''ESRO-2B'' or ''Iris'' (''International Radiation Investigation Satellite''; sometimes ''Iris 2'') or sometimes ''ESRO II'' (or ''ESRO 2''), was a European astrophysical spin-stabilised research

satellite A satellite or artificial satellite is an object intentionally placed into orbit in outer space. Except for passive satellites, most satellites have an electricity generation system for equipment on board, such as solar panels or radioiso ...

which was launched in 1968. Operated by the European Space Research Organisation, ESRO 2B made astronomical surveys primarily in

x-ray X-rays (or rarely, ''X-radiation'') are a form of high-energy electromagnetic radiation. In many languages, it is referred to as Röntgen radiation, after the German scientist Wilhelm Conrad Röntgen, who discovered it in 1895 and named it ' ...

and solar particles detectors.

Spacecraft

ESRO-2B was an cylindrical

spacecraft A spacecraft is a vehicle or machine designed to spaceflight, fly in outer space. A type of artificial satellite, spacecraft are used for a variety of purposes, including Telecommunications, communications, Earth observation satellite, Earth ...

with a length of 85 cm and a diameter of 76 cm. On 10 December 1968 (approx 195 days since mission start) the on-board

tape recorder An audio tape recorder, also known as a tape deck, tape player or tape machine or simply a tape recorder, is a sound recording and reproduction device that records and plays back sounds usually using magnetic tape for storage. In its present ...

suffered a mechanical failure. This effectively ended the two X-ray experiments as they did not provide any significant data return from then on. Other experiments could still be operated through ground radio links. ESRO-2B was launched on a Scout B rocket into a highly elliptical near-polar orbit on 17 May 1968. Its predecessor satellite, ''ESRO-2A'' (sometimes ''Iris 1'') failed to reach orbit on 29 May 1967, launching on a Scout B rocket from Vandenberg AFB SLC-5. The cause of failure was malfunction of the third stage of the rocket, preventing the satellite from reaching orbit. ESRO-2A was similar to ESRO-2B except it weighed a little less (74 kg). Spin-stabilised, ESRO-2B had a spin rate of approximately 40 rpm and re-entered Earth's atmosphere on 8 May 1971 after completing 16,282 orbits.

Instruments

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 Cosmic rays are high-energy particles or clusters of particles (primarily represented by protons or atomic nuclei) that move through space at nearly the speed of light. They originate from the Sun, from outside of the Solar System in our ow ...

protons. While designed for solar observations ESRO-2B is credited with the detection of X-rays from non-solar sources. The instruments 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

References

{{reflist 1972 in spaceflight European Space Agency satellites