Relatavistic Projectiles

[erik_t]

I suspect that would be the case, yes. It depends a great deal on how long you're willing to let your sandbox coast.

[Ariphaos]

I suspect that would be the case, yes. It depends a great deal on how long you're willing to let your sandbox coast.

You can only pull so much of that before a miss is guaranteed. Past a hundred light-years or so, the tidal forces inflicted by individual moons and asteroids will be enough yank Earth out of your weapon's path.

Which adds another layer to the problem Wong presented - there are a very finite number of star systems within say, a thousand light-years. A lot, to be sure, but you have the entire resources of the Solar System to watch them individually and with great redundancy should you wish to, but nothing stops a defending system from taking apart a dwarf planet to build a monitoring network. You're not even necessarily looking for an attacker, even - it's just a side benefit of the various observations and experiments and taking SETI to an absurd level anyway.

[Teleros]

Sure the Star Wars universe has the power generation capacity of DOOM

For a SW RPG, this is the problem - it has some very powerful technology at its disposal. For starters, FTL sensors and such will have a much easier job of detecting any incoming ships / missiles / whatever than lightspeed sensors. Second, planets can have shields capable of stopping incoming fire of near-Death Star proportions - if they're up, the sand will likely just impact it and not harm the planet much, if at all.

However, sabotaged shields or a lack of shielding in the first place will be much easier, but then raises the question of why the defenders don't have something so common that Echo Base on Hoth had one (albeit only a theatre shield, not a planet-wide one). This was why the Death Star was such a fearsome weapon - it could destroy planets in spite of the tremendously powerful shields they had, and all in the form of a single vessel rather than a large, well-equipped (and expensive) fleet of warships.

[Surlethe]

Well there is the potential for the detonation of the sand as it hits the atmosphere to blow away the mass of the sand behind it and therefore decrease the efficiency of the attack. Whether or not it would be enough to make this a less than biosphere destroying attack I don't know. Based on a bit of searching to find the mass of a grain of sand (.23 to .67mg) each grain is equivalent to a 0.03-0.09 kiloton explosive, provided I did all my math right. Now that is significantly less than any high altitude nuclear tests I could find conducted by the US or the USSR (1.2 kt was the smallest) so depending on the shape of the sand cloud and the effect of the blowback it might be possible to not kill everyone.

What are you talking about? What conceivable mechanism could the first impacts possibly use to reverse the incredible momentum of nearly 500,000 tons of sand moving at 0.99c?

I'm not saying it would reverse the course of the sand, but as the first grains hit the atmosphere the resulting explosions could start slowing down the successive grains of sand and possibly incinerate some of the sand above the atmosphere as well thereby reducing the overall effectiveness of the attack. I don't know how large an effect those initial detonations would have but I thought I would raise the issue as being something different than if it was a single large impactor. Or am I simply overestimating the effect of the initial detonations or underestimating the momentum of each grain of sand?

You're not thinking physically. The kinetic energy of the sand has to go somewhere; it doesn't just vanish, as you seem to think it does. Your thought process seems to be based on your intuitive picture of someone dumping sand - sure, there's a lot of it, but it's all spread out and when the first sand hits the atmosphere it will explode and the explosions will cause a shockwave and disperse or vaporize the sand behind, right? Not quite, because your intuitive picture is based on things moving very slowly.

Come back to physical basics: conservation of energy. The first grain of sand hits the atmosphere at 0.99c. What happens? Obviously, its kinetic energy is transferred to the atmosphere as heat. What about the explosive blowback? Well, suppose it causes a pressure wave to move up through the atmosphere, perpendicular to the trajectories of the following grains. This will slow them down, right? Sure - but how? By draining kinetic energy through friction - which in turn heats the air. Could it vaporize them? Possibly, but remember: the constituent molecules will still be traveling at 0.99c, and will end up transferring their kinetic energy to the atmosphere anyway via collisions.

