A fairytale end to a loooong slog!

After quite ordinary weather all of yesterday, things started to improve around sunset - first we were treated to a black eagle flyby & then the sky cleared up :)  The seeing was also better than we've had up here in a long time & so it was that IQ's last night turned out to be a particularly memorable one... 

It was cool too having Paul learning the ropes - seen here receiving the SALT Astronomer Force from The Master, Petri!

But the highlight of the night, & indeed the culmination of the enormous IQ effort, was obtaining this magnificent image (with a freshly stacked primary mirror & great seeing) - stars with full width half maxima of 1.1 arcseconds over the entire field of view!!

We were ready to celebrate with the images obtained the night before, but it was a great privilege to be able to see what the telescope's capable of in good seeing - truly a fairytale end to the IQ campaign!

The big bottle has joined the collection that's marked previous milestones in SALT's life & there will no doubt be more to follow as we edge closer to full science operations over the next 6 months :)

All packed up & ready to go home, Darragh was readily coerced into leaving a note on the front door for the Tech Ops Team that'll be in first thing tomorrow morning...

A picture that's worth a thousand words/hours/days!  & for those who want more of the gory details, see Darragh's latest IQ report to the SALT Board.

We'll be back in about a month or so to throw the party to end all parties!  In the meantime, good luck with the rest of the work guys - it's been an *Absolute Blast* working with you all, it's with heavy hearts that we leave you & this very special place...

Before & After!

Perhaps it's a bit late to be describing what the problem was, but since starting the on-sky testing we've dug out old images & it's worth looking back...  The most serious contributor to the SALT IQ nightmare was the focus gradient, which meant that only a small portion of the 8 arcmin field could be kept in good focus at any given time.  By adjusting the telescope's focus, different parts of the field could be optimised, but always at the expense of other regions.  This in itself was unacceptable, but the focus gradient also exposed a variety of other horrors, including mutilated stars in regions that were out of focus & severe astigmatism.  Finally, there was the hideous notion that all of these woes somehow vary unpredictably due to a combination of factors...  Below is a typical bad IQ image, obtained with the Apogee camera in late September 2007.  Best focus is in the top right corner, the bottom left corner shows the mangled stars & overall the whole lot's just a Mess!

Fast forward through years of extensive detective work, the formulation of an extremely thorough repair plan, the 16 months it took to execute the plan & then wait for mediocre observing condtions to get the image below...  Uniform IQ over the entire field of view - The Focus Gradient Is Gone!! :) :) :)  But the good images aren't stable over time & one can see strange things going on when you take the telescope out of focus - the doubled images that we've dreaded all along!

That's where the auto-collimator instability came in & after fixing up the mount & then attaching the whole lot to the steel collar of the SAC, we obtained really beautiful images last night!  Still no focus gradient & after optimising the auto-collimator offsets, they didn't need to be tweaked throughout the night - the images weren't doubled or distorted any more :)  

What remains is a small amount of astigmatism, which we now know has to reside within the primary mirror (since we've fully re-aligned the SAC & tested the surface figures of its mirrors & found them all to be in great shape).  So that's the next step, but we're down to the finishing touches now! :)

SALT's looking like a telescope again!

We opened up the shutter just before sunset & enjoyed the photography-friendly light while the tracker cast shadow-monsters on the inside of the dome...

Yesterday Jonathan put in four more (very clean!) mirror segments near the bottom of the array.

Eben & Martin installed various dial-gauges (visible just to the left of centre in the image below) to measure the amount of movement between the steel and aluminium collars that attach the SAC to the payload.  Happily, these readings were only of the order of a couple of microns.

The major intervention today was to move the auto-collimator, previously mounted on the NRS, to a new attachment point on the bottom of the steel collar that's bolted to the SAC itself.  The small silver tube can be seen just above the SAC in the pic below.

This ought to improve the stability of the auto-collimator & since the sky looks good, we hope for healthier images later tonight!

Beefing up the auto-collimator mount

During the day Eben & co worked on making the auto-collimator mount a lot more stable than it was & conditions at the start of the night looked promising...

Sadly though, these were the best star images we managed all night, thanks to rapidly deteriorating seeing & then the arrival of a nasty cold front!  SIIIIGH :(

Farewell to a Cape Town landmark

After another frustrating night of hopelessly bad seeing, we packed up & drove back to Cape Town the next morning.  Coming in on the N2 we got a last close-up look at the Athlone cooling towers scheduled to be imploded the next day.  Thanks Tim for snapping this pic while I was driving!

Much of Cape Town turned out to watch, making traffic in the areas with the best views impossible, but a bunch of us watched from the roof of the SAAO.  A brief squall distracted everyone & prompted the demolition team to flip the switch about 4 minutes early - we were lucky to catch any of the action at all!

WOW :)  Google "Athlone cooling towers" for some great YouTube videos of the event!

Encouraging, but puzzling too...

Despite it still being gloomy & overcast by lunch time, the sky cleared up beautifully through the afternoon & straight after dinner we came up to start aligning the primary mirror.

The bizarre weather from yesterday was safely behind us & we settled in for a long night's observing!

The Apogee camera has to be moved around a 3x3 grid to image the entire focal plane of the telescope - shown below is one of the nine images from such a set.  The seeing wasn't ideal for much of the night, but encouraging images were obtained during intervals when the conditions improved. 

