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Matching the Classic Traveller Tech Tree in GURPS

This article was originally posted to Freelance Traveller's web site before August 2002, and was reprinted in the April 2011 issue of the PDF magazine.

Explaining the Problem

GURPS Traveller represents a valiant attempt to convert the Traveller setting into the GURPS mechanics. Unfortunately, that doesn't mean it's perfect.

The GURPS tech system was never really designed for a multi-TL setting in which there is regular trade between regions of different TLs. It can be done, but the effects are occasionally odd. For example, electronic devices are usually both half price and half cost after one TL, and 1/4 after two. Given the exchange rates in Far Trader, this implies  that any sane GTL 10 world will prefer to import GTL 12 products rather than use GTL 10 products. This isn't canonical; most worlds in Traveller apparently prefer to mostly use local products. However, in order to make the use of local products rational, the exchange rates can't be anywhere near the Far Trader values; simply negating the cost advantage of higher TL implies an exchange rate of 4:1 between 10 and 12, and negating the quality advantage as well implies an exchange rate of somewhere above 10:1.

In many ways, that's realistic for a 2 TL difference; using the World Bank definitions, if 'high income' (developed nations) are TL 7, one can pretty reasonably argue for 'upper middle income' (e.g. Brazil) states at TL 6, 'lower middle income' (e.g. the Philippines) at TL 5, and 'low income' (e.g. most of sub-Saharan Africa) at TL 4-, and the per capita GNP ratio between high income and lower middle income really is around 10:1. However, Traveller canon doesn't imply anywhere near that much difference in wealth and power between TTL 15 worlds and TTL 12 worlds. For that matter, I'm not sure if the difference between Regina and Rhylanor is really equivalent to the difference between 1900 and 2000; I'd think more like 1960 vs 2000.

That would put TTL12-15 as a single tech level in GURPS. However, aside from conflicting with the assumptions of Traveller players, is this really that bad? There are ways of creating distinctions within a single TL, and the truth is, there are many GTL 11+ technologies that are vastly inappropriate for Traveller.

What TL is the Imperium, Really?

If you look at available Traveller tech vs GURPS tech, the maximum TL of the Imperium does not appear to be 12. Running through common equipment types, we find:

Armor and Materials: The best armor in Classic Traveller is bonded superdense, with 14x the DR per unit thickness of steel, and about 8x per unit weight. That's equivalent to a mass multiplier of .07, which is similar to GTL 10 advanced metal at .06. Material Tech: 10.

Biotech and Medicine: Traveller isn't historically big on biotech; there's little evidence of genetic engineering, so the GTL could be as low as 7. The exception is the terrans uplifting apes and dolphins, which sounds like GTL 10 or so. Traveller medical tech, on the other hand, is pretty good; with the exception of instaskill (GTL 11) most of the wonder drugs in UltraTech look reasonable, giving an overall GTL of about 10. One can argue for GTL 9; Traveller drugs tend to have nasty side effects, and biotech is not exactly common.

Computers: Classic Traveller computers are quite primitive, at roughly GTL 7. However, CT also had robots; it didn't have AI, but it had advanced near-AI computers and computers could become spontaneously sentient. This sounds like GTL 9.

Drives/Gravitics: CT space drives are largely equivalent to GTL 11 reactionless thrusters; thruster plates were later set at TL11. CT contragrav is more like a thruster plate variant than the amazing performance GTL12 contragravity, so the average GTL is probably 11. GTL11 includes some force field tech that's vaguely gravity-related (deflectors, force weapons) but inappropriate for Traveller.

Electronics and Stealth: Traveller doesn't have intruder chameleon or holobelts, and doesn't really have anything quite like a multiscanner, though neural activity sensors and densitometers have some similarity. On the other hand, it does have instant chameleon, various forms of stealth, pretty good personal sensors, and the like. It doesn't have neutrino comms, though it does have meson comms which are similar if vastly larger. This sounds mostly similar to GTL9.

Exotics: black globes are a primitive and poorly understood force field; since a normal spaceship force field is GTL11, this sounds like a TL 10 prototype of a TL 11 system. Nuclear Dampers are GTL15, putting them well outside the range of any other Traveller tech, but Traveller dampers are quite large. Meson weapons and screens are a Traveller-specific oddity with no obvious GTL, but the GT rules for them are not obviously bad.

Power: energy densities in Classic Traveller were on the order of 250 megawatts per dton; by Fire, Fusion, and Steel this dropped to around 80 megawatts per dton. Including fuel volume, the actual energy density is on the order of 40 megawatts per dton, and around 2 megawatts per ton mass. GTL10 fusion is 40 megawatts per dton (and has no fuel requirement), 10 megawatts per ton mass, which seems to be in the same ballpark at least. GTL11 has antimatter, which is explicitly beyond Imperial tech, but not that far, so GTL10 is probably correct.

Weapons: meson weapons have no exact equivalent in GURPS, nor do fusion weapons (the GURPS fusion gun is a gravitic device which is not exactly equivalent to the Traveller weapon), though the standard GT assumption that a fusion gun is a compact plasma weapon is somewhat plausible. All other weapons in Traveller are available by GTL 10 (X-ray lasers), and there are GTL 10-11 weapons (such as paralysis beams and force blades) that are not canon for Traveller. Once again, GTL10 seems about right.

