Can a group put a lot of rockets on a piece of something floating in space and make it hit a stationary target on a planet with checks of course but can it be done?

Yes!

In fact, since a planet is a relatively immobile target, it's one of the easier pieces of astrometrics a ship might be called on to calculate. The biggest particular should be choosing the right rock: too small and you might not get through the atmosphere, too big and there won't be much left after the rock hits.

You should do a search for 'Rocks are not free citizen!'

Hmm I wonder if you could hide a mass amount of drop ships inside so that when it breaks you have a nice surprise inside.

I think you definitely could, but you'll have to be careful about who you pull the trick with.

Personally, the best reason to do that would be to get past a planetary defense net, since anyone without orbital defenses can't stop you from just parking in orbit and landing conventionally. But, any planet with orbital defenses is going to be watching for big rocks wandering towards them, if for no other reason than to prevent a natural disaster (see: the dinosaur die-off). Plus, anyone with decent deep-space augurs is going to see the burn required to move an asteroid into an Impactor orbit.

The irregularity and imballance of your asteroid is going to be the biggest problem. Can a ship's cogitator figure out the neccessary trajectory and speed, yep. Can it account for the uneven rotation of your asteroid, for the off-center ballance while thrusting, the effects of the asteroid hitting the atmo and breaking up into smaller pieces that make targeting a small area on a planet mostly luck...maybe? If all you want to do is hit the planet with a planet killer, you should be able to swiing it with a ship that has a salvage rig pretty easy. If you want to hit a particular target without making the planet unihabitable...that may be a much more difficult process. Also, if you have Stars of Inequity they have an event for a rogue asteroid on course for your colony. It isn't considered beyond even a single ship to prevent it. Consider that asteroids are not as tough as Roks (no armor plating), and the players can expect to fight multiple Roks in published adventures (Frozen Reaches).

So, rocks arent free:

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.

Thanks for crushing my dreams...it was just suppose to be at the right circumstance

Thanks for crushing my dreams...it was just suppose to be at the right circumstance

I feel that BossTroll's approach to this is amazing, and is perfectly in-character for the Imperium. Most people are not built around thinking outside-of-the-box with regards to technology is not something that has been done in the last ten thousand years or so. I do think it's an awesome dream, so here's some other ideas.

1) You train an elite group of fighter pilots to grapple onto a ship and make daring attack runs where they slingshot asteroids en masse at a planet. Much less accurate, but potentially more fun.

2) Fall to Chaos and use the Dark Mechanicus or Hereteks to build it anyway, although this will still take time and resources.

3) Take over an Orkish Warband and have them do it. Do not ask any questions under any circumstances, but they don't concern themselves with the laws of Physics. Things just work. I recommend daring them that they CAN'T hit that specific target on a planet. The more improbable the odds, the better a chance that the Orks just do it. Somehow.

Thanks for crushing my dreams...it was just suppose to be at the right circumstance

't was just tongue in cheek, mate. :-)

But a regular orbital bombardment will suit your players needs just fine. MOre accurate anyway ;-)

Thanks for crushing my dreams...it was just suppose to be at the right circumstance

't was just tongue in cheek, mate. :-)

But a regular orbital bombardment will suit your players needs just fine. More accurate anyway ;-)

And that text does mean that asteroids CAN be used this way, it's just very expensive.

strange, the edit function makes an extra post...

The math for what you're suggesting would be nearly impossibly complex, I'm trying to think what the relevant skills would even be. I guess if you had a party of super nerdy (as in a group where the average Int was 55+) characters and everyone made a bunch of difficult or worse checks on all the most Int based skills maybe.

See here's the thing even without the typical Imperial incompetance you're up against alot of things here, trhe first is that neither the projectile nor the target are stationary in relation to each other to begin with, the second is that the target is rotating and obscured/in cover more than half the time, the third is every object in between is going to have an effect on the trajectory. So take all that and then try to build the thing with the competance and knowhow of the Imperium and eeehh...

On the other hand if you have an Ork Mekboy in your group have him make a single challenging +0 check, if he makes it the rok hits the target. You have to account for that retard savant thing that defines those bastards.