sure.

louis · 2018-08-18 13:22:50

The premise is the steam rocket would be assembled in space and fly in the frictionless vacuum of space.

Terraformer wrote:

louis,
Try pulling yourself up by your bootstraps. Literally, try it. If you pull hard enough, you should be able to start flying. You need about 10 newtons of force for every kilogram you mass to do that, though.

louis · 2018-08-18 13:28:20

Just to add to that - if we do look at take off, the rocket still takes off even though the ground is "interfering" with the exhaust/thrust.

louis wrote:

The Earth has nothing to do with this hypothetical steam rocket. It's operating in the vacuum of space so don't know what you mean by the Earth reference.

SpaceNut wrote:
The mass of the earth is not attached to the rocket... add a chain between both and you do not move.

Terraformer · 2018-08-18 14:21:42

louis,

A spacecraft of 1 kg mass throws a 1 kg mass out the back with a speed of 1 m/s, imparting 1 N s of momentum to the craft. The important thing here is that the mass thrown out the back has momentum, relative to the spacecraft, of -1 m s, thus momentum is conserved. It's velocity relative to the craft is -2 m/s, since the craft is now moving at 1 m/s relative to it's position at rest, and the mass is moving at -1 m/s relative to it's rest position.

Now, if the craft was to recapture the mass, it would cancel the velocity of the craft, bringing it back to it's previous velocity of 0 m/s. The total momentum, likewise, would be 0 N s. So there wouldn't be any net gain in momentum.

SpaceNut · 2018-08-18 17:28:44

simply:
force = mass x acceleration
The exhaust gas even when it freezes still has the force in the exit direct of the rockets thrust. The moment that the ice strikes the funnel, umbrella it will pass that energy to the object in that exit direction and if that umbrella is attached to the rocket the thrust reaction and the momentum will cancel.

A solar sail works by that momentum energy passing from the sail in the direction of the solar wind and that is why it picks up speed as it exits the solar system.

louis · 2018-08-18 18:33:38

1. This is a theoretical discussion. I am not making any claims for steam rocket efficiency over other forms of rocket, although clearly if you could recycle propellant then that would be a major advantage over existing chemical rockets.

2. You claim that ANY interference with the thrust leads to a 100% rocket failure. GW I think it was stated that thrust extends into infinity (not something I disagreed with) and so, millions of us walking around in the hemisphere in which a rocket takes off will surely be interfering with the thrust as it climbs higher and higher...but rockets still fly. Also there will be aeroplanes in cutting across the path of the thrust. This sounds like magical thinking to me...that rockets will fall from the sky if you slightly disrupt the exhaust.

3. How do you explain a rocket taking off from a rocket pad if the ground is interfering with the exhaust?

4. So are you claiming that a rocket could take off if it was trailing a heat resistant chain from the middle of the nozzle or chains on the outside?

5. I think the EM Drive demonstrates that the equal and opposite reaction thing is a simplification. What's really happening is happening at the level of electromagnetic force fields. How could an exhaust remainder floating around in all directions be instantaneously affecting the flight of a rocket which might now be thousands of miles away - minutes away. It's pure magical thinking.

kbd512 wrote:

