Trying out new hardware for the M2 test

Upon our return yesterday, we were greeted by one of SALT's resident Rock Kestrels - she didn't seem entirely convinced that we ought to be here...

Our goal for the week is to test the new hardware for the M2 test.  This includes the new solid carbon fibre Faro probe extension which will allow us to reach otherwise impossible places...

  

The other new piece of gear is the target carrier that will locate within the hole in M5 to mark the optical axis of M2 for the null test.  The target carrier consists of a base that seats in the hole via a set of spiral-arm like flexures.

  

The next layer is a translation stage, that also relies on flexures, for adjusting the target in decentre...

  

& lastly, on top - the actual target holder part that includes a tip/tilt adjustment mechanism.

  

Since a change is alleged to be as good as a holiday, I went over to the far side of the plateau to see what Geoff's been up to in the electronics workshop during his standby week... It appears he's been keeping busy building a nifty new rack for SALT!

First fringes off M2!

We don't yet have all the hardware we need for the M2 test, but we can do a rough-&-ready trial run to check that it'll work as planned...

 

Here's the test frame carrying the interferometer, fold mirror & null lens.  A laser beam's sent out by the interferometer & bounced off the fold mirror that directs it through the plano-concave null lens, up to M2.  There the beam's reflected back through the system & returned to the interferometer where, if all goes well, fringes ought to be produced.

  

A flat paddle mirror on the back of M2 (the same one used to align M5 way back when, although now with a hole added to its centre) is used to get M2 squared up in tip & tilt & aligned in decentre with the optics onboard the test frame.

  

After making rough measurements of the axial spacings & adjusting the null lens & interferometer to get the despaces right - success!!  The first fringes from M2 :)  It's too soon to interpret the interferogram as nothing was aligned to anywhere near the proper tolerances - this was, afterall, just the "let's see if we can do this" week...

 

Great job guys!

Gearing up for the M2 test

Summer in the Hex River Valley - grapes Everywhere!  A truly beautiful scene in this magical place...

 

Meanwhile, in the clean room we're getting everything ready for the M2 null test.  Here's the fold mirror going into its cell.

  

The SAC's tilted to the operational angle of 37 degrees for the test & needs to be securely locked down in this position.

  

Before trying to align anything, we made sure all the hardware fits & works - first the fold mirror at the bottom of the test frame...

  

Then the null lens in its cell, attached to its kinematic mount.

 

So far so good - tomorrow we'll set up the interferometer on the frame & have a go at firing a laser through the system!

Taking M3 off!

The new engine hoist passed its load-test this morning so we're ready to remove M3 today! 

The M3 removal jig was set up & the relevant modifications were made (thanks Eben!), we'd run through the procedure check-list so everything's ready to go...

  

The clean room's more crowded than usual with the hoist & the M3 storage box in there as well.

The bolts attaching the M3 cell to the rest of the cage were removed & the 4 operators could then simultaneously, & very gingerly, crank down the car jacks to lower M3.

  

Once low enough to clear the cage, the cell was slid out along the "railway track" on its pair of "skateboards".

Proud fathers Francois & Ockert were there to greet the new arrival...

 

Hmmm - Almost as filthy as M5 was!

  

M3, still attached to the skateboards, leaves the rest of the SAC behind...

  

The lifting handles & straps were attached once the mirror was safely covered up.

 

With the hoist supporting the payload, the posts connecting the cell to the skateboards could be removed.  The precious cargo was then wheeled back to make space for the box M3 will live in for the next while.

  

Gently lowered into its snug new home...

 

At this stage it was time to take a closer look at the latest (& final!) SAC escapee - 60 kg of Zerodur with a spectacularly beautiful (surface) figure!

 

The attentions of a fish-eye lens turned M3 convex for a while...

But all reverted to normal once the 24-120 mm was replaced & the mirror cover prevented further bulging.

Lastly, the lid was bolted down & the box parked in a quiet corner of the clean room.

By now, having had 3 of its 4 mirrors extracted in the past few months, the corrector must be lamenting its poor performance & wondering what further indignities might lie ahead...

With M3 out the way, we got our first unobstructed view of M2 (looking up from below with a fish-eye lens in this shot).  From next week our attention will be on this mirror as we begin gearing up for the M2 null test!

M3 sprouts more buttons

To add to our stash of M3 metrology, we decided to attach Faro buttons to the flange where the M3 cell bolts on to the rest of the SAC cage.  Since we'd used up all the invar buttons we had, it was time for a change of style - enter "the peanut-clusters"!

 

Each is a set of 3 ball bearings, epoxied so as to provide a location point for the Faro probe.  5 pairs of these buttons were then glued to the top & bottom of the flange (within reach of the Faro when it's stationed on its lower base) & held in place by piranha clamps while the epoxy cured.

  

In its usual position, the Faro's attached to the same ring as the SAC & so there's no problem of relative movement between the 2.  However, when the Faro's down on its lower base (to reach the bottom end of the SAC), everything has to be Very solidly locked down.  Ockert to the rescue with some extremely beefy bottle screws, nothing floppy about this design!

 

Getting ready for M3 metrology

Most of the effort this week's gone into planning & preparing for the removal of M3. 

The other challenge has been to calibrate & test a new, extended Faro probe that will allow us to access the back & outer diameter of M2 through the SAC cage.  This is necessary in order to set up the coordinate system now that the pizza pan's in place near the top of the SAC, blocking our usual access.

The longer probe's quite tricky to handle so it's a team sport...

 

The calibration process is a real patience tester!

Fortunately we're insanely persistent so the humans did eventually triumph :)

Here we go again...

Happy New Year everyone!  We returned to the clean room today & were treated to one of Sutherland's more spectacular sunsets :)

Next on our list is the removal of M3 so that we can carry out the M2 null test...  That's going to be Quite a handful so there's a lot of planning & preparation to be done this week to make sure we're ready for all that.