Jumps, Time to Orbit, to 10D and 100D

[kaladorn]

Most versions of the TU have had time to orbit tables and ways to figure time to 10D and 100D. If I'm not mistaken, some of the numbers have been, OTOH, quite different one to another.

I've had an interesting thought though. Normally, leaving a planet, you start at rest (in the frame of ref of the planet) and move to a velocity. Your time to 100D is based on that "at rest" assumption.

But when you pop out at the other end of Jump, you preserve your velocity right? Well won't that mean that, in one sense, you're maybe still carrying the 'free' velocity you picked up by being on a planet orbiting its primary at a high speed (pick a number for earth, 78000 mph?). You don't just magically lose this velocity. Or is part of jump trying to sync up system to system such that you don't really notice this component of your velocity?

And the other part, let us say that before jump, you built up a velocity of 10000 kph. (Just picked the number out of the ether, so it might be ludicrious, but the point will remain). Your time to orbit (from 100D) would, if you were at rest, be the reciprocal of the time from orbit (at rest) to 100D. Only you aren't at rest. It seems to me the hotter you can come out of jump (only limited by your choice of fuel expenditure and your time from getting out of orbit to jumping), the shorter your trip in to the planet will be. You've got all that 'preserved vee' to bring in. But doesn't that throw all the existing tables out of whack?

Or am I missing something really obvious? One time would be 'at rest to jump' the other would be 'from jump to at rest' but you'd enter with a whacking starting vee.

It's late, I could be missing something....

 

[MrMorden]

Hmm...

Well, we know that jump fields are heavily influenced by gravity wells. It could be that the "retained" velocity is only that in *relation* to the nearest gravity well.

Sure it's what I like to call "GM halooey", but it keeps the Universe sane.

 

[far-trader]

Well CT used tables based on the assumption that any trip, either to the jump point or another world, would involve a halfway turnaround and deceleration. One of the reasons this was applied to jump as well is for simplicity but there are also valid safety reasons.

Let's say for example you are running to the 100d jump point from Earth in your free-trader at 1G. Normally you would accelerate for 186 minutes then flip and decelerate for 186 minutes ending up at rest (relative to Earth) at 100 diameters after 372 minutes.

IMTU you would in fact be running to a point and preserving some small vector such that your jump (if accurate) will cancel all relative motion with respect to your targeted destination, but for simplicity the system is fine.

Now if instead you want to accelerate all the way to the 100 diameters of Earth you get there after about 267 minutes. You've shaved 105 minutes off your trip, but wait, what happens when you come out the other end of jump...

Well for our example let's say you are headed for the historic midpoint station the Terrans set up to get to Barnard's star when they first discovered Jump, since your J1 can only get that far. Let's imagine they found a large deep space object, a size 1 worldlet.

In the normal procedure you come out at the 100 diameter point with no relative motion and you plot a course and arrive in about 133 minutes.

You instead chose to go hard and come out at it's 100 diameter of 160,000km and immediately punch the drives to decelerate all that saved up motion. Guess what? If you manage to avoid hitting it (pretty safe assumption) by the time you come to rest you are (at least) some 1,120,000km past it! Now you have to back track to it, and at 1G that'll take about 352 minutes.

Total trip both ends is about 608 minutes in the reckless example compared to 505 minutes if done safely at both ends. Bit of a tortoise and hare story, what?

So aside from the problem in this extreme example (the reverse situation might save you a little time, you do the math) why else would you not want to race all the way to the jump point? Well for one you don't know exactly where you'll come out in the destination system and if you come out at some incredible blistering speed and a lumbering hulk of an ore carrier happens to be plodding along in your trajectory that'll ruin your day fast. Multiply that by a few magnitudes if it's a busy port and everyone else is running for the 100 diameter at full acceleration too.

All that said I'd go with it's expected safety practice and except in times of war I expect even the Navy would run that way.

Now if you want to do the calculations for every jump and maximize your overall speed go for it, just remember to allow the chance that you come out with an imminent and unavoidable collision. And if you happen to misjump that may be even more likely.

edit - I should add, before anyone jumps down my throat about the likelyhood of a collision, that the chance of it happening is going to be very small, but more likely around smaller worlds, and if you go with jump masking even more likely. I've seen at least one person (well maybe even two, someone else might have done it too

) suggest the simple solution of outgoing traffic jumps from the 'north' polar region and incoming traffic jumps to the 'south' polar region to avoid collision problems.

