StarDestroyer.Net BBS

After a fair bit of digging, the only thing even resembling a rough estimate of AT-AT weight I have been able to find is the '2500 tons' on the Ground Combat page of the main site here.

Is there any way we can more reliably(or at least exactly) derive its weight? Also, is there any incident or quote in the various source material that narrows it down even a little?

in 'the empire strikes back' an at-at pulverises a snowracer with one foot, thus about a quarter of it's weight.
but whe luke has sabotaged the at-at an after a few internal explosions it falls, it doesn't give a shock one would expect because the most weight is in the body and that is the part that falls the highest.

I always thought that it must have some sort of repulsor field/gravity net reducing its weight so that its feet wouldn't sink into the snow or any other terrain. An actual vehicle of that size with such heavy armour would be unfeasable if its weight distrubution was so small, its why Tanks tracks are so wide, and even they get stuck in mud and soft terrain because of their weight on occasion.

What kind of weight is required in order to shake the ground from miles away with each footstep?

we can compare with other movies, like jurassic park.
we know that the t-rex's (weighing about 6 tonnes) footstep could be felt from quite a distance. also when the brachiosaures (70 tonnes) in the begining of the movie lands after standing on this hindlegs it gives quite an earthshake.
but there is also the dampening of the ground (rocks, snow or mud give all a different dampening effect)

maybe there is a calculation considering the weight of the vehicle, the height of the feet with every step and the speed of the feet while landing and the dampening effect of the ground.

freker wrote:we can compare with other movies, like jurassic park.
we know that the t-rex's (weighing about 6 tonnes) footstep could be felt from quite a distance. also when the brachiosaures (70 tonnes) in the begining of the movie lands after standing on this hindlegs it gives quite an earthshake.
but there is also the dampening of the ground (rocks, snow or mud give all a different dampening effect)

maybe there is a calculation considering the weight of the vehicle, the height of the feet with every step and the speed of the feet while landing and the dampening effect of the ground.

He meant what real weight is required, not what weight movie makers feel is required...unless of course you're suggesting they used a real 6 ton t-rex to get those shots?

freker wrote:we can compare with other movies, like jurassic park.

Uh, maybe it's just me, but I've got this strange feeling that comparing with other movies isn't exactly the most scientifically sound course of action..

Especially as the T-Rex was able to get inside that building at the end of the film without creating such massive ground shakes, or even any noise.

Luke did a number on one of the AT-AT's. His small bomb did what looked like a cascade of reactions on the the thing, causing it's head to go kablooie. We can reasonably assume that any antigravity mechanisms the AT-AT (if any) would be useless junk by this stage. Then we have the whole thing falling over and burying itself in the snow.

Anyone have the compressibility of snow handy?

If one assumes a class three earthquake, the energy release appear to almost exactly 2 GJ... but converting that to mass might be a little tricky and require a few more assumptions along the way. It's probably better to calculate the rough volume minus emptiness and then look at possible material combinations. Why would the mass be interesting, though?

nightmare wrote:If one assumes a class three earthquake, the energy release appear to almost exactly 2 GJ... but converting that to mass might be a little tricky and require a few more assumptions along the way. It's probably better to calculate the rough volume minus emptiness and then look at possible material combinations. Why would the mass be interesting, though?

Couldn't you get at least a ballpark estimate through KE = 1/2 (mv^2)? With the 30 meter height of the AT-AT, and assuming ~10 m/s^2 gravitational force (given that Chewbacca isn't bouncing off the ceiling), someone who remembers more physics than I do could figure the maximum velocity, and work back to get mass. It'd wouldn't be much better than a rough guess, since it's not falling straight down and it's only a rough gravitational estimate, but it's better than nothing.

The Dark wrote:Couldn't you get at least a ballpark estimate through KE = 1/2 (mv^2)?

Yes, but you have to estimate v. The kinetic impact has to be for one foot, if I remember their walking on Hoth correctly, one step at a time.

The Dark wrote:With the 30 meter height of the AT-AT, and assuming ~10 m/s^2 gravitational force (given that Chewbacca isn't bouncing off the ceiling),

I'm going to guess here that you're talking about the falling AT-AT. Calculating that is only relevant once you have estimated a mass. I don't see why we bother, though. If we end up with an impossible mass we just have to assume unmentioned cirumstances since the movie stands as is.

The Dark wrote:

nightmare wrote:If one assumes a class three earthquake, the energy release appear to almost exactly 2 GJ... but converting that to mass might be a little tricky and require a few more assumptions along the way. It's probably better to calculate the rough volume minus emptiness and then look at possible material combinations. Why would the mass be interesting, though?

