Kraven Kor Posted August 7, 2009 Report Share Posted August 7, 2009 So yet another question regarding my plans being more complicated than my knowledge of things... Travel times. My FTL is in two forms that work similarly - Wormholes and "Tunneling Drives" The first is what it sounds like, a naturally occurring anomaly in space-time that creates a shortcut to another point in the Galaxy. They are the fastest travel method available, found at the far reaches of a solar system and caused by the gravitational influence of two or more stars on their neighbors. Tunneling drives work on the same principle, except are artificially created by massive amounts of energy rather than stellar mass. Tunneling drives can also only create very short tunnels - so a trip of a single light year would take a dozen or so "jumps" (not really jumps, observers would see no flashy thing, the ship would simply appear to move at FTL, maybe with a blur or elongation effect, but locally the ship is not moving faster than it was, it is simply moving in a "tunnel" of space-time that is shorter than the natural topography.) Each tunnel is anywhere from a few light-minutes to a few light-hours in length, to the ship traveling through it (so it takes the craft up to several days to move through each tunnel segment), and can cross sections of real space up to several light years - deeper in space the tunnels can be larger as there are less objects and hazards to plot a course around. So a ship gets to the outer reaches of a system (several days travel using 1 to 3 G burns, depending on urgency), creates a tunnel, spends a day or five in that tunnel, gets about a half light year or more, creates the next tunnel, gets a few light years further, the tunnels then get shorter as it nears destination, then you are at the edge of destination system and have to use traditional methods to get to the actual planet or station. So what would be the math behind figuring total travel time? (There are a ton of links here on previous conversations I need to review.) Note: This is part of the reason I want a fracking excellent Star map to work with. The tunnel can only be created in deep space, but can get you anywhere so long as you chart around other systems or large objects, etc. It is incredibly risky in unknown space, too, as you have to have done extensive scans for deep space objects, debris, nebulae, etc. - it isn't hyperdrive, you are in "real space" when you move though you are kind of creating your own path through it. I thus need to have links from each system to each other system that shows distance and travel times, eventually, especially if I want to share this setting with others at any point. As almost every nearby object or star is of interest to the human race, I want to cover as much of the local area as possible, within which to distribute the various plot points and places of interest and such. Quote Link to comment Share on other sites More sharing options...
LoresLost Posted August 8, 2009 Report Share Posted August 8, 2009 Re: And now a Math question - figuring out travel times... Sir, I saw this and though that what is ment by the 'outer system' In our solar system At about 90 AU is what is called the termination shock, where the solar wind is lower then the speed of sound (not that is a really useful definition in space, handy for us to get our heads around) The heliopause is somewhere around 100 - 120 AU (This is the point where solar wind is stoped by the interstellar wind) At 1 to 3 G constant acceleration (using a linar (1/2)at^2 with a = 9.8meters/sec/sec) I get you have travaed 2.2 to 6.6 AU in three days which is from the inside of Jupiter's orbit to inside Saturn's orbit from earth. Is this where you Quote Link to comment Share on other sites More sharing options...
CptPatriot Posted August 8, 2009 Report Share Posted August 8, 2009 Re: And now a Math question - figuring out travel times... Kraven, there are a few questions that need to be addressed before you can answer that. What is the spacial relationship ratio between normal space and space in the tunnel? What is the variable that is affecting the tunnel lengths as you get closer to your destination? Is the spacial relationship changing as the tunnel lengths shorten? Quote Link to comment Share on other sites More sharing options...
Kraven Kor Posted August 8, 2009 Author Report Share Posted August 8, 2009 Re: And now a Math question - figuring out travel times... Kraven, there are a few questions that need to be addressed before you can answer that. What is the spacial relationship ratio between normal space and space in the tunnel? What is the variable that is affecting the tunnel lengths as you get closer to your destination? Is the spacial relationship changing as the tunnel lengths shorten? 1. It varies, and is a larger difference the further you are from a system. So the first tunnel might be 1/10 or so, the tunnels farther out 1/100 or more. I also misspoke in my first post, each tunnel would only take a few hours to traverse, not days, lots of little hops basically. 2. It is all about gravitational influence - the closer you are to a system, the more power it takes to create a tunnel, and the shorter that tunnel is. The drive uses energy to create a focused gravitational effect and essentially you create your own tunnel of space-time that links two points in space together, so you are combating naturally occurring gravitational forces to do this. 3. The tunnels closer to a system are both shorter (less time spent in them at standard speeds), and cross less distance (lesser ratio?) So yes, the relationship is different, shorter tunnels are distorting the distance differently. ----- Loreslost: One of my previous threads ended up postulating that it would take, at 1 G to 3 G burns (ie. doing 3 G burns occasionally and within safety limits for the crew), about 20 days to cross our solar system, given that you accelerate to the midpoint then decelerate at the same rate to your destination. I believe they quoted 12 days to get from Earth to around the orbit of Neptune. I'm thinking the point at which you can start up the tunnel drive will between the average distances of Uranus and Neptune, so long as you aren't near one of those planets when you do so. Wormholes will generally be found above or below the planetary orbits / disks / plane, and closer, about 30 to 40 AU from our sun and similar ratios above or below other stars based on their size (closer to smaller stars, farther from larger stars.) As you can see, my imagined ideas far surpass my knowledge Quote Link to comment Share on other sites More sharing options...
