Having read "Stick and Rudder" years ago has me curious about the flight characteristics of the CRS-16 booster. Airplanes and rocket might be different, but they both have to negotiate atmospheric forces. The last couple of days I've noticed several terms being used to describe this booster event. Both Elon and Scott Manley reference the distressed booster as spinning, suppose like a top, which seems accurate from an observers perspective. Flat spin or inverted spin (tail first reentry), also not sure if any of these terms work. The reference to spinning may create a misleading connection with the type of aerodynamic spin usually associated with a stalled aircraft. At this point I don't think we have the evidence (SpaceX does for sure) to determine whether any of the grid fins were stalled or generating some lift, albeit asymmetric.
During the descent there is noticeable pitch and yaw instability, yet the most obvious problem occurs along the longitudinal axis, normally associated with rolls. On this axis the grid fins appear to work much like ailerons. Not sure if the hydraulic failure leaves them somewhat loose in the slipstream or frozen. Video seems to indicate the fin on the right jammed in a hard-over position. During his post flight press briefing Hans Königsmann stated the vehicle was rolling. Tim Dodd also uses the word roll in his video explanation. Thoughts? Would also love to learn more on this topic from SpaceX.
Near term these reentries will remain exciting, for some us that will be always be the case. Watching a rocket slam backwards into the atmosphere, then stick the landing, nothing compares. And good luck to Blue Origin. It'll be interesting to see where they are on the booster return learning curve when they eventually get into orbit.
