How the hell do ground invasions work in Star Wars?

[The Romulan Republic]

Yes, that's a good point, but my point is that the planetary shield wasn't the target.

Also, they probably didn't have to go overland very far or face much opposition before reaching the generator because they were able to trick their way through the shield (or at least that was the plan-they didn't know it was a trap, of course). Normally, I gather, a force assailing an area protected by even a theatre shield (much less full planetary shielding) would face a long slog, probably under fire much of the way.

[Galvatron]

I can also imagine that any ships attempting to drop an attack force would be vulnerable to AA fire as well. While it may have been a cakewalk for the Empire at Hoth, a better defended world may have secondary batteries scattered across the planet to prevent such landings.

[The Romulan Republic]

I can also imagine that any ships attempting to drop an attack force would be vulnerable to AA fire as well. While it may have been a cakewalk for the Empire at Hoth, a better defended world may have secondary batteries scattered across the planet to prevent such landings.

If the batteries are themselves shielded, and/or in areas the enemy will be unwilling to bombard due to collateral damage, that ought to be highly effective.

A full planetary shield with sufficient numbers of ion canons and turbolasers on the surface to cover the entire planet ought to be damn near impregnable to outside assault, unless the enemy has firepower substantially greater than Death Squadron (remember that Imperial who said that the shield at Hoth could "withstand any bombardment"?) and is willing to accept massive collateral damage from unleashing such a bombardment.

Of course, their is still the possibility of slipping in saboteurs to blow up a generator from the inside and open a gap in the shield- this probably is a big part of why Jedi were so dangerous, because their abilities are well-suited to the role of infiltrators/saboteurs.

[Galvatron]

At the very least, it's a sound rebuttal to the "just drop a few walkers beyond the shield" tactic many seem to regard as such a no-brainer.

[Lord Revan]

Then again any sabotase mission has its own risks it again boils down to the same risk/reward calculation, if the risk is worth the reward then a mission of take out the shield would be attempted but if not I'd assume the empire would ignore or blockade the planet.

[Galvatron]

For those areas of the planet that aren't as heavily defended by stationary AA emplacements, I can imagine that a few squadrons of high-speed interceptors could prevent landing craft from deploying their payloads of troops and walkers as well. Of course, the landing ships would probably have fighter escorts of their own, in which case neither outcome would be certain.

[Adam Reynolds]

Another tactic that defenses are good for is the purpose of tying up enemy forces while you prepare for an offensive of your own. This largely seems to be what the CIS did just before Coruscant, in which they allowed the Republic to go on the offensive in the outer rim and leave Coruscant relatively vulnerable. This obviously backfired when their naval forces were defeated over Coruscant rather handily after Obi-Wan's fleet showed up, leaving CIS bases even more vulnerable.

[Galvatron]

I imagine Imperial jumptroopers would be useful in situations where AA fire makes it too dangerous to land a big dropship.

[fractalsponge1]

I imagine Imperial jumptroopers would be useful in situations where AA fire makes it too dangerous to land a big dropship.

Seems like that has similar issues - they jump in without heavy vehicles and there too many ways to kill infantry in the absence of heavy support.

[Shroom Man 777]

Not everything or everywhere is coated in AA though. Just land beyond the horizon of any direct energy weapon/line-of-sight anti-air systems... and avoid missiles. Then trudge through or use artillery or whatever.

[Abacus]

There are few planets with the kind of defenses that would match the descriptions above. I imagine only a select few can afford not only the cost of putting such a defense system in place, but also maintenance costs. I'd guess that only the planet Bastion had such a defense system.

[Galvatron]

I imagine Imperial jumptroopers would be useful in situations where AA fire makes it too dangerous to land a big dropship.

Seems like that has similar issues - they jump in without heavy vehicles and there too many ways to kill infantry in the absence of heavy support.

I imagine they'd have to be special forces commandos rather than garden variety stormtroopers. The idea would be for them to disperse and find ways to disable the local AA guns so the heavy transports can land.

[Galvatron]

There are few planets with the kind of defenses that would match the descriptions above. I imagine only a select few can afford not only the cost of putting such a defense system in place, but also maintenance costs. I'd guess that only the planet Bastion had such a defense system.

