Total and Spectral Solar Irradiance Sensor -2 (TSIS-2)

We live on a solar-powered planet. The Sun provides almost all of the energy that fuels life and drives the Earth’s ocean currents, seasons, weather, and climate. For scientists who study changes in Earth’s climate, energy from the Sun is a factor that they can’t ignore.

NASA's Total and Spectral Solar Irradiance Sensor – 2, or TSIS-2, will measure the Sun's energy input to Earth. Since 1978, various satellites have measured the Sun’s brightness above Earth’s atmosphere. TSIS-2 will add solar irradiance measurements to four decades of continuous data records. Unlike its predecessor TSIS-1, which operates from the International Space Station, TSIS-2 will ride on a free-flying spacecraft.

Measurements of Earth’s solar energy input is simply a measurement of the Sun’s brightness at the top of Earth’s atmosphere. TSIS-2 measures the brightness of the sun that reaches the earth, called total irradiance, as well as the distribution of that energy over ultraviolet, visible, and infrared wavelengths, called spectral irradiance.

TSIS-2 comprises two instruments, the Total Irradiance Monitor (TIM), and the spectral Irradiance Monitor (SIM). TIM measures total brightness and SIM measures spectral irradiance over a wavelength range that includes 96% of the energy in the solar spectrum. Both instruments are similar to those used for the TSIS-1 mission. Decades of measurements have shown the Sun's brightness fluctuates up and down by a small, but important ~0.1 percent over an 11-year solar cycle. While Earth’s upper atmosphere is sensitive to these changes in sunlight, this variation in total irradiance is too small to explain recent trends in global surface temperature rise.

Scientist who study the Earth’s atmosphere, for example to predict ozone layer recovery or to provide air quality forecasts, use computer models that need accurate measurements of the different wavelength bands of sunlight—spectral solar irradiance—reaching Earth. Particles and gasses inside Earth’s atmosphere react differently to individual wavelengths of light. For example, ozone blocks the most harmful ultraviolet rays, clouds absorb and emit heat radiation, and reflect visible light, and water vapor absorbs heat.

NASA’s Goddard Space Flight Center (GSFC) has overall responsibility for the development and operation of TSIS-2 as part of the Earth Systematic Missions (ESM) program. The Laboratory for Atmospheric and Space Physics (LASP) at the University of Colorado, Boulder, under contract with NASA, is building the TIM and SIM instruments to ensure the availability of this data to the scientific community. NASA plans to launch TSIS-2 in May 2025.