Warhammer 40K Fluff Discussion XV: You Must Be THIS Tall To Witness The Grimdark

[Forum Explorer]

There's 'regular 40k bonkers' and then 'bonkers even for 40k bonkers'. Even if you grant yourself a few factors of a billion or so leeway for 40K being nuts you're still nowhere near where you need to be to make such a scheme work.



I've always understood these things to be on the distance scale of orbiting satellites, i.e. orbital distances of hundreds or thousands of kilometres, not billions.



The idea of a continuous, dense sphere of defences stretching from Earth to Neptune is impossible on so many levels that 'cartoonish' would be a gross understatement. It would require orders of magnitude more materiel than the mass of the planet. It would require a constant stream of supplies that would bring far more random supply-ship captains to the Solar System than the number of interlopers it would keep out. If it's dense enough it would have to deal with the Kessler effect and maybe even the pull of its own gravity.



Why would these threats scare anybody if the chances of being caught are effectively zero? You can have the harshest penalties you want, if your rules are unenforcable people aren't gonna be deterred. This is like trying to pass a law regulating what parts of the sea fish can swim in.



With the kind of scaling we're talking about (to fill the entire volume of the Solar System with man-made structures at a density of at least 1 per 200,000 km radius sphere), I could easily see this consuming more resources than the entire industrial output of the Imperium. Obviously that latter number is very up in the air so I'm not going to try to get more in-depth on that, but we're talking here about 4x10²⁹ cubic kilometres of space. That's more than 10¹⁸ Earths. IIRC the Imperium is described as being about a million worlds? To supply 1 unit of defensive 'stuff' per 200,000 km radius sensor-range bubble (whether that's a space station or a patrol ship or a mine), every planet in the Imperium would have to supply 10 trillion of those units.

It is worth noting that your 1 per 200,000 KM number is the sensors of a small cruise ship (actually where did you even get that number?). And Terra has the most advanced defenses in the entire Imperium. So the number is almost certainly significantly larger.

In fact we know it is. Non-Terran planets are able to detect an invading fleet almost right from the moment they enter the solar system. How? By simple radio if necessary. But also because A) exiting the warp is very noticeable, b) ships generate heat, which is easily spotted, and c) most ships also generate light which is even more easily spotted also D) some systems have psykers to look for the mental readings of possible invaders.

The location of the object in question might not be 'real time', IE subject to light speed delays and the like. But when it comes to tracking objects in a solar system, that delay isn't all that big. So maybe that 200,000 km radius is the detection distance where things are in 'real time', which makes sense if that's a combat number.


But lets go back to a different point. Lets say none of that's true, and you're right. The chances of being caught is not zero but effectively 100%. Why? Because unless you are just flying in empty space the whole time and not going to any of the planets (in which case who even cares?), the planet will detect you, and because you didn't go through the checkpoints, the planet will then proceed to ruin the rest of your life (which sounds like a long time, but it really isn't. )

[Wraith]

EDIT: Here's a fun question: do warp routes' jumping-off points stay fixed with respect to local star systems over a galactic year? If so, does that mean the Warp is rotating?

In the Sol System, at the time of the Great Crusade/Heresy, the answer seems to be Yes.

The Imperium keeps what was called a Mandeville Point out near the orbit of Pluto, where warp-capable ships were supposed to eneter the system and then decelerate to sub-warp speeds and approach the Imperial planets under 'impulse' power. This also served as a blockade; anyone refusing to stop and be identified by the authorities would be immediately vaporised, and was the first line of defence when the Traitor Legions translated into the system. It's specifically described as THE Mandeville Point in the Garro story, Sword of Truth.

Which, in turn, offers a succinct solution to the question about Grey Knight recruitment. If there was only one safe place where traffic would enter the solar system - the Mandeville Point - then all they would have to do is station a Cruiser out there and wait for Black Ships to come to them. Then they board, pick out suitable recruits, and go their separate ways from there as they go to Titan and the Black Ships go to Terra.

[lord_khaine]

Then a pack of daemons straight up attacked the gates of the imperial palace. Failed entirely, but it encouraged the custodians to stop hanging around, playing cards with each other.

According to relevant Sources most Custodes dont spend much time playing cards.
I guess its hard with oily hands

[The Glyphstone]

I knew I remembered hearing something like that in a Garro story.

[LCP]

These defenses have been stockpiled for 10+ Millenia. And a lot should be from before old night. While I doubt every square km of the solar system is coated in defences, a good part of it would be. It's Holy Terra after all. The rest of the Imperium could fall but as long as Sol stands, there's still an imperium.

10 trillion units per planet. Let's assume a 'unit' is as small and cheap as possible, something like a sea mine with a tiny ion thruster + sensor array that don't add any real mass. Sea mines weigh about 700kg. That's 7x10¹⁴kg of mass supplied for every single planet in the Imperium. Taking a rough estimate I found on Google, that's about 7,000 times the total mass of all the man-made structures currently on Earth, purely in space mines. And that's from every single planet in the Imperium, even the feral worlds and the feudal worlds and the death worlds, and that's the cheapest, smallest version of this idea.

