Attacking Darius:

ThinksMarkedly wrote:Not really. We're not talking about radar or lidar, meaning it's a round-trip for the signal. Passive sensors can see the photons that were already on the way from the ship and simply got intercepted by the torpedo.

And those signals took time to get to the torpedo.

Loren Pechtel wrote:The real issue is that energy weapons aren't seeking at all, they can't compensate at all. They have to lead their targets by twice the time light takes to cover the distance. Thus long range energy shots will have abysmal hit rates.

tlb wrote:There is no reason that the missile cannot passively detect the ship's wedge and use that to calculate where the opening in the wedge should be when the light arrives. So it is not twice the lag time, but about 1.0167 times the light speed lag. Yes, there is uncertainty in this; but there is also multiple independently aimed rods that give a spread of beams with a chance to hit. Or with the graser torpedo there is time that will wiggle the beam.

Loren Pechtel wrote:It knows where the wedge is FTL. It doesn't know where the ship is within the wedge.

I agree and have said as much, both in the text I highlighted that you referenced in your response and in another post that I have included below.

You might point out that checking for the wedge only gives an approximate idea of the ships position, but that is true no matter how you try to pinpoint the ship. And it also is why a ship might be killed by a single weapon, but it usually requires multiple weapons converging from multiple directions to cause serious damage.

PS. Did you notice that I explained why I do not like mention of To End in Fire in this thread? In case you missed it, here is a repeat:

Because if I try to argue that the book did not get it wrong or that the conditions on Darius will be different; then I am stymied by the prohibition against spoilers. So your statement (and those by other people in this thread) get a free ride until the spoiler time period lapses.

I never accused you of supplying a spoiler, only that it was impossible to argue against your statement without supplying a spoiler myself; since simple contradiction is not an argument (see for instance the Monty Python argument sketch).

kzt wrote:The ship needs to turn to change it's vector. It only goes straight ahead. If you want to introduce deviations you need to roll, pitch or yaw. That moves the wedge, which is obvious to an observer and also takes a certain amount of time to do.

Though if the graser torp is closing from a broader angle, rather than coming nearly down the throat, then even significant changes in forward acceleration along would significantly alter the intersect point -- quite possibly beyond the graser torp's ability to correct for.

Imagine a WWII sub making a near broadside spread of torpedoes at a cruiser based on its measured speed of 28 knots; if the ship does a crash stop all the torpedoes will miss well ahead of it.


That kind of acceleration change will be somewhat visible via FTL, but seems like it can happen much faster than a bearing or pitch change from an SD(P) or CLAC.



But then if you've got a reasonable 3D zig-zag plan that you implement on approach it matters less how long it takes the ships to alter bearing for the next leg because the uncertainty caused by the multiple course changes before anything gets close makes it harder for the slower accelerating graser torps to even get close enough to intercept (at least not without dispersing enough so at least a few cover over all plausible courses that they're deprived of the concentration needed to be decisive)

tlb wrote:As both KZT and I have pointed out the passive sensors could be looking at the wedge for target positioning and velocity, therefore using information that arrived 60 times faster than the speed of light. So the target ship may only have 1.067 times the light speed time lapse to maneuver the ship.

You might point out that checking for the wedge only gives an approximate idea of the ships position, but that is true no matter how you try to pinpoint the ship. And it also is why a ship might be killed by a single weapon, but it usually requires multiple weapons converging from multiple directions to cause serious damage.

That's neither here nor there.

The point is that there are photons reflecting off the ship and being emitted by the ship (thermal photons) whic are on the way before the torpedo arrives at the location where those photons are. The wedge blocks / diffuses all photons going through it, but once there's direct line of sight to the ship, the torpedo can immediately see the ship.

Loren Pechtel wrote:

ThinksMarkedly wrote:Not really. We're not talking about radar or lidar, meaning it's a round-trip for the signal. Passive sensors can see the photons that were already on the way from the ship and simply got intercepted by the torpedo.

And those signals took time to get to the torpedo.

Yes, they did. But the point is that they were underway to the position the torpedo will be before the torpedo got there. So the time it took them is irrelevant to the calculation. But it does match the time the gamma-ray photons the torpedo will fire will take to get back.

Hence, single-way light lag, not round-trip.

kzt wrote:The ship needs to turn to change it's vector. It only goes straight ahead. If you want to introduce deviations you need to roll, pitch or yaw. That moves the wedge, which is obvious to an observer and also takes a certain amount of time to do.

Yes, it does. That means short-time evasions (less than one minute) are unlikely, The ship will still be turning when time runs out.

But I was talking about a 3D zig-zag course that changes every 10-20 minutes. That's within the time a ship takes to turn and therefore can significantly change its predicted position. See Jonathan's reply above.

ThinksMarkedly wrote:Not really. We're not talking about radar or lidar, meaning it's a round-trip for the signal. Passive sensors can see the photons that were already on the way from the ship and simply got intercepted by the torpedo.

Loren Pechtel wrote:And those signals took time to get to the torpedo.