louis wrote:
Hmmm... If it's sucked into the condenser unit at a speed slightly at or above the speed of the exhaust stream, I don't see how you get that effect. Put it another way, as I did to GW: why don't rockets fall out of the sky when you walk under their exhaust stream? There must be some limit to disruptive effects...my suspicion is the limit is what experts refer to as the plume boundary.
The reaction mass expelled from the rocket nozzle is pushing on the nozzle and whatever is connected to the nozzle, not something below the nozzle. That'd be why a rocket still works in the absence of any external body to push away from. If you could somehow survive walking under a rocket nozzle to collect the exhaust products, the exhaust from the rocket is still pushing on the rocket nozzle. Sucking up the combustion products at a higher velocity than their exhaust velocity behind the rocket nozzle would not change the basic physics of how that works. This is much like using a fan mounted to the deck of a sailboat to move the boat by blowing on the sail. It doesn't work that way in real life and no amount of magical thinking will change that. That'd probably be why we don't see any hovercraft with sails mounted ahead of the fans to improve their efficiency.
louis wrote:
The material collected in the condenser unit isn't held there - it's immediately pumped back into the boiler system. I could accept that you might be reducing the rocket's efficiency by some small percentage, but that doesn't affect the great merit of the theoretical PV/nuclear-steam-condenser rocket, which would be that you don't have to seek out new propellant, it's being recycled all the time...of course you can't achieve 100% recycling but even if you are getting 95%, it's a huge advantage in the vaccuum of space, allowing you 20 cycles of acceleration.
The "small percentage" that you're reducing the rocket's efficiency by is 100%. I guess that's a minor detail in the world of hypothetical propulsion systems that have never worked when tried in the past. If you stick to using electric propulsion systems with substantially higher Isp, then you don't have to invoke any of these fantasy rocket concepts that don't actually work and never will unless basic physics is repealed.
Using existing chemical rockets to attain orbital velocity, followed by electric propulsion for orbital transfers, are more than efficient enough to go to Mars affordably and reliably without the need for multiple gas tanker flights. The two propulsion problems are very different and require different solutions. Fortunately for us, both solutions are nearly in hand.

louis · 2018-08-18 18:59:00

OK...well accepting that, thrust doesn't carry at the same power into infinity does it, otherwise people in Miami would be blasted by rocket thrust? So there must be some point at which it rapidly decreases as the exhaust becomes disorganised (presumably through Brownian motion, I'm guessing). So part of my thinking is that one has the condenser unit outside the organised plume.

SpaceNut wrote:

simply:
force = mass x acceleration
The exhaust gas even when it freezes still has the force in the exit direct of the rockets thrust. The moment that the ice strikes the funnel, umbrella it will pass that energy to the object in that exit direction and if that umbrella is attached to the rocket the thrust reaction and the momentum will cancel.
A solar sail works by that momentum energy passing from the sail in the direction of the solar wind and that is why it picks up speed as it exits the solar system.

SpaceNut · 2018-08-18 19:23:54

The atmosphere obsorbs the force and spreads it across the mass that it comes in contact with. It is why the sound wave is carried to listeners far away. We measure sound in power and that is how the wave travels via the working fluid of air.

http://hyperphysics.phy-astr.gsu.edu/hb … nvsqs.html

https://motherboard.vice.com/en_us/arti … -buildings

Andreas_Firewolf · 2018-08-19 01:29:24

GW Johnson wrote:

Andreas_Firewolf likes the notion of electromagnetic accelerators. The science is good, the engineering technology still not so much. It's good enough now to build a railgun that throws a small artillery round. It was, until very recently, not good enough to launch even a small airplane or rocket, although the latest aircraft carrier has replaced the steam catapult with an electromagnetic one for trials.
This electromagnetic launch technology was first looked at about 1950, for flinging overweight bombers off the runway. Auxiliary rockets called JATO bottles proved to be far more practical for that application back then, and still are today. That is also exactly why some launch rockets add solid boosters. It's the same problem, just made worse by accelerating vertically upward directly against gravity.
GW

I do not have much practical knowledge about this subject, so I can not determine if you are right or wrong.
I am sure, your knowledge was sound a short while ago.

But in the past year there have been developments with hyperloop transportation. In a hyperloop system, the result largely depends on sucking out the air from the tube.
On Earth that is absolute essential. With a lot of air in the tube, you get an enormous heat problem as well as a resistance problem.
But when you suck the tube to near vacuum, it might work on Earth.

In space you do not have this problem. Neither on the moon or Mars. So perhaps it will work there without much effort.

When the science is solid, the question is not 'does it work' but 'are there engineers who can make it work'.
If engineers can make it work on Earth, it would make space-exploration a lot easier and probably safer.

Terraformer · 2018-08-19 01:40:05

louis, it's not that the plume is being interfered with that causes the ship to lose it's momentum, it's that it's the *ship* that's doing the interfering. If you had a lightweight platform in space that was taking the rocket blast, it would be pushed in the opposite direction to the spaceship. If it's a planet, that still happens, but the mass difference renders the effect imperceptible. If the lightweight platform was coupled to the spaceship, then (if it was absorbing all the blast) the spaceship would go nowhere.

You might want to buy a GCSE Physics textbook and have a read of it?

