A spectacular sunny, still, gorgeous day in Sutherland... Just as well, or else the new door panels for the HRS enclosure would've gone tumble-weeding across the Karoo & we hate it when that happens.
Once the doors are done, the guys will install the floor panels & we'll be able to clean up that room & unwrap the tank!
Most of the day's action was in the clean room where we managed to finish assembling the grating. Jürgen hunted down all the bits needed to set up the exposure meter mirror while I finished installing the last 4 adjusters on the grating cell.
This is the top of the grating with its 3 tip/tilt adjusters. The window in the middle is where the grating's counter-weight assembly attaches. The vertical line through the centre is the gap between the 2 sections that make up the grating mosaic. This is the ideal place to put an exposure meter mirror since it won't be stealing any light that comes off the grating.
Here's that very mirror - attached to a jig to prevent it from getting bent or twisted. This tapered sliver is made of aircraft-grade aluminium, diamond-turned to produce the appropriate spherical figure.
No space for a fragile sticker!
It's about now that our cortisol & adrenaline levels began to spike - working directly above the impossibly vulnerable grating surface which could no longer hide beneath its protective cover.
A perfect fit - the tiny mirror practically disappears in the gap in the centre of the grating :)
With the exposure meter mirror in place, it was time to check that mounting it had not introduced any kind of twist, since that destroys the output image quality. So, once again we had to tip the grating over onto its side - all the while being extremely careful not to grab anywhere on the optical surface!
A light source was used to illuminate a parabolic mirror, which directed a collimated beam onto the grating & exposure meter mirror.
The exposure meter mirror then produced an image on a make-shift screen positioned near the parabolic mirror. The fact that this image was round at best-focus & similarly elongated on either side of focus confirmed that the tiny mirror was not being twisted.
Just to prove that HRS really is a spectrograph, here are a couple of "spectra" seen while the grating was being illuminated!
Happy with the installation of the exposure meter mirror (visible here as the dark strip centred in the yellow gap), we could proceed with the counter-weight assembly. Although this wasn't quite as bad as fiddling around near the optical surface, one is painfully conscious of how easy it would be to drop one of the small bolts into "the coffin"!
Yet another crafty mechanism, designed to offer enough degrees of freedom to allow the counter-weight to move freely while still being securely attached to the grating.
This is the part that the shaft that holds the counter-weight will attach to. The big brass weight will go on once the grating's been installed in the tank as there's no need for extra weight &/or complexity at this stage!
This brought us to the final & most terrifying stage in the grating assembly process: having to lift, invert & tilt the coffin before bolting it to the base structure - all with the grating surface maximally exposed...
This must be one of the cleanest engine hoists you'll ever find!
The process included attaching lifting eyes & straps to the coffin, positioning the engine hoist, lifting the assembly & placing it over a pair of rails securely bolted to the optical table. Next, the grating was very gingerly tipped/rolled over so that the optical surface ended up facing downwards rather than to one side.
With the whole unit resting comfortably on the rails (& us feeling much happier about having the delicate surface somewhat more protected facing downwards) we could undo the straps & attach them to the other set of lifting eyes on the top surface of the cell. Also good to check that the grating surface is still there ;)
The straps were then arranged so as to tip the coffin up when lifting it. Thus it would be at roughly the correct angle for the docking exercise that was to follow. That too was non-trivial as it required stabilising the suspended grating & keeping an eye (but not a hand!) on the optical surface. As well as the little ears belonging to the exposure meter mirror, all while positioning the base & then lowering the coffin into position before bolting the two parts together.
So there we have it: the heart of the instrument! One last pic before attaching the cover...
All done & safe at last! The remaining challenge was for Jürgen & I to try to calm whatever was left of our frazzled nerves...
A bottle of wine went down well between the six of us (team photo below), along with dinosaur steaks & pancakes for dessert.
All in all, a Fine day!
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