Thingmaker and Craft Design question

[Major B]

Please check my work and provide feedback on my results:

I am completing a fighter design. One of the variant models is an attack model mounting a slug thrower.

I mounted the slug thrower following the design rules for a firmpoint mount. The result is a weapon taking up a half ton of volume with range R=6. The fighter is produced at TL14 and the weapon is an ultimate (TLSE=Ult) TL-11 model so the final Mod is +2 (TLSE mod +4 and T1 mod -2).

I need ammunition for this thing so devoted a half ton as an ammunition hopper.

First question: How many rounds can a half ton hopper hold?

Slug throwers fire size=2 slugs (page 366) that are explosive and have pen=2 (page 369).

To find the volume of one size=2 slug I went to Thingmaker. On poage 613, the length of a size-2 "thing" is equal to size.

Though not specified, this means a value extrapolated from the size code. From the chart on page 622, size=2 means 7.5 cm so L = .075 m.

From page 623, using a cylinder profile, width and height both equal L / 2 or .0375 m.

Volume = L x W x H = .075 x .0375 x .0375 = .00105 m3.

My half ton hopper has a volume of 6.75 m3. Divide that by .000105 and you get 64,000 rounds in the hopper (assuming no waste space or room required by the feed mechanism).

Second question: How many rounds does the slug thrower fire per "shot" in combat?

Since the width of the round is 37.5 mm, I looked up some 37mm gatling guns for comparison. The T249 and T250 models were six-barrel gatlings designed in the 50s and fielded into the 57-62 time frame so they are TL 6-7.

The rate of fire listed on wikipedia and confirmed on another site is 3,000 rpm in anti-aircraft mode or 120 rpm versus ground targets. However, the weapon was fed using a 192-round drum so the effective rate of fire would be limited by how fast the crew could relaod drums of ammunition (and 192 rounds of 37mm ammunition would be a bit heavy to be easily tossed around).

Considering the TL11 model would have an automated feed mechanism and assuming that the system was not limited in firing by the requirement to keep the barrels cool (because this is not a CPR like the T250 but more likely a Gauss system), and to avoid a fraction in the result all led me to a SWAG of 400 rounds per "shot" meaning the hopper holds 160 "shots."

I don't think there is any official answer so does this seem reasonable to those of you with more knowledge of weapon systems or more background in the T5 starship weapons?

 

[robject]

Major B, you are one of the more experienced people with T5 Starship Design. And you've got more follow-through and knowledge of such things than I.

You'll benefit from someone who knows about those weapons, rather than who knows about Traveller5, because I think you're on the leading edge of T5 design.

 

[Major B]

Rob, thanks for the kind compliment but I like to work in groups because there are more people to catch my mistakes.

And another thing - in many places where even the T5.09 update leaves unanswered questions the most important thing to help find or create an answer is understanding what Marc's intent was when he wrote that part. In that department you have much more insight than anyone on this site except maybe Don.

If you have anything that may help there, please share it.

 

[robject]

Wow, it's like you're so on target. No, really.

Ok, first off, I agree with your method. Debugging is a parallelizable activity.

Next, I agree with your purpose. Taking Marc's intent is key not only to producing stuff for T5, but also is the way to generate GOLDEN errata suggestions.

So, in summary, I'm not dismissing your post. Just clarifying your experience level here. And piling on a bit.

 

[Reban]

The unsatisfying answer: T5 assumes unlimited ammo for Slug Throwers and Missiles (although T5.9 gives us enough info now to figure out storage volume) in ship combat.

I like the way you've reasoned this out though. I think about these sort of details when putting together a design too.

A couple of things

I find the ThingMaker volume for cylinders a bit granular (its not Pie x r² x h). I think what it actually produces is a roughly cylindrical block so I'd take your 0.375m and call it a 35mm round which is a caliber we're more familiar with as a vehicle weapon.

There no such round as a 35mm x 750mm that I know of. Presumably about two thirds of that length is the case, or maybe the whole thing if its caseless or telescoped? And its that long because all that propellant is needed for space ranges? "Space guns" aren't something Janes IHS have a reference book for.... yet.

How many rounds per shot? I would say thats up to you to decide. The number of shots per combat round is abstracted in the combat task. I'd assume the the number of rounds per burst are actually variable and linked to the fire-control system. At long ranges more rounds in a burst might actually increase the chance to hit.

