After almost two years in orbit at asteroid Bennu it’s nearly go time for OSIRIS-REx—or, should I say, Touch-and-Go time! Later today, October 20, starting at 1:50 p.m. EDT (17:50 UTC) the van-sized spacecraft will begin its descent toward the surface of Bennu, culminating in the attempt to siphon up at least 60 grams of…