I agree, so that is how i ran with it, both from "how things work in our universe" and "how the fluff works in warhammer40k" reason. Arguably both the Necrons and Tyranids do indeed have "non warp" FTL travel method, but it is implied that the Necrons at least do this by some teleport/cheating rather then actual FTL travel and the imperium certainly should not have any. The calculator here linked (presumably for use inside planetary systems) have no such limitation and will have you traveling at 5-10 times the speed of light between star systems or 25 000 times the speed of light to the closest galaxy.

While there off course is no need to dwell on such as most sub-warp speed is within a star system and too much realism/math can ruin a story it seems nice to have a framwork to work with and i am curious how other GMs have done it. Personally i have no intention of limiting my players from using thewarp - but i like to have a reason that the warp is nescessary (i.e no post-lightspeed) and it certainly follows the fluff that there is no FTL.

My explorers will certainly have to stick with 99,99% speed of light (or slower), but so does everyone else (sans necrons) in the universe.

For comparison: a Lunar Class Cruiser going from Terra to Alpha Centauri (a distance of 4,5 light years) will be spending 612 days in transit according to the calculator. (Which, i presume, will be 306 days accelerating and 306 days de-accelerating, going at the peak (after 306 days of accelerating at 4,5 gravities) 4,4 times the speed of light. (if it did not bother to de-accelerate it would arrive after 495 days - but going at a speed close to 6,3 times the speed of light and thus overshoot its target by quite a bit).

The solution i went with instead is to have the Lunar Class Cruisier accelerate for 78,6 days (at which time it is at 99% light speed if continually accelerating at 4.5 gravities) - then keep that speed for 1475 days, then another 78,6 days to de-accelerate).

The "problem" is that this means that if keeping sublight speed - travel between Terra and Alpha Centauri will take 1631 days if keeping sub-light speed vs 612 days if allowing, as the calculator does, for higher speeds.

So a word of caution if using the calculator over longer distances - either allow for super-fast-many times the speed of light travel (just handwave it or re-write the fluff accordingly), or re-write it so that it has a max speed rather then continue to accelerate after hitting the speed of light.

Bilateralrope said:

It seems we agree with the max speed. I guess i interpreted the fact that your calculator allows for FTL speeds to mean that you wanted it like that for game/fluff reasons. My question is really what other GMs would allow in their game in terms of absolute maximum speed. As mentioned i go with 99,99% myself - at that point continually accelerate will require insane amounts of power and you have very little to gain (i.e you can always go faster - but you will never quite reach 100%) so expending an insane amount of energy to go from 99,99% to 99,999% and then again to 99,9999% etc. has little benefit.

My calculations (as described above) in the answer to the previous poster does indeed, over long idistances, accelerate until "close to light speed" then "coasts" on that speed until they have to start de-acceleration to avoid missing their target. I feel the numbers work well and i am happy with them.

As mentioned it is less the calculations i have trouble with rather then being curious as to how other GMs think of the matter and if they really, like the calculator does, allow for FTL.

I agree with you on B) BUT it is implied through the fact that the ships in question DO have given speed in VU for strategic rounds that they do have the ability for quite strong gravity acceleration.

An Interceptor can go 10 VU (standard) per strategic turn (30 minutes) which actually is something like 12 gravities of acceleration if starting from 0 velocity. I considered this a bit extreme (and incredibly fuel heavy) suitable only for short-term tactical engagements. And settled for a 10 gravity sustained (i.e for hours) acceleration - which though uncomfertable is not deadly in a well suited enviroment, supine position and limited duration even without dampeners - though if would take for granted that any "good" combat vessel designed for both interplanterary and inter-atmosphere combat would have some dampeners since the technology is obviously available in the universe. "Borrowing" an Orc ramshack shuttle which i can imagine is closer to a primitive rocket that works half on gunpowder, half on stolen nuclear technology and half (sic) on psychic power, however, is likely to create a "crushing" experience for the explorers should they choose to press THE BIG RED BUTTON!

