As with other component tower modules, the SAM tower can function even when low on power. It has a lower rate of fire than the Hover MLRS, but has a much higher health, able to survive a bombing run from an Orca bomber with timely repairs. Three SAM towers would be enough to reliably shoot down an Orca bomber or a Banshee.
References
↑Stojsavljević, Rade, and O'Miley Ryan. Command & Conquer: Tiberian Sun: Operations Manual. Las Vegas, Nevada: Westwood Studios, 1999.