[technology] Imperial starship propulsion (sub-light)

[CELS]

42 days is alright by me. A bit longer than I would have imagined, but there you go.  How much difference do we imagine there will be between different ships though? Will the fastest ships in the Imperium (e.g. Inquisitorial Black ships) be able to make the warp zone in half that time? Will most transports in the Imperium spend double that time, or three times?

I know, I know... "it depends". Fuel, engine, star mass, and so forth. But it'd be nice to throw out some numbers based on what has been agreed upon. It'd be silly if we later discovered that the average freighter, not having the advanced technology of the Venturer, would actually spend a whole year in transit.

[JRaup]

And while there is no water in space (nor does it care if you scream), there are at least trace gasses, which could produce a wake like effect.  Not saying it should happen, just that it could happen.

I have my doubts that given the average density of interstellar gases are going to create a significant "wake" effect, since they're - what? - 1 atom per cubic centimeter? 

Even at the velocities that are being discussed?  Not being an astrophysicist, or having any real grounding in the theories, it was more of a layman's take, so take it with that in mind. 

See, I don't think it would matter if you have reaction or reactionless drives for this.  Even a reactionless drive wouldn't be able to stop on a dime as it were.  And as I see it, the type of drive wouldn't change the combat environmentals all that much either.  You'd still have to account for the movement of the target, your movement, distortions, etc. 

Reaction-based and reactionless thrusters have a completely different "feel" when applied in a sci-fi universe, though.  Or at least completely different in my experience, since it relies upon use rather than merely the passage of time.

I don't see much difference myself honestly.  To me a drive is a drive.  But from a story POV, I can see advantages and disadvantages to both.  I guess it's in how you spin the descriptions. 

The concept of an efficiency coefficient could work for all of us.  The key to that I think would be in defining how many "old" drives there are compared to "new" drives.  What's the most common drive type, and how prevalent is it?  How rapidly do "new" drives get out into the universe?

The answer to that question depends primarily on who gets the most advanced drives and, in this case, the point at which the "STC" for fusion torch drives becomes available (which has about the same delta-v, but an increased acceleration).  Or perhaps even antimatter drives, which I believe have been mentioned with regards to G/DAoT ships, but which I also felt were more appropriate for "military" vessels.

Works for me.  Like I said before, I have no issue with stratifying the tech.  I find it fits in very well with the established cannon. 

The "efficiency" of the drive therefore depends on the "tech level," which defines the overall "mps" (or how much delta-v) the drive system can generate with a given amount of fuel.  This requires the in-universe answering of the question as to what level of technology does the Adeptus Mechanicus allow the Imperium at large to access.  Our previous answer is that it was Low Martian, or TL 10.  But what about the Imperial military?  Do they allow them access to Common Martian?

Now that is a question.  IMO, the AM allows some of the common and some of the experimental out to the Imperial military.  But not all.  There's a degree of paranoia in the AM about the Imperium that I believe causes them the hedge their bets, and retain some things just for themselves.  The Titan Legions for example, are loaned to the Imperial military, but are not part of the Imperial military (no matter what the Imperial military thinks).

Well, yes, you could just blow past the defensive positions, but would it really be a good idea? 
"Ha!  We blew past those chumps at Io!  Never saw us coming."
"Hey boss, what's that in front of us?"
"What?  Oh crap!  That's Saturn!"
*SMACK*

Assuming that the "jump point" is that close to Saturn.  It is unlikely that this would be the case.  Furthermore, you can always jump to another point along the warp zone.

It was just an example.  The object(s) a ship could collide with if moving too fast to maneuver out of the way are myriad.  It could be meteors, asteroids, moons, space stations, 67 Mustangs..

But this raises another issue.  Can you just jump willy-nilly to and from warp space?  Or do you have to "spin up" the jump engines first?  And is there a reset/recharge time after making a jump?

I'm not sure I like the Babylon-5 route with warp gates and the like, though I could see how it would fit in with the existing fluff actually.  But I would be more in line with the idea of an area, rather than a singular fixed point, which is conducive for ships entering/exiting from the warp.  Not the globe concept as given, but more of a window on that globe.

