GURPS Spaceships and Traveller

[Rupert]

Originally Posted by Fred Brackin

I knew there were reasons I never played (or even bought more than a sample for) those editions. The gross breaks in ship capability made possible by that rule would be one of thsoe reasons.

Funnily enough, in MegaTraveller they needed to do this to fit everything in. In MT the Type S Scout is a TL15 design because you can't make everything fit at lower TLs. Not the best design system ever.

[Rupert]

Originally Posted by Pomphis

Thanks. My idea does reduce the size of the jump drive, yes. As you noted, some systems are "bigger" in Spaceships, especially armor. Even minimum armor takes 15% of the ship´s mass and it´s almost impossible to have more than 4 times minimum armor on even the heaviest warships. Compare that to the DR 100 minimum in GT and the DR 130,000 of a Tigress.I am still wondering whether I should permit force screens to help warships get decent dDR. Using one system as jump drive with only cost and power requirement changing by JNo is a good idea.

With smaller systems, minimal armour is only 5%. I use the common house-rule that armour can be spread over the whole hull, no matter where it's placed, as well.

[Rupert]

Originally Posted by Pomphis

The J-2 Trader is not the problem. The problem is the Azhanti High Lightning with J-5 (11+ systems), 2 G (1 system), armor (3 systems), a spinal mount (3 systems), other weapons (1 system), hangar (1 system), control room (1 system), habitat (1 system), nuc damper (1 system), meson screen (1 system), and 24 systems even without a power plant.

Well, unless the spinal mount really is that huge in the original, a fixed major mount is generally sufficient. The AHL's spinal mount just happens to come in at 5% of its displacement, so calling it a major mount is probably okay.

As for the nuclear damper - you don't need a full-sized one, as even a proximity explosion in SS is assumed to be under 100 yards away. One suited to a SM+6 ship masses 5-tons and can fit in a 'cabin' space in the habitat. Cheating, but I don't see why you'd need a bigger one. As in HG they aren't terribly big (though they do use enough power that small ships probably can't power them) I don't think this ruins anything. Meson Screens should be full-sized, I think (in HG they too were small, but they did use a lot of power, and power requirements scaled with ship size).

[Rupert]

Originally Posted by AlexanderHowl

Strangely enough, I usually design spacecraft on the assumption that each metric ton of mass provides sufficient space for approximately one metric ton of liquid hydrogen (~14 cubic meters per metric ton) in order to make them compatible with some of the existing real spacecraft designs. It actually fits fairly well with the dimensions given in Spaceships. Since armor takes up very little space (0.125 cubic meters per metric ton for steel to 1.1 cubic meters per metric ton for ice), any spacecraft with armor will likely have more internal space that their mass indicates.

Once you start putting armour on a spaceship, you're not looking at one that's built like a modern one at all.

In my opinion, 5 tons (or tonnes, or long tons, it doesn't really matter at this level of precision) per 14 m^3, which happens to roughly be 100 cubic feet per ton, or a good rough guide. It's been used as a rough guide for ships and general loose cargo for a very long time, and it's been useful over that time. Spaceships of the sort Traveller imagines are built much more like sea-going ships than modern space vessels and stations, so it's suitable for them (fuel tanks aside).

A streamlined SM+10 spacecraft is probably going to be a cylinder 200 meters long and 20 meters in radius, giving an internal volume of ~168,000 cubic meters (assuming the top 50% is conical). An unstreamlined SM+10 spacecraft is probably going to be a cylinder 100 meters long and 20 meters in radius, given an internal volume of ~126,000 cubic meters. If they both have three components of steel armor, they have 1500 metric tons of steel, which only takes up <200 cubic meters (sloping allows the greater volume of the streamlined vehicle to receive equivalent DR to the unstreamlined vehicle). Of course, this means that the steel armor is only 13 mm thick, which means that it is a very strong steel (something like 2800 Maraging Steel).[/QUOTE]Sloping only works if you can be sure that the attack is coming from a particular direction. There's a reason SS assumes that streamlined ships will end up with less DR for the same armour mass.

As for the armour - you're asking it to be 2-3 times (depending on which dDR you use) as good as RHA. RHA isn't the best armour steel in the world, but it's not that bad.

If you assume a SM+10 cylinder about 300 feet long about 65 feet in diameter, with a volume of about 955,500 ft^3 (within 0.5% of my target of 1 million cubic feet for 10,000 tons). It has a surface area of about 68,000 ft^2. 1500 tons (3,000,000 pounds) of steel over that area gives 44.1 pounds per square foot, or about 1 inch (and DR 70). That's 'close' to what the tables in SS gives. It also doesn't involve a very fat cylinder that probably warrants +1 to it's size modifier for being blocky.

