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Tweaking the Jump Drive

"Jump drives are rated from 1 to 6: the number of parsecs which can be travelled in one week. Actually, making any jump takes about one week, regardless of the distance travelled."
-- Classic Traveller, Book 2 - Starships, Travelling chapter

"Jump fuel under the formula (0.1MJn) allows one jump at the stated level. Ships performing jumps less than their maximum capacity consume fuel at a lower level based on the jump number used."
-- Classic Traveller, Book 2 - Starships, Design & Construction chapter

That is the classic Traveller jump drive, moving the starship the jump number of parsecs per week (i.e. hexes per turn) at a fuel consumption of 10% of the ship's tonnage per jump number.

The characteristics make sense from a game-mechanics point of view, given GDW's previous track record of straight wargames. Jumps all take the same time (a week-long strategic turn) and move in specific one-parsec increments (hexes on the strategic map). The fuel consumption provides a practical handicap in the starship design system to constructing very high-jump ships.

However, when Traveller premiered in 1977 (before the introduction of the official "Third Imperium" campaign universe), most game masters were used to compulsive tinkering with homebrew campaign backgrounds. This resulted in a lot of homebrew rules tweaks, including those for jump drives. Here is a compilation of jump drive tweaks accumulated over the years, with sources when known:

Tweaking Fuel Consumption

The most common tweak was to decrease the jump fuel consumption to allow long-range cruising, reducing or eliminating the need to refuel (or skim) each system. At the time Traveller premiered in 1977, most gamers were already familiar with Star Trek, and Star Wars had hit the theaters only months before; neither of these familiar far-future starship paradigms included frequent refueling.

The convention established by game masters during Expeditions Ltd's sojourn with Traveller (Wayne Shaw and Don Rollins, Cal State Fullerton, Fullerton, California, 1977-78) was to reduce fuel consumption by a factor of 10 -- a jump consumed only 1% of the ship's tonnage in fuel per jump number. Unfortunately, this completely eliminated the handicap high Jump puts into the compromise of ship design, begging the question of "Why not, then, allocate 10 jumps worth of fuel in all ship designs?"

Also in the late Seventies, Steve Marsh in his "Chain of Stars" campaign notes used a less-severe version of this: reducing fuel consumption by a factor of 2, on the rationale that "you could always jump back."

A variant of this was the idea of "Super-refined Fuel" (from an unknown non-GDW supplement, circa 1978-80) -- very expensive high-grade fuel which halves fuel consumption.

Looking back on all of these, a compromise solution would be to have refined fuel consumed at the 5% half-rate and unrefined fuel at the full 10% rate, further increasing the contrast between the two. Ships would still need to allocate the 10% per Jump in design, because of the possibility of using unrefined, but would still get the range increase ("you can always jump back") when using refined.

Another alternative is to change the fuel consumption for higher jumps from a linear progression to some other progression, making high jump speeds much more economical. For example, a square-root function (keeping the 10% for Jump-1) would progress like this:

Jump Number Tech Level Fuel Consumption
Stock Square-root
J-1 9 10% 10%
J-2 11 20% 14%
J-3 12 30% 17%
J-4 13 40% 20%
J-5 14 50% 22%
J-6 15 60% 25%
J-7 16 70% 27%
J-8 17 80% 28%
J-9 18 90% 30%

Freelance Traveller editor Jeff Zeitlin has proposed an alternative jump drive (the Lyman Drive) with a similar concept to the above but whose fuel consumption was based on the frequencies of photon emission of excited hydrogen atoms.

Tweaking Jump Speeds

Trimmable Duration -- what if all jumps didn't take a week? What if jump number indicates an actual FTL speed, like Star Trek's Warp Factors? With this tweak, a jump number moves you any number of parsecs at that "jump speed"; a ship with a Jump-4 drive could jump four parsecs (taking one week), three parsecs (taking 3/4 week), two (half a week), or one (1/4 week).

This breaks down the smoothest around TL12 (a decent Tech Level for a "low-tech" Classic Traveller campaign):

Jump 7+ -- though in official Traveller, "jump speeds greater than Jump-6 are impossible", High Guard's progression of jump drives could be extended to Jump-7 at TL16, Jump-8 at TL17, etc. Fuel consumption would become impossible under Classic Traveller unless some of the Fuel Consumption tweaks (the ones reducing jump fuel consumption) were also used or Megatraveller's TL16+ antimatter engines (with their vastly-reduced fuel consumption) are invoked. The latter would make TL16+ ships (usually Ancient artifacts) that much more exotic. And desirable.

Superjump drives -- though "jump speeds greater than Jump-6 are impossible", a misjump roll could theoretically move a ship 1D x 1D hexes -- an effective speed of up to Jump-36! One speculation (never tried in any campaign, as far as I could tell) was to have an ultra-tech "Superjump" that moved the ship at up to the square of the superjump drive rating -- sort of a "controlled misjump". Such "Superjump Drives" would probably be larger and more expensive than standard jump drives, and available only at much higher tech levels (Say, Superjump-2 (aka Jump-4) at TL15, SJump-3 (Jump-5 to 9) at TL16, SJump-4 (Jump-10 to 16) at TL17, etc.)

"Superjump" was originally proposed to give reasonable travel times over really huge interstellar empires (Third Imperium-size or larger - remember, both Star Trek and Star Wars were big-universe paradigms of the time). Especially since there was a "can-you-top-this" tendency among some game masters and game designers to have the biggest, highest-tech, and most powerful campaign universe (for example, FGU's Other Suns had FTL speeds measured in effectively tens of parsecs per hour).