As above, one can argue that this is the "probability wake" of a drive exiting the warp from the stable warp route.  Even so, it is suggested to be an incredibly large volume of space on the order of 8 billion-odd (or more) cubic kilometers.  That's not really a practical volume to defend, mine or whatever. 

Not quite sure I follow here.  I'm not seeing how the "probability wake" and window concept go together here.  Probably something simple and obvious that I'm over looking, but there it is.

The volume of space is not all that "bad" to manage IMO.  No, you're not going to be able to mine it in any practical sense.  But you can monitor it.  It is not unreasonable to think that remote sensors could be set up to cover that area of space.  Given what we can do now with seismic, motion, heat, and SONAR sensors, it's not a huge leap.  One could then tailor patrol routes to maximize security. 

This should only apply to developed systems.

[

quote author=JRaup]In my thoughts, yes, a ship could just enter and exit the warp anywhere outside the system shadow, but the energy and safety factors would generally be prohibitive. 

Mirrored here by fuel and, of course, whatever game mechanics that you use to control warp travel.  Hopefully Rogue Trader will introduce those to the 40k universe.  (I have my doubts that they will, or at least they will be what many of the people interested in those rules would like to see... )[/quote]

Agreed.  I don't think any official supplement will deal directly with space travel or combat.  Or if it does it will be a very generalized system.

I think there must be something for CnC in system.  Now, how far into a system before it takes control is another matter.

Indeed.  To be honest, for massively developed systems like hiveworlds or worlds on major shipping routes...?  I do believe that there is an arbitrarily established perimeter at which ships do begin to get "funneled," but that truly is going to vary from world to world.  For example for the Terran system I would imagine that it lies at least at Jupiter...

So... interesting argument, and well taken with the caveat that it truly depends on the world and strategic choices in question.  We can make more of this in our descriptions of the individual worlds, or perhaps someone can even work up a guideline based upon the star type and world type as to what this might be.

Agreed.  I too would think that there is some sort of standard set up, depending on system type, star type, location to or on a shipping route, etc.  Though I would almost expect each system to be unique in some aspect.  There are just far too many variables at work, from number of celestial bodies in a system, to the proximity of warp events, to properly account for in a standardized scheme.

Yeah, I see this as well.  We're arguing granny smith apples vs. golden delicious IMO.  But the synthesis of these discussions should prove..."fruitful"...

*kaboom-tisch...*

Thank you!  Thank you!  I'm here all week.  Be sure to check out the buffet, and tip your waitress well.

Cool.  The concept I think does apply, if only tangentially.  I think this kind of goes to the heart of a lot of what we're discussing, even if it has strayed a bit..

Yep, even though it wasn't specific I feel that this thread was designed to discuss sublight drives.  We all are fairly familiar with the operation and "rules" that govern the warp drive.

I guess I just want it to all work together in a semi-logical fashion.  I'm just getting a sense of this is this, and that is that, and never the twain shall meet when it comes to this.  Probably just my own biases showing through though.

However, when it comes to logistics, stability is better.

An accepted truism at Anargo.

One also has to consider how many navigators are there in the Imperium.

Anargo considers them to be very rare, rather than what is in essence a "servitor" class, one for every ship.  Indeed, we argue that the short-distance "calculated warp jump" is by far the most common type of jump, and thus is moderated by the system of major, minor, and feeder trade routes - stable warp routes - that criss-cross the subsectors, and which also exist between the subsectors themselves.

In short, we've been there, done that, and have the T-shirt.  Indeed, one of the things that we've been waiting for is to get sufficient numbers of the worlds finalised so that we can begin to build up this skein of systems using a defined series of trade guidelines (modified to 40k), rather than just pulling them out of our bottoms.

Ahhh, OK.  I don't think I've come across those discussions as yet (A lot of meaty stuff to wade through here).  And I like the approach here. 

I haven't come across that yet (warp times).  But I'll keep reading.  I probably won't agree with the conclusion, but that's neither here nor there.     

