posted
No, I'm not accusing Bernd of being inconsistent! Instead, he has some new commentary in the "Inconsistencies" section of Ex Astris Scientia, and of course it deserves the usual level of careful scrutiny.
In the department of "I always had the nagging feeling there was something wrong but I couldn't put a finger on it", the new pages point out the inconsistencies in navigation and propulsion, weapons and tactics, and some tech miscellany. Lots of good points there.
In the first category, though, Bernd says that a solid or forcefield-based jet reverser attached to the impulse engines would not alter the net force on the ship. This isn't true, as the end result will still be that the exhaust jet is directed forward, thus transferring momentum in that direction and giving the ship momentum in the opposite direction. The internal structure of the engine does not matter - internal forces will cancel out, save for the one opposite the final exhaust direction.
In the second one, I found no nits to pick. Darn.
In the Miscellany category, I'd suggest that the oddly shaped "forcefields" are based on the same technology as the "shields". That is, their effect is based on gravitons trapped in a subspace field. The abruptness of the forcefield effect in the direction normal to the field surface would then be easier to explain - an effect is only created in the region where there are trapped gravitons, and that effect doesn't obey the 1/r^2 rule any more than the other gravitic tech (say, deck plating) of Star Trek does. As for the ability of even a single generator to create an oddly shaped subspace field to suspend the gravitons in... I doubt subspace follows 1/r^2, either.
On the same vein, I gather that "magnetic" boots are based on gravitic tech, too. They just use a catchy name that has alternate meanings. If any technology in Trek is cheap, reliable and easily miniaturized, gravitics is (by necessity, because artificial gravity always has to be present in even the most unlikely locations for production reasons).
As for stairs as an alternative to turbolifts, Kirk's old ship had plenty. There was that vertical ladderway easily accessible from the curved corridor set, and often seen used. And ST2 showed the crew operating efficiently without turbolift access anywhere below the top three decks. Either there was a big staircase somewhere (as Probert originally intended), or then using the stairs wasn't all that hard after all.
The E-D crew seldom resorted to vertical Jeffries tubes as an alternative to turbolifts. There just wasn't an obvious need to go from one deck to another during a crisis: most of the heroes would sit on the bridge, while LaForge and perhaps Data would sit at Engineering, and nameless professionals would man the torp bays or the phaser control rooms and so forth, so the heroes needn't go there.
Vertical access was only needed for LaForge to access crucial damaged systems - and those systems all seemed clustered around the Jeffries tubes anyway (which is a separate yet very annoying nit). If the crew had to resort to crawling, it was not because the turbolifts were hiccuping - it was because the whole ship, lifts and doorways and corridors and the unseen staircases alike, was locked up by malfunctions or malevolently used security protocols.
Voyager had a greater problem with this: a small number of competent crew had to access vital systems distributed on multiple decks, and they were *always* crawling around. The "locals" just couldn't handle the crises. And there were indeed episodes where people were trapped on a certain deck by what looked like a simple turbolift failure or general power failure.
quote:Originally posted by Timo: In the first category, though, Bernd says that a solid or forcefield-based jet reverser attached to the impulse engines would not alter the net force on the ship. This isn't true, as the end result will still be that the exhaust jet is directed forward, thus transferring momentum in that direction and giving the ship momentum in the opposite direction. The internal structure of the engine does not matter - internal forces will cancel out, save for the one opposite the final exhaust direction.
Final exhaust direction is irrelevant. Rockets, jets, et cetera all operate by imparting force on the spaceframe of the vessel, be that a shuttle, aircraft, or what-have-you. The exhaust does not "push against" anything to produce thrust, though that is a common misconception.
(It's kinda accurate in reference to hovercraft, where the engine exhaust is contained and provides a cushion of air, but that's not what we're talking about.)
Some sort of physical device built to reflect the exhaust toward the front of the vessel would, by default, have to be connected to the vessel. Therefore, the net acceleration on the starship spaceframe would be zero.
The only way such a system would work would be if some sort of device could grab the exhaust products, redirect them forward, and in the process cause the exhaust products to impart a new force on the spaceframe, providing an accelerative force against the ship (albeit in a bass-ackwards direction).
G2k
-------------------- . . . ceterum censeo Carthaginem esse delendam.
posted
Referencing the 'reverse exhaust' discussion.
1- A close look at the ventral surface of the E-e's impulse bays shows 4 rectangular vents - which I interpret to be reverse-direction thrust ports.
2- However - I must disagree with the argument that a force field-based thrust reveral nozzle would be ineffective: a- The plasma would be vented forward at high speed. b- There is a verifiable degree of 'momentum feedback' with shields (if a meteor of bolt of energy hits the external shields, the ship as a whole is shaken. I assume that the momentum is transferred back to the generators (which therefore must be braced and welded down).
