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Old 12-19-2014, 09:47 PM   #1
BraselC5048
 
Join Date: Oct 2012
Default Linear shaped charge to cut through DR 1900?

Anyway, in the field of weapon design I need a linear shaped charge (manually placed) to cut through starship armor, which could be as much as DR 1900. It can't just make a hole, it has to cut through it along its length. The idea is to string a bunch of them together (rigid sections) in a circle to blast a large opening through an armored airlock hatch. (The pressure door gets the armor's full DR to protect it, as it's on the other side.) Obviously it's going to be heavy, rigid and short, but it doesn't need any more portability than somebody being able to carry it from the storeroom to the airlock. It'll take a bunch of sections to make a man sized hole, of course.

What I'm wondering is how much it would weigh per foot, so I can get some idea of the size, weight and number of sections. It will do maximum damage automatically, and if it gets the (10) armor divisor, instead of the (5) armor divisor the flexible but much smaller cord of the same basic thing from High Tech gets, (which weighs 0.5 lb per foot), it would need to do 6dx6(10). If it's stuck with the (5) divisor, then it would be closer to 6dx11 (5). Which going by the "Blowing stuff up" section of Basic and scaling (assuming the charge from High Tech is the equivalent of .11 lb TNT), would be 137 lb or so for a 1ft section. Which is outrageous. If it gets to do 6dx6 (10), again scaling, it would weigh 41 lb for a 1ft section. Which is actually pretty close to what I had imagined for a 1 or 2 foot section.

So use the 6dx6(10) scaling, and 41 lb per foot long section?

Or would it be better to use one smaller charge to cut partway through, then place another one in the same sport to finish the job, or would that not work with shaped charges at all?
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Old 12-19-2014, 10:20 PM   #2
Anaraxes
 
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Default Re: Linear shaped charge to cut through DR 1900?

Per B415, a 6dx6 explosion takes 6x6 / 4 = 9 lbs of TNT. Divide by the REF of your futuristic explosive. 6dx11 would be 11^2 / 4 = 30 lbs. I think the charges are smaller than your calculations suggest.

This doesn't seem far out of line, as the rounds for the 120mm tank gun on the Abrams weigh about 50 lbs, which includes the propellent and case, and not just the warhead.

A shaped charge works by focusing its energy into a small jet (often assisted by lining the explosive with a liner of metal (or techy whatever) to be vaporized and propelled. (See this pic.) The hole it makes is much smaller than the actual charge, so you couldn't tunnel through with a bunch of the same charge. They wouldn't fit into the hole. You might be able to dig a little deeper in the same hole, but my understanding is that the proper standoff distance is also important.
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Old 12-19-2014, 10:35 PM   #3
BraselC5048
 
Join Date: Oct 2012
Default Re: Linear shaped charge to cut through DR 1900?

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Originally Posted by Anaraxes View Post
Per B415, a 6dx6 explosion takes 6x6 / 4 = 9 lbs of TNT. Divide by the REF of your futuristic explosive. 6dx11 would be 11^2 / 4 = 30 lbs. I think the charges are smaller than your calculations suggest.

This doesn't seem far out of line, as the rounds for the 120mm tank gun on the Abrams weigh about 50 lbs, which includes the propellent and case, and not just the warhead.

A shaped charge works by focusing its energy into a small jet (often assisted by lining the explosive with a liner of metal (or techy whatever) to be vaporized and propelled. (See this pic.) The hole it makes is much smaller than the actual charge, so you couldn't tunnel through with a bunch of the same charge. They wouldn't fit into the hole. You might be able to dig a little deeper in the same hole, but my understanding is that the proper standoff distance is also important.
The multiple charge idea was aligning the second charge over the hole made by the first one. Since the rules from Basic don't really seem to apply to odd situations in terms of absolute numbers, I used them to figure out how many times bigger the charge needed to be, and then multiplied the weight per foot for the flexible linear shaped change in High Tech by that.
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Old 12-20-2014, 12:04 AM   #4
The_Ryujin
 
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Default Re: Linear shaped charge to cut through DR 1900?

Assuming that the linear shape-charge in High-Tech uses C4 as it's explosive filler, then even if you use meta-stable hydrogen (REF6) it'll just up the damage to 6d but I would agree that it wouldn't be far off to say that advances had been made that give it an AD of 10.

So in this case, assuming an REF of 6 (which is about as good as it's gonna to get barring super science or nukes), you'd need a cord that weighed about 14lbs per foot so I think that some kind of energy weapon based cutter might be a better idea at this point. DR 1900 is pretty beefy.
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Old 12-20-2014, 04:10 AM   #5
fula farbrorn
 
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Default Re: Linear shaped charge to cut through DR 1900?

if time permits, wouldnt some kinda thermal charge work better ?, reading up on the rules for thermal lances, i see that they treat materials as ablative or semi-ablative, in that case it would first eat up the DR and then start to chew its way through the hull itself, if breaching has to be fast, try a EFP ?, you have a tripod that you place on the hull, putting the EFP at the proper distance, then you detonate it and it punches through making a Mouse hole for entry
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Old 12-20-2014, 04:15 PM   #6
BraselC5048
 
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Default Re: Linear shaped charge to cut through DR 1900?

