Favorite type of FTL?

[Admiral Valdemar]

If that is the in universe explanation, fine, but it is completely illogical, and you should realize that (abuse of lagrange points is one of my pet peeves in sci fi, which is why I am harping on it here). A lagrange point is in no way fundamentally different to any other orbit - it still has a net gravitational force toward the primary.

It's funny you're calling something illogical based on a drive that is physically impossible. The logic is quite clear: a wormhole can only be opened safely where no forces are present to attract such an object and disturb it in whatever way, shape or form out of a pre-calculated vector. That they can also make these jumps in deep space is the logical conclusion of this, whereas within a system it is seemingly not a good idea without being within an L-point or orbit where such practice can be done (though I don't think you'd want these sorts of things going on around a planet with their traffic, that and they'd be even easier to defend than L-points anyway).

The concept of there being no gravity is stupid anyway, since gravity is universally applicable, which is why we can only rely on the illusion of gravity not having an effect with respect to free fall orbital motion, wherever it may be. Obviously such drives are dependent on gravity's interaction being kept to a minimum (the opposite extreme being trying to jump next to a neutron star or black hole).

Heh. Well, not to put too fine a point on it (sorry), the point to the points used in these drives is to put some limitations on the stardrives.

Back in the old days (pre-1970s), the popular limitation was the ship could only enter FTL flight when it was sufficiently far away from the gravity of a planet or sun. I dunno who invented it, but all the authors copied it.

John W. Campbell jr. used it in his novel ISLANDS IN SPACE (1931). He used technobabble about the artificial space warpage of the stardrive being interfered with by the natural space warpage of a planet's gravity. This is total hogwash, but it almost sounds reasonable.

Niven and Pournelle popularized (if not invented) the idea of limiting FTL entry to specific points in space. MOTE IN GOD'S EYE has their points determined by "lines of equipotential thermonuclear flux" between two stars, which is more hogwash. The game INDEPENDENCE WAR uses Lagrange points, which is clever.

But the whole purpose is to introduce some limit on the stardrive. You could just as well limit FTL entry to the time of proper phase of the moon or when the proper planetary conjunction occurs, or if enough four-leaf clovers with pixie dust are burnt in the ship's engines, or something.

It's just that a gravity based limit sounds all real and scientific.

Jump-gates have the same effect, whatever mechanics they have, I imagine. I like the STL aspect of being able to see any approaching ships months before they're even close to parking into any orbit. There is one incident in a certain novel where such a predicament is expected, however, the approaching ship arrives earlier than expected, thanks to inertia manipulation allowing the ship to go faster on the same engines and pull more than one gee to decelerate faster than otherwise anticipated. It'd be like setting off a signalling flare at night in a ship approaching a port, only your ship was right outside the port and the flare came from a parked buoy klicks away, giving the impression of a quicker arrival.

[Ariphaos]

It can fuck up causality, just like wormholes.

Alcubierre devised a new metric, which means applying solutions like that are based on the Minkowski metric don't necessarily apply, at least as far as I understand it. See Kuroneko's post here. I can't claim to understand it much better than I did when I posted in that thread, however :-/

Just had a look at Atomic Rockets. There is a good point here, not original with me; it's not a good idea to throw around relativistic kinetic-kills in a solar system you want to have some use for afterwards. Numbers in the double-digit teraton range are typical when discussing stuff like this.

I have seen a bombardment weapon concept which is out and out nasty. The only problem is that it would take years to reach target. Simple really; a Bussard ramjet with terminal guidance. With enough runup this could smash a planet, easy.

Not really. Eventually, you are running up against the interstellar medium, and then the interplanetary medium.

At relativistic speeds, its effects are not trivial. At 86% of c, a square meter of surface area is going to be exposed to a few tons of TNT worth even in the unusually rarefied local interstellar medium for every trillion kilometers it passes through. Lorentz contraction is going to make your projectile even less aerodynamic, and it's going to shine like a beacon, announcing its presence to the Galaxy, even if you somehow managed to hide the obscene amounts of heat you needed to release in firing the thing.

You can't really do this effectively from a distant star. You need to do it from nearby. If your target's sphere of influence stretches for several light years, this does not become a trivial means of wiping them out.

Even if the target doesn't, it's a potential waste of immense energy resources. Years of advancement is going to go by and all they need to do to make the attack bearable is to through successive clouds of dust in the way.

[Admiral Valdemar]

Because logic doesn't apply to the impossible, am i rite?

Bingo.

Any orbit can be considered to do this. Orbits are easy to precaculate, and nothing will disturb you that you won't see (such as a passing planet) and anticipate in your calculations.

If by not being disturbed you mean no forces will act upon it, I have explained twice already that a Lagrangian point does not fit this description. They are no different in any way than a 'regular' orbit.

With that fact, saying something works at a Lagrangian point but not in any other orbit is not logical. It is an arbitrary limitation, no better than completely made up technobabble.


