I'd like to know how they cut/released the tether, and if there's any fallback in case 1st release attempt fails. The entire mission is fucked if the tether release failed, or if the sky crane tries to fly away while still tethered.
They use explosive bolts that attach the tether to the deck of the rover. They're almost 100% fool proof. Here's a Wikipedia entry, they're called pyrotechnic fasteners and NASA uses a lot of them.
I don't know how they achieved it specifically, but there is a moment in the broadcast[0] they did where they show the umbilical on the rover and mention that it was cut. I'm curious as well how they did it!