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quote:Originally posted by Treknophyle: Referencing the 'reverse exhaust' discussion.
1- A close look at the ventral surface of the E-e's impulse bays shows 4 rectangular vents - which I interpret to be reverse-direction thrust ports.
2- However - I must disagree with the argument that a force field-based thrust reveral nozzle would be ineffective: a- The plasma would be vented forward at high speed. b- There is a verifiable degree of 'momentum feedback' with shields (if a meteor of bolt of energy hits the external shields, the ship as a whole is shaken. I assume that the momentum is transferred back to the generators (which therefore must be braced and welded down).
If there are forward-facing ports near the shuttlebay, they could be used as reverse thrusters. However, they would either have to have their own power source, or else the IPS reactors would (A) have separate outlets for the thrust, closing off the rearward ones or (B) the reactors themselves would have to turn to blast in a new direction.
As for the "vented forward" argument, the principle is that first, the fusion reaction exhaust would have pushed against the front part of the reactor, exiting out of the tail and producing forward thrust.
Any system which causes the exhaust to reverse direction (even a forcefield) will be doing nothing more than "bouncing" the exhaust toward the front of the ship, canceling out the forward thrust and bringing the thrust total down to zero. Just because the exhaust products are now headed forward does not mean that the ship must now move backward.
If you need confirmation, take a nasty little cheap-o plastic toy car . . . something light, but big enough to tape a balloon to. Take the balloon (blown up with air), tape the bottom of it to the car, and then let go and watch the car fly.
Now, attach something big and flat to the back of the car. It doesn't matter what it is . . . it can be a big flat piece of cardboard, a sail/parachute, or a nifty something designed to redirect the airflow backward. As long as you do your job well, the car isn't going to move.
The only way it would move the way you want it to would be for you to make something to catch all of the air out of the balloon, hold it, and then blow it out toward the front of the car. But, it would just be easier to turn the original balloon around, or the whole car.
G2k
-------------------- . . . ceterum censeo Carthaginem esse delendam.
quote:Originally posted by Guardian 2000: Any system which causes the exhaust to reverse direction (even a forcefield) will be doing nothing more than "bouncing" the exhaust toward the front of the ship, canceling out the forward thrust and bringing the thrust total down to zero. Just because the exhaust products are now headed forward does not mean that the ship must now move backward.
Hogwash.
There are two ways to look at the problem, both of which are equivalent and give the same answer.
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First, consider the ship and any assorted engines and thrust deflectors as a black box. The only things coming out of the black box is a stream of particles moving faster than the ship in the direction of travel. To conserve energy and momentum, the black box must be accelerating in the opposite direction. That's basic physics.
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Second, consider the transfer of momentum at the level of particles, starting in the fusion drive. The fusion engine is imparting energy to the particles along random orientations which imparts no net momentum to the ship. Some of the particles bounce off the sides of the engine, but this happens in a symmetric fashion so there is no net transfer of energy (some of the particles hit the top accelerating the ship upwards and the particles reflect downwards; some of the particles hit the bottom, accelerating the ship downwards and the particles reflect upwards). Some of the particles hit the front of the engine, accelerating the ship forwards while the particles reflect backwards. The rest of the particles escape from the engine without a (net) transfering energy to the ship (i.e. they do, but it is offset by the particles that started off going forwards).
The net result of this is that there is a stream of particles leaving the engine to the reverse while the ship is given a forwards momentum. Note that all of the particles that leave the engine must have a negative direction - and all particles must leave the engine eventually or it will clog up.
Now this stream of particles impacts a thrust reverser and reflects forwards. This imparts a negative momentum to the ship. Note that ALL of the particles leaving the engine impact the thrust reverser and transfer negative momentum, while only particles which impacted the front of the engine imparted positive momentum. Thus, there is a net negative momentum imparted to the ship.
If this were somehow balanced (i.e. the same number of particles impact the front of the engine as the impact the back) the ship would still experience a negative momentum increase. For example, if the initial momentum imparted to the particles was not omnidirectional (imagine you're running an ion drive which acts like a microscopic rail gun) then just imparting positive momentum to the particles (i.e. towards the front of the engine) necessarily imparts negative momentum to the ship. The particles then bounce off the front of the engine (a bit of positive momentum), then off the thrust diverter (a bit of negative momentum). Since the latter two particle bounces cancel each other out, you are left with the initial negative momentum from the particle generation.
Both of these viewpoints (black box & watching particles) match, which is what you'd expect.
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Your car/balloon/cardboard example is flawed. First, in most cases, the balloon is going to have only just enough energy to move the car without the cardboard in place (i.e. given air resistance and friction, it's not imparting 10x the energy to get the car going, probably only around 2x). Secondly, the air bouncing off the cardboard primarily goes off to the sides; it is not a unidirectional thrust diverter. More than likely, this reduces the available energy from 2x to 0.5x and thus the car doesn't move.
