Figure 1.1: SOHO spacecraft schematic view
The SOHO spacecraft (Fig. 1.1) will be three-axis stabilized and point to the Sun within an accuracy of 10 arc sec and have a pointing stability of 1 arcsec per 15 minutes interval. It will consist of a payload module which accommodates the instruments and a service module carrying the spacecraft subsystems and the solar arrays. The total mass will be about 1850kg and 1150W power will be provided by the solar panels. The payload will weigh about 640kg and will consume 450W in orbit.
SOHO is planned to be launched in July 1995 and will be injected in a halo orbit around the L1 Sun-Earth Lagrangian point, about 1.5x10km sunward from the Earth. The halo orbit will have a period of 180 days and has been chosen because, 1) it provides a smooth Sun-spacecraft velocity change throughout the orbit, appropriate for helioseismology, 2) is permanently outside of the magnetosphere, appropriate for the ``in situ'' sampling of the solar wind and particles, and 3) allows permanent observation of the Sun, appropriate for all the investigations. The Sun-spacecraft velocity will be measured with an accuracy better than 0.5 cm/s.
SOHO is being designed for a lifetime of two years, but will be equipped with sufficient on-board consumables for an extra four years.