Why would anybody build this? How would the Imperium have any industry to spare to build anything else?

It's worth mentioning, the most successful assault anyone led onto anywhere even near Terra was the Necrons. They invaded Mars. And managed to stay on the surface for approximately three seconds before being completely vaporized. This was considered a major failing in their defenses.

Sure, but there's no reason you can't achieve this kind of protection with defences that are close-in to the planet.

It is worth noting that your 1 per 200,000 KM number is the sensors of a small cruise ship (actually where did you even get that number?).

Rogue Trader. The Active Augury spacecraft action (for any vessel) has a range of 20 'void units'. I did some searching around and took the largest interpretation of void units I could find.

(Also I assumed perfect packing density of detection bubbles, which is being a bit over-generous since spheres don't tesselate. In reality if you're going to try to fill that volume you're going to need more things to account for the overlap inefficiency - or else accept some blind spots)

In fact we know it is. Non-Terran planets are able to detect an invading fleet almost right from the moment they enter the solar system. How? By simple radio if necessary. But also because A) exiting the warp is very noticeable, b) ships generate heat, which is easily spotted, and c) most ships also generate light which is even more easily spotted also D) some systems have psykers to look for the mental readings of possible invaders.

Come on, light and radio waves? From an object that's maybe 1km long at a distance of 8-9 AU? The ship would have to be incredibly bright to be visible.

Magical explanations like the Warp and psykers, sure, those can work. But you still have an enormous volume of space to cover to actually catch somebody once you've spotted them, and you have to travel fast to have a meaningful response time (and do you want your patrol ships boosting up to a sizeable fraction of the speed of light in the vicinity of Terra? What if there's an accident?). Why try when you can just enforce your 'checkpoints' closer to the places you care about and make these mind-boggling costs disappear? Going back to the ocean analogy, this is like trying to police the whole Pacific in order to regulate who can approach San Francisco.

Case in point...

If there was only one safe place where traffic would enter the solar system - the Mandeville Point - then all they would have to do is station a Cruiser out there and wait for Black Ships to come to them.

[The Glyphstone]

Using shipboard sensors to judge the reach of larger and more powerful installations is like assuming ships duel at a range of 300m because that is the range of a lascannon. If the Imperium takes, say, Ganymede and turns it into a single gigantic moon-sized sensor array, it could have immense detection reach. All they need is to spot 'something' appearing where it shouldnt be and vector in the closest patrol unit for a look. Considering it takes weeks for a ship under plasma drive to reach the interior of a gravity well (RT), plenty of time to build an intercept or assemble defensive units.

[Forum Explorer]

Rogue Trader. The Active Augury spacecraft action (for any vessel) has a range of 20 'void units'. I did some searching around and took the largest interpretation of void units I could find.

(Also I assumed perfect packing density of detection bubbles, which is being a bit over-generous since spheres don't tesselate. In reality if you're going to try to fill that volume you're going to need more things to account for the overlap inefficiency - or else accept some blind spots)



Come on, light and radio waves? From an object that's maybe 1km long at a distance of 8-9 AU? The ship would have to be incredibly bright to be visible.

Magical explanations like the Warp and psykers, sure, those can work. But you still have an enormous volume of space to cover to actually catch somebody once you've spotted them, and you have to travel fast to have a meaningful response time (and do you want your patrol ships boosting up to a sizeable fraction of the speed of light in the vicinity of Terra? What if there's an accident?). Why try when you can just enforce your 'checkpoints' closer to the places you care about and make these mind-boggling costs disappear? Going back to the ocean analogy, this is like trying to police the whole Pacific in order to regulate who can approach San Francisco.

Case in point...

Ah, I see it now. And yeah, It was kinda as I suspected. 200 000 KM is the minimum distance for a success that will reveal everything significant. With proper upgrades on the proper ship that number rises to a minimum of 300 000 KM. And that's the minimum. Every degree of success increases that number by 5, and at max skill you can potentially have 10 degrees of success. So you get a range from 300 000 KM to 800 000 KM. And again, that's literally detecting everything important about an enemy ship, including stuff like how many weapons it has and what kind of engine it's using, even if the ship is running dark.

Also again, this is using stuff that's available to Rogue Traders, who, while powerful, do not have access to the level of technology available to Terra.



Why not? First off the average size of a warship in 40K hangs around 2-3 KM, with only the smallest support ships being less then that. Secondly, we've detected millions of asteroids which don't emit any light or heat that are around that size with nothing more then modern technology. Thirdly light and heat are stupidly easy to detect in space because space is dark and cold. Fourthly there's no stealth in space so you can't really eliminate light or heat either.

Seriously, with modern technology we can spot a space probe out by Uranus in less then a second. And that's an object the size of a car. Not the size of a town with about the same number of people.

