In system travel times

[kristof65]

I'm having a hard time coming up with numbers that sound "right" for my project.

Assuming the m-drive technology of Traveller, but an FTL system that requires you to leave the outer boundries of a stellar system to utilize it, what kind of AU distances sound "right"? Kind of like the 100d limit for planets, but on a much larger scale.

In otherwords, if your FTL could take you to the outer boundries of a steller system, but you had to "hoof it" the rest of the way on m-drive, how far out would it be reasonable for routine traders to travel in-system to complete their business? Particularly when there may be other systems near by that have a "smaller" boundry.

Hmm - not explaining that very well. Let's take a real world analogy. When you're driving down a highway, when it comes time to stop for food or gas, most people will drive further along and take the exit where the fast food restaurants and gas stations are right there, rather than taking a two lane road a few miles into a town - even if they could get better food and cheaper gas in that town.

So if there were a highway system connecting star systems, what's a reasonable distance in AUs away from that "highway" for a star system to be for it to be considered accessible. I do realize that part of that determination will be how habitable the system is as well.

 

[Ishmael]

when using gravity at the 100d limit for earth as the real limiter of jump-drives ( .000025g's ), Sol's jump shadow comes out at close to 5 AU's. While it isn't an absolute limit, people who choose to engage jump closer to the star than that risk misjumps.

 

[kristof65]

Thanks, but I'm not really worried about computing "jump shadows".

What I'm really looking for is what kind of real space travel times would people find acceptable if they can use an FTL to move onto another system that is "closer to the highway" so to speak.

The alternative FTL drive system I'm working on can travel at about 30 minutes per light year - BUT it can only do so along certain routes. Which means that any given star system these routes pass by are "off the highway", so to speak.

So how far off the highway in AUs would it be reasonable for "normal" people to travel via m-drive? 10 AUs? 20 AUs? 100AUs? 1/2 a LY?

 

[Ishmael]

sorry..I misunderstood

I guess I'm a bit hung up on how in-system travel affects a Trav Universe.
I generally play lower tech levels than OTU so manuever drive can end up being measured in tenth's of a g and that makes in-system travel pretty ponderous. But I prefer the 'gritty' hard-boiled noir feeling that gives.... pretty much like 2300AD

I think I may go with the "high jump numbers can be used to shave time off of travel" from the "what a difference a day makes" thread..

 

[grymlocke]

how long do you want to drive in the space RV?

assuming most LS (life support) systems seem to be based around the 30 day operation period and it akes a week perjump, that leaves three to 'wander into town'. Assume a week to refuel an a week to get back to the highay... So, I'd say, how far can you wander in a week? based on drive rating ofcourse.

 

[EDG]

I think it would really be dependent on your setting. Figure out how fast you want the M-drives to be, and then pick a reasonable distance/travel time from that.

 

[kristof65]

how long do you want to drive in the space RV?

Exactly. I know that for garden worlds, and those desiring isolation from an interstellar community, the distances people are willing to travel will be longer than for a barely habitable world with no easily extracted resources.

assuming most LS (life support) systems seem to be based around the 30 day operation period and it akes a week perjump, that leaves three to 'wander into town'. Assume a week to refuel an a week to get back to the highay... So, I'd say, how far can you wander in a week? based on drive rating ofcourse.

Hmm - didn't thik to consider Traveller "standard" Life support systems - only fuel and power plant ratings. May have to factor that into things somehow - time to check the rules.

I think it would really be dependent on your setting. Figure out how fast you want the M-drives to be, and then pick a reasonable distance/travel time from that.

In order to minimize ship building system redesign, I'm going with the standard Traveller m-drives. As it is, ships for my setting will have to be redesigned - the FTL unit is smaller, but ships will tend to carry larger m-drives, power plants, and more fuel for longer operating times.

 

[Rikki Tikki Traveller]

So, lets throw some numbers out and see what we get...

Assume 1 week travel time from the outer system to the habitable planet at 1g. That makes total trip times 3 weeks. Add 1 week in port and you have a nice 1 month jump cycle.

1 week at 1g with a mid-point turn around... (punches calculator)

That means the travel distance is about 12 AU.

Figure the habitable planet orbits at 1AU from the star, so 13 AU from the star.

