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As the title suggests, I was wondering if there were any planetary based weapons that could destroy an orbiting Imperial Cruiser, that was of imperial origin, could a vortex missile do it? Or would it be less straightforward than that?

Cheers!

i think basic nova cannons and other planetary defensive weapons would be capable.

Planetary Defence Lasers are capable of doing so. I think in Storm of Iron there's a planetary torpedo defence installation too. No real reason (other than not STC allowed) that any ship based Imperial weapon could not be based on a planet. I suspect it would take multiple shots from Imperial weaponry though. They'd have to penetrate the void shields of the vessel first.

As for a vortex missile in particular, I'm unsure if they can be scaled up to naval warfare. If a normal battlefield one was set off in the right place though it could well destroy or at least cripple the ship.

Usually they're described as batteries of equivalent to naval weapons.

You do get naval torpedos which can be fired from the surface. One appears in storm of iron, which targets the ground. And one appears in the first blood angels book, where it knocks a chaos space marine battle barge out of orbit.

For information about planet to orbit weapons and their relative strength compared to cruiser weapons and durability please refer to BFG rulebook page 146, specifically the entries for defence laser silos, missile silos, and planetary air bases.

Realistically it would be hard for a surface weapon to target and destroy an orbiting vessel due to the distances involved, especially if the ship was randomly adjusting course to protect itself.

Conversely static surface weapons would be ridiculously easy to track and destroy from orbit.

 Ugly Green Trog wrote:
Realistically it would be hard for a surface weapon to target and destroy an orbiting vessel due to the distances involved, especially if the ship was randomly adjusting course to protect itself.

Conversely static surface weapons would be ridiculously easy to track and destroy from orbit.

It's not nearly so clear-cut as that; like many SF/scifi related things, there's a lot of "meta" stuff involved, like tech base, development of a planet, where the strategic objectives are, strategic/tactical doctrine, yadda yadda yadda, etc etc ad nauseum.

In the case of 40K, planetary installations can boast firepower and durability comparable to an orbiting warship, and there's enough evidence throughout numerous sources that alternative deployment methods are sometimes required because the desired target is defended by heavy anti-orbital weaponry. One of the short stories in the Damocles anthology, for example, gives the reason for why a proper drop pod assault isn't possible by a small force of two SM squads- the ship that they took would have to close into low orbit, which would be within range of the anti-orbital guns of the city that they're supposed to cleanse of Tau presence.

Realism-wise, planets tend to be a bit of a clusterfeth of gak that messes with accurate targeting. Depending on technical assumptions, a planetary defense laser can easily be more durable and longer-firing than an equivalent warship installation, on account of the defense battery being able to use the planet as a heat sink, and bury most of its important bits (FCS, C3, power supply) deep underground, beyond the reach of enemy fire. Similarly, there's also plenty of room for submarine-deployed anti-orbital lasers, which could even be fired from underwater, or more likely operated as a "hit and run" weapon, that surfaces, fired, and then dives and hides once more. For missile armaments, it's entirely possible that semi-disposable anti-orbital missile artillery could be deployed a la the WW2-era Katyushas, at which point if you see it, it's already fired, and the only thing you scragged was a $10k truck, instead of the $10 million missile payload it carried (and already fired) at your $10 billion spaceship.

But again, this is generally dependent on your going in assumptions. It's entirely possible that it could be as you say, but it's equally the case that it might be the complete opposite. It could be considered a bit of a Purple-vs-Green conundrum.

If you'd like to know more, then I'd refer you to the website "Atomic Rockets", which has a lot of useful information on the subject.

Planetary defense installations do have a distinct advantage over a ship - they can be as large as needed while the ship can only fit so many things. Planetary power stations aren't limited to what fits in a hull, targeting installations can be large and widely spread out and might even get targeting data from orbital assets before the ship is in range to pinpoint ground targets. And the guns could be much larger than you'd fit on a warship since space isn't a problem.

Ground installations might well get to shoot while the cruiser is still outside the range of it's own guns.

A ground-based torpedo is basically an ICBM. Hell, some ship torpedos are half the size of a Saturn rocket or more.

 Melissia wrote:
Usually they're described as batteries of equivalent to naval weapons.

