• Welcome to the new COTI server. We've moved the Citizens to a new server. Please let us know in the COTI Website issue forum if you find any problems.
  • We, the systems administration staff, apologize for this unexpected outage of the boards. We have resolved the root cause of the problem and there should be no further disruptions.

Jump Space concepts and questions

Hal

SOC-14 1K
Hello Folks,
I figured I'd toss out a few random thoughts here and get some people's input on them. Perhaps some kind soul will have figured out an answer to this and tell me where my thinking has gone wrong.

Jump space exit points do NOT rely upon having a planetary or solar mass handy to precipitate them out of jump space.

Given:

1) Jump durations are 168 hours plus or minus 10%. This gives us a temporal displacement of 151.2 hours on through 184.8 hours. This total time displacement is such that there are 33.6 hours (or 120960 seconds) between early or late exits from jump space.

Fact:
Earth travels around the sun at a speed of 1 AU x 2 x Pi / (365.25 days x 24 hours x 3600 seconds/hour) or roughly 18.5 miles per second. Earth's diameter is roughly 7926.397 miles with a 100 planetary diameter range of 792639.7 miles.

Question: how long of a window does a navigator have when plotting for an exit point that REQUIRES earth's physical presense to precipitate him out of Jump space?

Answer: The navigator has to aim his ship such that it coincides with that mystical 100 diameter limit. The Navigator must also plan on his ship exiting where the planet will BE in the future rather than where it is NOW (after all, the trip in Jump space lasts 168 hours +/- 10%). As a consequence, the window of opportunity to "hit" his targeteted destination is equal to the 100 Diameter radius divided by the planet's speed to Move 100 diameters. Dividing 792639.7 by 18.5, we get some 42845.23 seconds worth of time before Earth has moved 100 planetary diameters. This is roughly 11.9 hours of window time. Keep in mind that I have kept this example simple because the sun itself is moving at a rather fast speed which adds to the problem and the earth's orbit is not a perfect circle - which means at times its speed relative to the sun is slower and at other times, relatively faster.

Problem: what happens when a ship targets for the earth's future position, and the ship is either 11.91 hours early or 11.91 hours late? Sure, the ship *might* be "caught" by the sun's 100 diameter radius, but what if it isn't? What if instead of aiming for earth, the pilot had been aiming for Jupiter - whose 100 diameter limit is no where NEAR the sun's 100 diameter limit?


Tentative Answer: if it is required to exit at the 100 diameter limit of a star or a planet or anything else - that "variable" aspect of 10% is more than enough to Miss a planet or star (just based on the star's velocity alone!). This "jump space" model has some flaws in it that make it unsuitable for use with Traveller as we know it. Oddly enough? I've looked through the rule books of the following:

GURPS TRAVELLER: jump dur = 168 hours +/- 10%
TRAVELER TNE: Jump Dur = Roll 1d6, 6,7, or 8 days
Classic Trav: Jump dur = approximately 1 week
Megatraveller: Jump dur = 1 week

I don't know where my copy of T4 Traveller is, so I can't include that in it.

All in all, I almost wish that Traveller had just flat out said:

a) jump duration is based on pilot skill. If Duration is variable - then make it so that good navigators are worth it. Since the limits are +/- 10%, why not make it so that pilots who attempt to shave off time can make the effort to shave off time and if they fail, LOSE time instead.

b) keep jump space duration relatively stable such that instead of missing by up to 16 hours either way - make it so that the miss is by a matter of a few hours at most either way (closing the missed window of opportunity flaw pointed above)

c) make Jump space duration exact and predictable. Duration is precisely 168 hours and any longer duration an obvious sign of misjump. Either that, or make the misjump duration exactly 168 hours as well - making the jump space physics an unchanging one.
 
I don't remember ever having read anything that said a jump exit MUST be at the 100 diameter limit.

I've read that if a jump exit point is too close to an object, it will be pushed out to the 100d limit.

But you can calculate your jump exit point to be just about where you want it, and as far away from any objects in space as you want.

I can remember off the top of my head several references to exploration expeditions jumping into empty space, with no objects around. They didn't require some object to help pull them out of jump space.

And the military applications: There are several reasons military vessels wouldn't want to be at the 100d limit of an object when exiting jump. Maybe an attack fleet is gathering in an empty hex to organize for a jump into enemy territory. Maybe a scout ship wants to do some system recon, and enters the system at its furthest reaches so it can check things out undetected and unobserved.

There are references in canon of ships jumping into empty space and leaving fuel caches there for later use. There were no objects there to precipitate an exit from jump.
 
In The Traveller Adventure for CT one of the scenarios, Trade War, involves ambushing an enemies' ships in deep space at a secret rendezvous, the coordinates of which were obtained by industrial espionage. It is referred to as a breakout point. No mention of any gravity wells.
Come to think about it, in the same adventure supplement the PCs get a set of demountable tanks for their fat trader which allows them to use a deep space jump to get off a jump main. Once again no mention of a deep space object.
 
I don't recall anything about there needing to be a body to get out of jump. Though if you are a merchant you would want to end up as close to your target planet as possible. (Travelling at 1G accelleration can take you a while to get there.) Even a trip to the local gas giant can take quite a while. It is all about how fast you can get turned around.

I will admit I had never taken into account that planets and stars are moving. (And at a fairly swift pace.) For simplicity, if you were to jump long (Temporally if that is a word.) or short, if you had a planet targeted the gravity could still dump you about where you wanted to be.

I personally think there is already too much math involved in space travel and believe it would take away from adventuring. (Just like I would prefer the economic model to actually work so you don't have to spend much time thinking about it.)

