Ramming Speed

[tkdguy]

Yesterday, I was talking to a friend about playing a starship combat game. He's under the impression he can build a ship designed to ram another ship with minimal damage to his own vessel. I disagreed, citing the speed of the ships involved would be great enough to vaporize both ships. Okay, relative velocity counts for a lot, but the ramming ship needs to be able to move quickly enough to actually hit its target. Besides, spacecraft generally don't move at the speed of sailing ships. Who's right? Assume interplanetary flight is available, but not FTL.

[ghost-angel]

Re: Ramming Speed

 

I guess it would depend on the technology and defenses of the Ramming Ship vs the Rammed Ship.

 

What you really have to consider is can the structure of the ship doing the Ramming withstand the impact?

 

Assuming some kind of Ramming Beam placed at the front, and given that there's no environmental counter-force (i.e. in sailing ships the Water will push back) once you make the initial impact and start to transfer momentum from Rammer to Rammed you may just end up with another spaceship stuck to the front of your yours.

 

You'd have to take into account relative Vectors as well, if it's head on the guy with the highest velocity will win. If it's a Ram to a side it could just get pushed out of the way or have the rammed ships vector changed, it may sustain little damage at all - since there's nothing to "push against" in space to keep the rammed ship in place.

 

Or, if the relative velocities are different enough, the Rammer could end up just going right through the Rammed ship, leaving a nice mess behind.

[tkdguy]

Re: Ramming Speed

 

I see. How much damage is done to the ramming ship?

[braincraft]

Re: Ramming Speed

 

Depends on the speed of the ships. If we're talking battleships moving at relatively low velocities (no more than a few hundred miles per hour) then a ship with a significant materials advantage and/or impacting a sturdy area of its own structure with a vulnerable area of its target might not be too badly damaged by a ram... especially if it crashes through and doesn't get bounced.

 

It's hard to imagine anything moving at greater speeds doing well in a crash, even a controlled crash. You'd need sufficiently advanced tech to prevent the crew from being pulped by the change in acceleration from the impact.

 

Of course, if the ship is functionally invulnerable and has impossibly powerful acceleration and the crew is in an artificial gravity field that normalizes their inertial frame, you can pretty much do what you want, but that's the handwavey answer. If you're breaking the laws of physics, you can get whatever result you decide is possible.

 

On another front, you'll notice that most vehicles are not made for ramming other vehicles. Even tanks can get bogged down if you put a big enough or tough enough truck in front of them.

[Comic]

Re: Ramming Speed

 

There's all sorts of possible mechanisms that could be considered 'ramming structures' in space combat that might be workeable.

 

Extend a wide spray, net or other form of breakaway nanotubes, and your ship even on a near miss (say a 50 mile long dragline, making 80 km's "near" in space) could effectively shred another vessel. As well, if built to take advantage of the collision of such a lanyard device with an opponent, your own ship could use the pull to change orientation and direction in combat, like a dragline, while the other ship is whipped around experiencing torque and stresses it would never have been designed for.

 

'Ram' by ejecting mass from your own ship as you approach another, and then veering off.

 

Did you see Galaxy Quest? Sometimes it's not the ship you're flying in that you use to do the ramming, but the payload your ship is concealing behind it.

[ghost-angel]

Re: Ramming Speed

 

Honestly? from none to lots.

 

I mean, being in space and futuristic, are force fields involved? superhard metals or ceramics? Is it going to be like ramming a Modern Destroyer with a Trireme? It really won't matter how well designed that trireme is for ramming, it's going to lose.

 

In fact, pre-iron/steel ships it's thought that naval rams were built in such a way as to sheer off as they ships impacted to prevent damage to the rammer (like crushing their own hull).

 

And from all accounts as I understand it ... naval ramming wasn't all that effective anyways.

[tkdguy]

Re: Ramming Speed

 

Depends on the speed of the ships. If we're talking battleships moving at relatively low velocities (no more than a few hundred miles per hour) then a ship with a significant materials advantage and/or impacting a sturdy area of its own structure with a vulnerable area of its target might not be too badly damaged by a ram... especially if it crashes through and doesn't get bounced.

 

It's hard to imagine anything moving at greater speeds doing well in a crash, even a controlled crash. You'd need sufficiently advanced tech to prevent the crew from being pulped by the change in acceleration from the impact.