Now, like I said, I like the idea of jump points in stories, since they offer several plot advantages, but the L-point restriction just doesn't make sense.

So I take it you missed the part where I addressed the standard orbital idea and how it's a Big Mistake™ with regards to a militarised atmosphere and pirates.

[Admiral Valdemar]

At relativistic speeds, its effects are not trivial. At 86% of c, a square meter of surface area is going to be exposed to a few tons of TNT worth even in the unusually rarefied local interstellar medium for every trillion kilometers it passes through. Lorentz contraction is going to make your projectile even less aerodynamic, and it's going to shine like a beacon, announcing its presence to the Galaxy, even if you somehow managed to hide the obscene amounts of heat you needed to release in firing the thing.

You can't really do this effectively from a distant star. You need to do it from nearby. If your target's sphere of influence stretches for several light years, this does not become a trivial means of wiping them out.

Even if the target doesn't, it's a potential waste of immense energy resources. Years of advancement is going to go by and all they need to do to make the attack bearable is to through successive clouds of dust in the way.

Those dust clouds better be dense then, because otherwise you're not doing anything but ablating an RKV that is going to hit in a more scattered state which does nothing to reduce the KE of the weapon. You're also need foresight, since seeing the thing approach and reacting to it is going to be mighty hard without one massively good sensor net of system wide scale with tremendous time-on-target abilities. And that's to deal with one. There's nothing saying a race that can make such weapons doesn't have a handy AU length of railgun ready to ripple off a few dozen of these at you in short succession.

No matter how advanced you are, dealing with relativistic weaponry is a real bitch and the equivalent of ICBMs today.

[Patrick Degan]

Joe Haldeman used a variation on the portal idea for The Forever War —natural Kerr wormholes generated by spinning black holes, or "collapsars" as they were referred to in the novel. The nice little twist on this idea is that it still took months of acceleration to get a ship up to the minimum .99c velocity to safely enter the collapsar at the right vector to make the jump to the next collapsar (enter it the wrong way and you fall into the singularity and are crushed out of existence instead). Then a ship had to decelerate to enter the target star system. Which tended to pile up huge time-dilation penalties so that the novel's protagonists ended up more than 1100 years from the time they first entered the military service. FTL and yet still no escape from relativity.

[Lord of the Abyss]

It has parts that spin or otherwise move in higher dimensions/through time, and it moves the ship as a reactionless drive by being an unbalanced engine; the net kinetic energy of all the moving parts doesn't cancel out, but moves the drive and ship. Yes, I know that violates physical laws; I don't recall the name, but it should have been called the "Screw Physics ! Drive"

Yes, we know it as the infamous Dean Drive, which was the original "net kinetic energy of all the moving parts doesn't balance out." drive. I'm sure A. Bertram Chandler read about the Dean Drive in John W. Campbell's promotional article in Astounding magazine.

I knew that it was based on that, but couldn't recall the name or details; thanks.

[Arrow]

Now, like I said, I like the idea of jump points in stories, since they offer several plot advantages, but the L-point restriction just doesn't make sense.

What restriction would you suggest instead?

[Ariphaos]

Those dust clouds better be dense then, because otherwise you're not doing anything but ablating an RKV that is going to hit in a more scattered state which does nothing to reduce the KE of the weapon.

More scattered state. Read your own sentence again. A bit of dust weighing a single gram will impact a projectile moving at 86% of C with a force equal to 20 kilotons, all directed into the projectile.

So you hit the thing with a few of these, and one of two things can happen

1: Its course gets deflected (said gram is imparting half a million kg•m/s worth of momentum onto the projectile. If impacting 20 AU out, and the projectile weighs a tonne, the projectile will now miss.)
2: It gets scattered into a radius larger than the planet, significantly reducing the amount of energy the planet receives.

You're also need foresight, since seeing the thing approach and reacting to it is going to be mighty hard without one massively good sensor net of system wide scale with tremendous time-on-target abilities.

...did you miss my post entirely? The interstellar medium alone is going to make the projectile shine. It actually imparts a meaningful amount of energy.

In the local interstellar medium (a bubble of abnormally rarefied gas due to a local supernova), there is about 1 atom per 14 cubic centimeters.

Pretty thin gas, yes?

So, you're zipping your projectile along, let's say it's a long, thin rod with a face of about one square centimeter, fired at 86% of c for ease of math (where kinetic energy equals annihilation energy). Distance is irrelevant, here, we'll just use the local ISM of .07 atoms/cc.

So, every second, it's hitting over 1,800,000,000 hydrogen and helium atoms (mostly hydrogen, so we'll ignore the latter), with a total collision energy equal to their annihilation energy.

This is about 0.000000000000003 grams.

Annihilation energy is c^2, or 89875517873681764 times that, in joules.

