LAC on LAC warfare

ThinksMarkedly wrote:

Jonathan_S wrote:Spider drives do have a medium to work against to potentially redirect their heading without losing momentum! Their spider drive nodes are essentially overpowered tractor beams and literally punch through to grab against the Alpha wall itself and pull the ship forward.

In theory, if the mounts and beams can take the strain, a spider drive should be able to grab a spot off to one side and use that as a skyhook style pivot to redirect its existing momentum onto a new heading!

I don't think that's at all how it works.

So far we haven't heard anything about the spider drive's acceleration being related to the ship's speed in real space. That means the medium the drive is pushing or pulling against is, like light, at a constant speed relative to the ship. Speeding up to 0.8c doesn't make light travel at only 60000 km/s to you, it's still at the speed of light. So the alpha wall is probably too.

What's more, unlike a jet, the spider drive has only one way to interact with the medium and that's the spider itself. A jet accelerates with the turbofans (and afterburners and whatever) using good, old Newton's Third Law, but changes direction using its surfaces.

Finally, even if it had a way of dumping all its velocity and turning, it would be limited by how much the grav plates can compensate. A fighter pilot feels a lot of G forces always during turns because their velocity vector is changing direction, but not very much magnitude.

In other words, the spider drive is not very different from a wedge: it allows for violating Newton's Third Law and Conservation of Momentum (and whether energy is conserved is anyone's guess), but not Newton's First and Second.

OTOH we know that the spider drive ships have their trilateral summitry because they need drive nodes pointing off in at least 3 different directions in order to pull themselves forward. My assumption is that they need three points of contact to avoid the spider beams pulling them off to the side.

So the turn would just be to not use the nodes on the other two spines to counteract the off balance force of one spine's worth of emitters.


Now it can't reverse course instantly, and the exact speed at a reasonable acceleration depends on the length of the spider tractor. Let's assume that the crew doesn't want to experience 1+ g towards the walls so we need to hold the lateral acceleration down to something the grav plates can completely handle; say 50 gees.

And, huh. Turns out I should have done some math before posting, since my intuitive visualization was wildly wrong.

If a spider drive accelerates for 1 hour at 150g it builds up a velocity of 5,292 km/s. To reverse that vector normally it would need to flip over and accelerate for 2 hours at that same 150g so it's now headed the other way at 5,292 km/s. (first hour to cancel its velocity; 2nd hour to rebuild it in the other direction)

If instead it uses its spider drive to make a sweeping turn of 180 degrees, keeping the lateral acceleration below 50g, it takes nearly 9.5 hours!!!
At 5,292 km/s, to keep the lateral acceleration below 50g, I calculate that it needs a turning radius of 57,500,000 km. A circle that large has a circumference of about 361,283,155 km so at 5,292 km/s it'd takes about 68,270 seconds to go all the way around; or half that to make just a 180.


So as I said, it looks like my intuition was badly wrong. It doesn't matter that it has medium to work against because unlike an airplane it still can't turn harder than it can straight line accelerate so being able to grab something to pivot yourself isn't actually faster than changing heading and then accelerating.

munroburton wrote:It'd take the better part of a hour to somersault a superdreadnought.

https://infodump.thefifthimperium.com/e ... ton/128/1/

A typical SKM DD can alter her heading (but not necessarily her vector, of course) by 90 degrees in about 100 seconds; an SD would need about twelve minutes for a 90-degree turn. (The difference in roll rates is not as a great, although it also favors the smaller ship by a largish margin.

But I'm not sure if the spider ships need make 90 degree turns at all. If their drives can grab and push in and from any directions, then they don't need to rotate in the same way that impeller warships have to.

Though to be fair at the time RFC wrote that a typical SD has a straight line acceleration of around 400g and now the RMN ones are up over 600. So their angular acceleration may have also improved; somewhat reducing the time it may take them to turn around.