The moral of the story is that however you slice it the energy is going to be dumped into the atmosphere unless some of the particles miss the planet entirely (or pass through it, which seems to me to be highly unlikely - but could happen, if my intuition is off). Actually, if there's a large burst of EM energy backwards that vaporizes some of the incoming sand, more of the impact energy will be transferred to the planet than otherwise.

[Surlethe]

Vapourizing it won't necessarily help that much. A sufficiently massive cloud of fast-moving vapour could potentially do serious damage to a planetary biosphere as well. It depends on whether it disperses enough so that most of it avoids the Earth entirely.

Let's see if I can do this physics thing without being Gibbs-slapped again. There's another caveat that supports your point: seen from Earth, time moves more slowly in the frame of the RKV, so the dispersal of the vapor cloud will proceed more slowly than expected from a classical standpoint. (Much more slowly, in fact: by a factor of about 7, if we're talking about the 0.99c case.)

[erik_t]

I suspect that would be the case, yes. It depends a great deal on how long you're willing to let your sandbox coast.

You can only pull so much of that before a miss is guaranteed. Past a hundred light-years or so, the tidal forces inflicted by individual moons and asteroids will be enough yank Earth out of your weapon's path.

Oh I was thinking light-months at the most. Note that given magic-engines that can get anything up to 0.99c, there's no reason to assume that an attack vector will exactly coincide with the locations of other star systems.

[Ariphaos]

Let's see if I can do this physics thing without being Gibbs-slapped again. There's another caveat that supports your point: seen from Earth, time moves more slowly in the frame of the RKV, so the dispersal of the vapor cloud will proceed more slowly than expected from a classical standpoint. (Much more slowly, in fact: by a factor of about 7, if we're talking about the 0.99c case.)

The problem with any sort of RKV, is that it's far too easy to discount the colossal fusion reactor at the heart of any near-type II civilization we can currently comprehend. Half a million tonnes of sand at .99 of c is still less energy than the Sun puts out in a second. 3.84E26 watts > 2.7E26 joules.

It goes far beyond just the feasibility of the defense, however. Creating the defense evolves naturally out of creating an observation, exploration and power distribution network. Creating a way to attack with RKVs is not so natural.

Oh I was thinking light-months at the most. Note that given magic-engines that can get anything up to 0.99c, there's no reason to assume that an attack vector will exactly coincide with the locations of other star systems.

Light-months away? How in the hell are you going to hide that?

Giving the attacker magic and the defender none is also amusing. The defender does not, however, need magic to defend in this scenario, just a willingness to sacrifice a few planetoids to build a sufficiently dense sensor net.

[avatarxprime]

You're not thinking physically. The kinetic energy of the sand has to go somewhere; it doesn't just vanish, as you seem to think it does. Your thought process seems to be based on your intuitive picture of someone dumping sand - sure, there's a lot of it, but it's all spread out and when the first sand hits the atmosphere it will explode and the explosions will cause a shockwave and disperse or vaporize the sand behind, right? Not quite, because your intuitive picture is based on things moving very slowly.

Come back to physical basics: conservation of energy. The first grain of sand hits the atmosphere at 0.99c. What happens? Obviously, its kinetic energy is transferred to the atmosphere as heat. What about the explosive blowback? Well, suppose it causes a pressure wave to move up through the atmosphere, perpendicular to the trajectories of the following grains. This will slow them down, right? Sure - but how? By draining kinetic energy through friction - which in turn heats the air. Could it vaporize them? Possibly, but remember: the constituent molecules will still be traveling at 0.99c, and will end up transferring their kinetic energy to the atmosphere anyway via collisions.

The moral of the story is that however you slice it the energy is going to be dumped into the atmosphere unless some of the particles miss the planet entirely (or pass through it, which seems to me to be highly unlikely - but could happen, if my intuition is off). Actually, if there's a large burst of EM energy backwards that vaporizes some of the incoming sand, more of the impact energy will be transferred to the planet than otherwise.

