A document discusses a mechanism that uses flex-pivots in a parallelogram arrangement to provide frictionless motion with an unlimited lifetime. A voice-coil actuator drives the parallelogram over the required 5-cm travel. An optical position sensor provides feedback for a servo loop that keeps the velocity within 1 percent of expected value. Residual tip/tilt error is compensated for by a piezo actuator that drives the interferometer mirror.
This mechanism builds on previous work that targeted ground-based measurements. The main novelty aspects include cryogenic and vacuum operation, high reliability for spaceflight, compactness of the design, optical layout compatible with the needs of an imaging FTS (i.e. wide overall field-of-view), and mirror optical coatings to cover very broad wavelength range (i.e., 0.26 to 15 μm).
This work was done by Jean-Francois L. Blavier, Matthew C. Heverly, Richard W. Key, and Stanley P. Sander of Caltech for NASA’s Jet Propulsion Laboratory. NPO-47317
This Brief includes a Technical Support Package (TSP).
Optical-Path-Difference Linear Mechanism for The Panchromatic Fourier Transform Spectrometer
(reference NPO-47317) is currently available for download from the TSP library.
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Overview
The document discusses the development of the Panchromatic Fourier Transform Spectrometer (PanFTS) at NASA's Jet Propulsion Laboratory (JPL), aimed at enhancing Earth atmospheric science through satellite remote sensing. The PanFTS is an imaging spectrometer designed to measure pollutants, greenhouse gases, and aerosols, contributing to NASA's Science Plans and advancing our understanding of climate and atmospheric chemistry.
Central to the PanFTS is a Michelson interferometer, which splits incoming radiation into two paths—one fixed and one variable. By varying the optical path length difference, the instrument produces an interferogram that can be analyzed to reveal the composition of the observed atmosphere. The spectral resolution of the instrument is dependent on the maximum optical path difference (OPD), necessitating precise control of the moving mirror's motion.
To achieve the required performance, the Optical Path Difference Mechanism (OPDM) has been developed. This mechanism must translate a 14 cm mirror through a 50 mm stroke at a constant velocity of 0.833 mm/s with less than 1% error in velocity and maintain tip/tilt errors below ±1 μrad over a lifespan of three million strokes in a vacuum at -100 °C. The OPDM employs a novel four-bar linkage parallelogram design with flexural pivot bearings, driven by a non-contacting linear voice coil actuator. This design ensures smooth, frictionless motion, eliminating the need for lubrication and theoretically providing infinite life.
The document highlights the importance of achieving extremely smooth linear motion, as the interferometer is sensitive to minute disturbances. The OPDM's performance is validated through internal measurements, demonstrating that it exceeds the required specifications. A second OPDM is under construction to test its performance in a space-like thermal vacuum environment, simulating five years of continuous operation to assess any changes in velocity stability or force requirements.
Overall, the PanFTS represents a significant advancement in spectrometer technology, with the potential to provide high-resolution measurements across a broad spectral range, from thermal infrared to ultraviolet. This capability is crucial for understanding the interactions between atmospheric constituents and radiation, ultimately aiding in climate research and environmental monitoring.
