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Jump Proceedure


I was wondering something about jumpspace courses, specifically about a ships point of entry/exit to jump space. In OTU in a settled patroled system are ships required to use particulare patch of space to jump out or more importantly jump into? It seems to me it would make customs, search and rescue, and system defence alot easier since there would be defined shipping lanes to patrol rather than trying to cover an 100 diameter area. You pop into normal space and some SDB or patrol cruiser hails you runs the usual inspections and collects any taxes/duties. You head in system all safe and secure feeling knowing that the system patrols are concentrating along this corridor lane cutting down on response time instead of spread wide all over the place. And of course if some ship pops out of jumpspace or is detected making for the 100 diameter limit outside an approved shipping lane it and not screaming a signal GK or such its assumed to be a pirate/smuggler/invader and brightens the day of some bored gunner's mate.
So does work like that and I've just never run across the reference or is it a 100 diameter free for all?
If you use 'jump masking' from G:T (as I understand it) then you will have the 100 diameter (or greater due to masking) free for all. This is what I use, but I do have a number of entry/exit shipping lanes from the High port/world out to the 50 diameter limit to control ships near the high port world. This can add to transit time of a ship going to/coming from the 100 diameter limit.
Anything written in any of the Traveller books is a suggestion. The degree to which these suggestions are followed is entirely up to the referee.
Hello TheBrain,

I agree with you on a system establishing standard outbound jump entry points and traffic channels to them. The area is probably going to be large since, IIRC from another variants rules set, that if another ship is to close a misjump occurs. However, establishing a jump exit point is still going to include a fairly large area. Consider that both the departure and destination systems are moving in space and that a jump can last 168 hours +/-10%. Of course I'm guessing on this last bit, which is based on my limited knowledge of aircraft and ship navigation. For an airplane wind can either shorten or lengthen flight time. Headwinds slow the plane down, while tail winds give it a boost. At sea wind and wave action affects arrival time in a similar fashion as the wind on a airplane in flight.

Anyway, the above is my two cents worth and I agree that a system will probably patrol certain areas for arrivals in the 100D limit. Also, if you use jump masking, which IIRC came from an article for either CT or MT, then even more area is opened up.
It does make sense that there would be defined entry/exit points, if only for efficieny/safety's sake. The Battletech universe has similar procedure in its canon, with jumpships customarily jumping into either or two standard areas within a system. Any ship jumping in-system at any point either than the standard points is considered non-friendly until an ID can be made. I don't see why Traveller would do anything different (and Battletech came after Traveller, so maybe there was some cross-fertilization?)
Some thoughts...

If you miss exiting jump space at the point you plotted for - by as little as 1 turn (20 minutes), Earth will have moved some 20,000 miles. If you include the Sun's motion, you will have missed your intended aim point by 180,000 miles. That is just missing it by 20 minutes!

You may want to decide what frame of reference you're dealing with when it comes to "corridors" and the like.

Marc Miller wrote a piece for JTAS (electronic) which states accuracy of navigation is on the order of 3,000 kilometer's per Parsec jumped. Thus, a two parsec jump may miss by as much as 6,000 kilometers. ;)

This means that you have to decide what it means when a ship misses its exit point by a few hours and the like...
With reference to the Battletech jumpships, they utilise an instantaneous transfer type drive, where one minute the ship is at one point in space and the next its at its destination. This is as opposed to the Traveller model, whereby a ship is in other-dimensional Jumpspace for a week (give or take a day).

The Battletech Jumpship also can only jump from and to areas of gravitational stability, limiting it to the system nadir and zenith points or (if you want to be sneaky) to "pirate points" created by the various LaGrange/Trojan points scattered around a system. As far as I recall, Traveller (of any type) has no such limitation, other than the 100D limit for safe Jump operations.

Shipping lanes in Traveller are going to be defined more by system astrography and the fuel supplies of the jumping vessel than by any other requirement. For instance, every captain worth his salt is going to want to make sure his ship is fuelled up and ready to go as soon as possible after entering a system. That limits most vessels to exiting Jumpspace as close as possible to a supply of fuel in the target system.

