Solar Radiation and Thermospheric Satellite

Taiyo

Mission type	Solar-terrestrial research
Operator	ISAS
COSPAR ID	1975-014A
SATCAT no.	7671
Spacecraft properties
Manufacturer	Nippon Electric Company
Launch mass	86 kg
Dimensions	0.75 m × 0.65 m (diameter × height)
Power	15 watts
Expedition
Ended	June 29, 1980
Start of mission
Launch date	February 24, 1975, 05:25 UTC
Rocket	M-3C No. 2
Launch site	Kagoshima Space Center
Orbital parameters
Reference system	Geocentric
Regime	Low Earth/Medium Earth
Periapsis altitude	260 km
Apoapsis altitude	3,140 km
Inclination	31.54°
Period	120 minutes

Solar Radiation and Thermospheric Satellite (SRATS), also knows as Taiyo ("Sun" in Japanese) or Shinsei-3, 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. Taiyo completed its mission before re-entering Earth's atmosphere on June 29, 1980.

The satellite had a shape of octagonal cylinder (or prism), weighing 86 kg. It orbited the Earth in an elliptical orbit with a periapsis of 260 km and an apoapsis of 3,140 km, at a 32-degree inclination. 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.

Instruments

Taiyo instruments

Taiyo had seven science instruments:

• Solar X-Ray Detector (SXR): Designed to observe solar X-rays in two energy ranges (5.9-9.5 keV, 9.5-11.5 keV) and measure charged particles near the Earth's radiation belts.
• Lyman-alpha Radiation Monitor (SXU): Measured solar hydrogen Lyman-alpha radiation to study the Sun's chromosphere.
• Geocoronal and Middle Ultraviolet Radiometers (GMV): This system combined the Middle Ultraviolet Radiometer (MUV), which measured reflected solar light from atmospheric ozone, and the Vacuum Ultraviolet Photon Counter (GUV), which analyzed geocoronal emissions.
• Bennett Ion Mass Spectrometer (CPI): Examined ion composition in the upper atmosphere, identifying H+, He+, and O+ ions.
• Retarding Potential Analyzer (RPA): Measured ion density and temperature using voltage sweeps across ion traps.
• Electron Temperature Probe (TEL): Recorded electron temperature variations, capable of measuring up to 4000 K.
• Gyro-Plasma Probe (IMP): Analyzed electron density distribution through high-frequency impedance measurements.