13 is a bit rough, so I suggest calling it 10 or 15 AU. Saturn orbits at about 10AU from Sol as a point of reference.

So, 10 AU from the planet your travel times are APPROXIMATELY (accelerate 1/2 way, turn around, decelerate 1/2 way):

1G: 6.3 days
2G: 4.5 days
3G: 3.7 days
4G: 3.2 days
5G: 2.8 days
6G: 2.6 days

 

[tneva82]

when using gravity at the 100d limit for earth as the real limiter of jump-drives ( .000025g's ), Sol's jump shadow comes out at close to 5 AU's. While it isn't an absolute limit, people who choose to engage jump closer to the star than that risk misjumps.

How's that? Traveller rulebook says 140 million km's from sun to sol and atleast wikipedia puts au as 150 million km's(earth's distance from sun). Therefore 100 diameter would seem to be less than 1 AU.

What am I missing here?

 

[hdan]

How would those numbers change if you didn't decelerate? Jump keeps your velocity, so you can decelerate on the "other side", as it were.

Though you'd better hope your jump calculations were on target. If you come in too close, you'll overshoot your target. (Maybe a Navigation roll to use some other planet's gravity to break you on the way in?)

 

[Rikki Tikki Traveller]

Well, things would be faster...

Actually, I should have included these numbers in my first post.

10 AU constant Acceleration/Deceleration, again these are APPROXIMATE:

1G: 4.5 days
2G: 3.2 days
3G: 2.6 days
4G: 2.2 days
5G: 2.0 days
6G: 1.8 days

 

[Rikki Tikki Traveller]

Just as an FYI, I did some playing around with the math and figuring out travel times for long distances simplifies to a pretty easy equation.

Taking into account all of the different unit conversions and being willing to accept 10% error yields the following formulas:

(accelerate-turn-decelerate):

T = 2*sqrt(D/A)

(constant Acceleration)

T = sqrt (2*D/A)

WHERE:
T is the time in DAYS.
sqrt is the "Square-root" function
D is the distance in AU.
A is the acceleration in G's.

This is NOT exact, as I said it is within about 10% of the actual numbers, and tends to be a bit longer than actual detailed calculations would give you. For in-game use, it is quite handy.

 

[kristof65]

when using gravity at the 100d limit for earth as the real limiter of jump-drives ( .000025g's ), Sol's jump shadow comes out at close to 5 AU's. While it isn't an absolute limit, people who choose to engage jump closer to the star than that risk misjumps.

How's that? Traveller rulebook says 140 million km's from sun to sol and atleast wikipedia puts au as 150 million km's(earth's distance from sun). Therefore 100 diameter would seem to be less than 1 AU.

What am I missing here?

he's talking about using relative gravity to compute the jump shadow, rather than physical diameter. For Earth, the gravity pull it has at the 100d point is much less than the gravity pull Sol has 1 AU. If you make the jump shadow for both Sol and Earth based on the same relative gravity, then either Sol's jump shadow extends out to 5 AU, or Earth's jump shadow is much less than 100d.

 

[kristof65]

Just as an FYI, I did some playing around with the math and figuring out travel times for long distances simplifies to a pretty easy equation.

Thank you. I was trying to figure this out myself, but was having problems because to start with, I can't find what Traveller book had the travel time formulas. I'm pretty sure it was in one of the MegaTraveller books, but I can't find my box those are in at the moment (darn remodeling).

 

[Rikki Tikki Traveller]

I didn't use the Traveller book. I used the equations of motion for constant acceleration and did the unit conversions.

I know it was in the CT LBBs (but wrong).

This is not Traveller, this is just Math.

 

[kristof65]

Yeah, I know it's just math. Actually, I wouldn't say that - I'd say it's just physics. It's just not a formula I deal with daily or even weekly, and sorting out the actual formula I needed from what was available was a hassle. IMHO, a large part of math and physics isn't solving the actual problems themselves, but sorting out which formula to use in the first place.

I'm pretty good at solving the actual equations, even without a calculator, but I'm horrible at knowing which formula/equation to use in the first place unless it's related to architecture or electronics. Constant accelaration is not among those - until this moment, I wasn't even sure what name to give the formula. This is a result of despite being pretty good at solving math problems, I wasn't very good at getting along with my high school science teachers, and I got kicked out of physics class - not once, but twice - with two different teachers. What physics I do know is a result of working with electronics, architectural engineering, college astronomy classes and self teaching.