 

[kaladorn]

Assume I know where I'm going. Assume I'm carrying vital medical supplies or running from pirates. I may *have* or *need* to keep the hammer to the floor right up until jump time.

Then when I jump, assume that my navigator is no idiot and that I am more than likely going to come out pretty close to where I want with the orientation I want. I plan to come out pointed right to arrive at my planet without overshooting, given I know my decel vector.

In the best case, my continued acceleration gives me a significant time savings point to point.

If I misjump: Bad things could happen, or not. I can come out anywhere from another system to open space to you name it. If I come out with merely another vector, since my chosen one is 'at the planet', then chances are the worst off I am is off somewhere in space having to turn around (bad, but worth the risk if you have a good nav-O and have a pressing need to do this). Not really a lot of risk of failure, all told. And the failure probably won't threaten your ship.

Re Collision Hazards: In order for me to be threatened, I have to jump out in such a way as to immediately intersect another vessel (either not possible or near zero probability) or to be on a collision course (our vectors will cross). However, if *I* am not a lumbering ore carrier, say I have 2 or 3G acceleration, I can easily adjust course within well under a minute.

Now, would you care to calculate, arriving at a sphere of 100D around a typical size 7 planet, so 700,000km radius, just how much traffic that system has to have coming and going fot this to be even as likely as winning the lottery while being struck by lightning?

I give you, more likely with smaller worlds. But even then, your traffic would have to be hugely heavy to hav esomething that was *that* close and also where you both were incapable of altering course sufficiently in the available time.

It's a nice try, and you are right that you'd normally *not* try to build up a ludicrous speed because of the small likelihood of danger, but traders who would otherwise go bankrupt, military ships, people fleeing pirates or the law, couriers, ships with perishable cargo, medical ships.... all of these have reasons for running the risk.

And that really changes some of the travel times....

 

[kaladorn]

Assume I know where I'm going. Assume I'm carrying vital medical supplies or running from pirates. I may *have* or *need* to keep the hammer to the floor right up until jump time.

Then when I jump, assume that my navigator is no idiot and that I am more than likely going to come out pretty close to where I want with the orientation I want. I plan to come out pointed right to arrive at my planet without overshooting, given I know my decel vector.

In the best case, my continued acceleration gives me a significant time savings point to point.

If I misjump: Bad things could happen, or not. I can come out anywhere from another system to open space to you name it. If I come out with merely another vector, since my chosen one is 'at the planet', then chances are the worst off I am is off somewhere in space having to turn around (bad, but worth the risk if you have a good nav-O and have a pressing need to do this). Not really a lot of risk of failure, all told. And the failure probably won't threaten your ship.

Re Collision Hazards: In order for me to be threatened, I have to jump out in such a way as to immediately intersect another vessel (either not possible or near zero probability) or to be on a collision course (our vectors will cross). However, if *I* am not a lumbering ore carrier, say I have 2 or 3G acceleration, I can easily adjust course within well under a minute.

Now, would you care to calculate, arriving at a sphere of 100D around a typical size 7 planet, so 700,000km radius, just how much traffic that system has to have coming and going fot this to be even as likely as winning the lottery while being struck by lightning?

I give you, more likely with smaller worlds. But even then, your traffic would have to be hugely heavy to hav esomething that was *that* close and also where you both were incapable of altering course sufficiently in the available time.

It's a nice try, and you are right that you'd normally *not* try to build up a ludicrous speed because of the small likelihood of danger, but traders who would otherwise go bankrupt, military ships, people fleeing pirates or the law, couriers, ships with perishable cargo, medical ships.... all of these have reasons for running the risk.

And that really changes some of the travel times....

 

[far-trader]

Originally posted by kaladorn:
Assume I know where I'm going. Assume I'm carrying vital medical supplies or running from pirates. I may *have* or *need* to keep the hammer to the floor right up until jump time.

Then when I jump, assume that my navigator is no idiot and that I am more than likely going to come out pretty close to where I want with the orientation I want. I plan to come out pointed right to arrive at my planet without overshooting, given I know my decel vector.

