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Noclevername
2011-Nov-06, 02:00 AM
I'm working on designing a form of FTL travel for a story. In order to meet certain story needs, I've come up with the following:

The "jumpdrive" works by pulling a ship out of spacetime and then "dropping" back into it at another location. However, there's a semi-random component to where you re-enter both space and time. You might get there in a fraction of a second, or in ten years. (This means that for some short trips your effective "speed" may actually be slower than light.) And you can't appear at a specific point in space, but somewhere within a sphere of probability centered on your intended destination. The further the jump, the larger the uncertainty of where you'll end up.

The ship can't reenter time prior to the point it left, so the drive can't be used to travel into your own past. It also cannot re-enter space if there's a high enough density of mass occupying that space-- so no appearance inside an atmosphere. If either of these things is attempted-- accidentally or intentionally-- then you are randomly "bounced" and might wind up hundreds or thousands of lightyears from your point of origin, and decades or centuries in the future.

There is a physical limit to how much mass can be transported in this way, and certain requirements limit further how much mass you can carry. Activating the drive requires a tremendous amount of energy, so a large power source is needed. You retain your momentum relative to your destination point but on a random vector, so a large amount of fuel or propellant is needed to stabilize and match orbits with your destination planet. Emerging into normal space releases a burst of vaccuum energy in EM form, so you must have heavy shielding to avoid frying your own ship.

The reasons that I've designed the drive to work this way is that I want settled Earthlike planets* with a "frontier" feel. With no way to schedule regular shipments, each world has to be fully independent as soon as possible.** With the mass you can carry limited, there's not likely to be much industry to start with. The possiblity of miscalculated jumps sending you into the future means that I can "skip" over events and choose when a particular chapter is taking place.

It also prevents the formation of an interstellar empire-- the advantage always goes to the defending planet unless they have no space defenses at all. The random jump factors prevent coordinated fleet activities, and prevents a warship from showing up on someone's doorstep except by sheer luck. The mass limitations curtails the weapons that can be carried. And appearing in a huge burst of energy means you can't sneak up on anyone.


* I plan to "cheat" a bit on finding planets compatible with Earth life. Only one or two per thousand life-bearing terrestrial planets will be suitable for settlement, though.
** There is a specific procedure to determine the habitability of a planet; a group of scientists stay on the planet for one full local year growing Earth crops and livestock, and examining local life. (The ship must remain in orbit and contain a backup supply of food for that entire period, further limiting the cargo and passenger mass that can be carried. There is artificial hibernation though, so carrying passengers is like carrying cargo.)

Please feel free to pick holes in this system now, and to point out any unforseen consequences that I have not already addressed.

Rhaedas
2011-Nov-06, 05:10 AM
Sounds a bit like some FTL drives that have been discussed for some space games, particularly the randomness of not knowing exactly where you might come out. Also has a feel of the drive used in Asimov's Foundation's Edge, where it's described more on how travel works, and how their new ship is able to calculate multiple jumps at once making it much faster than any other.

Noclevername
2011-Nov-06, 03:29 PM
Sounds a bit like some FTL drives that have been discussed for some space games, particularly the randomness of not knowing exactly where you might come out. Also has a feel of the drive used in Asimov's Foundation's Edge, where it's described more on how travel works, and how their new ship is able to calculate multiple jumps at once making it much faster than any other.

Being compared to Asimov, even in a tangential way, is a great compliment. Thank you. :o

As for multiple jumps, you have to stop and recalculate your position and time passed after each jump to make the next one, otherwise the random factors build up very rapidly. You also have to stop and discharge waste heat after every jump -- the drive is doing a lot of work.

Theoretically you could go anywhere in the universe, but in practice you'd have no control over where and when you wound up. The probability sphere would expand to infinity if you tried going to even a local galaxy like Andromeda. Your life support would probably give out before you got home. You'd probably have to find the nearest compatible planet and "go native".

PraedSt
2011-Nov-06, 04:28 PM
Are the uncertainties in locational and time somehow dependent? For example an inverse relationship- if you land very close to your target you arrive much later, but if you arrive very quickly you arrive quite a distance away? Or are the two uncertainties not related at all?
Also, what would be the maximum uncertainty in a short trip- say Earth to Alpha Centauri? Or even a "unit" trip of 1 light year?

Noclevername
2011-Nov-06, 04:53 PM
Are the uncertainties in locational and time somehow dependent? For example an inverse relationship- if you land very close to your target you arrive much later, but if you arrive very quickly you arrive quite a distance away? Or are the two uncertainties not related at all?
Also, what would be the maximum uncertainty in a short trip- say Earth to Alpha Centauri? Or even a "unit" trip of 1 light year?