[LeSwordfish]

Correct me if i'm wrong but we already know where the space probes are, more or less. We put them there, and we knew where to start looking, neither of which would apply with a hostile craft.

[Silverraptor]

I had an interesting dream last night relating to 40k. There was some old cryptic Eldar prophecy that was being fought over and when it was found and listened to, by multiple sides at the same time that couldn't directly kill each other at that point, everyone seemed to realize what it meant and every side took off for Terra.

The prophecy said to some effect that there was a special gate into the warp that lead to the ultimate power that could be wielded by mortal hands, where the mortal would be the true master of this power and be the one in complete control over everything, including the warp itself. The location of this gate was in a city that was completely lost and then covered over it with a layer of concrete, lost by the cities built on top of it.

It took me a moment to realize (in my dream addled state where things don't make complete sense) why Orks, Space Marines, Eldar, the Inquisition, and the forces of Chaos were all gunning straight for the area of Italy on Terra Earth. Apparently the answer was the warp gate was in Atlantis when that city was lost and the city was built over with concrete, which was a Roman invention (hence Atlantis had to be around Italy somewhere). After I made my "Ahhhhhh" moment, I sat back and watched the carnage as Italy became a huge battleground between the 5 sides as the Imperial Guard of Terra tried to sandwich themselves in between to save Terra.

As to how any of these sides knew about the myths of Atlantis or Rome discovering concrete, I don't know and I'll just leave that up to Dreams just not making sense.

[Shadowy]

According to relevant Sources most Custodes dont spend much time playing cards.
I guess its hard with oily hands

Always check your sources.

[LCP]

So you get a range from 300 000 KM to 800 000 KM

Sure. Let's take that estimate and double it for 1,600,000 km detection radius. That buys you a factor 28 increase in the volume covered by each ship. That barely even makes a dent in the number of zeroes you need to knock off the volume of the solar system for a "cover every inch" style project to be feasible.

I wrote down all the numbers earlier, I feel like you can check this for yourself with any further finagling you want to do. The ratio between space to cover vs. space you can cover with 1 thing is on the order of 5 quadrillion. Take the biggest boosts to space you can cover and number of things you can deploy and see how many zeroes you can knock off the end of that number; I'm pretty sure you're never going to get it down to something approaching 1 with any remotely feasible in-universe explanation.

If the Imperium takes, say, Ganymede and turns it into a single gigantic moon-sized sensor array

I could crunch some numbers here about the flux of EM radiation you might receive from a km-scale spaceship at various distances from Ganymede, but tbh I feel like I'm gonna leave that to anybody who wants to do it at this point. Instead I'd just point you to my comment above: you have a factor of five quadrillion you need to shed. Considering you can't really deploy more than 1 Ganymede in the solar system (maybe order 10 if you're converting every moon you can get a hold of), how many zeroes do you plausibly think it's going to knock off?

Or, continuing the Pacific Ocean analogy: this is like building a really tall tower on Tonga. Yes it will be more efficient than a ship with a crow's nest, but the ocean is still too big, and there are still fundamental limits to your detection technology (whether it's human eyes or EM antenna, the inverse square law is still gonna getcha eventually). We've found small objects in space because we have been searching intensively for over a century. Continuously monitoring the entire night sky for objects down to 1km scale at distances out to Neptune's orbit is beyond any astronomer's wildest dream.

Not to mention all this is just the passive detection problem. If you want to

...spot 'something' appearing where it shouldnt be and vector in the closest patrol unit for a look.

then you need patrols at a speed and density such that they can reach the spot where you saw something before that information becomes irrelevant. And even if you can actually achieve that, that means the solar system is full of high-mass spacecraft whizzing about at relativistic speeds. That seems to me to be exposing yourself to far more danger than you're keeping out.

[The Glyphstone]

Ultimately I think you're barking down the wrong tree. We have as empirical, canonical fact that this is how they do it - ships are only permitted to vector into Terra in a specific zone or zones. This implicitly means that they can detect when ships warp in from a different location, else the prohibition would be meaningless. So focusing on reasons why it's impossible is ultimately going nowhere, when instead it'd be a more productive use of time to come up with reasons why it's possible. Maybe the theoretical Ganymede-dar isn't simply scanning for EM radiation, but has a brigade of Psykers wired into it who can sense the ripple-disturbances of a warp transition and convert that into intelligible sensor data, the same way Astropaths can translate telepathic messages into coherent information. Maybe at some point in the next 28,000 years we discover a type of sensor technology we don't have today. Maybe Terra has a magical Omnihamster who sees all points in the galaxy simultaneously, but cannot see why kids love Cinnamon Toast Crunch.

[LeSwordfish]

This implicitly means that they can detect when ships warp in from a different location, else the prohibition would be meaningless.

