Got a Real World Weapons or Armour Question? Mk X

[Knaight]

The most plausible speculative idea is sublight travel using sufficient quantities of handwavium to keep the crew alive over the centuries it'd take to get anywhere interesting (suspended animation, advanced cloning). This requires only the assumption that it's probably easier to change the rules of human biology than it is to change the rules of physics ('design' a better human as it were).

Generation ships are significantly more plausible speculative ideas.

[Spiryt]

Not realistically. The amount of energy per unit of area being deformed is what honestly matters, not the velocity compared to the mass of the impact.

A slower, larger weapon could penetrate more armour, so long as the amount of energy it can convert into work over the same target area is higher, but all things otherwise equal, faster always = better.

Well, really, what matters depend on material deformed, displaced, torn apart etc.

Depending on material, it's thikness, support etc. time in which energy is being spent can really matter a lot.

With body armour, could it become that you need to use slower, bigger weapons like a pole-axe?

Well, type II bulletproof vest can hold off bullets of quite considerable energy.

While it probably wouldn't help at all against pole axe, despite it much lower 'energy output'.

But with modern military there's 3039 responses to light vest, before damn polleaxe. Starting with more powerful gun.

[Autolykos]

What are the most plausible speculative ideas for space travel which come to mind?

These are my guesses, sorted by plausibility.

1. Bite the bullet and accept long travel/communication times. - very likely
2. Finding a way to create stable and passable wormholes in a controlled way (you'd need materials with negative energy density for that, and we have no idea what they would look like). - hard, but perhaps possible
3. Finding a flaw in general relativity and exploiting it. - unlikely, the theory held together fine until now
3a. Finding a way for FTL communications (it is already proven that quantum entanglement will not work, even though it seems to be FTL), and replicating the object where you want it to arrive. - if 3. works, this is the most likely candidate IMHO

- At this point we're definitely crossing the crackpot threshold (if we haven't already) -

3b. Finding a way to remove an object's inertial mass. - How would one even do this, and what side effects could that have?
4. Removing the ship from our space-time completely (perhaps by enclosing it in a "bubble" of it's own space), so it doesn't need to travel in our universe at all. - If we can build wormholes, why don't we take one with us?
5. Using hypothetical FTL particles ("tachyons") as reaction mass. - Do they even exist? How could we catch, store and use them?
6. Find a way for "true" teleportation. - How is that even supposed to work? No theories or observations even hint at such a possibility.


If you're just interested in plausible-sounding ways for interstellar travel that don't immediately fall apart once a physicist looks at them (even though they aren't based on actual science), you could take a look at Sword of the Stars. They have (in the latest expansion) six different alien races, each with an own semi-plausible way of interstellar travel.

[Yukitsu]

If you're travelling at "light-speed travel" you can probably meet those power requirements! ;-)

Not necessarily. Moving that fast requires certain "cheats" to get around Einstein. Cheating to get around Newton's laws is probably going to prove to be harder.

[Tarinaky]

Not necessarily. Moving that fast requires certain "cheats" to get around Einstein. Cheating to get around Newton's laws is probably going to prove to be harder.

In the universe there are large numbers of high-energy events, daily. Any such 'cheat' is (by logic) one of threefour things:

1) Requires energy in excess of that released by even the most energetic stellar events (and thus of dubious practical use).
2) So unstable as to disappear before it can be measured (and thus of dubious practical use).
3) Occur frequently in nature (begging the question of why no empirical evidence of such exists)

Edit: Just thought of a fourth one...

4) Or require some exotic material not present in abundance in nature... (again... making it of dubious practical use)

[Yukitsu]

Well, really, what matters depend on material deformed, displaced, torn apart etc.

Depending on material, it's thikness, support etc. time in which energy is being spent can really matter a lot.

Not as much as you'd really think. Energy lost over time works equivalently as both projectiles do work. Unless the pole-axe does less work on the body armour, but does the same amount on the body underneath, it's not considerably more efficient than the bullet.

Well, type II bulletproof vest can hold off bullets of quite considerable energy.

While it probably wouldn't help at all against pole axe, despite it much lower 'energy output'.

But with modern military there's 3039 responses to light vest, before damn polleaxe. Starting with more powerful gun.

A type 2 vest stops only around 7545.888 joules of energy, the approximate energy of a bullet.