~270 joules, every second, for every square centimeter of face your projectile has. This has an equilibrium temperature of well over three thousand kelvin...

Anything moving at such a speed is going to begin vaporizing before it passes Neptune's orbit (unless you use something that can withstand temperatures better than carbon), and is going to have experienced a not particularly ignorable amount of momentum change, which is going to be difficult to predict properly.

It is, in fact, going to be glowing like a light, being ablated into a plasma, and would promptly be announcing itself to our sensors about the time it was passing the heliopause or so.

Rather hard to imagine Earth being too concerned about it with another couple of centuries of probes and telescopes watching the skies.

There's nothing saying a race that can make such weapons doesn't have a handy AU length of railgun ready to ripple off a few dozen of these at you in short succession.

You can't fire a spherical projectile and expect it to work. You need a very long, very thin, very carefully accelerated rod in order to even hope to get away with this. Thus, it won't involve a railgun, though a coilgun may make an attempt.

[Ariphaos]

Err, doh, need to divide by another thousand since it's grams and not kilograms. Thought something was off.

.27 joules per cc still amounts to an equilibrium energy of 2,700 watts per square meter. This is still a bit over 500 Kelvin (if I'm doing my math right this time >_>), which would be harder for modern sensors to pick up before getting much closer to Earth, but for civilizations at technological parity (a civil war, say, which is much more likely), it's not going to be the same level of problem.

[Catman]

Yeah, may as well not make too much of an explanation.

I use my own version of the warp scale for continuity, and I don't bother with that. At least I knew already that warp drive was impossible or some shit, so I didn't bother with the pretend science.

What bugged me about Okuda's scale was that many speeds past warp 9 didn't appear to be more than a miniscule bit smaller, even Warp 9.6 just cut an hour off of travel time to a nearby star, so I revised it and jacked up the post warp 9 speeds, making it more sensical to go at 9.6 in an emergency, so that it takes you minutes or a few hours to get to a system, and not around a day.

[Winston Blake]

It is most emphatically not.

If an object at L4 or L5 is perturbed, it is brought back toward the point by the Coriolis effect, causing it to orbit the point. This has the same effect as a 'traditional' gravity well on transportation - getting away from it requires some delta-v. For this reason, space dust tend to accumulate around those points, just like would happen if there was a mass at the point.

...and if an object at L1, L2 or L3 is perturbed - wait, your general claim about L-points being gravity wells is screwed. Since I-War gives no suggestion as to what Lagrange points are used for FTL, your L4/L5 point proves nothing. Further, Lagrange points do not act just like there was a mass there - objects at L4/L5 orbit in a weirdo kidney shape, completely unlike any actual mass.

IIRC in the I-War-verse, Capsule jumps need very 'flat' space to work (as in classic scifi where planetbound FTL would ruin the cool usage of spaceships). So in I-War, you can either go very far away from all the planets in a system, or you can go to a Lagrange point, which IIRC is wrongly described in-game as a place where the gravitational forces balance each other.

However, I think that at L1, space actually does go 'flat'. Both masses are pulling in opposite directions to make a local potential maxima. From a rationalising perspective, that might be the one they use. This idea might work for your universe's FTL too - a single L1 point for every planet in a star system. It depends on whether you just want quick interstellar travel, or interplanetary too.

Or if we ignore the 'flat space' thing, there's no reason to judge any bunch of mathematical points as better than any other. Maybe the Capsule Drive really just needs points of zero gradient in the rotational frame, which is what L-points are defined as.

Who knows, maybe streams of magical bogulons coming from the centres of the two masses need to hit the Drive at a fixed angle for the duration of the jump. If the delicate Drive must be undergoing no net force just before and during activation, then you're limited to an unpowered path that's static relative to the masses, hence Lagrange points. What's that I hear you say, 'elliptical orbits'? Shut up.

[Dooey Jo]

It can fuck up causality, just like wormholes.

Alcubierre devised a new metric, which means applying solutions like that are based on the Minkowski metric don't necessarily apply, at least as far as I understand it. See Kuroneko's post here. I can't claim to understand it much better than I did when I posted in that thread, however :-/

I'm not sure I see how it can get around the problem of using two separate FTL signals, as in the example on the page. The third observer's Minkowski diagram may not be valid, but the argument acknowledges that and does not depend on it. Perhaps it is impossible to use the Alcubierre metric in such a fashion.

[Admiral Valdemar]

More scattered state. Read your own sentence again. A bit of dust weighing a single gram will impact a projectile moving at 86% of C with a force equal to 20 kilotons, all directed into the projectile.

So you hit the thing with a few of these, and one of two things can happen

1: Its course gets deflected (said gram is imparting half a million kg?m/s worth of momentum onto the projectile. If impacting 20 AU out, and the projectile weighs a tonne, the projectile will now miss.)
2: It gets scattered into a radius larger than the planet, significantly reducing the amount of energy the planet receives.