WD139/140 for the originals.  There are some potential ones here that we might be using, but their application isn't quite yet... solid.  Thus I'm biased towards the originals, even if I think that the ones here have greater potential in the long run.

IMO, start with the WD articles (I have those issues in a box somewhere), and generate what works.  The GW stuff to my mind is just a bit too arbitrary, and not designed for use with an RPG.  That's something to keep in mind, the end use of the material.  A lot of the older GW fluff was done with only the TT game in mind.  So things like warp travel times were irrelevant to the actual game play, and could be set at anything.  They could have said it takes 5 years to go 1 lightyear and it would have had no bearing on the game.  So not only is the context of the universe at had important, but the context of how and in what form the materials designed will be used.

I think I'm out of step with you in part because I'm not just looking at the "science" aspect.  Yes, that is an important factor, and goes a long way to establishing a solid back story.  But I also see a need to make whatever gets put down "practical."  Not is a strict "can this work" science sense, but in a larger "can the Imperium work like this" sense.  It's one of the reasons I get hung up about travel times.  I look at the economic, political, communication, and military aspects, and say to myself "this just can't work."

I do not think that are approaches are mutually exclusive, except where I use the "reality" (as much as possible and with full realisation that we're dealing with a fictional universe) to expose the holes in the Imperium.  We have to accept that it has existed for ten millennia, even if the majority realise that it is through designer fiat, so being aware of the glitches and perhaps even exploiting them in continuing narrative is, for me, acceptable.  Similarly, it's part of the reason that I'm not particularly inspired by the parochial and thematic approach of Dark Heresy--I don't want to have earlier and later medieval Europe shoved down my throat, but would rather see it as a progressive system wherein it will fail or grow stronger by making given choices.

Erm, but there we go.

I don't think we're being mutually exclusive either, just out of step.  Same road, same goal, just different sides of the street.

I too don't care for the narrow focus and rail road approach of DH.  Give me the tools to represent the universe.  I want to explore it all, not just some alley with no outlets.  I'll expand on the medieval aspects below.

Suffice to say, though, that the Imperium isn't going to break because it takes 10 months for a ship to get from the warp zone to a mainworld, especially given the standard argument with regards to the efficiency of the Adeptus Administratum.  (Just out of interest, we argue that the Adeptus Administratum is actually rather efficient, but also recognise that they're dealing with a shed-load of information exchange--that's one helluva bandwidth.)

Oh, that's a whole other can of worms.     And one better suited for a different thread.

With my readings on the 40K verse, I get the sense that there is some level of central authority, but then I look at various fluff pieces and such, and don't see how that can be with all the various "restrictions." 

This is assumed, yes, but it is far more diffuse than most people seem to recognise.  In this it seems very much like feudalism coupled with true 'empire.' 

However, my bias or socio-cultural framework is more influenced by late Republic/early Imperial Rome than later medieval Europe, even if some feudal aspects are throw into the mix.

Now you see, I take a different view here.  I don't rely on the Medieval, or even the Roman Imperial models.  Yes that have a place, and some elements are present, but not the whole.  I look at things through the lens of the Victorian age.  I see the Imperium much more in the vein of the 19th Century Empires.  With in that category you have just about everything you could look for, from the retrograde of the Ottomans, to the industrial powerhouses of Germany and Britain, to the chaotic miasma that was China.  It also lends a certain "romanticism" that would not otherwise be present IMO.  It's also more defined and refined that the earlier potential models. 

Time to split this part off form the discussion.  Any particular way the new thread should be named?

Cool.  I'll read up on that later.  Hopefully it will better ground me in what everyone else's thought processes are.

Please remember that it needs to be modified given the more recent discussions, with that article being written well over 5 or more years ago to offer a "narrative" to the warp...

Acknowledged.  At the very least it will get me more up to speed with what's gone on before, to in theory prevent me from rehashing old arguments (again).

As I said above, this could work, as long as the end result is satisfactory.  Really, the mechanical/science specifics are somewhat irrelevant to me, as long as they have a logical "natural" flow to the fluff of it.

