This is a Vela mission. She goes through the tongue door and then the life door. Go through an opening in the glowing-window room and fly up onto the top of that room. This leads into Cortex. Don't forget to go through the holes to pick up some tribals.

Blast through each membrane, grabbing more tribals along the way. You'll get into the central area with the platforms. Time your jumps to get up to the top. The Oxygen tank is up near hte top. Head all the way back out. There's a life force door at the end.

You'll hit a big guy, a few random rooms, and another big guy. Now you'll hit a room with water. Swim through the underwater tunnel. You'll get to the specialist magazine, which you need to get into the mines. There's a Floyd mission in here too, to collect DNA strands.

Jet Force Gemini Walkthrough