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https://en.wikipedia.org/wiki/Vacuum
https://en.wikipedia.org/wiki/Vacuum_energy
INTRODUCTION TO THE PRINCIPLES OF VACUUM PHYSICS
light travels in a straight line unless there is a medium or gravity to make it change or bend in direction....
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"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?"
No, I never said a word about any "energy" of any sort going anywhere. Learn to read the words as written.
I said: the matter stream ejected from the nozzle will continue to move at its ejection speed "forever" in the ejection direction, out in deep space. A massflow rate times a speed is the thrust force upon the rocket, if the nozzle expansion were "perfect", meaning all the way down to vacuum as the exit pressure. That expansion is not perfect, but the pressure x area term is quite small compared to the momentum term in any decently-designed nozzle.
The massflow in the plume does not change, nor does its velocity, out in deep space. Not ever. That product is also the plume capture force in any sort of "catcher's mitt" equipment intended to stop that plume. Equal magnitude force, just oppositely directed.
By the way, there was an actual flying example that proves the point we have been trying to make to you. It was the "Skycycle" vehicle that Evel Knievel used in his unsuccessful Snake River Canyon jump, a few decades ago. That was a subsonic flying vehicle designed by Bob Truax himself, featuring a steam rocket for propulsion. It had parachute recovery, intended to be deployed during the descent once across the canyon. All Knievel had to do was let go of his handlebar-style handgrip in the cockpit, that released the chute.
The parachute deployed at liftoff, and captured part, but not all, of the steam rocket's exhaust plume. This greatly reduced the net thrust during the "burn", so that the vehicle fell way far short of flying all the way across the canyon. That's why the jump attempt failed. You can see in the video steam till moving at high speed getting past the parachute, that's confirmation that only part of the plume was captured by the chute. Which in turn is why the net thrust was not totally zeroed. Had the chute captured it all, the vehicle would never even have lifted-off at all.
In case you don't know, Bob Truax was one of the early pioneers in rocketry over here in the US in the years during and after WW2. I've met him and talked to him, specifically about the "Skycycle" steam rocket, its flight controls, recovery gear, and the failed jump attempt. He thinks Knievel accidentally triggered chute deployment during launch by letting go of the handlebar. There's not a lot to point at for proof, but it does make sense, given the way the chute deployment was to be triggered, plus the sudden violence of the launch.
GW
Last edited by GW Johnson (2018-08-19 22:24:57)
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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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 in front 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.
Perhaps you are right, but I am not completely convinced.
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If you accelerate an object without friction or resistance, and you keep the acceleration the same, then the amount of energy needed for the acceleration would remain the same.
In space you have conditions that are close to this ideal situation.
On the moon and on Mars you have to overcome gravity, but you are not troubled by air.
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Getting it to work on Earth would be difficult, to say the least.
Imagine an air-tight tube.
Before launching you suck out as much air as possible.
The tube is closed with an air-tight lit.
You launch the container and during the launch you continue to pump out air in front of the container.
When the pumps are controlled by a computer, this should not be a big problem.
Just before the container reaches the end of the tube, the lit is opened by the computer.
If the opening is 2000 or 3000 meters above sea-level, you have a lot less air.
That would alleviate the air-problem a bit.
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Another problem would be the resistance between the container and the tube.
If they make physical contact, it will not work.
But if there is a distance between the tube and the container, say 10 to 12 cm,
and the container is kept in the middle of the tube with electro-magnetism,
then the friction would be kept at a minimum.
If the distance between the tube and the container can be controlled and it can vary a little bit,
it might be possible to make a curved tube. As long as the curve is not to sharp.
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Hyperloop transportation is doing almost the same thing.
Developers believe they can reach a speed over 1000 km/hour.
The Delft hyperloop team (from the Dutch technical university of Delft) believe they can make that happen.
Moving from Amsterdam to Paris in 30 minutes.
And the trajectory can be curved a little bit.
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What I suggest is not much different.
But the speed I am aiming at, is much greater.
So I am not saying that it can be done. Engineers should answer that question.
But based on what hyperloop engineers expect to accomplish, I am quite confident
that a very large EMA for launching space-vehicles from Earth will become possible in the next decade.
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Perhaps I should put it a bit stronger.
If one can accelerate a hyperloop-vehicle to 1000 km/hour,
it seems almost certain that China, Russia and the USA are already developing EMA-like structures for launching military planes.
If you can launch small military planes like you shoot grenades, it would be a main advantage.
Your plane can stay in the air much longer, since you don't waste any fuel taking of.
Every day it is getting better and better and we create a golden future.
