The Total and Spectral Solar Irradiance Sensor 2 (TSIS-2) is a satellite designed by NASA to measure the Sun's energy input to Earth. 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 onboard the International Space Station.