A Multifunctional Structures Approach for Deployable In-Space Optomechanics
Michael Echter, PhD Defense
Friday, March 30, 2018
The DISCIT (Deployable In-Space Coherent Imaging Telescope) research effort at MIT Lincoln Laboratory seeks to develop a 0.7 meter diameter deployable sparse-aperture primary-mirror telescope that leverages advances in HSC (high strain composite) deployable structures and piezoelectric actuation technologies. A system such as DISCIT could provide affordable, high-resolution, persistent space-based imaging in a low-SWaP (size, weight, and power) design over existing technologies. A key challenge with deploying a sparsely filled primary in an imaging telescope is the precision required to collocate the mirror segments relative to the other optical components. The research presented here expands upon the underlying DISCIT architecture of HSC hinges by integrating piezoelectric patch actuators with the structure itself to induce in-plane strains for post-deployment shape correction, creating a multifunctional structure for deployable in-space optomechanics.
An outline of multifunctional and deployable structures will first be presented, providing an overview of deployables for in-space applications and the techniques traditionally used. A look at how DISCIT previously implemented HSCs for precision deployables follows and the novel, active HSC hinge with integrated actuation will be introduced. Both simulation and experimental testing were used to design the active HSC hinge, starting with mechanical testing of the composite material for developing several finite element models. The validation of these models will be described along with a custom algorithm that was written for selectively placing the actuators to control specific degrees of freedom for precision optical alignment. Experimental testing and results will be presented which showed the deployment precision of the active HSC hinge to achieve better than 2.5 micrometers piston and axial positional repeatability and 20 microradians pitch and roll angular repeatability. Finally, a preliminary closed loop controller demonstration will be discussed for a single degree of freedom, which achieved an actuation resolution of better than 25 nanometers over a 15 micrometer range.