MOONS update - end-to-end testing of science configurations with FPUs
05 Apr 2024



MOONS front end systems integrated and tested in science operations scenarios.

Two scientists in front of MOONS rotating front end.



MOONS rotating front end which looks a complex bit of machinery made up of concentric circles and sensors.There are two major components to MOONS (the Multi-Object Optical and Near-infrared Spectrograph) the cryogenic spectrograph, which contains all the cameras and detectors, and the rotating front end, which is the interface of MOONS with the Very Large Telescope. 

While smaller than the eight-ton instrument, the rotating front end is still two tons and 2 meters across (around the same size and weight as an average hatchback car) and contains a significantly larger number of moving parts. Most notably 1000 FPUs (Fibre Positioning Units), each capable of independent movement to reach different science targets (stars or galaxies) in each position of the sky, enabling MOONS to simultaneously observe up to 1000 of those objects at a time.

Unsurprisingly, coordinating the FPUs to ensure seamless operation is incredibly complicated. Two motors in each FPU manoeuvre them into the right position and, while the instrument software system tracks each one of these movements, there is a metrology system that works out exactly where each FPU is at any given time, when required. Twenty acquisition cameras send corrections to the telescope pointing to ensure that the FPUs are well aligned on the sky at all times. The rotating front end is also equipped with a calibration unit that can illuminate the fibres with well-known lamps, allowing astronomers to remove instrumental effects from their collected science data.

Astronomers using MOONS will use a dedicated Observing Preparation Software to create their observations by inputting various parameters such as target coordinates, telescope offsets, observation time, and any required calibrations. All this information is stored in what is called an Observing Block and sent to the Very Large Telescope in Chile.

Astronomers can formulate these Observing Blocks months in advance and then, when it is time for these observations to be done, the MOONS Software is in charge of orchestrating the full process and streamlining the operation of all the MOONS components. This complete end-to-end operation has now been successfully tested in the lab at UK ​ATC.

Gregor Soutar, Software Engineer at UK ATC, said: “We moved all of the fibre positioners to their scientific targets for the first time; matching scientific configurations on the sky, on fields MOONS astronomers will want to observe. Component parts of this process had been tested in isolation, but here they were successfully operated as one unified system. Our lab setup at UK ATC in Edinburgh allows us to emulate the MOONS control room as it will be at Paranal, making it possible to thoroughly test the functionality of the instrument. Moving the fibre positioners to scientific targets represents a significant milestone for MOONS and is the culmination of many years of work, from an inspiring team of people. The only thing we can't do yet is gaze into the skies above the Very Large Telescope in Chile through MOONS, that is still to come."

Find out more about MOONS.