1) The Carthage was already significantly damaged.
2) A Karuna is pretty big--not a destroyer, sure, but larger than any GTVA corvette. Couple that with the absurd number of Apocalypse antimatter torpedoes, flak munitions, and the reactor itself, and you get one hell of a punch (and bang).
3) The Karuna would be ramming at speeds around 60 m/s....that's considerable.
4) The Colossus skewered that Orion with heavy beams before it even got close. Not exactly much of a ramming attack (with poor speed, to boot).
5) Square-cubed law (IIRC) implies that the Colossus would be made out of (or built to be) far, far sturdier stuff than your average Orion. The attempted ramming was at the frontal armor of the ship, which is probably one of its thicker points.
6) I'm not sure you could even call it a ramming--I always got the impression that Koth's ship was largely gutted by beams before it really hit the Colossus (as in, it blew up before any real ramming occurred).
7) If at first you don't succeed...you've got a lot more options at your disposal. Another Karuna, and/or another Sanctus. And/or the rest of the task force just unloading into the crippled Carthage with Apocalypse spam, point-blank mass-driver shells, gauss cannon fire, and even some PDT and Burst Flak fire for the cherry on top.
1. Probably not relevant for the purposes of this discussion. I don't see huge chunks of it floating off so it's retaining most of its mass.
2. The front end of a Karuna (a lot of the front in fact) is mainly its two mass drivers. In overall size and overall mass it's at best the same. This also means that the part of the ship which will make contact is much more likely to crumple and absorb energy from the impact rather than remain rigid enough to transfer it.
Also assumes a complete lack of safety systems for the munitions, which is very much inconsistent with the need to handle ordnance safely. BP has consistently gone out of its way not to paint anyone as dumb. This ammunition is almost certainly all boresafe.
3. 60m/s still isn't that much.
4. Again, it's not like huge portions of the ship necessarily disappear.
5. Square-cube law applies only in consistent gravity. No, artificial gravity doesn't count, the mere fact they have it means they can futz with the specific gravity of any portion of the ship as they like. (Hell, there may not be reason to actually have gravity in large portions of the ship in combat, or even normally.)
6. While this is possible, the reality is it usually does make ramming contact and the mission is designed for it.
7. Ramming is by definition an option of last resort unless your ship is specifically designed for it. The Wargods are a major portion of the UEF's defense. They represent an asset years, possibly more, in the making, and are not to be sacrificed casually. If it is remotely possible to save the ships and crew then you should; only when it became clear this was no longer in the cards was ramming considered.
1. Le sigh. Okay, no chunks are flying off because the Freespace engine can't do things like that without the ship blowing up entirely. This is why you don't see chunks of anything flying off a Hecate when it's down to 1 hitpoint. Even so, what definitely DOES matter is that the Carthage's structural integrity, armor, power/systems, and damage control are all significantly compromised. The Carthage, IIRC, always ends up with between 45 and 72 percent of its health by the time the Impereiuse shows up.
2. Not really. Sure, it's not particularly dense, but it has a lot more than a couple mass drivers. It's got huge sections of thick armor plating, a half-dozen main cannons, and a good amount of structure in general. Not ideal, of course, but sufficient. Besides, it's easier when you're ramming an area whose armor has been shredded and punctured like swiss cheese (and damaged hull integrity in the entire section in general).
3. It is when you're talking about a massive warship. And again, ramming the side of a ship that's taken a huge and thorough beating in most cases (a decent beating in the rest).
4. Actually, yes, that is exactly what happens. The BGreen's pierce right through the Orion, and unless there's still Orion-matter in the pillars of gigaton-level plasma beams, that's a ton of matter that just got removed from the equation. It's also traveling in the opposite direction of the Orion's velocity, slowing it down. Then, an Orion (at least FS2-era Orions) generally does not have good speed or acceleration. Next, the Orion's structural integrity got ripped to shreds, meaning that the effectiveness of a ramming would be reduced--the ram would crumple and break apart entirely upon significant contact.
5. Not just in gravity; acceleration and other forms of force are at play as well. Square-cube law applies when you have a massive starship propelling itself with huge engines at significant speeds--if the Colossus' "skeleton" was made out of tissue paper, it would fall apart when maneuvering.
6. Same points of above apply. And if a significant number of playthroughs in the mission result in the Orion failing to even touch the Colossus, it kind of says something about how good of a ramming attempt it was in the first place (low speed, severely compromised hull integrity, brief contact with target hull before the entire ship falls apart).
7. Seemed to be a first resort for those kamikaze bombers/fighters attacking that Orion back in FS1 (which were quite destructive). Oh, and the Nelson in WiH's intro, where it literally utilized ramming as a first resort. The entire plan was to have the cruisers punch a "hole" through the formation so that the Nelson could ram the Atreus. The Nelson didn't even seem to have taken any damage prior to that, as well. Also, I think DE counts as last resort--you need that ship dead, no matter the cost.
8. The mission's name is ****ing DELENDA EST. "The Carthage must be destroyed." "Also, I think Carthage needs to be destroyed." The phrase meaning "the mentality of NEEDING to destroy X, no matter how long it takes or how difficult it might be." Everyone in the briefing repeatedly hammers home how killing the Carthage is a huge deal--it's less about the strategic or tactical victory, and more about the political one. If you believe that killing this ship will likely cause the war to lose major favor within the GTVA population (and maybe leadership), that's more valuable than capturing two Agincourts. Or three. And they're clearly not afraid to die, or to face long odds. They clearly view the destruction of the Carthage as the likely end of the war (at least figuratively) whether they survive or not. Saving a couple Karunas is really not going to help much in the long run, but killing the Carthage is a game-changer. Oh, and they all knew better than to think a frontal assault on a Titan and Chimera (complete with advanced fighters and bombers) would last more than a minute or two. So if you send the Indus and Yangtze to run because they're the only ones who can escape (wait, what about that Sanctus that jumped in with you in the beginning? Aren't cruisers more subspace maneuverable?), and the rest of the force starts tearing apart the Carthage (using it as a shield of necessary) and ramming it. It's a hell of a lot better for a diversion--I'm not sure the Imperieuse and Hydra even had to slow down as they obliterated the UEF ships one-by-one.