[SPACESHIP] UT Weapons on a Small Spaceship.
 

I'm building a relatively small (30 tons) shuttle inspired by the Condor Shuttle in GURPS Space Adventure “Raid on Sterling” for the 3rd Edition, made mostly for atmosphere flight and reaching low orbits. It has a weapon but mostly for fighting on the atmosphere and not for Space Combat.

Besides the whole RoF issue, I find that the power of the Spaceships weapons is too strong for the purpose of the weapon itself that is more to fight against lesser targets than other Spaceships. I want to put a Heavy Chaingun, 15mmCL from UT in it.

How should I do that? Give the Shuttle a Cargo space and then apply the cost of the Heavy Chaingun?

Re: [SPACESHIP] UT Weapons on a Small Spaceship.
 

Just counting the gun plus ammo as weight against a cargo hold would be the simplest way. If it's mounted in a proper turret, I'd add the cost and weight of a Powered Tripod Mount (UT151) to cover that.

If you wanted to add in a gunner to control it, you could reasonably just install a second Control Room for the gunner, pay for the gun and mount, and assume the weight of the gun and a reasonable amount of ammo is included in the Control Room.

Consider that a major weapon system with a Very Rapid Fire gun has a 2.5cm (25mm) autocannon with 1400 rounds of ammo, doing 6dx6 pi++ damage with a RoF 100 and Acc 8 (including all fire control). I've a house rule that Spaceships weapons have a rate of fire of 1/10 as a base, going to RoF 1 for a RF weapon and RoF 10 for a VRF weapon when used in normal GURPS combat to tame the weapons a bit, and using this the 25mm cannon would have only RoF 10.

Compared to the above, a 15mm chain gun with mount coming to about 150 pounds isn't too far off, so it seems fine to me.

Re: [SPACESHIP] UT Weapons on a Small Spaceship.
 

36D6 pi++ it definitely too much. To be fair even the 30D6 of the Medium battery is too much (and again the RoF in atmosphere isn't officially explained in the rules at all so from where you got your 100? ) and let's not forget that those weapons have a supposed range of 3000 miles in the atmosphere against the 9000 yards of the Gatling gun.

Re: [SPACESHIP] UT Weapons on a Small Spaceship.
 

A turret should probably be capable of holding a weapon of mass equal to one-tenth of the equivalent cargo mass (to account for the ammunition, articulation, computers, power cells, stabilization, etc.). In the case of a SM+5 shuttle, a medium turret would probably be able to hold a 100 lb weapon, so an ETC Heavy Chaingun would probably not be unreasonable. Its Spaceships RoF would probably be Ultratech RoF×5, to account for 3+ seconds of aiming between bursts, so 60 rounds per space combat turn. If we assume 50% of the mass of the turret is ammunition, the turret could hold around 2000 rounds, so around 33 space combat turns of firing.

Re: [SPACESHIP] UT Weapons on a Small Spaceship.
 

Allocating an entire weapons system for weaponry in spaceships is actually arming it pretty heavily. A Major battery is enough to give a tank its main gun, and if building battleships you shouldn't allow them to use major batteries because then they would literally tip over.

Just allocating cargo space for the chain gun should work. If you want a fancy turret, figure out the weight for that: 200lbs or the weight of the gun again is probably a good starting point (whichever is higher).

As a note, spaceships guns don't scale down as fast as they should. I have an alternative SM to Caliber System for that. If you use a 1/3rd size system (spaceships 7) and a very rapid fire gun with the above table you have a 15 mm cannon with ROF 10 doing either 15d pi++ or 20d pi++ depending if you use the stingy damage calculation or the generous one.

Re: [SPACESHIP] UT Weapons on a Small Spaceship.
 

And how will you fire a gun in cargo without opening the cargo hold and ruining the aerodynamics of the ship? How do you avoid giving enemies a perfect interior shot into the ship? How are you actually aiming and loading the weapon? Batteries and turrets account for such things, cargo holds do not.

Re: [SPACESHIP] UT Weapons on a Small Spaceship.
 

