Defending the AT-ST
Posted: Thu Jan 18, 2007 2:04 am
Reviewing the recent post on the ST-v-SW.net blog on the AT-ST, I was reminded that the AT-ST, maligned though it is, is not necessarily that bad of a vehicle overall. Some of this will probably work into the next update series somewhere.
With all due respect, therefore, let us review the AT-ST's true capabilities. Saxton cites blueprints as giving the AT-ST model a height of some 8.13m. From this and the blueprints, I estimate roughly that the AT-ST has a total volume of roughly 12 cubic meters; this is primarily concentrated in the box "head" (8), with a significant engine block (2) and fairly spindly legs (1 ea). Overall, this is a vehicle with a mass of no more than 20 tons fully loaded, and we may best guess it to be around 15 tons.
Check this figure: With two 1.3 m^2 feet, this gives us a pressure of 10 pounds per square inch while standing on both feet; pressure is fairly low. The AT-ST does not leave that much of a footprint.
The ST-v-SW.net estimate of log mass is, of course, a gross overestimate in some regards. The log measured in question is not 67.75 px in overall diameter (a deliberate overestimate), but the more modest 57.7 px, i.e., 1.27 instead of 1.49m. The length, being based on the very end-piece diameter (1.5m) is not so bad an estimate; the likely density is on the order of 800 rather than 1750, meaning that the log properly only has a mass on the order of 9.1 metric tons (10 imperial tons.) The fact that the projectile is moving so slowly means that ST-v-SW.net's generousity in declaring the log to be in effect a ~10 cm diameter projectile is justified.
Recall that a ~9.1 ton log moving at 12 m/s is sufficient to defeat - although not actually necessarily penetrate - the armor. The mode of failure is structural. I would say, however, that the armor supplies a level of protection on the order of the minimum required to stop this projectile. I would say the margin of error for impact protection is probably only 10% in either direction from this critical threshold
I estimated this off-hand (napkin-style calculation) to be possibly as much as 55-80mm RHA of side armoring. Nathan Okun, however, has detailed projectile models - which, although they are not intended to handle this particular case, provide a good estimation. The minimum degree of protection that can be penetrated by the projectile described above is ~47mm of homogenous steel, which is to say that we have 47+/-5mm RHA of protection on the sides. Traditional vehicle armoring doctrines would give us 2-3x as much on the front as on the sides, meaning that the AT-ST is armored as well as a WWII-era main battle tank (40 tons) or modern light/medium tank (25-30 tons).
This is actually quite heavy armoring for a light fighting vehicle. For reference, the GAU-8 Avenger 30mm cannon - a very destructive gun indeed - penetrates 69mm RHA at 500m and 38mm at 1000m - meaning that the AT-ST is actually somewhat resistant to 30mm fire, and - barring viewport shots - completely resistant to normal anti-material rifles, assault rifles, etc. You can stick your best elephant gun right up against the side at a perfect angle and fire - and it won't go through.
The legs are, of course, a poor target - both slender and essentially solid metal, which are basically only vulnerable to tripping. You're pretty much aiming at a car-sized box bobbing around on stilts.
Reality check: Blaster rifles, in Star Wars, have roughly the destructive power in the range of modern anti-elephant and anti-material rifles. The AT-ST is probably quite adequately armored against Star Wars infantry - especially considering that an "energy bolt" is likely to leave more energy behind in the armor.
AT-STs' main guns fire shots in a 1-10 megajoule range; by comparison, the M1 Abrams puts out a maximum of 6.9 megajoules per shot. AT-STs have firepower that is best classed as being somewhere in the range of modern MBTs - perhaps a bit weaker, but having two guns and a higher rate of fire makes up for that on the offense.
Further, the AT-ST only requires a crew of two to operate. Ammunition and fuel are probably essentially unlimited by modern standards - fusion engines plus blaster cannons are a wonderful combination.
All in all, leaving aside the great height that would make it an easy target to spot and the failure of its designers to slope the armor adequately, the AT-ST is a fine light fighting vehicle by modern standards.