Mighty big assumptions there, given I doubt your projectile is going to inflate to planetary scale so quickly, if at all. Assuming you somehow make this massive 20 AU diameter particle shield. None of this negates multiple projectile attacks either.

.did you miss my post entirely? The interstellar medium alone is going to make the projectile shine. It actually imparts a meaningful amount of energy.

In the local interstellar medium (a bubble of abnormally rarefied gas due to a local supernova), there is about 1 atom per 14 cubic centimeters.

Pretty thin gas, yes?

So, you're zipping your projectile along, let's say it's a long, thin rod with a face of about one square centimeter, fired at 86% of c for ease of math (where kinetic energy equals annihilation energy). Distance is irrelevant, here, we'll just use the local ISM of .07 atoms/cc.

So, every second, it's hitting over 1,800,000,000 hydrogen and helium atoms (mostly hydrogen, so we'll ignore the latter), with a total collision energy equal to their annihilation energy.

This is about 0.000000000000003 grams.

Annihilation energy is c^2, or 89875517873681764 times that, in joules.

~270 joules, every second, for every square centimeter of face your projectile has. This has an equilibrium temperature of well over three thousand kelvin...

Anything moving at such a speed is going to begin vaporizing before it passes Neptune's orbit (unless you use something that can withstand temperatures better than carbon), and is going to have experienced a not particularly ignorable amount of momentum change, which is going to be difficult to predict properly.

It is, in fact, going to be glowing like a light, being ablated into a plasma, and would promptly be announcing itself to our sensors about the time it was passing the heliopause or so.

Rather hard to imagine Earth being too concerned about it with another couple of centuries of probes and telescopes watching the skies.

So you've no light speed lag here now. Because you do realise seeing it and then racting before it hits at relativistic speeds is really next to impossible without defences already in place, and therefore, taken into consideration.

You can't fire a spherical projectile and expect it to work. You need a very long, very thin, very carefully accelerated rod in order to even hope to get away with this. Thus, it won't involve a railgun, though a coilgun may make an attempt.

Who the hell said anything about a spherical projectile? You also conveniently miss we already accelerate rods in railguns! Why would we be using shot?

And good luck stopping my .99 c ripple of a dozen several thousand tonne DU crowbars. Even if you did magically see them in time to sound the alarm, there's no defence mechanism for such weapons. Even if vaped to multi-klick expanding clouds, that energy is hitting your planet either way.

[Arrow]

After this discussion, I'm seriously thinking about stripping FTL from my verse (leaving only artificial gravity and super powerful reaction drives as the only handwavium), and moving the setting to some very well developed colony system thousands of years in the future. There's still plenty of conflict and drama without FTL. I find it too difficult to create a description of a drive that preserves the drama of space conflict without putting restrictions on it that are obviously bullshit.

[Patrick Degan]

After this discussion, I'm seriously thinking about stripping FTL from my verse (leaving only artificial gravity and super powerful reaction drives as the only handwavium), and moving the setting to some very well developed colony system thousands of years in the future. There's still plenty of conflict and drama without FTL. I find it too difficult to create a description of a drive that preserves the drama of space conflict without putting restrictions on it that are obviously bullshit.

Quite true. You could posit a rather extensive solar civilisation 10,000 years in the future with thousands of orbital habitats scattered all over the system and still have many of the same dramatic conventions of SF in galactic settings. Does make things easier from a plausibility perspective as well as greater economy in writing.

If I was going to write an FTL device into my SF, I'd probably go with the portal/stargate idea and feature point-to-point jumps for star travel, which is a bit closer to what might —might— be permissable under physical law as we understand it (not saying that it is). It also is a bit more believable that the engineering for such devices would be separate from your ships entirely, and it puts a good set of limitations on the action.

[Ariphaos]

Mighty big assumptions there, given I doubt your projectile is going to inflate to planetary scale so quickly, if at all. Assuming you somehow make this massive 20 AU diameter particle shield. None of this negates multiple projectile attacks either.

No need to make it a particle shield, if you have the tech to fire something meaningful at .99c, you have the tech to spew dust clouds at half that rate in the same direction with a few days' notice.

And it's a cloud, of course it's going to stop multiple attacks unless you set up multiple vectors. It only needs to ensure enough of a density that your projectile will turn to plasma.

So you've no light speed lag here now. Because you do realise seeing it and then racting before it hits at relativistic speeds is really next to impossible without defences already in place, and therefore, taken into consideration.

Of course I'm referring to defenses already in place, but how are they going to be 'taken into consideration'?

Your .99c projectiles require ~1e18 joules of energy to fire per kilogram of mass at a bit over 50% efficiency. This amounts to ~1,500 tonnes of deuterium per kilogram per shot, or (more likely) a similarly large-scale investment of solar energy. There is a limit to how much of this you are going to be able to throw.

