Mission Success Hinging on a Hinge

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One very critical moment in our mission was the opening of the sunshade. The sunshade is a 1/2 inch thick disk of rigid foam core spanned by a bar and held shut by an electrically triggered latch. When the WASP payload reached float and was under coarse azimuth control the latch would fire and the sunshade would open. Should it not open, or only partially open, we would get no images of star fields and the mission would be a failure.

The video below shows the moment of truth. We were unfortunately not able to see the opening live. We were headed back to Boulder but we tried to stop in a Starbucks a few minutes before when we knew it should open to check out the live CSBF webcast. Sprinting in, Jed whipped open Zach’s computer and navigated to the feed. It was past the time the shade should have opened and to our horror it looked like the shade did not open. It should have been flipped up above the baffle. Before Jed and Zach got too depressed, Kevin and Nick shared a little secret they had. Nick watched the opening on his phone and saw something that was quite unexpected.  The sunshade BROKE OFF of the baffle upon opening. That is why it still looked like it hadn’t opened. The WASP team and some people at CSBF called us shortly after to confirm what had happened since we had told them to watch for the opening at the determined time. They saw the same thing, it broke off.

Great! We thought we had just launched a rather large frisbee off into NM from 125,000ft! As it turned out, the sunshade came to rest between our optics and flight computer and stayed there all the way through decent and until recovery. It now resides in a telescope lab of Southwest Research Institute in Boulder, CO.

While we laughed it off at the time, after a bit of thought we hypothesized that this was a material failure of the foam core. We tested the opening of our sunshade multiple times in a CSBF thermal vacuum chamber and hundreds of times in the lab. We suspected this was likely a fatigue failure. It just so happened that on the couple-hundredth time opening, the foam core gave out. When we got the sunshade back that was indeed the case, it was the foam core material itself that failed.

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