Of course, this presumes that the inbound vessel isn't deliberately trying to avoid being detected. The 100 diameter scramble is probably what allows piracy to be so rife in the OTU and leads to such Traveller-esque staples as the 440dt Patrol "Cruiser" and the gas-giant lurking tactics of most SDB squadrons. Given the computing power and the accuracy of the charts available to Traveller crews (generally speaking - this might not apply after a period of prolonged deterioration such as The Long Night or during the Virus Era), ships should be capable of pretty much hitting their marks every time. This would lead to greater probabilities of ships emerging within specific "catchment areas" in a system and that would be where the majority of customs cutters and patrol ships would be waiting.

One thing I'm not certain on - do Traveller astrogators calculate their jump emergence points before they jump or afterwards, just before jump emergence? I always assumed they calculated a "rough" jump to the system in question first and then refined their exit coordinates during the jump to put them somewhere near where they wanted to be. Or maybe that's just me wanting to keep the guy busy for a week and earning his keep!
"One thing I'm not certain on - do Traveller astrogators calculate their jump emergence points before they jump or afterwards, just before jump emergence?"

It has to be done before - once you're in jump, nothing can affect your course.

(Cue jump mask/shadow debate that out-flames even the political rants...)
Question: is it the drive or the computer that precipitates re-entry to N-space at the 100 diameter limit?

If it's the computer, then the ship's sensors must be capable of detecting the minute curvature of the gravity well. This would imply that the ship's sensors do receive N-space information even in J-space. If so, the navigator should be able to easily plot a course to any gravitic anomoly such as a LaGrange point or even a beacon with a gravity field generator. By the same logic, the navigator should be able to fix his position in N-space while still in J-space, allowing him to make corrections or alter his precipitation point.

If it's the drive that cause precipitation, then the navigator doesn't have much of a choice where to re-enter N-space; he just bulldozes ahead along his course until the ship runs into a gravity well and drops out of J-space. Seems kind of willy nilly to me and pitty the navigator who points his ship in the direction of a void. Maybe that's how they did it in the old days when jump drives were as likely to explode as get you where you wanted to go. Then again, this would explain more misjumps.

IMTU, I use the computer method and most civilian vessels are limited in their ability to alter the computer programming. Jumps happen between beacons set at safe distances from navigation hazards, military installations, and major orbital structures. The beacons emit a J-space detectable code sequence and when the doppler shift is detected by a passing ship in J-space, the computer initiates precipitation. Multiple locations of interest in the system (fueling points, off-world colonies, asteroid mines) would have their own beacons. As stated in previous posts, this makes it easy for Customs and the local defense force to monitor ships entering the system in addition to making commercial shipping a whole lot safer. Turn off or alter your computer's beacon recognition software and you may violate the clauses and stipulations of your Admiralty insurance.

Altering the software is not something civilians are used to doing anyway (merchies do not stray from the shipping lanes). On the other hand, scouts and Navy navigators are used to jumping into systems without beacons or leaving the shipping lanes. One reason that IMTU an ex-mil or scout navigator is a real prize to pirates or smugglers.
What I was getting at with the Battletech reference was not so much the jump mechanics itself, but the after-jump procedures.

Battletech jumps are safest when the ship jumps in-system at a specified distance from the star (10 AUs, I think), but the main reason the senith and nadir points are used is for traffic control; only two space stations need to be constructed and that makes customs and non-jump in-system commercial operations much more efficient.

Normally, the jump points are large enough to handle regular traffic without too much risk of "interfacing" with incoming J-ships, but een so, it's standard procedure for the Btech J-ships to use their (tiny) station-keeping drives to maneouvre away from the jump point to the recharging point (sometimes a station, most times simply a point in space not ar from the jump point and technically still considered within the jump point).