The two uncertainties are essentially independent.

I haven't worked out the exact formula yet-- there are factors such as local gravity and stellar motion which affect the level of uncertaintly. Let's say a light year jump has a basic 99% chance of appearing within ten light-minutes of the target planet; a ten light year jump has a 98.9% or so chance, etc. Since most of the settled worlds are hundreds or thousands of LY apart, it quickly adds up. A series of shorter jumps becomes necessary for relatively accurate navigation. And you have to avoid appearing inside a nebula or other region of high density, or risk a random bounce. Most captains will pause outside a system and observe it for a while, in order to make sure their navigational charts are accurate enough for an in-system jump. Most settled systems will also contain navigational aids and beacons.

PraedSt
2011-Nov-06, 06:38 PM
I think this jump drive mitigates against planetary expansion. But it sounds like a fun drive to have. I'd probably build one of those colony ships and just randomly explore.

Noclevername
2011-Nov-07, 01:37 AM
I think this jump drive mitigates against planetary expansion.

Yes, I'm thinking there have to be multiple trips to each world just to populate each colony planet enough to avoid inbreeding. For that matter, it might be a good idea for each ship to carry a supply of frozen embryos along just in case they get lost/bounced and have to go native in some distant galaxy.

Solfe
2011-Nov-07, 04:06 AM
There is a physical limit to how much mass can be transported in this way, and certain requirements limit further how much mass you can carry. Activating the drive requires a tremendous amount of energy, so a large power source is needed. You retain your momentum relative to your destination point but on a random vector, so a large amount of fuel or propellant is needed to stabilize and match orbits with your destination planet. Emerging into normal space releases a burst of vaccuum energy in EM form, so you must have heavy shielding to avoid frying your own ship.


I like it so far, but the section above sounds like a weapon rather than a liability.

If everything about arrival is random except for velocity, a warship should be studded with weapons in every direction. Do this with a squadron of ships and you could dump weapons like mines or missiles into orbit around a planet. Not only would the defenders have to deal with really short response times for direct fire weapons, they would have to clean up the stuff zipping around the planet in relatively stable orbits. Of course the attackers would have to be prudent so as not to lob perfectly good missiles/mines in directions that will cause them to leave orbit or slam into the planet.

You might even have cases where opponents see each other a few light minutes or hours away and jump to unleash a preemptive strike. In some cases one side might be able to time things so there is no time to detect the strike. Say by traveling via FTL from one light minute to one light second distance from the target and unloading lasers (EDIT: and then jump away). It sounds like the the ships are armored enough to survive a strike from a couple of lasers, but the short response time is going to really impact the crew. Frayed nerves might not cover it. :) It almost sounds like a shark attack.

Tobin Dax
2011-Nov-07, 05:26 AM
. . . . And you have to avoid appearing inside a nebula or other region of high density, or risk a random bounce.

How dense is "high density" Many nebulae have fewer than 1000 atoms per cubic meter. If the drive is that sensitive, you'll never be able to stop bouncing within a reasonable distance of any planet.

Rhaedas
2011-Nov-07, 05:41 AM
How dense is "high density" Many nebulae have fewer than 1000 atoms per cubic meter. If the drive is that sensitive, you'll never be able to stop bouncing within a reasonable distance of any planet.

More specifically, does the drive fail because of having to move the mass* that occupied the chosen space, and too much "resistance" makes the ship skip, kind of like skipping stones off water by having them hit at a certain angle? Or is it more gravity driven, where if there's too much of a dip in the space-time fabric it throws off the coordinates and gives a translation error in the transit?

* I visualize something like a hole opening that the ship slips through, and any appreciable gases would get shoved out from that point, maybe creating some type of shock wave of energy from them getting excited, like a neon tube.

Noclevername
2011-Nov-07, 06:08 AM
I like it so far, but the section above sounds like a weapon rather than a liability.
At a close enough distance, it could be, but the odds of appearing anywhere near your target are minimal.



If everything about arrival is random except for velocity, a warship should be studded with weapons in every direction. Do this with a squadron of ships and you could dump weapons like mines or missiles into orbit around a planet. Not only would the defenders have to deal with really short response times for direct fire weapons, they would have to clean up the stuff zipping around the planet in relatively stable orbits. Of course the attackers would have to be prudent so as not to lob perfectly good missiles/mines in directions that will cause them to leave orbit or slam into the planet.

As I said, the odds of arriving anywhere close to the planet's orbit are minimal (see post #5) making "short defense times" implausible, and ships would arrive years apart in time, making "sqadrons" impossible.