Cancer Posted August 9, 2009 Report Share Posted August 9, 2009 Re: And now a Math question - figuring out travel times... Coming at this from the top of the problem rather than the bottom.... How big a star map are you looking to create (in terms of number of inhabited or inhabitable systems)? And do you want it rooted in reality (that is, use real stars centered on Sol as a beginning point)? EDIT: Never mind, I found your answer to this in your YASMT thread. You do realize that the number of time computations you have to perform goes roughly as half of the square of the number of stars in your map, right? Unless you do some serious pruning (as in, throw away all but one in a million or so), with a map size of +/- 1500 LY from Sol, with a rough density of one star per cubic parsec in our part of the Galaxy, there's several hundred million stars in that space? I think you're going to have to resort to programming to get these tasks done. Quote Link to comment Share on other sites More sharing options...
Cancer Posted August 9, 2009 Report Share Posted August 9, 2009 Re: And now a Math question - figuring out travel times... ... Loreslost: One of my previous threads ended up postulating that it would take, at 1 G to 3 G burns (ie. doing 3 G burns occasionally and within safety limits for the crew), about 20 days to cross our solar system, given that you accelerate to the midpoint then decelerate at the same rate to your destination. I believe they quoted 12 days to get from Earth to around the orbit of Neptune. Is it really necessary to get your ship back down to around zero velocity before you can make your tunnel/jump? That's an important, and explicit, decision about space travel in your game-world. FWIW, the dispersion of stellar velocities among older stars (stars like the sun) is several tens of km/sec. Zero velocity with respect to our Sun will not be zero velocity with respect to the star of another system. If your interstellar travel system doesn't handwave away those velocity differences, then you have a rather variable and substantial amount of energy and momentum needed in the velocity-matching process, even absent whatever needs you have for your FTL process. I'm thinking the point at which you can start up the tunnel drive will between the average distances of Uranus and Neptune, so long as you aren't near one of those planets when you do so. Wormholes will generally be found above or below the planetary orbits / disks / plane, and closer, about 30 to 40 AU from our sun and similar ratios above or below other stars based on their size (closer to smaller stars, farther from larger stars.) I assume by "size" you mean mass for the other stars. That's the obvious choice, but it's not the only one possible. Choosing mass means that gravitation is limiting your stardrive. You could choose something different, like total energy output ("bolometric luminosity") or even stellar output in a particular wavelength regime ... this would happen if, for instance, it was something about the electromagnetic radiation environment rather than the gravitational environment/space curvature was the critical limit on your stardrive. Quote Link to comment Share on other sites More sharing options...
Kraven Kor Posted August 10, 2009 Author Report Share Posted August 10, 2009 Re: And now a Math question - figuring out travel times... Is it really necessary to get your ship back down to around zero velocity before you can make your tunnel/jump? That's an important' date=' and explicit, decision about space travel in your game-world. FWIW, the dispersion of stellar velocities among older stars (stars like the sun) is several tens of km/sec. Zero velocity with respect to our Sun will [u']not[/u] be zero velocity with respect to the star of another system. If your interstellar travel system doesn't handwave away those velocity differences, then you have a rather variable and substantial amount of energy and momentum needed in the velocity-matching process, even absent whatever needs you have for your FTL process. No. In fact you have to be moving at quite a clip and have a trajectory that matches where your tunnel will be "moving" - when you create the tunnel it stretches and skews space in front of you and you have to be moving "with the current" when this occurs. I assume by "size" you mean mass for the other stars. That's the obvious choice, but it's not the only one possible. Choosing mass means that gravitation is limiting your stardrive. You could choose something different, like total energy output ("bolometric luminosity") or even stellar output in a particular wavelength regime ... this would happen if, for instance, it was something about the electromagnetic radiation environment rather than the gravitational environment/space curvature was the critical limit on your stardrive. Gravitational effects on Space-time are the basis for the drive. --- And I don't intent to map each star to each other star. Having a somewhat accurate model for determining how long it will take to move 47 LY would be helpful, though. I'll only be creating a few dozen "links" as common routes of travel between the 20 or so systems I intend as important locations in the game. Quote Link to comment Share on other sites More sharing options...
Kraven Kor Posted August 10, 2009 Author Report Share Posted August 10, 2009 Re: And now a Math question - figuring out travel times... There is also the further complication that you can't really tunnel through or past another system - so really long distance tunnel trips are impractical as you have to go way around stars that are in between you and the destination. I'm sure there are a few long distance trips with no "stopovers" but mostly you can only fly to a star's nearby neighbors by any means - longer trips mean going star to star to star. Quote Link to comment Share on other sites More sharing options...
Cancer Posted August 10, 2009 Report Share Posted August 10, 2009 Re: And now a Math question - figuring out travel times... No. In fact you have to be moving at quite a clip and have a trajectory that matches where your tunnel will be "moving" - when you create the tunnel it stretches and skews space in front of you and you have to be moving "with the current" when this occurs. That means that you don't necessarily want to do the deceleration for half your trip while in normal space inside the solar system. In fact, you may want to continue accelerating along your chosen velocity vector. That would shorten your in-system travel times substantially from what you were told before (your description makes it sound like the numbers you quoted are for an accelerate the first half, decelerate the second half flight plan). Foregoing the deceleration on the second half does put all the work of getting back to "zero" velocity with respect to the destination star into the manuvers at the end of travel, but if you're sending information rather than bulk matter that's OK. Let me push some numbers around and if I get something useful cobbled together I'll post it. Quote Link to comment Share on other sites More sharing options...
