Compact Total and Spectral Solar Irradiance Sensor Mission Concept Study (CTSIS)

We intend to propose an Instrument/Measurement Concept Demonstration (IIP-ICD) to develop a detailed mission concept for a next-generation solar irradiance observation system that employs a robust and affordable mission architecture to provide future continuity of the measurement of total solar irradiance (TSI) and spectral solar irradiance (SSI). Solar irradiance, along with Earth reflected and emitted radiance, is one of the longest and most fundamental of all climate data records derived from space-based observations. Measurement of TSI and SSI, and the monitoring of small long-term changes, is necessary for the understanding of Earth's climate. The LASP-built Total and Spectral Solar Irradiance Sensor (TSIS-1) instrument has been operating on the ISS since 2018, and LASP is currently building the TSIS-2 instrument with an anticipated launch in late 2023. With the understanding of the need to make these measurements in perpetuity, and the advent of advanced technologies which allow for equivalent and better measurement accuracy on CubeSats and SmallSats, LASP and ESTO have embarked on the design and launch of pathfinder missions which have and will prove the ability to provide solar irradiance measurements using smaller, low cost, reliable platforms. The first demonstration was the launch of Compact Solar Irradiance Monitor (CSIM) which demonstrated the ability to make equivalent measurements with a CubeSat form factor. The next demonstration will be the ESTO-funded Compact Total Irradiance Monitor (CTIM) mission with a planned launch in 2022. The natural technical evolution is to develop a single, compact system, which includes both the Total and Spectral Irradiance sensors. This new platform, which LASP is calling the Compact Total and Spectral Solar Irradiance Sensor (CTSIS) will enable robust, long term, low cost, resilient measurements. During the first phase of the planned 12-month study two to three distinct mission architectures will be identified, such as a small constellation of 12U CTSIS CubeSats with a two-channel CSIM and a four-channel CTIM versus a 50 kg class CTSIS SmallSat with a three- channel CSIM and a four-channel CTIM. In parallel, we will summarize desired modifications to future CSIM and CTIM instruments based on lessons learned during the CSIM flight and the CTIM I&T, and the estimated impact of these modifications on the cost and performance of future CSIM and CTIM instruments. Next, the team will work through a manufacturing, build, calibration and storage plan of the different mission architectures, followed by the development of a mission timeline for each architecture. Finally, these inputs will allow us to estimate the lifecycle cost, and the resiliency of each architecture. These results will be compared directly against the estimated cost and resiliency of a "build to print" implementation using the heritage TSIS-1 instrument designs, similar to TSIS-2. These results will be summarized in a final report at the conclusion of the study. The ultimate goal of this study is to identify and document a new mission architecture, leveraging the CSIM and CTIM instruments, which will provide solar irradiance measurement continuity at a significantly lower cost, and greater or equal resiliency, than a TSIS-1 rebuild. Entry TRL at the CTSIS system level is TRLin = 2 with a planned exit TRLout = 3.

Enabling lower cost innovative remote sensing instrument development from concept through breadboard and demonstration

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