As an "explorationist-simulationist," reality negotiates with the context of the universe.  I'm fine with people getting "reasonable" travel times between the warp zone and the mainworld, but it should inform subsequent materials.  Having a slower trip making the journey in half the time as a faster ship would make very little sense unless there was a reason for that (such as the faster ship having almost no fuel left).

In short, there should be consequences for choice and action.

I'm completely on board with this.  You should not just be able to do something with there being no consequences.  Where I find myself in disagreement though is in what those choices and consequences are, at least to a degree.  I'd rather not put too many limitations on things just to comply with "reality" (defined however you wish).  Well, that and I suppose that I'm not much of simulationist when it comes to SciFi, at least not in the same sense as a historical gamer.  Let me see if I can better clarify.  If I'm playing a WW2 game, I want it to reflect that era, the choices, the consequences, the equipment, etc accurately.  If I'm playing a SciFi game, I want the rules to reflect that universe, not ours.  As it is a SciFi setting, it does not have the same limitations or requirements that a historical game does.  So, if a mechanic or rule, or what not reflects that universe, even though it flies completely in the face of our own reality, I have no issue with it.

I'm most familiar with PhP boards, none of the ones I'm on have this neat feature. 

*whispers*

This is a PHP and MySQL board.  Wheres you meant phpBB?  We haven't used that software for some time so I'm not really that familiar with it and its limitations any more.

D'OH!  *smacks self in head*  Yes, I meant phpBB. 

Like I sort of said above, I think this all goes hand in hand.  I think things have to work as a whole, and not just as individual aspects.  It all has to fit together, or it just kind of falls apart once you take a step back and look at things.  Like the 40 year cross-Imperial transit time.  It may sound good, and have legitimate rationales, but to my mind, it just doesn't work on the whole.  Too many other things become suspect as a result.

Not quite sure why the 40 year period doesn't work since it really just defines regions of political effectiveness and influence on a much smaller level.  But then again the idea of centralisation and the Imperium has been questionable since the start, even if like the 'fluff' on the anthropogenic nature of the Chaos Gods it has been there for quite some time.

The political analyst and historian in me screams that it won't work.  That it will collapse in on itself, fracture into a thousand different shards, never to be put back together.  (Stupid voices in my head!)  But I'll expound upon that in another thread..

[Kage2020]

And now the quote-fest happens in full...   First the relevant bits to the thread, and then the sidetracks.

42 days is alright by me. A bit longer than I would have imagined, but there you go.

Well, to put it in perspective.  If we use the Fusion Torch statistics (basically roughly the same as the Fusion Drive but with a 1,000 times more powerful... hand-waved somehow) and multiple fuel efficiency by 10 (we're now 10,000 more efficient than "realistic") a ship like the Venturer (1.5G, 1,500 mps total, but only use 650 mps for acceleration and then another for deceleration) could quite reasonably travel from Terra to the Warp Zone as we have previously defined (17.26 AU) in 30.3 days, and take 18.2 hours to get up to speed.

If I halved the multiplier and had two fuel tanks, it would be the same.  On the other hand, if I kept only the one fuel tank it would be: 61.2 days and 9.1 hours to achieve the cruising speed.

If I used the original value (x10) and had two tanks such that it could use 1,250 mps of fuel, then it could make the journey in 13.96 days with an additional 38 hours to achieve that velocity.  With four tanks (6,000 mps) it might use 2,750 mps to accelerate and make the journey in 5 days after 83 hours (3.46 days).

My sense at this point is that it would be too much to multiply by 10, but to use the Fusion Torch and a multiplier of 5.

Nyargh, I'm sure that is helpful, but not truly meaningful.  I'm just throwing numbers at you.  Using the Venturer as an example and assuming 1.5 G acceleration and one or more fuel tanks of x5 efficiency (750 mps), then the travel times would be if one assumed that you accelerated to the maximum and left around 20 mps for manoeuvres, then (boost/acceleration+coast time at "maximum velocity"):

Fuel 1	Fuel 2	Fuel 3	Fuel 4	Fuel 5	Fuel 6
11.1 hrs + 50.2 days	22.5 hrs + 24.3 days	33.8 hrs + 15.8 days	45.2 hrs + 11.4 days	56.6 hrs + 8.7 days	68 hrs + 6.8 days	79.3 hrs + 5.4 days

Of course, by the time you get beyond one or two fuel tanks, you're talking a significant volume/mass of the ship being dedicated to fuel.  With six fuel tanks, you've taken up just under a third of the volume in "gas" alone.

