Solar and Heliospheric Observatory (SOHO) Spacecraft Overview
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    [The text in this file was compiled by Matthew Knight, University of
     Maryland from online resources made publicly available by the SOHO
     website.]

The SOHO spacecraft was launched in December 1995, however the LASCO
instrument did not begin regular observing until January 21, 1996.
It has operated nearly continuously since then except for an
interruption from June 25, 1998 until October 22, 1998.  Smaller
unplanned interruptions have occurred periodically, and pre-planned
interruptions for routine maintenance, calibration, and satellite
control have occurred, and will continue to occur until the conclusion
of the mission.

The SOHO spacecraft is three-axis stabilized and pointed towards the
Sun with an accuracy of +/- 10 arcseconds per 15 minutes.  It consists
of a Payload Module to accommodate the instruments and a Service Module
carrying the spacecraft subsystems and solar arrays.  SOHO occupies a
halo orbit at the Earth-Sun L1 Lagrangian point to obtain uninterrupted
sunlight. The design life was two years, but on-board consumables were
sufficient for at least an extra four years of operations, and the
nominal mission end is now March 2007.

Twelve instruments comprise the payload, producing a continuous stream
of data at 40 kilobits/seconds, except when the solar oscillations
imager Michelson Doppler Imager (MDI) operates in high-bit-rate mode,
producing 160 kilobits/seconds.  The high-bit-rate mode is used during
scheduled daily eight-hour periods or during dedicated campaigns.
Magnetic tape stores data between telemetry contacts with the Experiment
Operations Facility, located at NASA-GSFC.  For more information, see
B. Fleck, V. Domingo, and A. I. Poland, editors, Solar Physics, V. 162,
1995.

References
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Fleck B., V. Domingo, A.I. Poland, The SOHO Mission, Solar Phys., 162, 
  1-531, 1995.