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GNIRS Recovery

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Picture of the Gemini Near Infra-Red Spectrograph.

GNIRS being hoisted at Gemini South.

Special Call for Proposals at Gemini South to fill GNIRS Bright Time

GNIRS: What Happened

At the end of April, GNIRS was warmed up for routine cold head service. In the process of servicing the cold heads, the fast warm-up system and vacuum pumps were left on over the weekend; this has always been the normal operating procedure.

The GNIRS fast warm-up system has been used on the order of a dozen times without incident. The system has a completely independent controller that shuts off power to the heater resistors when the temperature set point is reached. It is independent of all other Gemini and GNIRS software. For some unknown reason the controller failed, resulting in continuously heating GNIRS until it reached temperatures near 200° C for an undetermined period of time. The fast warm-up system did not have thermal fuses or circuit breakers.

When Gemini staff arrived on Monday, they recognized there was a problem and shut the heaters off. They then allowed GNIRS to passively cool for several days with the pumps running. After the instrument had cooled, the dewar was opened and the main components inspected by a team of Gemini engineers and scientists. The “Phase 1” assessment was carefully planned with input from the NOAO staff that built GNIRS.

After the initial inspection, it was obvious that some components were damaged, but many were clearly fine. Interestingly, vaporized plastic and resin condensed on the window, the outer vacuum jacket and radiation shields, which were the coolest parts (near ambient temperatures). Much of the interior was relatively clean of condensation.

In summary, the science detector, detector mount*, OIWFS detector*, fiberglass struts, plastic delrin spacers, filters*, window* and some sensor diodes were damaged. Asterisks indicate components for which spares are presently available.

The dewar and optical bench, most mechanisms, wiring, motors and electronics appear to be okay. As of May 11, we are still uncertain about the status of the gratings, the optical coatings and surfaces of the diamond turned mirrors, the cold head displacers, and the slit mechanism (delrin). These will be inspected in detail shortly.

Picture showing the contamination formed on the inside of the window.

Contamination on the inside of the window was an early indication that all was not well in the dewar.

Pictures demonstrating the structural damage that GNIRS suffered.

GNIRS suffered some structural damage to the fiberglass struts that support the full weight of the optical bench.

Picture showing an example of some struts cracked.

The fiberglass resin did not survive the baking and some of the struts cracked or broke.

Photo of the engineers inspecting the instrument.

As the engineers looked deeper, the full extent of the damage started to become apparent.

Picture showing some melted plastic.

Everything with a low melting point melted.

Picture of melted plastic in certain parts of the instrument.

In particular, the delrin plastic spacers used in filter wheels and lens assemblies melted, and will need to be replaced. The filters and possibly some other optics may need to be cleaned or re-polished and re-coated, or replaced if necessary.

Picture of the Science detector with hole in it.

Unfortunately, the science detector was lost. Note the holes in the InSb Aladdin 3 detector—a close inspection shows the bump bonds and MUX underneath. Indium has a low melting point, and the array was damaged beyond repair.

Indium is used to bump-bond the InSb detector to the underlying Si multiplexer. Indium is also used as an electrical insulator connecting the cold strap to the detector mount.

Picture of wiring, connections and insulation that appear have survived the incident.

The wiring, connectors, and insulation all appear to have survived.

GNIRS: The Next Phase

We are now entering the second phase of damage assessment, including testing all the motors and wiring. We are also testing possible techniques for cleaning the optics and other surfaces. The composition of the residue is being identified at a lab in Santiago. We are carefully examining everything in greater detail and looking into procuring replacement parts, including a new Aladdin array. To help us with the full assessment, Jay Elias (the GNIRS PI, NOAO) and John White (Gemini-North instrumentation engineer) have been on Cerro Pachón working with the Gemini-South team of engineers.

GNIRS: Recovery Plan

Once we have a full assessment of the damage, we will know what work needs to be done to bring GNIRS back to full functionality. At that point we will decide where to perform the work, and whose help will be needed to do it. It is worth emphasizing that GNIRS is not lost—the vast majority of its parts are fine. The work to fix GNIRS will be significant, though, and it will take several months. At a minimum, we will need to rebuild the fiberglass supports and reassemble the instrument. We will need to inspect the cooling systems. Some of the optics will need to be cleaned, and some may require re-polishing and re-coating. All the optics will have to be realigned and the mechanisms tested. A new array will be installed, tested, and characterized. Finally, we will recommission GNIRS on the telescope.

Gemini’s multi-instrument queue provides flexibility in dealing with the temporary loss of GNIRS. An agreement with NOAO to leave Phoenix at Gemini for the rest of 2007 is being negotiated. A special call for proposals was issued inviting proposals for additional bright-time programs using GMOS, T-ReCS and Phoenix. NICI commissioning is under way now, and the NICI campaign may begin in 2007B when NICI commissioning is complete. These will all be important steps to insure that the full scientific potential of the telescope is met while this unfortunate setback with GNIRS is fixed. GNIRS is one of our most important facility instruments, and we are optimistic about getting it back on line as soon as practical.

GNIRS has been a very productive instrument and has produced some excellent science as indicated by the following links:

We will make every effort to bring GNIRS back to science operations in a timely manner.

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