I also posted a calculator one page back that calculates the sub light travel speeds and time dilution - but i was not able to compare it to yours as when opening yours i find set values rather then variables. (by the looks of it we have used the same formulas though)

In any case as per the points Alesseo brought up and having checked a bit more around in the fluff it does see that the imperium never travels at relativistic speeds. I think i will go back to limit ships to speeds at around 1% lightspeed. You can go further - but, especially in places with lots of debris, you will most likely blow out your void shields rather fast and if not stress out your plasma drives from the weeks of constant acceleration/de-acceleration.

Considering how "relatively" easy void shields go down from a poor macrobattery shell or how dangerous it can be to traverse an asteroid field even with void shields up it makes perfect sense that no sane captain would risk his ship going to relativistic speeds where every spec of dust will hit harder then the best macrobattery shells.

It also goes well to give some feeling of isolation - if you are trapped behind a warp storm, or have the bad luck of getting stranded with a faulty warp drive you best, through some adventure means no doubt, wait it out/ find some help / alternative means of transportation - you cant just stock up on food, aim for the nearest star system and fast forward five years.

Odd, that file should open as an excel compatible spreadsheet, but my apologies if it does not. Also I have read back and see you have indeed posted a calculator, for which I am grateful - I will begin comparing it with my own immediately to try and lock down my incorrect 'perceived time figures' as the margin of error becomes untenable above 200 light years currently.

I feel that the two main camps 'can and can't' are mainly a semantic issue, which aside from constructive conversation such as this regarding the physics and feasibility of the matter, is fairly mute when considered in a gaming perspective. The simple fact that any warp capable ship likely just doesn't have the space for the sheer quanatity of additional plasma storage and provisions means that even if they could make a 4 light year or more relativistic journey, they would be limping and likely suffering a civil war of sorts on board by the time that they get there. The end result is that relativistic travel is so unlikely to be considered an option for any vessel not designed to do so (and so disruptive to the time-scale of the average rogue trader game), that it is unconscionable regardless.

Another way to exclude it regardless of scientific leanings, is the torsion stress the hull would experience 'turning around' to decelerate, as it is 40k canon that retro thrusters just aren't designed for continual long bursts on the same scale as the primary drive. Eldar and Necrons may be capable of sudden deceleration due to their unique drive properties, but Imperial (and most Xeno) vessels would require an about face to fire their primary drive as a deceleration tool. As a supporter of relativistic travel as a canon element of sub-light trading vessels in the Imperium (fiction as written in Dark Heresy, but we all know the consistency that GW keeps with it's prime fiction, despite Fantasy Flight actually keeping a fairly smooth flow of PF between books ), I prefer to design Chartist vessels with this in mind, drawing them as dual-engine monstrosities with extreme spinal strength and little need for turning above the slowest of velocities (so as not to shatter the hull with torsion stress).

In closing, I feel that the inclusion of relativistic travel serves the same purpose as many of the temporal anomalies open to warp travel; hearsay stories or 'glad that wasn't/isn't us' thought provocation on the part of the GM. Standard use for the players is awkward and generally takes away from the game in my opinion. The inclusion of such topics as curiosities and stories can add a richness to the players' experience, further highlighting them as blessed with a Warrant that allows them to explore the galaxy in their own lifetimes, instead of relying upon their offspring to carry on a dynastic mission of exploration.

All the best in your gaming,

Sokahrthumaniel

In space, turning a ship around should not produce any undue stress, unless done while still under thrust.

Simply stop applying main thrust, flip the ship around with maneuvering jets, re-apply thrust.

Or am I missing something?

You are correct, I was mainly providing a 'reason' (as scientifically inaccurate as it may be) for those opposed to the possibility of relativistic travel in the 40k setting, to have a reason to dismiss the idea without outright wrangling over the mechanics of it.

But yes, you are completely correct, and a sensible captain would flip their vessel the minute they stop noticeable acceleration and await the time to fire their deceleration burst.

Just thinking about the 1% of c speed limit. Crunched some numbers (ignoring accel/decel time, I don't have the math to handle that!) and assuiming a 2 week travel time looks like safe warp distance is about 25 au away from where you started from, about between Uranus and Neptune in our solar system.

Interestingly enough, closely reading the RT book section that quotes the 1% speed limit, it makes no mention of decelerating when jumping and no mention of accelerating after exiting the warp. So I guess the ship must keep it's inertia up in the warp!