I would be interested in what values others have used for allowing interplanetary flight for small craft though. I think the biggest limitng factor is that while the plasma drives on a huge craft can create endless energy - a small craft has a limited storage capacity and is thus limited by the delta-v. But i have to admit that is purely speculation from my side and "how i like to limit interceptors/guncutters from racing around the star system on their own but rather have short term operations and limited engagements" - curious to hear what other gms allow for though.

As for Warp Travel VS FTL i guess it comes down to preference. When i say FTL i mean travel in "realspace" - as such the warhammer 40k universe seems to have the same limitations as ours do. You can not travel FTL in realspace- you can however take shortcuts through the warp that allows you to exit at a position that is further from where you were then light speed would allow - but you have not actually travelled the distance.

I.e in the same sense that the traveling from one edge of a blank paper sheet to the other will be significantly longer then if you can fold it and cut across. You have not actually "moved" FTL - but you have changed position that WOULD have required FTL if you moved the full distance in real space.

Don't the q'orll still cross vast distances (they have a sizable empire) in ark ships (that are advanced and dangerous to attack) that are all sublight?

HappyDaze said:

Just what the hell are you talking about now?

Over time all stars die. All people die. Just because all of us don't die in front of you doesn't mean we're immortal. Get a grip.

Over time all things will happen.

bobh said:

What I'm talking about is that you've made a claim that "all events, over time, are common" and that this is not an appropriate response to traveling back in time via the Warp. In fact, it is quite uncommon compared to the standard results. You need to get a grip on the conversation, because it's pretty obvious to me that you don't know what you're talking about here. Nice display of hurt outrage though...

Arkamit said:

You are right in that such trips do break my calculator. In fact, my calculations above tell me trips of around 110 AU in a ship with an acceleration of 5.6g will break it because it uses Newtonian equations, not relativistic ones, because the Newtonian equations are simpler. I consider that acceptable for a few reasons:

- Most trips between star systems will be done using the warp to travel faster than light*. If they want to make a trip that long with their STL drives, it means that there is some unusual circumstance (warp storm making the warp less safe than normal, destroyed warp drive, major player stupidity) that allow me to fudge things.

- I don't expect distances that long to come up often, and when they do I don't expect players to care about the exact distances, so I don't tell them unless they ask (they didn't). Instead they care about the time the trip takes, so I tell them that.

*Could someone give estimates for how long it takes to travel between Earth and Alpha Centauri via the warp ?. Both with and without a navigator.

Well, assuming you've already achieved a safe distance, and are ready to jump: the jump from Sol to Alpha Centauri is actually too small for the difference between Navigated and Calculated jumps to make a difference with regards to the overall journey speed (as it's just within range for a Calculated Warp Jump).

Depending on how the warp currents are flowing, and what the local warp-realspace time dilation factor is, you're looking at something between 3.5 hours to a day of travel time (according to the material universe, anyway: aboard ship, you're probably only going to experience between 7 to 30 minutes), but your calculation time and set-up for the jump could be a good 5-6 hours, if you don't have a Navigator. With a Navigator, you don't have to plan and pre-program your course corrections before you enter the Immaterium, so call it maybe an hour to make basic calculations and spool up the Geller Field and Warp Engines.

So- Sol > Alpha Centauri (calculated)- between 8.5 and 30 hours once a jump zone has been reached (experienced- between 5h7m and 6hr30m)
Sol > Alpha Centauri (guided)- between 4.5 and 25 hours after reaching Sol jump zone (experienced- between 67 and 90 minutes).

There was a handy-dandy chart showing the canon warp speeds floating around on the old fora, and it's probably still around on the internets. I got lucky and found a scrawled set of calculations based on it in my GM notes. I'll track the whole table down and post it (and as far as I'm concerned, said table makes warp travel waaaaay too fast).

Bilateralrope said:

Should be "fairly" accurate for "objective" time (i.e as seen from terra) until your speed pass light-speed.