Overall, it looks like the maximum GTL of the Imperium is usually 10,  rising to around 11 in gravitics, and down to around 9 in electronics and biotechnology.

Applying Tech Level to Prices

As discussed above, a difference of one GURPS TL makes a lot of difference in value. This can be handled by exchange rates, but produces a few weird effects, and is confusing. My solution is fairly simple: list all prices in Imperial credits, which are considered to be prices on the interstellar market. For GTL10 equipment, use the list cost; for lower tech equipment (note: this means the item is actually built to lower-tech specs), multiply cost by 0.3 for GTL9 equipment, 0.1 for GTL8 equipment, and 0.05 for GTL7 or lower equipment. Thus, for example, an ACR (GTL9, $1,274) is actually Cr 380, while a gauss rifle (GTL10, $3,029) remains at Cr 3,029.

These prices are in Imperial Credits, which is usually workable enough. However, on a world with relatively low trade, many imported items may be hard to find, or at a substantial markup; on a world that wants more trade, the buying power of Imperial Credits may be increased (on the minus side, CrI may be rather difficult to obtain). The degree to which this is true is up to the GM, though in general the effects should be more visible on worlds that are low population or low tech. Worlds with low grade starports will usually have quite limited supplies of CrI, but may not be very interested in acquiring more.

For worlds in the interstellar community, per capita production may be estimated per the table below. Note that one CrI should be interpreted as around $20 in modern currency, making a TL 7 world similar to a modern western state, and a TL 15 world immensely rich by modern standards.

0 1-3 25
1 4 50
2 5 100
3 5 150
4 5 200
5 6 300
6 6 500
7 7 1000
8 8 2000
9 9 3000
10(A) 9 4000
11(B) 9 6000
12(C) 10 8000
13(D) 10 11000
14(E) 10 15000
15(F) 10 20000
16(G) 11 30000

What Goods are Available at What TL

While Traveller TLs from 12 to 15 are fundamentally the same TL in GURPS, there is some distinction in Traveller. This is handled by limiting which GTL 10 technologies are actually available. The normal rules are as follows:

At TL 16, all GTL 10 options are available; a reasonable subset of GTL 11 equipment is available at 4x cost.

At TTL 15, all GTL 10 options are available. GTL11 regular and super thrusters are available. Fusion power uses GTL10 stats, but is double cost ($100/lb). Prototype GTL 11 devices may exist (as per TTL 16), but are not on the general market, and generally cannot be purchased.

At TTL 14, power plant size increases by 50%, cost is multiplied by .75 ($50/lb). Meson communicators are unavailable, meson weapons are limited to 100T weapon bays. Genius computers are not available. Max jump is 5, max G-comp is 5.

At TTL 13, advanced armor and structural materials are unavailable; personal armor should be limited to TL 9 equipment. Electronic devices must be purchased 'cheap', with doubled size and half cost; many other components should also be cheap. Max jump is 4, max G-comp is 4. Fusion weapons are only available as large weapons (6,400 kilojoules and above).

At TTL 12, X-ray lasers are unavailable, max jump is 3, max G-comp is 3. Power plant size is doubled, cost is halved ($25/lb). Meson guns are only available as spinal mounts.

At TTL 11, most equipment is only available with GTL9 stats (but use the normal 30% cost modifier for GTL9 equipment). GTL11 regular, but not super, thrusters remain available. Fusion plants with TTL12 stats remain available through TTL 9. Max jump is 2, max G-comp is 2.

At TTL 10, thrusters are no longer available, but contragravity is.

At TTL 9, advanced GTL9 materials are no longer available; personal armor should use GTL8 stats, at the normal 10% of cost. Plasma weapons are no longer available.

Specialized Traveller Tech

Contragravity (TTL9): Contragravity is the lower-tech equivalent to reactionless thrusters; a CG drive has twice the thrust of an equivalent reactionless drive, but is limited to a total thrust of 200% of the local gravitational field. Available as regular thrusters at TTL9, super thrusters at TTL12.

Meson Guns (TTL11): Meson weapons have twice the cost of a particle beam of the same TL, and are otherwise identical.

Meson Screens (TTL12): Meson screens are force field variants that protect from meson weapons. Weight is (DR * area)/10,000,000 tons, price is $2 million per ton, power consumption is 40 megawatts per ton. Maximum DR is 10,000 at TTL 12, 20,000*(TTL-12) at higher TLs. Available 'cheap' at TTL13-.

Nuclear Dampers (TTL12): Per mile of radius, 10 tons, 2 dtons, $2 million, 800 MW. Maximum radius is 1 mile at TTL12, 3 * (TTL-12) at higher TLs. Available 'cheap' at TTL13-. May be very small if desired; a sphere with a diameter of 1' is 1 lb, $100, 80 kW.

Neural Activity Sensors (TTL13): Treat as a GTL9 bioscanner at TTL13, GTL10 at TTL15.

Gravitic Scanner (TTL12): Detects active gravitics; use the stats of a radscanner, the effects of a gravscanner. Like most electronics, must be 'cheap' until TTL14.