StarDestroyer.Net BBS

I'm a little curious about the effects of the gravity shadows of stellar components like planets and stars on the FTL travel.

From what I recall a ship traveling in hyperspace cannot travel too close to a mass shadow without risking being dragged out, or even destroyed, by the interaction between hyperspace and gravity.

The core of the galaxy is said to be nearly impossible due to the fact that the stars are so densely packed together that it creates very few 'lanes' that one can safely travel down. The problem I have with this idea, if its correct, is that if this is true then it means that the stars gravity well is felt through hyperspace over a range of several light years since even in the core the stars should still have a decent amount of separation. But we've seen several instances of ships emerging from hyperspace relatively close to planets, well within a solar system, and coincidentally well within the gravity well of a star. So you can see the dilemma, just how far does the gravity shadow extend in SW hyperspace?

Is there any evidence that the Hyperspace routes are faster because of lack of stellar mass close to them? Or are they faster to travel because they are precisely mapped and the ships navigation computers can plot several course changes so that an impact or close up with a supernova is avoided? Afterall we are talking about velocities in the 100k+ the times of light. The precision necessary to avoid impact with anything at those speeds appears kind of incredibly astounding.

Just take an old toothbrush, a sheet of paper and a bit of color. But color on the old toothbrush and flip the color on the sheet of paper by using your thumb. That will make a lot of tiny spots. And now chose two points and try to draw a line with a fine pencil between them without hitting the the other points. that might give an idea of how precise a hyperspace course must be.

Well thats my idea about it. It's not really about the gravity shadows but more about the amount of them in your way.

Is the hyperdrive a straight line FTL or can the SW-ships actually maneuver within hyperspace?

If they are straight line travel than you can go wherever you want to go but with many short jumps and correction to the course. The Hyperspace routes would be faster because you can make longer jumps without fear of playing chicken with a supernova...

Lord Anubis wrote:I'm a little curious about the effects of the gravity shadows of stellar components like planets and stars on the FTL travel.

From what I recall a ship traveling in hyperspace cannot travel too close to a mass shadow without risking being dragged out, or even destroyed, by the interaction between hyperspace and gravity.

The core of the galaxy is said to be nearly impossible due to the fact that the stars are so densely packed together that it creates very few 'lanes' that one can safely travel down. The problem I have with this idea, if its correct, is that if this is true then it means that the stars gravity well is felt through hyperspace over a range of several light years since even in the core the stars should still have a decent amount of separation. But we've seen several instances of ships emerging from hyperspace relatively close to planets, well within a solar system, and coincidentally well within the gravity well of a star. So you can see the dilemma, just how far does the gravity shadow extend in SW hyperspace?

Short answer: the authors didn't think it through as more than a convenient plot device/one-line one-off excuse for plot limitations. No one ever sat down and thought about consistent rules.

tezunegari wrote:Is there any evidence that the Hyperspace routes are faster because of lack of stellar mass close to them? Or are they faster to travel because they are precisely mapped and the ships navigation computers can plot several course changes so that an impact or close up with a supernova is avoided?

Which would result in-those courses being faster due to lack of stellar masses being close to them.

Afterall we are talking about velocities in the 100k+ the times of light. The precision necessary to avoid impact with anything at those speeds appears kind of incredibly astounding.

Not really. Even at the core of our galaxy stars make up less than a quintillion of the volume of space. You'd have to be REALLY unlucky to accidentally hit one.

Just take an old toothbrush, a sheet of paper and a bit of color. But color on the old toothbrush and flip the color on the sheet of paper by using your thumb. That will make a lot of tiny spots. And now chose two points and try to draw a line with a fine pencil between them without hitting the the other points. that might give an idea of how precise a hyperspace course must be.

Not really. Assuming your spot is 1mm across and represents a star 1 million km in diameter. The closest spot, representing the star closest to Earth's sun, on that sheet of paper would be 40 million kilometres away.

Is the hyperdrive a straight line FTL or can the SW-ships actually maneuver within hyperspace?

The EU occasionally claims it's straight line only but overall they apparently CAN maneuver under hyperdrive.

If they are straight line travel than you can go wherever you want to go but with many short jumps and correction to the course. The Hyperspace routes would be faster because you can make longer jumps without fear of playing chicken with a supernova...

They should be able to make arbitrarily far jumps mostly either way because space is, essentially, really really empty.
What DOES require precise jump calculations is the fact that as often as not hyperspace jumps ARE aimed at massive bodies, namely planets, and if you DO overshoot you're bound to run into it.

Some sources claim the gravity cut-off is a safety to prevent crashing into a navigational hazard. If it were as simple as that, then a ship could escape an Interdictor cruiser by turning the safeties off. (Might not be easy for a civilian ship, but one would expect that designers of military ships would take this into account.)

