From now until next spring should prove to be an exciting period for ESA's Scientific Programme: ESA is preparing to launch an unprecedented six scientific satellites on three missions in six months. Each mission will be ground-breaking in its own right: one mission will investigate the infrared sources deep in outer space, another will study the Sun and its characteristics, and the third will explore the magnetosphere around the planet Earth.
The Infrared Space Observatory, or ISO, will lead the trio into space. It will be launched on an Ariane-4 rocket early in the morning of 17 November (Central European Time) from ESA's launch site in Kourou, French Guiana. It will be followed a few days later by the Solar and Heliospheric Observatory, or SOHO, which will be launched by an Atlas IIAS rocket from Cape Canaveral, USA. Finally, in April 1996, four Cluster probes will be carried into space on the inaugural flight of Ariane-5.
Many scientists both in Europe and around the world have been patiently awaiting these missions: the state-of-the-art instrumentation onboard the satellites will gather information that will help to answer some of the long-standing scientific questions - What is 'dark matter'? How are stars 'born'? How do changes on the Sun, sunspots for example, affect the climate on Earth?
These missions also demonstrate the high technical standards of ESA and European space industry, which strived to develop what had not been built before: four spacecraft flying in a 'cluster' or tetrahedron, for example, or a spacecraft that must be kept cool, at absolute zero, at all times. The missions are also a tribute to successful international cooperation: two were developed in conjunction with other international space agencies, NASA and Japan's Institute of Space and Astronautical Sciences (ISAS) and all involve the participation of institutes around the world.
The infrared region of the wavelength spectrum is of great scientific interest. Many astronomical sources are surrounded by clouds of dust and gas that act as an interstellar 'fog', obscuring the astronomical objects and making it very difficult to observe them with visible light. Owing to its longer wavelength, infrared radiation can pierce through this fog and bring astronomers information about the conditions inside.
ISO will be the world's first true astronomical observatory in space operating at infrared wavelengths - and the only one for the next ten years. It will be used to observe all classes of astronomical objects, ranging from planets and comets in our own Solar System right out to the most distant galaxies.
The SOHO spacecraft will station itself 1.5 million kilometres from the Sun, on the Sun-ward side of the Earth, where the gravity of the Earth and the Sun are in balance. From that vantage point, it will study the processes that heat the outer atmosphere of the Sun to millions of degrees and propel the continuous stream of plasma known as the 'solar wind'. SOHO will also sample the solar wind as it blows towards the Earth, where it influences our planet's environment.
Earlier missions to explore the Earth's magnetosphere have shown how dramatic the interaction can be between near-Earth space and the solar wind. An incredible range of phenomena have been observed - the shorting out of satellite components in orbit, power surges in long transmission lines, and disturbances in short-wave radio broadcasting, to name a few.
The Cluster spacecraft will address, in unprecedented detail, the structure of electromagnetic fields and the distribution of particles in the solar wind and the Earth's magnetic field. To do so, Cluster will have four identical satellites flying in a kind of pyramid formation - another first - to investigate the phenomena in three dimensions.
Each of these exciting missions is described in detail in the rest of this special science issue of the Bulletin.
ESA Bulletin Nr. 84.