Launched on 17 May 1968, ESRO-2B had an elliptical orbit with (initially)
apogee 1086 km, perigee 326 km, and inclination 97.2 degrees. The orbital
period was 98.9 minutes. It was the first successful ESRO satellite launch.
ESRO (European Space Research Organisation), was the forerunner of ESA.
ESRO-2B was also known as Iris. The satellite was mainly intended to study
X-ray and particle emissions from the Sun, however, it is credited with some
extra-solar observations. The spacecraft was cylindrical in shape, with a
0.76 m diameter and a 0.85 m height. It weighed 80 kg. The failure of
the on-board tape recorder in December 1968 (after roughly 6.5 months
of operation) was catastrophic for the 2 X-ray experiments. They
did not provide any significant data return after that time. The
satellite reentered the atmosphere on 8 May 1971.
Solar and radiation belt protons and alpha particles, protons in energy range 1-100 MeV
High-energy solar protons and alpha particles 0.4 - 0.8 GeV
Flux and energy spectrum of primary electrons (1 - 13 GeV)
Solar X-rays 1 - 20 Angstroms
Solar X-rays 44-60 Angstroms
Solar and galactic protons (35 MeV - 1 GeV) and alpha particles (140 - 1200 MeV)
The satellite carried seven instruments to detect high energy cosmic rays,
determine the total flux of solar X-rays, and measure trapped radiation,
Van Allen belt protons and cosmic ray protons. There were 2 X-ray
instruments: one designed to detect 1-20 Angstroms (consisting of
proportional counters with varying window thickness) and one designed to
detect 44-60 Angstroms (consisting of proportional counters with thin mylar
windows). While geared primarily for solar observations, the detectors are
credited with the detection of non-solar X-ray sources.