A magical 2 kilogram halberd flying through the air (Ie, ignoring the body weight behind it) needs to be moving at only 180 or so meters per second to match that energy. For reference to that, my golf swing clocks in at 3 times faster.

[Yukitsu]

In the universe there are large numbers of high-energy events, daily. Any such 'cheat' is (by logic) one of threefour things:

1) Requires energy in excess of that released by even the most energetic stellar events (and thus of dubious practical use).
2) So unstable as to disappear before it can be measured (and thus of dubious practical use).
3) Occur frequently in nature (begging the question of why no empirical evidence of such exists)

Edit: Just thought of a fourth one...

4) Or require some exotic material not present in abundance in nature... (again... making it of dubious practical use)

That's not actually logic. Stating that you must use high energy events to exceed light (a losers bet) is basically playing it by Einstein's rules and losing. If we do find a way around the speed of light barrier, it'll probably involve something other than "pour in more energy" since that squares off to pretty high values once you start to get to within a chunk of the speed of light.

[Spiryt]

A type 2 vest stops only around 7545.888 joules of energy, the approximate energy of a bullet.

A magical 2 kilogram halberd flying through the air (Ie, ignoring the body weight behind it) needs to be moving at only 180 or so meters per second to match that energy. For reference to that, my golf swing clocks in at 3 times faster.

7545 J is energy of some really serious heavyweight/long barrel bullet so I'm pretty sure that you mixed something up.

Also, there's no possible way that 2kg halberd will be even approaching that energy, with or without wielder....

Tiger woods solid hits had been clocked at around 60m/s at the club head, so I somehow doubt that you do it 3 times faster than 180.

Dr. Williams in his armor tests clocked halbers etc. at about 200J

Absolutely top level throwers give javelins about 360 J of starting KE.

And so on, and so on - you really mixed something up big here.


And in the end, shape, velocity, material, and generally how energy is being spent will have drastically more meaning than total energy.

Football kicked by powerful player can easily exceed energy of most arrows etc. and it obviously won't penetrate any armor any time soon, nor harm anybody seriously - for extreme comparison.

In terms of bullet vs pollaxe -

pollaxe spike thrust will have way more momentum, among other things, than bullet, less drag from material penetrated (less velocity) way higher sectional density, etc.

So with way lower energy, it can stab trough things that will disperse bullet energy and stop it.

[Tarinaky]

That's not actually logic. Stating that you must use high energy events to exceed light (a losers bet) is basically playing it by Einstein's rules and losing. If we do find a way around the speed of light barrier, it'll probably involve something other than "pour in more energy" since that squares off to pretty high values once you start to get to within a chunk of the speed of light.

I didn't say it was logic. I said it followed from logic. I didn't show the argument because I'm lazy.

Something other than "pour in more energy" is Option 4) Exotic matter.

[Yukitsu]

Yeah, early morning physics when you start with miles as your unit generally leads to some form of failure (I forgot what a mile was when doing that, off by magnitude of 10). On the other hand, I found a calculator.

Now that I don't have to eyeball it, 2kg*m^2/1=7545, m=(7545/2)^-2, m=61 (eyeballing without checking to a diff of 120 was pretty bad, but it does take a while doing square roots by hand. )

Which happily is the velocity of Tiger Wood's golf swing.

I'm going to still contest that the 200 joule halberd swing is nonsense, as that implies the halberd was traveling at about m=(200/2)^-2, m=10. 10 meters per second. Unless that was only 200 joules of energy imparted on the target after impact, using an accelerometer, rather than 200 joules of kinetic energy, but the bullet number I gave above isn't work, it's the total kinetic energy of the bullet in flight.

As a further, when you say "has more momentum", the calculation for momentum to work is identical to converting momentum to joules, then joules to work. If the halberd has more momentum, it ends up having more energy, not less. I'm guessing just like how ballistic vests are actually stab resistant (a poor wiki search getting 109 joules of work imparted being blocked) more energy on a stab, and more energy on the bullet will cause more damage.

[Spiryt]

Halberd weights way more than Tiger's club, so it cannot be expected to be swung nearly as fast.

10 m/s is perfectly reasonable, some 7-9 m/s is pretty typical for fully committed punch of trained boxers. Halberd head has a lot of advantage in velocity due to leverage, but with it's mass and arms moving way slower holding the haft, being close to body, it's shouldn't beat those significantly.

