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So as the question states: do the Warhammer 40k factions possess a way of faster than light sensoring? More specifically: if spaceship A fires a laser at spaceship B which is lets say 10 lightseconds away, does B "see" that it is being fired at and might even make some kind of evasive maneuver?

And on a similar note on planetary defenses: as far as I understand it the distance between Terra and Mars for example is already approximatly 250 lightseconds, so around 8 minutes for a Laser. Therefore I assume the planetary defenses would have to seriously give lead to adjust for the targets movement if they want to fire at something approaching from the neighboring planet, let alone the edge of the system. Do they at least "see" the approaching ships with FTL speed?

Just a random thought I had when thinking a bit about some fluff story. Is there anything about it in the canon?

I don't think that many projectiles in 40k move at the speed of light, per say - lasgun bolts, probably the closest thing to actual light itself, can be dodged by skilled non-enhanced humans. So, yes, spaceships are capable of seeing and "can" dodge, if they weren't so ponderously large.

Regarding the tracking of FTL ships - the way that most vessels in 40k travel FTL is via the Warp, and while that can be tracked via a psuedo-bow wave (at least, I think that's how they describe it in Vigilus Ablaze?), it's not at all accurate or reliable, like most 40k tech.

You can really dodge a lasgun bolt in the fluff? I mean... how? It travels at the speed of light, doesn't it?

Regarding FTL ships: I'm sorry, I think I failed to sufficiently explain what I meant:
Imagine a System similar to Sol: An enemy fleet drops out of warp somewhere around the distance of Neptune and begins approaching Earth. A sensor array with an astropath on Neptune warns Earths defenders and they switch on their defense satelites and space stations. At this point, with the enemy fleet approaching at sublight speed, those would need at least minutes, maybe hours to reach Earth. It would be interesting if the defense lasers in Earths orbit can already track them and try to fire some Lasershots (traveling at light speed) or if they have the same minutes to hours delay between the enemy fleets actual position and were they see them.

And viewing from the approaching fleet: the difference between FTL sensoring and not would be that with FTL sensor I can see the batteries on a planet I'm approaching firing before the lasers hit me (as the travel at light speed), without I would only see them firing the moment I get hit (as the flash from the shot travels as fast as the laser bolt/ray).

Dodging is not so much dodging the lasgun shot itself, but dodging before the shot is fired, based on the firer's body language telegraphing where the shot will be going. Even without directly seeing the firer, rapid evasive movements will also cause misses because the firer just can't line up the shot all.

Pyroalchi wrote:
You can really dodge a lasgun bolt in the fluff? I mean... how? It travels at the speed of light, doesn't it?

Well, that's the thing - I don't think they do travel at the speed of light, much like in Star Wars.

Regarding FTL ships: I'm sorry, I think I failed to sufficiently explain what I meant:
Imagine a System similar to Sol: An enemy fleet drops out of warp somewhere around the distance of Neptune and begins approaching Earth. A sensor array with an astropath on Neptune warns Earths defenders and they switch on their defense satelites and space stations. At this point, with the enemy fleet approaching at sublight speed, those would need at least minutes, maybe hours to reach Earth. It would be interesting if the defense lasers in Earths orbit can already track them and try to fire some Lasershots (traveling at light speed) or if they have the same minutes to hours delay between the enemy fleets actual position and were they see them.

And viewing from the approaching fleet: the difference between FTL sensoring and not would be that with FTL sensor I can see the batteries on a planet I'm approaching firing before the lasers hit me (as the travel at light speed), without I would only see them firing the moment I get hit (as the flash from the shot travels as fast as the laser bolt/ray).

Yeah, lasers in 40k don't seem to fire at FTL speeds, nor are engagments usually taken at the kind of range you're describing. In 40k, your typical space combat is done at the kind of ranges where you can see your enemy with the naked eye, and boarding actions are a considerable factor. Local orbital defence platforms and star forts are similarly reduced in range.

For instance, in the Solar War, where Horus invades the Solar system with his Traitor Legions, there are multiple spheres of defence, and it seems that defences from one sphere aren't exactly capable of engaging ones that threaten another - so when the Alpha Legion attack Pluto, Terra's defence weapons can't (or don't) engage.