You might even have cases where opponents see each other a few light minutes or hours away and jump to unleash a preemptive strike. In some cases one side might be able to time things so there is no time to detect the strike. Say by traveling via FTL from one light minute to one light second distance from the target and unloading lasers (EDIT: and then jump away). It sounds like the the ships are armored enough to survive a strike from a couple of lasers, but the short response time is going to really impact the crew. Frayed nerves might not cover it. :) It almost sounds like a shark attack.

You can't make short jumps that accurately-- I should have explained there's a lower limit. As for jumping "in then out", as I said in post 5 you can't do that. It takes time before you can do another jump (think BSG). And FTL warships that have enough spare room for mass to carry heavy lasers or other longrange weapons will be automated combat drones. As will, most likely, any longrange defensive ships anywhere near a defending planet. Their "nerves" won't get frayed.

Noclevername
2011-Nov-07, 06:19 AM
How dense is "high density" Many nebulae have fewer than 1000 atoms per cubic meter. If the drive is that sensitive, you'll never be able to stop bouncing within a reasonable distance of any planet.

The density is low enough in some nebulae to avoid a bounce, but transitory regions of higher density do occur even within a thin nebula and "there are no old, bold pilots". Not everyone follows this nebula policy, though of those who don't, many are on the missing list.
And a cautious captian will generally stay well clear of a "reasonable distance" of a planet when planning a jump to lessen the odds of just that. They'll just cross the space physically. No one opts for haste on these starships.


More specifically, does the drive fail because of having to move the mass* that occupied the chosen space, and too much "resistance" makes the ship skip, kind of like skipping stones off water by having them hit at a certain angle? Or is it more gravity driven, where if there's too much of a dip in the space-time fabric it throws off the coordinates and gives a translation error in the transit?

* I visualize something like a hole opening that the ship slips through, and any appreciable gases would get shoved out from that point, maybe creating some type of shock wave of energy from them getting excited, like a neon tube.

I'd say it's more gravity based: gravity is one of the variables that goes into a jump calculation.

Jens
2011-Nov-07, 07:20 AM
Just to make it sort of believable in a sophisticated way, I think you could frame it in terms of quantum uncertainty, that somehow the ship is warping to another dimension where quantum effects work on a large scale, so the ship is seen as a virtual particle, and if you know it's velocity you can't know the location and vice versa, or something along those lines. The more you know where you are, the less you know where you're heading, I suppose. The stellar entanglement drive.

PhysicsJM32
2011-Nov-07, 09:02 AM
The idea sound cool!
A few questions:
1)What is the thermal output of the drive like?
2)Does it output deadly forms of energy (i.e. nuclear radiation, high doses of microwaves, gamma rays, etc?
3)Just as a thought excise, what would happen if the drive was activated in the vicinity of a singularity(or does the gravity lower the probability of materialization in locations such as this to levels where it would be virtually impossible?
4)Would there be a possibility of the conserved velocity from prior to the jump being converted into angular momentum upon arrival, or would straight line velocity prior to a jump only be converted to straight line energy in another direction.
5)Would it be possible for an external force to deliberately stop the drive dropping the ship out into real-space in a particular location?

Noclevername
2011-Nov-08, 12:23 AM
Just to make it sort of believable in a sophisticated way, I think you could frame it in terms of quantum uncertainty, that somehow the ship is warping to another dimension where quantum effects work on a large scale, so the ship is seen as a virtual particle, and if you know it's velocity you can't know the location and vice versa, or something along those lines. The more you know where you are, the less you know where you're heading, I suppose. The stellar entanglement drive.

For certain spoilerish reasons, it has to stay in the "it works but we're not sure how" category. There's a good reason why. ;)

Tobin Dax
2011-Nov-08, 01:06 AM
The density is low enough in some nebulae to avoid a bounce, but transitory regions of higher density do occur even within a thin nebula and "there are no old, bold pilots". Not everyone follows this nebula policy, though of those who don't, many are on the missing list.
And a cautious captian will generally stay well clear of a "reasonable distance" of a planet when planning a jump to lessen the odds of just that. They'll just cross the space physically. No one opts for haste on these starships.

Okay, but this UT article (http://www.universetoday.com/34074/interplanetary-space/) gives the density of particles in interplanetary space (around Earth) as 5 particles per cubic centimeter, which is 5 million particles per cubic meter, and that's characteristic of some nebulae. If nebulae cause a bounce, so will most locations within a solar system. And if the uncertainty in the end point of the jump is on the scale of Astronomical Units, you're again practically guaranteed to not be able to arrive within light-days of a planet (at a minimum).