Indeed! That's the stats that they were given in the BFG rulebook, anyway. Page 146 describes three types of surfaced-based defenses you could have: Laser silos (acted as lances), missile silos (acted as torpedoes), and air bases (generated attack craft). The book doesn't specifically state what the size or warhead of the missiles are, but given their stats it stands to reason they would be the same plasma torpedoes Imperial warships employ. No mention of a surface-based Nova cannon, though there is no reason to think that the short list in the BFG rulebook is all-inclusive.

The better question is if you really want to blow up a kilometer plus long object in orbit that's going to act like a fragmentation grenade detonated near you. See the Endor Holocaust after the destruction of the Second Death Star.

But, if you don't care about skyscraper sized objects raining on your head, you certainly can blow up a ship in orbit. Planets, especially fortress worlds or Adeptus Astartes monastaries typically have ginormous lance (laser) batteries able to blast targets out of orbit. IIRC, they typically are also stronger than most lance batteries outside those mounted on large battleships, as they can generate more power. There's more free space on a planet, so you can store bigger reactors to power even more powerful shots to carve through void shields.

There are indeed planet based weapons capable of firing on orbiting ships. They're roughly the same weapons as on the ships themselves. Planet based lance, macrocannon, and missile silo emplacements.

Planet based weapon systems are individually more powerful than the guns mounted on the ships due to not having size constraints, they're also usually very well shielded as well. Both by being underground and having actual shields. Especially since ships have to go into low orbit to fire on the planet, thus putting themselves in range of the planetary guns. Many planets have truly formidable defenses.

Defensive emplacements like this are usually so strong that it forces attacking forces to land elsewhere on the planet and neutralize the guns before the ships can move into position.

 Grey Templar wrote:
There are indeed planet based weapons capable of firing on orbiting ships. They're roughly the same weapons as on the ships themselves. Planet based lance, macrocannon, and missile silo emplacements.

Planet based weapon systems are individually more powerful than the guns mounted on the ships due to not having size constraints, they're also usually very well shielded as well. Both by being underground and having actual shields. Especially since ships have to go into low orbit to fire on the planet, thus putting themselves in range of the planetary guns. Many planets have truly formidable defenses.

Defensive emplacements like this are usually so strong that it forces attacking forces to land elsewhere on the planet and neutralize the guns before the ships can move into position.

Ships don't need to go into low orbit. The orbit of the planet can be calculated from outside the system or even greater distance, slap some thrusters on a large chunk of rock or metal, and sent directly to where the enemy installation will be in a year's time. There is no friction in space, just fire a torpedo several years in advance.

That presumes, however, that a "destroyed" ship explodes. It's more likely- and is generally the case in 40K, AFAIK- that the ship is "hulked"; the majority of the hull is torn open to vacuum, hemorrhaging air, supplies, and personnel into the void, and completely unable to fight back or even really run away... but otherwise "relatively" intact.

Realistically, a ship is more likely to be "hulked" than explode, but this is more due to the fact that fission plants will be built with substantial safeguards, and fusion reactors have a bit of a built-in safeguard in that it's really really hard to make a fusion plant go into a catastrophic failure mode a la a meltdown*.

40K does seem, like many sci-fi franchises, to have powerplants that have substantially destructive fail-deadly modes... but they also tend to not happen. Using the only source I have on hand, the BFG rules, you roll 2D6 for catastrophic damage; it's only on a 9-12 that the ship actually explodes in a type of fail-deadly mode, while on 2-8 (~64% of all results) the ship is hulked, and just drifts forward a random distance.

It might also be on fire, and receive further damage, depending on if you roll 2-6 (straight drifting) or 7-8 (blazing).

Amusingly enough, it would seem that 40K has safer naval vessel scale power generation systems than Star Trek, given that most warships, when "destroyed" are left as mostly-lifeless hulks, rather than expanding fields of debris.

*Fusion reactors are hard to force into a fail-deadly meltdown on account of the difficulties involved in sustaining the fusion reaction. Containment vessel breaches of the fusion plant is more likely to cause a localized explosion as the plasma explosively decompresses, but will otherwise leave the ship fairly intact.