Not necessarily. Once in realspace there'll be only a few specific vectors you can expect a ship to be on: anything approaching a planet from outside those, or that the guardposts can't vouch for, gets shot on sight. It's easy enough to jump the fence at my workplace, but that doesn't mean we have 100% camera coverage being watched at all times.

[LansXero]

Isnt the reason 'because without the Astronomican to guide us we would end up landing on a Terra covered by dinosaurs or into the gravity well of a star'? So there are fixed points where you can reasonably expect to exit the warp more or less in the same age you left, and if you wanna get all sneaky-like you can either risk being ripped apart by warp currents / have your navigator go insane and leave you stranded in the warp forever / take several generations to arrive at sub-light speed

[Wraith]

Given the nature of the Imperium - specially, the Administratum - LeSwordfish's analogy is probably about right. With their level of tech it's possible that they can detect warp-translations anywhere in the system (various novels have sensor ranges of light years rather than kilometres), but getting that information to someone who can actually do something about it? That's the tricky part....

So there are fixed points where you can reasonably expect to exit the warp more or less in the same age you left, and if you wanna get all sneaky-like you can either risk being ripped apart by warp currents / have your navigator go insane and leave you stranded in the warp forever / take several generations to arrive at sub-light speed

Yep. Entire "shipping lanes" of the warp are charted and used as reliable, relatively safe ways of getting from one place to another, and those lanes change from season to season. Brave - or reckless - captains can brave other routes, but that tends to end poorly for them.

Otherwise, regularly visited systems have their planets and similarly notable celestial bodies' orbits charted and recorded, and incoming ships have set points where they can translate into system while reliably avoiding them.

[Forum Explorer]

Correct me if i'm wrong but we already know where the space probes are, more or less. We put them there, and we knew where to start looking, neither of which would apply with a hostile craft.

Yes, but we didn't find it by looking it up and then checking if it was actually there. We saw a light, and then looked up what was in that spot to discover we were staring at the space probe

Sure. Let's take that estimate and double it for 1,600,000 km detection radius. That buys you a factor 28 increase in the volume covered by each ship. That barely even makes a dent in the number of zeroes you need to knock off the volume of the solar system for a "cover every inch" style project to be feasible.

I wrote down all the numbers earlier, I feel like you can check this for yourself with any further finagling you want to do. The ratio between space to cover vs. space you can cover with 1 thing is on the order of 5 quadrillion. Take the biggest boosts to space you can cover and number of things you can deploy and see how many zeroes you can knock off the end of that number; I'm pretty sure you're never going to get it down to something approaching 1 with any remotely feasible in-universe explanation.

Sure, off of that number which I already said is demonstrably false. Seriously. The fluff in lots of books has them detecting fleets at stellar ranges. It's not an uncommon feat. You just got the number wrong so I felt the need to correct it in the first place.

But the more important part is the rest of my post. Which you ignored. We can already detect objects that give off light meters long at the very edge of our solar system. 40K sensors are better then ours, so it's not a surprise that they can duplicate that feat.



Basically, if your point is that the number in Rogue Trader is too small, then hey I agree! Good job, you decisively proved that. It's a good thing that nothing else in 40K uses that number. Other then that, well stealth isn't really a thing in 40K. Not in space anyways. The guys who sneak up in space cheat by not travelling through space in the first place (Eldar, Dark Eldar, and Necrons)

[LCP]

Ultimately I think you're barking down the wrong tree. We have as empirical, canonical fact that this is how they do it - ships are only permitted to vector into Terra in a specific zone or zones.

Really? And it's confirmed that these restrictions start out at the orbit of Neptune/Saturn and not, say, in a small bubble around Terra and Mars? What's the source on that?'

Here's the 'realistic' picture that I think is completely consistent with what's written:

This allows for the defences around Terra and Mars to be as beefy as you want; any amount of over-the-top description of how scary and restrictive they are will still fit.

And here's the 'bigger engineering project than a Dyson sphere' version that I'm arguing against:

As far as I can see the only reason to believe case B is even remotely conceivable is purely out of the spirit of hyperbole. It's not physically possible. Maybe for something like the C'Tan where they transcend our laws of physics, but not for an empire built on technologically stagnant human toil.

Heck, at the end of the day, if the Imperium could build this, why are the rest of their military forces so small? Why didn't the 13th Black Crusade get obliterated by the concentrated firepower of millions of warships the second it came out of the Warp? This is a military endeavour that puts the Great Crusade in the shade the same way that World War 2 does a fight between two tribes of chimps.

EDIT: There is of course another way to get the 'one permitted route from the edge' condition without this crazy construction, which is Wraith's solution - just post a ton of guard ships at the one and only drop-out point from the Warp and ferry visitors to and from their destination in close escort. As long as there's just one entry point you ever have to worry about, that works.

Yes, but we didn't find it by looking it up and then checking if it was actually there. We saw a light, and then looked up what was in that spot to discover we were staring at the space probe

I'm confused about what you're referring to here. Every space probe we know of was put into space by humans. Their courses were plotted out in advance. Without touching a telescope you can look up where they're meant to be at a given time after launch. On top of which, the ones that send data back are actively trying to tell you their location.

