The NASA Plankton, Aerosol, Cloud, and ocean Ecosystem (PACE) mission Ocean Color Instrument Team has completed the prelaunch radiometric characterization of the thermal response of the Ocean Color Instrument (OCI). The radiometric performance of the ultraviolet to visible (UVVIS) and visible to near-infrared (VISNIR) grating spectrographs and the shortwave-infrared (SWIR) filter spectrograph of OCI were characterized during the thermal vacuum testing of the instrument conducted in September and October of 2022. The thermal characterization test program will be outlined, along with the derived radiometric dependencies on temperature. For the UVVIS and VISNIR spectrographs, the change in radiometric response with temperature is consistent with theoretical models of the measured detector performance and is on the order of 0.15% per °C. For the SWIR spectrograph, the change in radiometric response with temperature in on the order of 0.04% per °C. For the UVVIS spectrograph, uncertainties in the radiometric measurements as the detector temperatures varied by ∼10° C were less than 0.15% for wavelengths of 350 − 593 nm. For the VISNIR spectrograph, uncertainties were less than 0.11% for wavelengths of 625 − 867 nm. For the SWIR spectrograph, the typical uncertainties were less than 0.15% for all bands. Since the expected temperature range for the instrument on orbit is 0.5° C, OCI meets the design goals for upper limits on radiometric uncertainties due to thermal effects.
Lunar Ice Cube, scheduled to be launched on ARTEMIS I in late 2021, is a deep space cubesat mission with the goals of demonstrating 1) a cubesat-scale instrument (BIRCHES) capable of addressing NASA HEOMD Strategic Knowledge Gaps related to lunar volatile distribution (abundance, location, and transportation physics of water ice), and 2) cubesat propulsion, via the Busek BIT 3 RF Ion engine. The mission will also demonstrate the AIM/IRIS microcryocooler for the first time in deep space. BIRCHES integration is nearly complete, with several changes made to the thermal design to improve detector performance. Final preflight instrument testing and calibration, our ongoing concern to be emphasized here, have been delayed due to the mandated closure rules of NASA facilities. Lunar Ice Cube, along with two other cubesats deployed from ARTEMIS I, Lunar Flashlight and LunaH-Map, will be the first deep cubesat missions to deliver science data to the Planetary Data System.
The Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) mission represents NASA’s next investment in satellite ocean color and the study of Earth’s ocean-atmosphere system, enabling new insights into oceanographic and atmospheric responses to Earth's changing climate. PACE objectives include extending systematic cloud, aerosol, ocean biological and biogeochemical data records, making essential ocean color measurements to further understand marine carbon cycles and ecosystem responses to a changing climate, as well as improving knowledge of how aerosols influence ocean ecosystems and, conversely, how ocean ecosystems and photochemical processes affect the atmosphere. PACE objectives also encompass management of fisheries, large freshwater bodies, and water quality and reducing uncertainties in climate and radiative forcing models of the Earth system. PACE observations will also provide information on radiative properties of land surfaces and characterization of the vegetation and soils that dominate their reflectance. The primary PACE instrument – the Ocean Color Instrument (OCI) – is a hyperspectral imaging radiometer that spans the ultraviolet to shortwave infrared, with a ground sample distance of 1-km at nadir. This includes continuous collection of spectra from 340 nm to 890 nm in 5 nm steps. The PACE payload is complemented by two multi-angle polarimeters with spectral ranges that span the visible to near-infrared region. Scheduled for launch in late 2022-to-early 2023, the PACE observatory will enable significant advances in the study of Earth’s biogeochemistry, carbon cycle, clouds, hydrosols, and aerosols in the ocean-atmosphere system. We present a brief overview of the PACE mission, followed by a discussion of the capabilities and design concept of OCI.
Lunar Ice Cube (LIC) is one of 13 6U cubesats that will be deployed by EM1 in cislunar space. LIC along with Lunar Flashlight and LunaH-Map, all focused on the search for volatiles but with very different payloads, will be the first deep space cubesats designed to address goals for both demonstrating new technologies and collecting scientific data. Effectively, as their developments are occurring in parallel, they are acting as prototypes for future deep space cubesats missions. One useful outcome of this ‘experiment’ is to evolve a working paradigm for the development and operation of compact, cost-capped, standardized (supporting subsystems) spacecraft to serve the needs of diverse user communities. The lunar ice cube mission was developed as the test case in a GSFC R and D study to determine whether the cubesat paradigm could be applied to deep space, science requirements driven missions, and BIRCHES was its payload. Here, we present the design and describe the ongoing development, and testing, in the context of the challenges of using the cubesat paradigm to fly a broadband IR spectrometer in a 6U platform, including a very harsh environment, minimal funding and extensive need for leveraging existing assets and relationships on development, and minimum command and telemetry bandwidth translating into simplified or canned operation and the collection of only essential data.
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