Basically, I don't think 40k has many weapons that engage at the speed of light in the first place. Of course, if someone wants to correct me on that, I'm all ears.


Automatically Appended Next Post:

Iracundus wrote:
Dodging is not so much dodging the lasgun shot itself, but dodging before the shot is fired, based on the firer's body language telegraphing where the shot will be going. Even without directly seeing the firer, rapid evasive movements will also cause misses because the firer just can't line up the shot all.

In the same way you'd "dodge" a bullet, yes, but I'm pretty sure that Space Marines and some lucky/well trained/experienced Guardsman can and do see and react to lasgun bolts.

BFG scale according to Andy Chambers, from when he posted on the BFG mailing list years ago, is 1 cm = 1000 km.

For the Imperium, long range ship weapons (not counting Nova cannons) have an effective range of 60cm so 60,000 km. Well under a light second, as that would be just under 300,000 km.

40k is definitely not hard sci-fi. Sometimes it barely qualifies as sci-fi at all, so looking at it too seriously usually shows dozens of things that make no sense and doesn't really explain anything.

That being said... in theory, if you wanted to hit something with a laser beam that is one light-minute away, you'd of course have to aim at where it'll be in one minute. If you know the target's trajectory and speed then it's really simple to calculate its future position, but if one minute is enough for that ship to change course, then it's capable of dodging.

Anything going faster than light is usually explained with warp shenanigans, so maybe some kind of astropath could detect an incoming shot and tell the captain to steer to the side or something like that. Psykers and astropaths are notoriously unreliable though, so trying to dodge would be very random. This might explain why space battles happen at relatively short range. It's like "classical" ship-to-ship battles: you can't dodge a broadside, so the difference is in positioning and maneuvering.

OK, that cleared up a lot of things somehow, thanks a lot.

The question that somehow still sticks is why would anyone in the HH approach Terra from the plane instead of "from above". If the defence spheres cannot really shoot outside of their immediate (in stelar relation) vicinity, why not skip Pluto, Neptune etc. and just drive directly to earths northpole.
Or on another note: since it is easy to calculate were a planet will be in a minute or an hour: drop out of warp, fire a huge load of lasershots at the expected position of the planet, go back into warp. They should only realize what's happening the moment the lasershots impact. But in the end, as you said: it does not have to make perfect sense physically.

Pyroalchi wrote:
OK, that cleared up a lot of things somehow, thanks a lot.

The question that somehow still sticks is why would anyone in the HH approach Terra from the plane instead of "from above". If the defence spheres cannot really shoot outside of their immediate (in stelar relation) vicinity, why not skip Pluto, Neptune etc. and just drive directly to earths northpole.

Because Terra has 360x360x360 degree protection from it's own personal defences. It's not a case that defence platforms can't "see" very far, it's that their weaponry (like most 40k weaponry) doesn't boast the range to properly engage targets from one side of the system to the next. There wouldn't be a blind spot, so to speak, more of a blind "range".

Or on another note: since it is easy to calculate were a planet will be in a minute or an hour: drop out of warp, fire a huge load of lasershots at the expected position of the planet, go back into warp. They should only realize what's happening the moment the lasershots impact. But in the end, as you said: it does not have to make perfect sense physically.

Firstly, dropping out of Warp guns blazing is exceedingly dangerous. Your vessel doesn't just "drop" out, you need to deactivate your Gellar Field, recouple all your gun batteries, rearm them (because you didn't want armed gun batteries while in the Warp, that's an accident waiting to happen if one of your more fragile crew-slaves gets possessed), and make a firing solution. Then, if you want to disengage from the inevitable counterattack (because you almost certainly were discovered, unless you had a dedicated stealth vessel with some kind of cloaking or slipped in under the cover of some astrological anomaly), you need to do all the above, in reverse, and hope you get out in time.