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I think I said somewhere above that the latest US Navy aircraft carrier has an electromagnetic catapult replacing the steam catapult, and Kbd512 commented upon it, too. It is going out there for sea trials, nothing is certain yet whether this technology will really work in the real world. If it doesn't, the Navy will tear it out and put the steam system back in.
Being able to fling an aircraft to 200 knots off a flight deck, or to fling a small projectile to km/s speeds with a railgun, are both a very long way from being able to fling a launch vehicle even part way to orbit. Just because something "works" in a lab experiment does NOT mean a scaled-up design works in the real world.
I suggest we maintain the dream of electromagnetic launch without expecting anything soon, and watch where the EM catapult and railgun items lead over the next few decades. They've taken decades to get where they are now.
GW
Last edited by GW Johnson (2018-08-22 09:42:44)
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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Yes, GW, I believe you wrote something like that. And I agree with you, when you state, that we can not be certain that something works, until it is really realized.
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I wrote:
"If one can accelerate a hyperloop-vehicle to 1000 km/hour,
it seems almost certain that China, Russia and the USA are already developing EMA-like structures for launching military planes."
When I wrote that, I did not think about aircraft carriers, but very long structures to get more acceleration.
On land.
If we can get it to work, it could be great for the defence of Europe against possible Russian aggression.
If Europe would build a few dozen EMA-like structures near the border and it is possible to launch a great number of drones in a short time, it would alleviate the threat of Russia.
But first we have to build one that actually works.
Every day it is getting better and better and we create a golden future.
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Well, meanwhile, solid rocket JATO bottles have 7 decades proven experience launching overweight airplanes quickly. Size it up bigger, and you can even launch without a runway (a big motor named ZLL that flung an F-100 Super Sabre straight into the air back in the 1960's). It's not like we cannot do the mission without an EM launcher, because we can. And we have, since WW2.
GW
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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Andreas,
An EMALS for spacecraft might shave off the first 2km/s of the dV increment (that's nearly Mach 5.8, or thereabouts, and the rocket or payload will definitely have to have a substantial heat shield to prevent boiling the propellant in the tanks and subsequently bursting them), but then you'd need the vehicle to provide the rest of the 7km/s dV to accelerate into and circularize the orbit. The forces involved that low in the atmosphere are considerable, to say the least. The fact that no other country has an EMALS in an advanced state of development should tell you that it's not an easy thing to do. The US Navy has spent billions on their system, yet it's still not quite ready for prime time. It's flinging a relatively lightweight aircraft, in comparison to any orbital class rocket with a decent payload, to a measly 135 knots, and it's already overstressed some of the airframes without acceleration profile modification.
The bottom line is that this stuff is hard to do for a reason. Dive into the physics of the problem and you're talking about tech that either doesn't exist or barely works at all in less demanding applications.
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Couple that with the waverider or x38 and you now have a means to orbit in a flash.....
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SpaceNut,
NASA / USAF / contractors had to invent new materials for the nose of Waverider and the propellant tank insulation to withstand the searing heat and that thing was quickly accelerated from the upper stratosphere to the edge of the atmosphere to sustain less than a minute of hypersonic flight. I would love to see someone make this work, but they most definitely have their materials science problems cut out for them. If anyone manages to do this from a dead stop on the ground, then they should win a Collier Trophy for outstanding aeronautical engineering achievement and a Nobel Prize for materials science. It's a DARPA-hard problem.
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Airbreathers don't work at the edge of space. All airbreathers have thrust sort-of proportional to internal pressure, with internal pressure a more-or-less fixed trend of ratios to ambient atmospheric pressure, varying with speed. Twice nothing is still nothing, so airbreathing flight above about 125,000 feet altitude is pretty well nonsense. Drag may be low up there, but weight does not decrease with air density. This is exactly why there is such a thing as "service ceiling" in flight vehicle design.
"Waverider" is not a new concept, nor is it any sort of magic. At supersonic and hypersonic speeds, flat bottomed objects generate more lift for the drag than round-bottomed objects. This is because the surface pressures are directed vertically on a flat bottom, but not a round bottom.
The XB-70 Mach 3 bomber of 1965-ish was a "waverider", and that term was in the advertising hype about it back then. They didn't use that term earlier on, but for its supersonic dash speed of around Mach 1.2, the mid-1950's F-100 Super Sabre was also a waverider: it had a flat bottom, too. Ineffective subsonically, but it did help during supersonic dash. Every supersonic two-engine top fighter ever since has had some aspect of the flat bottom waverider idea built into it.
X-51A flew successfully 2 times of 4 attempts at a rocket-boosted Mach 5 speed, somewhere near 100,000 feet, to test a hydrocarbon-fueled scramjet for 3-minute burns. That scramjet did NOT accelerate the vehicle, by the way.