How do you get that RoF of 10? At best you have an RoF of 5 definitely not 10.

Re: [SPACESHIP] UT Weapons on a Small Spaceship.
 

Sorry, you are correct. I've got an error stuck in my head where each level of rapid is x10.

Subtracting the weight from the cargo hold is not the same as sticking the gun in the cargo hold and using it from there. I agree that it needs to be mounted in order to be useful, and the way its mounted will effect both the additional weight cost and the circumstances of its use. I wouldn't require a spaceships systems turret, especially a full sized turret for a comparatively light gun. Having the turret weigh x10 the weapon weight is a touch excessive, especially when suggested caliber for SM+5 ships is 10cm.

Re: [SPACESHIP] UT Weapons on a Small Spaceship.
 

If you look at the table on Spaceships, p.58 you can see that each level of rapid fire gives x10 as many shots per turn as the last. As the 'Weapons in Ordinary Combat' box (p.66) does not mention any adjustments to RoF when switching to normal GURPS combat, most people assume that the RoF for a 20-second space combat turn would apply.

I choose to assume that the actual rate of fire is 1/10th as much as that, so normally a spaceship weapon fires once per 10 standard turns, in order to make spaceship weapons a bit less apocalyptic and more in line with the performance of Ultra-Tech's weapons.

Re: [SPACESHIP] UT Weapons on a Small Spaceship.
 

Reloading time for large caliber rounds is going be longer, though I think that the majority of the low RoF comes from the assumption of aiming in the Acc calculations. A 2cm gun (a VRF SM+5 Medium Weapon) is doing a minimum of 30d(2) pi++ against targets in normal combat, fires 5 rounds per second, and can accurately target objects from 100 miles away without halving damage. Such a weapon is capable of tearing up most targets fairly quickly.

Re: [SPACESHIP] UT Weapons on a Small Spaceship.
 

Actually, it must be firing more than 5 rounds per second, as SS explictly says it's allowing for 3+ seconds of aim. Thus it cannot be firing for more than 5 seconds in every 20s Spaceships turn, so it must have at least RoF 20.

The base RoF is at least 1/20. An 'improved' weapon has at least 1/10. A RF weapon must have at least RoF 2. An improved RF weapons has RoF 4+, and an improved VRF weapon RoF 40+.

So, my current game rule of 1/10, 1, 10 for normal RF and VRF is in error, and I'll be adjusting it, probably to 1/5, 2, 20 for the base weapons, and 1/3, 4, 40 for improved weapons.

Re: [SPACESHIP] UT Weapons on a Small Spaceship.
 

Of course, it's possible for those weapons to have ammo feeds or charging cycles that don't permit sustained fire at the maximum rates. Under the rules angle you're taking, it would be entirely possible that VRF weapons have RoF 20 but need 3 seconds downtime between bursts.

A different angle, obviously not authorial intent in writing Spaceships considering the order of releases and text, would use a couple bits from Tactical Shooting. Follow-Up Shots (p14) from a mounted weapon allows you to aim once and then pour on fire at full without stopping to aim again. You keep the Acc bonus for aiming, though I think not the bonus for extra turns of aiming. That loss, however, can be made up by a turret mounting getting a +4 bonus for bracing instead of +1 (p75). That would allow an interpretation where spaceship gunners aim for one second per target in a round and then fire at cyclic rate for the rest of the time.

Re: [SPACESHIP] UT Weapons on a Small Spaceship.
 

But it would actually have to be braced, unlike the weapon in the cargo hold example. Another thing to consider is ammunition. A 2cm VRF weapon takes up the equivalent of 1,000 lbs of mass and possesses 500 lbs in just ammunition.

Re: [SPACESHIP] UT Weapons on a Small Spaceship.
 

A) I don't believe anybody at all has talked about a weapon in a cargo hold, as opposed to representing a turret on the ship that way - which makes perfect sense since there's already a gradient between weapon batteries and cargo holds in the RAW.

B) Even if it was literally in the cargo hold, if you put it on any kind of mounting such that it is even possible to use, that would make it braced.