Through an innovative public-private partnership, a new generation of high-fidelity imaging spectrometers has been designed for the detection and measurement of methane (CH4) and carbon dioxide (CO2) plumes from super-emitters to help improve accounting and enable reduction of greenhouse gases in the Earth’s atmosphere. Two identical instruments, built concurrently at NASA Jet Propulsion Laboratory (referred to by JPL as the Carbon Plume Mapper project “CPM”) and Planet Labs as part of the Carbon Mapper Coalition, will measure the spectral range of 400 – 2500 nm with a spectral sampling of 5.0 nm. The identical optical design comprises a three-mirror anastigmat (TMA) telescope and Dyson form spectrometer which reduces volume and mass for a fast (F/1.8) optical system. The instruments will be integrated into Planet-built Tanager satellites and launched into low-Earth orbit (LEO). This work describes the assembly and alignment of the two identical instruments. At the subsystem level, both instruments follow the same procedure. For telescope alignment, the mirrors are first coarsely aligned with a coordinate measuring machine (CMM) and then finely aligned in a double-pass interferometer setup. The spectrometer subsystem is aligned onaxis using a commercial lens alignment instrument for precise, non-contact measurements. The telescope and spectrometer alignment results and performance are presented and compared. At the system level, the procedures deviate due to the separate and unique optical ground support equipment (OGSE) configurations utilized by JPL and Planet to implement the same instrument design. Both end-to-end optical alignment configurations are discussed, and the final CPM performance is shown with a focus on the five key and driving imaging spectrometer performance requirements.
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.
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