 Wyzilla wrote:

 Grey Templar wrote:
There are indeed planet based weapons capable of firing on orbiting ships. They're roughly the same weapons as on the ships themselves. Planet based lance, macrocannon, and missile silo emplacements.

Planet based weapon systems are individually more powerful than the guns mounted on the ships due to not having size constraints, they're also usually very well shielded as well. Both by being underground and having actual shields. Especially since ships have to go into low orbit to fire on the planet, thus putting themselves in range of the planetary guns. Many planets have truly formidable defenses.

Defensive emplacements like this are usually so strong that it forces attacking forces to land elsewhere on the planet and neutralize the guns before the ships can move into position.

Ships don't need to go into low orbit. The orbit of the planet can be calculated from outside the system or even greater distance, slap some thrusters on a large chunk of rock or metal, and sent directly to where the enemy installation will be in a year's time. There is no friction in space, just fire a torpedo several years in advance.

This presumes that tactical/strategic consideration can be made that far in advance. Circumstances can and probably will change drastically in that timeframe. It also presumes that the enemy is a complete and utter moron, and won't be able to intercept said ordnance. There's enough evidence in 40K, that low orbit stationkeeping is required for accurate ortillery fire. If you want to just burn an entire world, then sure, higher orbits (or your mentioned torpedo drop) can work just fine... but the Imperium generally seems to hold such measures in reserve as a last resort. Most of the time they seem to want to take planets intact, so that's not necessarily the best of ideas.

It is also the case that, as I mentioned a little earlier, planetary surfaces tend to be a clusterfeth of ridiculous proportions in terms of sensor clutter. Fighting in space could be likened to two preeminent marksman with tripod-mounted, high-accuracy sniper weapons taking aim at each from across a football field.

Doing a space-to-surface fire support mission is like sticking said marksman in the middle of the Amazon. The amount of clutter can make it very difficult to actually pick out things you want to destroy with utter impunity.

 Wyzilla wrote:


Ships don't need to go into low orbit. The orbit of the planet can be calculated from outside the system or even greater distance, slap some thrusters on a large chunk of rock or metal, and sent directly to where the enemy installation will be in a year's time.

You do if you want to actually take the system in a timely manner. And you do realize that if they can hit a ship in orbit that is actually actively trying to avoid being hit they'll definitely be capable of shooting down an asteroid?

There is no friction in space, just fire a torpedo several years in advance.

Actually, that's not entirely true. There is a lot of dust and microscopic particles floating around in space. Plus solar radiation itself actually applies pressure, enough to where actual sails that use Solar wind as a propulsion method are under serious consideration as a method of moving about our solar system. Enough to throw your calculations off by quite a bit.

And again, you're not always going to have years to wait for your torpedo to hit its target. That just gives your opponent a few years to shoot it down.

Whiskey144 wrote:
That presumes, however, that a "destroyed" ship explodes. It's more likely- and is generally the case in 40K, AFAIK- that the ship is "hulked"; the majority of the hull is torn open to vacuum, hemorrhaging air, supplies, and personnel into the void, and completely unable to fight back or even really run away... but otherwise "relatively" intact.

Realistically, a ship is more likely to be "hulked" than explode, but this is more due to the fact that fission plants will be built with substantial safeguards, and fusion reactors have a bit of a built-in safeguard in that it's really really hard to make a fusion plant go into a catastrophic failure mode a la a meltdown*.

40K does seem, like many sci-fi franchises, to have powerplants that have substantially destructive fail-deadly modes... but they also tend to not happen. Using the only source I have on hand, the BFG rules, you roll 2D6 for catastrophic damage; it's only on a 9-12 that the ship actually explodes in a type of fail-deadly mode, while on 2-8 (~64% of all results) the ship is hulked, and just drifts forward a random distance.

It might also be on fire, and receive further damage, depending on if you roll 2-6 (straight drifting) or 7-8 (blazing).

Amusingly enough, it would seem that 40K has safer naval vessel scale power generation systems than Star Trek, given that most warships, when "destroyed" are left as mostly-lifeless hulks, rather than expanding fields of debris.

