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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 16 May 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 18 October 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 8 May 1971, shortly after 0300 UT. No playback data has been available since 10 December 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.

Nation: Europe
Type / Application: Research, cosmic radiation and solar astronomy
Operator: ESRO
Contractors: Hawker Siddely Dynamics, Matra
Equipment: see above
Propulsion: ?
Power: Solar cells, batteries
Mass: 74 kg (#2A), 89 kg (#2B)
Orbit: 334 km × 1085 km, 97.2
Satellite COSPAR Date LS Launch Vehicle Remarks
ESRO 2A (Iris 1) 1967-F05 30.05.1967 Va SLC-5 F Scout-B
ESRO 2B (Iris 2) 1968-041A 17.05.1968 Va SLC-5 Scout-B


  • NSSDC Master Catalog