Multilayer active shell mirrors for space telescopes

Abstract

A novel active mirror technology based on carbon fiber reinforced polymer (CFRP) substrates and replication techniques has been developed. Multiple additional layers are implemented into the design serving various functions. Nanolaminate metal films are used to provide a high quality reflective front surface. A backing layer of thin active material is implemented to provide the surface-parallel actuation scheme. Printed electronics are used to create a custom electrode pattern and flexible routing layer. Mirrors of this design are thin (< 1.0 mm), lightweight (2.7 kg/m 2 ), and have large actuation capabilities. These capabilities, along with the associated manufacturing processes, represent a significant change in design compared to traditional optics. Such mirrors could be used as lightweight primaries for small CubeSat-based telescopes or as meter-class segments for future large aperture observatories. Multiple mirrors can be produced under identical conditions enabling a substantial reduction in manufacturing cost and complexity.An overview of the mirror design and manufacturing processes is presented. Predictions on the actuation performance have been made through finite element simulations demonstrating correctabilities on the order of 250 − 300× for astigmatic modes with only 41 independent actuators. A description of the custom metrology system used to characterize the active mirrors is also presented. The system is based on a Reverse Hartmann test and can accommodate extremely large deviations in mirror figure (> 100 µm PV) down to sub-micron precision. The system has been validated against several traditional techniques including photogrammetry and interferometry. The mirror performance has been characterized using this system, as well as closed-loop figure correction experiments on 150 mm dia. prototypes. The mirrors have demonstrated post-correction figure accuracies of 200 nm RMS (two dead actuators limiting performance).

Next-generation active telescope for space astronomy

“…Larger apertures and shorter wavelengths require better wavefront control (WFC) to reach a diffraction-limited focal spot and here active segmented mirrors are an enabling technology. Observations into the mid-IR require cool optics-Spitzer, Herschel, Planck, and WISE point the way-and technology demonstration active mirrors 27 have demonstrated function down to 28 K. These mirrors have also shown that cryogenic mirrors need not be figured (polished) at cryogenic temperatures but can be built using room-temperature processes and will have the desired optical figure when cooled. 29,30 Depending on the launch vehicle, the telescope is then boosted to Sun-Earth L2 or carried there within the Starship bay.…”

Review on thermal and mechanical challenges in the development of deployable space optics

“…15. The CoreSat mounts two fixed mirrors, whereas the MirrorSats hold a thin-shell CFRP deformable mirror as described by Steeves et al 113 The large deformable mirrors are mounted on a 3 DOFs platform (piston, tip-tilt) for coarser rigid body motions, providing very high authority control. Reattachment of the MirrorSats is achieved through an electromagnetic docking mechanism, which makes the MirrorSats fall into a Kelvin clamp, which provides a repeatable reattachment.…”

Optics technology for large-aperture space telescopes: from fabrication to final acceptance tests

“…25 is the 0.42 m in diameter, demonstration prototype, active primary mirror for the LATT project. Another example of an active primary for space applications relies on a multilayer active shell approach for a CFRP substrate, with a sheet of piezo material as the active layer [225].…”