Except when they do explode, the plasma reactors 40K ships use turns into a miniature star that goes full supernova- dumping radiation, plasma, and shrapnel on everything unfortunate enough to be caught in the very large blast radius.


Automatically Appended Next Post:

 Grey Templar wrote:

 Wyzilla wrote:


Ships don't need to go into low orbit. The orbit of the planet can be calculated from outside the system or even greater distance, slap some thrusters on a large chunk of rock or metal, and sent directly to where the enemy installation will be in a year's time.

You do if you want to actually take the system in a timely manner. And you do realize that if they can hit a ship in orbit that is actually actively trying to avoid being hit they'll definitely be capable of shooting down an asteroid?

Which is why you aim your macrocannons/bombardment cannons and fire continuous volleys to pump rounds down rage and make it impossible to shoot down. Especially when their batteries are typically too large to intercept enemy munitions (especially when if the munition has its own fuel source, it will simply continue to accelerate until a certain point).

Also if you're besieging a planet in 40K, you have all the time in the world unless it's Necrons. Warp Travel is horrifically slow, and reinforcements take ages to actually arrive. Besides depending on the acceleration of the object or sling-shotting it, years can easily turn into months or less.

There is no friction in space, just fire a torpedo several years in advance.

Actually, that's not entirely true. There is a lot of dust and microscopic particles floating around in space. Plus solar radiation itself actually applies pressure, enough to where actual sails that use Solar wind as a propulsion method are under serious consideration as a method of moving about our solar system. Enough to throw your calculations off by quite a bit.

We already are capable of launching probes into asteroids, and are already planning a manned mission to an asteroid. Hitting one with a projectile is child's play. Hitting a planet is even easier. Radiation doesn't knock your projectile off course, gravity wells do. Alternatively if a missile or torpedo has its own fuel source, you can use the gravity of another planet to actually accelerate it by orbiting it several times to serve as a sling-shot.

The besieger dictates the battlefield when assaulting a planet. There should never even be a need to physically engage the enemy or risk getting shot at unless you're being rushed.

And for all the Imperium bitching about how it wants worlds intact, it completely forgets how durable planets are. The Chicxulub Asteroid hit Earth with the energy of a hundred teratons and utterly failed to kill off life on the planet. It experienced a nasty natural disaster, but that isn't even an problem for the Imperium as the average Hive World is WORSE off than Earth during the snowball effect when the atmosphere is filled with dust that blocks out sunlight and causes the temperature to plummet. There is zero reason why the Imperium simply can't fly up to a world, drop an ungodly powerful bomb on it, then just pick off any survivors and set down colonists. They don't care about the health of the biosphere to begin with. Nukes also cause zero permanent damage to a planet. You could drop a hundred H-Bombs with the energy of a hundred megatons each and the planet wouldn't even notice. All that might interfere with continued use is radiation, but it's not like the Imperium cares about its civilians.

 Grey Templar wrote:

 Wyzilla wrote:


Ships don't need to go into low orbit. The orbit of the planet can be calculated from outside the system or even greater distance, slap some thrusters on a large chunk of rock or metal, and sent directly to where the enemy installation will be in a year's time.

You do if you want to actually take the system in a timely manner. And you do realize that if they can hit a ship in orbit that is actually actively trying to avoid being hit they'll definitely be capable of shooting down an asteroid?

There is no friction in space, just fire a torpedo several years in advance.

Actually, that's not entirely true. There is a lot of dust and microscopic particles floating around in space. Plus solar radiation itself actually applies pressure, enough to where actual sails that use Solar wind as a propulsion method are under serious consideration as a method of moving about our solar system. Enough to throw your calculations off by quite a bit.

And again, you're not always going to have years to wait for your torpedo to hit its target. That just gives your opponent a few years to shoot it down.

In regards to solar sails, photon pressure is unfortunately very negligible under most conditions... as in, you need exceedingly (read: impractically) light platforms in order for it to have a measurable effect. Dust/microscopic particles can also be considered negligible as well; Voyager hasn't been affected by such variables, and it was launched with what, 1960s/1970s era hardware?

Pretty sure that 40K, for all its "technological decline", can still do just as well.

But yes, time-on-target is a major, unavoidable issue.

