Abstract:  The resolving power of space-based telescopes and other remote-sensing spacecraft is dictated by the wavelength of light in which it observes and the diameter of its collecting area (i.e. the primary mirror). To ensure that diffraction is the only limiting factor in performance, the entire optical path of the telescope must be accurate to a fraction of a wavelength of light – often 10s of nanometers over 10m class structures.  This challenge is further complicated by the need to cryogenically cool the telescope such that thermal emissions from the spacecraft do not overwhelm the target signal.  Active mirror technologies can overcome these challenges by providing in-situ wavefront correction capabilities to compensate for a variety of optical errors. In this talk I will provide an overview of the design, manufacturing, and testing of two lightweight active mirror technologies.  The first is based on thin carbon fiber laminates along with a sequence of functional layers to produce a multi-layer structure.  The second implements lightweight silicon carbide substrates with discrete stack actuators.  Details on the performance of these structures as well as methods to control their shape will be provided.  Considerations for operation at deep cryogenic temperatures will also be presented, including studies to develop zero-dissipation actuators.  In the second part of this talk, I will detail the design of a custom wavefront sensor capable of estimating mirror figure errors to sub-nanometer precisions.  The sensor, which implements the phase-contrast technique, modulates phase variations into intensity changes that can be readily sampled by a pupil-viewing detector.  An overview of the system, numerical predictions on its precision limits, and preliminary experimental results will be presented.

Biosketch:  Dr. John Steeves is a researcher at NASA’s Jet Propulsion Laboratory (JPL) in the Advanced Deployable Structures Group. Prior to joining JPL, he completed his PhD at the California Institute of Technology under the guidance of Professor Sergio Pellegrino where he developed active composite mirrors for future space telescopes.  His research interests are centered around the design, manufacturing, and testing of lightweight precision structures with a particular focus on those that have a high degree of integrated actuation capabilities.  At JPL, Dr. Steeves is responsible for a number of technology development efforts related to future space-based telescopes including active mirrors, cryogenic actuators, advanced metrology systems, and starshades.  He also serves as a design team member on several ongoing NASA proposals including the Origins Space Telescope (OST), the Habitable Exoplanet Imaging Mission (HabEx), and the Galaxy Evolution Probe (GEP).