Kraven Kor Posted August 10, 2009 Author Report Share Posted August 10, 2009 Re: And now a Math question - figuring out travel times... Thanks! Hopefully you find that "fun" and I'm not tricking you into "work" Quote Link to comment Share on other sites More sharing options...
L. Marcus Posted August 10, 2009 Report Share Posted August 10, 2009 Re: And now a Math question - figuring out travel times... Cancer balances checkbooks for relaxation. Quote Link to comment Share on other sites More sharing options...
novi Posted August 10, 2009 Report Share Posted August 10, 2009 Re: And now a Math question - figuring out travel times... First, I question your logic on how far around stars you have to go - the vast distances separating stars makes it unlikely that you'd get close enough to most intervening stars to affect the operation of the drive system as I understand it. Also, the stated operation of your drive system is at odds with your intended method of navigation. If it takes less energy to activate the drive and you travel further with each activation when you are in deep space, it is both cheaper and faster to stick to deep space and avoid star systems other than your destination. If in deep space you can create one tunnel that crosses a light-month, while it takes up to a dozen tunnels to get a light-month away from a star, what is the point in going close to a star? Other, of course, than that's where everyone lives. Another question I have to ask, for the tunneling drive, does it works against absolute gravitational potential, or is it a function of space-time curvature? The former simply wants to be as far away as possible from all large objects. The later also cares about the arrangement of the large objects. If the drive only works in regions of 'flat' space-time, it will function as normal at great distances from stars. However, you can also make it work much closer to stars by using the Lagrange points. These are areas where the gravitational pull of two large objects, usually a star and a planet, are equal, and thus space-time is relatively 'flat' there. Things get a little tricky from there - what are the restriction on where you can form your exit point? Does it have to be in the same region of FST, or just a region of FST, or can it be anywhere? But back to your original question, figuring transit times - this really depends on the exact number you have for your drive system. But it basically breaks down into a two-piece equation - the cruise phase and the system phase. For the system phase, this becomes a constant based on your rules - it will take roughly the same amount of time and number of jumps to get from the system into deep space where you use the cruise phase, where it is a simple matter of figuring out your average FTL speed, and thus travel time. Let's say that you have to get .1 light-years, or a little over a light-month, out to be considered in deep space. Let's call that 10 jumps, and that standard practice is to schedule 3 days for that, though it can be done in under 2. Then we need to know how fast ships can travel in deep space. One could complicate this with the ship performing real-space acceleration during this, but simple economics and safety factors suggest that the ship probably coasts through most of the tunneling phase. Here is where you pick a number that makes the travel times work out how you would like. The only constraint here is that it should be noticeably faster than travel out of the system, which with that example works out to one light-year every 20 days when in a hurry. Any further questions? Quote Link to comment Share on other sites More sharing options...
Kraven Kor Posted August 10, 2009 Author Report Share Posted August 10, 2009 Re: And now a Math question - figuring out travel times... First' date=' I question your logic on how far around stars you have to go - the vast distances separating stars makes it unlikely that you'd get close enough to most intervening stars to affect the operation of the drive system as I understand it.[/quote'] Fair enough, chalk that up to space being unimaginably large and this being a symptom of that. Another question I have to ask, for the tunneling drive, does it works against absolute gravitational potential, or is it a function of space-time curvature? The former simply wants to be as far away as possible from all large objects. The later also cares about the arrangement of the large objects. If the drive only works in regions of 'flat' space-time, it will function as normal at great distances from stars. However, you can also make it work much closer to stars by using the Lagrange points. These are areas where the gravitational pull of two large objects, usually a star and a planet, are equal, and thus space-time is relatively 'flat' there. Things get a little tricky from there - what are the restriction on where you can form your exit point? Does it have to be in the same region of FST, or just a region of FST, or can it be anywhere? Potential, mostly. The whole idea is I don't want FTL Death Fleets popping up in convenient local orbit with little to no warning. So the entrance and exit point both have to be in the outer reaches of a star system. Edit: And Entry/Exit is a misnomer - a ship flying FTL 10 LY will be seen by telesopes as an elongated signal some years down the road. They don't ever really leave normal space, so they have to deal with all objects and gravitational fields that may be on their course. Realistically, this means you can come in closer to a system by avoiding the plane of the planetary disk, but not by much since at the macro level the mass of our solar system makes for one huge gravitational field when you look at it from afar. But back to your original question, figuring transit times - this really depends on the exact number you have for your drive system. But it basically breaks down into a two-piece equation - the cruise phase and the system phase. For the system phase, this becomes a constant based on your rules - it will take roughly the same amount of time and number of jumps to get from the system into deep space where you use the cruise phase, where it is a simple matter of figuring out your average FTL speed, and thus travel time. Let's say that you have to get .1 light-years, or a little over a light-month, out to be considered in deep space. Let's call that 10 jumps, and that standard practice is to schedule 3 days for that, though it can be done in under 2. Then we need to know how fast ships can travel in deep space. One could complicate this with the ship performing real-space acceleration during this, but simple economics and safety factors suggest that the ship probably coasts through most of the tunneling phase. Here is where you pick a number that makes the travel times work out how you would like. The only constraint here is that it should be noticeably faster than travel out of the system, which with that example works out to one light-year every 20 days when in a hurry. Any further questions? They move through the tunnels at about a 1 G burn as normal, mostly because the normal engines are fairly efficient and the only "artificial gravity" is created by forward thrust - most interstellar craft are built like flying towers, with the top being "front." And yes, I'm wanting about 5 to 10 days to get to Alpha Centauri, and then several months to reach the outer limits of Human Space (~40 LY). Quote Link to comment Share on other sites More sharing options...
