Post by Dr. Scott Walter describing why the Starship heat tiles may be falling off:
We learned a lot from examining the half dozen intact tiles that Nick was able to retrieve.
TL;DR: the attachment process is likely flawed, and not the tiles themselves. Here is why.
Nick recovered many fully intact tiles on the beach within days of the launch. He also found some shattered tiles, but those tiles had be run over by cars or trodden by horses on the beach. So it is not clear whether the tiles broke apart on the orbiter during launch, or later after impacting the water or when washed ashore.
Each tile is affixed to the orbiter with three fastener pins. These pins are welded to the orbiter skin, and not likely to easily break off. The suspicion has always been that where the pins affix to the tiles is the weak point. When under load either the tiles fracture, or the anchors rip out, as if in drywall.
But that does not seem to be the case. The image of the back of the intact tile shows the anchors neatly in place with no signs of damage.
Because the tiles were discovered so soon and so close to the launch site, they were likely shook loose from the vibrations of launch, or soon after from aerodynamic loading. If they were fragile, then they should have shattered, or the anchors torn loose. Apparently, they did not. Even after impacting the water (yes they are light, so likely floated down at low velocity), and being roiled in the surf.
If the fastener pins dislodged from the skin, then one would expect to see them still attached to the tiles. They are not. Plus if loading is enough to rip the pin welds off the orbiter, the tiles should have shown damage or the anchors failed ahead of that. Only intensive vibrations could account for that possibility. Not aerodynamic loads.
Mostly likely, where the fasteners clip onto the tiles is unclipping. Why is a mystery. We all know a clip fastener is nearly impossible to remove, and special tools and tricks are needed to unclip. And that's if a clip is even designed to unclip. These clips are likely design to be one-way. They go on, but you can't unclip them.
Could there be some strange vibrational mode that allows the clips to dislodge? Maybe. We know bolts untighten when under vibration, and is the reason for loctite. Still this usually requires a lot of time. To happen seconds or minutes after launch is indicative of an unknown failure mode. Or the clip heads of the fasteners are failing or snapping off.
The other likelihood, is the tiles were not properly snapped on. With 18,000 tiles packed tightly together, it may be difficult to verify proper installation of every tile. It could just be a quality assurance issue. It's really hard to see back there.
Another remote possibility, is that stacking, destacking, tanking and detanking, and thermal expansion are the culprits that start to wiggle the tiles loose prior to launch. Given the multiple attachment points, all the pins would need to cooperate in the process. If one is stubborn it should require the tile to fail, rather than simply slip its bonds.
Unfortunately, we do not yet know how the tiles will perform under the stresses of re-entry. I am confident from thermal management that they will do fine. But they can't do fine if they don't remain attached. We need to see if they are too fragile to survive re-entry loading. But if they can, then the problem may only be the fastener design. If so these tiles remains a viable solution in the near term for Starship until better alternatives are explored.
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