 

Of course, if the ship is functionally invulnerable and has impossibly powerful acceleration and the crew is in an artificial gravity field that normalizes their inertial frame, you can pretty much do what you want, but that's the handwavey answer. If you're breaking the laws of physics, you can get whatever result you decide is possible.

 

On another front, you'll notice that most vehicles are not made for ramming other vehicles. Even tanks can get bogged down if you put a big enough or tough enough truck in front of them.

The first paragraph was what he was arguing (although he was using a trireme as an example); my point is listed in the rest of the post. My campaign wouldn't have any advanced material, and the thrust involved would pretty much ensure relatively high velocities. I'd probably use the Full Thrust game which backs up my arguments by its design, but I'm geting into the actual physics of it.

[tkdguy]

Re: Ramming Speed

 

Honestly? from none to lots.

 

I mean, being in space and futuristic, are force fields involved? superhard metals or ceramics? Is it going to be like ramming a Modern Destroyer with a Trireme? It really won't matter how well designed that trireme is for ramming, it's going to lose.

 

In fact, pre-iron/steel ships it's thought that naval rams were built in such a way as to sheer off as they ships impacted to prevent damage to the rammer (like crushing their own hull).

 

And from all accounts as I understand it ... naval ramming wasn't all that effective anyways.

Basically, assume "realistic" designs with armor uniformly distributed. No force fields or other types of handwavium.

 

Edit: Thanks for the answers, guys. It's helping me a lot with my campaign design.

[tkdguy]

Re: Ramming Speed

 

There's all sorts of possible mechanisms that could be considered 'ramming structures' in space combat that might be workeable.

 

Extend a wide spray, net or other form of breakaway nanotubes, and your ship even on a near miss (say a 50 mile long dragline, making 80 km's "near" in space) could effectively shred another vessel. As well, if built to take advantage of the collision of such a lanyard device with an opponent, your own ship could use the pull to change orientation and direction in combat, like a dragline, while the other ship is whipped around experiencing torque and stresses it would never have been designed for.

 

'Ram' by ejecting mass from your own ship as you approach another, and then veering off.

 

Did you see Galaxy Quest? Sometimes it's not the ship you're flying in that you use to do the ramming, but the payload your ship is concealing behind it.

Sorry, I missed your post the first time around.

 

I had thought about unmanned drones ramming the ship after they had fired all their weapons. I would treat those as missiles, of course. And they'd be dstroyed upon impact.

 

That would also work in my campaign, since the spacecraft use projectile weapons and nukes.

[Cargus10]

Re: Ramming Speed

 

If you don't have some techno-magic "forcefield" or super-nano-armor or similar, then pretty much any "realistic" speed is going to have a really bad effect on everyone involved. Robinson's First Law of Space Combat says that anything moving at about 3 km/s will, upon impact, release roughly the same kinetic energy as an equivalent mass of TNT would release when exploding.

 

And 3 km/s in space ain't all that fast.

[Cancer]

Re: Ramming Speed

 

What Cargus10 said.

 

Another thing to keep in mind: the speed of sound in steel is about 5 km/s. Impacts at speeds much higher than that will be hypersonic, which means forces of impact propagate through the impactor slower than the impactor's velocity into the collision. The picture of collisions you have from the crash test dummy films is wrong for the hypersonic case: the crumpling of metal happens only when each segment of metal hits the target, not before. That means everything is pancaked before anything else occurs. There's no time for the dummies to bounce off the steering column, air bag, or anything else.

 

With planets, this is what gives rise to impact craters: the incoming bolide penetrates into the planetary surface several times its diameter before the back end of the bolide learns it's suffered a collision. The bolide ends up getting completely smashed, almost painted onto the surface of the hole it's plowed into the target planet, before the kinetic energy of impact gets thermalized (that is, equilibrated into every outlet channel for energy, including heating up the material). That usually means there's enough energy by a long ways to vaporize the bolide, so there ends up being a blast that excavates a hole in the planet.

 

On a non-solid target like a ship, things would be much more complex ... a small impactor might punch a hole clean through the target.