novi Posted August 10, 2009 Report Share Posted August 10, 2009 Re: And now a Math question - figuring out travel times... Potential, mostly. The whole idea is I don't want FTL Death Fleets popping up in convenient local orbit with little to no warning. So the entrance and exit point both have to be in the outer reaches of a star system. Edit: And Entry/Exit is a misnomer - a ship flying FTL 10 LY will be seen by telesopes as an elongated signal some years down the road. They don't ever really leave normal space, so they have to deal with all objects and gravitational fields that may be on their course. Realistically, this means you can come in closer to a system by avoiding the plane of the planetary disk, but not by much since at the macro level the mass of our solar system makes for one huge gravitational field when you look at it from afar. Not so much. First off, even if the ship was bright enough to be seen at interstellar distances, once the photons from the ship leave the zone of FTL travel, they go back to traveling at the speed of light, reaching you after the ship in deep space does. It's only one they get closer to the system and the jumps get shorter that light can finally outrun the source. On the other hand, if they actually travel down a tunnel-like region of space, you'd be able to spot the ship ahead of time if you manage to look down the length of the tunnel, though that would be a good trick. Nextly, there doesn't seem to be much in interstellar space. There's a little bit of gas, by which I mean a really good vacuum, a little bit of dust and sand, and the occasional comet. There might be rogue planets, but not many, so you can consider anything popping up to be plot dependent. Lastly, the plane of the solar system has little effect on the overall shape of the depth of the gravity well - the sun only contains 99.86% of the mass of the solar system, and Jupiter at .1% of the total mass, so the difference in how close you could get in plane vs. off plane is likely only a small fraction of an AU. They move through the tunnels at about a 1 G burn as normal' date=' mostly because the normal engines are fairly efficient and the only "artificial gravity" is created by forward thrust - most interstellar craft are built like flying towers, with the top being "front." And yes, I'm wanting about 5 to 10 days to get to Alpha Centauri, and then several months to reach the outer limits of Human Space (~40 LY).[/quote'] in that case, you're looking at effective cruise speeds of one light-year every day or two. Though don't forget, you've got the acceleration phase of short jumps getting from the outer system to deep space, plus the in-system cruise of 10 days on either end. One more thing, but those are really, really, really efficient engines you have for moving in system, as in they'd better be non-newtonian. Assuming one-gee constant acceleration out to 25 AU, that'll take about 10 days and the ship will be traveling at 2.8% of the speed of light at that point. If, as you insist, the ship is still in normal space and has to deal with everything there, it's better have really good force fields - hitting a 130 pound rock at that speed has as much energy as a megaton of TNT. Quote Link to comment Share on other sites More sharing options...
Kraven Kor Posted August 11, 2009 Author Report Share Posted August 11, 2009 Re: And now a Math question - figuring out travel times... I figure in 30 years, much less 300, we'll have miniaturized and refined the technology enough to have high-power, high-efficiency ion or plasma drives that can achieve that (given another as-yet-impossible power source.) All the faster probes we've recently sent are ion drive powered and have cut travel to, say, Saturn or Jupiter down to less than a year. Just extrapolating from there I don't see why my idea is entirely unfeasible. Though I am fully aware it is "rubber science" I suppose I'm trying to settle for "believable" (and internally consistent) And again, thank you to everyone who answers my silly questions. I really do appreciate it. Quote Link to comment Share on other sites More sharing options...
Kraven Kor Posted August 11, 2009 Author Report Share Posted August 11, 2009 Re: And now a Math question - figuring out travel times... And as for shielding, I'm thinking the nature of the tunnel keeps any small objects out of the way. But that doesn't cover in-system travel. I don't really want "force fields" but had thought about magnetic deflectors for particle weapons and for protecting against particles during high-speed travel. But I'd think a magnetic shield - if able to deflect large-ish objects at all - would just make the explosion of a small object happen in front of the ship, which at that speed may as well be inside the ship. Quote Link to comment Share on other sites More sharing options...
