Vacuum adhesion of Starbug fibre optic positioning robots in high-altitude ground-based astronomy instrumentation

Starbugs are self-motile fibre optic positioning robots developed by AAO-MQ. MANIFEST (MANy Instrument FibrE SysTem) is a facility class Instrument which will operate up to 900 Starbugs on the Giant Magellan Telescope (GMT). The FOBOS (Fibre-Optic Broadband Optical Spectrograph) Fibre Positioner is a facility class Instrument which will operate up to 1800 Starbugs on the Keck Telescope. Starbugs deliver an optical payload to the location of an astronomical object on the telescope focal plane. The Starbugs are made from a pair of concentric Piezoceramic Tubes (PZT), and a high-voltage waveform is applied to the PZT to create an actuation. Staging of the waveform creates successive microsteps, on the order of 3-20 mu m each, at a driven frequency of 100Hz. The Starbugs are adhered to the Glass Field Plate (GFP) using an ancillary vacuum system, which must provide sufficient adhesion force to maintain the Starbug GFP position in the high-altitude environmental conditions at Mauna Kea (MKO) and Las Campanas Observatory (LCO) sites. The minimum vacuum adhesion requirements to achieve Starbug GFP position were used to specify the vacuum pump flow rate and operational head pressure. The vacuum adhesion requirements were experimentally obtained using the Starbug Test Stand, located in Sydney, Australia. The Starbugs Test Stand vacuum adhesion requirements were parametised for dry air mass flow rate and head pressure, and then corrected for the 95th percentile environmental conditions at MKO and LCO. The vacuum system numerical model was verified by the TAIPAN instrument. When corrected for ambient atmospheric conditions at the UK Schmidt Telescope (Siding Spring Observatory, Australia), the numerical model could predict the steady state vacuum pump speed with 1.29% variation from the measured vacuum pump speed recorded by the TAIPAN Instrument control software. This capability of the numerical model will be used for real-time condition monitoring of the Starbugs Instruments.