DescentBB

In the area where you get the yellow key, there is a cache of weapons and an invulnerability sphere. You can enter by either end and when you enter the end that takes you directly into the area where you can see the cache, the exit is sealed over by a grate until you enter the tunnel at the other end of the room. If you shoot through the grate, then fire a guided missile, you hit a switch and that open the entrance at the other end of the cache area. I thought that once you hit that switch, you could open the door to the cache area but I cannot open it. Is there another switch?

OK, so this is more than a month since you asked the question. I only just now read the question...

On PlanetDescent I posted some instructions on getting to that cache.

Here's a linky