Yeah, I had been thinking that if the initial explosions can slow the leading edge fo the incoming sand cloud enough then the sand will start colliding with itself while still above the atmosphere with most of the energy radiating out in space. I know that if the process is confined entirely to the atmosphere that it's really not helping matters any as the energy will still get absorbed by the atmosphere. Thanks for pointing out the bit about the vaporized sand though. I had forgotten to think about the incoming high speed vapor. So even if what I was thinking could happen, happened it still wouldn't matter and would make things worse.

[Darth Wong]

One thing should be pointed out about lasers and heat beams: they do not need to be powerful or intense enough to vapourize things a la most sci-fi movies. Let's say you had a huge laser which could not vapourize anything or blow apart buildings etc., but which could increase the thermal equilibrium point of an entire planetary hemisphere by 30 degrees. The target planet would still be in huge trouble unless they had detected your plan and put their own countermeasures into effect with lots of lead time.

[18-Till-I-Die]

Didn't those aliens from Futurama do that? They turned some weapon on Earth that started raising the temperature daily, but it was by some absurd amount like a hundred degrees a day. Still that's...an interesting idea. Kind of takes WMDs into a weird passive agressive stage.

[Darth Wong]

1 degree a day would be more than enough to bring the enemy to ruin if you can keep it up for a month. That's nowhere near enough time to do anything about it unless he has been planning his countermeasures for a long time or has some absurd kind of resources to draw upon.

It would actually be uniquely horrifying, in a way. Like a slow-motion genocide, with riots and anarchy as people fight to get on transports to flee the slowly cooking planet.

[starslayer]

Let's see if I can do this physics thing without being Gibbs-slapped again. There's another caveat that supports your point: seen from Earth, time moves more slowly in the frame of the RKV, so the dispersal of the vapor cloud will proceed more slowly than expected from a classical standpoint. (Much more slowly, in fact: by a factor of about 7, if we're talking about the 0.99c case.)

You forget length contraction. If we give the sand grains some random thermal motion, this will drag their velocity vectors ever so slightly away from straight. Now space looks much shorter in that direction, not the original one, and the cloud appears to expand classically, in both frames - once you disentangle all the relativistic effects. Not that this much matters unless the sand is released and vaporized a very long ways away from the planet; going at .99c doesn't leave the sand much time to disperse if it is vaporized within a few light-seconds to minutes from the target.

[xammer99]

Sure the Star Wars universe has the power generation capacity of DOOM

For a SW RPG, this is the problem - it has some very powerful technology at its disposal. For starters, FTL sensors and such will have a much easier job of detecting any incoming ships / missiles / whatever than lightspeed sensors. Second, planets can have shields capable of stopping incoming fire of near-Death Star proportions - if they're up, the sand will likely just impact it and not harm the planet much, if at all.

However, sabotaged shields or a lack of shielding in the first place will be much easier, but then raises the question of why the defenders don't have something so common that Echo Base on Hoth had one (albeit only a theatre shield, not a planet-wide one). This was why the Death Star was such a fearsome weapon - it could destroy planets in spite of the tremendously powerful shields they had, and all in the form of a single vessel rather than a large, well-equipped (and expensive) fleet of warships.

First in general, wow thanks for the awesome discussion guys.

Second, the prevalence of shields is a great point. So, a couple of more questions.

1. Given what we know about the shields of Alderaan from EPIV, could said load of sand overload planetary shields? Also planetary shields can be overcome in the longish term by general planetary bombardment (from Clone Wars I believe, where they talked about hammering down planetary shields during the "outer rim sieges").

Here is a bit about detecting emergence from Hyperspace.

An interesting phenomenon associated with hyperspace travel was Cronau radiation. This was a short, but powerful burst of radiation which was generated when a ship entered and left hyperspace. It could be detected by properly aligned sensors from a few light-seconds away, often well outside normal sensor radius. This was how the Rebel base on Hoth was able to prepare for the oncoming attack when Admiral Ozzel mistakenly took the Executor and its battle fleet out of hyperspace too close to the system, rather than approaching stealthily from outside the system.