The "lost captains" idea is a nice one, but these are the repercussions. And you asked. ;)

Noclevername
2011-Nov-08, 01:50 AM
Okay, but this UT article (http://www.universetoday.com/34074/interplanetary-space/) gives the density of particles in interplanetary space (around Earth) as 5 particles per cubic centimeter, which is 5 million particles per cubic meter, and that's characteristic of some nebulae. If nebulae cause a bounce, so will most locations within a solar system. And if the uncertainty in the end point of the jump is on the scale of Astronomical Units, you're again practically guaranteed to not be able to arrive within light-days of a planet (at a minimum)

The "lost captains" idea is a nice one, but these are the repercussions. And you asked. ;)
(bold mine)

I did. OK, so thinner nebulae are possible re-entry points while denser ones are off-limits. Keep in mind that it's possible to bypass a nebula entirely since you aren't physically crossing that space.

There's also the one-in-a-trillion chance that you might jump right "into" a planet or star and bounce. So a cautious distance isn't a bad thing.

The minimal distance "micro-jump" should have an uncertainty sphere of several (1-20?) light-seconds, that will make it possible to do an in-system jump without getting too close to your target and risking a bounce, or too far for practical travel.


It's a risky sort of drive.

Noclevername
2011-Nov-09, 11:12 AM
The idea sound cool!
A few questions:
1)What is the thermal output of the drive like?
2)Does it output deadly forms of energy (i.e. nuclear radiation, high doses of microwaves, gamma rays, etc?
3)Just as a thought excise, what would happen if the drive was activated in the vicinity of a singularity(or does the gravity lower the probability of materialization in locations such as this to levels where it would be virtually impossible?
4)Would there be a possibility of the conserved velocity from prior to the jump being converted into angular momentum upon arrival, or would straight line velocity prior to a jump only be converted to straight line energy in another direction.
5)Would it be possible for an external force to deliberately stop the drive dropping the ship out into real-space in a particular location?

1) It takes roughly 1 hour to deploy an average ship's thermal radiators* and cool down the drive. This time decreases slightly during the story as technology improves.
2) It's usually charged by a reactor (fission at first, later fusion as the technology advances), but the really dangerous radiation comes from outside the ship-- the drive generates a "bubble" of rapidly-decaying exotic-matter particles around the ship, which cut off the space around the ship from normal spacetime. Coming back into normal space releases a burst of energetic photons, mostly in the gamma range. I haven't nailed down the exact amount of energy involved.
3) If you're too close to it, you'd probably do a random bounce.
4) Straight line to straight line.
5) The ship is isolated in a bubble of its own spacetime for an immeasurably small moment. Essentially it exists in its own little pocket universe and in a practical sense, there is no "external" anything during a jump.


* The size of the bubble puts a size limit on the ship, which is why the radiators are usually folded up during a jump.

Solfe
2011-Nov-09, 01:45 PM
I really like the idea of maintaining velocity through the jump. I can easily picture a ship jumping in at high speed for a little recon and doing a neat little gravity whip around the planet to slow down and come back. Perhaps they time it so the loop around the planet leaves time for a choice between jumping away or staying the course.

Noclevername
2011-Nov-09, 02:04 PM
I really like the idea of maintaining velocity through the jump. I can easily picture a ship jumping in at high speed for a little recon and doing a neat little gravity whip around the planet to slow down and come back. Perhaps they time it so the loop around the planet leaves time for a choice between jumping away or staying the course.

Since you have little control over when you'd arrive, as in what year, you have no way of knowing where in its orbit the planet will be when you pop in; you also have to take into account the star's motion relative to your last jump. The arrival velocity is also on a random vector, so you could come out facing the wrong way. But you'll have plenty of time for recon as you match your velocity and course to the planet's orbit and then chase it down.

Sorry, I'm spoiling all your fun here. :)

Noclevername
2011-Nov-09, 05:38 PM
I thought of a partial solution to the above; do multiple micro-jumps around the system until you "luck into" a trajectory facing roughly where you want to go. But you'd only do so if you have energy to spare and/or are low on propellant, because it's both energy-intensive, and increases the risk of a bounce. You also ideally should ask permission from the colony world, since you may be delaying your arrival by months or years via time-jump.

Since the bubble size is limited, perhaps the ship's main rector should be designed to retract into or closer to the ship for a jump, and then extend away for normal flight to limit the crew's radiation exposure (it goes without saying that the crew and passengers would ride out a jump in the "storm cellar".) Or would a telescoping reactor boom add too much complication to an already complicated ship design?

