Bitterman is now much closer to the Big Gun, yet there is one more obstacle in his path - a major Strogg power plant. Taking it out would severely disrupt the enemy defences.
The reactor, however, cannot be destroyed directly. Its coolant system must be disabled first, so that it would overheat. Then, the waste disposal facility must be shut down as well, so that the power plant is flooded with toxic sludge. Only then will the reactor fail and blow up, opening the way to the Big Gun.