| ESRO 2B | |
| Mission Type: | Astrophysics |
| Operator: | ESRO |
| Cospar Id: | 1968-041A[1] |
| Satcat: | 03233 |
| Launch Date: | UTC[2] |
| Launch Rocket: | Scout B |
| Launch Site: | Vandenberg SLC-5 |
| Decay Date: | 8 May 1971, shortly after 03:00 UT |
| Orbit Epoch: | 16 May 1968, 22:09:00 UTC[3] |
| Orbit Reference: | Geocentric |
| Orbit Regime: | Low Earth |
| Orbit Inclination: | 97.2 degrees |
| Orbit Period: | 98.9 minutes |
| Apsis: | gee |
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 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.[4]
ESRO-2B was an 89kg (196lb) cylindrical spacecraft 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 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,[5] 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).[6]
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.[6]
Seven instruments were carried aboard EROS 2B[2] 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.[4] While designed for solar observations ESRO-2B is credited with the detection of X-rays from non-solar sources.[2] The instruments were: