May 21, 2018 - The Auxiliary Telescope for LSST has arrived safely on the summit of Cerro Pachon, and its heaviest parts have been lifted into its enclosure building by crane. Meanwhile, in Tucson, preparations are being made for the assembly and testing of the calibration equipment that will be mounted on the Auxiliary Telescope (AT) in order to measure atmospheric transmission during LSST operations (as described in this recent news item). In early May, twenty-three shipping boxes containing the cryostat and associated peripherals arrived at the Project Office workshop in Tucson. The cryostat contains the sensor that will be used to image spectra from the AT’s spectrograph. The spectrograph is also being built in Tucson and is scheduled to arrive at the Project Office workshop soon.
A team led by Telescope and Site Calibration Hardware Scientist Patrick Ingraham is currently testing the cryostat system, and successfully imaged a 1951 US Air Force resolution test chart to demonstrate the cryostat and sensor survived shipping. The cryostat is a Telescope and Site deliverable that was constructed in Boston, capitalizing on the expertise of individuals from several institutions. Dr. Chris Stubbs, Harvard physics professor and current member of the LSST Project Science Team, is the Principal Investigator for the cryostat system. Project manager Kirk Gilmore and software scientist Tony Johnson from SLAC are currently in Tucson preparing the system for integration with the spectrograph instrument.
Inside the cryostat is a sophisticated 4K x 4K detector that has a cutting-edge, highly-segmented design which allows it to read out data from a light source in less than 2 seconds. Additionally, the detector is thicker than previous versions, making it very sensitive to red photons and allowing it to detect light in the near-infrared spectrum.
The cryostat, which works like a big, double-walled thermos, insulates the detector and the cooling system inside the cryostat keeps the area around the detector at about -100 degrees Celsius (-150 F). The extreme cooling reduces heat-caused noise that could limit the sensitivity of the detector. The low pressure in the cryostat also prevents condensation from forming on the detector.
When the spectrograph arrives it will be attached to the detector, allowing for full calibration of the system using a spot plate and telescope simulator, which imitates what one would see when observing light from a star. The detector will record the light, and display the image data on a computer screen for the team to analyze.
The cryostat and spectrograph will be shipped from Tucson to Chile at the end of 2018. When the full system arrives on Cerro Pachon, it will be assembled on the bottom floor of the AT enclosure for testing, and then mounted on the Auxiliary Telescope in time for the AT’s engineering first light, which is currently scheduled for early 2019.