Andreas_Firewolf · 2018-08-19 04:31:07

Suppose an EMA would be build in the USA and one could use the Rocky Mountains to get elevation?
If you would build it on a flat surface, like the Great Salt Lake, you would have to build a construction going one or two miles up in the sky.
That might be a problem.
But if you would roughly follow the shape of a (stable) mountain, it might be more cost effective.
.
A big question for engineers would be:
Must the EMA be absolutely straight or can it have a slight curve?
If it has a curve, is it possible to keep the container in the center of the tube with magnetism?
It seems mandatory to prevent direct contact between the container and the tube.
.
Suppose the EMA is manufactured in segments of perhaps 20 or 50 meters.
Each segment has pumps, that pump out the air.
Before launching, the air is sucked out of the tube of the EMA as much as possible.
During the launch the pumps in front of the container could pump out remaining air.
It should be possible to control this with a computer.
.
Perhaps it would help if the air that is pumped out in front of the container is pumped in behind the container,
but I have some doubts about that design.

louis · 2018-08-19 14:03:45

I can accept that. But equally I can't accept that thrust retains the same compact directional energy level into infinity...it must decline, surely through interaction of particles disturbing the compact flow. So the issue is at what distance does it start to decline and does it decline rapidly or slowly? If it's fairly rapidly, then it seems to me one can envisage a steam rocket ship that has a small thruster with an efficient condenser. I think you need to unimagine a huge rocket with a 400 metre plume and think about something that has a much smaller exhaust trail, let's say 1 metre...and let's also imagine periodic burns, and the condenser collecting the dispersed water particles in a unit that might be say up to 50 metres ' distance from the nozzle.

Terraformer wrote:

louis, it's not that the plume is being interfered with that causes the ship to lose it's momentum, it's that it's the *ship* that's doing the interfering. If you had a lightweight platform in space that was taking the rocket blast, it would be pushed in the opposite direction to the spaceship. If it's a planet, that still happens, but the mass difference renders the effect imperceptible. If the lightweight platform was coupled to the spaceship, then (if it was absorbing all the blast) the spaceship would go nowhere.
You might want to buy a GCSE Physics textbook and have a read of it?

Terraformer · 2018-08-19 15:59:00

It spreads out, but the particles (assuming they remain in a vacuum and are unaffected by gravity, of course)) keep going in the same general direction with the same speed. If you collect all of them, your collector needs to be large enough to, well, collect all of them, which you can't do without also collecting their momentum and cancelling your own.

kbd512 · 2018-08-19 16:37:45

louis wrote:

1. This is a theoretical discussion. I am not making any claims for steam rocket efficiency over other forms of rocket, although clearly if you could recycle propellant then that would be a major advantage over existing chemical rockets.

This thread is yet another magical thinking discussion that detracts from any useful discussion. This idea has already been tried numerous times and in numerous ways. If it could possibly work, we'd use it. Since it doesn't, we don't. You can argue your position until the cows come home, but physics won't change to suit your thinking, my thinking, nor anyone else's thinking.

louis wrote:

2. You claim that ANY interference with the thrust leads to a 100% rocket failure. GW I think it was stated that thrust extends into infinity (not something I disagreed with) and so, millions of us walking around in the hemisphere in which a rocket takes off will surely be interfering with the thrust as it climbs higher and higher...but rockets still fly. Also there will be aeroplanes in cutting across the path of the thrust. This sounds like magical thinking to me...that rockets will fall from the sky if you slightly disrupt the exhaust.

I never made such a claim. I claimed that the reaction mass expelled from a rocket nozzle reacts on or off of the rocket nozzle and whatever the rocket nozzle is connected to. Putting a device under the rocket nozzle to capture the exhaust products would result in zero net velocity change if that device is also connected to the rocket. Rockets fly because they push enough reaction mass out the back of the rocket nozzle to overcome the force of gravity. Their operating principle is no different in practice than a jet engine, except that they carry their oxidizer with their fuel.

GW claimed that the velocity of the reaction mass used to change the velocity of the rocket doesn't change, in the absence of an external force like a gravity well or pressure differential. However, the acceleration achieved is a constant force directly related to the exhaust velocity of the rocket's exhaust product(s). That has been very well explained by GW and SpaceNut.

