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Uninterrupted and overlapping satellite instrument measurements of Earth’s radiation budget from space are required to sufficiently monitor the planet’s changing climate, detect trends in key climate variables, constrain climate models, and quantify climate feedbacks. The Clouds and Earth’s Radiant Energy System (CERES) instruments are currently making these vital measurements for the scientific community and society, but with modern technologies, there are more efficient and cost-effective alternatives to the CERES implementation. We present a compact radiometer concept, Trutinor (meaning “balance” in Latin), with two broadband channels, shortwave (0.2–3 μm) and longwave (5–50 μm), capable of continuing the CERES record by flying in formation with an existing imager on another satellite platform. The instrument uses a three-mirror off-axis anastigmat telescope as the front optics to image these broadband radiances onto a microbolometer array coated with gold black, providing the required performance across the full spectral range. Each pixel of the sensor has a field of view of 0.6°, which was chosen so the shortwave band can be efficiently calibrated using the Moon as an on-orbit light source with the same angular extent, thereby reducing mass and improving measurement accuracy, towards the goal of a gap-tolerant observing system. The longwave band will utilize compact blackbodies with phase-change cells for an absolute calibration reference, establishing a clear path for SI-traceability. Trutinor’s instrument breadboard has been designed and is currently being built and tested.

The purpose of the ARCSTONE project is to more accurately measure the spectral lunar reflectance so the Moon can be used as a high-accuracy SI-traceable exo-atmospheric calibration standard for Earth-viewing instruments in low-Earth orbits. The spectral range is 350 nm to 2300 nm with less than 4 nm sampling. Radiometric modeling indicates the mission goal of better than 1 % (k=1) absolute accuracy is achievable. To reach this goal, the instrument will measure solar and lunar irradiances with a single set of optics, thereby minimizing the impact of long-term optical degradation via a temporally-close ratio method. SI-traceable results will be obtained by scaling the solar irradiance measurements to the calibrated, on-orbit Total and Spectral Irradiance Sensor (TSIS) observations. To date, a first-generation ARCSTONE prototype has been developed and is undergoing system-level characterizations. A more compact second-generation engineering design unit that will fit in a 6U CubeSat is under development.

The SAGE IV (Stratospheric Aerosol and Gas Experiment) Pathfinder looks towards ushering in the next generation of the SAGE family of instruments, leveraging solar occultation to retrieve vertical profiles of aerosols and gases in the stratosphere, providing high precision calibration data for other instruments. A development funded through the NASA Earth Science Technology Office (ESTO) Instrument Incubator Program (IIP) SAGE IV Pathfinder is designed to extend the data record from the SAGE III scanning grating spectrometer with a multispectral imaging approach. Solar disk imaging improves the data collected by providing: (1) absolute pointing information; (2) measurements of atmospheric refraction effects; and (3) measurements of solar disk anisotropy. This additional information relaxes traditionally tight constraints on attitude knowledge, stability, and pointing control making a free-flying 6U CubeSat instrument feasible. Early estimates show this approach might reduce the cost of SAGE continuity missions by as much as 90%. A key benefit of the SAGE IV Pathfinder design to future missions is the versatility of the resultant telescope subsystem. The F/5.25 telescope resulted in

Calibration accuracy and long-term precision are key on-orbit performance metrics for Earth observing spaceborne sensors. The accuracy and consistency of environmental measurements across multiple instruments in low Earth and geostationary orbits are directly connected to the scientific understanding of complex systems, such as Earth’s weather and climate. It is common for instruments to carry on-board references for calibration at various wavelengths, but these are subject to degradation with time spent in-orbit, and also increase complexity, mass and power requirements. ARCSTONE is a mission concept that provides a solution to the challenge of achieving and maintaining required instrument calibration accuracy on-orbit in the reflected solar wavelength range. As an orbiting spectrometer flying on a small satellite in low Earth orbit, ARCSTONE will provide lunar spectral reflectance with accuracy sufficient to establish the Moon as an SI-traceable absolute calibration standard for past, current, and future Earth weather, land imaging, and climate sensors in both low and geostationary Earth orbits. The ARCSTONE instruments are required to provide spectral measurements in a thermal environment that varies by 40 °C or more depending on whether the instrument is in direct sunlight or shade. A Structural, Thermal, and Optical Performance (STOP) analysis is conducted to assess the robustness of these instruments in this thermal setting and to highlight areas for possible design improvement. The analysis is performed for transient thermal environments representing a thermal vacuum chamber (TVAC) test. Analysis was performed for both the ultraviolet – visible (UVVNIR) and infrared (SWIR) instruments, however, this paper will focus solely on the UVVNIR instrument. Additional considerations for the future flight units are presented, including modeling effects of preloads and sliding of lenses in their mounts on outcomes of the thermoelastic model. The ARCSTONE instrument design has been optimized based on the results of this analysis.

The Giant Magellan Telescope (GMT) is 25 meter diameter extremely large ground based infrared/optical telescope being built by an international consortium of universities and research institutions. It will be located at the Las Campanas Observatory in Chile. The GMT primary mirror consists of seven 8.4 meter diameter borosilicate mirror segments. Two seven segment Gregorian secondary mirror systems will be built; an Adaptive Secondary Mirror (ASM) to support adaptive optics modes and a Fast-steering Secondary Mirror (FSM) with monolithic segments to support natural seeing modes when the ASM is being serviced. Wind excitation results in static deformation and vibration in the telescope structure that affects alignment and image jitter performance. The telescope mount will reject static and lower frequency windshake, while each of the Faststeering Secondary Mirror (FSM) segments will be used to compensate for the higher frequency wind-shake, up to 20 Hz. Using a finite element model of the GMT, along with CFD modeling of the wind loading on the telescope structure, wind excitation scenarios were created to study the performance of the FSM and telescope against wind-induced jitter. A description of the models, methodology and results of the analyses are presented.

The preliminary design of the 25 m Giant Magellan Telescope (GMT) has been completed. This paper describes the design of the optics, structure and mechanisms, together with the rationales that lead to the current design. Analyses that were conducted to verify structure and optical performance are summarized. Science instruments will be mounted within the telescope structure. A common instrument de-rotator is provided to compensate for field rotation caused by the alt-az tracking of the telescope. The various instrument stations and provisions for mounting instruments are described. Post-PDR development plans for the telescope are presented.