Shield strength...

[weemadando]

Clone Wars Volume 2 has the siege of a shielded city with the statement from the Clone Commander that the 4 month anticipated time to deplete their shield is running to schedule. Given what we know of firepower that can be brought to bear, what does this tell us about the strength of a city shield?

[Surlethe]

If we only have one Venator (a piddly low estimate) bombarding from space with heavy cannon, that's 3e24 W; (3e24 W)(4 months)(29 days/month)(12 hours/day)(3600 s/hour) = 1e31 J. Is that the sort of thing you're getting at?

[weemadando]

Yeah, and given that it was Obi-Wan and Anakins Open Circle Fleet/Army that was besieging and we could see continuous ground bombardment and can infer that in order to maintain the most effective and truncated siege that orbital bombardment would be used as well...

Does anyone know the size of the Open Circle fleet and how many serious ground pounding units they could deploy to maintain a bombardment?

[Surlethe]

The wookieepedia gives several thousand Venators; of course, it's a wiki, so take it with a grain of salt. If all several thousand were bombarding, you'd need to up the shield estimate by three orders of magnitude and something like a factor of three, or to 9e34 J. Interestingly, that's a ten-thousandth of the Death Star blast.

I can see one problem with using an orbital bombardment to calculate the shield strength, and that's because (IIRC) we see the dome of the shield, so the turbolaser bolts would have to enter the atmosphere first, and, given the strength of HTLs, I would think this would have disastrous effects on the planet's atmosphere.

[weemadando]

Indeed, especially seeing as the clones and jedi were encamped within LoS...

[Cykeisme]

Well, we're not sure how much energy turbolaser bolts bleed off into the atmosphere on their way in. It's possible that only minuscle amounts of energy aren't transferred from the heavy guns into the shield's neutrino re-radiators.

Of course, even a small fraction of bleed-off would still be a huge amount of energy to dump into a planetary atmosphere.. so.. well.

[Spartan]

In this case they might not have had capital ships bombarding the city's shields at all. It could be just ground forces bombarding it.

Just a thought though, the city was provisioned to hold out at least a few months. So, much for a week long seige starving the population into surender. If your relief doesn't shoe up in 4 months, they aren't coming.

[apocolypse]

Well, we're not sure how much energy turbolaser bolts bleed off into the atmosphere on their way in. It's possible that only minuscle amounts of energy aren't transferred from the heavy guns into the shield's neutrino re-radiators.

Of course, even a small fraction of bleed-off would still be a huge amount of energy to dump into a planetary atmosphere.. so.. well.

IIRC there isn't supposed to be any energy transferred to atmosphere. I believe that's what Saxton summarized, and the SPHA-Ts fired on Geonosis didn't display any, despite being equivalent to HTLs.

[Lazarus]

Isn't it possible that the beseiging forces weren't using orbital bombardment due to the damage it would do to the planets biosphere? If the Republic wanted the planets intact, then perhaps they would not employ such damaging methods, opting instead for ground based bombardment weaponry. The siege would take longer, but if the Republic have time on their side, this isn't a problem.

[Noble Ire]

Isn't it possible that the beseiging forces weren't using orbital bombardment due to the damage it would do to the planets biosphere? If the Republic wanted the planets intact, then perhaps they would not employ such damaging methods, opting instead for ground based bombardment weaponry. The siege would take longer, but if the Republic have time on their side, this isn't a problem.

Well, the fact that ground troops are deployed into the city as soon as the shield is down rather than the artillery leveling it, I think its fairly safe to assume they wanted at least that area intact, and probably the planet as well.

[Spartan]

Lazarus wrote:

Isn't it possible that the beseiging forces weren't using orbital bombardment due to the damage it would do to the planets biosphere? If the Republic wanted the planets intact, then perhaps they would not employ such damaging methods, opting instead for ground based bombardment weaponry. The siege would take longer, but if the Republic have time on their side, this isn't a problem.