Also I think spider drives would sometimes need to change heading to acceleration for a couple reasons.
1) it'd probably be a lot more engineering work to create spider node projectors that are capable of angling over far enough to simply pull the ship backwards; they'd probably need to be able to pivot at least 150 degrees to do that, while to pull it forward they might need only a few degrees of travel (or if the beams can be angled somewhat without moving the mount then they could be totally fixed).

2) my understanding is they have their trilateral symmetry, with 3 spines each mounting spider drive projectors, because they can't tractor all the nodes to a spot directly ahead of the ship. So they need to balance pulls to 3 different areas; each one off to one side of the line of advance, to pull the ship straight forward rather than pulling it diagonally

3) It needs a large number of spider projectors in order to achieve full acceleration (that's why unmanned spider drones/torps; even those as big as the graser torp, are so slow - even large drones/torps aren't large enough from the number of projectors you'd need for high accel. And the ship can only use all it's projectors when pointed along the direction of acceleration.

4) The grav plates are arranged on the deck floors, and at high accel they can't completely counteract the experienced acceleration. So accelerate backwards or sideways are high velocity and the crew it getting shoved into the ceiling or walls at up to 5 gees!

Now all that said, if the accel is kept low enough for the grav plates to completely handle (say under 50g) then even fixed projectors could crab the ship somewhat to the side simply by not using the other 2 spines to balance (or fully balance) the off axis pull from one spine. And if they can pivot to at least 90 degrees then the ship would be able to pull itself straight sideways in the direction of any one of its three spines (or if the projectors can handled lateral pivot/pulling then it could pull itself sideways in many more directions by using varying power on a pair of spines)

Still even if it has the most flexible projector pointing ability, with all the seemingly unnecessary engineering challenges that requires, I don't think it can pull itself in all possibly directions without changing its heading - and due to the grav plate placement most maneuvers probably do involve pointing the nose in the desired direction of acceleration.

Use the grab method to kill acceleration first before making the turn. The turning radius should be a lot smaller then. Akin to trying to corner in a Ferrari at high speeds. You must kill your acceleration first. The grab method should be able to kill accel much faster, then corner at optimum velocity. The maneuver is simply grav plate limited as impeller ships are compensator limited.

Also, it seems as if spinning on the xy axis bringing the underbelly of the spider facing the 90° direction of change should be more efficient.

cthia wrote:Use the grab method to kill acceleration first before making the turn. The turning radius should be a lot smaller then. Akin to trying to corner in a Ferrari at high speeds. You must kill your acceleration first. The grab method should be able to kill accel much faster, then corner at optimum velocity. The maneuver is simply grav plate limited as impeller ships are compensator limited.

Also, it seems as if spinning on the xy axis bringing the underbelly of the spider facing the 90° direction of change should be more efficient.

You do not kill acceleration, you use acceleration to kill velocity. Yes, the turning radius is smallest if you kill all forward velocity, then rotate to accelerate 90 degrees from the previous direction. However I would need to work it out whether that is the fastest way to get where to you want to be, since the hypotenuse is shorter than the sum of the other two sides.

Additional Compensation Possibilities

There's something else I've been meaning to broach. The MA is touting the notion that the point on the tinkering line where the Beowulf Code says should not be crossed—and labels it as dangerous and irresponsible—is unrealistic. The MA is out to prove to the galaxy that extreme genetic tampering is beneficial to mankind, even if hideous gills are formed to allow breathing underwater. One way the MA can make their point is . . .

1. A human body which can withstand much higher g-forces.

2. An advanced MA equivalent of our current high-tech g-suit, used by our astronauts and aviators today.

3. The MA can even lock themselves into a mechanical seat which additionally compensates for high g-forces and which also doubles as a version of the RMN's shock frame. IOW, the MA may have to prepare to make high-gee maneuvers just as the RMN has to lock themselves in shock seats to prepare for battle.