For reference i updated my little excel sheet to also factor in the time dilution if anyone might find it of interest.

javascript:void(0);/*1293871925864*/

The "objective" values should be fairly similar to your calculator and the subjective time dilution should not really come into effect until one approaches 10-15% of lightspeed. (note that if you put in really high values excel might show the speed as 100% of light speed - but that is purely because of number roundings and will only happen if you are move at 2,5 times the diameter of the galaxy in one go.

And for Alesso.

May i ask - where would one find the information regarding the "calculated"/non-piloted jumps?

I was looking for it some time ago and the only reference i could find was that it worked (barely) over small distances - but anything above 4-5 light years was pure luck in regards to when and where you would exit. Are there any suggestions/guidelines to model further calculated jumpes? I have been playing it as something that only works between star systems neighboring each other on well established routes or longer, as a last resort, with all bets being off as to when/where you exit.

As for piloted jumps - what i have been using is the rulebook suggestion that two close star systems by a well travelled route is 1 day - modified from 1/4 to 4 times based on the pilots skill and luck. Suggesting that Terra-Alpha Centauri would be between 6 hours to 4 days for the ship if they avoid any mishaps. Given that Alpha Centauri-Terra is probably the most mapped/used route in the universe one could argue that it would have a 1:1 dilution between realspace and the warp and would thus take 6h to 4d in realspace also. If we were talking the same distance, but a less used/mapped path it would probably suffer the usual 12:1 realspace:warp dilution meaning a 72h to 48days in realspace based again on the skill. (arguably the "base" 1 day would also be changed as apropriate) In any case the currents in the warp, especially in the wild koronus sector, will matter more then the actual distance you travel.

I pulled my info from the original Rogue Trader book, as well as some from 2e 40k, and the old Space Fleet.

Calculated jumps are at the limit of their accuracy at about 5 LY, anything further and you pass the prediction horizon for warp currents. Since without a Navigator you can't sense or see warp currents while in the warp itself, you can't make course corrections. That being the case, the implication was always that you translated back into real space after a parsec or so, recalculated and jumped again.
Actually, come to think of it, that was expressly stated in the original Rogue Trader book, and was supposed to be the reason for Man's galactic dominance- no other race has Navigators, so barring cheating (like Necrons, who do their FTL in real space, and the Eldar who have their network of stable warp portals)
the Imperium is/was guaranteed an advantage in strategic movement speed.

I'll also note that originally, ships were apparently limited to .01c in real space. This has been contradicted in a number of places, but as it hasn't been specifically repudiated, it is still technically canon.

There is a copy of the fluff from Space Fleet available here

Weird. Double posted. Removed duplicate content via edit.

bobh said:

What he's getting at, and I agree with, is that the time travel/fickleness of the warp concept is used in Warhammer 40k backstory mainly as a Deus Ex Machina plot device (i.e. Storm of the Emperor's Wrath in Age of Apostasy eating Vandire's fleet). The number of recorded instances of ships that either wind up flung into the far future or into the recent past are very very few, maybe 100-500 in entirety. Compare this abstractly with the billions of ships plying warp routes throughout the Imperium on a daily basis. That's billions of jumps every day that don't end in calamity or bizarre events. If this was a daily occurrence the Imperium would simply cease to function. There's a reason that the book says that time travel jumps should be part of a coherent GM plot and never ever based on a random roll.

I do agree however that warp travel in general should be based on GM fiat and never the exact same amount of time twice.

Bilateralrope said:

My understanding of special relativity (and the Lorentz scale) is that time dilation gets noticeable around 0.6-0.7C. Below that it maxes out at about 1.2x dilation?

Alasseo said:

That is actually very interesting, many thanks for the link.

After doing a re-check in the rulebook it does actually mention the 1% limit in the Rogue Trader rulebook also. On p312 it says " ..... and the ship's speed reaches approximately 1% of of light speed. After several weeks of travel the ship arrives at the first destination" (destination being the "safe to jump to warp zone" outside the star system gravity wells). It does seem indeed per the rulebook it is suggested that 1% light speed is the max - which will certainly slow down warp travel a lot if combined with having to jump well outside celestial bodies.

