MLSCube – A Microwave Limb Sounder for continuity of stratospheric observations in a 6U-CubeSat form factor

We propose to develop technologies needed for a 6U CubeSat instrument measuring profiles of the composition, humidity, and temperature of Earth's upper troposphere, stratosphere, and mesosphere with the vertical resolution, spatial coverage, precision, and accuracy required to derive essential Earth System Data Records. The instrument will provide continuity for the Aura Microwave Limb Sounder (MLS, launched in 2004), generally considered to represent the "platinum standard" for such measurements. The composition of the upper troposphere and stratosphere (UT/S) plays many roles in influencing and responding to changes in surface climate. Factors such as potential injection of aerosols into the stratosphere for "geoengineering" and recently identified rogue emissions of ozone-depleting CFC-11 underscore the need for a robust quantitative understanding of those roles and their future evolution, founded on a continued record of reliable observations. Recent technology development efforts, including several funded by ESTO, have enabled dramatic reductions in mass/power/volume/cost for future such instruments. Presently, however, no viable route to making such observations from a CubeSat-class spacecraft exists, mainly because of the requirement for a large (e.g., 60cm) aperture. A CubeSat-class MLS-type instrument represents a much-needed advance, given the far more frequent opportunities that exist for CubeSat deployments compared to other mission profiles. "MLSCube" uses phased-array techniques to synthesize a 60cm electronically-steered aperture for limb emission observations, tunable over 316–358GHz, consisting of 24 individual receiver elements, each employing piezo-electrically-driven moving silicon lenses to aid in beam steering and sidelobe reduction. A set of identical custom System on Chip (SoC) devices will provide individual synchronized phase- and frequency-tunable 108–116GHz oscillators for each element. These will then be frequency-tripled and combined with the atmospheric signals in a Schottky diode mixer. Micromechanical switches and in-waveguide targets will be used for radiometric calibration of each element, replacing traditional but bulky switching mirrors and associated optics. The Intermediate Frequency signals will be amplified and sent through programmable attenuators, then combined for beam forming and analyzed with a 3GHz bandwidth SoC 4096 channel spectrometer that will produce spectra. Various schemes for in-flight active beamforming calibration will be developed and evaluated. While some components are high-TRL, the overall concept is currently TRL-3. The proposed three-year effort will include validation of a four-element 183GHz prototype based on devices nearing completion developed under other programs. This will be followed by fabrication of 12 of the 24 array elements needed for the 340GHz-MLSCube instrument. These will then be integrated, along with the previously developed backend spectrometer subsystem, into a 6U CubeSat form factor (leaving space for the remaining 12 elements and 2U for spacecraft components). The partial system will be extensively calibrated, and subjected to flight-like vibration, thermal vacuum, and radio frequency interference and compliance testing, followed by a re-calibration, demonstrating TRL-5. The recent Earth science Decadal Survey identified the parameters measured by MLSCube as key targeted observables within the "Ozone and Trace Gas" opportunity in the "Explorer" line. In addition, MLSCube is ideally suited for demonstrating potential continuity measurements in any suitably-targeted "Earth Venture-Continuity" opportunity.

Increase scientific understanding of natural phenomena using remote sensing

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