The already have the planet, assuming they can maintain space superiority; what's the rush. The city will fall eventually. The real question is why in this case could they not simply march into through the shields. Like say at: Hoth, Genosis, Naboo, etc. My guess is that these shields are somehow different or there are other concerns.

[Surlethe]

There's the possibility the shield is also a particle shield; however, I would think the main issue is that there is no possibility of support or suppression fire for a ground assault through the shield.

[Mad]

If we only have one Venator (a piddly low estimate) bombarding from space with heavy cannon, that's 3e24 W; (3e24 W)(4 months)(29 days/month)(12 hours/day)(3600 s/hour) = 1e31 J. Is that the sort of thing you're getting at?

Unfortunately, this doesn't account for shield recharge and dissipation rates. It does give some limited information into the reliability of planetary shields, though.

It would be more helpful to know whether or not the shield was expected to fail because it was slowly overloaded (constant input greater than its maximum dissipation rate leading to overheating and eventual equipment failure) or if the shield was expected to fail from the large sustained momentum transfer over that period. (I'd expect the former to be more likely if the word "deplete" was used.)

Or if the shield simply ran out of fuel. That would also make sense as I can't see how they could predict equipment failure due to overheating four months in advance. (This does assume they had reliable information on the available fuel.) This is also more in line with what the word "deplete" implies.

[NRS Guardian]

There's the possibility the shield is also a particle shield; however, I would think the main issue is that there is no possibility of support or suppression fire for a ground assault through the shield.

All theater shields have a particle shield component. Unless you want to argue Vader could have taken out the Hoth shield if he only used the missiles on the Executor or brought along a VSD, or argue that if the AATs had fired their base-mounted rocket shells they could have taken the Gungans. Plus the AAT main guns are more similar to AT-TE main guns so that suggests that AAT main guns are projectile weapons. It could be the city shield was more powerful than the Hoth or Gungan shields providing too much resistance to be overcome by even walkers, or they figured it would be suicide to send infantry and walkers through without covering fire.
Edit: Your second suggestion seems to be the most likely.

[Surlethe]

If we only have one Venator (a piddly low estimate) bombarding from space with heavy cannon, that's 3e24 W; (3e24 W)(4 months)(29 days/month)(12 hours/day)(3600 s/hour) = 1e31 J. Is that the sort of thing you're getting at?

Unfortunately, this doesn't account for shield recharge and dissipation rates. It does give some limited information into the reliability of planetary shields, though.

True. If I understand what we know of shield mechanics (and I'm not sure I do), though, this would still supply a lower limit, which is what I was getting at.

It would be more helpful to know whether or not the shield was expected to fail because it was slowly overloaded (constant input greater than its maximum dissipation rate leading to overheating and eventual equipment failure) or if the shield was expected to fail from the large sustained momentum transfer over that period. (I'd expect the former to be more likely if the word "deplete" was used.)

That makes sense.

Or if the shield simply ran out of fuel. That would also make sense as I can't see how they could predict equipment failure due to overheating four months in advance. (This does assume they had reliable information on the available fuel.) This is also more in line with what the word "deplete" implies.

I'd think if they knew the approximate dissipation/recharge rate and the rate of input energy, they could extrapolate the time it would take to bring the shield down because of equipment failure, and set their schedule around that.

[Mad]

True. If I understand what we know of shield mechanics (and I'm not sure I do), though, this would still supply a lower limit, which is what I was getting at.

Not really. Taking some simplified (and low) numbers, if a shield system has 1 TW dissipation rate and can survive 5 TJ before failing, then a single 6 TJ shot will bring it down while a cannon that fires a 2 TJ shot every second would require at least 4 shots, or 8 TJ to bring down.

Obviously, 8 TJ is not the lower limit to bring down the shield if a single 6 TJ shot can do it.

Likewise, 1e31 J to bring down the shield can't be the lower limit when there was 4 months of recharging and heat dissipation going on the whole time.

I'll try to go into more detail when I have more time if needed.

