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