MICADO is the Multi-AO Imaging Camera for Deep Observations, a first light instrument for the Extremely Large Telescope (ELT). It will provide the ELT with diffraction limited imaging capacity over a ~53-arcsec field of view, while operating with the Multi-Conjugate Adaptive Optics (MCAO) module MAORY (0.8-2.5 μm). Here, we present the design status of the MICADO derotator, which at the same time serves (i) as crucial mechanical interface between the cryo-opto-mechanical camera assembly and the instrument support structure and (ii) as high-precision image and wavefront sensor derotator to allow for 50 µas astrometry over the entire MCAO corrected field. Additionally, first test results are presented which were obtained with a derotator prototype based on a scaled 1:2 test bearing. The derotator test stand is essential to explore the limitations of the preferred bearing type in the context of the given requirements. The technical difficulties addressed by the design include: (i) design of adequate mechanical interfaces to minimize mass, deformation and the effect of the warping moment on the bearing and (ii) analysis of the friction-related stick-slip effects at low tracking velocities for the implementation of a suitable position-velocity closed-loop control system. Furthermore, our prototype setup is used to develop and test the required control concept of this high-precision application.
This paper describes the development of a Carbon Fiber-Reinforced Plastics (CFRP) structure for the interferometric instrument LINC-NIRVANA (LN) at the Large Binocular Telescope (LBT) Arizona, USA. This structure carries all components between the two "bent" Gregorian foci of the individual telescopes necessary to combine the light of the two arms coherently.
Especially developed for aerospace and defence, CFRP materials now find widespread use across a number of other applications where their special properties are beneficial. We will profit in LN from the good rigidity, high strength, low thermal expansion, low mass and high damping properties of CFRP.
An extended Finite Element Analysis was performed to simulate the properties of the structure for different telescope positions and different temperatures.
We built a 560 mm x 550 mm x 385 mm test piece of the LN optical bench for flexure tests to confirm the results of the Finite Element Analysis.
The complete LN instrument with a mass of 7.5 tons will be mounted at a tilting unit to simulate the different telescope positions.