@Fortinbras "time dilution gets noticable around 0.6-0.7c. Below that it maxes out at 1.2 dilution?

You are correct. If you want - you can check my calculator/excel sheet as linked above if you wish to test it out. It follows "our universe" physics on the matter. If you enter 1 LY of distance at 1 gravity you will see a 1.2 dilution at 0.75c, less then that is not very significant - and less then 0.14 or so is almost not noticable. Going faster though will ramp it quickly - but the real "fun" dilation does not kick in until you start pressing against the light speed barrier (0,99c+) where it will ramp up exponentially, both in energy and dilution.

If anyone is interested the formula to calculate time dilution (i.e the lorentz factor) it is at gamma = t / SQRT(1-v^2/c^2). It is fairly simple with t being proper time/difference (replace by 1 for a 1:X comparison) and v being velocity and c light speed in vacum.

For fun you could off course also calculate the ships mass (which will dramatically increase with the dilution) and length (which will decrease)

1% of light speed seems ridiculously slow to me. As an example: In the classic "hard" sci-fi novel The Mote in Gods Eye the Macarthur (The main battleship in the book) accelerates to 6% at full burn at a constant rate of 4g's for five days to get to port without any real problems other than the crew having to lay strapped in to couches for the duration.

I am inclined to agree actually. And for purely in-game reasons it seems a bit "steep", simply delaying departure/arrivals significantly.

I will probably be keeping with the "realistic" slower then light continued acceleration - it is not as it can be exploited and at least gives the players a possibility of travel without the warp should there be any reason to. Its a tough choice - wasting years of their lives - but at least it is possible. With 0.01c it is simply not feasable.

It also begs the question - why the 1% limitation exists (though arguably one should not ask such questions in a fantasy settings - it never hurts to have some thought into the hows and whys in my opinion)

Lack of energy from the plasma drives prevents them from accelerating at a longer period of time? From the way the space ships are described i seem to get the idea that the plasma drives can produce (though at limited amounts and with no storage facilities) endless energy

Stress in the ship/crew from the prolonged acceleration? They will not suffer more Gs then they do in combat - and while the extended length is a possible threat one should think that the gravity plating and what not would help. If anything they could just reduce the acceleration to 1g or so meaning they will get the good speeds still, just a bit slower.

Speed being too dangerous/voidshields breaking? Once you start going "fast" - the small dust and whatnots in the universe will hit the ship/void shield HARD. Void shields obviously are somewhat limited in what they can absorb - impacting with a small rock at reletivistic speeds will hurt a lot more then any enemy macro batteries ever can.

So it migth simply be the best excuse is that speeds above 1% will put too much strain on the void shields and going (much) faster will lead to the void shields failing and the ship getting ripped apart by dust.

Fortinbras said:

I was thinking of that book through this whole discussion of reaching the jump point.

There's a scenario for you (from the book): the crew, following an old warp-route map jumps out in system only to find the star has (since after the map was made) blossomed into a red super-giant. "Your voidshields flare to life as you find you've transitioned into real space just outside the corona of a red super-giant!"

In the novel Salamander, a Salamander strike cruiser transitions out in the middle of a solar storm (waves of stupidly huge solar flares). The bridge's viewport shutters automatically open, searing half the bridge crew with the solar radiation before they can get the shutters closed again.

@Arkamit

I will probably be keeping with the "realistic" slower then light continued acceleration - it is not as it can be exploited and at least gives the players a possibility of travel without the warp should there be any reason to. Its a tough choice - wasting years of their lives - but at least it is possible. With 0.01c it is simply not feasable.

STL travel between systems simply is not feasible and isn't used in the lore either. A ship with a warp drive damaged beyond repair is stranded and should better hope there's some good samaritan within range of their astropath.