Bastion is a relic of the old EU. AFAIK, it doesn't exist in the new canon. However, I wouldn't be surprised if planets like Corellia, Chandrila and Mon Cala have robust defenses like the ones we've been discussing here.

Also, in the real world there are such things as self-propelled anti-aircraft weapon, thus a planetary defense force wouldn't necessarily have to rely on stationary AA batteries to shoot down Imperial dropships.

I'd like to see fractalsponge1 design something like that.

[Abacus]

Bastion is a relic of the old EU. AFAIK, it doesn't exist in the new canon. However, I wouldn't be surprised if planets like Corellia, Chandrila and Mon Cala have robust defenses like the ones we've been discussing here.

Also, in the real world there are such things as self-propelled anti-aircraft weapon, thus a planetary defense force wouldn't necessarily have to rely on stationary AA batteries to shoot down Imperial dropships.

I'd like to see fractalsponge1 design something like that.

I was talking more about ground-to-space weaponry, than your general run of the mill AA weaponry. The single ion cannon that the rebels had at Hoth was only able to defend a single quadrant of space, which it adequately did. To cover an entire planet with ion cannon and planetary grade turbolaser batteries, capable of being a true threat to capital ships.

I don't see Chandrila being like that, personally. I've always felt that Chandrila followed, slightly, the same course set by Alderaan -- borderline pacifist. Corellia has always been much more militant and Mon Calamari also has had more reason to be armed -- especially during the Clone Wars.

I figure most of the important core worlds are fortified however, at least by a full planetary shield.

[Galvatron]

Which leaves me a question for the calc-minded: how many such ion cannons would it take to defend an entire planet?

[NecronLord]

Thirty eight. That's a joke answer but you get a cookie for knowing where it's from.

I think that'd depend on the minimum altitude of an attacking ship; in reality we could get away with two guns like that, mounted on mountains and able to depress somewhat, because we could target a vessel many many planetary diameters away. But with Star Wars ships being able to drop out of hyperspace anywhere, you could require quite a few.

[Galvatron]

Okay, so how many cannons on planet that's also encompassed by an impenetrable shield positioned somewhere in the upper atmosphere? Wasn't Coruscant's shield like that?

[Abacus]

I always figured that planetary shields projected somewhere in the upper thermosphere, or higher. But that's just me.

[Galvatron]

As did I, but NecronLord is right: the shield's altitude would determine the minimum altitude of any attacking ships, which in turn determines how much of the sky any planetary defense cannons need to cover.

[Simon_Jester]

Presumably you can open passage in the shield for outgoing ion cannon bolts to pass through; the Rebels did at Hoth. So the issues are still the same. You want to avoid having REALLY big, ten thousand kilometer-high blind spots where none of the cannons can fire because they'd have to shoot through the ground.

Two isn't going to cut it because of the curvature of the planet- for example, if you mount each gun at one of the poles, then even if you built fifty-kilometer towers to give better elevation, the guns still can't depress very far without the ion bolt hitting the ground. For instance, on top of such a tower the horizon is eight hundred kilometers away. Assuming the planet has the same radius as the Earth...

High school geometry powers, ACTIVATE!

Okay, using similar triangles I can estimate...

800/(50+6371) = (50+x)/800
0.1246*800 = 50+x
49.7 = x

The 'x' here represents how far 'below' the horizontal the horizon appears to be. I should not have been surprised to get an answer so close to fifty, but whatever.

Anyway, the point is that you can only angle your gun 'down' at an angle of, um... inverse sine of (99.7/800) is 7.16 degrees... before your bolt hits the ground. If you only put guns at the poles, the zone you can't even point a gun at will be an isosceles triangle, with a base equal to the planetary diameter, and a height of, um... fifty thousand kilometers.

So subtracting a bit for planetary radius, with two guns you have a blind spot that stretches up as high as 44000 kilometers over the equator, and covers prety much the whole temperate zone(s) of the planet to an altitude of several thousand kilometers. Furthermore, even if you are shooting at targets above the blind spot but somewhere over the equator or even the temperate zone, your ion bolts will have to pass through hundreds of kilometers of atmosphere, sideways. This may have undesirable side effects like weakening the bolt, irradiating the atmosphere, or causing major shock waves and EMP problems for people on the ground.

