1. Introduction

The study of the spectral and temporal behaviour of sources over a wide range of energies is of primary importance for the understanding of the mechanisms that, in several instances, produce spectral features localized in different regions of the electromagnetic spectrum. This fact has become more and more evident in the last years, when the efforts made by several scientists to organize complex campaigns of simultaneous observations with different satellites and ground-based facilities have been rewarded by excellent results.

BeppoSAX, Satellite italiano per Astronomia X, is the first X-ray mission with a scientific payload covering more than three decades of energy - from 0.1 to 300 keV - with a relatively large area, a medium energy resolution and imaging capabilities (resolution of about ) in the range of 0.1-10 keV. This capability, in conjunction with the presence of wide field instruments primarily aimed at discovering transient phenomena, which could then be observed with the wide band instruments, will provide an unprecedented opportunity to study the wide band behaviour of several classes of X-ray sources.

BeppoSAX is a major program of the Italian Space Agency (ASI) with participation of the Netherlands Agency for Aereospace Programs (NIVR). The mission development is supported by a consortium of scientific institutes, The BeppoSAX Consortium, composed as follows:

• Istituto Astrofisica Spaziale (IAS), C.N.R., Frascati and Unita' GIFCO Roma
• Istituto di Fisica Cosmica ed Applicazioni Informatica (IFCAI) and Unita' GIFCO, Palermo
• Istituto Fisica Cosmica e Tecnologie Relative (IFCTR), CNR and Unita' GIFCO, Milano
• Istituto per le Tecnologie e Studio Radiazioni Extraterrestri (ITeSRE), C.N.R., Bologna and Universita' di Ferrara
• Space Research Organization of the Netherlands (SRON), The Netherlands
• Space Science Department (SSD), ESA, Noordwijk, The Netherlands.

The Max Planck Institute for Extraterrestrial Physics has supported the tests and calibrations of the X-ray optics and the focal plane detectors.

Prime industrial contractors are Alenia Spazio for the Space Segment and Nuova Telespazio for the Ground Segment.

The structure of this paper is as follows: in Sect. 2 we illustrate the satellite and scientific instruments; in Sect. 3 we describe the operations; in Sect. 4 we show the scientific capabilities of the instruments and in Sect. 5 we illustrate the main scientific objectives and the program of the mission.