Up around 100,000 feet, the friction heating is reduced, because heat transfer coefficients at otherwise the same speed are very crudely proportional to atmospheric density raised to the 0.8 power. You can heat sink your way through a few-minute flight at hypersonic speeds with ordinary materials, if you cool the structure with the fuel you burn in the engine, or simply use ablatives. Only the ablatives support steady-state flight hypersonically, the other new super materials are not yet ready for prime time. In an airbreather, there is just not enough fuel to cool everything.
ASALM-PTV was a demonstrator for a supersonic strategic-capable cruise missile that flew 7 times back in 1980. It was no scramjet, it was a subsonic-combustion "ordinary" ramjet with an integral solid booster packaged within the combustor. It also had the flat bottom to make it a waverider, and needed no wings. I worked on this thing. We liked to say that 6.5 of those 7 flight tests were letter-perfect.
Its design mission was to cruise at 80,000 feet and Mach 4, with an average Mach 5 terminal dive transient onto its target. It needed no exotic materials to do this, only stainless steels. We had a throttle runaway accident on the first flight, so the vehicle accidentally accelerated to fuel exhaustion at Mach 6 and 20 kft-ish altitude. This was a short transient which it survived by heat-sinking, its flight envelope called for no more than Mach 3-ish at such low altitudes. ASALM accelerated from Mach 2.5 to Mach 6 in a matter of seconds, solely on ramjet propulsion.
That flight test mishap set the airbreathing Mach 6 speed record in 1980 which stood until 2004, when NASA's X-43A hydrogen scramjet finally broke it, in its first successful flight (1st of 2 successes out of 3 attempts). If you consider a 3 second burn at a rocket-boosted constant Mach 7 something the airbreather actually did, which it did not! The booster rocket did all the work getting there, same as X-51A. The NASA boys were cheering how they finally broke ASALM's record, but none of them were old enough to know what an ASALM was.
Damn, I'm old, ain't I?
The way to do this from a standing start is no mystery, either.
You build an airplane of stainless steels on its exterior (titanium is not a high-temperature material, by the way), and protect the leading edges with slow ablatives (like carbon-carbon). This airplane has as its main propulsion the same sort of ordinary ramjet (like ASALM) with an integral solid booster (like ASALM), plus some small auxiliary LOX-jet fuel rockets.
You line the combustor and nozzles with one-shot ablatives, and design it to be easily swapped out of the airframe like an internally-carried JATO bottle. The small liquid rockets fire in parallel with the ramjet to reach high altitudes in seconds on a near-vertical trajectory, so that you don't burn off all your ramjet fuel just climbing, at Mach 3-ish.
Pull over and accelerate in ramjet alone to Mach 3.5-4-ish cruise for intercontinental range, somewhere between 80 and 120 kft. You have Mach 5 to 6 dash speed available in hostile territory, although that cuts your total range. The small liquid rockets give you divert or go-around capability when you glide to landing. They burn the same jet fuel as the ramjet.
You do this with a Mach 3 shock-on-lip inlet and takeover speed. The combustor ablator is DC 93-104. The nozzle ablative is silica phenolic. The stainless steels are martensitic grades like D6ac, and austenitic grades like SS 316. There's no mystery here. It's just that nobody has yet pulled all these things into one airframe concept, and actually built one.
The gravy-train DARPA projects over the last 3-ish decades have been too focused on scramjet and combined-cycle (both still a long way from ready-for-prime-time) to actually build and fly a real hypersonic airplane. We could have done this 3 decades ago, actually.
GW
Last edited by GW Johnson (2018-08-24 10:18:11)
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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GW,
I meant to suggest that someone in DARPA should look into an EMALS track / ramp (at least a couple kilometers long and located somewhere in the Rocky Mountains) to electromagnetically accelerate a small launch vehicle to between 2km/s and 3.5km/s at about 10g (perhaps not suitable for humans, but still useful for cargo like rocket propellants, water, liquid O2 / N2, food), whereupon an ordinary rocket engine takes over to provide the remaining 5.5km/s to 7km/s dV increment to orbit. A partially evacuated launch tube, the lower starting pressure, and the ability to "point" the tube in the intended direction of travel would drastically simplify the problems associated with the launch vehicle.
I would imagine this to be a multi-billion dollar undertaking, but the end result would be a launch system that could support two to three launches per day. I would set a target payload of 5t to ISS. By my math, in a single year of operation with 48 standard 5 day work weeks and a single launch per day, that works out to 1,200t per year. If you can launch twice per day, then you can come close to exceeding the total tonnage ever sent into orbit in a single year. At three launches per day, you've grossly exceeded the total tonnage ever sent to orbit.
