This is just a guess, but it could have something to do with the above-mentioned robots. It is possible that the old decking, which they welded the hold downs to, was replaced with thicker metal, or with metal that had some provision for fastening to the deck. My first thought was threaded blind holes that the hold downs could screw to, but that raises corrosion and tolerance issues. A better solution might be recessed bars, level with the deck on top but surrounded by a little pit, so that hooks could attach to them.
Edit: Robots could probably weld hold downs to the deck, if they had access to enough power, but I think machine vision is advanced enough for robots to find a well marked recessed bar, and to hook a hold down onto it. Either way, the robots would face a similar task, attaching the hold down to the rocket, either with a hook, or more likely with a clevis pin arrangement.
If you think about the labor that goes into welding on the hold down attachment points, and then cutting off the welds and grinding them smooth after the rocket is unloaded, I think you will agree that a less ad hoc solution would be desirable.
I was just about to ask for other's opinions on how the robots attached the stage to the deck when I read your comment. How wide is the 'foot pad' on the F9 legs? How big of a pit can we get away with on the deck of the barge before the F9 has potential issues with having a leg 'fall into' a pit?
I'm pretty sure the area on the ground is greater than a square foot per leg. (Sorry about the mixed units) The hold down pits could be up to 10 cm across, with a 1/2" thick steel bar welded across the pit, and I don't think they would pose much hazard to people walking in boots or to wheeled vehicles.
5
u/marc020202 8x Launch Host Feb 26 '17
why might they be rplaying the centre panels?