I'd think if they knew the approximate dissipation/recharge rate and the rate of input energy, they could extrapolate the time it would take to bring the shield down because of equipment failure, and set their schedule around that.

Possible, but if the shield failure is due to equipment failure from overheating or mechanical stress, I would expect predictions to be problematic since such failures can be pretty random. (Take several processors and overclock them enough, and they'll fail after differing periods of time.) I'd expect there to be too many factors involved for it to be simply that SW manufacturing tech is that consistent. (i.e., previous wear and tear on the shield.)

[Darth Wong]

They can't be using full-power blasts on an inhabited world, otherwise there would be too much collateral damage (if they were so uncaring about civilian casualties they would just flatten the planet's surface from orbit). They must have to modulate their weapon fire in some particular way to minimize its environmental effects without giving the system time to recharge. That would explain the very long delay required to bring down the shield.

[Spanky The Dolphin]

If we only have one Venator (a piddly low estimate) bombarding from space with heavy cannon, that's 3e24 W; (3e24 W)(4 months)(29 days/month)(12 hours/day)(3600 s/hour) = 1e31 J. Is that the sort of thing you're getting at?

12 hours a day? Don't you mean 24?

By the way, weeks and months are different in SW, so it's actually 35 days/month * 4 months = 140 days, rather than 116 days.

[Spartan]

Surlethe wrote:

There's the possibility the shield is also a particle shield; however, I would think the main issue is that there is no possibility of support or suppression fire for a ground assault through the shield.

Yeah, my first thought was the lack of air support, because they could just walk right in with they're armor/mech forces.

Then again when the shield comes down they attack with what? Rocket men, and lightly protected chicken walkers!

I'm still wondering why the planet lacked full planetary shields anyway. It must not have been that important to the CIS war efforts.

[Noble Ire]

Then again when the shield comes down they attack with what? Rocket men, and lightly protected chicken walkers!

Well, its not like we saw more than a few seconds of the actual invasion.
Besides, the jumpjet troopers would actually be pretty effective at taking out entrenched anti-armor positions.

I'm still wondering why the planet lacked full planetary shields anyway. It must not have been that important to the CIS war efforts.

It could have been already taken down or bypassed, although the lack of an apparent battle with CIS forces for control in orbit suggest it simply wasn't that important a position for them, but still significant as to require the Circle Fleet's focused attention.

[Spartan]

Noble Ire wrote:

Well, its not like we saw more than a few seconds of the actual invasion. Razz
Besides, the jumpjet troopers would actually be pretty effective at taking out entrenched anti-armor positions.

Yeah, rocket men always put a smile on my face.

It could have been already taken down or bypassed, although the lack of an apparent battle with CIS forces for control in orbit suggest it simply wasn't that important a position for them, but still significant as to require the Circle Fleet's focused attention.

True, but the Open Circle fleet in CW looked to be a single floatillia of 12 Venators. Maybe its was just a portion of the fleet.

[His Divine Shadow]

They can't be using full-power blasts on an inhabited world, otherwise there would be too much collateral damage (if they were so uncaring about civilian casualties they would just flatten the planet's surface from orbit). They must have to modulate their weapon fire in some particular way to minimize its environmental effects without giving the system time to recharge. That would explain the very long delay required to bring down the shield.

The only time it would be dangerous to be firing at full power would be just before the shields fail incase a turbolaser blast bleeds through and hits the city. SW weapons don't tend to bleed of their energy into the atmosphere otherwise as AOTC shows.

So the republic forces could just fire at full power until they are nearing shield failure, then they can reduce power to just above the shields dissipation rate and slowly fill the energy sinks remaining capacity. The shield likely shuts down the moment the energy sinks are full so it won't explode or overload / destroy itself.

But 4 months to fill that remaining capacity, sounds myysterious to me, unless they got big frickin' energy sinks.

[Manus Celer Dei]

By the way, weeks and months are different in SW, so it's actually 35 days/month * 4 months = 140 days, rather than 116 days.

What an intresting little nugget of information. Where's that from?