Who the hell said anything about a spherical projectile? What the fuck? You also conveniently miss we already accelerate rods in railguns! Why would we be using shot?

...because a railgun is not going to be suitable for acceleration to the speeds needed, and it sure as hell isn't going to be shooting out a long, thin projectile at .99c in one piece at the micro to nano arcsecond level of accuracy you require.

And good luck stopping my .99 c ripple of a dozen several thousand tonne DU crowbars. Even if you did magically see them in time to sound the alarm, there's no defence mechanism for such weapons. Even if vaped to multi-klick expanding clouds, that energy is hitting your planet either way.

Hmm.

At a Lorentz contraction factor of about 7, it's experiencing 14.8 billion collisions per second per cc (from its reference frame), or roughly 1,320,000 watts per square meter in the local ISM.

The average ISM of the Milky Way would render it an expensive plasma weapon (ten times as dense, it would vaporise anything up to and including carbon). At such speeds, the IPM becomes a shield, though it won't get to ablate much.

The issue is is that even this extremely tenuous medium needs to be accounted for. In fact, when Earth passes out of the local bubble, .99c is actually too fast, and it's potential vulnerability to interstellar weapons fired that such speeds is only temporary.

This is all also assuming you have a thorough enough knowledge of the intervening medium to make such an attack with sufficient accuracy.

Should probably also do some calculations regarding the blueshifted light from the Sun, though I don't think that will do much.

[Gustav32Vasa]

My favourite drive is the hyperspace window from Stargate. You more energy you pump into it you faster you go. The Asgard travel million of lightyears is minuets.

My second favourite is the jumdrive from Asimovs Robot, Empire and Foundation stories. There you require better calculations to travel faster. Crossing the galaxy in half hour with the lastest computer.

[Admiral Valdemar]

No need to make it a particle shield, if you have the tech to fire something meaningful at .99c, you have the tech to spew dust clouds at half that rate in the same direction with a few days' notice.

And it's a cloud, of course it's going to stop multiple attacks unless you set up multiple vectors. It only needs to ensure enough of a density that your projectile will turn to plasma.

Again, such a massive open area is working against you. Even if you had thousands of ships within the area of Sol, there's nothing saying you can get them to a certain point in the very brief window needed to set up such a passive defence network. The projectile will be coming in at just under light speed, your ships had better be close to such an entry vector, or have magi-technology drives to be there within any reasonable time period. The bigger the sphere, the longer traversal time or more ships/defence craft needed.

That alone is forcing you to expend massive amounts of resources just to hope to counter maybe one or two such RKVs.

Of course I'm referring to defenses already in place, but how are they going to be 'taken into consideration'?

Your .99c projectiles require ~1e18 joules of energy to fire per kilogram of mass at a bit over 50% efficiency. This amounts to ~1,500 tonnes of deuterium per kilogram per shot, or (more likely) a similarly large-scale investment of solar energy. There is a limit to how much of this you are going to be able to throw.

If you've conquered the not insignificant task of interstellar travel at all, you've likely gotten to the point of producing antimatter in vast quantities too, or have another method of producing vast amounts of energy on demand that we don't know yet. The use of a simple torch drive or a railgun assembly using fusion weapons to accelerate a large enough projectile will be doable. It just depends on the resources you're willing to expend, but the defence systems for such an attack will be even more resource intensive. That's the problem, similar to modern strategic weapon strikes and defences today.

...because a railgun is not going to be suitable for acceleration to the speeds needed, and it sure as hell isn't going to be shooting out a long, thin projectile at .99c in one piece at the micro to nano arcsecond level of accuracy you require.

You assume the railgun is working in the classical sense. I'm talking about a bomb pumped system similar to a Daedalus like set-up. You also assumed the projectile would be tiny, around a tonne. That would make for a pretty short lived projectile. Something the size of the space shuttle would be a better, albeit harder to accelerate, projectile.

Hmm.

At a Lorentz contraction factor of about 7, it's experiencing 14.8 billion collisions per second per cc (from its reference frame), or roughly 1,320,000 watts per square meter in the local ISM.

The average ISM of the Milky Way would render it an expensive plasma weapon (ten times as dense, it would vaporise anything up to and including carbon). At such speeds, the IPM becomes a shield, though it won't get to ablate much.

The issue is is that even this extremely tenuous medium needs to be accounted for. In fact, when Earth passes out of the local bubble, .99c is actually too fast, and it's potential vulnerability to interstellar weapons fired that such speeds is only temporary.

This is all also assuming you have a thorough enough knowledge of the intervening medium to make such an attack with sufficient accuracy.

Should probably also do some calculations regarding the blueshifted light from the Sun, though I don't think that will do much.