I've heard an idea that Interdictors project a constantly-fluctuating gravity field that the hyperdrive can't compensate for, and so it must be shut down or else it will run the risk of destroying itself. I can't recall offhand if that idea was shot down or not, but let's run with it for now: a ship traveling in hyperspace near the core would experience gravity wells changing much more quickly than it would on the rim. One would have to plot a course that was within the capability of the ship's hyperdrive to compensate for.

Of course, the Kessel Run poses a problem for this hypothesis: the idea is that a faster ship is needed to get closer to the black holes to make the run more quickly. Faster also means moving in and out of gravity wells more quickly. Or it could mean that a faster hyperdrive can handle more drastic changes in gravity wells or that it clears the well before taking damage.

Mad wrote:Some sources claim the gravity cut-off is a safety to prevent crashing into a navigational hazard. If it were as simple as that, then a ship could escape an Interdictor cruiser by turning the safeties off. (Might not be easy for a civilian ship, but one would expect that designers of military ships would take this into account.)

You know my stance on this. It IS a safety mechanism, but a valid one. Gravitational fields exert some form of stress on ships while in hyperspace, and ships must be properly prepared for the force vector.

I've heard an idea that Interdictors project a constantly-fluctuating gravity field that the hyperdrive can't compensate for, and so it must be shut down or else it will run the risk of destroying itself. I can't recall offhand if that idea was shot down or not, but let's run with it for now:

I don't recall anyone shooting down my idea while in SB or SD, although I WAS in Basic shortly after　I debutted that idea here on SDN.

Of course, the Kessel Run poses a problem for this hypothesis: the idea is that a faster ship is needed to get closer to the black holes to make the run more quickly. Faster also means moving in and out of gravity wells more quickly. Or it could mean that a faster hyperdrive can handle more drastic changes in gravity wells or that it clears the well before taking damage.

Or it could mean that faster ships have a much higher tolerance for stress exerted by mass shadow, not an illogical one when one considers that a ship that's accelerating faster would presumably be under more stress than one that's accelerating slower.

My opinion with this is that Einsteins theory of gravity carries over into hyperspace, so yes, you can cross gravity wells, but you still need to account for their presence. Assuming that a sun sized star has a roughly 2 light year hyperspace footprint around it, then when you have rigel sized stars your talking about a hyperspace footprint of up to a few hundred lightyears.
If space is curved around stars like this then careful navigation would need to be done to assure that as your course curves with spacetime, that you don't get sent spiraling into a star. Its technically straightline travel, but with all the stars in the galaxy, your course will look more like a series of swooping curves, arcs and loops.

Maybe I'm not understanding what you're trying to say here, but we see starships jump in and out of planetary orbit all the time. The Falcon jumping away from Tatooine, the Rebels fleeing Hoth, Luke jumping to Dagobah(sp), The Tyderium jumping to Endor, the Rebel fleet jumping to Endor. They don't come out of hyperspace 2-100ly from the system, they jump directly into it.

Hyperspace is normal space from a tachyonic perspective, so yes relativity carries over. That said the rest of your post doesn't track.


And as to Mad's above "disable the safeties" idea... who says that you can in anything but an extremely customized ship? Given the level of devastation a tachyonic collision can cause, I'd imagine they would make them as tamper proof and idiot proof as possible. One guy turns it off to make his run a little faster, and he kills a few billion people as a result. Any sane engineer or company is going to to everything they can to make sure that doesn't happen.

your misunderstanding what I'm saying.
under Einsteins theory of gravity, the Earth actually warps spacetime, if it obviously warps stars and other heavier objects a good deal more, a good example of this is this clever little game Death Star Battles. In that game, you can see how large bodies effect the path of the projectile. Assume now that the projectile is a ship in hyperspace and you have some idea of how hyperspace flight would look. Yes you could approach planets, but if you weren't careful with your approach, you'd end up in one, or flung out into deep space.

Somebody tell me he DID'T just appeal to game mechanics.

Batman wrote:Somebody tell me he DID'T just appeal to game mechanics.

He didn't. He used accurate modeling of real effects in a game as a demonstration of the property he is talking about. Try reading his whole post, or, barring that, getting a basic education so you can understand what he is trying to say.

thanks Ender,
and the rest of you, If I have to take the time to make pictures to show this, its going to be really pathetic. I thought you guys would have some idea how gravity actually works. It really isn't that complicated. Let me try again.
Imagine space is like a flat piece of rubber, with parts pulled down by heavier materials. The moons, stars, and planetary systems all deform the fabric of spacetime. Now if you want to roll a ball from one place to another, its obviously going to curve on its course and spiral down into one of the heavy places unless special care is taken to make sure it stays on track.
This is high school level physics people. It isn't that complicated, and honestly, you probably shouldn't be discussing it if you don't understand it.