(see my example and * note below)

Well yeah, that's why I said you could do the calcs for each jump, because you may not be able to keep the hammer to the floor right up to jump depending on your target destination.

A slightly different example than your own equally valid reasons. Suppose a Corsair has 3G drives burning hot to run from the Navy SDB that just popped out of the gas giant. It's a long run out to the GG 100d and they'll build up a lot of speed, naturally they want to plot a jump to a similarly sized target to conserve that vector. The Captain picks the GG in the next system so teh ship can refuel and head for the hideout. Half way out the SDB scores on the thrusters, they're down to 2G, time to recalculate the destination for the reduced deceleration it'll have. As they near the 100d those dang Navy hounds score another hit on the thrusters and now they only have 1G to reduce the vector (after building up a lot of 3G and 2G), and they're going to overshoot. The Captain had better be thinking too that the next shot might take out the thrusters completely and then they'll be jumping into a system pointed right at the GG (see my * note below) with a ton of velocity and no way to change course. Or will they then be aborting the jump and surrendering to the nice Navy boys, hoping they think it worth their time to catch up and capture them as opposed to letting them drift off into deep space forever.

* A wise old Captain once taught me "Never plot a Jump with a vector aimed at anything you don't want to run right into." Truly words to live by

Originally posted by kaladorn:
In the best case, my continued acceleration gives me a significant time savings point to point.

Not just in the best case but in several cases, i.e. any smaller body to a larger or like sized one. Assuming no problems of course.

Originally posted by kaladorn:
Re Collision Hazards:

Now, would you care to calculate, arriving at a sphere of 100D around a typical size 7 planet, so 700,000km radius, just how much traffic that system has to have coming and going fot this to be even as likely as winning the lottery while being struck by lightning?

I'd really rather not, way too many MTU vs YTU variables for one thing, though perhaps I should have said more than "very small" chance since that's pretty arbitrary. I agree it would be on the order of several milliion to one at a guess, but multiply that by the traffic of the Impreium over the course of a couple thousand years. How many times do you think lightning has struck those lottery winners?

It probably only takes once to get the Ralph Nader's up in arms

Or not. One thing I know is people (in general) have an exceedingly poor grasp of the realities of chance and usually worry to extremes about things with little chance of hurting them while not being worried nearly enough or at all about the things that are very likely to.

Originally posted by kaladorn:

It's a nice try, and you are right that you'd normally *not* try to build up a ludicrous speed because of the small likelihood of danger, but traders who would otherwise go bankrupt, military ships, people fleeing pirates or the law, couriers, ships with perishable cargo, medical ships.... all of these have reasons for running the risk.

And that really changes some of the travel times....

Thanks, not sure I was trying to do what you thought though. I was just outlining the accepted practice in CT (sensible or not). I wasn't looking for the "real" reason for you, just throwing that out with some plausible reasons.

Yep there will always be exceptions to the norm, especially when PC's are involved.

One thought I forgot to add was the Jump calculation itself being very dependent on your vector and position at the instant of Jump. The faster you're going the harder the calculation is going to be, maybe, maybe not. It could be a simple prediction exercise.

Or maybe the opening to Jumpspace gets distorted if you tumble with a high velocity or maybe it can't even form properly, leading to a catastrophic misjump. True there is precedent for some vector carried through jump.

I recall having a MTU rule for TNE that imposed a total vector limit on traffic equal to your max acceleration. This was for safety so you could stop in one turn at full burn.

For all we know it could be that Jump won't work (and again a catastrophic misjump results) if you have a high velocity relative to the destination's gravity well. This works better if YTU only allows 100d jump precipitation (no deep space jumps) which I've always preferred for MTU.