If you've gotten to the point of being able to use RKVs with any degree of accuracy, then these objections are null and void. A planet is a pretty big target still, and this assumes there won't be any minor corrective adjustments for terminal guidance. Of course, this is also why you fire multiple projectiles to cover any CEP issues you may encounter with the system at your disposal, again, the same as with ICBMs today using MIRVs. In fact, there's nothing stopping you having such a munition on a much larger RKV. Your single target then becomes several smaller ones upon entry to the solar system, making durability less of an issue, but opening up the potential strike area.

And that's not all. I can instead send a great many decoy RKVs that splash against your shield, say they're typically only a few tonnes in mass and a metre square on the front. If you have some really good detectors, you can pick these up easy enough. Additionally, with regards to ablation from ISM impacts, you could equip foil shields on the RKV too to deal with most of the damage and have the bonus of dealing with any other obstacles of sufficient voluminous proportions put in the way of the projectile.

But then I throw the odd one or two far thinner, far longer rods that are on the order of kilometres long, but a few cm^2 in frontal area. This is practically undetectable against most of your star field. You're now left wondering which one of these targets may be the real hard hitter, only the major one may not even be seen and pass right through your defensive barrier just after one of the decoys cleared it in self-annihilation. It takes only one such missile to cause a world of hurt, and there could be plenty of these flying out from larger mother munitions that are detected earlier, but cluster bomb smaller munitions outwards, some decoys, some the tiny wire type.

This means your shields have to be far, far more comprehensive to deal with such a threat, again, fulfilling the idea of you expending more resources to deal with a single large RKV incoming.

[Ariphaos]

Again, such a massive open area is working against you. Even if you had thousands of ships within the area of Sol, there's nothing saying you can get them to a certain point in the very brief window needed to set up such a passive defence network. The projectile will be coming in at just under light speed, your ships had better be close to such an entry vector, or have magi-technology drives to be there within any reasonable time period. The bigger the sphere, the longer traversal time or more ships/defence craft needed.

Thousands?

Wtf is this, Star Trek level mobilization? You get to expend more power in a shot than the world uses in a month, and you would not have trillions of vehicles running around?

Hell, it's not even a defense network. The same setup that you use for the attack - massive arrays of coils - can be used to enact a defense. Your assault is light-days away, the cloud gets shot at you, from Earth, at similar (but less energy intensive speeds), meeting your attack a few less light-days away, then one light day less, then another light day less, and so on and so forth. Thousands of AUs out.

That alone is forcing you to expend massive amounts of resources just to hope to counter maybe one or two such RKVs.

Considering the amount of resources you are expensing to fire these RKVs, trivial.

If you've conquered the not insignificant task of interstellar travel at all, you've likely gotten to the point of producing antimatter in vast quantities too, or have another method of producing vast amounts of energy on demand that we don't know yet.

...now you're resorting to handwavium. That we can launch a cloud of dust in your projectile's direction is a given. That we'll have antimatter at a whim is not. Beyond which, I meant that this is not going to be a trivial drain on your society's energy reserves. 11 kilograms worth of matter to fire a 1 kg projectile that won't even make it to the target intact.

The use of a simple torch drive or a railgun assembly using fusion weapons to accelerate a large enough projectile will be doable.

Maximum speed for a fusion drive is ~20% of c or so. No self propelled projectile - even antimatter - is going to reach such speeds. At which point you just GRB the target planet anyway.

It just depends on the resources you're willing to expend, but the defence systems for such an attack will be even more resource intensive. That's the problem, similar to modern strategic weapon strikes and defences today.

Array of coils orbiting Earth will do for both defense and civilian high speed launch and recovery of vessels.

You assume the railgun is working in the classical sense. I'm talking about a bomb pumped system similar to a Daedalus like set-up. You also assumed the projectile would be tiny, around a tonne. That would make for a pretty short lived projectile. Something the size of the space shuttle would be a better, albeit harder to accelerate, projectile.

Hmm? Bomb pumped system would not achieve the needed velocity, and the rails themselves would turn to plasma as the projectile itself is torn apart by magnetic flux. And now you're talking about doing this with a hundred tonnes? 1e23 joules of energy?

If you've gotten to the point of being able to use RKVs with any degree of accuracy, then these objections are null and void.

Blueshifted solar output is not...

...christ, forget my dust idea, I'm an idiot, just point an insignificant fraction of the dyson swarm at your impotent attack and be done with it.

[Knife]

Now, like I said, I like the idea of jump points in stories, since they offer several plot advantages, but the L-point restriction just doesn't make sense.

What restriction would you suggest instead?

As in what, their use?

I prefer the jump drives too, in a literary sense, you can focus on where the people and cities are rather than deep space, and focus on defensable points.

In universe that would be a restriction. In one of my stories, my jumpdrive (I called it a slide-drive) goes from gravity well to gravity well. More or less a tunnel effect/worm hole than the NBSG jump drive but....

