An Alternate look at Jump and travel times

[Murph]

IMTU Jumps are instantaneous. Your travel time comes from having to transit from the Jump point to the world. If you look at the travel times published in the various Traveller material, it looks like moving from jump point to planetary orbit using less than 6G, will take many hours, possibly days.

Isn't this more in line with the time factors that MM and crew intended? I certainly does not affect play that much since you still can take a week to get to the jump point, and a week to get to the next planet.

 

[aramis]

IMTU Jumps are instantaneous. Your travel time comes from having to transit from the Jump point to the world. If you look at the travel times published in the various Traveller material, it looks like moving from jump point to planetary orbit using less than 6G, will take many hours, possibly days.

Depends highly on your threshold for "many."

Size A world, 1G, 8.8 hours from orbit to jump point. MT IE p.92

Note that this is biggest world and slowest drive in common use. Everything else is faster. Not even half a day. Landing adds an hour.

Isn't this more in line with the time factors that MM and crew intended? I certainly does not affect play that much since you still can take a week to get to the jump point, and a week to get to the next planet.

No. What you've done is eliminate the commo lags that make adventuring and spec-trading sensible.

See, the scoutships can jump as fast as they can refuel, so comm-lags will be on the order of 6 hours round trip, including the hour to check the email, check the inventory, and send a quote. You can do practical EFT at that speed. Your credit history is relatively accessible with those comm speeds.

You'd have comm lags to a sector capital on main routes of a few seconds to jump point, probably under a hour while the next jump scheduled loads, then an hour per system on the main routes, possibly less for major worlds connected to each other.

The difference between liners and traps becomes so financially ugly that tramps won't have legit work at all in major systems, only in backwaters and smuggling.

 

[Murph]

I also think that ships should have only 5%/jump number in fuel to make it more economical for trade, not spec trade, but trade. Also if you look at the numbers both in CT and T5, it takes up to a week to get to the jump point, and then a week(+) in jump, then another week+ moving into a system. Read the Mote in God's Eye by Pournelle for what I am describing as a system. I think it would be more reflective of the time lags that MM intended, even granting light speed commo lags which would speed up things, but the travel times in/out system always get glossed over. Space Travel is boring.....

 

[McPerth]

I also think that ships should have only 5%/jump number in fuel to make it more economical for trade, not spec trade, but trade. Also if you look at the numbers both in CT and T5, it takes up to a week to get to the jump point, and then a week(+) in jump, then another week+ moving into a system. Read the Mote in God's Eye by Pournelle for what I am describing as a system. I think it would be more reflective of the time lags that MM intended, even granting light speed commo lags which would speed up things, but the travel times in/out system always get glossed over. Space Travel is boring.....

In Pournelle books, as in Starfire, jump points are fixed and few, so you don't have to go just out 100 D from a planet to jump, but you must reach the specific Alderson point (Warp point in Starfire) to the intened planet (or to a halfway planet, if no point to your target planet is in the system), making insystem trips quite longer.

Even so, Pournell does not speack (at least I don't remember, teres quite a longtime since I read it) about communications, but the time log might also come from having to go through several systems due to the Alderson points configuration and sending the messages from point to point while insystem, again akin of the Imperial Starfire communications infrastructure.

Whith Traveler jump, that allows you to jump to any planet in rage of your drives from any point over 100 D of the departing planet, times are too short to keep with the OTU millieu.

Making the fuel needs reduction you suggest allows too easily multiple jumps (even high jumps, as a J6 ship would need "only" 60% of its volumen to make 2 jumps without refuelling). One of its main effects in the OTU (at least that I can think about now) would be to make battle lines more extended in watrs, as the capability to make two consecutive jumps would allow you to "bypass" the defended planets by jumping into an empty hex and jumpiga again deeper in enemy rear.

The implications are multiple, one of them being you need a larger fleet to patrol a more extensive area to avoid those deep raids...

Not saying it cannot work in YTU, of course, nor that the resulting milieu would not be interesting, justa that it would not be OTU millieu, not any millieu attainable by useing Travellr rules as they are...

 

[Marchand]

If you take account of a star's 100D limit and the effect of stellar "jump masking", you can add days to the time needed to reach a jump point. This applies mainly to worlds orbiting smaller type M and K stars.

The reason is that the 100D limit is linear with respect to the sun's size (clearly), whereas the star's luminosity (and therefore the star's "habitable zone") drops off with the square of distance from the star.

