Why didn't the Countermeasure nullify the Hammer of Dawn Satellite Array?

Solution 1:

The Imulsion Countermeasure Weapon was created to destroy lambent cells using targeted radiation.

The Wiki linked above states the weapon's range as:

Range: Planet-Wide

The weapon uses targeted radiation, and as our planet's atmosphere blocks out harmful radiation from space, its possible that Sera's atmosphere is very similar, and could act as a barrier for the weapon, confining its effective area to just the planet, not the satellites orbiting.

Gears 5 minor spoilers (from Act 1):

As for how it did not destroy the imulsion in the satellite you launch in the first Act of Gears 5, the satellite you find in the old research facility is a prototype, one that was created before the main imulsion powered satellites the player can use in Gears 1. Thus it could have been created with an impure imulsion power source. It still functions as we see later, but quickly loses connection.