It keeps the characters and ships at a reference point rather in the vast openess of space. But in universe it would leave vast streches of space you can't get to.

[Winston Blake]

Further, Lagrange points do not act just like there was a mass there - objects at L4/L5 orbit in a weirdo kidney shape, completely unlike any actual mass.

Have you ever seen orbits modeled around bizarrely shaped asteroids?

No, I haven't, and the thought didn't occur to me. Still, L-points aren't gravity wells.

However, I think that at L1, space actually does go 'flat'. Both masses are pulling in opposite directions to make a local potential maxima.

L1 is exactly the same from a physical perspective as the orbit of the secondary. It means one thing and only one thing: your orbital period is equal to the period of the secondary.

That doesn't make sense to me, but anyway I figured there must be a point where the two forces balance, and since L1 sits between the two, I guessed (hence 'I think') that they were the same location.

[snip]

In any case, while I lack the needed skills to complete this to the final answer, you can see all my logic used here to get to this intermediate step. Nowhere in any of this math did gravitational effects cancel out.

Now, what might be interesting is to find a point where A_sun = A_earth, which should be trivial, but certainly isn't a Lagrange point, since they have entirely different definitions! Let's work this one out.

I haven't worked through your calculations, but I can see that this local potential maximum point isn't going to be in the same spot as L1.

[snip]

The negative answer doesn't make sense, since that would have the sun and earth both pulling you in the same direction, so the solution is to be

2.6 x 10^8 meters away from the sun, lined up to be directly between it and the earth, and the net gravitation acceleration is zero. (This number feels wrong to me, btw, so you'll want to check my work before running with it).

Intuitively, it seems to me that the answer should be closer to 5e10 meters. But my logic above should be fine, I probably just made an arithmetic error in my head (or my intuition is wrong). In any case, it is all there to examine if you are interested.

I remembered there was a satellite orbiting at the Sun-Earth L1 point, so google gave me this somewhat poorly worded wikipedia quote:

It is about 1.5 million kilometers from the Earth. Gravity from the Sun is 2% (118 µm/s²) more than at the Earth (5.9 mm/s²), while the reduction of required centripetal force is half of this (59 µm/s²). The sum of both effects is balanced by the gravity of the Earth, which is here also 177 µm/s².

Since the gravitational forces should be different by 2%, L1 can't be the point we're looking for. Still, it's probably nearby, so by the time I-War takes place they may colloquially call it 'the lagrange point'. It doesn't seem to have a name as far as I can find.

Anyway, the point I am trying to make here is there should be a point where gravitational forces cancel out in the restricted situation with two large masses and one tiny object, but it isn't any of the Lagrangian points.

Point conceded. Still, these local maxima could serve as neat-o science fictional jump points.

[Admiral Valdemar]

Thousands?

Wtf is this, Star Trek level mobilization? You get to expend more power in a shot than the world uses in a month, and you would not have trillions of vehicles running around?

Hell, it's not even a defense network. The same setup that you use for the attack - massive arrays of coils - can be used to enact a defense. Your assault is light-days away, the cloud gets shot at you, from Earth, at similar (but less energy intensive speeds), meeting your attack a few less light-days away, then one light day less, then another light day less, and so on and so forth. Thousands of AUs out.

You're the one talking of defending a system at 20 AU out. You are NOT going to be doing that with a handful of ships, even with inertia discounted and perfectly efficient AM drives.

Considering the amount of resources you are expensing to fire these RKVs, trivial.

Not if you want to actually detect and then actively defend at 20 AU out, or more, it isn't.

...now you're resorting to handwavium. That we can launch a cloud of dust in your projectile's direction is a given. That we'll have antimatter at a whim is not. Beyond which, I meant that this is not going to be a trivial drain on your society's energy reserves. 11 kilograms worth of matter to fire a 1 kg projectile that won't even make it to the target intact.

Asimov arrays and the like would be more than enough. You certainly don't need to use all of your fusion reactor capacity to do something that big ball of fire in the sky gives you for free.

Maximum speed for a fusion drive is ~20% of c or so. No self propelled projectile - even antimatter - is going to reach such speeds. At which point you just GRB the target planet anyway.

That's why you're using a RAIR instead, which has no such limits. You just need a good chunk of fuel to get to the desired speed, since you don't have the problem of needing to slow down on entry to a system.

Again, there's that or a bomb pumped launcher. You're going to have to use a lot of energy, but we're assuming this isn't a concern if you're, y'know, trying to smash planets from a neighbouring system.

Array of coils orbiting Earth will do for both defense and civilian high speed launch and recovery of vessels.

Those coils are going to cover every square klick of the planet? Why not just make a Dyson Sphere and be done with it?

Hmm? Bomb pumped system would not achieve the needed velocity, and the rails themselves would turn to plasma as the projectile itself is torn apart by magnetic flux. And now you're talking about doing this with a hundred tonnes? 1e23 joules of energy?