The latest 35mm Rheinmetall Oerlikon Millennium Gun has a rate of fire from 200 rounds per minute in single shot mode to 1000 rounds per minute in burst mode. But thats a TL8 gas revolver cannon. A TL9+ Slug Thrower could have a higher rate of fire because of a different mechanism, better cooling or super science.

One thousand rounds per minute sounds good and doesn't break suspension of disbelief for me. Three thousand rounds per minute for a Gatling version also sounds good especially for the CIWS roll to create a curtain of lead when intercepting a missile.

You could do what I do sometimes and pull out Fire Fusion and Steel or Guns Guns Guns and have a look at the numbers for a similar weapon.

Here's another thought; Mounts are supposed to be completely self contained... so that half ton of ammo is actually extra ammo to whatever is stored on the mount. The Mount contains the weapon, ammo, power source, control panel, and probably enough room for a gunner to manually operate it (although in the case of a fighter weapon its probably not necessary).

 

[Reban]

Taking Marc's intent is key not only to producing stuff for T5, but also is the way to generate GOLDEN errata suggestions.

Yeah here's the thing; above I used the phrase; "The number of shots per combat round is abstracted in the combat task.".

But I've re-read the Combat chapter and its isn't really.

Marc's intent (I think) is that the Space Weapon Task should represent a shot or number of shots taken by a weapons system. Thats fine for a laser beam, but then he went and added Missiles, and the two don't mesh well in my brain.

The Space Weapon Task decides if you hit.

P.389 uses the phrase "Success produces a Hit".

It should probably say Success produces a number of Hits based on the Mount.

Depending on if you've chosen a Single or Quad Turret you'll get 1 to 24 Hits or rounds on target.

Have a look at it and see if I've got that right, because it certainly seems the way its written.

 

[robject]

Well you've hit on something I'd been thinking about for a few days recently, but also something I'd heard here on COTI months and months ago -- namely, that an exceptional task-roll-failure (i.e. double sixes) could be interpreted as a weapons jam or an "out of ammo" alert.

That could work for space combat as well as personal combat.

 

[Reban]

I'm still trying to reconcile how "proper missiles" i.e. Size 5, might interact with Mount Effects. That's one of those Golden Errata points.

A weapons jam result might work best because in GunMaker you have Battlefield over-rides. For ACS weapons I'm not sure how useful it is given the timescale for combat. There's time to recycle the feed or reboot the system.

Remember for energy based weapons the ammo is the power on the mount. So out of ammo becomes? Off-line maybe? Requiring a Gunner or Tech to beat it with a wrench


Also for Major B's information (although I'm sure you know). A Size-2 round may be 75mm long but it could also be anywhere from 40mm to 200mm long.

In other words Size-2 rounds represent 20mm to 100mm caliber rounds.

 

[Major B]

Reban, thanks for the thoughtful feedback. Here is some back:

The unsatisfying answer: T5 assumes unlimited ammo for Slug Throwers and Missiles (although T5.9 gives us enough info now to figure out storage volume) in ship combat.

I agree pretty strongly. Tracking ammo consumption is tedious so I can understand omitting it from personal combat but it is an important element of ship design so it has to be considered even if not to the fullest extent of the detail that could be put into it.

I find the ThingMaker volume for cylinders a bit granular (its not Pie x r² x h). I think what it actually produces is a roughly cylindrical block so I'd take your 0.375m and call it a 35mm round which is a caliber we're more familiar with as a vehicle weapon.

True but it gives a workable number for those like me who majored in history because math makes my brain hurt.

How many rounds per shot? I would say thats up to you to decide. The number of shots per combat round is abstracted in the combat task. I'd assume the the number of rounds per burst are actually variable and linked to the fire-control system. At long ranges more rounds in a burst might actually increase the chance to hit.

The latest 35mm Rheinmetall Oerlikon Millennium Gun has a rate of fire from 200 rounds per minute in single shot mode to 1000 rounds per minute in burst mode. But thats a TL8 gas revolver cannon. A TL9+ Slug Thrower could have a higher rate of fire because of a different mechanism, better cooling or super science.

One thousand rounds per minute sounds good and doesn't break suspension of disbelief for me. Three thousand rounds per minute for a Gatling version also sounds good especially for the CIWS roll to create a curtain of lead when intercepting a missile.

Okay, you just gave back the number that I was thinking about first and then second-guessed as being too easy. That means I should have gone with my first SWAG. 1,000 rounds per "shot" is not going to be exact but is a good round figure to use as a mean and it means that a hlaf ton hopper holds roughly 64 "shots."