Thus, you can either have speed, or endurance.  That's with x5 the standard fuel of a Fusion Torch at TL 12, or High Martian. At Low Martian, or the kind of stuff that the Adeptus Mechanicus might be handing out to the Imperial military (assuming that everyone agrees with that), then it would be more akin to (1.5 G, 75mps base):

Fuel 1	Fuel 2	Fuel 3	Fuel 4	Fuel 5	Fuel 6
0.83 hrs + 669.71 days	2 hrs + 283.2 days	3.1 hrs + 179.6 days	4.3 hrs + 131.5 days	5.4 hrs + 103.7 days	6.5 hrs + 85.5 days	7.7 hrs + 72.8 days

And with an x10 modifier (1.5 G, 150 mps):

Fuel 1	Fuel 2	Fuel 3	Fuel 4	Fuel 5	Fuel 6
2.0 hrs + 283.2 days	4.2 hrs + 131.5 days	6.5 hrs + 85.5 days	8.8 hrs + 63.3 days	11.1 hrs + 50.2 days	13.5 hrs + 41.6 days	15.6 hrs + 35.4 days

Does that give a general sense of the times involved?  The first table shows the G/DAoT Venturer with its more advanced technology, but also with the fuel efficiency.  The second and third tables show the "40k" version (based on TL) if one assumes that it is "Low Martian." 

We can, of course, fiddle with these numbers for Anargo in general, but it would ultimately mean that it might be more interesting to explore "antimatter drives" as the standard in the G/DAoT (3,600 mps per fuel tank with x10!--9 days to the warp zone on one tank of fuel!), and leave the Fusion Torch at the x10 - I hope not x15! - for the Imperium.

How much difference do we imagine there will be between different ships though? Will the fastest ships in the Imperium (e.g. Inquisitorial Black ships) be able to make the warp zone in half that time? Will most transports in the Imperium spend double that time, or three times?

If a ship dedicates a lot of its internal space to fuel tanks?  Yep, it could make the trip rather very fast, especially with the "fuel multipliers" that we're experimenting with.

Even at the velocities that are being discussed?  Not being an astrophysicist, or having any real grounding in the theories, it was more of a layman's take, so take it with that in mind. 

Well, you could make some quick calculations.  The ship has a transverse section of about 300m (if I over-estimated), or 810,000 m^2.  Travel for one second at 500 mps (which is really quite fast) is about 805 kps (805,000 mps) or 0.26c.  In that period, therefore, "displaced" atoms will number approximately 652,050,000,000 atoms (6.5205x10^11), or 0.000000000000011% of a mole of molecular hydrogen, or about 0.00000000000000107 grams...

In other words, really quite a small number.  Of course, it's going to act as a fluid medium, and so you're going to effect a much larger amount of material but still... Not a huge amount of material.

(And I'm sure that someone will put those numbers right... )

I don't see much difference myself honestly.  To me a drive is a drive.  But from a story POV, I can see advantages and disadvantages to both.  I guess it's in how you spin the descriptions. 

It's quite simply a matter of "resource management," something which some people are admittedly not that bothered about.  Reactionless thrusters are "on" as long as they have "fuel," working to top efficiency, undiminished.  Reactionless-based thrusters are basically "no brainers," while reaction-based have more flexibilty... and more problems.  You can burn less fuel and last longer, or more fuel and get their "quicker," options which aren't available with the reactionless thruster.  And if you link those together?  Then you've just created another reaction-based thruster.

If you don't see the difference, then that argues either to my ability to explain the concepts, or your lack of interest in that particular avenue of RP.

It was just an example.  The object(s) a ship could collide with if moving too fast to maneuver out of the way are myriad.  It could be meteors, asteroids, moons, space stations, 67 Mustangs..