Couldn't you get at least a ballpark estimate through KE = 1/2 (mv^2)? With the 30 meter height of the AT-AT, and assuming ~10 m/s^2 gravitational force (given that Chewbacca isn't bouncing off the ceiling), someone who remembers more physics than I do could figure the maximum velocity, and work back to get mass. It'd wouldn't be much better than a rough guess, since it's not falling straight down and it's only a rough gravitational estimate, but it's better than nothing.

20,408 tons, assuming it fell a distance of 20 meters (AT-AT is 23.5 meters tall, eyeball distance from "hump" to "belly" at 3.5 meters) and 1 g planet. Which I highly doubt is the actual mass as it is able to walk.

nightmare wrote:If one assumes a class three earthquake, the energy release appear to almost exactly 2 GJ...

Does it make much of a difference that we're not measuring an "earthquake" in the strictest sense of the word, but a "snowquake"? Snow would transmit vibration differently from rock.

Wyrm wrote:

nightmare wrote:If one assumes a class three earthquake, the energy release appear to almost exactly 2 GJ...

Does it make much of a difference that we're not measuring an "earthquake" in the strictest sense of the word, but a "snowquake"? Snow would transmit vibration differently from rock.

As much experience I have of snow and ice, I have no idea what difference a "snowquake" would make. Maybe looking up alpine avalanches would shed some light.

Wyrm wrote:

nightmare wrote:If one assumes a class three earthquake, the energy release appear to almost exactly 2 GJ...

Does it make much of a difference that we're not measuring an "earthquake" in the strictest sense of the word, but a "snowquake"? Snow would transmit vibration differently from rock.

I'm no expert but I expect such a 'snowquake' would require more initial energy as snow is more compressable than rock and might absorb the impact energy instead of sending it away as a wave. I've heard extremely cold ice can become hard like rock, but I don't expect Hoth is cold enough as human life is possible without sealed environment suits.

If there was an underground lake... but that's just stupid

Would it be more useful to determine how heavy it can possibly be and not sink into the ground without antigrav fields? Unless it is made of aluminum I think it would need such fields anyway, so it might have an effective weight close to the maximum anyway.

Darth Wong wrote:What kind of weight is required in order to shake the ground from miles away with each footstep?

Considering how little the center of mass bobs with each step I imagine the number is unfeasibly big

Ender got 20,408 tons falling 20 meters to produce 2 GJ (for a category 3 earthquake), and I don't think the main body bobs more than a few meters with each step, maybe 3, so that's ~ 6 times more mass and maybe more--such a monster cannot walk on snow!

for the record, I figured that for the one luke takes out and collapses, not for the walking. Walking would require video timing and frame counting and such to get the velocity.

So basically, we write the shaking off as a quirk of the geological strata on Hoth transmitting vibrations really well and say the AT-AT is "really heavy."

I'm gonna go ahead and assume an AT-AT falling over would be about the same as if you took a massive helicopter, picked up a coast guard cutter, then dropped it from about the same height on the ground.

and chock the lack of vibrations up to a stabilised camera.

The only real land vehicle I can think of that compares to an AT-AT in sheer scale is the NASA MLP (Mobile Launcher Platform), which, though only being about one quarter the height, is far wider and bulkier than the Imperial weapon. IIRC, the machine weighs around 4,125 tons; obviously, the corrolation is hardly exact (especially since we know little of an AT-AT's metallurgical composition), and such a weight might not account for the tremors we see in ESB, but it does give a rough base for comparison.

I haven't watched TESB in a while, but I only recall a few apparent "quakes". Might those be the transports landing? I also don't remember if there was a break in camera to allow the AT-AT's time to leave the transports.

For sure, if the tremors were felt a mile away then Luke ought to have been a bit shaken up in his jog directly underneath the AT-AT.

Howedar wrote:I haven't watched TESB in a while, but I only recall a few apparent "quakes". Might those be the transports landing? I also don't remember if there was a break in camera to allow the AT-AT's time to leave the transports.

For sure, if the tremors were felt a mile away then Luke ought to have been a bit shaken up in his jog directly underneath the AT-AT.

The walker footfalls are clearly audible in Echo Base, and snow is shaken loose from the ceilings.

I guess I'm not 100% convinced that they're footfalls, instead thinking they might (or even must) be something else.

I am not an expert in geology, but I can't reconcile the shaking of an underground base several km away with a person being able to run at a normal gate several meters away.

I again emphasize that I haven't seen the movie in several years. Perhaps this apparent contradiction is unavoidable.

Wasn't the run in question completely contained between the lift and fall of an AT-AT step, though?

I don't believe so. Could be wrong.