Here's another thought; Mounts are supposed to be completely self contained... so that half ton of ammo is actually extra ammo to whatever is stored on the mount. The Mount contains the weapon, ammo, power source, control panel, and probably enough room for a gunner to manually operate it (although in the case of a fighter weapon its probably not necessary).

I thought the answer to that question was too hard so I shortened my list to two. We would need to add a level of detail to "How Weapons Work" to answer that question effectively but there may not be appetite for that right now. Until then though, I assume that the weapon holds one "shot" per weapon (so a T4 holds four weapons with one loaded shot each) and anything beyond that requires reloading.

Anyone else have thoughts on this or is there something in T5.09 that I missed that specifies this?

Yeah here's the thing; above I used the phrase; "The number of shots per combat round is abstracted in the combat task.".

But I've re-read the Combat chapter and its isn't really.

Marc's intent (I think) is that the Space Weapon Task should represent a shot or number of shots taken by a weapons system. Thats fine for a laser beam, but then he went and added Missiles, and the two don't mesh well in my brain.

The Space Weapon Task decides if you hit.

P.389 uses the phrase "Success produces a Hit".

It should probably say Success produces a number of Hits based on the Mount.

Depending on if you've chosen a Single or Quad Turret you'll get 1 to 24 Hits or rounds on target.

Have a look at it and see if I've got that right, because it certainly seems the way its written.

I need to share this with Dalthor as we traded some e-mails on this subject this morning.

I'm still trying to reconcile how "proper missiles" i.e. Size 5, might interact with Mount Effects. That's one of those Golden Errata points.

I agree. Missiles are one of the things we know so much more about now since we have so much more detail on guidance and effectiveness and other stuff, but we still don't know how many are carried in a T2.

Also for Major B's information (although I'm sure you know). A Size-2 round may be 75mm long but it could also be anywhere from 40mm to 200mm long.

In other words Size-2 rounds represent 20mm to 100mm caliber rounds.

Check. I used the mean value listed on the top of table 3a, page 622, rather than fiddle with the decimal values. Because history major.

 

[Epee]

An Ultimate version of any firearm (not including Gauss weapons) is almost certainly a light gas weapon; that is they use compressed Hydrogen/Oxygen rather than Nitrates as a propellant. I come to this conclusion based on the Gunmaker examples and the number of rounds they contain.

Light Gas guns currently take two forms:
1. A research version which uses a vacuum-purged barrel to produce interplanetary-like velocities. This form I would deem too complex and bulky for small arms. Also, given the infrastructure required and contemporary advances, they will probably be skipped by the military with the tech moving straight to Gauss weapons.

2. An internal combustion form which essentally injects a hydrogen/oxygen mix into the chamber behind the projectile and ignites it. These produce little if any velocity increases over nitrates but offer far smaller volumes needed for propellants and decreased recoil for a given velocity due to the greatly decreased mass of the propellent. The T4 3mm "Staple Gun" would be a prime example of this technology.

 

[Major B]

That's interesting Epee. Thanks.

I have two questions if you can provide more information:

1) Since we are talking about a turret or firmpoint mounted weapon do you think that it could be in the first form you mention?

2) Does this propellent system make my estimate of 1,000 rounds per "shot" implausible?

 

[Reban]

What about ETC and Binary firearms?

I guess Hydrogen/Oxygen propellants qualify as Binary. Are ETC propellants all nitrate based? I've seen water/aluminium slurry listed as a plasma propellant for ETC. Again I guess that also qualifies as a binary propellant so the two technologies overlap.


For a turret or firmpoint mount I would assume there'd be a purge system built in to all the "launcher" systems including the other missile types. Even lasers and particle beams should have the ability to remove any atmospheric gasses left in their mechanism/beam-emitters when they enter space.

Remember those L x H x W calculations yesterday that gave you a block 75mm long by 37.5mm high and wide?

That essentially is what caseless ammunition would look like. A block of propellant with the projectile embedded inside.

If you use a separate Hydrogen/Oxygen propellant you need to think about using a certain amount of your half ton ammo hopper for the projectiles and a certain amount for the Oxygen and Hydrogen containers. I've no idea what those proportions might be.

Regarding the number of rounds carried, it might be a good idea to look at the mission of the fighter and weapons system.

