Organization/Nation: ESA and U.S. (2)
Objective(s): L1 Libration Point
Spacecraft Mass: 1,864 kg
Mission Design and Management: ESA and NASA
Launch Vehicle: Atlas-Centaur IIAS (AC-121 / Atlas IIAS no. 8206 / Centaur II)
Launch Date and Time: 2 December 1995 / 08:08:01 UT
Launch Site: ESMC / launch complex 36B
1) SUMER solar-ultraviolet emitted radiation experiment
2) CDS coronal diagnostic spectrometer
3) EIT extreme ultraviolet imaging telescope
4) UVCS ultraviolet coronograph spectrometer
5) LASCO white light/spectrometric coronograph
6) SWAN solar wind anisotropies experiment
7) CELIAS charge, element/isotope analysis experiment
8) COSTEP suprathermal/energeticparticle analyzer
9) ERNE energetic-particle analyzer
10) GOLF global oscillations at low frequencies experiment
11) VIRGO variability of solar irradiance experiment
12) MDI Michelson Doppler imager
Results: The ESA-sponsored Solar and Heliospheric Observatory (SOHO) carries twelve scientific instruments to study the solar atmosphere, helioseismology, and solar wind. Information from the mission allows scientists to learn more about the Sun?s internal structure and dynamics, the chromosphere, the corona, and solar particles.
The SOHO and Cluster missions, part of ESA?s Solar Terrestrial Science Programme (STSP), are ESA?s contributions to the Inter-Agency Solar Terrestrial Physics (IASTP) program. NASA contributed three instruments on SOHO as well as launch and flight operations support.
About two months after launch, on 14 February 1996, SOHO was placed at a distance of 1.5 million kilometers from Earth at the L1 Libration Point. The spacecraft returned its first image on 19 December 1995 and was fully commissioned for operations by 16 April 1996.
SOHO finished its planned two-year study of the Sun?s atmosphere, surface, and interior in April 1998. Communications with the spacecraft were interrupted for four months beginning on 24 June 1998, but, after intensive search efforts, controllers managed to regain full control by 16 September.
Barring three instruments, the spacecraft was functional and was declared fully operational once again by mid-October 1998. SOHO?s original lifetime was three years (to 1998), but ESA and NASA jointly decided to prolong the mission, enabling the spacecraft to compare the Sun?s behavior during low dark sunspot activity (1996) to the peak (around 2000).
One of SOHO?s most important discoveries has been locating the origin of the fast solar wind at the corners of honeycomb- shaped magnetic fields surrounding the edges of large bubbling cells located near the Sun?s poles. SOHO remains in its halo orbit, circling L1 once every six months.
Editor's Note: This mission profile was originally published in Deep Space Chronicle: A Chronology of Deep Space and Planetary Probes 1958-2000, by Asif A. Siddiqi, NASA Monographs in Aerospace History No. 24. The text has been updated to reflect events that occurred after the book's publication in July 2002