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Laboratory for Atmospheric and Space Physics


Solar irradiance is one of the longest and most fundamental of all climate data records derived from space-based observations. TSIS-1 is a dual-instrument package that will acquire solar irradiance measurements from the International Space Station for five years. TSIS-1 will provide critical data in determining the natural forcing of the climate system and will ensure the continuity of the solar irradiance climate data record.

TSIS-1 consists of the TIM and SIM instruments, TPS, microprocessor unit, fine sun sensors, and support equipment. Because the TIM and SIM are designed to operate nominally in a solar-viewing orientation they are mounted on a gimbaled platform that accommodates targeting independent of the ISS attitude. The instruments and their associated supporting flight segment systems are depicted in the Figure below.

TSIS-1 includes the following two instruments:

  • The Total Irradiance Monitor (TIM) instrument: measures total solar irradiance (TSI) that is incident at the outer boundaries of the atmosphere.
  • The Spectral Irradiance Monitor (SIM) instrument: measures solar spectral irradiance (SSI) from 200 nm to 2,400 nm (96 percent of the TSI).


The TIM and SIM instruments are designed similarly to those currently flying on the Solar Radiation and Climate Experiment (SORCE) satellite, which launched in 2003 and is now more than nine years beyond its prime-mission lifetime. TSIS-1 is required to continue the 38-year record of TSI, extend the newer 14-year record of SSI, and to provide highly accurate, stable and continuous observations that are critical to understanding the present climate epoch and for predicting future climate.