A Masking Screen (aka "Mask") is created when a ship releases a cloud of water vapor into space. The vapor crystallizes and forms a protective cloud surrounding the ship.
Besides making the ship more difficult to hit, a masking screen absorbs energy from a laser. If a ship is hit by a laser while masked, the normal amount of damage is divided in half (fractions are rounded up). The result is the number of damage points inflicted on the target ship.
A masking screen has exactly the same effect on a laser fired out of the screen as it does on a laser fired into the mask. If a ship surrounded by a mask fires its lasers, resolve the attack as if the defending ship is masked.
Another drawback is the explosive pyrotechnics (technically, subatomic fusion) created, should the mask be intersected by a necro-beam. If this happens, the amount of damage rolled is doubled (fractions are rounded up). The result is the number of damage points inflicted on the target ship.
A screen lasts as long as the ship travels in a straight line at its current speed. If a ship or space station in orbit around a planet creates a masking screen, the mask will last though one complete orbit.