Funny, because the Daedalus system never had that problem, and this is exactly the same principle but with a "dumb" projectile going along a disposable rail assembly (I never said anything about it being a permanent railgun). And why won't it achieve such speeds?

Blueshifted solar output is not...

Assuming you pick it up in the interference from the decoys, of course.

...christ, forget my dust idea, I'm an idiot, just point an insignificant fraction of the dyson swarm at your impotent attack and be done with it.

I knew you'd see the light!

[Ariphaos]

You're the one talking of defending a system at 20 AU out. You are NOT going to be doing that with a handful of ships, even with inertia discounted and perfectly efficient AM drives.

Don't need to, my point was that there will probably be trillions of vessels in our sensor grid by such a time as when we can drop 10^23 joules through a coilgun.

Beyond that, though, the actual defensive launch can be launched from Earth itself, anyway.

Not if you want to actually detect and then actively defend at 20 AU out, or more, it isn't.

It is.

If someone has sufficient observational capacity to resolve and track Earth's perturbations from light-years away, they will also have the capacity to see a difference of a couple thousand kelvin in the background.

Asimov arrays and the like would be more than enough. You certainly don't need to use all of your fusion reactor capacity to do something that big ball of fire in the sky gives you for free.

Correct, but it's still a significant energy investment, at least, before your target has spread a significant part of their industry across their star system, meaning this attack is more likely to instigate a form of MAD. (Well, they'll have already had to anyway, can't see any way around that).

That's why you're using a RAIR instead, which has no such limits. You just need a good chunk of fuel to get to the desired speed, since you don't have the problem of needing to slow down on entry to a system.

Again, there's that or a bomb pumped launcher. You're going to have to use a lot of energy, but we're assuming this isn't a concern if you're, y'know, trying to smash planets from a neighbouring system.

...you're just making this a lot more difficult than this needs to be. Just use a coilgun. No need to fuck with bomb pumped or any other hoolaha you're talking about. The only step then is, why are you directing your star's light through all these contraptions when you can just aim it at your target?

Those coils are going to cover every square klick of the planet? Why not just make a Dyson Sphere and be done with it?

A set of orbiting magnetic coils that can be rearranged to fire and receive ships, or other cargo. Very practical. A dyson swarm would be well within Mercury's orbit, anyway. Anything larger is a vast waste of resources.

Funny, because the Daedalus system never had that problem, and this is exactly the same principle but with a "dumb" projectile going along a disposable rail assembly (I never said anything about it being a permanent railgun). And why won't it achieve such speeds?

Daedalus had a top speed of all of .12 c. I'm not saying so much that you -can't-, it's just like adding pennies to a trillion dollar bank account for billions of dollars worth of resources. Say you're doing a thousand of these, you can skip all these extravagant steps and fire another one instead.

Assuming you pick it up in the interference from the decoys, of course.

No, that's not my point.

You could not, for example, perform this attack such that it crosses within Mercury's orbit before it reaches Earth. You simply wouldn't be able to so perfectly predict how much of your projectile got boiled away, and therefore how much the Sun pushed your projectile through simple light pressure. Hell, if it's thin enough, it'll just vaporize your projectile.

So you see this attack coming, all you have to do is focus a bit more light in the region from whence the attack came. You don't even need a whole lot of it, because the projectile is blueshifting the light by a factor of 7.

I knew you'd see the light! :mrgreen:

And that's not the end of it.

Someone was just stupid enough to throw and r-bomb at you. What do you do? Aim your sun at them.

There is only one defense against this - move your planet. Random adjustments on the order of a tenth of a micron per s^2 will be plenty.

Roughly taking 6x10^17 watts of energy for Earth.

[Lord Zentei]

Because logic doesn't apply to the impossible, am i rite?

Bingo.

If so, then the premise of this website is rather in trouble, eh what?


Anyway: as for my vote, it goes to Warpdrive/Hyperdrive, assuming that it can be interdicted somehow: i.e. no "jump and nuke" manouvers. The Warp is really just hyperdrive with monsters in it.

Jump drive can be made to work OK if it is restricted to specific points (though in that case, one ends up with blockadable bottlenecks which may not be desirable) or regions such as far from a stellar object (which require "regular travel" which may be interdicted as normal).

[Illuminatus Primus]

Damn, I thought that I could edit these.

Well, if you need a further explanation form this, it's that I think that a Wormhole drive is more realistic.

Which is like saying pink magical fairies are more realistic than blue magical fairies.

My personal favorite is the Maeda drive. Ship is converted into pseudomaterial which moves at c to its destination, with time not advancing for the crew during the transition. Yeah, I'm plugging my own piece of handwavium--I'm entitled (though I'm pretty sure others have come up with the same thing before me). Of course, it's not FTL, so it's useless to you.

Really its just teleportation without a "rematerializing" component on the recieving end.