ThinksMarkedly wrote:Yes, they did. But the point is that they were underway to the position the torpedo will be before the torpedo got there. So the time it took them is irrelevant to the calculation. But it does match the time the gamma-ray photons the torpedo will fire will take to get back.

Hence, single-way light lag, not round-trip.

What you are missing is that during the time that "those signals took" "to get to the torpedo" the ship can move; what the torpedo sees is not the present image of the ship, but a view of it from the lapsed time ago. So overall the effect is that aiming has to allow for movements based on the round-trip time, not the one-way time. That mistake may be why you discount that the missiles primary sensors are looking at the wedge, with only secondary sensors that might be looking at the light speed image of the target.

ThinksMarkedly wrote:But I was talking about a 3D zig-zag course that changes every 10-20 minutes. That's within the time a ship takes to turn and therefore can significantly change its predicted position. See Jonathan's reply above.

Yup. Sometimes you'll avoid a threat. Sometimes you'll instead present a threat with a present.

"The Japanese force zigged and zagged to throw off any undersea pursuers. And then came that bit of luck that often tips every battle. The Japanese ships zigged one more time, straight into the path of the Archerfish. The sub took its chance. At 3:15 am on November 29, it fired six torpedoes. Four hit."

tlb wrote:What you are missing is that during the time that "those signals took" "to get to the torpedo" the ship can move; what the torpedo sees is not the present image of the ship, but a view of it from the lapsed time ago. So overall the effect is that aiming has to allow for movements based on the round-trip time, not the one-way time. That mistake may be why you discount that the missiles primary sensors are looking at the wedge, with only secondary sensors that might be looking at the light speed image of the target.

Not exactly. The torpedo always sees where the ship was a single-way-time ago. From the point of view of the ship, the torpedo reacts to its evasions at round-trip-time.

The primary sensors can indeed see the wedge in FTL, but the torpedo has seen that wedge for the past half hour already. But that doesn't tell the torpedo where precisely the ship is within the volume it determined the wedge to be. Assuming the torpedo can generate an intercept with that wedge, it still needs to clear the wedge in order to see the ship.

To traditional missiles, GA ships would indeed have rolled their wedges, presenting the worst scenario from the missile's point of view: perpendicular to their base velocity vector. This is where my calculations are correct: once the sensor clears the wedge, it can pinpoint where the ship was single-way-time ago. The ship will continue to move, which is why said warhead must either have multiple beams to bracket all positions or it must be close enough that it can swing the beam to a position the ship must occupy within that time.

For a torpedo, we have to assume the ship will not have seen the torpedo coming until far too late. I maintain that the shell of Ghost Riders will see something, but by the time the torpedo is within 15 seconds from target. They'd need to see the threat earlier to interpose the wedge completely.

The calculation I made assumed the worst case scenario for the torpedo, which is unlikely. It calculated the minimum distance or maximum velocity the torpedo could be at so it can fire full 3 seconds at where it has seen the ship or predicted it will be, in that perpendicular case.

ThinksMarkedly wrote:

tlb wrote:What you are missing is that during the time that "those signals took" "to get to the torpedo" the ship can move; what the torpedo sees is not the present image of the ship, but a view of it from the lapsed time ago. So overall the effect is that aiming has to allow for movements based on the round-trip time, not the one-way time. That mistake may be why you discount that the missiles primary sensors are looking at the wedge, with only secondary sensors that might be looking at the light speed image of the target.

Not exactly. The torpedo always sees where the ship was a single-way-time ago. From the point of view of the ship, the torpedo reacts to its evasions at round-trip-time.

The primary sensors can indeed see the wedge in FTL, but the torpedo has seen that wedge for the past half hour already. But that doesn't tell the torpedo where precisely the ship is within the volume it determined the wedge to be. Assuming the torpedo can generate an intercept with that wedge, it still needs to clear the wedge in order to see the ship.

To traditional missiles, GA ships would indeed have rolled their wedges, presenting the worst scenario from the missile's point of view: perpendicular to their base velocity vector. This is where my calculations are correct: once the sensor clears the wedge, it can pinpoint where the ship was single-way-time ago. The ship will continue to move, which is why said warhead must either have multiple beams to bracket all positions or it must be close enough that it can swing the beam to a position the ship must occupy within that time.

For a torpedo, we have to assume the ship will not have seen the torpedo coming until far too late. I maintain that the shell of Ghost Riders will see something, but by the time the torpedo is within 15 seconds from target. They'd need to see the threat earlier to interpose the wedge completely.

The calculation I made assumed the worst case scenario for the torpedo, which is unlikely. It calculated the minimum distance or maximum velocity the torpedo could be at so it can fire full 3 seconds at where it has seen the ship or predicted it will be, in that perpendicular case.

Side walls also block precise line of site to the ship generating them - So a ship with sidewalls and bucklers should keep a torp from getting a good location of the actual ship's position relative to the wedge - however it should be able to get a decent reading on the location of the wedge itself.

Of course this is the same as localizing New Jersey from the Moon. (or worse)