I'm not claiming the MA can put compensators and grav plates out of business, but the three additional measures above in addition to their grav plate just might tip the scales. Besides, who knows what they may achieve to advance grav plate technology if they can steal certain Manty secrets. Since their ships don't have wedges, necessity is certainly their mother of invention. The rest of the galaxy has simply never needed to delve as deeply into grav plate technology. Jus' sayin'.

tlb wrote:You do not kill acceleration, you use acceleration to kill velocity.

That is applied to the traditional method of slowing down. Jonathan's method could utilize both negative acceleration and "dropping the anchor" by pulling at the Alpha Wall. A Dragsters parachute.

I made the point long ago that we keep making the mistake of trying to pigeonhole MA inventiveness and solutions to fit with traditional technology. It isn't, it can't be, and we shouldn't bank on it. MA technology is a completely different paradigm, and their solutions go in completely different directions by necessity. It is their traditionally, centuries long, misaligned thinking which delivered the Spider Drive to them in the first place.

tlb wrote:...since the hypotenuse is shorter than the sum of the other two sides.

That is trigonometry. Calculus tells us that the area inside the curve is also more efficient, or smaller.

tlb wrote:You do not kill acceleration, you use acceleration to kill velocity.

cthia wrote:That is applied to the traditional method of slowing down. Jonathan's method could utilize both negative acceleration and "dropping the anchor" by pulling at the Alpha Wall. A Dragsters parachute.

"Dropping the anchor" is negative acceleration, the same as a dragster's parachute!!!

Yes, there might be genetic changes that allow much more g-force on the body. Other SF authors have suggested things like filling the lungs with a fluid that could transport oxygen and carbon dioxide, maybe in a pressure cell so blood would continue to supply the brain, rather than pooling in the legs. But whatever is done the spider drive produces less acceleration than the wedge and compensator combination.

tlb wrote:...since the hypotenuse is shorter than the sum of the other two sides.

cthia wrote:That is trigonometry. Calculus tells us that the area inside the curve is also more efficient, or smaller.

I would have called it geometry, since it is just a special case of the rule that the shortest distance between two points on a plane is a straight line (a geodesic on a more complicated surface).

tlb wrote:

tlb wrote:You do not kill acceleration, you use acceleration to kill velocity.

cthia wrote:That is applied to the traditional method of slowing down. Jonathan's method could utilize both negative acceleration and "dropping the anchor" by pulling at the Alpha Wall. A Dragsters parachute.

"Dropping the anchor" is negative acceleration, the same as a dragster's parachute!!!

Yes, there might be genetic changes that allow much more g-force on the body. Other SF authors have suggested things like filling the lungs with a fluid that could transport oxygen and carbon dioxide, maybe in a pressure cell so blood would continue to supply the brain, rather than pooling in the legs. But whatever is done the spider drive produces less acceleration than the wedge and compensator combination.

Context!!! For the sake of this conversation, it isn't. Negative acceleration is flipping the ship and accelerating in the opposite direction. The Pavel Maneuver. Friction-induced deceleration is not negative acceleration.

tlb wrote:"Dropping the anchor" is negative acceleration, the same as a dragster's parachute!!!

cthia wrote:Context!!! For the sake of this conversation, it isn't. Negative acceleration is flipping the ship and accelerating in the opposite direction. Friction-induced deceleration is not negative acceleration.

I do not agree, but why do you say this is "friction-induced"? Certainly you would flip the ship to make effective use of the gravity plates, but anything done to slow the ship's forward velocity is negative acceleration. The acceleration is the change in velocity divided by the amount of time for that change; so if the change in velocity is negative, the acceleration is negative by the rules of mathematics.

The important point is that this change in velocity (however you accomplish it and whatever words that you want to use to describe it) have an effect on the contents of the ship, including the crew, which have to be counteracted by the gravity plates. Those gravity plates and the effects on the crew of the change in velocity limit how abruptly the ship can maneuver.