||This article contains orbital elements but does not include an epoch, or date when those elements, which typically vary over time, were correct.|
|Launch mass||89 kilograms (196 lb)|
|Start of mission|
|Launch date||6 March 1968, 01:55:08UTC|
|Launch site||Vandenberg SLC-5|
|End of mission|
|Decay date||8 May 1971|
|Perigee||326 kilometres (203 mi)|
|Apogee||1,086 kilometres (675 mi)|
ESRO-2B or Iris (International Radiation Investigation Satellite) was a European astrophysical spin-stabilised research satellite which was launched in 1968. Operated by the European Space Research Organisation, ESRO 2B made astronomical surveys primarily in x-ray and solar particles detectors.
ESRO-2B was an 89 kg (196 lb) cylindrical spacecraft with a length of 85 cm and a diameter of 76 cm. In December 1968 (approx 195 days since mission start) the on-board tape recorder suffered a mechanical failure. This effectively ended the two X-ray experiments as they did not provide any significant data return from then on.
Seven instruments were carried aboard EROS 2B designed to detect high energy cosmic rays, determine the total flux of solar X-rays and to measure Van Allen belt protons and cosmic ray protons. While designed for solar observations ESRO-2B is credited with the detection of X-rays from non-solar sources.