The "stability" of Warp travel that allows the Imperium to function is provided by well-charted, semi-permanent Warp routes. For example, the Scintilla-Cyprus Vulpa Corridor A may allow travel from the agri-world to the hive world in 3 days reliably, while the return trip usually takes 7 days. This is stable enough to allow for supply of the hives of the sector capital. The Scintilla-Cyprus Vulpa Corridor B may be another stable route that requires 18 days either way, but is wider than A, allowing for safer traversement by Navigatorless Chartist vessels. While at the very same time, going from Cyprus Vulpa through the open Warp rather than either corridor may take anywhere from two hours to 150 years subjectively, while in realspace you may arrive anywhere from a thousand years from now to a week ago.

The Warp itself is chaotic, relying on rules unknown to Mankind, if any exist at all. But Mankind can and has found semi-stable pathways through it, allowing for the construction of a galactic empire with reasonable reliable shipping times.

But, when you go off those beaten paths, there is literally no telling how long it might take you to get somewhere, if you make it at all. Here be spacial-temporal disassociation. Off the charted routes, ships move at the speed of plot, not by some defined system. That's why one of the steps in the navigation rolling is the GM sets the base time that will be adjusted. The GM can set that base time at whatever suits the needs of the adventure, and the Navigator takes it from there.

And sometimes, the Navigator may spot a current flow through the Warp, take it, and after several trips the Explorers discover it's a stable route. That route may be a more valuable treasure than anything that lies at either end of it, as such stable routes allow reliable shipping and supply and - if the travel time is low enough - could provide a good location to set up massive operations on the scale of a hive city, assuming the route also has worlds which can supply it along its length.

It may be that they simply choose not to accelerate beyond .01c; consider that the example and description in that link were or a typical merchantman on a cargo run. Any ship in that position isn't going to put unnecessary strain on systems or burn more fuel than it needs to. It will choose the most economically sound course (pun intended).

Now consider that the stated reason (according to that link) that they go so far out to the jump zone is because otherwise the particle density is too high any deeper in the gravity well.
Likewise, consider that Bussard ramjets only work because they are travelling so fast the effective particle density of interstellar hydrogen increases to a usable level.
(I know, 40k doesn't use Bussard ramjets, but the concept of higher speed ≈ higher particle density is useful)
Now suppose that .01c is slightly less than the velocity at which the effective particle density would get high enough to potentially cause a mis-jump, even that far out of the gravity well.

If you're going to have to put extra stress on a ship slowing it back down to 1% light speed (remember, any acceleration, deceleration, maneuvring or whatever is going to put more stress on a ship's systems, especially compared to coasting), it becomes a question of whether the benefit (possibly getting to your destination a couple of weeks earlier) is worth the cost of the extra fuel/reaction mass you're burning, and the x number of hours you've just taken off its' service life.

Of course, in combat, you may well want to go faster than that anyway, and even outside you may decide it's worth it (and possibly pay for it by using some of the time you just saved on the way out to travel to a more distant jump point).

I know, I was the one who brought the 1% c limit up, but I've just gone back and re-read it. It doesn't specifically state an upper limit for sub-luminal speeds (although obviously 3x10^8 m/s would be the absolute upper limit), it just states that on a typical journey, a ship will reach ~.01c. It also implies that the trip out to the jump zone can take several weeks at that speed, but it doesn't state it explicitly: they could be accelerating at 6 G for 14 hours and coast the rest of the way at that speed; they could carry on their burn to go faster and make turn-around at the right time to reduce their velocity to 1% c; they could choose to accelerate far more slowly. All three interpretations could fit the text.

I'm curious, does the Imperium have some kind of technology to counteract the g force generated by the ship's movements? I'm afraid my lore is a bit scant. I know they have gravity plates that create artifical gravity in the ship, but I wasn't sure if they could do anything about acceleration or real gravity.

I ask because people keep mentioning rather huge numbers of g's for acceleration. 5 for a few seconds is enough to black out people who aren't used to it, and even the most experinced/hardened are going to pass out from a few seconds at 10g.

I seriously doubt that anyone would be able to handle 6g for more than a couple minutes, so accelerating at 6g for several hours simply won't work. Unless of course there is some method to cancel out those gs on the crew. I suppose if one had grav plates in the walls facing the prow, and turned them on when accelerating, you could cancel it out that way.

