Solar Radiation and Thermospheric Satellite (SRATS), also knows as Taiyo ("Sun" in Japanese) or Shinsei-3,[1] was a space probe developed by the Institute of Space and Astronautical Science (ISAS) at the University of Tokyo.

The probe was launched on February 24, 1975, from Kagoshima Space Center by M-3C-2 rocket.

Its mission was focused on upper atmospheric physics, X-ray and UV solar radiation, and the Earth's ionosphere.

[2] The satellite had a shape of octagonal cylinder (or prism), weighing 86 kg.

The satellite's primary goal was to investigate solar X-rays, ultraviolet radiation, and the distribution of ions and electrons in the Earth's upper atmosphere.