Miniaturized Microwave Absolute Calibration (MiniMAC) for Sounders and Imagers on SmallSat and CubeSat Platforms

Successful demonstration of the Temporal Experiment for Storms and Tropical Systems Technology Demonstration (TEMPEST-D) mission has proven that microwave imagers and sounders on CubeSats are capable of well-calibrated, stable, low-noise observations. For 22 months, TEMPEST-D has successfully performed global passive microwave observations at 5 frequency channels from 87 to 181 GHz, focusing on clouds, precipitation and humidity profiling. Additionally, the Tropospheric Water and Cloud Ice (TWICE) IIP-13 task successfully demonstrated a multi-frequency, wide-band millimeter/sub-millimeter wave instrument measuring at 16 frequencies from 118 to 850 GHz with size, weight and power for 6U CubeSat deployment. TWICE science goals focus on ice cloud particle size and humidity & temperature profiling, key for the NASA Earth Science strategic areas of Climate Variability and Change and Weather. TWICE was selected for feasibility studies for Aerosols, Clouds, Convection and Precipitation (ACCP) in the 2017 NAS Earth Science Decadal Survey. A combined version of the water vapor profiling channels of TEMPEST-D and the temperature profiling channels of TWICE is ideal to address NOAA's goals for next-generation LEO weather satellite systems. NOAA envisions a new generation of operational LEO constellations of small satellite sensors, to provide global coverage with 2-3 hour repeat times. Advantages of small satellite constellations include: (1) increased temporal sampling globally; (2) reduced cost and scalable sensor deployment depending on available resources, launch opportunities and satellite longevity; and (3) capability for rapid infusion of new technology. To accomplish a well-calibrated small satellite constellation, we envision one microwave sounder with SI-traceable brightness temperature calibration, complemented by many lower-cost small satellites with microwave sounders to accomplish 2-3 hour sampling. In collaboration with NIST and Duke University, we propose a three-year task to develop a NIST-traceable Miniaturized Microwave Absolute Calibrator based on metamaterials on organic-based printed-circuit boards (PCBs) at millimeter-wave sounding channels from 50 to 220 GHz. Metamaterial-based microwave absorbers fabricated on thin, organic-based PCBs hold promise for microwave sounders on CubeSats. The thin, conformal surface represents a significant weight improvement in ferrite-loaded epoxy absorbers and provides a uniform physical temperature for improved calibration accuracy. Commercial vendors supply multilayer PCBs with core thicknesses less than 25 microns with moderate permittivity and low dielectric loss tangents. Currently, these thin substrates are used in high-speed digital and mixed-signal applications, but good microwave properties have recently been demonstrated well above 200 GHz. A critical task is to develop a metamaterial pattern capable of broadband operation at millimeter-wave sounding channels from 55 to 220 GHz. This task will be carried out through both analytical and numerical modeling, and results will be supported by fabricated prototypes and experimental validation. The metamaterials will be tested in an anechoic chamber at NIST to validate both brightness temperature and reflectance. The entry TRL of the microwave absorbers is 2, and due to testing of these calibration subsystems in a laboratory environment, the exit TRL is 4. The technologies developed for MiniMAC will significantly benefit the microwave remote sensing community. First, the NIST brightness temperature target will enable SI traceability of various microwave sounding sensors. This will enhance instrument evaluation, increase data repeatability among instruments, and enhance the historical record of microwave sounding data. Second, the physically thin metamaterial absorber will improve system SWaP and physical temperature homogeneity and knowledge for CubeSat microwave calibration targets.

Accelerate mission development and reduce risk by developing critical components and subsystems for advanced instruments and observing systems

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