However, our excitement was tempered by significant IQ variability on a timescale of a couple of seconds which we don't yet understand.  The most likely source of this instability is the auto-collimator &/or the interferometer - two instruments mounted adjacent to the SAC on the NRS to control its attitude (tip/tilt) & focus (Z)  with respect to the primary mirror.   These pieces of equipment will undergo extensive testing over the next few days...

Bye Bye Okkie!

Although the clean room action's dried up now, there's still plenty going on next door in the spectrometer room where RSS is being put through its paces...

High hopes for getting more data tonight were dashed when the weather packed up spectacularly, much faster than any of us have ever seen!

On the up side though, this facilitated an excellent send-off for Ockert who's off to Wisconsin for a few weeks & then when he returns he'll be based at the SAAO in Cape Town.

In Sutherland, regardless of the temperature, the best conversations tend to happen while standing around outside (preferably close to a fire).

Some kinds of head-gear convey authority & have the potential to inspire respect among colleagues...  But those with huge floppy ears don't so much - we really ought to have done more to protect David & Vic from themselves!

Back in the lounge (on the Winnie The Pooh couch), 3 other bears dealt with the paparazzi in different ways.

& over on the bench - fortunately within reach of a fire extinguisher - these two worked through how to say their painful goodbyes.

All too much excitement for our brave host, who's admittedly been running a little low on beauty-sleep lately...

With friends that leave your house looking like this at 2am, who could blame Ockert for moving back to Cape Town?!

& then there was light!!

The first job for the day was to get the Apogee stage assembly installed on top of the tracker...

A crisp Karoo sunset viewed from the CCAS tower was followed by the squaring up of the camera stage.

A small mirror (the one from the old paddle mirror in fact - flash back about a year for that story) was placed on the stage & the alignment telescope's auto-reflection observed.  Rotating the Rho stage gave feedback for the "Rho Boys" (Charl & Ockert) to adjust the tip & tilt of the camera stage.

With the stage appropriately set up, the Apogee camera was put in position & fired up.

After a primary mirror alignment, the anxious team looked on, willing the telescope back to life as it attempted to track stars for the first time in 16 months... 

Nothing's ever simple in this game, but a while later we had stationary (albeit hugely out of focus) stars in the field of view!

The out of focus images were used to tweak the auto-collimator offsets to reduce coma & then adjustment of the tracker in Z sorted out the focus to give reasonable looking stars.  Sadly, by that stage the seeing had deteriorated to >2.5 arcsec so we couldn't really assess the Image Quality, but overall it was a Fantastic Night & we're keeping fingers crossed for better conditions tomorrow...

A characteristically cautious observation from Darragh was: "Well - we haven't made anything worse!" - which really is quite remarkable when you consider the extent of the SAC interventions & our collective previous experience in this business!

No raptors were harmed during this alignment...

While we drove home on Friday, the guys up here worked on getting the tracker fully operational.  A critical safety mechanism is a set of radial plugs that connect the SAC to the lower frame of the hexapod.  These plugs will pull out & freeze the system if for any reason things try to move beyond the safe envelope.

Once the sun sank low enough this afternoon, we opened up & started working on the alignment.  This led to a charming, but potentially disasterous, encounter with one of the resident kestrels as it decided that the open CCAS hatch might lead to the ultimate nesting site!  With the kestrel hovering just outside the hatch, eagerly peering in, we eye-balled one another from just over a metre apart before the humans in the tower agreed that it was time to close up...  Play was suspended until it was dark enough for all the kestrels to be in bed!

Although there's a perspex cover over the hole in the floor of the NRS (large circle in the image below), we still get to see shiny M5 (smaller circle) below the triangle holding the alignment target!

After we'd finished getting the target co-planar with the Rho stage, using the alignment telescope up in the CCAS tower, the target could be removed.

The cover over the SAC was removed too & the SAC reference mirror bolted on to the back of M4.

The reference mirror could then be viewed with the alignment telescope & the bolts holding the NRS to the Rho stage adjusted to set the tip & tilt of the SAC.

This all went remarkably well so tomorrow we'll be able to hoist the camera stage assembly onto the tracker & get that set up!

Never a dull moment!

Francois & James have been grafting away to get the stage for the Apogee camera all squared up & ready to go.  It'll be put on the tracker as soon as we're finished with the various alignment processes being conducted from up in the CCAS tower.

All the hardware from the SAC work's seriously cluttering up the place so the gang tried to persuade the tank-like installation platform to follow the NRS smiluator (which fortunately travels on wheels) to leave the loading bay.

There was nothing too elegant about the process until Sir Eben rode in on his trusty forklift & rescued the hardware in distress...

After lunch, software engineer Deon - eager to enroll in the local radio-control flying club - was presented with his first plane.  Although lacking some of the characteristic features of an aircraft, the attendant 1.4 kW prop-swinging device promises to compensate for most things...

Preliminary bench tests conducted in the kitchen indicate significant hair-drying potential at the very least!

Next, it was time to take down the primary mirror cover so that we could get back to our alignment work in the evening.

Nice to see that all the mirrors are still there!

The team made remarkably short work of the procedure.  Perhaps it should become part of the daily routine for the SALT Astronomer & SALT Operator on duty to remove & deploy the cover - the way observers on the small telescopes need to open & close their mirror covers every night? ;)

With the primary mirror available to us again, we lugged the alignment telescope & various other bits & pieces back up the CCAS tower & set about getting everything lined up.  Weather permitting, we hope to go on-sky sometime next week!