From LSST: “LSST’s Auxiliary Telescope”


Large Synoptic Survey Telescope

February 6, 2018


In tandem with LSST’s construction on Cerro Pachón, a smaller telescope will soon be assembled on nearby calibration hill, a short distance away from the main LSST Facility. LSST’s 1.2-meter Auxiliary Telescope will measure atmospheric transmission, which refers to how directly light is transmitting through the Earth’s atmosphere in a given spot, as opposed to being absorbed or scattered. Because the presence of certain molecules and particles in the atmosphere will change the color of light detected by the LSST telescope, data collected by the Auxiliary Telescope, as it mirrors the nightly movements of LSST, will inform the catalog corrections that need to be made to LSST data in order to render it more accurate.

Elements in the atmosphere that affect how light is detected by a ground based telescope like LSST include water, oxygen, and ozone, as well as aerosols like sea salt, dust from volcanoes, and smoke from forest fires. The presence and quantity of these elements varies from night to night, so the Auxiliary Telescope will provide this important complementary data for LSST throughout survey operations. According to Calibration Hardware Scientist Patrick Ingraham, “Having a dedicated auxiliary telescope supporting the main telescope is somewhat unique, and it will increase the quality of data produced by LSST.”

The Auxiliary Telescope itself wasn’t built from scratch; it’s an existing telescope that has been repurposed for its role in the LSST survey. Since being moved from its original location on nearby Kitt Peak in May, 2014, it’s been housed in the workshop at LSST’s Project Office in Tucson, AZ. Refurbishment work has included replacement of all the telescope’s electrical parts including the motors and the position encoders, which record the exact position of the telescope at any given time. Mechanically speaking, the telescope is largely unchanged. Its mirrors, which were removed while work was done, will be recoated and replaced once the telescope arrives on Cerro Pachón; they are currently in separate protective crates that will protect them during shipping.

Currently, the subcontractor working on the refurbishment project is almost finished with the wiring of the telescope’s electrical components. Once that’s complete, the telescope will undergo functional testing of its mechanical and electrical systems. Individual tasks that make up this testing include driving the telescope toward its upper and lower limits and ensuring the system will shut off before those limits are reached (preventing damage to the telescope), testing for excessive vibration, and testing the speed at which the telescope slews, or moves from one spot to the next. Extensive functional testing is critical now, because once the telescope is on Cerro Pachón there won’t be sufficient facilities to easily make repairs. Optical testing of the telescope will occur after the telescope is installed in its facility on the summit and re-integrated with its mirrors.

Once the telescope is officially ready to be shipped from Tucson to Chile, the individual telescope assemblies will be packed in custom crates, and these crates will be loaded into a shipping container. It will take about 2 months for the shipping container to get from Tucson to Cerro Pachón. Once there, the telescope will be installed in a few pieces, with a crane, through the dome of its facility on calibration hill. Photos of the Auxiliary Telescope in the workshop , as well as the facility on Cerro Pachón (link is external), can be viewed and downloaded from the LSST Gallery.

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LSST telescope, currently under construction at Cerro Pachón Chile
LSST telescope, currently under construction at Cerro Pachón Chile, a 2,682-meter-high mountain in Coquimbo Region, in northern Chile, alongside the existing Gemini South and Southern Astrophysical Research Telescopes.

LSST Interior
LSST telescope, currently under construction at Cerro Pachón Chile.

LSST/Camera, built at SLAC
LSST/Camera, built at SLAC

The LSST is a new kind of telescope. Currently under construction in Chile, it is being built to rapidly survey the night-time sky. Compact and nimble, the LSST will move quickly between images, yet its large mirror and large field of view—almost 10 square degrees of sky, or 40 times the size of the full moon—work together to deliver more light from faint astronomical objects than any optical telescope in the world.

From its mountaintop site in the foothills of the Andes, the LSST will take more than 800 panoramic images each night with its 3.2 billion-pixel camera, recording the entire visible sky twice each week. Each patch of sky it images will be visited 1000 times during the survey. With a light-gathering power equal to a 6.7-m diameter primary mirror, each of its 30-second observations will be able to detect objects 10 million times fainter than visible with the human eye. A powerful data system will compare new with previous images to detect changes in brightness and position of objects as big as far-distant galaxy clusters and as small as near-by asteroids.

The LSST’s combination of telescope, mirror, camera, data processing, and survey will capture changes in billions of faint objects and the data it provides will be used to create an animated, three-dimensional cosmic map with unprecedented depth and detail , giving us an entirely new way to look at the Universe. This map will serve a myriad of purposes, from locating that mysterious substance called dark matter and characterizing the properties of the even more mysterious dark energy, to tracking transient objects, to studying our own Milky Way Galaxy in depth. It will even be used to detect and track potentially hazardous asteroids—asteroids that might impact the Earth and cause significant damage.

As with past technological advances that opened new windows of discovery, such a powerful system for exploring the faint and transient Universe will undoubtedly serve up surprises.

Plans for sharing the data from LSST with the public are as ambitious as the telescope itself. Anyone with a computer will be able to view the moving map of the Universe created by the LSST, including objects a hundred million times fainter than can be observed with the unaided eye. The LSST project will provide analysis tools to enable both students and the public to participate in the process of scientific discovery. We invite you to learn more about LSST science.

The LSST will be unique: no existing telescope or proposed camera could be retrofitted or re-designed to cover ten square degrees of sky with a collecting area of forty square meters. Named the highest priority for ground-based astronomy in the 2010 Decadal Survey, the LSST project formally began construction in July 2014.