And one could smack into the ship if it came out travelling a mere 0.001 mps.

But this raises another issue.  Can you just jump willy-nilly to and from warp space?  Or do you have to "spin up" the jump engines first?  And is there a reset/recharge time after making a jump?

It's unlikely that you're going to find an answer to this in the canon.  Personally I take the stance that it takes a number of hours, at the least, but there we go.

Not quite sure I follow here.  I'm not seeing how the "probability wake" and window concept go together here.  Probably something simple and obvious that I'm over looking, but there it is.

"Probability wake" also refers to the probability of a ship arriving at any given targetted point.  Thus the implication is that it's as much a window as a bullet is to scatter shot.


And now the less relevant stuff, for which you have my apologies for starting it and/or perpetuating it.

I guess I just want it to all work together in a semi-logical fashion.  I'm just getting a sense of this is this, and that is that, and never the twain shall meet when it comes to this.  Probably just my own biases showing through though.

There is, however, a fundamental disconnect between sublight travel and warp travel... One occurs in one universe by a separate set of principles, while another in another universe by a different slew of principles.

Ahhh, OK.  I don't think I've come across those discussions as yet (A lot of meaty stuff to wade through here).  And I like the approach here. 

And some of it has been lost to the vagaries of time, or the laziness of people (myself perhaps more than others) making backups.  Much of it, though, merely awaits to be put on the website or even something as mundane as being transcribed.

IMO, start with the WD articles (I have those issues in a box somewhere), and generate what works.  The GW stuff to my mind is just a bit too arbitrary, and not designed for use with an RPG.  That's something to keep in mind, the end use of the material.  A lot of the older GW fluff was done with only the TT game in mind.  So things like warp travel times were irrelevant to the actual game play, and could be set at anything.  They could have said it takes 5 years to go 1 lightyear and it would have had no bearing on the game.  So not only is the context of the universe at had important, but the context of how and in what form the materials designed will be used.

Point by point to try and prevent too much quoting:

• We do use the articles, but it's always nice to have access to the ones that have been left in different countries, that someone doesn't have access to in one form or another, etc.
• All values selected for warp travel are going to be arbitrarily determined by something.  This does not make them unusable to RP unless you're making a value judgement such that, for example, "long travel times are not appropriate for RP."
• Current 'fluff' is also primarily written with the wargame in mind.  I'm afraid that I'm not really counting Dark Heresy in this mix since I haven't seen it doing anything visionary.
  
  

I'll expand on the medieval aspects below.

This reiterate the point that we need to create separate threads and leave this thread to sublight propulsion.  It might be laudable to realise the interconnectedness of everything, but it certainly makes for messy discussion.

Now you see, I take a different view here.  I don't rely on the Medieval, or even the Roman Imperial models.  Yes that have a place, and some elements are present, but not the whole.  I look at things through the lens of the Victorian age.  I see the Imperium much more in the vein of the 19th Century Empires.

I make no assumption that I'm inventing anything, but my own stance is to use the Roman example as a basis, mix it with a bit of feudalism, but ultimately to set the "tone" of the universe in the mindset of the "just getting to the Renaissance..."  Mostly.

But that's no never mind.

I'd rather not put too many limitations on things just to comply with "reality" (defined however you wish).

Reality in the context of the universe.  If this means to you that you can pull out any idea for the expediency of the narrative...?  Well, that might be more problematic.  This is not about mechanics or rules, but about the reality of the universe, so very much in keeping with you suddenly introducing laser weapons into your historical game because you happened to need lasers.

Kage

[Dragon Lord]

Even at the velocities that are being discussed?  Not being an astrophysicist, or having any real grounding in the theories, it was more of a layman's take, so take it with that in mind. 

Well, you could make some quick calculations.  The ship has a transverse section of about 300m (if I over-estimated), or 810,000 m^2.  Travel for one second at 500 mps (which is really quite fast) is about 805 kps (805,000 mps) or 0.26c.  In that period, therefore, "displaced" atoms will number approximately 652,050,000,000 atoms (6.5205x10^11), or 0.000000000000011% of a mole of molecular hydrogen, or about 0.00000000000000107 grams...