Tweaking Jump Effects

Jump Shock (aka "Bamf-and-Barf") - Physiological effects ("Jump Shock") from entering/leaving Jumpspace (or at least on a misjump) were sometimes added (and even became semi-canonical in the game's TNE incarnation). The most common of these jump-shock effects was some form of nausea or motion-sickness effect (pushed to the limit in the above-mentioned Other Suns), hence the common name of "Bamf-and-Barf".

"Jump Time Dilation" -- Around 1980, Wayne Shaw related to me some variant jump drive effects he had heard about (unknown source, about 1979-80) -- a jump takes one week in the outside universe, but no time passes aboard a ship in Jumpspace. As far as the crew knows, they power up, engage the jump drive, and BAMF! They're parsecs away and a week later. This would result in something like the famous "time dilation" effect of high sublight speeds, "but for a completely different reason." This could be used to add unique "flavor" to the campaign; the only in-game problems would be having to re-sync the ship's clocks at each port and having to keep two ages -- chronological (outside universe) and biological (taking the no-time-in-Jump effect into account) -- on the character sheets.

Weird Misjump Effects -- The basic Classic Traveller misjump kicks the ship out in a random hex anywhere within 36 hexes of the start point, with a small chance of the engines blowing up if things went really bad. (In actual play, most game masters were merciful and dropped you into a hex with a system, giving you a chance to re-jump and find your way back to civilization; otherwise, it would have been "everybody roll up new characters" with a good chance of a "player mutiny".)

Adding additional misjump effects was a way to introduce "weird" or "horror" elements into the normally hard-edged and straightlaced Traveller paradigm. ("What lives in Jumpspace? We don't know, and we don't want to know... Cthulhu...") The most threatened of these (but never to my knowledge actually used) involved the "caught in the push" effects from "The Philadelphia Experiment".

Background: "The Philadelphia Experiment" was a UFOlogist urban legend about secret force-field experiments during World War 2 that resulted in accidental teleportation -- and bad misjump effects. Like "you go into Jumpspace, but you never quite come out" -- spontaneous teleportations, interpenetrations, insanity, and spontaneous human combustion. All covered up by The Government Conspiracy, of course. An overview of this urban legend can be found at http://www.ecafe.org/philadelphia/index.htm (This link appears to be defunct. Corrected info appreciated) or http://unmuseum.mus.pa.us/philex.htm, with a more detailed writeup at http://www.softwareartist.com/philexp.html and evidence that the "Allende Letter" that started it all was a hoax at http://www.parascope.com/en/articles/allende.htm.

A recent development along these lines came from Chris Litzau, game master of a non-Trav space campaign (St Clair, Michigan, c. 2000) - he introduced a Superjump drive (much faster than the standard Jump drive in the campaign) with much worse misjump effects, using the SF/horror movie Event Horizon (Paramount, 1997, available on video) as a model.

Event Horizon is basically an SF version of the horror theme of "the evil place" -- in this case, a starship which disappeared years ago testing a new type of Jump drive reappears as a derelict. When a patrol ship docks to investigate, they find out the hard way that the deserted ship is haunted/"possessed" by whatever happened during the misjump. Chris's commentary:

"The movie shows a pretty good example of how a bad (but not catastrophic) drive failure can turn out. On a catastrophic one, the crew would have returned as well - as Cenobites! (From Clive Barker's Hellraiser series - KP) For added nightmares, go through the 'flash frames' near the end for some disturbing imagery."

Tweaking the Jump Map

The original (1977) printing of Classic Traveller Book 3 --Worlds and Adventures -- included the following table for randomly-rolling jump routes between two systems:

Index the two ports at each end of the route and their distance in parsecs. Roll 1D; if the number rolled is greater or equal to the number on the table, a jump route exists between the two. A "1" indicates a jump route will always exist between these ports; a "-" indicates no jump route can exist. To simplify mapping, do not roll redundant routes (such as two ports two hexes apart which are already connected by two one-hex routes).

Starport Types Hexes Distance
1 2 3 4
A-A 1 2 4 5
A-B 1 3 4 5
A-C 1 4 6 -
A-D 1 5 - -
A-E 2 - - -
B-B 1 3 4 6
B-C 2 4 6 -
B-D 3 6 - -
B-E 4 - - -
C-C 3 6 - -
C-D 4 - - -
C-E 4 - - -
D-D 4 - - -
D-E 5 - - -
E-E 6 - - -

At the very least, this table allows "by-the-dice" placement of X-boat/Courier networks and established commercial/communication routes, giving the "terrain" of space within the subsector/sector. The arrangement of these randomly-rolled routes can suggest political divisions (two webs of routes with no connection are probably two different "pocket empires"), identify choke points and bottlenecks, and give a feel for the flow of commerce in and through the area. (And since navies exist to protect that commerce, the strategic situation for military campaigns.)

But the implication was that these jump routes were not just well-travelled or X-boat routes, but had something to do with jump drive operation itself. Perhaps heavily-travelled routes wear a "groove" in Jumpspace that eases the jump for following ships...

Do you have a Jump Drive tweak that you want to share? Send it to Freelance Traveller at submissions@freelancetraveller.com. We will post them to our Shared Tweaks page.