Microsatellites and space station for science and technology utilisation

The main results of an ESTEC study on microsatellites and the International Space Station (ISS) are shown herein. One of the original objectives of the space station has been to be a staging post for assembly, check-out and deployment of satellites and deep-space missions. ISS will not be equipped to process and launch large spacecraft requiring complex assembly and propellant operations, but deployment of a microsatellite might still be feasible and advantageous, as other international partners show similar interests. The assembly, launch and retrieval of small satellites with ISS (e.g. up to 225 kg, 100 W of power from body mounted solar cells or 225 W from solar panels, size less than 1.6 x 0.8 x 1 m, 250 b s(-1) to 2 kb s(-1) of up and down link data) is a future but a technically viable option to raise the attractiveness of LSS for those payloads whose requirements would not be satisfied by internal or external accommodation on ISS. Two classes of payloads were identified: (1) Space Station investigation (SSI) type; (2) Space Station exploitation (SSE) type. SSI payloads conduct investigations of direct interest to ISS as electromagnetic, radiation and particle near-environment (ISS sniffers). Instead, SSE investigations are totally unrelated to ISS and they make solely advantage of its infrastructure and facilities. For the latter it will be necessary to compare the same experiment with and without ISS in the mission scenario, as a proof of effectiveness (in costs and/or scientific return) with respect to satellites launched by traditional means. Such effectiveness may be represented by (i) simplicity of design, e.g. the proximity of ISS eases the TT&C subsystem, (ii) servicing and re-utilisation for successive experiments, (iii) readiness to launch when a specific and unpredictable event occurs (e.g. supernovae). Different scenarios and implementations have been studied for launch and operations. Safe orbital trajectories have been identified also without a propulsion system. In case of a on-board propulsion system, about 50 kg for cold gas fuel and another 50 kg for dry propulsion system, were found necessary for a mission lifetime in ISS neighbourhood (within 50 km) up to about 6 months. The study has conceived 13 proposals in disciplines ranging from metrology and general physics, to space science and technology, as examples of potential applications but in no manner constituting an exhaustive picture of user interests. An SSI experiment for the analysis of ISS environment was selected as potential first mission. (C) 1997 Elsevier Science Ltd.