Gentleman John said:
Hmm. Not quite. As I remember things, the sand cloud had a velocity based on the initial velocity of the launching vehicle The tactic then was to come in behind the sand and allow it to degrade laser fire from an enemy in a known position. No need to know when your enemy is going to fire. But you do have to worry about it blocking your fire.
Yep, in Mayday and Book 2 CT, a sandcloud has the same velocity as the ship that launch it. In Mayday, there are sandcloud counters that move, in a straight line, after being deployed.
I spoke with LKW one time about sand back when I used to participate on the TML. He said that the sand was Marc's idea, and that he envisioned their use kinda like depth charges, adapted for space.
So, cannisters are launched. The sand explodes and spreads. And, it's up to the pilot to keep the ship between the sand and the enemy ship.
Note that this isn't that hard to do given the distances involved in space combat. You don't need enough sand (volumn) to cover the entire ship. You've just got to get enough out and away from the ship to put a barrier between you and the far, distant, way-the-hell-out-there enemy.
---Ship-----------Sand---------------------------------------------------Enemy
If you hold your thumb up towards the sun, you can block it out. Same principle for the sand. The enemy is so far out there that you only need a little sand to block all incoming fire. If the enemy shifts position, it will take him a long time (minitues to hours) to change the angle so that his shots won't pass through the sand--giving the defensive ship plenty of time to make adjustments.
If you really want to go with sand being a last minute thing for laser fire, the answer is obvious. Just have a laser capable of operating in two modes: a low-power mode to paint the target and a high-power mode to damage it. If you detect the paint, you know you're about to be hit and launch the sand.
What I've said above is the "CT" way of handling sand. Other versions of Traveller have speculated that sand is used in a different method (TNE used the point-defense model, for example).
I prefer the CT explanation. It makes some sense. It's simple and practical. And, I think it's fun to have the sand marker on the hex map. (Or, I just assume the sand is between the ship and the enemy if using Range Band movement).