Remember to save before you board the ship, as there's no way back this time. Clear the aliens in the chamber where you arrive, then head into the narrow corridor to the north-west. The platform there will take you to a recharger and switch 1. After flipping this switch, head for door A which is now open. Head on for a while until you reach a large room with a radioactive section in the center. Switch 2 is hidden on an inside wall of this section. Hit it, then flip switch 3 behind door B. Door C has been opened, leading to a large circular area. Jump off the side, find switch 4 to the north, and flip it. After that head to the south end of the room, where an elevator is located. This elevator leads to a corridor with a 3x recharger, as well as also taking you back to the upper level of the circular area. Pass door D and follow the long corridor that awaits you. Open the door when you reach the end, open the door there. Behind it is a maze-like area, with switch 5 to the west, and door E to the east. Of course you need to flip switch 5 before you can head for door E.
In the corridor that follows, a much-needed recharger is superbly hidden in a corner, so first stop to use it before going to the platform a few steps further. Stepping on the platform activates it and will take you to a dark, doughnut-shaped room. There are many niches here containing ammo, however, only the two southern ones hold doors. (Hint: there are several tanks here, but if you're quick getting through this room you can outrun them easily. Braver players should, of course, stay and kill the lot of them.) The north door leads to the reactor control room. When you arrive, flip switch 6 to access circuit panels 7, 8 and 9, which will destroy the reactor core.
Hurry back to the corridor you used to get here and return to the
doughnut-shaped room. This time use the door/lift in the south niche,
which will take you back to the circular area with the radioactive
pit. Retrace your steps all the way back to the chamber you arrived
in, from where you can now teleport out. Now on to Electric!