As for the actual fusillade of shots - against a sufficiently important target (which I imagine this is, seeing as you want to avoid it directly), they will most likely have void shields that are either permanent, or could be set up relatively swiftly, which wold tank the worst of the firepower. Because as much as you can predict where they will be, they can predict where your shots will be too - because it's still sub-light, and an Astropath could feasibly sense your arrival before you even took the shot, because of your Warp exit. Speaking of the Warp exit, in my understanding, most Mandeville points aren't exactly "close" to the planet itself on an astrological scale. There's still quite a bit of range you'd be needing to cover sub-light if you needed to get in range (because again, while in realistic sci-fi, there's no "optimium range" in space, 40k isn't "realistic" sci-fi.)

Even if they don't have void shields up and ready, and they didn't see the actual lasers, the thing about 40k lasers is they're either pretty weak (like what you'd find on an escort-class vessel), or would require MASSIVE amounts of energy (lance batteries, mounted on capital ships), and in both cases, are unlikely to kill a planet in one strike. Sure, you could use macrocannons or kinetic rounds, but they'll take even longer to travel. Most Exterminatus tier weaponry would require you to have orbital supremacy or some boots on the ground to pull off. At best, you could cripple a Hive City with a lance strike, if they don't set up void shields, but you could honestly do so much more if you brought an escort and assaulted the planet itself.

Thanks for the comprehensive answer, that really covers what I was wondering about. I did not have anything specific in mind, I just could not really wrap my head around spacebattles in a setting with speed of light weaponry but without FTL sensors. But as you and others said: if engagement distances are short (astronomically) and lasers are not that massive, it makes a lot more sense.

Pyroalchi wrote:
Thanks for the comprehensive answer, that really covers what I was wondering about. I did not have anything specific in mind, I just could not really wrap my head around spacebattles in a setting with speed of light weaponry but without FTL sensors. But as you and others said: if engagement distances are short (astronomically) and lasers are not that massive, it makes a lot more sense.

40k isn't a universe that works on IRL logic or any other kind of logic except for Rule of Cool. As a result, laser weapons are more like Star Wars lasers (relatively slow moving), oftentimes inferior to mass-impact kinetic weaponry, and space combat is more akin to broadsides and galleons.

keep in mind that ships in 40k are huge ponderous beasts I doubt they can dodge lasers as they are fired but it likely takes a bit for a ship to fire. and ships during this time are twisting, turning and making things difficult.

The Lance weapons of BFG are Lightspeed.

At no point are they described as being dodgeable.

No ship's rules describe them that way.

Ships either use brute powered shields, holofield targetting scramblers, repairing metal, or clouds of expendable spores to absorb the energy of the strike.

But no ship's in 40k dodge Lance attacks

 Sgt_Smudge wrote:

Pyroalchi wrote:
OK, that cleared up a lot of things somehow, thanks a lot.

The question that somehow still sticks is why would anyone in the HH approach Terra from the plane instead of "from above". If the defence spheres cannot really shoot outside of their immediate (in stelar relation) vicinity, why not skip Pluto, Neptune etc. and just drive directly to earths northpole.

Because Terra has 360x360x360 degree protection from it's own personal defences. It's not a case that defence platforms can't "see" very far, it's that their weaponry (like most 40k weaponry) doesn't boast the range to properly engage targets from one side of the system to the next. There wouldn't be a blind spot, so to speak, more of a blind "range".

Or on another note: since it is easy to calculate were a planet will be in a minute or an hour: drop out of warp, fire a huge load of lasershots at the expected position of the planet, go back into warp. They should only realize what's happening the moment the lasershots impact. But in the end, as you said: it does not have to make perfect sense physically.

Firstly, dropping out of Warp guns blazing is exceedingly dangerous. Your vessel doesn't just "drop" out, you need to deactivate your Gellar Field, recouple all your gun batteries, rearm them (because you didn't want armed gun batteries while in the Warp, that's an accident waiting to happen if one of your more fragile crew-slaves gets possessed), and make a firing solution. Then, if you want to disengage from the inevitable counterattack (because you almost certainly were discovered, unless you had a dedicated stealth vessel with some kind of cloaking or slipped in under the cover of some astrological anomaly), you need to do all the above, in reverse, and hope you get out in time.