In other words, really quite a small number.  Of course, it's going to act as a fluid medium, and so you're going to effect a much larger amount of material but still... Not a huge amount of material.

(And I'm sure that someone will put those numbers right... )

Astrophysicist to the rescue!
(Though to be honest I haven't really gone through it in that much detail)
Based on the density of the solar wind I get the mass of particles with which the Venturer would collide at about 4 or 5 orders of magnitude larger than Kage's estimate, that still is barely anything however, even when one takes into account that they will generally be moving at 400-750km/s outwards themselves.
A rough comparison in my head suggests that the pressure on the Venturer as a result would be comparable to, possibly a bit less than, the radiation pressure due to the light emitted by the Sun.
Also the plasma that makes up the solar wind, or equivalent is so diffuse that you will not really get much in the way of a 'wake' rippling out into the surrounding wind particles on meaningful timescales.

Of course, by the time you get beyond one or two fuel tanks, you're talking a significant volume/mass of the ship being dedicated to fuel.  With six fuel tanks, you've taken up just under a third of the volume in "gas" alone.

Out of curiousity how does the volume taken up by one or two tanks plus the 'engines' themselves and the warp drive, etc. compare with the typical indication in the background that the 'engineering' section of a ship takes up roughly one third of the vessel (at least for military ships, probably less for transports and civilian vessels)?

The Fusion Torch with a x5 multiplier and 1 or 2 fuel tanks seems to provide a reasonable time to reach the jump zone, however the Low Martian alternative, even with the x10 multiplier only gives reasonable times at the 5 or 6 fuel tanks range.
I would be sort of tempted to say that perhaps High Martian (the stuff they keep for themselves) is a Fusion Torch with x10 while the stuff they give out to the Imperial military is a Fusion Torch with x5 (the slightly smaller difference than might overwise be the case being a result of the fact that the ability to move troops, etc around fairly rapidly is somewhat integral to the survival of the Imperium, and thus other Imperial authorities being slightly more insistent that Mars release the technology.  The lower TL drive with a x10 modifier and something in the range of 2-4 fuel tanks would be used on less advanced military vessels (perhaps those built on less developed worlds) and civilian vessels.

Matter-antimatter drives are I suppose a possibility for Age of Technology vessels, drives using an artificial black hole (which if memory serves can be used to extract one third of the rest mass of the fuel as energy) would be another possibility.

All values selected for warp travel are going to be arbitrarily determined by something.  This does not make them unusable to RP unless you're making a value judgement such that, for example, "long travel times are not appropriate for RP."

If you have a look through the Imperium forum you should find a thread entitled 'Changing the warp travel times'  that contains the ASP discussion on warp travel times.

[Kage2020]

Based on the density of the solar wind I get the mass of particles with which the Venturer would collide at about 4 or 5 orders of magnitude larger than Kage's estimate, that still is barely anything however, even when one takes into account that they will generally be moving at 400-750km/s outwards themselves.

I merely assumed an even distribution of molecular hydrogen in a 'solid state,' rather than considering the fluid dynamics of the situation, nor the probability of individual hydrogen molecules interacting with those outside of the direct flight path.  I can think things through, but that doesn't mean that I have the expertise to follow it through.   Indeed, the last time I did any rigorous astrophysics was in... 1993.  Ye gadz.

Also the plasma that makes up the solar wind, or equivalent is so diffuse that you will not really get much in the way of a 'wake' rippling out into the surrounding wind particles on meaningful timescales.

And certainly not that it is going to have a significant impact upon the momentum of another vessel... There are times when the marine analogies begin to fail, even though it is always good to think about the possibilities.

Out of curiousity how does the volume taken up by one or two tanks plus the 'engines' themselves and the warp drive, etc. compare with the typical indication in the background that the 'engineering' section of a ship takes up roughly one third of the vessel (at least for military ships, probably less for transports and civilian vessels)?