We do know that the gravitational warping of space/time does occur. IIRC they mention something about it in one of the first Wraith squadron books where Corran was calculating a hyperspace jump. He was able to use the greater speed of the X-wings to cut closer to the gravitywell and not pulled into the sun. The trade off was using more fuel to achieve the necessary speed.

Tsakara wrote:thanks Ender,
and the rest of you, If I have to take the time to make pictures to show this, its going to be really pathetic. I thought you guys would have some idea how gravity actually works. It really isn't that complicated. Let me try again.
Imagine space is like a flat piece of rubber, with parts pulled down by heavier materials. The moons, stars, and planetary systems all deform the fabric of spacetime. Now if you want to roll a ball from one place to another, its obviously going to curve on its course and spiral down into one of the heavy places unless special care is taken to make sure it stays on track.
This is high school level physics people. It isn't that complicated, and honestly, you probably shouldn't be discussing it if you don't understand it.

The thing of it is though, it comes down to a question of tolerances. The strength of gravity follows the inverse square law. If the extremely weak field they would feel quite a ways out, like your suggestion of limits puts forth, is enough to make the ship divert, how do they drive deep into it to arrive in system? If you can push to charge deep into it to get in system, why not make your "deep path" a secant instead of the radius, and save yourself the time and difficulty of getting around? I suppose a case could be made for fuel and energy and "deep paths" being costly, but given the state of the galactic economy that is a bit hard to sell.

As IP pointed out above, the real problem is that this was never fully hashed out.

maybe they don't dive straight into the system, maybe they spiral down into them and out of them. We have no evidence to say they don't and at the speed that FTL travel takes place at, it wouldn't slow them down too much.

Ender wrote:

Batman wrote:Somebody tell me he DID'T just appeal to game mechanics.

He didn't. He used accurate modeling of real effects in a game as a demonstration of the property he is talking about. Try reading his whole post, or, barring that, getting a basic education so you can understand what he is trying to say.

I'm not used to game mechanics actually being ACCURATE, okay? My bad for dismissing it simply because it was from a game, I should have looked beyond that. And just for curiosity's sake, what is your definition of a 'basic' education? Because for most people, relativity (general OR special) doesn't figure into that. (If you're saying that 'I' should have at least a token understanding of those since I debate here, guilty)

Um-there's exactly ZERO evidence for the spiralling in on the destination and ALL of available evidence shows them straight-lining for the target.

Batman wrote:Um-there's exactly ZERO evidence for the spiralling in on the destination and ALL of available evidence shows them straight-lining for the target.

And what evidence would that be?

Batman wrote:

Ender wrote:

Batman wrote:Somebody tell me he DID'T just appeal to game mechanics.

He didn't. He used accurate modeling of real effects in a game as a demonstration of the property he is talking about. Try reading his whole post, or, barring that, getting a basic education so you can understand what he is trying to say.

I'm not used to game mechanics actually being ACCURATE, okay? My bad for dismissing it simply because it was from a game, I should have looked beyond that. And just for curiosity's sake, what is your definition of a 'basic' education? Because for most people, relativity (general OR special) doesn't figure into that. (If you're saying that 'I' should have at least a token understanding of those since I debate here, guilty)

Think of it as a physics simulator than. Unlike real life, you can get accurate ones for space more easily- no friction.

Relativity at its heart is simple- the speed of light is the same for all observers and goes from there. Knowing some of the effects isn't too bad. Of course, actually understanding what it implies would probably be beyond a basic education. Or nonspecific college for that matter.

Ender wrote:And as to Mad's above "disable the safeties" idea... who says that you can in anything but an extremely customized ship? Given the level of devastation a tachyonic collision can cause, I'd imagine they would make them as tamper proof and idiot proof as possible. One guy turns it off to make his run a little faster, and he kills a few billion people as a result. Any sane engineer or company is going to to everything they can to make sure that doesn't happen.

If safeties to prevent collisions were the only thing keeping a ship from jumping out of an interdiction field, then the ability to disable those safeties for a quick jump out of the field would be a highly desirable feature for military and probably smuggler ships. Hence the hypothesis for stress on the hyperdrive equipment itself, which would mean that disabling the safeties would be futile: the hyperdrive would be destroyed.

Tsakara wrote:This is high school level physics people. It isn't that complicated, and honestly, you probably shouldn't be discussing it if you don't understand it.

No, it's pretty complicated. The rubber sheet model is a representation of potential fields and orbits, not general relativity's spacetime curvature. Newton's law of gravitation is what you mean, and what's used in that game.