If you're looking for validations maybe that'll do or spawn some thoughts

Anywho, just a few more ideas to bounce around. I think I like the idea of a certain misjump risk for attempting jump at high speed. That would still allow it to be done when needed with as you say an assumed (and real) risk, and validate the reason it is not generally done and perhaps even not allowed for commercial traffic. I'm just not sure how to make it work. I'll ponder it though. This is an interesting thread even if it's wandering a bit

 

[The Oz]

IMTU, I have always said that the vector a ship has entering jump =relative to the destination= is the vector it will have coming out. As a result, IMTU ships (including merchies) routinely aimed their outgoing vector and jump exit point so that their vector on leaving jump would aim towards the planet, within their decel capability to make the velocity match with the destination. This led to "jump points," places in space where ships would tend to jump from or arrive at that gave the best times planet to planet. These points moved around the planets in accordance with their orbits. All this was part of the data in the Library Data program and available for all charted star systems. Part of the Navigator's skill in charting a jump was to put the ship on the right vector and coming out of jump at just the right point so that the trip would be as short as possible. The "jump points" were usually patrolled if assets were available, to keep the pirates away.

I also included in this the relative motion of the two stars. Usually this is pretty small between two close stars, and so could be ignored or dealt with by the ship's maneuver drive, but I did carefully create a few star systems where the relative velocity was very high (or in one case, on an unusual direction as the star was an extra-galactic intruder, although no one knew that at the start) and jumping from one star to another where there was a considerable relative motion led to a need for lots of acceleration or deceleration before jump (or after jump, if you wanted it that way, but you'd better make sure your jump point didn't end up pointing your vector at something you didn't want to hit).

The end result of including relative motion (the amounts of which I made up, after some quick research to determine usual amounts) was to add extra "topography" to the sector. Some worlds that were only Jump-1 apart were more than 2 weeks apart when you included the accel/decel times, and I created a "ladder" of stars that led from the low relative velocity worlds through two stars of higher relative velocity up to a really high relative speed star. The high-speed star was only 3 parsecs away from the star at the start of the ladder, but it was actually faster to reach it by jumping four times at Jump-1, building up your velocity along the way.

This was long ago, and I just wrote the relative velocity data down on the subsector data form. Today I'd want to find some way to encode it on the subsector/sector map, and I'd also want to think of how to include jump masking in this.

Did any of this make any sense?

 

[far-trader]

Originally posted by The Oz:

Did any of this make any sense?

Very much so, and you put quite well some of what I was poorly aiming at

Especially the part about Jump points and routes.

 

[kaladorn]

Oz, nice post. Good ideas too.

The only thing I see worthy of note (applies to my comments too): Jump is 168 hrs + or - 10%. That's a 32 hour window. Earth would have moved (if I recall my trivia) probably about 2.5 million miles in that time. So, normally one probably aims to come out of jump in such a way as to cut a chord across the orbit circle from the position where the planet would be at 152 hours to the position where it would be at 184 hours. Thus if you'll be 'on line' and your vector will be well lined up. Coming straight at it (as if it were a crossing target) is doomed to be a bad plan.

 

[far-trader]

Good point about the moving target over the jump time variability kaladorn. Now why did that never occur to me before?

Not sure about the distance though. Your 2.5 million km is close if we're talking relative to the Sun, except it should be +/- like you said, so closer to as much as about 1.8 million km ahead or behind.

If however we take the speed and distance relative to the galctic core it's up to 15 million km off. That'll take about a day at 1G. And which would be (more?) correct from the perspective of Jump space?

To go one step further, for no good reason, and use the Earth's speed relative to our local group of galaxies it's not much worse at about 18 million km.

Of course the above presumes I did the math right

It is late

I've always used the operating theory of no deep space jumps and you need a gravity well to kick you out of Jump space. That and the old +/- 3,000km (iirc) per parsec error to that point. That'll put you out much closer to your goal than the above.

So we are left to ponder why? Perhaps there is some hidden force that connects to the gravity well of your destination and pulls you into it and hence the small margin for error from your intended destination.

Back to the carrying a favorable vector through jump for a second. Unless there is some hidden force that keeps you (relatively) bearing down on the gravity well how do you know your vector is going to be pointing in the right direction at all? I know it maps to real space so the idea is you set up your tumble and vector appropriate for what you want at the other end. Is it just me or does that get difficult when you have a vector in all but the simplest cases?

This is all getting too complicated (or I'm getting too tired

) time to call it a night.

 

[The Oz]

Originally posted by far-trader:

I've always used the operating theory of no deep space jumps and you need a gravity well to kick you out of Jump space. That and the old +/- 3,000km (iirc) per parsec error to that point. That'll put you out much closer to your goal than the above.

