Fall 1924: What will the Admiralty build next

Adding a laser head to a RD that lets you fire a weapon on the other side of the system poses some interesting challenges. 1st is that you are either going to destroy the RD when you "fire" the weapon or you are going to have to work on the RD to carry the leserhead and something to move it in the direction of the target. Possibly piggyback and jettison the laser head so it can be a safe distance from the RD before it's flight time initiates.
2nd is that you are going to slow down your RD by adding weight....just the laser head or some cobbled up missile/warhead and then drag it around as the RD does it's normal job.
3rd: how close do you have to be with that laser head if your going to be able to be able to engage the target. Without some sort of booster missile systems you going to drop the laser head on a convergent vector and maneuver the RD away (if you don't want to loose the RD) but your still going to have to be "close".
4. What are you using to power the LH and if attached so some motor, what are you using to power the motor....and how long can they maintain sufficient to be used?
5. one laser head, how many laseing rods? Presuming you just have one (size of the LH package) are you confident you are going to sufficiently disable (destroying would probably be a Golden BB shot) whatever it is you are engaging so you can run it down and ....whatever....after you have shot it?
Still, you have an interesting ambush weapon if your expecting bad company

Brigade XO wrote:Adding a laser head to a RD that lets you fire a weapon on the other side of the system poses some interesting challenges. 1st is that you are either going to destroy the RD when you "fire" the weapon or you are going to have to work on the RD to carry the leserhead and something to move it in the direction of the target. Possibly piggyback and jettison the laser head so it can be a safe distance from the RD before it's flight time initiates.
2nd is that you are going to slow down your RD by adding weight....just the laser head or some cobbled up missile/warhead and then drag it around as the RD does it's normal job.
3rd: how close do you have to be with that laser head if your going to be able to be able to engage the target. Without some sort of booster missile systems you going to drop the laser head on a convergent vector and maneuver the RD away (if you don't want to loose the RD) but your still going to have to be "close".
4. What are you using to power the LH and if attached so some motor, what are you using to power the motor....and how long can they maintain sufficient to be used?
5. one laser head, how many laseing rods? Presuming you just have one (size of the LH package) are you confident you are going to sufficiently disable (destroying would probably be a Golden BB shot) whatever it is you are engaging so you can run it down and ....whatever....after you have shot it?
Still, you have an interesting ambush weapon if your expecting bad company

Well it can't be that difficult a problem since Manticore was already fielding this system back in At All Costs. Mistletoe is precisely an RD with a warhead 'strapped' to it. (Laser head ones were used to kill Havens Moriarty platforms and additional ones with regular nukes were used to thin out the orbital missile pods)

Now they did imply that you'd be unlikely to sneak one of those into effective range of a warship or fort -- but against anything else they can be a nasty shock.



I don't recall whether it explicitly said, but I assume that they let the RDs blow up rather than trying to get fancy and separate the warhead first.

Jonathan_S wrote:Well it can't be that difficult a problem since Manticore was already fielding this system back in At All Costs. Mistletoe is precisely an RD with a warhead 'strapped' to it. (Laser head ones were used to kill Havens Moriarty platforms and additional ones with regular nukes were used to thin out the orbital missile pods)

Now they did imply that you'd be unlikely to sneak one of those into effective range of a warship or fort -- but against anything else they can be a nasty shock.

The difficulty is the time searching.

Mistletoe and the MAlign's Silver Bullet had a lot of time to search for their targets while running very slowly under stealth. They were not trying to get anywhere in a hurry, so they not only could but wanted to keep their acceleration down.

The proposed solution here is closer to a Hasta, which is trying to get somewhere in a hurry. That is much harder to hide and has the limitations that Brigade and you mentioned.

As an alternative, large-aperture grazers. The idea is to increase the effective range, by a lot.

The physical limit is that grazer beams spread out with increasing distance. How much? The physical limit is that a grazer beam, wavelength lambda, emitted by a circular aperture, wavelength R, spreads out through an angle roughly lambda/R in size, where the angle is in units radians. For a 1 Angstrom grazer and a 1 meter wide aperture, the angular spread is about 10^-10 radians, meaning the beam will have added a meter to its size, doubling its diameter, at a distance of 10^+10 meters or ten million kilometers. At a distance of a billion kilometers, 10^12 m, the beam will be 100 meters across.

