Week 15 of the Early Operations system optimization period
No nighttime observations were acquired with the Simonyi Survey Telescope this week.
Late last week, the team observed elevated vacuum pressure within the LSST Camera (LSSTCam) cryostat relative to baseline, and increased current draw from the ion pumps that are used to maintain vacuum during normal operation, indicating a likely vacuum leak in the LSSTCam cryostat. Out of an abundance of caution, the team paused nighttime operations while gathering further diagnostic data. The team localized the probable site of the vacuum leak using targeted helium sprays, and then conducted a definitive test by squirting a small amount of alcohol near the suspected leak site, one of the vacuum feedthroughs into the LSSTCam cryostat. By adding alcohol to the site, the leak was (temporarily) completely blocked, sending the vacuum pressure down to its baseline pressure under good operating conditions. The blockage by the alcohol shows that low viscosity material can wick deep into the “crevasse” and fully block the leak. Rubin Observatory and partners at SLAC and NOIRLab have identified a suitable sealant that is expected to permanently seal the leak. To summarize, the vacuum leak is localized, is reachable in the current hardware configuration, and there is a plan to permanently seal the leak with a readily available sealant material. LSSTCam remained safe throughout this period.
After the sealant has been applied, the material will be allowed time to cure, and cryostat vacuum levels will be closely monitored to establish nominal operations. Once the repair is confirmed, the team would resume nighttime observing.
During the current downtime, the team conducted tests using multiple configurations of the currently operational dome louvers to study the thermal environment and ventilation within the dome.