Detail of the darker-colored ablator at the center the APS engine thrust chamber. Compare with the
on display at the Cradle of Aviation.
This is the second APS thrust chamber (i.e., the one which was inaccessible
when I took the previous batch of photos); once tipped over, the light
available in the interior of the engine was more favorable than the other.
The line going down the side at about the 8:00 position appears to be a water
stains, rather than any sort of structural damage. I understand that the
thrust chambers were acquired by the former Michigan Space & Science Center from a
federal surplus action at Johnson Space Center, where they'd been located in a
back storage area, so it's possible that the discoloration happened long ago.