Momentum of halberd also is perfectly simple thing:

Bullet of 8 g and velocity of 400 m/s will have energy of 640 J and momentum of about 3.2

Some simple model of halberd with about 3kg of whole weapon and hand moving about 12 m/s on average will be 216 J with momentum of about 36

Of course, there will be subtleties in it, but generally, due to way lower mass, and energy due to great velocity, bullet will have way lower tendency to stay on course, it's energy will be likely spent up for many other interactions.

[Yukitsu]

Halberd weights way more than Tiger's club, so it cannot be expected to be swung nearly as fast.

10 m/s is perfectly reasonable, some 7-9 m/s is pretty typical for fully committed punch of trained boxers. Halberd head has a lot of advantage in velocity due to leverage, but with it's mass and arms moving way slower holding the haft, being close to body, it's shouldn't beat those significantly.

Halberd's still have about a meter distance from the point at which it's held. That distance makes a big difference in terms of how fast it will be moving. Slower than 61 probably (though Tiger by no means has the world's fastest swing speed.), but I'd have to say a 10 m/s based on trying to finish a guy off, trying to get through his armour would be too slow for the job.

Momentum of halberd also is perfectly simple thing:

Bullet of 8 g and velocity of 400 m/s will have energy of 640 J and momentum of about 3.2

Isn't this the kind of bullet that gets stopped by a type 1 vest? At those lower energy ranges, the way the armour works, there's a case that lower energy, more weight makes a difference, as the flexible armour doesn't stretch at all when cut (meaning it doesn't have the same work applied to it.) In that case however, even the mass is largely irrelevant, it's the fact that they're doing different types of work.

Some simple model of halberd with about 3kg of whole weapon and hand moving about 12 m/s on average will be 216 J with momentum of about 36

Of course, there will be subtleties in it, but generally, due to way lower mass, and energy due to great velocity, bullet will have way lower tendency to stay on course, it's energy will be likely spent up for many other interactions.

I think modern vests are stab resistant at those energy ranges though, so unless you're hitting harder, that may very well not bypass the body armour. After all, solid plates are currently used to stop serious rounds, not soft cloth armour, though I may be confusing type 2 and 3 with type 1 and 2 here.

*As a note, we're using slightly different equations here. I'm going with the SI unit for joule instead of the Ek calculation, which is simply 1/2 the SI unit, but since it's basically a linear relation, not much of a difference in terms of comparison.

[Spiryt]

Isn't this the kind of bullet that gets stopped by a type 1 vest?

no, those are getting stopped by better II and IIa, according to data I've found. Velocity stated mentions that at 400 m/s there would be still decent chance of penetration.

I think modern vests are stab resistant at those energy ranges though, so unless you're hitting harder, that may very well not bypass the body armour. After all, solid plates are currently used to stop serious rounds, not soft cloth armour, though I may be confusing type 2 and 3 with type 1 and 2 here.

The test apparently require level 3 to resist 45 J from 10 - 20m/s knife with some weight simulating arm holding, so I don't think 216 is very unrealistic.

According to Wiki, but I guess they wouldn't fail at coping these nij standards.

To endure higher energies, one needs metal additions generally. Completely different material, so is being penetrated differently.

[Yukitsu]

no, those are getting stopped by better II and IIa, according to data I've found. Velocity stated mentions that at 400 m/s there would be still decent chance of penetration.

The test apparently require level 3 to resist 45 J from 10 - 20m/s knife with some weight simulating arm holding, so I don't think 216 is very unrealistic.

According to Wiki, but I guess they wouldn't fail at coping these nij standards.

To endure higher energies, one needs metal additions generally. Completely different material, so is being penetrated differently.

OK, NM, as I'm apparantly shifting numbers down 1 slot each based off lousy memory. Type 3 can probably resist a pole axe, but I'm thinking type 2 just gets cut instead, since it's IIRC mostly soft.

[Spiryt]

Some data for quick reference:

95% of knife attacks averaged around 70 J


http://www.nij.gov/nij/pubs-sum/183652.htm

Here's mentioned data about resistance from dropped weight that simulates knife and an arm.


As far as "resisting pollaxe" goes, it must be noted that even "typical" pollaxe could vary quite a bit in dimensions, and provide at least 3 different 'modes' of attack : top spike, axe blade and hammer with very different protrusions possible.