I have always wondered how the jump drive could be so accurate in jump distance (one part in 10 billion, according to MT) and yet so wildly inaccurate in jump duration. Must be some strange aspect of jump physics....

Back to the carrying a favorable vector through jump for a second. Unless there is some hidden force that keeps you (relatively) bearing down on the gravity well how do you know your vector is going to be pointing in the right direction at all? I know it maps to real space so the idea is you set up your tumble and vector appropriate for what you want at the other end. Is it just me or does that get difficult when you have a vector in all but the simplest cases?

I never really thought about it before and just assumed that the ship (and its vector) remained pointed just as it was when the ship went into jump. It's an interesting question: what does happen if the ship uses thrusters (or even the maneuver drive) while in jump? Can you accelerate in jump? Alter your attitude? I don't recall ever hearing anything about this one way or the other.

 

[TheEngineer]

Hi,

another question regarding jump routes..

If there any comment in the official ruleset, that a Jump route has to be a STRAIGHT line from A to B ?
I did not found anything like that.

AFAIK there is just mentioned that the "jump route is calculated".

Regards,

Mert

 

[kaladorn]

I got the impression from something Thrash said that the route must map 1:1 to that in realspace (now, is that straight? That's another question!). As for a specific canon citation (what you want), I leave that to another to provide as I can't think of one.

 

[TheEngineer]

Hi Thomas,

the answer to this question is quite essential, because if a jump route could be plotted with "curves", we would have no problem with any jump masking effects and still stay in canon with those intervening objects.

This would also enable you to approach the 100D limit of a destination by setting a "matched vector" route towards the planet.

The Jump-Astrogator would just calculate a route around disturbing objects. Mostly the range modification would be neglegtable compared to the overall distance.

IMHO this would put together all the attributes of jump space travel, is consistent with canon stuff and is also somehow logical.

Any more thoughts...?

Regards,

mert

 

[TheEngineer]

Hi Thrash,

no missing "h"

So to analyse the sentence...
"if you plot a straight line..." does not mean IMHO that just MUST plot a straight line.

I guess here we have another area of interpretation.
Perhaps You could ask Marc Miller if he also intended to only allow "straight" jumps.
If yes, we would have to figure out what straight means in our universe regarding modern astro physics.
If no, we all could be happy again and there is no need to discuss effects of delayed travel times caused by jump masking and intervening objects

.
I really would prefer the second choice as it might be a real compromise.

Regards,

Mert

 

[Andrew Boulton]

"2. SO, if you plot a jump in a straight line from here to there

So the obvious solution is not to plot it in a straight line!

 

[TheEngineer]

Hi Andrew,

yes, that could be our handwave.
Somehow, fairly simply and also logical.

Perhaps thats the reason why nobody cares about it for the last 25 years

Regards,

Mert

 

[Andrew Boulton]

The way I've always understood jumpspace, it's a meaningless question anyway. It's not part of the "normal" universe.

Take a sheet of paper. This represents part of our universe. Draw two dots on it, spaced well apart. These represent where you are now and where you want to go to. A straight line drawn between them would represent the shortest route through real space. There may or may not be obstacles in the way.

Now fold the paper in half so the dots are a couple of milimetres apart. THIS SPACE represents the course through jumpspace.

Or so I thought.

 

[kaladorn]

Andrew,

There may well be rules regarding how you can fold jumpspace. This may require a straight line path.

Chris:

I meant 'you said' in the context of 'you quoted in this discussion'.

And I agree with Mert, reading those two sentences does tend to suggest that it *might* be possible not to plot a straight line jump (while we still maintain a 1:1 mappign with realspace).

Mert:

If Citizen Thrash is right, Jump Shadowing will affect so many of the worlds that I'm not sure you're buying much by writing out Masking.

 

[far-trader]

Hmm, here's a thought. Perhaps Jump Masking/Shadowing is most problematic at the ends of the jump, entry and exit, and less so through jump after you're completely in it? Maybe not on the money MWM idea wise but easy to use. If not that then something like The Engineer's idea of curved plots and matched vectors sounds pretty interesting, nice idea that

That could also explain two different arrival times for ship's jumping together, eddies in jump space (now how did he get there

) plotted around or simply carried along once the rough entry, course and exit are plotted. Kind of at the mercy of the flow of Jumpspace. Very interesting...