SORCE

SORCE measured total solar irradiance (TSI) and solar spectral irradiance (SSI) across the ultraviolet, visible, and near-infrared wavelengths using instruments including the Total Irradiance Monitor (TIM), Spectral Irradiance Monitor (SIM), Solar Stellar Irradiance Comparison Experiment (SOLSTICE), and XUV Photometer System (XPS). The TIM instrument measured total solar irradiance with an absolute accuracy of approximately 0.01%, helping establish the most precise record of solar energy output from space.

SORCE was launched on January 25, 2003, aboard a Pegasus XL rocket from Cape Canaveral, Florida. The satellite far exceeded its planned 5-year mission lifetime, operating for nearly 17 years until it was decommissioned in February 2020. SORCE's long operational life provided an invaluable continuous record of solar irradiance spanning more than a full 11-year solar cycle.

SORCE's Total Irradiance Monitor (TIM) measured a slightly lower value of total solar irradiance than previous instruments, around 1,361 watts per square meter rather than the previously accepted 1,365. SORCE data showed that solar irradiance variations of approximately 0.1% occur during 11-year solar cycles, contributing to natural climate variability but not explaining recent global warming. The satellite's spectral measurements helped scientists understand how different wavelengths of solar radiation affect atmospheric chemistry.

The Total and Spectral Solar Irradiance Sensor (TSIS-1), deployed on the International Space Station in December 2017, continued SORCE's measurements of solar irradiance. TSIS-1 carries the Total Irradiance Monitor (TIM) and Spectral Irradiance Monitor (SIM), similar to SORCE's instruments. This overlap ensured continuity of the crucial solar irradiance climate data record that began in 1978.