 Wyzilla wrote:
Except when they do explode, the plasma reactors 40K ships use turns into a miniature star that goes full supernova- dumping radiation, plasma, and shrapnel on everything unfortunate enough to be caught in the very large blast radius.

True that may be, but the likelihood of such a catastrophic explosion (or an even worse warp engine breach) is outweighed by the statistical likelihood of the ship simply being left adrift, possibly burning. AFAIK in the fluff- and I'm a bit rusty on this I'll admit- ships rarely explode, and mostly end up hulked. Even taking the BFG rules as absolutely accurate*, it's only around 36% of the time (IE, a tad over 1 out of 3) that such catastrophic results occur.

*It's my opinion that the BFG rules have a higher incidence of catastrophic explosions because exploding spaceships are pretty cool for wargaming purposes.

 Wyzilla wrote:
And for all the Imperium bitching about how it wants worlds intact, it completely forgets how durable planets are. The Chicxulub Asteroid hit Earth with the energy of a hundred teratons and utterly failed to kill off life on the planet. It experienced a nasty natural disaster, but that isn't even an problem for the Imperium as the average Hive World is WORSE off than Earth during the snowball effect when the atmosphere is filled with dust that blocks out sunlight and causes the temperature to plummet. There is zero reason why the Imperium simply can't fly up to a world, drop an ungodly powerful bomb on it, then just pick off any survivors and set down colonists. They don't care about the health of the biosphere to begin with. Nukes also cause zero permanent damage to a planet. You could drop a hundred H-Bombs with the energy of a hundred megatons each and the planet wouldn't even notice. All that might interfere with continued use is radiation, but it's not like the Imperium cares about its civilians.

It's not about personnel or biospheres, it's about the man-made infrastructure. Most of the time, the Imperium is either conquering uninhabited balls of dirt, of fighting wars of defense/reconquest on worlds that they already have substantial infrastructure on. It is a really bad idea to just bomb those worlds into oblivion and then mop up whatever's left alive, because doing so destroys most of the reason that said ball of dirt is desirable in the first place: all the industrial infrastructure that's present.

Yes yes, you can argue that they'll just have to rebuild it anyways after fighting a bloody battle through it all, but the point remains that it's generally easier to fix it than it is to start from scratch.

There's all kinds of planet-based defenses that can cripple or destroy a ship in orbit. Also, capital ships in this setting are rarely fast-moving vessels. The various space-battle games of the franchise are based around naval combat scenarios, not dog-fights between kilometers-long vessels.

 Psienesis wrote:
Also, capital ships in this setting are rarely fast-moving vessels.

Only relative to other sci-fi universes.

Given that BFG had a rough time equivalent that 1 turn = 5 minutes, even the slowest capital ship with a speed of 20cm was traveling at a speed of roughly 240,000 kph. That's 2% of the speed of light if my math is correct.

Thats fast enough to where you start having time distortions due to relativity.

 Psienesis wrote:
There's all kinds of planet-based defenses that can cripple or destroy a ship in orbit. Also, capital ships in this setting are rarely fast-moving vessels. The various space-battle games of the franchise are based around naval combat scenarios, not dog-fights between kilometers-long vessels.

Capital ships move EXCEPTIONALLY fast, as do all naval ships. They just can't bank for gak. But ships move at a fraction of C. IE stupidly fast.

Oddly enough, 40k is much more realistic in this regard than other universes like Star Trek.

In order to have engines worth anything, you need a very large ship. Bigger engines means faster ships, despite the increased mass the economies of scale work out in favor of a larger ship. Smaller is only faster in atmospheres where there is a massive amount of friction. Large mass does of course mean you can't change direction very easily. Inertia is a heartless b-word.

Of course that gets broken by the inclusion of fighter craft as a practical method of fighting, but we couldn't expect reality to hold for long.

Like many things, small parasite "fighters" being viable or not is typically dependent on the going-in assumptions that are made regarding technical capabilities.

Small fightercraft work in 40K and Star Wars, but not Star Trek.

 Grey Templar wrote:
Oddly enough, 40k is much more realistic in this regard than other universes like Star Trek.