Artificial gravity, inertial dampening and anti-gravity are three applications of the same technology (as are tractor beams and repulsor shields, incidentally), so yeah. No guarantee that they can alter the gravitational plane fast enough to keep up with hard maneuvring, or that people aren't going to feel some spill over along the axis of delta-v (this is 40k, after all), but they aren't going to get knocked out by g-forces unless something goes horribly wrong.

And until you start reading stuff like the Honor Harrington novels, you really haven't seen high acceleration. They have ships that routinely travel under ~512g acceleration, at velocities approaching .8c...

Given how healthy Imperial Guard regiments seem to stay in spite of year-long voyages to battlefields I'm going to have to say that Earth-normal is the standard gravity aboard a ship, but that hard maneuvering would be felt the same way a ship heaving to would.

It is and yes it is.

Cifer said:

it is and yes it is (several aliens among them the Q'orll use it as their standard). Not fun though when everyone else is zipping around in IoM ships though.

I have been working on a sub-light calculator for various 'relativistic traveller' species and the likes in the 40k background, presented here. (Note that the 'perceived' time reference in playing up a little, but for the purpose of anything representing a Chartist journey [about 5ly per hop at most] it holds sufficiently)

I would like to point out that in Dark Heresy and Rogue Trader itself it is pointed out that Chartist vessels frequently travel at relativistic speeds to get between their 'cluster' trader routes. Though they take a fair while to get there, the effects of spatial contraction and time dilation at excessive speeds will result in a drastically shorter perceived journey, compared to the elapsed time at relatively 'stationary' solar systems on the path of travel.

To use the calculator presented above, input the distance in ly and the acceleration (max. sustainable accel shown on the ship data entry in either Rt core or ITTS) to get a very rough estimation of the time and speeds involved in such a journey. Personally I err on the side of 25% of listed value as a 'long slow burn' to represent the fact that a 5.4 gee acceleration (in the case of the orion) is only possible for a certain length of time without blowing the plasma drives.

Also note the 'Deep Void Run' entry is the RT core book. The durations involved in relativistic travel far exceed the 6 month lower limit of ship supplies, and in many cases your crew will have starved to death (likely after a mutiny) long before they arrive at their destination. I have represented this (with regards to Chartist vessels) by ruling that the space taken by the warp drive is given over to additional parts for life support systems, additional banks of plasma storage for the acceleration/decceleration burns, and much more food and water (say a rough figure of 2 [relative] years worth before making tests for attrition to represent the 'short voyage' nature of a Chartist trader).

In closing, it is my beleif that warp drives are not too fast, as only the most stable routes will provide best case journeys. In such cases warp travel is meant to be pretty impressive. The simple fact of most travel is that clement 'weather' is uncommon, and circuitous jump routes with many exits and entries into the warp are required for the shortest perceived and 'real' time of travel. For short distances the warp drive may have a pretty severe disparity, but it's raw speed and the problem of 'distance increases disparity between traveller and observer time reference' not applying in a concrete manner (as the navigator can 'check the weather' to get a broad idea of time disparity) makes it the tool of choice for any species wanting an empire of any stability. (For example; in 'common' conditions the 1:12 ration results in a 2 days hop to a close-by star taking 24 days to the 'outside observer, compared with a mere 1:2 disparity (rounded for simplicity) for many short-hop relativistic journeys. The relativistic speed time disparity will rapidly increase, whereas warp travel has a relatively 'concrete' dispariity, allowing for more accurate time measurement and less 'i am 30 and my son is 300' temporal shenanegans).

The feudal nature of the Imperium is extant due to the relative unpredictability of warp routes, not warp drive itself, but if they were to only rely on Chartist shipping, the sheer amount of real-time elapsed during relativistic runs would result in only the smallest of clusters being functional in any codependant fashion. Hive worlds would quickly die-off as their air and food run out.

Thanks for toleraring my ramble, and enjoy the calculator!