Development and Demonstration of an All Solid-State 4.7 THz spectrometer Enabling Measurements of Thermospheric Winds, Temperature, and O Density

TeraHz Limb Sounder (TLS) is a low-mass, low-power, high spectral resolution heterodyne spectro-polarimeter operating in the TeraHz (THz) frequency regime designed to remotely measure thermospheric wind, temperature and atomic oxygen density profiles from a low-earth orbit platform. It resolves the Doppler line shapes of the atomic oxygen emissions at 2.06 THz (145 micron) and 4.7 THz (63 micron) and uses their polarimetric properties to improve its measurement precisions. Under the support of previous G/IDES program (2/2013-1/2016) and H-TIDS program (3/2016-2/2019), we have designed and fabricated a receiver prototype for the 2 THz channel of TLS and successfully demonstrated its technology feasibility and performance. While the 2 THz channel of TLS is optimized to provide lower thermospheric measurements, we propose here to develop the 4 THz channel and demonstrate its measurement capability at higher thermospheric altitudes using the same innovative low-size, mass and power receiver design approach. The 4 THz channel of the THz Limb Sounder (TLS) instrument will be developed and performance demonstrated under this proposed Heliophysics Technology and Instrument Development for Science Program (H-TIDeS) investigation. It can, for the first time, measure neutral wind profiles globally during both day and night in an altitude region where most of the ion-neutral energy/momentum coupling takes place and the neutral atmosphere responds to external energy inputs. These measurements provide critical observational constraints to the complex dynamics in the coupled lower atmosphere/thermosphere/ionosphere/magnetosphere system, as highlighted in the 2012 HDS and 2014 Heliophysics Science and Technology Roadmap for 2014-2033. This H-TIDeS instrument unequivocally supports the science objectives of DYNAMIC (Dynamical Atmosphere Ionosphere Coupling), a 2014 Roadmap recommended a Solar Terrestrial Probes (STP) mission, which directly benefits future Heliophysics mission planning and implementation. In addition, TLS is compact, small, light-weight, low power and ideal to support future cost-effective science missions in implementing the Decadal Survey DRIVE (Diversify Realize, Integrate, Venture, Educate) initiative. This proposed H-TIDeS ITD effort is a joint project between The Johns Hopkins University, Applied Physics Laboratory (JHU/APL) and NASA Jet Propulsion Laboratory (JPL). The TLS development leverages on the chip fabrication capability and recent advances in our 2 THz mixer technology made at JPL. Because scientific payloads on future NASA Heliophysics missions, including DYNAMIC, is likely resource-limited and cost-constrained, in this proposal we seek characterization and demonstration of a compact, low mass and low risk THz instrument that fits within Explorer-class mission constraints. Under the proposed 36-month HTIDeS project (3/1/20 to 2/28/23), we will mature and optimize a compact, low-mass, low-power, and low-noise 4.7 THz receiver concept to meet both Heliophysics science and programmatic requirements. We will design, build and integrate a single-element TLS receiver system at 4.75 THz with the sensitivity and stability required for wind measurements. This THz receiver system will be operated at 120-150 K ambient temperature, which is achievable with passive radiators in space. This HTIDeS project, focuses on the THz receiver system integration, optimization, and demonstration of two key subsystems developed under our currently funded efforts: (1) high-yield local oscillator chain and (2) low-noise THz mixer. The successful completion of this proposed HTIDeS project will not only reduce implementation risk/cost for future DYNAMIC-like mission, but also shorten instrument development time.

Support NASA's Heliophysics strategic science objectives to understand the Sun and its interactions with Earth and the solar system, including space weather. This will be achieved by developing/demonstrating instrumentation technology necessary to address the following science goals: Explore the physical processes in the space environment from the Sun to the Earth and throughout the solar system; Advance our understanding of the connections that link the Sun, the Earth, planetary space environments, and the outer reaches of our solar system; Develop the knowledge and capability to detect and predict extreme conditions in space to protect life and society and to safeguard human and robotic explorers beyond Earth.

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