I always assumed it was Professor Anders, who lifted the ring up as she did at the end of HW2. This is why the ring is still mostly intact.Another thing, I have a suspicion that Chief is the one who is trying to light the ring, not Cortana as so many people believe. The reason is to destroy the domain. We see this in the trailer where Chief walks into the control room and what else can he be there for other than to light up the ring? It’s so obvious, or at least it always has been to me. It’s possible Cortana somehow intervened and and annihilated the section of the ring with the control room. How she does this I’m not sure. Maybe with a Guardian.