NASA's Total and Spectral Solar Irradiance Sensor-2 (TSIS-2) will measure the Sun's energy reaching Earth. This includes total solar irradiance (TSI), the overall Sun’s brightness, and spectral solar irradiance (SSI), the distribution of energy across different wavelengths. It is the latest mission for this important solar irradiance record that has been observed from space since 1978. It builds on the instruments from its predecessor TSIS-1 that helped to advance our understanding of the Sun's influence on Earth's ozone layer, atmosphere, clouds, and ecosystems. Monitoring solar variability is critical for assessing Earth's energy imbalance and Sun’s influences on our home planet.

TSIS-2 consists of two instruments: the Total Irradiance Monitor (TIM) and the Spectral Irradiance Monitor (SIM). These instruments are similar to those on TSIS-1. TIM measures the Sun's total irradiance, while SIM measures spectral irradiance across a broad wavelength range over ultraviolet, visible, and infrared wavelengths. NASA's Goddard Space Flight Center (GSFC) leads the development and operation of TSIS-2. The Laboratory for Atmospheric and Space Physics (LASP) at the University of Colorado is building the TIM and SIM instruments. While TSIS-1 is currently operated on the International Space Station, TSIS-2 will be launched on a free-flying spacecraft in 2025 to ensure uninterrupted solar irradiance observations. Details can be found at https://eospso.nasa.gov/missions/total-and-spectral-solar-irradiance-sensor-2.