Quote:
Originally Posted by The_Ryujin View Post
Assuming that the linear shape-charge in High-Tech uses C4 as it's explosive filler, then even if you use meta-stable hydrogen (REF6) it'll just up the damage to 6d but I would agree that it wouldn't be far off to say that advances had been made that give it an AD of 10.

So in this case, assuming an REF of 6 (which is about as good as it's gonna to get barring super science or nukes), you'd need a cord that weighed about 14lbs per foot so I think that some kind of energy weapon based cutter might be a better idea at this point. DR 1900 is pretty beefy.
Assuming the cord in High Tech had REF of 1.4, than going to 1.7 cuts the weight down to about 33 lbs for a rigid 1ft long section. Which is light enough for the job it has to do.

And that's thing - it's only going to be used cut through starship airlock armor from the airlock of another starship or boat. Likely get several guys to move a pile of them maybe the 50-100 feet at most from the storeroom (where they will always be, sitting in a box, right up until the time to use them comes), to the airlock or boat deck, not remotely under fire, then spend a minute or two setting the charges, set a time fuze and back the ship off several meters, then board the enemy ship.

It's not designed to be something carried by soldiers, or anybody else, on a daily basis. As long as it weighs 33 pounds, a crewman or marine can carry two of them at a time to where they're needed, and several guys will be running them, and they won't be carrying other equipment at the same time, they can just set it down for they're doing it. It'll take a bunch of them, 20 sections for a 4ft x 6ft hole, but there's room for them on a starship. There would also be on maybe a second's longer delay a big plain HE charge in the middle of the armored plug door to knock it over. I wonder if you would need corner sections, or just initially blow a single charge extending past where you want it, then the main charges would extend past that.

The downside is that the time required generally is enough time set up a hot reception on the other side. The defenders have the option of whether the inner airlock door (several feet past what we just blew up) is going to be open or closed. Open gives you a clear field of fire for the MG positions you've set up, but also exposes them to fire from heavy weapons from the attacker's ship.

Also likely is another set of smaller charges for less well armored ships like frigates, cruisers and destroyers. The advantage would be being able to get through it faster, with fewer, longer and lighter sections.

Also, going back to the 105mm recoilless rifle, 6dx7 shell impact damage will actually punch through a DR 70 bulkhead without needing an armor divisor at all. Maybe just a strengthened shell with no armor divisor, slightly less powerful blast and fragmentation, and a base fuze? Also an actual AP shell in case they armored the target, but that would have far less effect on the other side.
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Old 12-20-2014, 05:03 PM   #7
BraselC5048
 
Join Date: Oct 2012
Default Re: Linear shaped charge to cut through DR 1900?

Hang on, I don't know what I did for scaling last time, but this time around, assuming 1.7 instead of listed 1.4 like last time, I would up with just 20 lb for a foot long section that does 6dx6(10). (It will always inflict maximum damage as a contact explosion.)

Possibly light enough for a few of them to go with a landing party. Won't go through the front of a modern MBT (DR 1680, doubled versus shaped charges), but will go through the side (a little less than half that). As a foot long line instead of a pencil sized jet, it's going to do a heck of a lot more damage on the other side, easily knocking it out.

Going for a 5dx5 (10) section, useful against all cruisers, I wound up with just 10 lb for a 1 foot long section, or more accurately it will be 20 lb for a 2 foot long section.
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Old 12-20-2014, 08:05 PM   #8
Rysith
 
Join Date: Oct 2013
Default Re: Linear shaped charge to cut through DR 1900?

Quote:
Originally Posted by BraselC5048 View Post
The downside is that the time required generally is enough time set up a hot reception on the other side. The defenders have the option of whether the inner airlock door (several feet past what we just blew up) is going to be open or closed. Open gives you a clear field of fire for the MG positions you've set up, but also exposes them to fire from heavy weapons from the attacker's ship.
That argues (especially since weight and time aren't that much of an issue) for a secondary anti-personnel charge as part of the breaching procedure - set off the breaching charge and then set off the in-setting equivalent of a giant claymore mine. That should help with establishing a foothold in the enemy ship, at least.
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Old 12-20-2014, 09:11 PM   #9
Anthony
 
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Default Re: Linear shaped charge to cut through DR 1900?

The problem with comparing with a single shaped charge is that you want to make a linear cut, not a narrow hole, so you multiply the weight by the length of the desired cut. Looking at UT, a 100m shaped charge or HEMP round will blow through DR 1900, but it probably only makes a 1" hole, so you need 12 of them per foot...