But the more important part is the rest of my post. Which you ignored. We can already detect objects that give off light meters long at the very edge of our solar system.

Again I'd like to know what object specifically you're referring to that's been detected at this range (the asteroid belt is nowhere near as far away as Saturn) - but I did address this. Yes, you can see small stuff far enough away, with a good enough telescope, with a long enough exposure. Having that kind of resolution on the entire sky, all the time? That's a different question entirely and that's what my original calculation is trying to show. Being able to see a needle and being able to find a needle in a haystack (or maybe more appropriately in a gigantic, empty warehouse) are two different problems.

If imaging things at these distance were as trivial as you seem to believe, we would have an exhaustive map of the solar system by now. You wouldn't see the many news stories that crop up each year of new objects being discovered within the solar system. Astronomers have done a few all-sky surveys and they take years to complete, sampling one tiny bit of solid angle at a time, making a minute adjustment of your telescope, letting it sit, adjusting again, etc. That's where the problem of scale comes in.

[Forum Explorer]

I'm confused about what you're referring to here. Every space probe we know of was put into space by humans. Their courses were plotted out in advance. Without touching a telescope you can look up where they're meant to be at a given time after launch. On top of which, the ones that send data back are actively trying to tell you their location.



Again I'd like to know what object specifically you're referring to that's been detected at this range (the asteroid belt is nowhere near as far away as Saturn) - but I did address this. Yes, you can see small stuff far enough away, with a good enough telescope, with a long enough exposure. Having that kind of resolution on the entire sky, all the time? That's a different question entirely and that's what my original calculation is trying to show.

If imaging things at these distance were as trivial as you seem to believe, we would have an exhaustive map of the solar system by now. You wouldn't see the many news stories that crop up each year of new objects being discovered within the solar system.

Sure. But like I said they detected it and then looked it up.


Voyager 1 in 2013. I gave you a link to it. And for over time, it took them 1 second to do. Seriously read the link I gave you, detecting light and heat in space is really really easy.

[LCP]

OK, and as I and LeSwordfish said, Voyager is a probe whose course was already known. Narrowing the solid angle you have to search by knowing which direction to look in the first place is how you cut out all those orders of magnitude that I was showing earlier.

An object on the distance scale of a metre subtends a solid angle of about 10^-22 steradians when it's at the orbit of Neptune. If you know where it is to begin with, that's not a problem. If you have to search the entire sky, it's going to take you up to 10²² tries (give or take a few orders of magnitude) to find it. At any sane sampling frequency that's going to run you to many times the age of the universe.

It's the needle in the warehouse again. If I tell you the exact coordinates where you can find it, you'll spot it easily. If I just tell you it's somewhere in here, you're going to be looking for a long time.

[lord_khaine]

Always check your sources.

Before trying to correct someone. Always double check.
Else you risk looking silly when proven wrong.

According to relevant Sources most Custodes dont spend much time playing cards.

Relevant bit bolded. So far we have 1 Custode playing 2 games of cards in total that we know off.

[Xenopax]

Actually where would Voyager be by the return of Guilliman? I like to imagine it hit an Xeno planet and became their God. Now there's Xenos looking for the "God Humans"

[LeSwordfish]

Actually where would Voyager be by the return of Guilliman? I like to imagine it hit an Xeno planet and became their God. Now there's Xenos looking for the "God Humans"

It's travelling at about 61000km per hour, and has stopped accelerating, I think, which suggests in the next 38000 years it will have travelled about two light years... or about halfway to the nearest star.

Space is big.

[Wraith]

EDIT: There is of course another way to get the 'one permitted route from the edge' condition without this crazy construction, which is Wraith's solution - just post a ton of guard ships at the one and only drop-out point from the Warp and ferry visitors to and from their destination in close escort. As long as there's just one entry point you ever have to worry about, that works.

The source that I'm thinking of is probably a mix between Shield of Truth and Deliverance. It's been about 3 years since I listened to either audiobook to pass the time while at work, when I was of course distracted by work so forgive me if I skip the finer details or misremember something.

Generally speaking, by the time of M31 the solar system is full of junk. And by junk I mean everything from scrap and asteroid debris, to other ships going about their business; I know that space is big and all, but 'relatively speaking', the Sol system is cluttered.

Also generally speaking, entering the warp in a battleship is a huge, and very violence, event. Some of these ships are 15km in length, and the warp entrance generated by their egress from real space is many times bigger - big enough to suck an entire other battleship in with you, if you're within visual distance of them. Corax deliberately does it to a Sons of Horus (I think?) ship with his flagship, and it freaks the hell out of everyone else on his bridge who didn't ever imagine such a daring thing.