PraedSt
2011-Nov-09, 06:02 PM
Would you mind if I suggest a different solution to your requirements? I like the drive, but it just seems too complicated.

From your OP (I've bolded some relevant bits):


The reasons that I've designed the drive to work this way is that I want settled Earthlike planets* with a "frontier" feel. With no way to schedule regular shipments, each world has to be fully independent as soon as possible.** With the mass you can carry limited, there's not likely to be much industry to start with. The possiblity of miscalculated jumps sending you into the future means that I can "skip" over events and choose when a particular chapter is taking place.

It also prevents the formation of an interstellar empire-- the advantage always goes to the defending planet unless they have no space defenses at all. The random jump factors prevent coordinated fleet activities, and prevents a warship from showing up on someone's doorstep except by sheer luck. The mass limitations curtails the weapons that can be carried. And appearing in a huge burst of energy means you can't sneak up on anyone.


* I plan to "cheat" a bit on finding planets compatible with Earth life. Only one or two per thousand life-bearing terrestrial planets will be suitable for settlement, though.
** There is a specific procedure to determine the habitability of a planet; a group of scientists stay on the planet for one full local year growing Earth crops and livestock, and examining local life. (The ship must remain in orbit and contain a backup supply of food for that entire period, further limiting the cargo and passenger mass that can be carried. There is artificial hibernation though, so carrying passengers is like carrying cargo.)

In your universe, distances are vast, candidate planets are very rare, and you have hibernation technology. Why not go with a "standard" FTL drive, but limit to top speed to say 2xLS? You'd get the isolated settlements that you want, with none of the plot headaches of a random drive. And as your story progresses, so can the drive technology- to 2.5xLS, then 3xLS, and so on.

Noclevername
2011-Nov-09, 06:17 PM
The "randomness" is under the control of the writer so it isn't truly random. Mine is a universe with intelligent design, or halfway smart design anyway. ;) It's meant to be complicated: I need my characters to face certain challenges. Without giving away too much, I've set it up the way it is to meet certain story requirements.

You know what they say... getting there is half the fun!

Solfe
2011-Nov-09, 08:11 PM
My wife's car works exactly like this drive... all random vectors and and arrival times.

PraedSt
2011-Nov-09, 08:17 PM
The "randomness" is under the control of the writer so it isn't truly random. Mine is a universe with intelligent design, or halfway smart design anyway. ;) It's meant to be complicated: I need my characters to face certain challenges. Without giving away too much, I've set it up the way it is to meet certain story requirements.

You know what they say... getting there is half the fun!Don't say I didn't warn you :)

Drunk Vegan
2011-Nov-09, 08:18 PM
I thought of a partial solution to the above; do multiple micro-jumps around the system until you "luck into" a trajectory facing roughly where you want to go. But you'd only do so if you have energy to spare and/or are low on propellant, because it's both energy-intensive, and increases the risk of a bounce. You also ideally should ask permission from the colony world, since you may be delaying your arrival by months or years via time-jump.

Since the bubble size is limited, perhaps the ship's main rector should be designed to retract into or closer to the ship for a jump, and then extend away for normal flight to limit the crew's radiation exposure (it goes without saying that the crew and passengers would ride out a jump in the "storm cellar".) Or would a telescoping reactor boom add too much complication to an already complicated ship design?


Using this theme, you could include a dramatic scene in which the starship's sublight engines fail, and the ship's crew spend tense days making microjumps trying to get lucky and come out of FTL on a course close enough to intercepting the planet that they can let their inertia coast them up to the planet and then make minor adjusments to get into orbit using chemical rocket burns.

They have to have this stroke of luck before the fuel for the FTL runs out of course, or else they'll end up coasting through space until their water/food/air runs out.

If you're feeling macabre, maybe they don't succeed and we read about their final days...

Noclevername
2011-Nov-09, 08:30 PM
Using this theme, you could include a dramatic scene in which the starship's sublight engines fail, and the ship's crew spend tense days making microjumps trying to get lucky and come out of FTL on a course close enough to intercepting the planet that they can let their inertia coast them up to the planet and then make minor adjusments to get into orbit using chemical rocket burns.

They have to have this stroke of luck before the fuel for the FTL runs out of course, or else they'll end up coasting through space until their water/food/air runs out.

If you're feeling macabre, maybe they don't succeed and we read about their final days...

:shhh: I say nnnnnothing...

PraedSt
2011-Nov-29, 06:44 PM
How's it going?

Noclevername
2011-Nov-29, 07:26 PM
Slow, right now I have a lot of personal stuff going on. I've had to back-burner a lot of things. But I'll get back to it eventually.