I did recall that the formula's listed in the LBBs were wrong for some reason, so I didn't go there - but couldn't find it elsewhere in my readily availableTraveller collection, and couldn't sort out which formula to use online. I'm surprised it isn't in the MgT books anywhere.

And thats why I thanked you - because I know my own shortcomings in the area.

 

[Rikki Tikki Traveller]

I was lucky enough to be taking an orbital mechanics class at the time, so it brought all those formulas back to me and it was about the same time Traveller was worming it's way back into my heart, so it all fell together.

Besides, I think many people underestimate or overestimate how long it takes to get from Point A to Point B with constant acceleration.

Honestly, I didn't know how long it would take to get from Earth to Jupiter until I did the math. When I simplified everything, I was really surprised how they all seemed to cancel each other out and you get a very simple formula without any big conversion factors. Well, that's my math geek showing...

 

[Bygoneyrs]

You know this has always amazed me over the past 30+ yrs of playing Traveller/Gming it/collecting it all, that the focus some folks have placed on the number crunching stats. I mean what is important is that Traveller is a SciFi - Fantasy RolePlaying "Game", where we get together with our friends to play a game and have fun. I don't know any gamers that get together to crunch numbers for their main focus of fun, but instead it is the 'game play within the Traveller campaign' that people enjoy themselves.

I guess I feel sorry for the 'Collectors' of the Traveller game, because they seem not to actually play the game but instead hash over the mechanics to check real world math/physics and what not. Sorry guys but being a GM of Traveller with a 25+ yr old running campaign set in the Verge sector, the real way to have that record is to actually play the game and not stress the gear-head stuff. To each their own, but this is a Game where people play a game to have fun. Try to enjoy the SciFi flavor a little more and not worry about real world math/theory. Let your hair down a little and try to have some FUN!!!

Penn

 

[kristof65]

Actually, the only reason I'm number crunching is because I'm working on a setting I hope to release under the OGL. I want everything to "feel right" for the on the fly GMs as well as the number crunchers.

For playing purposes, I'm an on the fly guy. That's why I don't have the formulas down, even after decades of playing and enjoying Traveller.



That aside, there are people who actually enjoy crunching numbers - if that's the joy they get out of Traveller, I'm not going to look down on them.

 

[Shiloh]

What I'm really looking for is what kind of real space travel times would people find acceptable if they can use an FTL to move onto another system that is "closer to the highway" so to speak.

Well, a lot of the basic rule book stuff is based on a "2 new solar systems per month" timescale, with a week in jump, and a week between jumps which is *mostly* starport/planet based. If you were to deviate much from this sort of scale, some of the economic and political assumptions made would need reviewing to see if there was an impact.

The alternative FTL drive system I'm working on can travel at about 30 minutes per light year - BUT it can only do so along certain routes. Which means that any given star system these routes pass by are "off the highway", so to speak.

So how far off the highway in AUs would it be reasonable for "normal" people to travel via m-drive? 10 AUs? 20 AUs? 100AUs? 1/2 a LY?

It will depend very much on what a "normal" M-drive is. Assuming that you're looking at a similar spacing of worlds to "canon" Traveller, your stardrive makes the *interstellar* portion of the journey comparable to the canonical n-space part, so it would make an amount of sense to have the J-space section max out at about a week, so that's 3-4 days to J-point and the same from arrival point in N-space to the destination world. p145 gives you a table to work out how far that gets you... 96 hours is 2 AU at M-2.

At this rate, unless the hyperlane moves relative to the *mainworld*, there's going to be *significant* variability in journey times depending on where in their orbit the mainworlds are. If the hyperlane is 1 AU from both origin and destination, the journey distance could be anything from 2 AU (if they're both at closest approach) to 6AU (if they're both orbiting at 1 AU and at farthest distance from the lane). Assuming the lane is in the plane of the ecliptic... [Sing everybody! "The lane in space is main-ly in the pla-ane" - Ed]

The other thing that this will impact is spaceship design. A fast M-drive becomes more desirable since a M-5 ship spends half the time futzing about in N-space that a M-1 does, and takes up proportionately less extra tonnage compared with a doubling of the J-drive rating.