For Sol, it's breakeven - Earth is not far outside the Sun's 100D limit (150m km orbit vs about 139m km solar 100D).

For smaller stars, a habitable primary will orbit much closer to the star than the star's 100D limit. To take a [possible] real-world example, Gliese 667 Cc orbits about 18.8m km out from its primary; the primary's 100D limit is 55.4m km. That's about 37m km to cover to get out from the star's jump shadow, or about 35 hours at 1G.

 

[rancke]

If you take account of a star's 100D limit and the effect of stellar "jump masking", you can add days to the time needed to reach a jump point. This applies mainly to worlds orbiting smaller type M and K stars.

The reason is that the 100D limit is linear with respect to the sun's size (clearly), whereas the star's luminosity (and therefore the star's "habitable zone") drops off with the square of distance from the star.

For Sol, it's breakeven - Earth is not far outside the Sun's 100D limit (150m km orbit vs about 139m km solar 100D).

That's jump shadowing you're talking about (destination being inside a jump limit aka jump shadow). Jump masking is if there's a solar jump limit between you and the (unshadowed) destination. In such cases the extra time increases with the size of the jump limit.

For smaller stars, a habitable primary will orbit much closer to the star than the star's 100D limit.

The thing is, none of the rule sets or setting material reflect this, except for the GT rules, and as far as I can tell the GT rules ignore most of the ramifications, such as the increased freight and passenger prices ships doing trips that take more days would have to charge. :nonono:

I'm working on a writeup of the Heya system where I have Heya orbit a K6 V star and include the one-day trip from the solar jump limit to Heya. But no telling when or if I'll ever finish it.

At that, I've felt compelled to change the canonical K6 II star because that would have added weeks instead of a day to the trip and that didn't work at all for me. (Also, I think it contradicts previously published material about Heya). So even when I do finish it, it won't be canon-compatible.


Hans

 

[Marchand]

That's jump shadowing you're talking about (destination being inside a jump limit. Jump masking is if there's a solar jump limit between you and the (unshadowed) destination. In such cases the extra time increases with the size of the jump limit.


The thing is, none of the rule sets or setting material reflect this, except for the GT rules, and as far as I can tell the GT rules ignore most of the ramifications,

Thanks for the clarification.

It's a whole new ballgame, isn't it? Worlds around Ms and Ks are suddenly much less attractive from an economic standpoint, other things equal. Although possibly more attractive strategically, as enemies have to come at you from days away rather than hours.

Could we retcon it (or whatever the term would be) such that the 100D jump limit is just a rule of thumb applicable only around roughly planetary masses? For anything above the lower mass limit for fusion to start happening, it drops off to (complete handwave) 50D.

Er, or something

 

[HG_B]

Jump masking is if there's a solar jump limit between you and the (unshadowed) destination. In such cases the extra time increases with the size of the jump limit.

Here's a good visual on this. http://www.transhuman.talktalk.net/iw/Sol100D.xml

 

[Carlobrand]

Elsewhere, Aramis and Tjoneslo point out an alternate interpretation of jump shadow that provides about the canon results for most terrestrial worlds but shrinks it for suns and gas giants by taking density into account. Net result, after plumbing through the math, is that the "100 diameter limit" gets modified by the cube root of the density of the body, on the argument that the jump interference is caused by tidal stress - difference in gravitational pull between one point in space and another point slightly farther out from the planet.

http://www.travellerrpg.com/CotI/Discuss/showthread.php?t=31314&page=2

Most terrestrial planet are close enough in density to not bother with the math. The 100-diameter limit can be considered convenient shorthand, with some slight variation depending on how much of the world's core is iron, but not enough to sweat over unless you're a smuggler trying to evade the local constabulary or some such thing and have an urgent need for those extra few minutes. Most stars (and gas giants) are much less dense than rocky bodies, and the giant stars are far less dense than the typical main sequencers, so their limits get chopped by 2/3 or more, leaving us with jump shadows that permit the behavior shown in canon - unless your destination happens to lie on the other side of the local sun, and few of us go into that level of detail. So it's a model that restores canon rather than interfering with it.

It does create some challenges for the little red dwarfs, whose jump shadows actually increase because they're pretty dense: habitable zone for the main sequence M0 and most of the little subdwarfs lies inside the jump shadow - but then the little subdwarfs were errata'd out and aren't technically in the game anymore. For the M0, it's a matter of 40 million kilometers, so a bit under a day and a half at 1G, inconvenient but not game-changing.

