When you can’t just call Safelite to fix your windshield….

Car owners all either know what it’s like to see a rock hit their windshield, leading to them having to get it either filled or replaced, hopefully with an insurance payout rather than out-of-pocket, or they *will*.  With foreign object debris all over the place on the roadways, it’s inevitable.

It’s also inevitable in space, and far more dangerous — and more complicated to resolve, since it’s not like a guy in a van can just pull up, whip out some suction cups, and pop the old windshield off before popping in a replacement.  MMOD (MicroMeteoroid Orbital Debris) strikes are a routine fact of life in space, so when the only bay window ever sent into space went up, it was built to take some punishment.  In addition to featuring solid, armored shutters over each window, the Cupola’s windows are designed to take a beating from MMOD and still maintain the crew’s safety.  They are quadruple paned, with a pane of glass on the outside to take debris damage, a pane of glass on the inside to take scratch damage, and two 25mm thick panes of glass that can maintain the station’s pressure.  (It only needs one, but a second pane is provided for redundancy; if one fails, the other will hold the pressure.)  And they’ve even been designed for servicing; there’s a kit for replacing an entire window without depressurizing the whole station.  So, in a way, you can get Safelite up, except it’s not really Safelite, it’s the astronauts themselves, using a kit that would be flown up in one of the cargo ships (probably Dragon, with its ample unpressurized “trunk”) and then attached over the window during an EVA to maintain the station’s pressure while the window gets swapped out from the inside.

Just recently, during the Cygnus docking activities, astronauts noticed a new ding in the exterior debris pane of one window.  It’s been deemed insufficient to recommend replacement of the window, but they are going to keep the shutter over that window closed as much as possible, to protect against additional strikes that could further damage the debris pane.  It’s reassuring to know that the ISS crew knows what kinds of problems may come up, how to diagnose and deal with them, and exactly how worried they need to be at any time.  😉



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