Someone will say, what about the inverse square law? If I double the distance, don't I cut the power density by a factor of four?

The key issue there is: Double the distance *from what point*? The relevant point is not the front of the laser. It's not the back of the laser. It is behind the laser, for the system here, ten million kilometers behind the laser.

If you make the aperture 10 meters across, you reduce the angular spread by a factor of ten.

Of course, there is this minor issue of targeting.

phillies wrote:As an alternative, large-aperture grazers. The idea is to increase the effective range, by a lot.

The physical limit is that grazer beams spread out with increasing distance. How much? The physical limit is that a grazer beam, wavelength lambda, emitted by a circular aperture, wavelength R, spreads out through an angle roughly lambda/R in size, where the angle is in units radians. For a 1 Angstrom grazer and a 1 meter wide aperture, the angular spread is about 10^-10 radians, meaning the beam will have added a meter to its size, doubling its diameter, at a distance of 10^+10 meters or ten million kilometers. At a distance of a billion kilometers, 10^12 m, the beam will be 100 meters across.

Someone will say, what about the inverse square law? If I double the distance, don't I cut the power density by a factor of four?

The key issue there is: Double the distance *from what point*? The relevant point is not the front of the laser. It's not the back of the laser. It is behind the laser, for the system here, ten million kilometers behind the laser.

If you make the aperture 10 meters across, you reduce the angular spread by a factor of ten.

Of course, there is this minor issue of targeting.

It has been discussed before; the major parameter is the Rayleigh length, only after that distance is exceeded does the beam diverge linearly with distance. The last time I worked it out for Honorverse energy weapons it was somewhere around a light-minute (see the post indicated below).

However energy weapons in the Honorverse do not actually have the effective range that the theory indicates that they should. The author limits them to thousands of kilometers, I believe. This has been mentioned a various times in the forum.

(Spoilers) Future Technological Developments

phillies wrote:The physical limit is that grazer beams spread out with increasing distance. How much? The physical limit is that a grazer beam, wavelength lambda, emitted by a circular aperture, wavelength R, spreads out through an angle roughly lambda/R in size, where the angle is in units radians. For a 1 Angstrom grazer and a 1 meter wide aperture, the angular spread is about 10^-10 radians, meaning the beam will have added a meter to its size, doubling its diameter, at a distance of 10^+10 meters or ten million kilometers. At a distance of a billion kilometers, 10^12 m, the beam will be 100 meters across.

Says who?

Those aren't lenses made of physical, optical material. Those are gravitic lenses, using physics we don't know anything about.

It also stands to reason that if such a huge graser mount could have been done, it would have been done on OWPs and forts, with the ability to shoot down an enemy light-minutes away. Since that doesn't exist, there must be a reason why.

Of course, there is this minor issue of targeting.

Which, in addition to all the unknown physics, is a key impediment. Ships won't stay on a steady straight course if shooting from millions of km away is possible. A minute change is enough to evade a beam from 10 light-seconds away. An FTL sensor would cut the 20-second delay to a mere 10.16, but that's still too big.

tlb wrote:It has been discussed before; the major parameter is the Rayleigh length, only after that distance is exceeded does the beam diverge linearly with distance. The last time I worked it out for Honorverse energy weapons it was somewhere around a light-minute (see the post indicated below).

However energy weapons in the Honorverse do not actually have the effective range that the theory indicates that they should. The author limits them to thousands of kilometers, I believe. This has been mentioned a various times in the forum.

(Spoilers) Future Technological Developments

Energy range in the Honorverse is decreed to be 500,000 km against a target protected by sidewalls or 1,000,000 km if the target lacks protective sidewalls.

Though that sidewall range will vary a bit depending on the relative strength of weapons and sidewalls involved -- an SD can blow through a DD's sidewall at somewhat further range than the DD can get anything through the SD's.

(And then laser head range has recently increased from 30,000 km to 50,000 km; at least for the cutting edge navies)

ThinksMarkedly wrote:

phillies wrote:The physical limit is that grazer beams spread out with increasing distance. How much? The physical limit is that a grazer beam, wavelength lambda, emitted by a circular aperture, wavelength R, spreads out through an angle roughly lambda/R in size, where the angle is in units radians. For a 1 Angstrom grazer and a 1 meter wide aperture, the angular spread is about 10^-10 radians, meaning the beam will have added a meter to its size, doubling its diameter, at a distance of 10^+10 meters or ten million kilometers. At a distance of a billion kilometers, 10^12 m, the beam will be 100 meters across.