If you think this can possibly work, then I want you to inflate two balloons, one perhaps twice as much as the other, and connect both balloons to different ends of a plastic tube. There won't be any net change in velocity, just a pressure mediation between the two differentially inflated balloons. That's what you're talking about doing. The experiment might cost a few cents and a few moments of your time to complete. Let us know what you've learned after you complete that experiment.

louis wrote:

3. How do you explain a rocket taking off from a rocket pad if the ground is interfering with the exhaust?

Once again, the thrust generated from the rocket exhaust is pushing off the rocket nozzle, not the ground. There's nothing to "push off of" in space, but the rocket nozzle and rockets still work in space.

louis wrote:

4. So are you claiming that a rocket could take off if it was trailing a heat resistant chain from the middle of the nozzle or chains on the outside?

A rocket either has enough thrust to overcome whatever forces are preventing it from taking off in the direction opposite the rocket nozzle or it doesn't. It's as simple as that.

louis wrote:

5. I think the EM Drive demonstrates that the equal and opposite reaction thing is a simplification. What's really happening is happening at the level of electromagnetic force fields. How could an exhaust remainder floating around in all directions be instantaneously affecting the flight of a rocket which might now be thousands of miles away - minutes away. It's pure magical thinking.

Some things behave very differently at a subatomic level than they do at the atomic level and above. What that really demonstrates is that we know very little about magnetism, gravity, and the formation of matter. Knowing how to measure things confers no special understanding of how the thing being measured works or interacts with the rest of the universe, but it's a start. If we could control gravity, then we wouldn't need any propellants.

Chemical rockets operate at the atomic level and this discussion clearly pertains to chemical rockets. Regarding the rest of what you stated, reaction mass thrown out the back of a rocket at a constant velocity produces a constant force on the rocket in the opposite direction. We call that force "thrust", and it produces a constant velocity change in the rocket, apart from the fact that the rocket is also losing mass in the process.

GW Johnson · 2018-08-19 17:04:04

I noticed Louis did not respond at all to my post 30 above. That posting has (in qualitative form) the Newton's Laws descriptions of how a plume is produced, and what thrust it corresponds to, upon the item producing the plume, plus what the forces are on any "catcher's mitt" that fully intercepts such a plume.

I might add that this sort of analysis is experimentally verified in the design and implementation of jet blast screens at airports and military bases. For any such screen, down here in the atmosphere but at close range so that atmospheric drag and mixing haven't affected the jet blast plume very much, the force trying to blow away your screen is numerically equal to the nozzle thrust of whatever is producing the jet blast. I have myself verified this in actual testing.

Down in the atmosphere, the atmosphere itself is the catcher's mitt, which is why plumes down in the atmosphere have boundaries of finite extent in all directions. Out in space they do not, in the thrust direction. They take the form of a more or less conical plume, mostly contained within the same half angle cone as the nozzle, extending to infinity, given enough time. A minority of the massflow spreads wider, but to first order, the force required to stop the plume, on a catcher's mitt big enough to intercept it, is pretty much equal to the thrust of the nozzle that produced the plume.

That plume capture force is oppositely-directed to the initial thrust. If you physically connect said catcher's mitt to the rocket, then it feels both forces, which add to zero. That is EXACTLY what you do when you try to capture your own exhaust: you literally connect the catcher's mitt to the rocket. If you do this, you go NOWHERE. Because you have ZERO net thrust.

Louis, all of us have been trying to tell you this in multiple different ways and forms since this discussion of your recycling steam rocket started. The consensus here is in accord with Newton: you are wrong, we all are right. Time for you to revisit high school physics, in particular the chapter on impulse and momentum.

GW

SpaceNut · 2018-08-19 18:16:53

Andreas_Firewolf post 43 reply: EMA works on 3 magnetic arrangements repulsion, attraction and a combination of both to move the object that is in the tunnel tube that these are arranged within. The fields are pulsed to push or pull the object towards the end at velocity. While removing the air infront of the object would make it easier to move the issue is the in rush of pressure that will occur when you need to open it to make a launch possible from the arrangement of coils used to make it happen.

