ESRO 2B
{{Short description|Research satellite}}
{{Use dmy dates|date=March 2024}}
{{Infobox spaceflight
| name = ESRO 2B
| image = Esro-2b small.gif
| image_caption =
| mission_type = Astrophysics
| operator = ESRO
| website =
| COSPAR_ID = 1968-041A{{Cite web|url=https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1968-041A|title = NASA – NSSDCA – Spacecraft – Details}}
| SATCAT = 03233
| mission_duration =
| spacecraft_bus =
| manufacturer =
| dry_mass =
| launch_mass = {{convert|89.8|kg}}
| power =
| launch_date = {{start-date|17 May 1968, 02:06:00 |timezone=yes}} UTC{{cite web|url=http://www.planet4589.org/space/log/launchlog.txt|title=ESRO 2B|work=NASA|access-date=6 March 2013}}
| launch_rocket = Scout B
| launch_site = Vandenberg SLC-5
| launch_contractor =
| disposal_type =
| deactivated =
| last_contact =
| decay_date = 8 May 1971, shortly after 03:00 UT
| orbit_epoch = 16 May 1968, 22:09:00 UTC{{Cite web|url=https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1968-041A|title=NASA – NSSDCA – Spacecraft – Trajectory Details|website=nssdc.gsfc.nasa.gov|access-date=2018-05-01}}
| orbit_reference = Geocentric
| orbit_regime = Low Earth
| orbit_periapsis = {{convert|326|km}}
| orbit_apoapsis = {{convert|1086|km}}
| orbit_inclination = 97.2 degrees
| 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.{{cite web|title=ESRO 2B: May – December 1968|url=http://webapp1.dlib.indiana.edu/cgi-bin/virtcdlib/index.cgi/4646613/FID1/LHEA_CD/docs/heasarc/missions/esro2b.htm|publisher=University of Indiana|access-date=6 March 2013}}
Spacecraft
ESRO-2B was an {{convert|89|kg|abbr=on}} 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,{{Cite web|url=https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=ESRO2A|title = NASA – NSSDCA – Spacecraft – Details}} 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).{{cite web|title=ESRO 2A, 2B (Iris 1, 2)|url=http://space.skyrocket.de/doc_sdat/esro-2.htm|publisher=Gunters Space Page|access-date=6 March 2013}}
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 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