The implication between the two of these statements, is that it's not so much as that ships *can't* translate in-system within striking distance of Terra, because they certainly can in theory. It's more to do with the fact that they shouldn't, because they will almost always run the risk of tele-fragging themselves on another ship, or asteroid, or that the violent event-horizon where they exit the warp will contaminate nearby planets and wreak untold harm upon them. The warp itself churns and becomes ever more dangerous the closer you get to populated worlds, where emotions are concentrated by the presence of so many people in on small place.

That last point is especially pertinent; For all his boasting and threats, Horus needed to take Terra intact and sit upon the Golden Throne, otherwise he could never truly call himself the New Emperor. To do that he needed as much of his forces intact as possible - apparently, it was less bloody to arrive safely at Sol's Mandeville point and fight his way in, than it was to risk translating into real space closer to Terra and lose even more of his armada to mishaps.

There are other ways into the system. Even in Shield of Truth, Malcador informs Garro that while he was screwing around baby-sitting the ships full of suspected Traitors, several other smaller ships broke off from the flotilla and make it in-system safely and, ultimately, scott free. Similarly, smugglers and other covert entrances are mentioned in Master of Mankind, where Alpha Legion Astartes find their way to Terra undetected. It's possible, because the Imperium cannot patrol it's entire border in anything resembling an efficient way, but just incredibly risky even if they don't get caught by the authorities.

[Cheesegear]

There are other ways into the system. Even in Shield of Truth, Malcador informs Garro that while he was screwing around baby-sitting the ships full of suspected Traitors, several other smaller ships broke off from the flotilla and make it in-system safely and, ultimately, scott free. Similarly, smugglers and other covert entrances are mentioned in Master of Mankind, where Alpha Legion Astartes find their way to Terra undetected. It's possible, because the Imperium cannot patrol it's entire border in anything resembling an efficient way, but just incredibly risky even if they don't get caught by the authorities.

I know all about Mandeville Points. I'm pretty sure they're even mentioned in SoB; Exterminatus. It's the point in the System - any System, that is - where there is no chance at all of exiting the Warp near a stellar body. If the Solar System looks like this...

Spoiler

Show

...You'll arrive just outside Pluto every single time, you'll have to pass Neptune, Saturn, Jupiter and Mars to get to Earth. And the writers keep writing it this way. How could a Necron ship ever teleport past Mars' defenses!? Impossible!

Except the Solar System (and all Systems) actually looks like...

Spoiler

Show

Who cares about the shipyard and blockades at Pluto? Why not just enter the System on the other side, where Pluto isn't? See, not only is space really, really, really big. But planets also move. Every day. It's not just a case of 'Pluto is the only route in'. Because from Master of Mankind, and Praetorian of Dorn, we know for a fact that it isn't, and it shouldn't be. Because space is 3D, and planets move. Mandeville Points are canon. They also make no sense at all when you start doing hard maths like LCP is. Because space is really, really, really mind-boggingly big, and planets move - albeit extremely predicatively.

Unfortunately 40K isn't reality, and the Warp does exist, I will concede that any given ship trying to translate into a System by not using its Mandeville Point would have to be really, really good at maths, have access to a calendar, and also know the relative orbit speeds of all the planets in the System. Or, you know...Understand that it's not so much a Mandeville Point, as a Mandeville Ring. You know how big - roughly - any given System you want to translate into will be, at least in Imperial-controlled space (and then some). All's you have to do is show up further than that distance away from the Star.

So you translate into Sol's space, at the minimum safe distance that you can from what you know to be Pluto's orbit from Sol. Boom. You already know that you'll never hit a stellar body because you know the orbit of Pluto. Just stay outside that. However, in reality, on any given day, there's only a 1-in-250-year-chance that Pluto will even be where you are. Unless you make a conscious effort via arbitrary rules that ships have to enter outside Pluto.

Except as we all know, arbitrary rules don't mean anything, and Alpha Legion are confirmed to just do whatever they want...Except turns out that they attack Pluto anyway.

[LCP]

Who cares about the shipyard and blockades at Pluto? Why not just enter the System on the other side, where Pluto isn't?

[...]

Or, you know...Understand that it's not so much a Mandeville Point, as a Mandeville Ring

[...]

So you translate into Sol's space, at the minimum safe distance that you can from what you know to be Pluto's orbit from Sol...

Or remember that space is 3D and that you don't have to approach in the orbital plane of any of the planets. Not so much a Mandeville Ring as a Mandeville Sphere.

This is why I made my original post; you seem to be determined to keep dunking on 'bad writers' by making arguments that are only marginally less scientifically nonsensical.

[Cheesegear]

Or remember that space is 3D and that you don't have to approach in the orbital plane of any of the planets. Not so much a Mandeville Ring as a Mandeville Sphere.

lol. I said space was 3D, then kept referring to it in 2D.
I am actually angry at myself now for not writing that it was a sphere (well, more like an egg), myself.
It's even confirmed in the canon that the Orbital plane of the Galaxy doesn't even need to be used (e.g; Space Sharks). So why didn't I use that? Derp.