[eulmanis12]

Generation ships are significantly more plausible speculative ideas.

you might not need generational ships at first. Just ships with large supplies of food/water

Say "Near" and I use the term loosly future, colonization of "close" solar systems such as the Centari system. It is about 4 light years away. Suppose that hypotheticly a ship is built capable of .5 c, half light speed. That would make just a 8 year trip. A long time for a person to be cooped up aboard a ship, but its doable. Accelerating to .5 c can be done with no breaches of the laws of physics. It would need a huge amount of energy to accelerated the ship, but I'm assuming that a society advanced enough to plan a colonization of another solar system wouldn't have much difficulty putting a few nuclear reactors aboard a space ship


for "startrek level" future civilizations, teleportation is theoreticly possible, so is moving space around the ship instead of moving the ship through space. However these are only possible in "theory" and my source is sketchy at best about them. (Science Channel on TV)

edit, fixed error

[Conners]

Hmm... what is the feasibility of shrinking surrounding empty space? Like, not the objects in that space--just the space itself. I also wonder what the effects of moving through shrunken space might be.

[Tarinaky]

Hmm... what is the feasibility of shrinking surrounding empty space? Like, not the objects in that space--just the space itself. I also wonder what the effects of moving through shrunken space might be.

From what I understand... 1) It'd require matter with a negative mass-energy, and nobody knows what that means.
2) It'd require a lot of this unobtanium.
3) Once you hit light speed or more anything inside the 'bubble' is instantly cooked alive by Hawking radiation.

[Knaight]

Say "Near" and I use the term loosly future, colonization of "close" solar systems such as the Centari system. It is about 4 light years away. Suppose that hypotheticly a ship is built capable of .5 c, half light speed. That would make just a 4 year trip.

There are a few major problems with this.
1) If it is 4 lightyears away, and the ship is going .5 c it takes 8 years, and not 4.
2) You have to accelerate up to .5 c, and accelerate back down. Which puts this at .25 c and 16 years looking at averages, assuming that there is constant acceleration then constant deceleration. Given that accelerating to .5 c in 8 years involves accelerating at nearly 1g (9.5 ms^-2), the power requirements are fairly absurd. 9.5 ms^-2 is several orders of magnitude higher than anything likely to be realistic for a while. This actually ignores relativistic effects, which just make it worse.
3) The energy required to accelerate a ship at nearly 1g for 16 years straight is completely ridiculous.

[Telok]

It would need a huge amount of energy to accelerated the ship, but I'm assuming that a society advanced enough to plan a colonization of another solar system wouldn't have much difficulty putting a few nuclear reactors aboard a space ship

Just off the top of my head, there are two known ways to turn electricity into thrust. Lasers are the first way, but this site (which is reasonably accurate) lists the power requirements at 300 megawatts per Newton of thrust. The other way is to use a Bussard ramjet, which means you already had to accelerate to at least 0.1c in the first place.

The other engine types all require physical propellant of some sort. The rule of thumb here is that any such rocket will be about 2/3 propellant and 1/3 everything else.

[eulmanis12]

There are a few major problems with this.
1) If it is 4 lightyears away, and the ship is going .5 c it takes 8 years, and not 4.
2) You have to accelerate up to .5 c, and accelerate back down. Which puts this at .25 c and 16 years looking at averages, assuming that there is constant acceleration then constant deceleration. Given that accelerating to .5 c in 8 years involves accelerating at nearly 1g (9.5 ms^-2), the power requirements are fairly absurd. 9.5 ms^-2 is several orders of magnitude higher than anything likely to be realistic for a while. This actually ignores relativistic effects, which just make it worse.
3) The energy required to accelerate a ship at nearly 1g for 16 years straight is completely ridiculous.

Sorry about the very obvious math error, its fixed. As far as the acceleration goes, I'm assuming you could get up to speed before exiting our solar system, and decelerate in the same amount of time, leading to a total travel time of 8-9 with a round trip of about 17 years. As for energy, yes it would take an absurd amount. But aquiring absurd amounts of energy is just difficult, breaking the laws of physics is impossible. And even then, what makes you think that energy would be a problem for a civilization with enough spacefaring epericance to colonize a foreign solar system, Anti-matter, nuclear fusion, a new type of power generation that hasn't even been contemplated yet? These things could possibly provide more than enough energy given sufficent research and development. 700-800 years from now I don't see energy as being a problem.