[Spence]

Re: Ramming Speed

 

None of that really matters. It is your SH universe and the associated rubber science is all in your court

[Cargus10]

Re: Ramming Speed

 

You could assume the ships are surrounded by a cloud of foglets http://en.wikipedia.org/wiki/Foglet if your nano-tech is good enough. That would act as an inertial dampener and make the collisions less devastating.

 

Plus, foglets (or utility fog) is just so freaking cool in general, for a myriad of applications.

[tkdguy]

Re: Ramming Speed

 

Sounds like I was right after all. Thanks, folks. I'll wait until the weekend to rub it in; it's his birthday, you see!

[SuperPheemy]

Re: Ramming Speed

 

Well, an acceleration of 1g is 9.8 m/sec^2. Lets give a ramming ship a good 5 minutes to build up steam. That's 300 seconds. 9.8*300*300 = a velocity of 882,000 m/sec. Which is well and far below anything approaching C. But is still roughly 3.2 million kph.

 

Now, assuming that your Navigator is talented enough to actually hit something as small as a starship (we'll be generous and say it's a kilometer-long Star Destroyer) at this velocity. Mr. Newton's third Law states that the rammer is going to take as much energy as the rammee. If our ramming vessel is a thousand ton mass (roughly escort frigate sized). Then it's going to give and take 1000 tons * 882,000^2 meters per second or 7.8*10^14 meter-tons of energy.

 

To survive that (and were assuming the target isn't moving), we're gonna need some seriously BOUNCY rubber science.

 

Or to put it in a way that doesn't use so much math. Larry Niven developed a science-fiction tactic of grabbing a chunk of iron (like a skyscraper-sized meteor) and towing it at a sizeable fraction of C to throw at planets and crack them into little bite-size chunks.

[tkdguy]

Re: Ramming Speed

 

Agreed. I was talking about Newton's Third Law, which my friend is fully aware of.

 

BTW, the system I was talking about was the Full Thrust game, which states both ships would take damage. He hasn't read the rules, but he seems to want to break them already.

[The Monster]

Re: Ramming Speed

 

It strikes me (no pun intended) that part of the equation would need to factor in the effects of whatever method the ships use to avoid or resist impacts from random space debris. Even without man-made stuff, there are some things out there which can move pretty fast and hit pretty hard; presumably, ships have some way to counter those.

 

If it's primarily detect-and-dodge, then a ship deliberately built to ram would be a highly unusual cosntruction: the ship has to be nimble enough to actually hit a target that's capable of dodging high-speed objects without interrupting its normal activity, while at the same time being sturdy enough to withstand a heavy impact itself. If there's a speed-versus-weight issue at all (and even Star Trek has some), that could by itself render the proposed design moot. The only way to use your ramship woul dbe only after the target's engines or detectors were crippled, by which time normal weapons would work just fine anyway.

 

If the ships are sturdy enough to just tough it out under occasional meteor hits, then you might have something. At space-combat speeds, my guess is that the impact energy is so high that the ramship would itself be crippled or destroyed unless there was a huge difference in ship size (the image of destroyers ramming PT boats in WW2 comes to mind). Even where the ramship isn't KO'd, it coul dbe very hard to design systems that could compensate for the unpredictable velocity shifts from a collision (unpredictable in the sense that you can't predict, in the design phase, the dimensions of the target) - you very likely would end up with a damaged ramship that goes spinning off in a random direction until engines can compensate.

 

My summary? Even if it's possible, it would be so difficult (without invoking handwavium and/or trans-Star-Trek force fields) that it would be ineffective in all but the most unusual situations.

[Doc Democracy]

Re: Ramming Speed

 

Well, my take on it would be the kind of story you want to tell. It is easy to be right when neither side has any kind of real-life examples that they can use.

 

If you want to replicate high seas adventures, cept they are happening in space then of course the technology is available that will allow ramming to take place.

 

If you want a more tech based SF tale then you go the Star Trek way and use tractor beams, acurate phasers to engines and transporters to immobilise, disable and board opposition ships.

 

To me, the right answer would come down to the kind of tale and feel that the GM is looking for.

 

 

Doc

[Markdoc]

Re: Ramming Speed

 

To me, the right answer would come down to the kind of tale and feel that the GM is looking for.

 

 

Doc

 

Right. Who could resist a Space fleet game where the captain orders all the starships into line, crosses the enemy fleet to give them a broadside and then shouts at everyone to "Grab something solid, we're going to ram!"