Does the mission require sustained fire, or accurate sniping fire? How much capacity to carry ammo have I? You've already decided this by allocating a half ton of volume. These kind of questions should influence you in your design.

 

[Major B]

If you use a separate Hydrogen/Oxygen propellant you need to think about using a certain amount of your half ton ammo hopper for the projectiles and a certain amount for the Oxygen and Hydrogen containers. I've no idea what those proportions might be.

Regarding the number of rounds carried, it might be a good idea to look at the mission of the fighter and weapons system.

Does the mission require sustained fire, or accurate sniping fire? How much capacity to carry ammo have I? You've already decided this by allocating a half ton of volume. These kind of questions should influence you in your design.

Good point on the propellant. I originally assumed that the slug thrower would be a heavier version of the VRF Gauss Gun but now I am not so sure. If the mount uses any propellent then it will cut down the available space for ammunition.

The fighter is an attack model intended to support surface operations or to target surface-mounted sensors in space combat. I think it might also have utility in an anti-missile scrrening role.

It is only 10 tons so there is limited space for ammo. The fighter has no robust life support, just the standard 4 days, no facilities, and a crew of one so mission duration is limited. I would guess a typical mission would not exceed 8 hours and much of that would be in transit to and from the target area.

Rate of fire required would depend on the target but I don't think sustained or sniping describe what I envision. Burst describes it best and the length of burst would depend on the target with anti-missile being a longer burst than when firing at a fixed surface target. Anti-sensor fire would depend on the size of the target - the sensor clusters on a SDB would be relatively small and require a short burst while strafing a cruiser's flanks to destroy sensors would be one long burst that could be described as sustained. Don't assume that the half ton hopper is decided. It is a guess that has to be tested to see if it is enough. That is the purpose of this discussion.

This imprecision is why I have been putting quotation marks around the word "shots" - what I want is a plausible average rather than a precise number.

 

[Epee]

The following is complete speculation:
In the vacuum of space you wouldn't need to purge the barrel after the first shot or two. A designer may want to take advantage of the greatly increased velocity for space combat while remaining content with sub-1900 meter per second velocities for atmospheric operations.

Since the current method of fueling a vapor or gas fed chamber is an internal combustion engine rates-of-fire around 6k RPM should be possible. Although heat dissipation will be a challenge, especially in space.

Highly compressed hydrogen (700 bar) contains over 45 times the energy of gunpowder per weight so the space savings, assuming you're happy with gunpowder velocities within an atmosphere, will be huge. Propellant mass, not including the mass of the tanks themselves would only require 5 to 10 percent the mass of the projectiles (this is assuming an equal mass of oxygen which could be substituted by breathable atmosphere planetside).

 

[Reban]

Good point on the propellant. I originally assumed that the slug thrower would be a heavier version of the VRF Gauss Gun but now I am not so sure. If the mount uses any propellent then it will cut down the available space for ammunition.

Ah true, slug throwers could indeed include gauss guns, I'd forgotten that. If you go back to GunMaker it is indeed possible to build gauss guns and gauss gatlings.

Either way I don't think you have to worry about propellant. A 37mm x 75mm round is very long for a chemically propelled round so that length can be explained as "the case" containing the propellant. As a gauss projectile it makes sense too, although usually the lenght to width ratio of a gauss projectile is between 5:1 and 10:1.

The fighter is an attack model intended to support surface operations or to target surface-mounted sensors in space combat. I think it might also have utility in an anti-missile scrrening role.

For ground support you can always design a GunMaker weapon and mount it on a Firmpoint or just for comparison purposes. I'm interested in the overlap. Either way since both Personal and Space Combat don't track ammo use, how much ammo becomes a designer's background detail.

It is only 10 tons so there is limited space for ammo. The fighter has no robust life support, just the standard 4 days, no facilities, and a crew of one so mission duration is limited. I would guess a typical mission would not exceed 8 hours and much of that would be in transit to and from the target area.

Using your own figure of 160 "shots" and assuming one "shot" per combat round we get: 160 times 20 minutes equals 3200 minutes or 53 Hours of fire!

This imprecision is why I have been putting quotation marks around the word "shots" - what I want is a plausible average rather than a precise number.

The above back of the envelope calculation is really meaningless as its forcing numbers into an abstract system.

Probably the better way of approaching this is; I have a high rate of fire gauss gun capable of firing variable bursts depending on the target, so how much ammo do I need to carry?".