novi Posted August 12, 2009 Report Share Posted August 12, 2009 Re: And now a Math question - figuring out travel times... I figure in 30 years, much less 300, we'll have miniaturized and refined the technology enough to have high-power, high-efficiency ion or plasma drives that can achieve that (given another as-yet-impossible power source.) All the faster probes we've recently sent are ion drive powered and have cut travel to, say, Saturn or Jupiter down to less than a year. Just extrapolating from there I don't see why my idea is entirely unfeasible. Though I am fully aware it is "rubber science" I suppose I'm trying to settle for "believable" (and internally consistent) And again, thank you to everyone who answers my silly questions. I really do appreciate it. Not that I want to be a wet blanket or keep shooting you down, but I keep going there. It's just one of those cases where it's a passion of mine and I've learned some stuff. There's also the issue of things don't always scale the way you think they do, and also knowing where the boundary lines of normal physics are and what you need to go past them. I suppose my biggest problem is that you're using number one or two orders of magnitude larger than feasible. Ion and plasma rockets are the new, cool thing, but they are still function by Newton's laws, so we can actually make calculations about their performance. And the level of performance you want pretty much requires they run on anti-matter, tons per trip. For instance, the current fastest speed achieved with rockets is 16.26 km/s, whereas your ships regularly reach 8400 km/s, over 500 times greater. And as we remember from physics class, energy is based on velocity squared, so your ships require over 250,000 times more energy to get up to speed, plus another times several thousand because these are usable ships, not 1000 pound space probes. So we're easily looking at 10,000,000 times more energy to accelerate the ship, before we throw in rocket equations, which makes things even worse, since you have to account for the fuel you carry along to burn in flight. This, by the way, is why a lot of people write off interplanetary, much less interstellar, travel - it's way too expensive and troublesome without magic technology. Fusion power isn't up to the task you describe - it does a good job, but you'll probably top your acceleration out around .1 gee, which is a month of constant acceleration out to Neptune-ish. You could also accelerate faster, but coast for most of your trip, and get there in a month or two. Antimatter could give you the performance you want, but the trick is getting it. You could rubber science it away, but why stop at that point then? Realistic creation of antimatter, if you can consider such a thing, requires far more energy input than you'll get from the antimatter. The current 'most feasible' concepts involve planet-sized solar panels powering very large particle accelerators running at terrible efficiency, making what they produce ridiculously valuable. The other option is zero-point energy, which is pure rubber science. It is a real concept, but making use of it may be impossible in the real world. As such, it works however you say it does, but it essentially becomes unlimited free energy, which has other consequences, like massive global temperature increases. It also allows for smaller ships, since they have all the energy they need without having to worry scaling the generators up to larger sizes. It works, but now you have two types of rubber science, creating a precedent for more rubber science. Actually, the biggest problem in all of this is your assumption that people would have to have gravity in space, which leads to your postulate they would run their ship engines all the time to create Earth normal gravity. First, there is nothing wrong with zero-gee for a month or three, as long as you work out. Next, while we don't have actual data on long term fractional-gee experience, it's more efficient, should keep people healthy, and might even have some benefits as people don't fall as hard. Thirdly, you can also simulate gravity with centrifugal force. Didn't you ever watch Babylon 5? It's a bit of a pain to design around, but it is very efficient at simulating gravity once you start it up. I guess this is the point where you have to start prioritizing elements of the setting as to what you want most. Quote Link to comment Share on other sites More sharing options...
Cancer Posted August 12, 2009 Report Share Posted August 12, 2009 Re: And now a Math question - figuring out travel times... Whenever I see questions about interstellar travel in games and stories, I end up wiping my hands and throwing away real physics at some level. For the reasons you mention, space travel is really expensive in terms of energy and rocket tech is so limited with respect to the distances involved that going for real tech for your game puts you into regimes which, frankly, aren't that much fun to play in. That's why, although I share your enthusiasm for real physics, for the sake of a game I am willing to rubberize the science in tightly-prescribed ways. How you apply the magic rubberization to the laws of physics depends on what flavor of game you want. If you want Star Wars, then you chuck more or less all of physics into the barf can . If you want a game that feels "more realistic", then you can play speculation with assumptions at various places and see what falls out. (I admit I urge KK to go back to a real 3-D map, as difficult as that may make it to get a tolerable overview of your Human Space; 3-d really is a lot different from 2-d and the flavor will be there.) So back to KK ... if you assume you can get 1 g sustained continuous rocket thrust from Earth out to 30 AU or so, then you'll be going at roughly 3% of the speed of light. I assume that's enough to invoke your tunnel effect. What's the dependence of the FTL effective speed upon pre-tunnel speed? I missed that somewhere. EDIT: ok, I saw it above. Still nto very clear to me, but I'll push numbers around and post results, with as much detail as possible for explaining how & why I did what I did. Quote Link to comment Share on other sites More sharing options...
Nyrath Posted August 12, 2009 Report Share Posted August 12, 2009 Re: And now a Math question - figuring out travel times... I figure in 30 years' date=' much less 300, we'll have miniaturized and refined the technology enough to have high-power, high-efficiency ion or plasma drives that can achieve that (given another as-yet-impossible power source.) All the faster probes we've recently sent are ion drive powered and have cut travel to, say, Saturn or Jupiter down to less than a year. Just extrapolating from there I don't see why my idea is entirely unfeasible. Though I am fully aware it is "rubber science" I suppose I'm trying to settle for "believable" (and internally consistent) [/quote'] Unfortunately you've run into John's Law. http://www.projectrho.com/rocket/rocket3a.html#johnslaw Quote Link to comment Share on other sites More sharing options...
Cancer Posted August 16, 2009 Report Share Posted August 16, 2009 Re: And now a Math question - figuring out travel times... One final question for you, KK. Since we're doing rubber science with FTL, in fact, we can have interstellar travel take any amount of time we want. There doesn't have to be any kind of rigorous relation between travel time and distance or anything else; they can be handwaved away, or alternately, some odd physics can be shoehorned in and we see what falls out. How long do you want an interstellar trip to take? And when you give your initial answer to that, what do you mean by that time? (Remember, in Real Physics, FTL is equivalent to existing in more than one -- perhaps infinitely many -- places at once, and things moving at high speeds have slower-running clocks.) It sounds like with your chosen mechanic, you're fine with about a week to go from 1 AU to the jump site. So now, as a ball park estimate only, how much time do you want the interstellar portion of your planet-to-planet trip to take, from both the perspective of someone remaining on one of those planets, and someone making the trip? You are free to choose anything for the latter, while the former should be some amount not less than the same order of magnitude as the planet-to-jump point trip (that is, several days). Quote Link to comment Share on other sites More sharing options...
