This was conducted remotely from the Hilo Base Facility . We continue to prepare for commissioning .
GMOS-S Bubbles Eliminated !
A long-standing problem affecting the Gemini Multi-Object Spectrograph ( GMOS ) performance has been resolved recently . In GMOS a special optical oil is used between the different lenses to minimize interface surface effects , particularly loss of throughput by partial reflection , and degradation of image quality . Over time , minuscule leaks cause bubbles to appear in the interfaces between the lenses . Many of these bubbles can be filled again with small amounts of optical oil , as has been done on both GMOS North and South on several occasions . However , the lenses in the collimator assembly are embedded within the instrument , not allowing access to the filling ports — unless the instrument is disassembled , something which had never been done before . Yet this was the task before us .
To access the filling ports , a complete disassembly was required . We first designed and built an opto-mechanical alignment set-up , with a combination of lasers and detector read-out and alignment telescopes used to reference the collimator in its original position . After several months and a thorough study and characterization of the problem , the team spent a lot of time rehearsing the alignment techniques , until they felt confident enough to dismantle GMOS .
The mask mechanism , on-axis wavefront sensor probe , and the collimator were then taken out of the instrument . With the collimator now on the bench , the first step was to modify the system to allow for future filling without taking the instrument apart again . After that , we used a special set-up ( combining a small vacuum pump to extract the air , and a filling system to inject new optical oil ) to fill the bubbles . We then reassembled the instrument , confirming at every step the alignment and mechanical repeatability .
The results as measured with the detector all fell well within specifications ( the goal was to be within a 10 pixel difference , and there was a 4-pixel difference with respect to the starting position ). After the telescope shutdown , we fully checked and released the instrument for operation again .
Gemini South Shutdown Completed
Gemini South completed its annual telescope shutdown on August 31st . Some additional mechanical support staff from the National Optical Astronomy Observatory joined in — an example of sharing resources , which we expect to continue . The shutdown ’ s main objective was to carry out preventive maintenance on the acquisition and guidance unit ( A & G ). Excellent teamwork and cross-training ensured this system is ready for another year ’ s observations . Apart from the regular maintenance , an encoder on the science fold linear stage mechanism was replaced , restoring redundancy and skew detection functionality . After working in the lab to prepare the spare cable wrap motors , we replaced both motors for the elevation wrap , since one of them was drawing high currents . This marks the conclusion of an important task within our reliability program .
On Saturday August 18th , a full facility shutdown was required in order to install new cabling to the uninterruptible power supplies . Some time ago these units ( feeding the data center among other things ) were replaced with higher capacity ones , but the cabling prevented their use at full capacity . A small portable generator provided emergency power for some lighting at the work locations . The data center was switched off and all instruments powered down and started
20 GeminiFocus October 2018
This was conducted remotely from the Hilo
Base Facility. We continue to prepare for
commissioning.
GMOS-S Bubbles Eliminated!
A long-standing problem affecting the
Gemini Multi-Object Spectrograph (GMOS)
performance has been resolved recently. In
GMOS a special optical oil is used between
the different lenses to minimize interface
surface effects, particularly loss of through-
put by partial reflection, and degradation of
image quality. Over time, minuscule leaks
cause bubbles to appear in the interfaces
between the lenses. Many of these bubbles
can be filled again with small amounts of
optical oil, as has been done on both GMOS
North and South on several occasions. How-
ever, the lenses in the collimator assembly
are embedded within the instrument, not
allowing access to the filling ports — unless
the instrument is disassembled, something
which had never been done before. Yet this
was the task before us.
To access the filling ports, a complete disas-
sembly was required. We first designed and
built an opto-mechanical alignment set-up,
with a combination of lasers and detector
read-out and alignment telescopes used to
reference the collimator in its original posi-
tion. After several months and a thorough
study and characterization of the problem,
the team spent a lot of time rehearsing the
alignment techniques, until they felt confi-
dent enough to dismantle GMOS.
The mask mechanism, on-axis wavefront
sensor probe, and the collimator were then
taken out of the instrument. With the colli-
mator now on the bench, the first step was to
modify the system to allow for future filling
without taking the instrument apart again.
After that, we used a special set-up (com-
bining a small vacuum pump to extract the
air, and a filling system to inject new optical
20
GeminiFocus
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