The problem remains that GW has a true under-appreciation of scale.  Then again, I'm not particularly trusting the "reality" - or at least verisimilitude - of the GURPS system, but tend to trust it more because it at least tries to remain rationally coherent.  With that said, there are a total of 20 systems on board a ship abstracted through GURPS 4e Starships, each containing approximately 5% of the total "mass" of the ship.^*1  With that said, the following systems might be considered "engineering" specific:

• Warp Drive
• Three fusion torch engines.
• 1 fuel tank

You might throw in other systems in there, depending on preference, but those seem to be the ones that are commonly referred to when people think "engineering," with others being more "control" or "tactical" or whatever.  So that's 5 systems, or approximately 25% of the ships' mass.

I would be sort of tempted to say that perhaps High Martian (the stuff they keep for themselves) is a Fusion Torch with x10 while the stuff they give out to the Imperial military is a Fusion Torch with x5...

Right, then.  This is actually now more RPG statistics being dictated by BFG and personal expectations, which is really for the other thread (and is not inherently unreasonable), but here are the values:

Fusion Rocket (unmodified)
Thrust: 0.005G/engine
Fuel (per tank): TL 9, 12mps; TL 10, 60mps; TL 11, 180 mps; TL 12, 450 mps

Fusion Torch (unmodified)
Thrust: 0.5G/engine
Fuel (per tank): TL 10, 15 mps, TL 11, 45 mps; TL 12, 150 mps

Tech Level Assumptions
Low Imperial, TL 7
Standard Imperial, TL 8
High Imperial, TL 9 <-- Non-Adeptus Mechanicus intervention
Low Martian, TL10 <-- Adeptus Mechanicus intervention from this point on through the franchise
Common/Standard Martian, TL 11
High Martian, TL 12 (restricted; very few fields)

Matter-antimatter drives are I suppose a possibility for Age of Technology vessels, drives using an artificial black hole (which if memory serves can be used to extract one third of the rest mass of the fuel as energy) would be another possibility.

Otherwise known as "cosmic energy sources" for that last one... It can be explored for the G/DAoT version, though.

If you have a look through the Imperium forum you should find a thread entitled 'Changing the warp travel times'  that contains the ASP discussion on warp travel times.

I seem to remember the discussion was never finished, or at least applied...?  That is, a suggested means by which "coefficients" etc. could be explained in a meaningful way and related to the 'fluff' on the matter.  Might be misremembering that, though.

Kage

[Dragon Lord]

You might throw in other systems in there, depending on preference, but those seem to be the ones that are commonly referred to when people think "engineering," with others being more "control" or "tactical" or whatever.  So that's 5 systems, or approximately 25% of the ships' mass.

Considering that this was arrived at from a system entirely independent of GW derived figures that is quite a good correlation.
Given that then I would have no problem suggesting a typical vessel would have two fuel tanks, bringing the total up to 30% of the ship's mass.

I'm also happy that we have come up with a sensible solution with fusion drives, since these seem to best match the description of a 40k ship's sub-light drives as 'plasma drives'.

I seem to remember the discussion was never finished, or at least applied...?  That is, a suggested means by which "coefficients" etc. could be explained in a meaningful way and related to the 'fluff' on the matter.  Might be misremembering that, though.

Well I had got the formulae to a form I was happy with, but I'm not sure if we ever formally adopted them.

[Kage2020]

Well, the nature of warp travel with the new introductions form Dark Heresy are still be considered.  For example, one of the suggested reasons for the increased travel time of "Chartist Ships" is that to travel 10 light years they might end up travelling 100 light years, or some such.

I like the formulas that you produced, but the thing that I'm waiting for is enough coherent information to see whether we truly need to move away from the canonical travel times of WD139/140.

Kage

[Dragon Lord]

For example, one of the suggested reasons for the increased travel time of "Chartist Ships" is that to travel 10 light years they might end up travelling 100 light years, or some such.

As a result of sticking to 'stable' warp routes presumably rather than going 'as the crow flies' (if there is such a thing in the warp  )?  That seems reasonable and it would not be impossible to incorporate incentives to use 'stable' warp routes into the formula system, possibly giving them some sort of modifier to the warp coefficient to make them less variable in terms of travel time, if perhaps a little slower.