...

Three guns is better because you can (for example) mount them on the equator and get pretty good all-around coverage with much lower blind spots except directly over the poles. Four guns in a tetrahedron is better still- mount three in, say, the southern hemisphere somewhere between the tropics and temperate zones, and the fourth at the north pole.

I'd say that four guns is a reasonable minimum for a serious attempt at defenses, and it'll still have pretty significant, exploitable blind spots. Six guns in a cube would be better.

Eight guns in an octahedron (say, four spaced 90 degrees apart at 45 degrees north latitude, and four more offset from the others at 45 degrees south latitude) would provide reasonably good high altitude coverage, and would guarantee that no one of the ion cannons has to fire at more than forty-five degrees away from the vertical unless the target is uncomfortably close to the planet (say, within a few thousand kilometers).

I can do the math on the size of the blind spots for the octahedral or tetrahedral or cube arrangements, but it'd take some time.

You can keep escalating, of course- a dodecahedral or icosahedral arrangement would provide even better coverage, though the more such guns you try to mount, the harder it will be to find pieces of land to fit them all on. Even a cube or octahedron would probably require you to build one or more of the gun mounts on an artificial island or something. A tetrahedron might be doable, by contrast.

It would take a LOT of guns to provide good low-altitude coverage that had no blind spots below, say, 200-300 kilometers altitude. Several dozen, maybe hundreds. I could calculate that too if you like.

So realistically, the zone excluded by the planetary shield doesn't reach high enough to make the blind spots of the guns irrelevant. Unless you can afford hundreds of guns.

[Galvatron]

I wonder if there are planetary superlasers that act similar to the Death Star's in that they can converge to a point high enough above the planet's surface and then be redirected towards a target that would normally be out of their line of sight.

I imagine such a weapon would be tremendously powerful as well.

[Eternal_Freedom]

Thirty eight. That's a joke answer but you get a cookie for knowing where it's from.

I think that'd depend on the minimum altitude of an attacking ship; in reality we could get away with two guns like that, mounted on mountains and able to depress somewhat, because we could target a vessel many many planetary diameters away. But with Star Wars ships being able to drop out of hyperspace anywhere, you could require quite a few.

Stargate! "Between Two Fires" IIRC

Something that did occur to me earlier. Even in the old EU, planetary shields were commonplace but majo ground to space weaponry was rare. Given that a shielded planet can be besieged/bloackaded quite easily if they can't hurt ships in orbit, is it reasonable to think that the Empire allowed planet shields but severely restricted planetary defence weapons? TO make it easier to bottle up and bloackade rebellious planets without having to expose ships to serious risks?

[Elheru Aran]

Ground to space fire is more expensive than a ground protecting shield?

But it's quite possible that with the ease of sending ships to space in Star Wars, it may have come about that they decided that ground-to-space weaponry was largely unnecessary because if your enemy controls the space around you anyway, you're probably screwed in the long run and ground-to-space weapons only make sense in a limited tactical envelope, such as covering escapes to space like at Hoth.

[Galvatron]

Given that a shielded planet can be besieged/bloackaded quite easily if they can't hurt ships in orbit, is it reasonable to think that the Empire allowed planet shields but severely restricted planetary defence weapons?

Perhaps, but keep in mind that the wealthy inner systems probably also had strong representation in the Senate which could have mitigated any attempts to restrict their defenses.

On a related note, Jim Luceno invented anti-laser aerosols that were used by the Separatists during the Clone Wars. It only existed in the old EU, but I wouldn't be surprised if it gets recycled at some point.

[Shroom Man 777]

Aerosols' a smart idea. I bet we'll have that IRL for laser-weapons. Didn't they use weirdass sprinkler systems - or at least theorize that - as counter for laser-designated strikes?

Aside from Senate representation to ensure defense tech proliferation... a lot of that shit could be holdovers from the Clone Wars or the Old Republic. The historical 200 year old planetary shield generator!

Since like even the Ottomans used bombards for centuries!