Well played.

[LansXero]

lol. I said space was 3D, then kept referring to it in 2D.
I am actually angry at myself now for not writing that it was a sphere (well, more like an egg), myself.
It's even confirmed in the canon that the Orbital plane of the Galaxy doesn't even need to be used (e.g; Space Sharks). So why didn't I use that? Derp.

Well played.

Of course, the simple solution is to state that the necron stuff on Mars has a similar, albeit diminished, effect to the Cadian gate pylons (which we by now know were not unique to Cadia) and thus you do have a point, not a sphere or ring.

Then there is also the Astronomican, which behaves like a psychic beacon of consumed souls does, as in, however the hell the writers want it to. How many AUs does a beam of soul energy dissipate into? who knows :V. So sure you can avoid going through where its stronger, but then you'd be flying blind.

Finally, since space is full of debris and junk (more so after the heresy) its likely the 'safe' sphere is also full of chances to randomly exit into an asteroid.

[Wraith]

It's the point in the System - any System, that is - where there is no chance at all of exiting the Warp near a stellar body.

One possibility is that the Mandeville point - and thus the space stations, fleets and blockades all arranged there - are locked into a synchronous orbit with Pluto.

That would explain why all ships enter the system "near Pluto". The fact that they then always seem to pass by Neptune, Uranus, Jupiter and Saturn in sequence is probably a dramatic indulgence by the writers, but the first bit can make sense - insofar as anything 40k can.

So you translate into Sol's space, at the minimum safe distance that you can from what you know to be Pluto's orbit from Sol. Boom. You already know that you'll never hit a stellar body because you know the orbit of Pluto. Just stay outside that.

Maybe the Planet X Theory has been confirmed between M3 and M30?

Unless you make a conscious effort via arbitrary rules that ships have to enter outside Pluto.

See above. Pluto is a fortified relay/sensor station used specifically to detect incoming ships, to the theory is sound so far.

Of course, the simple solution is to state that the necron stuff on Mars has a similar, albeit diminished, effect to the Cadian gate pylons (which we by now know were not unique to Cadia) and thus you do have a point, not a sphere or ring.

"Necron tech is weird". That's pretty much their M.O., and while it's lazy writing it's usually true of everything they do. They could have teleported anywhere they wanted at any time, they just haven't chosen to do so yet.

Then there is also the Astronomican, which behaves like a psychic beacon of consumed souls does, as in, however the hell the writers want it to. How many AUs does a beam of soul energy dissipate into? who knows :V. So sure you can avoid going through where its stronger, but then you'd be flying blind.

Actually referenced in The Talon of Horus. Iskandar Kiyon and his ship the Tlaloc have to fly through the Astronomicon's "beam" at one point, and they're still somewhere inside the Eye of Terror. It's literally blinding light and some weird psychic phenomena stuff goes on, but the beam itself isn't particularly harmful.

Traditionally, the size of the Imperium is dictated by the range of the Astronomicon, in that once you go beyond the edge of the Milky Way you can't see it any more and thus can't navigate properly. So a radius of 50,000 light years, or 3.17+9AU, approximately.

[Voidhawk]

One thing that has not been pointed out: position and orientation in space is relative. Mandeville Points move.

A Mandeville Point is the warp equivalent of a gravitational Lagrange Point: a region where all the various forces influencing an object cancel out, and leaves a point of calm. At these locations, translating to and from the warp is relatively easy and safe. (Relatively here meaning "has similar fatal crash rates to car travel".) Most systems have more than one M-Point, but some will be nicer than others, and some will only lead you to certain warp-routes. And like L-Points, their position at any one moment depends on the current celestial configuration of the system. Certain systems are seasonably unreachable, because every so often their only Mandeville Point vanishes.

Sol has a number of M-Points, but the best and most stable follows Pluto around. Which is why Dorn covered it in guns.

Of course, you could try for one of the secondary M-points. They're secondary for a reason though: exiting at a less-than-optimal M-Point is a tricky proposition, and is liable to increase fatal-accident rates to that of drunk-driving. And of course, Dorn covered all the secondary points in space mines.

So, you want to exit the warp somewhere else entirely, huh? Well good luck to you, and I hope you brought a good navigator. Emergency-exiting somewhere without an M-point at all is just slamming your car through a wall and hoping the airbags work. Among the issues is that you have very little idea where exactly you'll come out. The Warp does not match 1-1 with realspace, and generally not even 3D-3D: the navigator can tell the direction of the Astronomicon, your rough distance to the nearest star, and the location of the M-points, but other than that it's pot-luck what you'll find when you exit the other side. Space may be mostly empty, but the warp tends to skip that in favour of the interesting bits (why it's useful for travel at all), so the chances of appearing inside a planet or colliding with another ship are much larger than you might expect. After all, that's where space-hulks come from: someone tried something smart, and collided with something.