Sokahrthumaniel said:

Technically, you could turn under thrust without any real problem. With a low enough angular acceleration, the force vector would not perpendicular component to make much stress. Then once you have some angular velocity, you could stop the angular acceleration and at that point swing around under thrust. The force vector would always be parallel to the spine of the ship.

llsoth said:

I've seen nothing that suggests that Imperial starships are configured to be flown in such a manner. They behave like ships from the age of sail much more than any true spacecraft. If a galleon doesn't do what you suggest, then starships in WH40K don't either.

HappyDaze said:

That is a bit of a fuzzy spot. There is no reason to think that newtonian dynamics dosent work normally, and that the reason that ships act the way they do isnt a technological one.

A ship with a damaged engine drops to speed 1 regardless of what speed it was going. This suggests to me that it doesn't follow the rules of physics as we know them.

Two ships engaged in boarding actions both come immediately to a dead stop. Physics are nowhere to be found...

Well now we're moving into game play abstractions somewhat. Though in literal terms I wholly agree with you, I will continue my discourse in the spirit of descriptive writing (or speaking when actually Gming) concerning what is happening (my players like alot of description about 'how' something is happening).

Let's take a pair of lunar class cruisers with speed 5, both heading at each other directly in the boarding scenario. The strategic turn in which boarding is initiated by Lunar A is, remember a whole 30 minutes of action in 'real time', and with 2.5 gees of acceleration (and thus likely deceleration if it is just a raw 'change in velocity' figure) it will decelerate from speed 5 (50,000 km per 0.5 hours or just over 27,000 meters per second) at a rate of 19.26m/s^2.

This will result in a complete standing stop in 24 minutes. Assuming, and it is a big assumption, that both vessels are interested in avoiding a collision (Lunar B sees boarding as preferable to losing the side of it's ship in a grinding impact) Then both vessels would be able to achieve a standing stop in 24 minutes, possibly less if their relative momentum/trajectory would result in them having a negligible relative velocity to once another. (For example Lunar A approaches B from the rear. If it can outpace B due to clever manouevering or the likes, and still approach from a negligible angle relative to B;s trajectory, it is possible it can grapple on with next to no problem, and 'force' a slow down by burning retros, threatening grave damage to both ships should they continue to move - and also reducing the probability of impacting on debris/having small matter cause harm to boarding craft due to relative velocity.)

As a final note on this specific example, I must note that a standing stop is in no way required, as 1VU is still a 10,000 km area, as long as the vessels are moving at say 1200 m/s or less, it'd take 5 turns or more before that would translate into a tabletop movement (not a problem in smaller combats, but it's more a mental picture than something to point out).

At the end of the day I am merely explaining how I like to run space combat in my games, with a fusion of pseudo (but preferably more realistic than not) science and fluff. The table top action paints everything in broad homogenised strokes as on the fly hyperbolic trigonometry and newtonian mechanics is just not fun. Whatever gives you all pleasure when running your games, and most importantly whatever makes your players have a great time, is the best path.

Good GMing and playing to all of you, and keep up the good debate!

Sokahrthumaniel

HappyDaze said:

My suggestion is, dont ever go there.

Once you consider rules to be more important than physics in that regard you would open up a whole can of worms. Sure the warp and the plasma drive might not be straight physics as we know it, but turning the ship should work as normal.

Its the usual, ill just jump 20 metres down, the rules wont kill me, in a different way.

Voronesh said:

I'd say that too much reliance on real-world physics will detract from a good WH40K story. In WH40K, physics yield to the needs of the story, and that means that continuous burn doesn't produce ever increasing speeds, and a 'coasting' ship that lacks thrust does slow down.

bobh said:

I'm reminded of something that supposedly transpired at a Star Trek convention in the late 70s. Gene Roddenberry and a few Star Trek producers were having a panel discussion when a young man stood to ask a question.

"Mr. Roddenberry, the transporter circumvents the Heisenberg Uncertainty Principle. How is this possible?"

Gene: "The transporter is equipped with a Heisenberg Compensator."

"But Mr. Roddenberry, how does the Heisenberg Compensator work?"

Gene: "It works very well, thank you. Next question please."

So it is with the technology in the 40K setting.

Attila-IV said:

That's awesome!

Thanks for the laugh.