long range laser

kzt wrote:

Sheriff Yoda wrote:Part of an energy weapons ineffectivness has to do with the fact that when you double the distance from a light source the intensity of that light is quartered and 2 light seconds is a HUGE distance. The moon is less than 2 light seconds from Earth. I'm not sure how that effects lasers but I'm sure like a light bulb the intensity does reduce as a factor of distance so that the sidewalls have less energy to deflect.

The inverse square law only applies to non-coherent point sources, so lasers don't behave that way. A Gaussian laser beam expansion is based on the square of the radius of the beam divided by wavelength. Look up Rayleigh length.

Which is why DW should have never introduced huge gamma ray lasers as standard armament, they maintain the ability to do damage to seemingly totally absurd distances, as in light hours to light weeks.

Provided the target is obliging enough to stay in one spot that whole time.

Sheriff Yoda wrote:Provided the target is obliging enough to stay in one spot that whole time.

Or if you can predict where it will be. Like, say, an space station kilometers in size that is orbiting a planet.

kzt wrote:

Sheriff Yoda wrote:Provided the target is obliging enough to stay in one spot that whole time.

Or if you can predict where it will be. Like, say, an space station kilometers in size that is orbiting a planet.

Point. However I think even this would be impractial in a system like Manticore. Someone would see the weapon and using the FTL com get a ship in position to intercept it with a wedge.

With Grasers the wavelength is so small that if you can achieve diffraction limited optical performance, dispersion is going to be inconsequential out to several AUs. There is no need for a mirror or lens to refocus the laser. All you need is FTL targetting updates whcih will double the range at which you are likely to score a hit.

catfish wrote:The function of the mirror isn't targeting. It is to concentrate the laser and compensate for dispersion. I doubt that a mirror would be able to withstand the laser, unless it was coated with handwavium.

Target doesn't have to be obliging. If Velocity vector is known and Accelleration vector is known, target position can be predicted. Weber hasn't given us enough info about what the potential uncertainty of the accelleration vector's magnitude and direction could be. However; slew rates seem to be on the order of only one radian per second and changes in accelleration don't seem to be instantaneous either, somewhere on the order of tens of gees/second. With these limitations on the evasive manauvers, a long range Graser should have a reasonable probability of scoring a hit at engagment ranges of a few Light Seconds. Having a forward deployed recon drone with FTL communciatiosn to provide targeting data would double the effective range. A Graser that could score a hit at 5 to 10 Light Seconds would be a serious game changer when energy engagement ranges are generally about 1/3 of a light seconds.

Sheriff Yoda wrote:

kzt wrote:

Sheriff Yoda wrote:Part of an energy weapons ineffectivness has to do with the fact that when you double the distance from a light source the intensity of that light is quartered and 2 light seconds is a HUGE distance. The moon is less than 2 light seconds from Earth. I'm not sure how that effects lasers but I'm sure like a light bulb the intensity does reduce as a factor of distance so that the sidewalls have less energy to deflect.

The inverse square law only applies to non-coherent point sources, so lasers don't behave that way. A Gaussian laser beam expansion is based on the square of the radius of the beam divided by wavelength. Look up Rayleigh length.

Which is why DW should have never introduced huge gamma ray lasers as standard armament, they maintain the ability to do damage to seemingly totally absurd distances, as in light hours to light weeks.

Provided the target is obliging enough to stay in one spot that whole time.

What you are proposing is bazically a Solar System defense laser network like what Niven had humans use against the Kzin when the Kzin first came calling. I could see something like it, using highly stealthed and very heavily armored (and very small cross section) drones as focal points.

I'm glad someone remembers the Kzinti Lesson.

Personally; I never found the idea that humans could hold Sol system against the Kzinti very credible. The light speed limitations against the range of lasers does apply and unless you have absurdly large apertures, the diffraction limitations of optical or even UV wavelength lasers don't allow "system defense" weapons.

My attitude changes somewhat after reading the Kzinti War series short story A DARKER GEOMETRY. If the ARM managed to collect some Tree of Life virus from Pst Pok's ship, then they can arrange for humans to become Protectors. I can see a the vault that must have been built at ARM headquarters. There is a vial of Tree of Life virus in a case with a sign reading, "BREAK GLASS ONLY IN CASE OF EXTREME EMERGENCY." This got me thinking that perhaps ther is some isolated location on earth with a high enough concentration of Thalium to grow viable tree of life. Imagine an isolated valley with a grove of Tree of Life in it. Some time perhaps about 5,000 to 10,000 years ago a childless human about 45 years old wanderred into this valley and ate from the Tree of Life. The result is history...

Cheopis wrote:What you are proposing is bazically a Solar System defense laser network like what Niven had humans use against the Kzin when the Kzin first came calling. I could see something like it, using highly stealthed and very heavily armored (and very small cross section) drones as focal points.

Kzinti ships, if I remember right, could only accelerate and decellerate rapidly a few times before needing to refuel, otherwise their acceleration was nothing even close to Honorverse ships, so the system defense lasers would not have really needed a lot of highly complex tracking to predict/counter acceleration for targeting, unless the kzin burned one of their valuable acceleration options, which would effectively require them to burn two (you have to stop to engage)

Honorverse ships on the other hand accelerate at a massive rate at any time, and any system defense laser system would absolutely require high precision FTL tracking gear AND mobile refocusing/tracking devices (drones or ships) in order to effectively target any undamaged naval vessel at less than knife-edge range.

The first time we met Kzinti, their ship matched course with a bussard ramship in deep, intersteller space. This implies an absurdly large delta vee. In spite of his science and tech background, Niven never considerred how much fusion fuel a ship would have to burn to boost up to nearly C. We are talking a fuel mass to ship mass ratio measured in the hundreds. Even worse is Niven and Pournelle's FUSION POWERRED PHOTON DRIVE. IF they'd done the math, (whcih those two are eminently qualified to do) they'd have realized that the specific impuse of a fusion powerred photon drive would be one-twentieth of the specific impulse of a simpler, fusion rocket.

That should make Weber feel better about my hammerring him ont he BC(P) debate.

Cheopis wrote:Kzinti ships, if I remember right, could only accelerate and decellerate rapidly a few times before needing to refuel, otherwise their acceleration was nothing even close to Honorverse ships, so the system defense lasers would not have really needed a lot of highly complex tracking to predict/counter acceleration for targeting, unless the kzin burned one of their valuable acceleration options, which would effectively require them to burn two (you have to stop to engage)

Honorverse ships on the other hand accelerate at a massive rate at any time, and any system defense laser system would absolutely require high precision FTL tracking gear AND mobile refocusing/tracking devices (drones or ships) in order to effectively target any undamaged naval vessel at less than knife-edge range.

Reviving this thread and changing the target of the system defense lasers from enemy ships protected by sidewalls to pods that are deployed by said enemy ships...

what would be the effectiveness of say SD strength grasers (or stronger) vs missile pods 5-6 light minutes out.

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possible defense against LACs too. just saturate the area along the vectors that the enemy lacs (once they have them) are going to use. the damage might be minor but even if the beams are diffused enough that they can only slightly melt at such long range instead of penetrate armor, the LACs' sensors would be F'd up.