Thursday, March 31, 2011

Popping segments in & swapping RSS bits

Janus & Luis are still working on the guidance system - both in the hardware & software departments.  This is a critical aspect of the telescope's functionality & something we'd really like to get going before RSS goes up next week.

In the meantime, Jonathan, Hitesh & Denville went about replacing one of the mirror mounts that'd suffered a broken flexure.

One gets a sense of the relative ages of the mirror coatings in this low-angle view of the segments.  It really isn't nearly as bad as this looks, a camera flash at this angle is particularly unflattering to even the cleanest of surfaces...

These mirror installations call for incredibly careful cherry-picker driving & Jonathan's got it taped!

Hands reach up from below the truss & guide the mirror into place.

Then 3 threaded rods attached to the mount from below prevent any clocking of the segment while it's being lowered into place..

Here are the cleanest segments along the bottom edge of the array.

Sinking into position...

The primary's way too much fun to photograph!

Very cool (almost) symmetries...

Once in position, a segement can be aligned to within about 50 arcsec in tip/tilt, just by matching it to its neighbours as viewed from the catwalk.  That's enough to get it within the course alignment capture range for the CCAS instrument.  The piston (Z) needs to be set with a spherometer which measures the height of the mirror with respect to those around it, then a full CCAS alignment takes care of the rest.  Individual segments are aligned in tip & tilt to about 0.1 arcsec & the RMS for the whole array comes out to no more than 0.3 arcsec RMS.

Over on RSS it was time to test the changing of the slitmask magazine, the filter magazine & the Fabry-Perot etalons.  None of them trivial operations, of course, but these guys do enjoy a challenge...

Prof Peter keeps an eye while Keith tries an etalon change.  The etalon handling jig (the contraption hanging from the cable ) isn't Quite ready so for now it's still easier to do this by hand, but the planned mods to the jig will make this a safer & simpler operation - especially when doing this up on the tracker!

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