Tsakara wrote:maybe they don't dive straight into the system, maybe they spiral down into them and out of them. We have no evidence to say they don't and at the speed that FTL travel takes place at, it wouldn't slow them down too much.

Why would they? Light doesn't follow a spiral path when moving through a typical solar system, are you saying something which moves a million times faster would?

Dooey Jo wrote:

Tsakara wrote:This is high school level physics people. It isn't that complicated, and honestly, you probably shouldn't be discussing it if you don't understand it.

No, it's pretty complicated. The rubber sheet model is a representation of potential fields and orbits, not general relativity's spacetime curvature. Newton's law of gravitation is what you mean, and what's used in that game.

Tsakara wrote:maybe they don't dive straight into the system, maybe they spiral down into them and out of them. We have no evidence to say they don't and at the speed that FTL travel takes place at, it wouldn't slow them down too much.

Why would they? Light doesn't follow a spiral path when moving through a typical solar system, are you saying something which moves a million times faster would?

First, of course you can use the rubber sheet analogy in GR.

Secondly, he's saying that they intentionally follow a spiralling path so that they don't drop down the potential as fast as a direct route would, and this is a decent way of explaining how ships can get into the inner system, but not travel too close to stars on longer journeys. That said, in order to be able to spiral in you need to be able to accelerate, and if you can accelerate, why not just decelerate as you approach, changing your speed as necessary to drop down the gravity well slowly enough to avoid damage. I suppose there could well be a minimum speed for hyperdrive (certainly in excess of c), so if that were the case then you would need to spiral in once you were at that minimum speed.

Now I have just done some calculations, i will post full details if people request, but I don't really want to type everything out as last time I gave the full details someone just ignored it and went "lol i think *stuff just demonstrated wrong* " just 2 posts below...

Heres the outline of how it might work.

Let us suppose that there is some quantity "stress" that the ship can only withstand a certain amount of, and this is what limits the closest approach to a star.

Now let us use the changing potential/force theory, and try and define this mysterious "stress" quantity as the rate of change of the (magnitude of the) gravitational force on the ship.
So Stress = dF/dt

and at speed v => Stress = 2GMm*vs/(D^2+s^2)

Now suppose we have a ship going at speed v in a straight line, and the course has the closest approach to a star at a distance D.

Now we parametrise the distance of the ship away from the point of closest by s.

So we've drawn a dot and a straight line (the ships path), and then theres a second line perpendicuar to the the first and through the point, and the second line is D long and the distance along the ships path from the point where the 2 lines intersect is s.

Now lets suppose that at the given speed v the ship has a distance D that is the closest it can go to the star at that speed. This is determined by the maximum stress the ship can sustain. So lets calculate that.

/snip calculation/

Stress(max) = 3*sqrt(3)*GMmv/(8*D^3) (where m=mass star, and m=mass ship)

now suppose we seek to get to a radius r0 at which our planet lies, without exceeding Stress(max). Lets try going in a slowly tightening circle or radius r.

What then is the maximum rate ( rdot(max) ) at which we can shrink the radius of the circle, r, without breaking our ship?

/snip more calculation/

rdot(max) = -3sqrt(3)*v*r^3/(16*D^3)

Ok, given this, what is our journey time from radius D to our destination r0?

/a bit more maths/

time = (8*D/3*v*sqrt(3))*[r0^-2 + D^-2]

So we have a finite journey time, and one that only increases linearly in D (as for the very large D we want D^-2 is tiny and irrelevant).


You can try plugging some numbers into that, but please don't fuck up the units. I'm off to wrap some presents.

Again, I will post the full calculation if people really want to see it, but I don't want to type/tablet it up during Christmas.

Edit: I suppose its worth mentioning that D is larger at the high speeds that you want for galactic/inter solar travel than for the low speed you can choose to approach the star at, so there's an additional level of optimisation you can perform on approach, heading straight for the target at high speed, decelerating as necessary then only once you need to (having reached minimum hyperdrive speed) switching to a spiralling approach or perhaps there's a better way of doing it, I haven't checked.

Oh cock. Just noticed that I didn't copy a 3 from the line before to the last line in my workings. It should read:

time = ((8*D^3)/(3*sqrt(3)*v))*[r0^-2 - D^-2]

Well, now we're still left with something that works and is finite, just a bit more sensitive than before.

Ender wrote:

Batman wrote:Um-there's exactly ZERO evidence for the spiralling in on the destination and ALL of available evidence shows them straight-lining for the target.

And what evidence would that be?

None, as it turns out. While there STILL is no evidence for them spiralling in (and I completely fail to see why they should need to do that) neither the movies nor the EU as far as I can tell explicitly say they DON'T.