There's no current economics problem with sending people into orbit with reusable rockets like F9 / F9H / BFR, so the focus of this system is durable cargo / consumables that accounts for the lion's share of the tonnage problem with using chemical rockets. We can continue to use small rockets for delicate cargo like humans and satellites and mega rockets for large vehicles like BFS.
I believe 5t of water equates to 5 cubic meters, so this would be the size of the payload bay. If the rocket had a dry mass of 7t, a wet mass of 50t, and an Isp of 300 for LOX/LCH4, then that works at to roughly 50t launch vehicle. I figure a bulk density of around 1,000kg/m^3 for the propellant combo. A 2m diameter vehicle would be about 18m in length. That's similar in size to a Minuteman ICBM. The total size and mass of the vehicle would go up if we wanted to recover the engines, but I think the tanks and support structures should be made of lightweight expendable composites to save mass.
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Rather than fight with unproven electromagnetic technologies, why not use ballistics as we know them for hardened payloads? Build a great big light gas gun, and use it to fling a Minuteman-sized object to supersonic speed at stratospheric height. That would be way too many gees for a human to ride, but hardened inert cargo would do fine.
The light gas gun tube could be a mile long, and floated vertically in the ocean. Put a frangible glass cover over the muzzle, and pump it down internally to a fraction of a psi. Put an oxygen-methane mix in the space behind your vehicle and explode it as a fast deflagration. Hydrogen is a lighter gas still, but far too easy to ignite accidentally, just flowing through tubes and nozzles. Oxygen is bad enough, requiring elimination of all greases.
The vehicle itself might as well be a two-stage solid rocket, which is a whole lot easier to harden for high-gee operation than any conceivable liquid system. The old Sprint ABM had a launch acceleration of ~100 gee. (The launch acceleration of a 5-inch/54 round is about 20,000 gee, so there is nothing magically-limiting about 100 gees here.) The Sprint ABM was decades ago. That means only your payload and its orbit-circularization propulsion need be specially hardened. The rest could be essentially off-the shelf mature technology.
There's nothing magic about any of this. It really could be done this way.
GW
Last edited by GW Johnson (2018-08-24 12:12:17)
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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What limitations are there for the length of a gas gun? Can it be built arbitrarily long?
Now I'm dreaming of a 20+ km launch tube built up a suitable mountain, flinging payloads up to 6 km/s into space.
"I'm gonna die surrounded by the biggest idiots in the galaxy." - If this forum was a Mars Colony
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GW,
I guess there are a variety of different ways this could be done, but the intent was to do this with a single staging event to ensure the expended stage returns to Earth, if not for reuse then only to prevent the accumulation of orbital debris. Is there a solid propellant formulation that can supply the rest of the dV increment without staging? I'm not opposed to a light gas gun if it can supply enough of the dV increment. That said, how difficult would it be to keep the barrel oriented correctly when it's floating like a cork in the ocean? Will this projectile-based system be like the guided artillery rounds the US Army uses that have steerable fins in the nose, possibly with cold gas thrusters for high altitude attitude correction?
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An interesting and murky tale about the supergun:
http://www.bbc.com/future/story/2016031 … am-hussein
What limitations are there for the length of a gas gun? Can it be built arbitrarily long?
Now I'm dreaming of a 20+ km launch tube built up a suitable mountain, flinging payloads up to 6 km/s into space.
Let's Go to Mars...Google on: Fast Track to Mars blogspot.com
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I believe that we have talked about using them for the moon as practical and within the ability of current technolgy once we are able to get there....
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Just using high-school-type constant-acceleration kinematics as V^2 = 2 a s, and doing the numbers in my head, I get roughly 80 km long for an average 10 gee ride to 4 km/s velocity.
This is 8 km long at 100 gee, and 0.8 km long at 1000 gee. These figures apply to both EM launch and gas gun launch. Best wild guess is that peak gee is about 3 times average gee in a gas gun configuration.
If you change the velocity, note the V-squared dependence. 8 km/s vs 4 will raise the dimensions by a factor of 4, not 2.
Conclusion: potentially useful technique for hardened cargo insensitive to gee. Not so very useful for gee-sensitive cargo or people, because the structures will have to be impractically large. The Great Wall of China got built once. Never again, or didn't anybody notice?
GW
Last edited by GW Johnson (2018-08-27 10:15:59)
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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Finding the Velocity of an Object Moving along an Inclined Plane
Since the ramp would be directional the benefits would be minimal for use....
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