pendragonman
Absent Friends Margrave
I take it you missed the bit at the end about misjump. In normal operations will you jump to a spot outside all gravity wells? I think not.
T5 Question about Maneuver Drives
- Thread starter Supplement Four
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I take it you missed the bit at the end about misjump. In normal operations will you jump to a spot outside all gravity wells? I think not.
esampson
SOC-13
You actually could re-enter space outside of a gravity well.
Imagine a rogue planet is drifting between systems at a reasonably high velocity. When you jump your jump line intersects the edge of the 100D sphere of the planet. However, since you do not exit J-Space until a week later, at the point where you clipped the 100D sphere, the planet has now moved off until it is over 1000D away from where you are. Even worse, its travel vector is nearly 180 degrees off of yours so you have to brake your own ships not insubstantial momentum with only 1% of your normal acceleration.
Of course in this case, as I said, I would probably plot a new jump that deposits me in a week a bit ahead and to the side of the rogue planet so that my drives are working at full efficiency, allowing me to brake into an orbit around the planet. Hopefully it will have water ice, hydrogen, methane, or something else I can use to fuel back up.
Note that for most ships, a misjump is going to mean arriving tanks dry. Few ships have more than a single maximum jump, and most ships are J1 or J2. So damaged or not, the J-Drive isn't immediately available most of the time. You're facing down a week or two of pure wait-time as you cruise in to the nearest fuel source, at 0.01G.
esampson
SOC-13
Actually, it would be a pretty poor design to arrive literally 'tanks dry'. Whenever I design a ship I typically try to give them enough fuel to run the power plant and maneuver drives for a month, in addition to their maximum jump.
Now that is clearly not enough fuel to make a Jump-1 out of the spot you're in, but it should be enough fuel to make a 'Jump-0' to chase down a rogue planet or something.
And this can also be deadly:
If you begin to accelerate from Earth to Pluto, and you accelerate all the way you can while you're still inside the 1000 D from the Sun, you'll have no time to brake your speed once you reach near Pluto, as its 1000 D zone will be quite smaller.
So, you must keep your accelerating time to match the smallest 1000 D zone if you're going to leave the Pirmary's one, or you will have serious problems to stop at your destination, so achieveing relatively slow speeds and having quite long trips.
I guess insystem jumps are quite more common with this kind of M drives...
esampson
SOC-13
It's a balancing act. You wouldn't simply accelerate until you leave the 1000D limit of the star, wait, and then start decelerating when you reach the 1000D limit of Pluto. Most likely you would accelerate up to a certain point, turn around and begin decelerating, pass beyond the 1000D limit of the star so your deceleration would only be 1% of efficiency, but that's still significant, and then complete deceleration after you enter the 1000D of Pluto.
While that sounds complex I'm sure that for a well trained navigator it probably isn't any more difficult than some of the problems they had to do on their certification tests.
Of course at a certain point it would also undoubtedly be preferable to just spend a week on the in-system jump. Economics says that that point would most likely be right around the time where the trip takes 7 days * Cost of ship without jump drive/Cost of ship with jump drive, so if the Jump drive costs about 20% of the cost of the ship then it would be in the neighborhood of a 9 day trip.
daltoncalford
SOC-12
Have any rules been published for fuel consumption for a J0?
I believe "J0" is more of a slang term for an in-system jump than an actual technical Jump Transition Level. J1 is used for any jump of 1pc or less, so presumably a "J0" uses the same amount of fuel as a J1 (regardless of distance up to and including 1pc max), according to RAW.
However, you could certainly house-rule that there is a difference. (Perhaps early TL-9 constructed J-Drives are actually "J0", and TL-10 is the first true "J1").
esampson
SOC-13
Other than I believe there is a mention that even in system jumps take a week I don't believe anything has explicitly been written. The rules do, however, technically cover a Jump-0 as something that takes no fuel (10% of the ship's volume times the jump distance) and 1 week of time. Since the ship is obviously travelling some distance there would still be fuel spent, but the amount would be pretty tiny (according to the rules, so see below). At its furthest from Earth Pluto is only about 1/4000th of a parsec away, so for a 100 ton Scout ship the needed fuel would be about .0025 tons.