2. It is a given that everyone uses hyperspace for strategic and even some tactical in system movement. So there is going to be a huge investment in tracking Cronau radiation, so I can easily see system wide networks for that. But given that _EVERYONE_ travels via this one method... how much attention is going to be reasonably paid to deep space relativistic threats? Engines capable of even accelerating something to a high % of light speed is going to be a pretty rare thing given that they just aren't needed.

3. Does anyone know if there is some sort of conservation of momentum with hyperspace travel? i.e. if you spend your acceleration time 500 LY away, and then hyperspace jump would you emerge at .9c or whatever?

[Samuel]

1. Given what we know about the shields of Alderaan from EPIV, could said load of sand overload planetary shields?

No.

how much attention is going to be reasonably paid to deep space relativistic threats?

They can see you hyper in to do your drop first so it shouldn't be a problem.

[Imperial Overlord]

Star Wars has FTL sensors. 1E26J or whatever the exact number turns out to be is plenty big, but Alderaan's planetary shield momentarily held off the Death Stars planet killer beam which is at least 1E38 or 12 orders of magnitude more powerful. So it should be possible for some planetary shields to withstand the sand blast.

Wars also has FTL sensors. Any mass traveling relativistically would likely be automatically tracked and throw up all kinds of warning signs. There's all sorts of counter measures that could be deployed (planetary shields, tractor beam nudges, etcetera), depending on the conditions.

Exiting at a precise point from hyperspace is very difficult. Thrawn used Interdictors to manage tactical hyperspace exits. If you're exiting close to the planet in order to minimize reaction time, then even a slight degree of error in exiting hyperspace could screw up the attack or wreck your ship.

If the attack succeeds, then you'll have to deal with the aftermath. Being Star Wars, a fair number of people are likely to be off world at the time and won't be pleased to learn that some genocidal dicks killed their friends and family. If just one of them has significant resources you can expect serious bounty hunter trouble. If the planet in question is a member world of a larger civilization that cares what happens to its member planets, then there's even more trouble in your near future.

[Teleros]

1. Given what we know about the shields of Alderaan from EPIV, could said load of sand overload planetary shields? Also planetary shields can be overcome in the longish term by general planetary bombardment (from Clone Wars I believe, where they talked about hammering down planetary shields during the "outer rim sieges").

Assuming the shields were the equal of Alderaan's? No. The Death Star 1, with a firepower in the 1e32 range (at least), was momentarily resisted by Alderaan's shields - the main site has some frame-by-frame analysis, but in short the shields were almost strong enough to stop the shot.

However, SW does have differences between ray- and particle- shielding, there are better and worse models of planetary shields, issues relating to sabotage or maintenance, and as you point out, they can be worn down over a long period of time. In fact, a sort of relativistic missile spam might be a cheap way of blockading a planet, at least until the defenders use FTL tech to neutralise your missiles before they hit.

2. It is a given that everyone uses hyperspace for strategic and even some tactical in system movement. So there is going to be a huge investment in tracking Cronau radiation, so I can easily see system wide networks for that. But given that _EVERYONE_ travels via this one method... how much attention is going to be reasonably paid to deep space relativistic threats? Engines capable of even accelerating something to a high % of light speed is going to be a pretty rare thing given that they just aren't needed.

Not sure much about the Cronau radiation, but on the issue of relativistic threats, they tend to require lots of time and planning, which means either a surprise attack or some sort of handicap for the defender, such as incompetence in not looking for such threats (I doubt SW civilisations are totally ignorant of such tactics) or an inability to, say, use FTL sensors to detect the gravitational field of half a million tons of matter. It's not much, but if you can detect a starship massing half a million tons that way you should be able to detect an incoming asteroid of equal mass too.

3. Does anyone know if there is some sort of conservation of momentum with hyperspace travel? i.e. if you spend your acceleration time 500 LY away, and then hyperspace jump would you emerge at .9c or whatever?

The movies certainly show them decelerating, but I'm not an expert on this I'm afraid.