But you do raise a valid point. Since Jump Space physics is so ill defined I guess you can makethe specifics work anyway the GM wants. (AFAIK it is intentionally poorly defined and little understood by both players and Citizens of the Traveller Universe.)
 
Jump drives have capacitors. Recycle it and use it for power during the time spent in Jump Space. (Ie. to run the lights entertainment systems, possibly even the ships computer.) You would use less fuel in jump space than in real space (since you aren't using the maneuver drive) anyway. Perhaps Jump space would be no fuel use at all. Or as in Heinlein's Friday, or Weber's Honorverse, perhaps Jump Space is a big heat energy sump.

Originally posted by Hecateus:
How do ships handle the heat generated from and during jump?
 
Since I think I was the one who brought up this thorny little issue....

1. We know a misjump can take you a long distance, or virtually no distance, but the distance it takes you is not relative to time in jump.

2. We know that normal jumps are about 151 to 185 hours in length. As I pointed out elsewhere and you bring up here, things like planets move a LONG distance in this model, as probably do satellites. This could change 100D limit locations, etc.

3. We know you can choose your exit vector.

4. We know that you come out, more or less, where you want to be.

This suggests some things:

1. In Waterborne Navigation, we have a concept of 'speed made good', that is to say regardless of how fast you actually were moving, what was your effective speed over an interval (this accounts for the fact you may have thought you were moving 4.5 knots, but due to leeway, currents, etc, you actually only made 3.5 knots).

In Jump terms, SMG for a jump can obviously vary from very fast (36 hex misjump!) to very slow (in system jump). So, 'velocity' such as the concept might apply, in Jumpspace is not constant.

2. Jump space arrival can be defined in two separate fasions: In terms of absolute coords (allowing you to jump into deep space) and in relative terms to a body that exerts influence in Jumpspace. This allows you to arrive near the 100D limit (if you don't blow your roll) of a moving object like a planet - moving both orbitally and as the galaxy itself rotates.

I think that will neatly explain how you can arrive within a close proximity to a planet despite the 20% variance on arrival time. The time is a product of the speed (a bit random) but the arrival point is 'with respect to target body'.
 
I'd always envisioned the return to normal space happened well above or below the plane of the ecliptic, in reference to the target star of the system. A binary or trinary arrangement complicated things a bit, requiring the precipitation to normal space to occur well outside the 100-diameter radius of the nearest stellar body (with the jump bubble being nudged further "north" or "south" according to the system's makeup) which took care of disastrous misjumps that might have resulted in the precipitation inside a star or planet.
A good navigator simply made transits to and from planets and starports easier and more efficient by having the vector pre-plotted so the ship's own delta-v wouldn't require an enormous adjustment upon arrival.
I based this on several assumptions, one being that there was much less of a chance of an accident above or below the ecliptic in highly-visited systems where ships are popping out of jumpspace almost willy-nilly. Jumping OUT of a system was handled anywhere a ship could grab enough distance from a gravity well.
 
Has anyone ever run a scenario where a world is Jump 1 + long M drive distance (say 50 days in M drive). This could be for various reasons, e.g. jump space only opens at a particualr place, the system orbits the weaker of a trinary star and J space open up in the prominent but worldless star).

If this does not offend J space concepts, its a good way of getting vast space stations in for refueling (and adventure!)
 
Hi,

once upon a time I had a setting in a Megabelt, at least a planetoid belt stretching from orbit 5 to 15 also extending quite far away from the plane of ecliptic.
The whole thing was of course motivated by Beltstrike.
Regarding in-system traveltimes it was a world on its own, with lots of different mining factions, abadoned mining areas, death zones, treasures etc.

The players primary goal was to find a fabulous, extraordinary large base inside an asteroid. At least the asteriod was a starship itself, equipped with (non-ancients) high TL stuff.
Secondary goal was to get along with this 1 mile long rock, without having it conficated by the Imperium, stolen by a faction etc.

Regards,

Mert
 
My cr0.02:

Certian conceptsd related to jumpspace are canon to the OTU (MTU != YTU != OTU)

Deep space jumps are possible given the technology of the 3I- the Battle of the 2 Suns at the end of the 4fw is an example of this as are the 'secret way stations' on the maps in the Regency Sourcebook. (Adventure 1 though to TNE).

You don't *need* a mass to percipitate you out of jumpspace. A sufficient mass *will* percipitate you out of jump space - with varying effects.

You cannot 'choose' your exit vector except in the fact that exit vector always equals entry vector - Book 5 iirc.

I don't have a citation for either of these but I'm pretty sure they're canon:

Insystem jumps are quite common for any trip that would take longer than a week or so - this includes trips across the system (avoid the primary's 100D limit!), to the outer system or to distant stellar companions. The Solomani used J drive for insystem hops well before discovering its interstellar capabilities.

Under certian rare circumstances you can misjump in time as well as space - i.e come out 500 years in the future but exactly where you intended.


Disclaimers:
Yes there are 'cooler' ways to handle all of the above. I have probably used some of them in my games over the years. Traveller Canon acts as a common frame of reference.

Yes - this definitely ignores the fact that things move - stars have proper motion (sometimes quite a bit) relative to each other and +-33 hours can make a huge difference in where you come out of jump space in relation to your desitination world.

Yes - conservation of mass and energy go right out the window when you play with jumpspace.

Handwave the above as you will


Personally I *like* a TU in which there must be a large mass at the exit point to percipitate an object out of jumpspace. It tightens up the strategic possibilities of interstellar warfare (chokepoints etc.) and ensure that you cannor misjump into the middle of interstellar space ("Okay guys - I hope we spent enough on these low berths - it's going to be a looonnnnggg nap")

Perhaps someday I'll sit down and write one :D

ciao

--michael
 
Back
Top