Of course that's strictly RAW and it isn't completely clear that it is RAI. Until something has been written any Ref would be well within their purview to say that the massive inefficiencies of such a short jump increase the amount of fuel radically, even go so far as to saying that you must spend at least a Jump-1 of fuel. Currently that's in the realm of house rules, however, at least to the best of my knowledge.
andycowley
SOC-10
An interesting thread .... hopefully I can add some value to the discussion..
Based upon the drives detailed in the T5 BBB it would seem that any travel 'in system' which would extend beyond the 1000D of the main star (around orbit 6 for a typical G5 V star) would favor the NAFAL drive which is designed to operate from 0.1G to 0.9G within 1/8 light year of a gravity source (about 8000 AU).... this leads to new and interesting starship design strategies for long range in-system travel to the outer system (but resupplying that outpost station in the Oort cloud @ ~50000AU remains problematical) ....
Secondarily .... G/M/N-drives and Lifters are REACTION drives (they 'reach out and grab the gravity ...and push against it) .... This means that whatever they are 'grabbing' must be of a significantly larger mass that the ship otherwise drive efficiency could be severely impacted .... While this is not detailed further in the BBB 'How maneuver works' it could lead to house rules on what would qualify as a large enough mass ....
EDIT; Someone up-thread asked whether ships exit J-space with their pre-jump vector ... That is answered on page 364 explicitly in the 'Accelerate to Jump Point' paragraph .... YES, a ships pre-jump vector is preserved while in J space and continues at jump exit unless you have a way of changing the vector while in J space with a non-gravity based drive (like a standard ejected mass (reaction) drive) ...
Based upon the drives detailed in the T5 BBB it would seem that any travel 'in system' which would extend beyond the 1000D of the main star (around orbit 6 for a typical G5 V star) would favor the NAFAL drive which is designed to operate from 0.1G to 0.9G within 1/8 light year of a gravity source (about 8000 AU).... this leads to new and interesting starship design strategies for long range in-system travel to the outer system (but resupplying that outpost station in the Oort cloud @ ~50000AU remains problematical) ....
Secondarily .... G/M/N-drives and Lifters are REACTION drives (they 'reach out and grab the gravity ...and push against it) .... This means that whatever they are 'grabbing' must be of a significantly larger mass that the ship otherwise drive efficiency could be severely impacted .... While this is not detailed further in the BBB 'How maneuver works' it could lead to house rules on what would qualify as a large enough mass ....
EDIT; Someone up-thread asked whether ships exit J-space with their pre-jump vector ... That is answered on page 364 explicitly in the 'Accelerate to Jump Point' paragraph .... YES, a ships pre-jump vector is preserved while in J space and continues at jump exit unless you have a way of changing the vector while in J space with a non-gravity based drive (like a standard ejected mass (reaction) drive) ...
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esampson
SOC-13
While you could certainly interpret a J1 as 'any jump of 1pc or less' I think it would be dangerous to do so. That would imply that a J2 is 'any jump that is more than 1pc and less than or equal to 2pc'.
While this doesn't seem at first to be a problem, it actually is, because since stars aren't actually set out with nice, neat geometric precision you are going to have plenty of cases where a star on the map is really 1.001 parsec away from another star but where it is still treated as Jump-1. Arguments about just bumping that star over one more hex because of the tiny fraction don't really hold up because that would jam them into the same hex as another star which actually is just under 2 parsecs away.
esampson
SOC-13
Pretty typically I would assume that the NAFAL drives are only used by people without access to Jump drives. While they are capable of operating further outside the Gravity well I would think that in most cases you would still be better off performing 'in system' jumps. Even if it took a full 10% of the ship in fuel to jump out and another 10% to jump back 1 week spent jumping out to the Oort cloud would be vastly preferable to the well over (since you have to accelerate and decelerate) 1/8 of a year to fly a NAFAL ship out that far.
