The Very Large Telescope array, or VLT, is the top facility for European ground-based astronomy. Consisting of four Unit Telescopes with 27-foot diameter main mirrors and four movable 6-foot diameter Auxiliary Telescopes, the telescopes work in conjunction to essentially form a giant 'interferometer.'

The ESO Very Large Telescope Interferometer lets astronomers see details up to 25 times finer than with the individual telescopes acting alone. Light beams are combined in the VLTI using a complex system of mirrors housed in underground tunnels. The various light paths must be kept equal to distances less than 1/1000 of a millimeter over a total distance of nearly 1100 yards. Precision at such a level means the VLTI can make images with an angular resolution in the range of milliarcseconds. So how precise is that? It basically equates to a resolution ability so fine that it's capable of distinguishing two headlights on a car – across the distance of the Earth to the Moon (or about 240,000 miles).

ESO has recently used 3D printing to prototype molds used to cast two new telescope components for used in the MUSE instrument in Chile which are part of the Adaptive Optics Facility project. The scientists and engineers there say 3D printing techniques offer a critical shortcut to creating the complex custom items often needed in astronomical instrumentation, and they add that they can deliver those components quicker and cheaper.

The German firm voxeljet AG created a structural part for a new sensor arm which was installed in the telescope to work with the MUSE instrument. The sensor arm itself is a metallic structure used to contain three flat mirrors which direct light beams into sensors used to control the active optics systems of the VLT and guide the telescope during observations.

Once a suitable virtual 3D model was made, a pattern was printed from polymethylmethacrylate, a type of thermoplastic. A mold was then created via lost-wax casting to provide a negative of the original shape. The finished piece was coated with a heat-proof ceramic. The ceramic was treated and hardened as the pattern was melted out to leave a ceramic shell which then served as a perfect die into which the aluminum for the final cast was poured.

Previous processes to make the sensor arm used beryllium, a lightweight metal, but as beryllium is highly toxic, it couldn't be safely machined or modified after the component was installed.

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