ESRO 2A, 2B (Iris 1, 2)

ESRO 2B (Iris 2) [ESA]

ESRO 2 (European Space Research Organisation), Iris (International Radiation Investigation Satellite) was a 75 kg spin-stabilized spacecraft On the launch of ESRO 2A, the third stage vehicle failed and the spacecraft did not achieve orbit. ESRO 2B was launched on May 16, 1968, into a near polar orbit. The main objective of ESRO 2 was to conduct a study of solar astronomy and cosmic rays. The ESRO 2 experiments had their counterparts in the NASA-OSO series. The purpose of the spacecraft was to provide continuity to the solar radiation observations carried out by OSO D launched October 18, 1967. The particle experiments were designed to continue similar measurements carried out by the Ariel 1 (UK 1) satellite.

Experiments on board were:

• Monitor of Energetic Particle Flux
• Solar and Van Allen Belt Protons
• Solar and Galactic Alpha Particles and Protons
• Primary Cosmic Ray Electrons
• Hard Solar X-rays
• Soft Solar X-rays
• Flux and Energy Spectra of Solar and Galactic Cosmic Ray Particles

The satellite had a spin rate of about 40 rpm and had completed 16,282 orbits of the earth before reentry on May 8, 1971, shortly after 0300 UT. No playback data has been available since December 10, 1968, following a mechanical failure of the onboard tape recorder. The failure reduced the data flow by about 80 percent, although a combination of Estrack (ESRO) and STADAN (NASA) tracking stations were used.