Soho: A modular spacecraft concept to allow flexible payload integration and efficient development

SOHO is a large spacecraft developed within the Solar-Terrestrial Science Programme (STSP) in the frame of a joint effort between ESA and NASA. STSP aims at providing a global observation of the Sun and of its influence on Earth environment. SOHO, located at the first Lagrangian point of the Earth-Sun system will directly observe the Sun and measure the interplanetary medium, while the Cluster programme composed of four spacecrafts orbiting around the Earth will analyse the space plasma physics and processes within the magnetosphere. Not less than 11 experiments are carried and serviced by the SOHO spacecraft to achieve the scientific objectives : — to investigate the outer layer of the Sun, — to study the solar wind, — to probe the interior structure of the Sun. This paper shows how a modular design can allow to manage the multiple and complex interfaces of such a spacecraft. First of all, a recall of the scientific goals of the payload instruments with associated constraints is made. Then the overall mission implementation is described and the main design features are detailed to show how a great flexibility can be offered in the design and development of the spacecraft : — modularity has governed the design of the spacecraft not only at mechanical level but also at electrical level for which simple and standardised interfaces have been used, — pre-integration of experiments, subsystems and modules allows minimisation of development risks.