 

Admission - I play Battlefleet Gothic occasionally, where starship ramming actions (and exhortations like "Grab your swords, brother marines - we are about to board!") do in fact occur. But I've never been able to take it seriously.

 

I would however cheerfully play in such a game as long as I was allowed to go "Yaaaar!" a lot.

 

As a GM, though, I'd let the player go for it. Assuming he could actually hit something with a movethrough at 17.7 million inches per phase (Hmmm, let me see: that's a pretty big minus on your diceroll....) taking half damage (and the resulting expanding cloud of plasma where the ships used to be) should prevent anyone doing it again....

 

cheers, Mark

[Cargus10]

Re: Ramming Speed

 

Ah, but didn't the original poster mention that this was a game of Full Thrust, or at least those rules are being used for the ships? In that case, you are constrained by tech assumptions.

 

But yeah, a game of space pirates and boarding actions could be fun...particularly if they got to fight space ninjas.

[SuperPheemy]

Re: Ramming Speed

 

Mechanically, I'd tie the maximum amount of ramming damage to the total DEF + BODY of the ramming vessel. And maybe take SIZE into consideration. Thus a SIZE 5 BODY 20 Fighter won't vaporize a SIZE 50 BODY 2000 Dreadnought (or in more graphic terms, the X Wing can crash into the Death Star and still allow Luke his moment of Glory).

 

In some respects, Kinetic-Kill weapons are just unmanned (or sometimes Kamikaze) vessels that are little more than engines, armor, and control surfaces designed specifically to ram larger vessels. With enough acceleration, such a weapon wouldn't even need much guidance, so long as it was vectored accurately at launch.

[Cargus10]

Re: Ramming Speed

 

You've just hit upon why reactionless drives are such a (potential) campaign-buster. Take a chunk of rock, ice, iron, or what have you and stick a reactionless drive on it and some kind of AI guidance. Aim it at a planet. Better yet, do that for several. Start out in the Oort Cloud, if you really need time to build up velocity (though aren't most reactionless drives "instant on"? All the folks that spot UFO's say so anyhow), and fire 'em all up. Pretty soon, you have a dead, dead planet. Wash, rinse, repeat.

 

Makes for ugly space warfare.

 

And it's hard to hand-wave around the problem without some....quirky rules, though it can be done. The Stutter-Warp drive, for example. Nicely done, though they did have to toss in that rule about how far you can go before servicing the engines...

[Kristopher]

Re: Ramming Speed

 

I guess it would depend on the technology and defenses of the Ramming Ship vs the Rammed Ship.

 

What you really have to consider is can the structure of the ship doing the Ramming withstand the impact?

 

Assuming some kind of Ramming Beam placed at the front, and given that there's no environmental counter-force (i.e. in sailing ships the Water will push back) once you make the initial impact and start to transfer momentum from Rammer to Rammed you may just end up with another spaceship stuck to the front of your yours.

 

You'd have to take into account relative Vectors as well, if it's head on the guy with the highest velocity will win. If it's a Ram to a side it could just get pushed out of the way or have the rammed ships vector changed, it may sustain little damage at all - since there's nothing to "push against" in space to keep the rammed ship in place.

 

Or, if the relative velocities are different enough, the Rammer could end up just going right through the Rammed ship, leaving a nice mess behind.

 

One thing might hold the rammed ship "in place" -- its own inertia.

[ghost-angel]

Re: Ramming Speed

 

One thing might hold the rammed ship "in place" -- its own inertia.

 

hence the note on Vectors. Hit a ship at a 90 degree angle to it's current Vector and without something to "push back" all you may end up doing is altering it's vector as there's no resistance from the opposite direction the rammer is moving in.

[Kristopher]

Re: Ramming Speed

 

hence the note on Vectors. Hit a ship at a 90 degree angle to it's current Vector and without something to "push back" all you may end up doing is altering it's vector as there's no resistance from the opposite direction the rammer is moving in.

 

There's still resistance, and it's still the target ship's inertia. The only way that there's no relative inertia is if the two ships are moving in the same direction at the same velocity. Any collision precludes that condition and thus involves some "resistance" from the target ship to being accelerated along a new vector.