...In SS3 per page 15 a die roll of 12+ is required for sand to incapacitate a missile.
In CT Book 2 page 17 sandcasters are defensive weapons designed to counter act the strength of incoming laser fire, there is no mention of the effects against missiles.
CT Book 5 page 18 states that sandcasters project a granular agent which obstructs light; when fired it interferes with incoming laser or energy weapon fire. The only place I found that sand affects missiles is on the Missile attack table, of course I probably missed the text.
Mayday when the target is in a sand cloud gives -1 DM against missile fire.
Based on the three of the above details a missile that can lock on to another missile has, I feel haven't tested the concept though, a better chance of taking out the incoming ordnance.
Your analysis is correct:
In Mayday, where a missile has about a 6 in 36 (1/6) chance of missing a ship (and where a missile can be shot at another missile with a 10/36 chance of hitting, which is a feature I liked), the sand gives the missile a -1 to its to-hit roll (effectively increasing the chance of a miss from 6 in 36 to 10 in 36).
In Book 2, where a hit is certain if the missile can intercept the ship, sand doesn't do anything to missiles. However, there's an awkwardly worded rule that states, "During the ordance launch phase, missiles
or sand which contacted a target in the preceding movement phase now explode or take effect." There's nothing that describes what "effect" sand is supposed to have, and the idea of sand moving and contacting a laser beam is absurd, so I interpret that as meaning at one time they were toying with the idea of having sand have some effect on missiles and then later dropped that idea, leaving that remnant as the only clue. Supplement 3 then tacks on a 1 in 36 chance of sand disabling the missile, per 25mm sand cloud.
Book 5 then re-introduces sandcasters as a significant anti-missile weapon: "Missiles must achieve the to hit number (or greater) on two dice. If a hit is achieved, then sandcasters, beam weapons (laser and energy; each type uses the beam section), repulsors, and dampers must be penetrated ..." The table gives a single missile a 10 in 36 chance of missing (exclusive of computer, size or agility), and it gives a battery of sandcasters about a 1 in 6 chance of disabling an equal factor of missiles.
So, it varies from a 6 in 36 chance of a miss to a certain hit on intercept to a 10 in 36 chance of a miss, with the sand either increasing the chance of a miss to 10 in 36, having no effect at all, giving a 1 in 36 chance of a miss, or increasing the chance of a miss to roughly 14 in 36 (26/36 * 5/6 = 21.667/36).
It's interesting how they had such widely different views of how missiles and sandcasters should work.
I was actually thinking more along the lines of anti-missile missiles deploying titanium or depleted-uranium kinetic-kill pellets in a shotgun pattern at waves of incoming missiles.
There was an antimissile concept where the antimissile missile instead spun out a kind of metallic net, with the idea that the inbound missile would hit the net with about the same effect as if it had hit that shotgun pattern of pellets.
Your idea works best in Mayday, where there's already a rule for missiles intercepting missiles and you just need to do something like throw in a bonus to-hit for your shotgun-antimissile.
It works in High Guard too, just use the sandcaster table to determine the roll needed to penetrate the antimissile volley. Only trick there is you'd have to declare beforehand, perhaps in the Precombat Decision Step, how many of your missile batteries were loaded with antimissiles, but you'd have to introduce some method to do it without announcing it to the opponent before combat, since he shouldn't know which of your missile batteries were loaded with what until the shooting happened - knowledge beforehand might influence his choice of targets.
For Book 2, it doesn't really say that you
can't shoot missiles at missiles. It just says missiles explode or take effect when they contact a target, and since missiles are moved about just like ships, it's conceivable you could maneuver a missile to intercept another missile. Iin that case, there's no difference between a specialized antimissile and any other missile and therefore no benefit in introducing a new missile type. Unless I've been misunderstanding that all these decades.
Along the lines of a true anti-laser sandcaster-missile, I would suggest a 1G1 engine just to get the sand clear of the ship and a warhead to disperse the cloud. This offers the advantage that for a few credits more per shot than a dedicated sandcaster, a ship can change 30 missile launchers into 30 sandcasters by simply reloading the missile racks. I think that sort of tactical flexibility would be useful ... offense when you want it and defense when you need it.
I like a versatile sand/missile launcher, never understood why they didn't do that in the first place. Sand canisters weigh the same as missiles in Book 2; given that the missiles are spacegoing and don't have to be specific dimensions to achieve aerodynamic ends, strikes me it wouldn't be terribly difficult to make a launcher that suited both.
