Also, once you have completed all 3 missions and return to the teleporter, it still won't 'light up' like the others in the desert. From memory (its been a while) you step onto the teleporter and you're set on fire (of sorts), you then need to step on to the 3 circular rocks around the teleporter (doesn't matter in which order).
After that, sit back, enjoy the cinematic, and then, well ..er.. you kill yourself

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Cheers.