As for the actual fusillade of shots - against a sufficiently important target (which I imagine this is, seeing as you want to avoid it directly), they will most likely have void shields that are either permanent, or could be set up relatively swiftly, which wold tank the worst of the firepower. Because as much as you can predict where they will be, they can predict where your shots will be too - because it's still sub-light, and an Astropath could feasibly sense your arrival before you even took the shot, because of your Warp exit. Speaking of the Warp exit, in my understanding, most Mandeville points aren't exactly "close" to the planet itself on an astrological scale. There's still quite a bit of range you'd be needing to cover sub-light if you needed to get in range (because again, while in realistic sci-fi, there's no "optimium range" in space, 40k isn't "realistic" sci-fi.)

Even if they don't have void shields up and ready, and they didn't see the actual lasers, the thing about 40k lasers is they're either pretty weak (like what you'd find on an escort-class vessel), or would require MASSIVE amounts of energy (lance batteries, mounted on capital ships), and in both cases, are unlikely to kill a planet in one strike. Sure, you could use macrocannons or kinetic rounds, but they'll take even longer to travel. Most Exterminatus tier weaponry would require you to have orbital supremacy or some boots on the ground to pull off. At best, you could cripple a Hive City with a lance strike, if they don't set up void shields, but you could honestly do so much more if you brought an escort and assaulted the planet itself.

Not to mention the 'mandeville point'. It's a 'height' above the star where you're far enough from the gravity well to enter/exit the warp safely.
Jumping deeper in-system is possible, especially with archeotech drives and a gifted navigator/sorceror, but with exponentially increasing risk.
For Sol, jumping much deeper in than the gas giants is basically suicide even without the Solar Defence Grid - that's why the main 'receiving points' - and navy bases - are at Uranus and Pluto.

I would also assume that the inter-lunar space would have very specific routes into the deeper parts of the Sol system. like a zigzag where at no point is the traffic into and out of the defence grid not covered by as many overlapping fields of fire.

on the topic of shooting, even if something is lightseconds away, you would still need to change the direction of many million tons of mass quickly, which is a completely relative term. Most likely not possible given the current understanding of physics. but who knows, dont necrons like shift thru space rather than accelerate->top speed->declerate, like they're in a spot and pop now they're over there?

Racerguy180 wrote:
I would also assume that the inter-lunar space would have very specific routes into the deeper parts of the Sol system. like a zigzag where at no point is the traffic into and out of the defence grid not covered by as many overlapping fields of fire.

on the topic of shooting, even if something is lightseconds away, you would still need to change the direction of many million tons of mass quickly, which is a completely relative term. Most likely not possible given the current understanding of physics. but who knows, dont necrons like shift thru space rather than accelerate->top speed->declerate, like they're in a spot and pop now they're over there?

Yes and no. They did but that's not been mentioned for a long time AKAIK because GW had a stupid and made up Dolmen Gates and stuck with them.

Building off what was said earlier about translating to real space near planets, I remember in Rynn's world (the crimson fists' novel about the devastating ork attack on their planet) that the astropaths gave warning when a large ork horde was moving towards their system and estimated that they would enter real space soon and then have a week until they reached their planet.

Instead, the orks stayed in the warp for a little while longer and appeared much closer to the planet. The gravity so far into the system destroyed over half the ork fleet immediately, and the fleet was still about 2 days sub-light travel away. This shows just how dangerous coming out of the warp anywhere near a planet is - even with two days yet to travel it's absurdly risky to show up that far in.

Counter to that the Battle of the Fang has the Thousand Sons arrive basically in orbit of Fenris because they're that good with Warp things.

Pyroalchi wrote:
Or on another note: since it is easy to calculate were a planet will be in a minute or an hour: drop out of warp, fire a huge load of lasershots at the expected position of the planet, go back into warp. They should only realize what's happening the moment the lasershots impact. But in the end, as you said: it does not have to make perfect sense physically.

A laser's range is limited by its coherence length which is a fundamental property of its generation. In practice only a few types of laser have coherence lengths of over 100km.

Even if 40K physics has managed to develop a better laser millennia in the future, you also have the problem of scattering. Even the vacuum of space is not really empty. There is thin gas and dust, particularly in a solar system. This would scatter the energy from a laser beam, particularly over a large distance.

Yes there are, in Devastation of Baal the Blood Angels are capable of detecting the approaching superluminal Tyranid vessels.