So unless you're Alpha Legion (who just sent off a million smugglers at every option, and didn't care that half of them crashed), you're generally better off just aiming somewhere you'll arrive in one piece.

But say you try something daring and have a fleet arrive off the normal routes, somewhere high above the solar-plane: what now? Well first of all, everyone knows you arrived: warp-transitions are loud events, literally a miniature warp storm, and worse when not at stable locations or done by multiple ships. Every astropath and navigator in the system likely heard you arrive, and would have noticed it didn't come from an M-Point. So the local defenders have your general location to begin pointing telescopes. Worse, you're now going to have to burn a vast quantity of delta-V coming down from your high-inclination orbit, so you'll be lit up like a Christmas tree against a background of nearly-zero other ships.

But at least you bypassed the defences, right? Well, yes and no. You bypassed the Pluto Fortress (or whatever local defences/sensors the Navy placed at the M-point), but moving into the system towards anything important will take on the order of weeks or months, depending if where you want to go is currently the other side of the star. Plenty of time for the defenders to vector a patrol-fleet towards you, who are scattered loosely around the system for just this reason. Or just fire a wave of homing-torpedoes (yes, the Tau aren't the only ones to get those).

And at the end of it all, if you do manage to push in, you STILL run smack into whatever planetary defences there are. For Holy Terra this includes Luna, the entirety of which has been dug out and turned into a battlestation, complete with massive lances that can write the Emperor's name on your ship from an AU out.

So, to numerate the situation:
1) The safe locations to exit the warp will be guarded and actively monitored.
2) Wherever you exit, navigators/astropaths will notice something is up.
3) While travelling inwards, defenders have plenty of time to send forces to intercept you.
4) Once you get to them, a planet of any importance will have their own static defences.

All of this combines to make naval combat a generally slow and ponderous affair, with manoeuvrers taking days or weeks, and engagements occurring only when both sides believe they are the superior, or have something to gain from bringing the other to battle.

Of course, this being 40k, there are exceptions. Firstly, after 10k years chaos forces learnt how to create possessed Daemonships. These hunt like sharks in the warp, can breach into realspace anywhere near a decent population of souls (cruisers or larger in BFG), and can retreat back into it again whenever and wherever they like. They are an absolute nightmare to try and deal with in a permanent fashion, and are a particularly nasty addition to any Chaos raiding force.

Secondly are the Eldar. Their ships travel through the webway (the warp being far too close to Slaanesh), emerging silent and unnoticed wherever a hidden gate allows (pretty much anywhere plot-relevant). They don't often use standard engines: Corsairs use solar-sails that give off very little detectable signatures, while Dark Eldar use Mimic-Drives that let them disguise their ships as any other kind they like (other than 'Nid or Necron). And their speed lets them fight exactly where and when they like.

Thirdly are the Tyranids. They move FTL through realspace (in a kind of gravity-tunnel-thing), dropping down to standard speeds at the edge of a system's Oort cloud. Thus, they generally bypass and ignore any Mandeville defences. The encroaching Shadow-In-The-Warp will notify any local astropaths and navigators of where the fleet is approaching from though, so patrols can generally be gathered at any inhabited worlds in time. But it also makes entering, leaving and navigating the warp incredibly difficult, so retreat or bringing in reinforcements cease being options very quickly.

Finally, and worst of all, are the Necrons. Their Inertialess Drives allow them to move at FTL and near-light speeds wherever and whenever they like, and even let them turn as normal while doing so. Their ships have a stealth technology second to none, giving off near-zero emissions even when under thrust, which makes detecting them and plotting firing solutions incredibly difficult. Which all adds up to how a trio of Shroud-class light cruisers zipped into Sol system, blew past the outer planets in less than a day, zig-zagged past the orbital defences, and landed on Mars. Of course, once they finally stood still they were instantly vaporised, but for landing an incursion there are none better.

[Cheesegear]

One thing that has not been pointed out: position and orientation in space is relative. Mandeville Points move.

A Mandeville Point is the warp equivalent of a gravitational Lagrange Point: a region where all the various forces influencing an object cancel out, and leaves a point of calm. At these locations, translating to and from the warp is relatively easy and safe. (Relatively here meaning "has similar fatal crash rates to car travel".) Most systems have more than one M-Point, but some will be nicer than others, and some will only lead you to certain warp-routes. And like L-Points, their position at any one moment depends on the current celestial configuration of the system. Certain systems are seasonably unreachable, because every so often their only Mandeville Point vanishes.

Which book is that in? Is that Praetorian of Dorn? It feels familiar. But I can't quite place it. And I feel like I was making it up. So I didn't post anything about it, so that's why I went for a Ring (sphere/egg) theory. I know it's possible to show up on 'side' of a System, but I also know that Mandeville Points exist for a reason. Is that Rogue Trader RPG stuff?

...I feel like I need to read Praetorian again. But that's okay. I want to.