novi Posted August 17, 2009 Report Share Posted August 17, 2009 Re: And now a Math question - figuring out travel times... I hope your not taking all our critiques in the wrong way - we all have certain ideas about the way the universe works. Having said that, I think we need to work out the ground rules of what you actually want to do. You're working on the world design for a Star Hero game you want to run. Is interstellar travel going to be an actual feature in this game? Or just something that happens in the background to other people? Will the PCs have their own small interstellar ship? Or can only very large ships travel FTL? Another assumption we differ on is how necessary gravity is. While something we are used to, and long term weightlessness does bad things to the human body, short-term exposure is tolerable. Defining those term can be problematic, though. Best guess is that advanced medicine and proper exercise will make one month of weightlessness easily tolerable with only minor effects, and over two months before serious issues start showing up. Also, an unanswered question is how much gravity is required by the human body? One gee is a quick answer, but with no good proof. Smaller values will provide some fraction of the benefit of full gravity, though we have no way of knowing exactly how it works out, but are much easier and economical to provide. Also, here's Wikipedia on artificial gravity Artificial Gravity And a final one, which seems to be driving many of your choices - you don't want to have warships dropping into planetary orbit by surprise. Agreed, that is not a fun scenario, but I think you may have erred too far to the side of caution here. The first question here is how likely that is to happen in the first place - how many warring navies are there in your universe, and how large are their fleets? Another consideration is that you've mentioned that ships need to be moving at a good speed in real space to even use the tunneling drive. This means that they'll be traveling well above orbital velocity even if they could pop out in low planetary orbit, and that it takes them as long to slow down as it does to speed up. So if it takes 3 hours to get up to speed, it'll take three hours to slow down, which will easily take them beyond the moon from low earth orbit. The amount of time to slow down is also likely to be an important safety issue, both in terms of rescue and in obstacle avoidance. Also, consider that there is still a useful range of speed between orbital velocity and full 1 light-year-per-day FTL. A tunnel from earth to Jupiter that takes 6 hours to cross is under the speed of light, but is still an enormous improvement on conventional travel times. It also might be possible to detect the usage of the tunneling drive, either/both from the initiating point or the end point. You're thinking that its some kind of gravitational effect? It could make gravity waves that could be detected before a ship has finished traveling through the tunnel, maybe using a detector like the one in this thread I'm pimping. Where was I? Oh yeah, there are more solutions to keeping FTL death fleets from nowhere conquering planets than to forbid FTL travel within 20 AU of an inhabited planet and introducing that tedious mucking about traveling in system for long distances. Were you just trying to stop the munchkins, or did you actually want ships to have to spend so much time traveling in-system? Quote Link to comment Share on other sites More sharing options...
Kraven Kor Posted August 17, 2009 Author Report Share Posted August 17, 2009 Re: And now a Math question - figuring out travel times... I hope your not taking all our critiques in the wrong way - we all have certain ideas about the way the universe works. Having said that' date=' I think we need to work out the ground rules of what you actually want to do.[/quote'] No, though I do find it odd that any mention of something not currently possible becomes complete and utter made-up handwavium. You're working on the world design for a Star Hero game you want to run. Is interstellar travel going to be an actual feature in this game? Or just something that happens in the background to other people? Will the PCs have their own small interstellar ship? Or can only very large ships travel FTL? FTL travel will be part of the game - I want to have the "space is big" feel to the game. A lot of the stories will revolve around the fact that information flows slowly between planets (no FTL comms) so a lot of the scenarios will be "Go to X and find out what the fark happened" or "We don't have time to wait 5 weeks for a comm ship to go back home and ask for instructions, we need a plan now." The PC's will usually be attached to a ship, though they won't have their own - again they are the United Terran Commonwealth's (space age UN) Special Forces. The FTL drive requires a pretty hefty power plant so only larger ships have them, but we're not talking kilometers long ships - most spacecraft are about Shuttle sized to the largest haulers or Battlecruisers which match up to current ocean-going superfreighters or larger Cruisers, respectively. FTL ships start at "Frigate" classes which are about Size 17 - just a bit bigger than the Space Shuttle. Another assumption we differ on is how necessary gravity is. While something we are used to, and long term weightlessness does bad things to the human body, short-term exposure is tolerable. Defining those term can be problematic, though. Best guess is that advanced medicine and proper exercise will make one month of weightlessness easily tolerable with only minor effects, and over two months before serious issues start showing up. Also, an unanswered question is how much gravity is required by the human body? One gee is a quick answer, but with no good proof. Smaller values will provide some fraction of the benefit of full gravity, though we have no way of knowing exactly how it works out, but are much easier and economical to provide. Also, here's Wikipedia on artificial gravity Artificial Gravity Many trips take several months, especially on older ships or trips with a lot of stops on space stations, and most people who work on ships end up spending a good portion of their lives in space. Medical Science in my campaign has come up with a number of ways to counteract some of the health issues resulting from space travel, but the best way is still deemed to be "artificial gravity" of some sort and exercise. While the gravity drive can affect gravity on a large scale, they have not figured out "gravity plating" or any way to have "real gravity" on