Friday, July 30, 2010

Deploying the primary mirror cover

This afternoon the guys put up the new primary mirror cover.  This version's much lighter than the one used when the SAC was taken down as it's made of parachute material, rather than thick canvas.  The cover was lifted with the dome crane, then attached to the top beam of the structure by Charl & Nicolaas in the cherry-picker.

They then expertly navigated around to collect the 6 ropes that had been strung up around the structure & tied those to the appropriate attachment points on the mirror sail.

Guys standing on the pier then pulled the respective ropes to unfurl the cover, first the bottom 3 positions (at 4, 6 & 8 o'clock) around the mirror.

Then the top 3 at 10, 12 & 2 o'clock.

The tent-like cover slowly took shape & all the ropes were securely fastened.  The blue section's seen from the high side of the mirror while the rest of the cover's black.

Excellent job everyone - a great way to end a busy week :)  Now we get to take some very deep breaths this weekend, before all the really scary fun starts on Monday...

Thursday, July 29, 2010

A target for squaring up the Rho ring

The alignment telescope & a large optical flat borrowed from Sunspace were used to check the performance of the stage assembly that will move the Apogee camera around the telescope's focal plane.  Some shimming & adjustment will be needed, but otherwise it all looks good.

Next, an alignment target needed to be placed on the tracker to allow us to get the Rho ring (to which the non-rotating structure, that will hold the SAC, is attached) squared up with the telescope's optical axis.  The CGH mount + tip/tilt & decentre actuator assembly was recycled for this purpose.

The mount + target was bolted onto the top of the payload.

In this CCAS tower view we see Charl sitting inside the non-rotating structure, ~13 m below us with the primary mirror a further 13 m below the tracker.  The mirror segments at the bottom of the array have been removed as a safety precaution in preparation for the SAC lift next week.

The alignment telescope in the CCAS tower had been set up on the central segment of the primary mirror so then the tracker was moved to its central position.  The Rho stage was rotated & with feedback from Darragh at the alignment telescope, Charl could mechanically adjust the target carrier. 

The target only had to be aligned with the telescope's cross hair to within the capture range of the target's actuator assembly - the fine adjustment will be done later with the precision stages.

Wednesday, July 28, 2010

The SAC collar shuffle

The dome crane had to be inspected & load-tested before being used to lift anything too interesting...

Then the SAC was carefully wheeled out of the clean room & parked in the loading bay. 

There it could be reached with the dome crane, which was attached to the aluminium ring of the NRS simulator.

The ring was detached from the simulator & the SAC lifted out.

This offered a great opportunity to take a good look inside & some people who've been missing from the real world for a long time slipped out through the hole in M3...

Ah Yes - SAC Man, one of the lesser-known superheroes of our time!

The terrestrial receiver was wheeled into position after plates had been bolted on underneath the steel collar.  The SAC was then lowered into the receiver & the plates bolted to the SAC installation ring.

At this stage the SAC was being supported by its steel collar so then the bearings between the steel & aluminium collars could be removed.  This allowed the aluminium collar (still attached to the aluminium ring of the NRS simulator) to be lifted off & prepared for its new home up on the payload.

Securely mounted in the terrestrial receiver, the SAC was wheeled back into the clean room where it was left to contemplate its future while the team set off in search of celebratory beverages...

Tuesday, July 27, 2010

Out of uniform at last!

With the SAC all sealed up, the clean room's become a civilian zone: no more silly blue outfits!!  There are a number of jobs going on in parallel now, including attempts to characterise the tilt of the chip in the Apogee camera (to be used in the on-sky testing) with respect to the camera's mounting flange.

The Apogee's relatively small detector will need to be moved to 9 positions in order to image the telescope's full field of view, but the advantage is that it contains no optics & thus can't introduce any new aberrations when we test the SAC's on-sky performance.  The electronics guys in Cape Town finished getting the the Apogee's translation stage assembly ready so that came up on the transport today.  Now we can characterise its behaviour & set it up for use on the telescope.

Up on the tracker, the Tech Ops guys installed & checked various bits of the equipment to be used in the SAC re-installation, which now looks like happening early next week...

