D1 Level 21 Oberon Mining Platform help please

[shim]

having problems finding the reactor in Level 21.. im guessing its the center pillar at the top, but when i try and open it, displays this door cannot be opened

http://fourth-chapter.com/Descent/scrn0001.jpg

is there a trigger i need to hit for the reactor doors to open?

thx

[Sirius]

http://moon.descentforum.net/descendarium/d1howto.html

[shim]

much thanks

[Alter-Fox]

I remember the strategy guide walkthrough on this level. It was a bit longer than usual. It's something of an unintuitive puzzle for sure.