Thursday, August 25, 2016

Installing the hexapod anti-gravity system

Janus has produced a master(ful) document describing all the many things that need to be checked, mapped & updated once the payload & instruments go back up.  These include the telescope pointing, the auto-collimator offsets, the FIF offsets for the different HRS fibres, all the fiducials based on fold mirror positions, the various guide probes, etc etc.  Getting all of that right as soon as we get back on sky is the secret to a happy ending to the shut-down.  While better throughput & reliability will be wonderful, enthusiasm is quickly lost if the telescope's not properly functional afterwards!  Hugely important too are all the RSS tests that were done before the instrument came down & which will be repeated before it goes back up - Astro Ops is responsible for reducing those data & checking that everything's back where it belongs before the instrument leaves the spectrometer room.

Janus briefing Ant & Paul on The document while √Čric reduces RSS test data
While that was happening in the control room, Johan, Nicolaas & Eben were busy up on the tracker installing the new hexapod anti-gravity system - aka the HAGS.  This looks a bit like knee-replacement surgery for the tracker, but in fact the new hexapod motors will only be installed early next year.  This temporary dislocation of the legs was necessary to allow the springs assemblies associated with the HAGS to be fitted near the apex of each pair of legs.

Johan supporting the lower section of the detached hexapod leg
This is the second of the 3 pairs of legs to be done, & the last set does not include the luxury of working from the relatively ergonomic tracker platform.  

This would be a tough enough job to do if the tracker was on the ground!
The idea is that the powerful springs push up on the tracker's non-rotating structure to unload some of the weight that would otherwise be on the ball-joints.  This will make the tracker more comfortable by relieving some of its joint pain...

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