There probably would be some edge cases were the efficiency of the NAFAL over the M-Drive would be enough to push off moving to a Jump drive, but you are still probably going to be in the neighborhood of trips only taking a bit over a week for the M-drive.
Same costs as J1.
An issue with N-Drives in particular is that they are limited explicitly to radial movement toward/away from the central gravity source (presumably they are highly focussed) and sacrifice lateral movement side-to-side.
N-Drives could certainly be used in the scenario we are discussing, but you would want some type of secondary propulsion for travel along non-radial vectors. N-Drives are primarily envisioned as an STL Interstellar Drive.
esampson
SOC-13
Could you provide a reference for that? (And no, I'm really not trying to be snarky or sarcastic. I'm just asking so I'll know for future reference. I would probably adjust it with a house rule in my own campaign for reasons given above but I would still like to know so that I can make it clear that what I'm proposing is a houserule/handwave rather than saying it isn't explicitly stated)
No, a J2 is any jump of 2 parsecs or less performed by a J2 drive. Fuel cost is 20% of ship's volume. If the J2 drive doesn't have a jump governor, it has to perform J2 jumps even at less than 1 parsec. With a jump governor drives can perform jumps up to its maximum number.
In any case, a 0 meter jump with a J1 drive costs 10% of ship's volume to perform. Unless it has been changed in T5.
Hans
andycowley
SOC-10
Agreed ... With the help of Wolfram Alpha I did the math and if you simply look at the distance traveled by a NAFAL drive in 168hrs (the typical jump time) assuming a stop at the destination point then a 0.1g N-drive can only go 0.6AU in 168hrs ...and a 0.9g n-drive only improves that to 5.4AU .... certainly not even close to the time/distance efficiency of a J1 drive which can travel 187500 AU in 168hrs .....
BUT ... I was thinking about situations where you actually wanted to maneuver when you got to your destination in the outer system so perhaps we can solve the 're-supply and/or explore in the Oort cloud' problem with a ship equipped with a J-drive to get there and a NAFAL drive to maneuver while there...
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esampson
SOC-13
Well, yes, I am assuming that it had a jump governor. If it didn't have a governor then it would certainly need to use the full amount of fuel. However, that would tend to be a special case as it requires an experimental, prototype, or early jump drive instead of a regular one.
I'm not really sure that has ever been established in previous editions, either. Again, I could be wrong, but could you direct me to something written rather than just 'common knowledge'?
esampson
SOC-13
As someone else pointed out, the NAFAL's acceleration is meant to be radial to the star, so it probably wouldn't be a good choice for maneuvering around out there.
One question I would have to ask is why you're going out there in the first place. If you are actively travelling to something like a tiny station on the heliopause of the system then you might just use the M-Drive with lower efficiency. Get your vector to match the projected vector of the station on your arrival, jump, and then even though your efficiency is low you don't need to do much in the way of maneuvering before you dock.
In the case of situations where you might need more acceleration, such as going to a small dwarf planet sitting out in the range of the Kuiper Belt or lurking in the Oort cloud, you would actually precipitate out within 1000D of an object large enough to allow you to use the M-drive at full efficiency, so again, no problem.
Of course there might be a case where you need to maneuver out there while not having large enough objects to use the M-Drive (such as flying around in a debris field held in a Trojan point). In that case I'd probably go with one of the older technologies like HePLAR, which is relatively fuel hungry compared to an M-Drive, but which should still be capable of giving you at least a modicum of maneuvering ability.
I found it in one of the T5 PDFs on my drive (well, 3 of them actually)...
"Jump Governors
A Jump Drive produces a Jump approximately equal to
its Jump number in parsecs, and no less than the next lower
Jump number. A Jump-4 drive can achieve up to 4 parsecs,
and more than Jump-3." (p.370)
Which means J1 is 0<D≤1Pc.
It's most explicit in the GT materials, tho - "An in-system microjump requires the same amount of fuel as a one-parsec interstellar jump." (GTIW p. 170). It's been the standard through all editions that the J# is the upper limit, not the lower.