The necessary mods were made to the SAC installation ring while it was up on the tracker, then it could be re-attached to the terrestrial receiver, in preparation for the SAC collar-shuffling procedure that's planned for tomorrow.

& up in the CCAS tower, we got the alignment telescope set up so that it can be used to align the SAC once its up on the tracker.

Monday, July 26, 2010

Stripping down all the test gear

We've now checked off all the items on the SAC-in-the-clean-room-to-do list!

Here's a last look at the whole production before we hauled off all the decorations: the interferometer, the alignment telescope, the Faro, the NRS super-structure, the braai gear & the SAC's various other life-support systems...

Then a lid was bolted on to the top of the SAC & it now sits waiting, patiently, while we get the clean room cleared out & the rest of the hardware ready for the lift.

Friday, July 23, 2010

Last few clean room jobs

We're still working through our checklist of jobs to do before the SAC can leave the clean room...  Next up: the installation of Blackbeard's Patch - a small baffle that needs to be suspended between M2 & M3.  While not an award-winning photograph, this flash pic does show how effectively the Nextel paint that we used absorbs light. 

The 3 attachment strings were ingeniously caught (fish-style) through the hole in M3 using a hook on a stick which was fed through the sides of the SAC cage.  The baffle was roughly centred  by eye with the 3 of us each tugging on our respective strings.  Then the fine alignment was done with the alignment telescope, by measuring the position of a tiny hole in the centre of the baffle (illuminated from below) & comparing that to the coordinates of the coat hanger reticle.

Removing the Faro labels around the outer edge of M4 had pulled some of the paint off so we opted for a bit of cosmetic touching-up.

With no scale bar in the image, one could be excused for assuming that the next item is one of the Space Shuttle's main engine nozzles...

But it's not.  While waiting for the paint on M4 to dry, we hauled out the very nifty new conical baffle for the central hole in M5 & carefully installed it.

Then took the coat hanger out from between M2 & M5 & put it back in its box for safe keeping.

After that, the paint on M4 was dry & the steering wheel could go back in...

& the repeatability of attaching the SAC reference mirror could be tested.

Lastly, it was time to blow the surfaces of M5 & M3 with compressed air to remove any dust before closing up shop for the weekend.

With all the new baffles in place, we took turns crawling in underneath the SAC & looking up through the hole in M3.  We leave it as an exercise for the enthusiastic reader to figure out what all one sees from this primary mirror type perspective!

Here's a similar view, but taken with a flash this time, & slightly off axis to provide more clues...

Watch this space as we hope to move the SAC out of the clean room on Monday to prepare for its return to the tracker later in the week!

Thursday, July 22, 2010

Fred's Farewell Braai

Another busy day in the clean room with lots of fiddly little jobs being taken care of.  One of the trickier ones was the removal of the small CGH, expertly done by Francois & a pair of nervous onlookers...

Trivial by comparison, but cathartic none-the-less, was the removal of all the bits of yellow duct tape used to label the Faro buttons & other measurement points on all the mirrors & dotted around inside the SAC.

In a meeting to discuss how to proceed in aligning the SAC with the Rho Stage after the corrector's back up on the telescope, it was decided that it'd be great to have a laser that can be set up in the same mount that the alignment telescope uses.  Not long after, Eben presented us with the new hardware that should do the job!

The real business of the day, however, was Fred's farewell party :(  This icon of the SAAO & integral part of the whole Sutherland scene is retiring after 32 years in the observatory game...  Memorable speeches by Darragh, Francois & Fred himself filled us with many wonderful memories & a huge sense of appreciation for the enormous contribution he's made to the SAAO & SALT & to the lives of the associated family of colleagues over the years.

Beer & a braai's never out of season, even in Sutherland in July!

For the record - no one was talking shop...  Really.

Meanwhile, over in the kitchen the conversation was surely even more interesting.

Could Fred & Charl have been comparing mirror alignment stories?  Probably not ;)

Siphelo & Zolisa - our 2 new SALT Operators have been trying all week to get Fred to agree to a brain transplant...

Sutherland said goodbye with a beautiful twilight & a line-up of Mercury, Venus, Mars & Saturn!

The end of an era indeed...  Ons mis vir jou al klaar, Meneer!