In order to have engines worth anything, you need a very large ship. Bigger engines means faster ships, despite the increased mass the economies of scale work out in favor of a larger ship. Smaller is only faster in atmospheres where there is a massive amount of friction. Large mass does of course mean you can't change direction very easily. Inertia is a heartless b-word.

Of course that gets broken by the inclusion of fighter craft as a practical method of fighting, but we couldn't expect reality to hold for long.

This brings up some interesting points too:

-due to actual engineering principles, some powerplant/engine types actually have a minimum practical size. We see this very obviously in 40K as actual warships are the only things that commonly zip around with warp motors; IE, it's not practical to make Warp-capable fighters
-bigger ships can not only carry larger engines, but also larger remass/fuel reserves. The catch is that this kicks off a Red Queen's Race in that in order to haul all of that around you need even more engine power and remass reserve, which means you get even bigger ships, etc etc

As a point of interesting trivia, one of the best examples of the idiocy of Star Trek naval design in reference to actual warships, is the Defiant vs the Galaxy; they're actually comparable in firepower, but the Defiant is like a quarter to a third the size of a Galaxy, if that. It mostly comes from the fact that the Defiants stripped out all the useless gak that a Galaxy had to carry around- civilian quarters, excessively large aquariums, the numerous (and also excessively large) holodecks, the presence of a large and well-equipped bar, things like that. The Defiant is all warship, instead of warship-science ship-explorer ship-whatever other useless things we can shove into it ship.

The Defiant also was sensibly shaped, unlike the stupid saucer design. AKA: Shoot the engines, Sever the little spine holding the engines to the saucer, etc...

The Galaxy-class was a science vessel. The Defiance class was a warship.

The scale given by Andy Chambers, who designed BFG, was 1cm= 1,000 km and the time scale a telescoping one with 1 turn = 1 hour at long ranges (like 60cm) and 1 turn = 15 minutes at short ranges (like 15cm).
( http://www.wolfedengames.com/battlefleetgothic/scale.htm )

An Imperial cruiser has a Speed characteristic of 20 cm and maximum move of 44cm on All Ahead Full special orders. That means at the absolute max that is 20,000 km in 15 minutes or 80,000 kph and 44,000 km in 15 minutes or 176,000 kph on All Ahead Full orders.

As for planetary defenses, with reference to the BFG rulebook p. 146, the average planetary defense laser silo packs almost as much firepower as the broadside of a Gothic cruiser, with greater range than the Gothic. Likewise, the average planetary defense missile silo has the launch capacity of a full cruiser, and the average planetary defense air base has enough short range aerospace fighters and bombers to match a Dictator cruiser.

From the old GW Armageddon 3 website archived at http://web.archive.org/web/20010820235454/www.armageddon3.com/English/Campaign/BFG/BFGmap.html

we can see the defenses of each hive on Armageddon comprised at least 4 air bases, 8 missile silos, and 8 laser silos. That kind of firepower would be enough to shred your average navy frigate, and even your average cruiser, if they tried to bombard the hive. Even if one takes Armageddon to be a more heavily defended than usual hive world, it still gives a rough gauge of the defenses a typical hive might have, which still is likely to overpower most spaceships.

some of the defense weapons are massive, well capable of taking out warships in orbit with ease. and one torpedo alone in a critical hit can cause massive damage.

In storm of iron the laser and torpedo batteries where deemed a threat enough that 3 or even 6 months was spent locating and tagging them for bombardment.

and they may not fire on the first ship, they might wait hidden till you try to land your transports, big, vulnerable and lacking armour. then boom there goes x % of your army in a single shot.

a titan is pretty invunrable, but its big transport ship is a juicey target for a oribital defense weapon laying in wait beneath the sand.

Ground based weapons have the advantages of, substantially more support systems allowing for greater power of shots, and greater firing rate, due to heat sinks and as mentioned power plants.

They can be 'more durable' due to being able to be based mostly underground and allowing again for more and more powerful shielding.

Downsides are mobility, they have none, that have a limited firing arc, and usually depend upon planetary rotation (if any) to target a ship in orbit.

If a world was bristled with them, like nearly every 20 square miles there is one at least, it would be a nightmare to invade, arguable not worth it. A planet that heavily defended would probably not be able to support anything worth protecting that much though due to the space they would take up. I imagine it is a sound strategy for orbiting moons though to be so heavily armed on worlds of extreme strategic value.