A point to consider is that if you're aiming for the star itself instead of one of the planets, the new model has you precipitating out inside the largest stars. This is weird but reasonable: the outer envelopes of the largest stars is actually so diffuse as to be about on a par with Earth's atmosphere 100 kilometers up - pretty close to vacuum. Ergo, if for some strange reason you're wanting to jump close to the surface of a supergiant star, you don't count on precipitating naturally but instead make sure you calculate your exit point just right. On the other hand, jumping close to the surface of a supergiant star sounds unhealthy for reasons that have absolutely nothing to do with the density of the gas you emerge into.

Add: Oopsie, that should be the K5 and the M0 main sequences with habitable zones inside the jump shadow, with 44 and 40 million kilometer jaunts to get outside the affected area.

 

[HG_B]

A point to consider is that if you're aiming for the star itself instead of one of the planets, the new model has you precipitating out inside the largest stars. This is weird but reasonable: the outer envelopes of the largest stars is actually so diffuse as to be about on a par with Earth's atmosphere 100 kilometers up - pretty close to vacuum. Ergo, if for some strange reason you're wanting to jump close to the surface of a supergiant star, you don't count on precipitating naturally but instead make sure you calculate your exit point just right. On the other hand, jumping close to the surface of a supergiant star sounds unhealthy for reasons that have absolutely nothing to do with the density of the gas you emerge into.

Ouch!

 

[leo knight]

Ouch!

Didn't that happen in "Mote in God's Eye"?

 

[McPerth]

Didn't that happen in "Mote in God's Eye"?

Yes, but there they have no option but to go there, as there was the only Alderson point to reach Mote system. In traveller, those points not being fixed (and not having the forcé fields that allow them enter inside the star), that would note be needed.

 

[CosmicGamer]

Variables, variables. Lots of variables.

What speed and direction is the ship moving when it exits jump? What is the direction of travel and speed of the destination in relationship to the ship? Is it automatically on an intercept course, standing still, or speeding in a random direction? I'd think not the first because jump has some random elements, like not always exactly one week, so I don't see how the orientation could be 100% dead on when you don't even know exactly when and where the ship or destination will be when you come out of jump.

What do different publications and versions say in regards to a ships speed and orientation?

How about the location of the destination? Why couldn't it be on the far side of the world?

What if there is a another planet in the current system or destination system that blocks the optimal, shortest "orbit to 100d limit"? Maybe you need to go out 110d, or go to a 100d limit on the other side of the current world for a optimal jump point.

Also the issues others have mentioned.

Here's a good visual on this. http://www.transhuman.talktalk.net/iw/Sol100D.xml

Nice graphic. Wonder if anyone can add in the complexity of a planet orbiting Barnard's Star?

I'm not so sure a simple equation does justice for those looking at the more detailed complexities.

Size A world, 1G, 8.8 hours from orbit to jump point. MT IE p.92

Without a computer program to calculate this all out after someone provids a HUGE amount of data on all the paths and speeds of the Traveller systems and worlds... I'll take the simple way out for my role playing gaming.

But it is fun to read and discus.

 

[whulorigan]

What speed and direction is the ship moving when it exits jump? What is the direction of travel and speed of the destination in relationship to the ship? Is it automatically on an intercept course, standing still, or speeding in a random direction? I'd think not the first because jump has some random elements, like not always exactly one week, so I don't see how the orientation could be 100% dead on when you don't even know exactly when and where the ship or destination will be when you come out of jump.

What do different publications and versions say in regards to a ships speed and orientation?

I believe canon in all versions of Travller have held that momentum is still conserved, Jump Space notwithstanding. This means that the momentum (specifically speed and direction of motion) of the ship will be identical to the values it had when entering jumpspace. So from an in-universe standpoint there would be no randomness in these values (although from a rules-mechanic standpoint you may need to randomly determine what those vectors are, unless your orbital configurations of star systems are very detailed in your Universe).

This is one of the reasons you would want a good Navigator/Astrogator - to make sure that the momentum values upon Jump space insertion are favorable upon Jump Space emergence. This is information that needs to be communicated to the pilot ahead of time in the originating system.

Of course, you could always house-rule that the laws of Momentum Conservation have a more complex formulation in light of the as-yet-undiscovered Jump Space Physics.

 

[HG_B]

I believe canon in all versions of Travller have held that momentum is still conserved, Jump Space notwithstanding.

MGT is completely silent on this point. It is left up to the GM to determine.