a spacecraft. So most are designed with one or more decks where "up" is the front of the ship so that forward thrust can be used by the crew for "artificial gravity." (Sorry, I like using quotes for some reason...) It seemed like a neat idea that I'm pretty sure I stole from some book or short story. And a final one, which seems to be driving many of your choices - you don't want to have warships dropping into planetary orbit by surprise. Agreed, that is not a fun scenario, but I think you may have erred too far to the side of caution here. The first question here is how likely that is to happen in the first place - how many warring navies are there in your universe, and how large are their fleets? Well, due to it not being possible via the "rules" I've already set, it isn't likely at all. Each of the species has a Navy more than capable of completely eradicating any other species from the Galaxy should they want to do so (Humans don't quite have this fleet yet...) but as a general rule all of the spacefaring races have found that there is more than enough space to have any need for Total Galactic War - because war is expensive. For a variety of reasons, the only real conflicts that have occurred happened long before Humans really came onto the scene and were eventually resolved diplomatically. For the sake of the campaign, most warships are used for internal disputes or the occasional rogue aliens and whatnot - lots of crime and conspiracies and diplomatic maneuverings, very little overt war. Edit: I kind of spaced something in this answer... I actually have a (likely flawed) "scientific" basis for this as well. Gravity bends space. We know this, it is the basis for a lot of our current physics. So my FTL concept is all about "Gravitic Propulsion" and I've gone through a number of pseudo-theories to arrive at this one. Basically, my setting will have "wormholes" but what they are is actually "eddies" in the topography of space-time caused by binary or trinary systems mass effect with nearby stars. IE, most binary or trinary systems will have "wormholes" to other nearby stars. These wormholes aren't some flashy cloud, you wouldn't even see them without delicate sensors, although flying into the aperture of one without special tech would result in a spectacular explosion and no more ship. They don't allow instant transfer - rather, they are a larger scale version of the tunnels that FTL ships create. So, you have an FTL drive that literally alters the topography of space-time in front of it - it generates an intense and shaped gravitational field in front of it that stretches and skews the existing space-time topography into a shorter tunnel allowing non-FTL speeds to cross vast distances. Creating this field close to any other field is, for the first part, much harder - it takes an inordinately larger amount of energy, and while spacecraft in my setting are going to have some impressive power supplies, they don't produce that much power. The second problem is that when you have too much conflict between one field and another they tend to do unpredictable things - like deposit one part of your ship in one place and a million other pieces in a million other places. Another consideration is that you've mentioned that ships need to be moving at a good speed in real space to even use the tunneling drive. This means that they'll be traveling well above orbital velocity even if they could pop out in low planetary orbit, and that it takes them as long to slow down as it does to speed up. So if it takes 3 hours to get up to speed, it'll take three hours to slow down, which will easily take them beyond the moon from low earth orbit. The amount of time to slow down is also likely to be an important safety issue, both in terms of rescue and in obstacle avoidance. Also, consider that there is still a useful range of speed between orbital velocity and full 1 light-year-per-day FTL. A tunnel from earth to Jupiter that takes 6 hours to cross is under the speed of light, but is still an enormous improvement on conventional travel times. It also might be possible to detect the usage of the tunneling drive, either/both from the initiating point or the end point. You're thinking that its some kind of gravitational effect? It could make gravity waves that could be detected before a ship has finished traveling through the tunnel, maybe using a detector like the one in this thread I'm pimping. Where was I? Oh yeah, there are more solutions to keeping FTL death fleets from nowhere conquering planets than to forbid FTL travel within 20 AU of an inhabited planet and introducing that tedious mucking about traveling in system for long distances. Were you just trying to stop the munchkins, or did you actually want ships to have to spend so much time traveling in-system? I want travel to take time for a variety of reasons. The players won't be really at the helm of their ship, but they might need to make decisions about where to go next or where something might have originated from, etc. I guess part of it is a desire to have a setting where actual space geeks won't immediately roll their eyes at Yet Another Trek Clone. I'm making a detailed map of real stars, researching the basics about them, only putting habitable planets in systems that current science deems may possibly have such (mostly G type stars, some K or F type, avoiding flare or variable stars, etc.) Then I'm making sure I have at least some consistency in travel times - if it takes 2 days to get to Alpha Centauri A, then we shouldn't be getting to Rigel in the same amount of time. I want all the tech to be more-or-less recognizable as "logical descendants" of current theories or cutting edge technology. I don't want to "move at the speed of plot" I want the plot to move at the "speed limit" of the science in the setting. I don't want McGuffin's in every scene - I want some actual science behind everything I do, even if it is "rubber science" I want it to be internally consistent. If it breaks the rules (as we currently know them) then I want an explanation of how and why and for that explanation to hold true across multiple scenarios. I'm real "smart" in the sense that I can figure things out relatively quickly, but I don't retain facts and figures very well. So my ideas are far outpacing my knowledge at this point, and simply going off to Wikipedia or Wolfram Alpha to "learn" a subject just doesn't work very well. I need interactive education and these forums have - for years now, on and off - served quite well for that purpose. Quote Link to comment Share on other sites More sharing options...