It's not absolutely ridiculously primitive - perhaps not very impressive, true, and not designed to withstand phasers - but I could probably sell AT-STs like hotcakes to modern militaries for a million each or so.
With all due respect, therefore, let us review the AT-ST's true capabilities. Saxton cites blueprints as giving the AT-ST model a height of some 8.13m. From this and the blueprints, I estimate roughly that the AT-ST has a total volume of roughly 12 cubic meters; this is primarily concentrated in the box "head" (8), with a significant engine block (2) and fairly spindly legs (1 ea). Overall, this is a vehicle with a mass of no more than 20 tons fully loaded, and we may best guess it to be around 15 tons.
Check this figure: With two 1.3 m^2 feet, this gives us a pressure of 10 pounds per square inch while standing on both feet; pressure is fairly low. The AT-ST does not leave that much of a footprint.
The ST-v-SW.net estimate of log mass is, of course, a gross overestimate in some regards. The log measured in question is not 67.75 px in overall diameter (a deliberate overestimate), but the more modest 57.7 px, i.e., 1.27 instead of 1.49m. The length, being based on the very end-piece diameter (1.5m) is not so bad an estimate; the likely density is on the order of 800 rather than 1750, meaning that the log properly only has a mass on the order of 9.1 metric tons (10 imperial tons.) The fact that the projectile is moving so slowly means that ST-v-SW.net's generousity in declaring the log to be in effect a ~10 cm diameter projectile is justified.
Recall that a ~9.1 ton log moving at 12 m/s is sufficient to defeat - although not actually necessarily penetrate - the armor. The mode of failure is structural. I would say, however, that the armor supplies a level of protection on the order of the minimum required to stop this projectile. I would say the margin of error for impact protection is probably only 10% in either direction from this critical threshold
I estimated this off-hand (napkin-style calculation) to be possibly as much as 55-80mm RHA of side armoring. Nathan Okun, however, has detailed projectile models - which, although they are not intended to handle this particular case, provide a good estimation. The minimum degree of protection that can be penetrated by the projectile described above is ~47mm of homogenous steel, which is to say that we have 47+/-5mm RHA of protection on the sides. Traditional vehicle armoring doctrines would give us 2-3x as much on the front as on the sides, meaning that the AT-ST is armored as well as a WWII-era main battle tank (40 tons) or modern light/medium tank (25-30 tons).
This is actually quite heavy armoring for a light fighting vehicle. For reference, the GAU-8 Avenger 30mm cannon - a very destructive gun indeed - penetrates 69mm RHA at 500m and 38mm at 1000m - meaning that the AT-ST is actually somewhat resistant to 30mm fire, and - barring viewport shots - completely resistant to normal anti-material rifles, assault rifles, etc. You can stick your best elephant gun right up against the side at a perfect angle and fire - and it won't go through.
The legs are, of course, a poor target - both slender and essentially solid metal, which are basically only vulnerable to tripping. You're pretty much aiming at a car-sized box bobbing around on stilts.
Reality check: Blaster rifles, in Star Wars, have roughly the destructive power in the range of modern anti-elephant and anti-material rifles. The AT-ST is probably quite adequately armored against Star Wars infantry - especially considering that an "energy bolt" is likely to leave more energy behind in the armor.
AT-STs' main guns fire shots in a 1-10 megajoule range; by comparison, the M1 Abrams puts out a maximum of 6.9 megajoules per shot. AT-STs have firepower that is best classed as being somewhere in the range of modern MBTs - perhaps a bit weaker, but having two guns and a higher rate of fire makes up for that on the offense.
Further, the AT-ST only requires a crew of two to operate. Ammunition and fuel are probably essentially unlimited by modern standards - fusion engines plus blaster cannons are a wonderful combination.
All in all, leaving aside the great height that would make it an easy target to spot and the failure of its designers to slope the armor adequately, the AT-ST is a fine light fighting vehicle by modern standards.
It's not absolutely ridiculously primitive - perhaps not very impressive, true, and not designed to withstand phasers - but I could probably sell AT-STs like hotcakes to modern militaries for a million each or so.