In the end, you're talking armor thicknesses where no-one is going to try to cut through them. They'll figure out how to bypass them, or if they don't need whatever is behind the door intact they'll just fire an APEX missile through it.
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Old 12-20-2014, 10:32 PM   #10
BraselC5048
 
Join Date: Oct 2012
Default Re: Linear shaped charge to cut through DR 1900?

Quote:
Originally Posted by Rysith View Post
That argues (especially since weight and time aren't that much of an issue) for a secondary anti-personnel charge as part of the breaching procedure - set off the breaching charge and then set off the in-setting equivalent of a giant claymore mine. That should help with establishing a foothold in the enemy ship, at least.
It's modern militaries. Everybody and his brother on the starship you're boarding is covered with DR 16-18 body armor everywhere except the head (DR 15 all-round ballistic plastic vacc suit bubble helmet), hands and feet (no DR). A claymore would likely cause no wounds at all. The best option is a enhanced fragmentation round from a 105mm ish weapon (pack howitzer or recoilless rifle, depending on the navy) set to airburst by a simple time fuze. Then there's the problem that everybody is likely behind barricades (think low walls, 5 ft high) including a DR 75 spare hull plate, with a LMG on a bipod on top, or a HMG on a tripod behind it. And the whole "vacuum greatly reduces the effective radius of explosive damage" issue. I once tried clearing an entrance by firing through the (oversized) airlock a HE bombardment missile, 2 tons of HE filler with a yield of 4 tons. It didn't work nearly as well as I hoped, although I also forgot completely about fragmentation damage, which might have driven the casualty care up. Basically the MG positions were on the sides of the cargo bay behind the airlock, and I expected them to be in the center, not that there was any choice of target area anyway.

Still, that is a consideration for both sides. The one time I defended against a boarding action, although also driven by it being a forward airlock with nothing more than a hallway behind it, I set up the MG positions firing down both corridors out of the 20ft ish long corridor straight back from the airlock, with no coverage of the entrance itself. Thee bridge was right behind one of them, they rushed it, and overran it, not helped by using bad Malf rules (since replaced) that had the MG jam after a few shots.

Quote:
Originally Posted by Anthony View Post
The problem with comparing with a single shaped charge is that you want to make a linear cut, not a narrow hole, so you multiply the weight by the length of the desired cut. Looking at UT, a 100m shaped charge or HEMP round will blow through DR 1900, but it probably only makes a 1" hole, so you need 12 of them per foot...

In the end, you're talking armor thicknesses where no-one is going to try to cut through them. They'll figure out how to bypass them, or if they don't need whatever is behind the door intact they'll just fire an APEX missile through it.
I actually scaled from the closest thing I could find, which is a flexible rope linear shaped charge in High Tech - actually the same thing I'm designing. So it's actually scaled from a linear shaped charge already. The difference is that High Tech's is a 20 ft spool of flexible cord that weights half a pound per foot, and mine comes in rigid 1 foot sections that weight 20 pounds each. Much heavier, 40 times in fact, and enough to blow a man-sized opening isn't portable - but it isn't intended to be. You simply have guys carry them to the airlock on your own ship, likely several guys, while 1-2 men actually place them while they're being supplied. Wouldn't work under fire, but you're not under fire. And my tech level is 8 + a bit of ^, and just about any equipment from Ultra Tech would be more advanced then what the campaign allows. I'm using technology from High Tech for the most part.

And the armor is proof against every weapon in the starship's storerooms. Not proof against the ship's weapons, but sometimes you have to board, and in a jump point ambush, where it takes 8 minutes for the second (or later) ship coming out of jump to get its drives working and lasers charged enough to go through your own armor at all, and your ship is capable of 6 G's and they're only 1000 km away, and they haven't had time to depressurize their hull, and it'll be almost as long for your own lasers to charge...

I actually ordered a boarding action against an enemy cruiser in exactly that bad spot. I also had the advantage of having just recalled the boats loaded with a total boarding party the size of their entire complement, so I had 170 men already armed and assembled for boarding, only needed to go up a flight of stairs. Never knew what hit them.

My defending was when my character was only a lieutenant, we were in a similar position, and a laser salvo to the bridge and common areas resulted it 3/4th of the crew being either dead, wounded or stuck without a vacc suit in a pressurized compartment with vacuum outside. I wound up winning the Medal of Honor (actually the SEH, it was a traveller setting run without GURPS: Traveller. Someday I'll release it as Traveller - 1750) for single-handedly defending the starboard stairwell against 17 marines, and therefore keeping them contained to a small area at the bow on one deck. Also personally accounted for half the boarding party being casualties, although some of that was done with others. The rest of our squadron was winning by weight of numbers, and they pulled out, and jumped away.

Any interest in me writing up a recap of that short action and putting it in a thread? The dice were rolling really hot that day, with tons of hits being rolled up as neck.
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