[Tarinaky]

Sorry about the very obvious math error, its fixed. As far as the acceleration goes, I'm assuming you could get up to speed before exiting our solar system, and decelerate in the same amount of time, leading to a total travel time of 8-9 with a round trip of about 17 years. As for energy, yes it would take an absurd amount. But aquiring absurd amounts of energy is just difficult, breaking the laws of physics is impossible. And even then, what makes you think that energy would be a problem for a civilization with enough spacefaring epericance to colonize a foreign solar system, Anti-matter, nuclear fusion, a new type of power generation that hasn't even been contemplated yet? These things could possibly provide more than enough energy given sufficent research and development. 700-800 years from now I don't see energy as being a problem.

Handwaving a new power source counts as breaking the laws of physics (as we understand them). If you're going to do that you might as well pull an infinite improbability drive (quantum tunnelling) along with it...

[Yora]

Hmm... what is the feasibility of shrinking surrounding empty space? Like, not the objects in that space--just the space itself. I also wonder what the effects of moving through shrunken space might be.

I think the general concept is, that you don't actually notice any change. It's not that everything gets pulled closer together, but that the "surface" of space itself shrinks and with it everything inside that space. And if I understood this single one thing of string theory, matter is actually energy which means you can shrink sub-atomic particles withouth affecting their behavior.
((But then the whole cosmic background radiation thing does not work, since the density of the universe would always have been the same. Damn... )

[Galloglaich]

Keep in mind the amount of energy in joules that it takes a sharp steel blade to penetrate something vs. a lead bullet are very different. As Alan Williams pointed out, arrows would penetrate with about 1/5 the energy of musket bullets. Knives tend to rather easily pierce almost all modern 'soft' body armor. In fact, interestingly, most modern 'knife-proof' vests, such as those used by US prison guards and English police, incorporate some element of mail (i.e. 'chainmail') in them, as that is one of the only designs which has proven reliably capable of stopping a knife thrust.

I think a 200j halberd strike would have devastating results against a threat level II or IIa vest! Especially with the beak.

G

[Knaight]

I'm assuming you could get up to speed before exiting our solar system, and decelerate in the same amount of time, leading to a total travel time of 8-9 with a round trip of about 17 years.

This isn't happening. I'm going to assume that by Solar System you mean the typical use of the planetary range, and aren't looking at the outer boundary of the oort cloud or similar. Even including Pluto at maximum distance, that is a mere 7.4 billion kilometers. Given that uniform acceleration within the Solar System means travel at .25c given prior assumptions, it takes all of 24000 seconds (rounded to 2 significant figures). Accelerating to .5c in 24000 seconds means accelerating at over 12,000 meters per second squared. That's not even remotely survivable.

[Tarinaky]

This isn't happening. I'm going to assume that by Solar System you mean the typical use of the planetary range, and aren't looking at the outer boundary of the oort cloud or similar. Even including Pluto at maximum distance, that is a mere 7.4 billion kilometers. Given that uniform acceleration within the Solar System means travel at .25c given prior assumptions, it takes all of 24000 seconds (rounded to 2 significant figures). Accelerating to .5c in 24000 seconds means accelerating at over 12,000 meters per second squared. That's not even remotely survivable.

Isn't the edge of the Heliosphere/the heliopause normally regarded as 'the edge of the solar system'?

Although I'm not sure it makes a massive difference on your figure since it's only a factor of 2 difference.

[Autolykos]

A type 2 vest stops only around 7545.888 joules of energy

I'm curious where you found that number, and how your source can be sure it won't stop 7545.889 J. :)

[Knaight]

Isn't the edge of the Heliosphere/the heliopause normally regarded as 'the edge of the solar system'?

Although I'm not sure it makes a massive difference on your figure since it's only a factor of 2 difference.

There are a few edges that get used, and I was using the one most people go by (hence including Pluto, despite it being a dwarf planet). Still, given that survivable accelerations are over two orders of magnitude lower than what I cited, switching to the heliopause isn't really significant. Any humans aboard are still dead, as are any other macroscopic animals. I can't really comment on the extent to which microscopic animals can survive high accelerations, but I wouldn't be optimistic.

[Yukitsu]

I'm curious where you found that number, and how your source can be sure it won't stop 7545.889 J. :)

Off memory (of a velocity and weight, not that number), but mixing up a type 2 and type 3 vest. Keep forgetting type 1s are the ones that basically don't get used anymore.

[Spiryt]

According to those NIJ standards, 7500 J is energy at which type IV (armor piercing rifle) vests will generally start to fail quite often.

Those are powerful loads, obviously from long barrels.