A Decade Long Mission Architecture to Provide Continuous Solar Irradiance Measurements: The Compact Total and Spectral Irradiance Sensors (CTSIS) Mission

Maintaining the solar irradiance data record is a high community priority as the Sun is the primary input driver to climate on Earth where the influence of total solar irradiance (TSI) and solar spectral irradiance (SSI) is recognized as being increasingly important to the Sun-Earth climate connection. This talk will focus on a detailed discussion of the both the motivation and technical feasibility of providing the climate-science community with continuous, space-based solar irradiance measurements using a joint instrument suite comprising the total and spectral irradiance instruments successfully demonstrated in the Compact Total Irradiance Monitor (CTIM) and the Compact Spectral Irradiance Monitor (CSIM) missions. We compare the compact instrument architecture against legacy missions such as TSIS-1 (operational on ISS since Jan 2018) and TSIS-2 (scheduled for launch in early 2025) and discuss a joint instrument architecture in a CubeSat or MicroSat form factor. We discuss lessons learned and improvements to be made for each instrument and summarize the engineering benefits and challenges of each platform. The proposed mission model offers a 10-year continuous measurement campaign involving staggered launches and overlapping operational timelines to allow on-orbit redundancy and instrument cross-calibration, resulting in 6 flight units over the decade. To cover this timespan, we would initially launch a pair of initial Compact Total and Spectral Solar Irradiance Sensors (CTSIS) joint-instrument units to lower the risk of a gap in the continuous record potentially due to early mission platform or instrument suite issues. This initial operational start would overlap with the TSIS-2 measurements for at least one-year. The timeline would then follow with a launch of a third unit when either of the on-orbit units has failed or has been on-orbit for 54 months (4.5 years). This launch pattern is continued throughout the mission. The joint instrument suite chosen for each CTSIS unit rests on the demonstrated heritage and operational success of the CTIM and CSIM CubeSats. The two ESTO CubeSat missions were a testbed for new detector technologies and associated instrument designs, and a proving ground for the reliability of the CubeSat platform. Both CTIM and CSIM replaced legacy detector technology for total and spectral solar irradiance measurements with new detectors based on silicon microfabrication and vertically aligned carbon nanotubes, which both improve detector performance and significant ease fabrication. Ultimately, both the CubeSat and a MicroSat architecture proposed are smaller, lighter, less resource intensive, more cost effective over multiple launches than the resources that would be required to span a decade with existing large TSIS-scale observatories and instrument designs.