It would seem logical that traffic control procedures in Traveller would be along similar lines. Why wouldn't commercial ships have certain designated areas to jump into, especially given the rather large margin of error involced in making the jump?
Originally posted by Psion:
Non-GT fan here:

What's Jump Mask?
Background history:
As I understand it, Marc Miller had started to lean towards the fact that Stars themselves would have the same 100 diameter jump limit that planets did. This was just before MT I gathered. GURPS TRAVELLER included this fact as part of standard procedure and including not only jump masking, but jump shadowing as well. Jump shadowing is based on the fact that an object casts a "shadow" in jump space as well as in normal space. In Jump space, your ship could be precipitated out of Jump space by this intrusive jump shadow. Put another way? Suppose you wanted to jump to Saturn from near earth. Unfortunately for you, the sun itself is between you and Saturn. In the OLD traveller rules, all you had to do was jump towards Saturn and that was that. Under the new rules, you now need to manuever such that the 100 diameter limit of the sun is not in the way of the jump between you by Earth, to where you want to go by Saturn.

Personally, despite the fact I'm a GURPS TRAVELLER fan, I do NOT Like nor will utilize Jump Shadowing at all. As they've written the rules up now, your ship can exit jump space in the middle of space between your exit point and your intended emergence point. This "jump space shadow" contradicts EVERYTHING I've ever enjoyed about Traveller from CT onwards. I'm sure that the people at SJGames also remembered their math correctly when they said "The navigator must make his roll, the engineer must make his roll, and the pilot must make his roll - or a misjump occurs". Say what?!!!! If you have 90% chance of success for each of the three individuals - and it requires all three to succeed for the ship to jump, the odds of a successful jump are .9 x .9 x .9 or 72% chance. A ship didn't have a chance of a misjump in CT unless it used unrefined fuel and/or it was operating past the last time it underwent maintenance or it was within 100 diameters of a planet. If it was using refined fuel, had its last maintenance done within 52 weeks, and was at 100.01 diameters out from the planet - it had ZERO chance of misjump.

Sometimes what GURPS does is NOT a bonus, but a major mistake. That's one of them in my opinion. However - players and GM's are free to choose what they like ;)
For what it is worth...

CT never went into all that much detail about what did or did not happen with Jump drives other than to state that the drive opens up a tunnel in jump space... I just spent the last hour or so looking at CT, MT, as well as TNE to see how each publication treated jump space. As early as MT, there were rules to the effect that on a 1d6 roll, 16% of the time the ship arrived early, 16% of the time the ship arrived late - the rest of the time it arrived after 7 days in jump space. This +/- 10% bull has been a recent (or so it seems) innovation... grrrrr.
Originally posted by Hal:
...As early as MT, there were rules to the effect that on a 1d6 roll, 16% of the time the ship arrived early, 16% of the time the ship arrived late - the rest of the time it arrived after 7 days in jump space. This +/- 10% bull has been a recent (or so it seems) innovation... grrrrr.
Even earlier, though not fully defined. At least as early as HG1 in '79 (and yes also in HG2) where it says "Any jump, regardless of number, takes approximately one week (150 to 175 hours)..."
Yeah, I don't think I'll be using that. ;)
Wise man.

IMTU what precipitates you back into real space is physics. Your course is locked in when you jump, and nothing anyone can do can change it, anymore than a cannonball can change its course after it leaves the gun.
Okay, I'm slightly heretical when it comes to jump. IMTU the jump drive opens a wormhole connecting the start point's frame of reference with the end point's frame of reference. The jumping ship is cocooned in a bubble of normal space which traverses the wormhole at an invariant speed. The membrane between the normal space bubble and the jumpspace wormhole is porous and allows heat dissipation, etc.

The end point of a jump wormhole is displaced by X number of parsecs spatially and by approx 1 week temporally. (Actually, the fact that the ship experiences approx 1 week as well is a coincidence: the journey could take 6 days and arrive in 7 days, or it could take 7 days but arrive in 6 days. The ship’s time and the universe’s time are only roughly equivalent!) Since there are 2 disparate frames of reference used the issue of a world moving due to a slight delay in exit doesn't exist. Also, since the exit point has a frame of reference based on the nearest large mass (usually a planet) an emerging ship has a similar momentum, in terms of direction and magnitude, as that large mass.