If you used a styrofoam cup as the diverter to direct the flow unidirectionally, I bet it would work just fine.
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Lastly, jet airliners use thrust diverters to slow the plane upon landing. This is practical evidence that the darn things do work.
quote:Originally posted by Joshua Bell: Lastly, jet airliners use thrust diverters to slow the plane upon landing. This is practical evidence that the darn things do work.
No, this is evidence that they needed a way to reduce the forward thrust from, say, %10 to %5 without stalling the engine.
The thrust diverters do not slow the plane, they divert the forward thrust that is keeping it from slowing. Hence the name "thrust diverters".
G2k
-------------------- . . . ceterum censeo Carthaginem esse delendam.
posted
The car+balloon+cardboard example is also flawed because of the cardboard itself. You're acting like the impulse engines just have a big flat forcefield behind them that the exhaust bounces off of. That's just silly. The forcefield should be shaped like a tube that comes out from the impulse engine and curves around to be pointing to the front of the ship. It would be no different than if a giant curved metal tube came out and redirected the exhaust to the front of the ship. Take your balloon and stick a straw into the opening, seal it, and make the straw curve around to point in the other direction. Then see which way it flies.
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posted
assuming of course we understand the way a forcefield works. maybe its more a scattering field than a 'wall'
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quote:Originally posted by Guardian 2000: Any system which causes the exhaust to reverse direction (even a forcefield) will be doing nothing more than "bouncing" the exhaust toward the front of the ship, canceling out the forward thrust and bringing the thrust total down to zero. Just because the exhaust products are now headed forward does not mean that the ship must now move backward.
Nope. When the exhaust is redirected the change of momentum is 2p not just p.
A particle heading aft with momentum p hits a forcefield (we'll assume that the collision is perfectly elastic) and bounces off with momentum -p.
The total change of momentum (from p to -p) is thus 2p.
So the ship gains forwards momentum of p when it first generates the particle and backwards momentum of 2p when it bounces the particle.
p-2p = -p.
The ship now has a total backwards momentum of p.
Of course, no collision is 100% elastic and the redirected particle can't be heading directly back the way it came (otherwise it would go straight back into the impulse drive) so the ship's backwards momentum would be less p but, giving Starfleet engineers some credit, that's only a change of magnitude not of direction.
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posted
Now that this confusion is out of the way, we might consider the possibilities offered by the transporter. That machine doesn't seem to preserve momentum or angular momentum - after all, it can handle surface-to-orbit transport just as fine as a ship-to-ship one.
Let's start easy. What about rigging a rocket engine inside the ship, and having the jet of propellant be transported back to the fuel tanks after it has been spat out by the rocket? An exhaustless drive that consumes no propellant. You only need the fuel that gives you energy for the rocket and the transporter - say, a fission or fusion reactor or something.
Or, if the transporter can give the required momentum and angular momentum to somebody who is transported from ship to surface, I guess it could also give such momentum to a jet of gas. No need for actual engines - just transport a puff of gas that will shove the ship in the desired direction, then grab that gas again and give it another dose of momentum, again and again and again until your ship moves at relativistic speeds... Your "engine nozzle" could be a hollow sphere at the heart of your ship, with the puffs of gas hitting the inner walls of the sphere.
And so forth and so forth. A machine that doesn't conserve momentum is a pretty darn impressive propulsion system, even if it can only handle a small amount of matter at a time. You don't need to transport an entire starship to get it moving...
Or does the transporter in fact conserve momentum? If so, where is it dumped? Some sort of huge flywheels which rev up when somebody beams up, and are tapped for momentum when somebody beams down? Heating and cooling of something by fiddling with the momenta of the molecules? That's pretty impressive, too. And a great weapon or way to get free energy, or then a horrid source of environmental damage if the transporter dumps the momentum on nearby planets and stuff.
Next week on Flare Forum: artificial gravity and how it causes 6.7-Richter earthquakes in Newton's grave...
posted
I'd guess that the transporter (and thus the ship) absorbs/supplies the required momentum. After all the change in momemntum for six humanoid masses going from standard orbit to planetary surface could be transfered to a starship sized mass without much effect on its orbital velocity.
If this works out then your transporter drive idea is a dud.
I think your rocket idea is dodgy as well. It would only work if the nature of the fuel wasn't changed. If you ignite the fuel (to release the energy needed to accelerate it to exhaust velocities) then the fuel will no longer be the same after use as before so transporting it back to the fuel tank would be pointless.
-------------------- "My theories appal you, my heresies outrage you, I never answer letters and you don't like my tie." - The Doctor
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