The tunnel tube must be perfectly straight as curves would cause friction and binding of the object to be launched. The object that is in the tube can also be inductive to making a field from the induced fields as well. A field can also be used to levatate the object within the tunnel tube as well to reduce friction. The longer the tube or tunnel arrangement is will allow for more speed to be picked up but there are limits as power of the fields to the mass of the object and how fast the fields can be turned on and off have limits based on materials to be used.

All of the fields are electrical and the power to make this happen is growing with each needed means to make it possible.

louis · 2018-08-19 18:32:01

Apologies for not replying...I am not mad enough to dispute Newton's laws in any meaningful sense, although having looked into this before, I have to say that it seems to me Newtonian "force" must be a fiction...maybe a good one, but a fiction nonetheless. In reality, there are only the four fundamental (real) forces of nature and those forces involve fundamental particles behaving in rule-obeying ways to other fundamental particles. I presume Newton was simply intuiting what happens at the level of the four forces.

Take the example of say a pile of bricks lying on top of a concrete slab supporting on some bricks. Newton (or at least the type of interpretator of him I have read) will say that as long as the bricks are on top of the slab the up force is equal to the down force...but what is happening when cracks appear in the concrete below the surface? Something is causing those cracks...but from everything I am reading, those cracks are caused by "nothing" because the heavy bricks are being counteracted by an "equal" force so it can't be the bricks causing the cracks, can it? To me, it's clear that the bricks are in electro-magnetic contact with the concrete and that is what explains the cracks below the surface - an extremely complex interaction at that fundamental force level.

Anyway, that's a diversion from the matter in hand which really comes down to whether you believe the force of the thrust continues on forever in the same manner or not.

So are you saying:

(a) That (in the vacuum of space) the energy from the thrust continues unabated for all infinity in the same organised, directional manner it leaves the nozzle?

(b) If the answer to (a) is yes do you have any references for that?

(c) If the answer to (a) is no, how long does it take for the thrust energy to dissipate?

With reference to (c) bear in mind that the theoretical steam rocket might not be pumping out huge amounts of thrust...maybe small regular "burns".

GW Johnson wrote:

I noticed Louis did not respond at all to my post 30 above. That posting has (in qualitative form) the Newton's Laws descriptions of how a plume is produced, and what thrust it corresponds to, upon the item producing the plume, plus what the forces are on any "catcher's mitt" that fully intercepts such a plume.
I might add that this sort of analysis is experimentally verified in the design and implementation of jet blast screens at airports and military bases. For any such screen, down here in the atmosphere but at close range so that atmospheric drag and mixing haven't affected the jet blast plume very much, the force trying to blow away your screen is numerically equal to the nozzle thrust of whatever is producing the jet blast. I have myself verified this in actual testing.
Down in the atmosphere, the atmosphere itself is the catcher's mitt, which is why plumes down in the atmosphere have boundaries of finite extent in all directions. Out in space they do not, in the thrust direction. They take the form of a more or less conical plume, mostly contained within the same half angle cone as the nozzle, extending to infinity, given enough time. A minority of the massflow spreads wider, but to first order, the force required to stop the plume, on a catcher's mitt big enough to intercept it, is pretty much equal to the thrust of the nozzle that produced the plume.
That plume capture force is oppositely-directed to the initial thrust. If you physically connect said catcher's mitt to the rocket, then it feels both forces, which add to zero. That is EXACTLY what you do when you try to capture your own exhaust: you literally connect the catcher's mitt to the rocket. If you do this, you go NOWHERE. Because you have ZERO net thrust.
Louis, all of us have been trying to tell you this in multiple different ways and forms since this discussion of your recycling steam rocket started. The consensus here is in accord with Newton: you are wrong, we all are right. Time for you to revisit high school physics, in particular the chapter on impulse and momentum.
GW

kbd512 · 2018-08-19 18:53:32

Louis,

Your observation about foundations cracking is explained by the mass of the structure and slab being pulled inward towards the center of Earth's gravitational field. Everything built on or near Earth is affected by Earth's gravitational field, which is created by the mass of the matter that comprises the Earth. As far as the question regarding what causes or creates gravity is concerned, all we really know about the answer to that question is that mass somehow causes or affects gravity. If you figure out the answer to that question, then we probably won't need to figure out how to make more efficient rockets.

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