Since the jump wormhole doesn't exist in our universe except at the ends no jump masking is applied except at the ends: an end point's initial position is translated directly away from any offending mass (both spatially and temporally) until the 100d limit is reached (leading to violent exit); the start point's position is distorted (increasing the chance of a misjump). A misjump is a malformed wormhole ... the exit point may distorted into a new point in space and time, the interior physics of the wormhole may be corrupted resulting in a ship getting ripped apart, there may not be an exit point at all (the jumping ship travels forever), the membrane my dissolve and the contents of the bubble subjected to jumpspace's incompatible physics (temporally fragmented and non-linear).

As to the original question: its a 100d free for all.

Regards PLST
My take on jump drive exits/entries etc, is that as previously mentioned the ship leaves the physical universe, spends a week within a jump bubble possibly within an alternate dimension, and finally precipitates out of jump a week or so later. Mass shadows of large objects can affect jump drives, causing a violent jump exit at the one hundred diameter limit, though jumping from Earth to Saturn with the sun in the way, shouldnt cause a problem as jump space navigation cannot be proven to be linear, e.g the ship does not travel from origin to destination in a straight line, indeed there have been some missjumps that have resulted in no movement whatsoever or travel in a completly random direction. IMTU universe when the astrogator generates the jump plot, he or she gets an accurate fix on the present position before selecting a destination exit point in the target system. If as the result of an error, that exit point happens to be within the gravity well of their destination world, then a violent exit back into N-space results, this is different to violently exiting into normal space everytime a mass shadow protrudes into the jump universe, as after all this would make jump travel even more inherantly dangerous than it already is, after all there are billions of heavy objects in any straight line between this world and Barnard's star for example (a mere Jump 2 away). Given that the bulk of jump fuel is used up on entry to jump, one such precipitation would mean a long cold death amongst the stars in a stranded vessel.

My own take on jump space is that the ship doesn't move at all during jump(conservation of momentum etc), whilst the jump drive subtley interacts with the movement of the universe over time (as plotted via the tumble of the drive.) In other words at the moment of entry to jump the ship dissapears for a week, stays in exactly the same spot whilst the remaineder of the universe continues to move on and then re-enters normal space once again in the same spot (relative to the ship), but at a totally different location in space. Given that as per Newton's findings we expect the universe to keep on moving in the same direction, you might naturally ask, how could that same ship get back to its starting point as the motion of the universe has carried it even further away. Well friends this is where that crucial jump plot generated tumble comes in, IMTU tumble is simply a fluctuation of the jump field pregenerated by the Astrogations computer that allows subtle changes (milimeters) in the position of the ship in jump, hence giving it a small forward or negative velocity in terms of the rest of the universe and its plotted destination.

As 99.9% of movement would be relative to the ship, you could argue that the vessel stays still, its just the rest of the universe that moves. I understand that this is messey, but hell, so is jump physics in any case.

To illustrate the point, it is estimated that between every heartbeat we as passengers aboard planet Earth chained to the forward momentum of the solar system travel through a distance equivalent to the distance between the Earth and the Moon, and that's in under a second, can you imagine the awesome distances you could 'travel' by blinking out of this movement for a week....

Travellers within the jump field would be unaware of any of the events occuring in the normal universe, and would be effectively sealed in their own little bubble of relativity, Hence the trip could take months, years or decades relative to the outside universe, though to the travellers aboard would only feel like a week, should a mistake occuring during jump entry or plotting courses etc (hence the common staple of miss-jumps etc).

I also postulate that higher jump numbers such as Jump 3 to 6 etc, require more powerful drives capable of an even greater interaction with the dimension of time allowing greater distances to br traversed within that same 'relative week'.

Just thoughts but for the time being they satisfy me whilst retaining all cannon aspects of jump drives. When I get a minute I will submit a larger piece on this to the site.