A Traveller starship with significant jump range will be bigger and less dense, and have more surface area to armour, but that's something that SS doesn't model (there are optional rules in Pyramid #3/34 for ships having less volume and thus being harder to hit and having more DR if they have a lot of dense armour).

[Pomphis]

Originally Posted by Rupert

Well, unless the spinal mount really is that huge in the original, a fixed major mount is generally sufficient. The AHL's spinal mount just happens to come in at 5% of its displacement, so calling it a major mount is probably okay.

As for the nuclear damper - you don't need a full-sized one, as even a proximity explosion in SS is assumed to be under 100 yards away. One suited to a SM+6 ship masses 5-tons and can fit in a 'cabin' space in the habitat. Cheating, but I don't see why you'd need a bigger one. As in HG they aren't terribly big (though they do use enough power that small ships probably can't power them) I don't think this ruins anything. Meson Screens should be full-sized, I think (in HG they too were small, but they did use a lot of power, and power requirements scaled with ship size).

Yes and thank you, but even so I am still at 21 systems before having a power plant. I will probably house rule that in addition to smaller systems (SM-1) much smaller systems (SM-2) are possible. The 10:1 ratio is even easier than the 1:3. That will help with the ND, and for the MS I may use your jump drive idea: the screen generator can be small, but it needs power as a normal size force screen.

[Aldric]

When I was looking at Spaceships to design a ship for a setting I doubt I'll ever play, I simply decided armor was not a system. Most ships would just get a basic armor layer, with ships designed for combat might have double or triple layer, some ships might be unarmored, or have unarmored sections.

It should probably affect other statistics, but since I was already looking at superscience for drives, it's not much of a problem

[AlexanderHowl]

From a realistic point of view, not having armor is a problem because armor is the hull of the spacecraft. In general, I believe that every spaacecraft should have at least one armor system, just to represent the mass of the hull, though a soft landing system could represent more disposable elements of a hull. In any case, any DR should either come from armor (or force fields in a superscience setting).

When it comes to doing spacecraft for Traveller, small systems are a must because of the nature of the setting. A Jump-1 drive would be a SM-1 system, meaning that a Jump 6 drive would be two SM systems. A Jump drive requires hydrogen equal to the size of the drives each jump (as coolant, not fuel, because of the simple fact that produce 100s of PJ of hard gamma and neutron radiation per metric ton of hydrogen spent would make life impossible for anyone in the spacecraft), so a Jump-6 drive would require two SM fuel tanks of hydrogen per jump. A Jump-6 spacecraft with decent endurance could have 3 armor, 2 jump drive, 1 control room, 1 habitat, 8 fuel tanks, 1 reactionless, 1 reactor, 1 weapon, 1 hanger, and 1 cargo, for 20 systems.

[Agemegos]

Originally Posted by AlexanderHowl

From a realistic point of view, not having armor is a problem because armor is the hull of the spacecraft.

Sez who?

Real spaceships are unlikely to have hulls, because they don't need buoyancy. They are more likely to consist of components attached to a structural frame.

Ships need hulls. Aircraft need fuselages. Spacecraft need frames.

In general, I believe that every spaacecraft should have at least one armor system, just to represent the mass of the hull

I don't believe spaceships need to have hulls. Furthermore, I believe that the mass of necessary structural supports ought to be implicitly included in the masses of the systems, since every system needs support anyway. I think treating structural support explicitly as an armour system instead of implicitly in the masses of the systems and the stats of the engines gives the designers one less system to work with, thus making the rules even coarser-grained, and does not compensate by improving things in any way.

In any case, the actual rules require a streamlined spacecraft to have at least one Armor system (for its front hull or central hull) — see Spaceships p. 9 under Spacecraft Hulls Streamlined. That implies that unstreamlined spacecraft do not.

[Agemegos]

Originally Posted by Pomphis

I will probably house rule that in addition to smaller systems (SM-1) much smaller systems (SM-2) are possible.

I think it's implicit that the "smaller systems" rule can be used recursively.

[AlexanderHowl]

Open frameworks can be mimicked through using external clamps. For example, a SM+10 LASH can have 3 armor, 1 control room, 1 habitat, 2 jump drives, 1 hanger, 5 external clamps, 4 fuel tanks, 1 reactor, and 2 reactionless. It can function as a 60,000 ton spacecraft when fully loaded, and it is capable of carrying 50,000 tons of cargo barges (3 armor and 17 cargo holds).

Without a hull, you would not have mass for cargo doors, air locks, and the other free systems of the spacecraft. Of course, you could instead have a structural component equal to SM-1, but it is just easier to assume that all of the mass of the free systems are part of the armor. I do think that there should be a Reinforced Structure component though that would give Damage Reduction equal to (number of Reinforced Structure components × 2).