The next generation of space telescopes will require large, segmented apertures for observations in the near ultraviolet through mid- and far-infrared regions to enable new science ranging from exoplanet characterization to precision astronomical observations that refine astrophysics models. To meet these challenges, we are developing instrumented (strain gauge) surface parallel actuators (SPAs) that are robust and can meet the stringent requirements of mass and cost per m2. We have developed a surface parallel mirror test piece and a set of flexured actuators that maintain compression in the piezoelectric stack elements at all times. The characterization work of these actuators is directed at understanding the performance of flexure piezoelectric multilayer stack actuator operation when embedded in the mirror. To determine the influence functions for each actuator position, we will report the measured stroke/strain and charge/capacitance versus voltage curves for all 42 preloaded actuators. Although designed to operate under close loop control via feedback from the strain gauge initial testing on bare lead zirconate titanate (PZT) stack actuators suggests that by driving the stack to a known domain state we could perform open loop control in the actuators to levels of ± 0.3 μm. We will also report on creep for the actuators and cross actuation for each unique actuator position as well as discuss approaches to mitigating the effect on open loop control error. Thermal studies of flextensional actuators embedded in analog rib structures down to 100K will also be presented.
The Carbon Plume Mapper (CPM) instrument is a high-fidelity imaging spectrometer developed to pinpoint, quantify, and track methane (CH4) and carbon dioxide (CO2) point source emissions. CPM is an optically fast F/1.8 Dyson spectrometer that operates over the spectral range of 400 – 2500 nm with a spectral sampling of 5.0 nm. Three diffraction grating designs were measured in a testbed to provide a reliable prediction of grating performance in a Dyson system to inform CPM grating design. This paper will detail the gratings, testbed design, measurement process, and data used to assess grating efficiency through wavelength (500-1700 nm) of three grating designs, both full aperture and sub-aperture for two field angles, polarized and unpolarized.
The next generation of space telescopes will require large segmented apertures for observations in the near ultraviolet through mid and far-infrared regions to enable new science ranging from exoplanet characterization to precision astronomical observations that refine astrophysics models. Recent concept studies, such as LUVOIR, HabEx, and Origins, and the future IR/O/UV Large Strategic Mission telescope for exoplanet characterization and general astronomy discussed in the 2021 Decadal Survey "Pathways to Discovery in Astronomy and Astrophysics for the 2020s” include segmented telescopes that are capable of observations in UV through IR bands and thus drive the need for optical surface performance at cryogenic temperatures. These spaceborne mirror applications require precision control, and these segments will require actuators for controlled surface displacements capable of operation at cryogenic temperatures (<150 K). This paper presents a testbed mirror design to test out new actuators and control strategies. This work is directed at understanding the performance of piezoelectric multilayer stack actuator operation down to 100 K, which will provide actuator designers the critical information needed to model and predict performance. The data reported down to 100 K include: displacement/strain and capacitance as a function of applied voltage, stiffness, hysteresis, blocking force, DC resistance measurements, thermal strains, and the coefficients of thermal expansion as a function of the electrical boundary conditions. The actuators include a strain gauge to allow for closed loop control. This approach allows for a comparison of potential open-loop control drive strategies and associated errors reported in previous work. Surface actuation measurements using flexure-based actuators on aluminum mirror segments at room temperature will also be presented. In addition, we will present techniques to optimize displacement per voltage using amplified piezoelectric flexures and the potential to develop mirrors that can be operated at cryogenic temperatures by carefully choosing flexure materials and geometry.
NASA’s next flagship mission, the Nancy Grace Roman Space Telescope, is a 2.4-meter observatory set to launch no later than May 2027. Roman features two instruments: the Wide Field Imager and the Coronagraph Instrument. The Roman Coronagraph is a Technology Demonstration that will push the current capabilities of direct imaging to smaller contrast ratios (∼10−9) and inner-working angles (3 λ/D). In order to achieve this high precision, Roman Coronagraph data must be calibrated to remove as many potential sources of error as possible. Here we present a detailed overview of the current plans for the Nancy Grace Roman Space Telescope Coronagraph Instrument Observation Calibration Plan, including identifying potential sources of error and how they will be mitigated via on-sky calibrations.
Primary mirror segment shape correction via Warping Harness (WH) control adjustment is key to obtaining the required image performance of the Thirty Meter Telescope (TMT). We analyzed two separate experimental activities to better predict the segment WH performance. First, we took measurements of WH influence functions and Singular Value Decomposition (SVD) modes on a prototype TMT segment and compared these to model predictions. Second, we applied the TMT control algorithm on-sky at the Keck Observatory during their segment exchange and warping activities. We then used these measurements to improve our WH control simulations to include the observed effects. Altogether, the prototype segment measurements, on-sky TMT control algorithm measurements, and detailed simulation helped to better predict segment correction performance for TMT.
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