novi Posted August 18, 2009 Report Share Posted August 18, 2009 Re: And now a Math question - figuring out travel times... KK, let me stop you right now and tell you that this discussion will be futile - you, me, and Cancer all have completely different ideas about how the universe works, and coming to any sort of consensus would require far more understanding of each other than is liable to come on this board in a reasonable timeframe. You have several features you've decided on for your universe that don't match the way I would imagine things, and you've also indicated that they're not up for argument. I would however like to say I think you're trying too hard. The more realistic you try and make your science and setting, the more holes and flaws that space geeks will poke in it. Just go for internal consistency, and you'll be far better off. Also, for the record, I think you have a tendency to overcompensate and push things too far in the opposite direction. Finally, you're trying to make it more complicated than it is to calculate how long it takes to travel between stars. Most players will easily accept whatever answer you give them for how long it takes, and the others were never going to be happy no matter what you do. Also, the size of space means that much of the extra calculation you're asking about are second and third order effects, aka rounding errors for much simpler math. Here is your formula: t = d / v + 2 * C t - time in days d - distance in light-years v - average velocity in light-years per day C - the amount of time in days it takes to travel from the inner system to deep space where you can engage the FTL drive Plug in your numbers and adjust things until you have times you can live with. This will produce results consistent enough for playability. Any thing more accurate you will have to figure out on your own. That is all. Novi Quote Link to comment Share on other sites More sharing options...
Kraven Kor Posted August 18, 2009 Author Report Share Posted August 18, 2009 Re: And now a Math question - figuring out travel times... I feel I've said something that somehow offends and if so I apologize... I'm not wanting to argue, I just want to have believable technology and - as you, and I, stated - internal consistency. I can't have that if I don't put a lot of thought into the (rubber or not) science. So I come here to have people smarter than myself pick apart my ideas - I won't take every piece of criticism to heart, but the more questions I am asked, the more counter arguments presented, the more real science I have thrown at me, the more concrete I'll be able to make my ideas. And hopefully I will be able to translate this from a Star Hero setting into my life long dream - writing good science fiction. And Novi - if possible, I'd love some details on what I'm overcompensating on... a bit confused by what you mean there. It seems more and more these days that my attempts to communicate on the internet result in... misunderstandings. So whatever it is that I'm doing wrong, I apologize. Quote Link to comment Share on other sites More sharing options...
novi Posted August 19, 2009 Report Share Posted August 19, 2009 Re: And now a Math question - figuring out travel times... I feel I've said something that somehow offends and if so I apologize... I'm not wanting to argue, I just want to have believable technology and - as you, and I, stated - internal consistency. I can't have that if I don't put a lot of thought into the (rubber or not) science. So I come here to have people smarter than myself pick apart my ideas - I won't take every piece of criticism to heart, but the more questions I am asked, the more counter arguments presented, the more real science I have thrown at me, the more concrete I'll be able to make my ideas. And hopefully I will be able to translate this from a Star Hero setting into my life long dream - writing good science fiction. And Novi - if possible, I'd love some details on what I'm overcompensating on... a bit confused by what you mean there. It seems more and more these days that my attempts to communicate on the internet result in... misunderstandings. So whatever it is that I'm doing wrong, I apologize. First off, I'm an idiot for coming back into a conversation I swore I was done with. Also, internet miscommunication syndrome is fairly common. By overcompensate, what I mean is that you identify a problem and then solve it by going excessively far to the other end of the spectrum, and introducing problems that are worse than the original problem. At least, that's the way some of your solutions strike my sense of judgment. In particular, the thing that has been most frustrating is that you claim not to want to handwave anything that you don't have to, but then you do it anyway and get amazed that we would call you on it. Namely, how efficient your rockets are. I don't care what you want to argue about improved technology, but there are actual hard laws of physics that govern the function of any rocket engine and how good of performance it could have. These are laws that are as proven as anything in physics possibly can be, Newton's laws of motion. So we can make actual calculations on speculative rocket engines. Now, I may not have understood you completely in your posting, but the worst case scenario reading of what you have said is that a ship could travel on a direct trip to the edges of human space, a trip which could take 4 months, and it could maintain an acceleration of 1 gee for the whole trip. During this trip, the ship will reach a speed of almost 17% of the speed of light, making a minute on the ship take roughly 61 seconds. How much fuel does it take to get the ship there? The Tsiolkovsky rocket equation will tell us. The delta-v is easy enough, 1 gee for 60 days is 50,803,200 meters per second , which we have to double because we have to slow down as well, for 101,606,400 meters per second. We then have to figure out what your rocket is like. Unless you want to play with antimatter, your most powerful option will be a direct-fusion rocket, in which the fusion by-products are vented straight out a magnetic rocket nozzle. By the time you are done accounting for all kinds of unavoidable losses from various engineering details, and then being generous in how much better late-generation engines could be, you're looking at something in the neighborhood of an effective exhaust velocity around 5,000,000 meters per second. So we plug those numbers into the equation and find that for every kilogram of ship, we need to bring along 668,990,219 kilograms of fuel. Remember, this will be cryogenic hydrogen and helium, so the tanks are even more obnoxious than usual. This is why I have a problem with you. Let's be a little more reasonable, and ask how much fuel it takes if we just have to spend three weeks at 1 gee. We drop down to 34 kilograms of fuel per kilogram of ship. Would these numbers be better if you had a more efficient engine? Yes, but good luck finding one. If you somehow had a 100% efficient fusion engine, in which all the energy of the fusion reactions was converted into motion of the ship, the ship would still require as much fuel as ship for the three week endurance option. And don't forget, liquid hydrogen and helium require cooling equipment and are not dense, about a tenth as dense as water. Am I misunderstanding you on some points? Almost certainly. But this is what I have been able to understand from what you have posted. If there are errors, feel free to correct me with very specific correct information. If you want specific answers, I will require precise inputs, not just vague descriptions accurate to the nearest A.U. or planetary mass. [/rant] Quote Link to comment Share on other sites More sharing options...
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