Automatically Appended Next Post:

 jhe90 wrote:
some of the defense weapons are massive, well capable of taking out warships in orbit with ease. and one torpedo alone in a critical hit can cause massive damage.

In storm of iron the laser and torpedo batteries where deemed a threat enough that 3 or even 6 months was spent locating and tagging them for bombardment.

and they may not fire on the first ship, they might wait hidden till you try to land your transports, big, vulnerable and lacking armour. then boom there goes x % of your army in a single shot.

a titan is pretty invunrable, but its big transport ship is a juicey target for a oribital defense weapon laying in wait beneath the sand.

Yeah, if there is a titan transport in orbit, and you are aware the titans have currently not landed, and you estimate you can take the whole fleet in an attack. You take out the ships, purposely cripple the titan ship, then take your time boarding and sweeping the titan ship. Why destroy the titans or any valuable war machines for that matter when you have a chance of capturing them.

Providing they are imperial titans, and the world is imperial. Obviously no good taking gargents, or trying to take elder titans, or daemonicly infested ones.

With the talk of dropping rocks on planets, here is an oldie but goody:

Rocks are NOT ‘free’, citizen.
Firstly, you must manoeuvre the Emperor’s naval vessel within the asteroid belt, almost assuredly sustaining damage to the Emperor’s ship’s paint from micrometeoroids, while expending the Emperor’s fuel.
Then the Tech Priests must inspect the rock in question to ascertain its worthiness to do the Emperor’s bidding. Should it pass muster, the Emperor’s Servitors must use the Emperor’s auto-scrapers and melta-cutters to prepare the potential ordinance for movement. Finally, the Tech Priests finished, the Emperor’s officers may begin manoeuvring the Emperor’s warship to abut the asteroid at the prepared face (expending yet more of the Emperor’s fuel), and then begin boosting the stone towards the offensive planet.
After a few days of expending a prodigious amount of the Emperor’s fuel to accelerate the asteroid into an orbit more fitting to the Emperor’s desires, the Emperor’s ship may then return to the planet via superluminous warp travel and await the arrival of the stone, still many weeks (or months) away.
After twiddling away the Emperor’s time and eating the Emperor’s food in the wasteful pursuit of making sure that the Emperor’s enemies do not launch a deflection mission, they may finally watch the ordinance impact the planet (assuming that the Emperor’s ship does not need to attempt any last-minute course correction upon the rock, using yet more of the Emperor’s fuel).

Given a typical (class Bravo-CVII) system, we have the following:
Two months, O&M, Titan class warship: 4.2 Million Imperials
Two months, rations, crew of same: 0.2 MI
Two months, Tech Priest pastor: 1.7 MI
Two months, Servitor parish: 0.3 MI
Paint, Titan class warship: 2.5 MI
Dihydrogen peroxide fuel: 0.9 MI
Total: 9.8 MI

Contrasted with the following:
5 warheads, magna-melta: 2.5 MI
One day, O&M, Titan class warship: 0.3 MI
One day, rations, crew of same: 0.0 MI
Dihydrogen peroxide fuel: 0.1 MI
Total: 2.9 MI

Given the same result with under one third of the cost, the Emperor will have saved a massive amount of His most sacred money and almost a full month of time, during which His warship may be bombarding an entirely different planet.
The Emperor, through this – His Office of Imperial Outlays – hereby orders you to attend one (1) week of therapeutic accountancy training/penance. Please report to Areicon IV, Imperial City, Administratum Building CXXI, Room 1456, where you are to sit in the BLUE chair.

For the Emperor,
Bursarius Tenathis,
Purser Level XI,
Imperial Office of Outlays.

The one thing a lot of sci fi fails to get across is the sheer vastness and scale of space (along with ships flying if there is an atmosphere)

In a lot of scifi (40k too) ships seem to hold a completely static orbit over a planet.

With such woefully inaccurate distances, static orbits and flying through an atmosphere whilst in space then it's very easy for ground facilities to own the gak out of naval vessels.

One does not simply shoot straight up (unless it's lances I guess)