Says who?

Those aren't lenses made of physical, optical material. Those are gravitic lenses, using physics we don't know anything about.

It also stands to reason that if such a huge graser mount could have been done, it would have been done on OWPs and forts, with the ability to shoot down an enemy light-minutes away. Since that doesn't exist, there must be a reason why.

Of course, there is this minor issue of targeting.

Which, in addition to all the unknown physics, is a key impediment. Ships won't stay on a steady straight course if shooting from millions of km away is possible. A minute change is enough to evade a beam from 10 light-seconds away. An FTL sensor would cut the 20-second delay to a mere 10.16, but that's still too big.

The question is: A ship moving at constant acceleration is no harder to hit than a ship that is stationary. 600 gees is 6000 m/s^2meaning in ten seconds the ship changes its position by 300 kilometers relative to no acceleration.How fast can a ship change its acceleration? Also, the ship must accelerate in the direction its wedge is pointing. How rapidly can that direction be changed?

phillies wrote:As an alternative, large-aperture grazers. The idea is to increase the effective range, by a lot.

The physical limit is that grazer beams spread out with increasing distance. How much? The physical limit is that a grazer beam, wavelength lambda, emitted by a circular aperture, wavelength R, spreads out through an angle roughly lambda/R in size, where the angle is in units radians. For a 1 Angstrom grazer and a 1 meter wide aperture, the angular spread is about 10^-10 radians, meaning the beam will have added a meter to its size, doubling its diameter, at a distance of 10^+10 meters or ten million kilometers. At a distance of a billion kilometers, 10^12 m, the beam will be 100 meters across.

Someone will say, what about the inverse square law? If I double the distance, don't I cut the power density by a factor of four?

The key issue there is: Double the distance *from what point*? The relevant point is not the front of the laser. It's not the back of the laser. It is behind the laser, for the system here, ten million kilometers behind the laser.

If you make the aperture 10 meters across, you reduce the angular spread by a factor of ten.

Of course, there is this minor issue of targeting.

Because the effective range in the Honorverse is so much less than the Rayleigh length for even small grasers, the question of spreading never really arises. Instead grasers are built in different sizes for different sized ships to increase the power output; for a given energy density the wider beam carries more power. For example in chapter 5 of Honor Among Enemies we find that Honor's Q-ships will be equipped with SD sized energy projectors:

But the undeniably fertile imagination of Hemphill's allies in BuShips had given her Q-ships some advantages the Peeps had never thought of. For one thing, their energy batteries would come as a major surprise to anyone unfortunate enough to enter their range. The Peeps' Q-ships had settled for projectors heavy enough to deal with cruisers and battlecruisers, but Hemphill had taken advantage of a bottleneck in the superdreadnought building schedule. Weapons production had gotten well ahead of hull construction, so Hemphill had convinced the Admiralty to skim off some of the completed lasers and grasers sitting around in storage. Wayfarer had barely half the energy mounts of her Peep counterparts, but the ones she did have were at least three times as powerful. If she ever got close enough to shoot anyone with those massive beams, her target was going to know it had been kissed.

phillies wrote:The question is: A ship moving at constant acceleration is no harder to hit than a ship that is stationary. 600 gees is 6000 m/s^2meaning in ten seconds the ship changes its position by 300 kilometers relative to no acceleration.How fast can a ship change its acceleration? Also, the ship must accelerate in the direction its wedge is pointing. How rapidly can that direction be changed?

Sufficiently fast, apparently. We know that slewing the wedge is possible because that's how ships turn and that it's faster than turning with thrusters, so even if you can only accelerate 600 gravities in one direction, you do have some perpendicular acceleration possible, which would change the direction of your main acceleration vector.

The ship doesn't need to move at 100% acceleration all the time either, though that is only a useful trick if it's performing a zig-zag course in the first place. If it's coming roughly straight at the beam emitter, changing the amplitude of the acceleration vector doesn't help evading the beam.