Design in Detail
The body is cylindrical, optimising the field of view of the experiments, which are accommodated around the rim of the main equipment platform on the upper side of the spacecraft. The spacecraft body is 2.9 m in diameter and 1.3 m high. The height was kept to a minimum to make optimal use of the fairing volume offered by the original launch vehicle.
This compact primary structure provides mass-efficient load paths to its mechanical interfaces. It consists of:
The overall design allows for parallel integration of all equipment with the MEP on one side and the central cylinder with the RCS components on the other.
Six cylindrical titanium propellant tanks with hemispherical ends are each mounted to the central cylinder via four CRFP struts and a boss. 650 g (of the total 1180 kg) of propellant is carried in these tanks.
Six curved solar-array panels together form the outer cylindrical shape of the spacecraft body and are attached to the Main Equipment Platform. The MEP provides the mounting area for most of the spacecraft units, the payload units being accommodated on the upper surface and the subystems, in general, on the lower surface. The five batteries and their associated regulator units that power the spacecraft during eclipse are mounted directly on the central cylinder.
At their lower ends, the solar-array panels support a ring accommodating many of the RCS components, including four radial 10 Newton thrusters. Four axial 10 Newton thrusters are mounted on studs on the upper and lower faces of the spacecraft. All thruster positions were carefully chosen to minimise the chances of contamination to the experiments.
Because the solar-array panels experience extremely low temperatures during eclipse, special care had to be taken in designing their attachments to the structure and the thermal insulation of their inner faces, in order to minimise the on-board heating requirements in eclipse. The inner equipment panel inside the central cylinder supports the single main engine, two high-pressure tanks and associated propellant-management hardware.
The central cyclinder carries aluminium interface rings at both its upper and lower ends. The lower ring is compatible with the Ariane 1.194 m diameter adaptor and separation mechanism (unchanged for Soyuz). The upper ring simulates the interface offered by the adaptor and is equipped with a separation mechanism. This allows two spacecraft to be stacked on top of one another, whilst themselves remaining identical to the maximum extent possible.
Two rigid, double-hinged radial booms on the upper surface of the Main Equipment Platform carry payload sensors. These booms are stowed for launch (as can be seen in the picture), as are the four payload wire booms and the two rigid, single-hinged antenna booms carrying the S-band antennas. The rigid booms consist of CFRP tubes with titanium-alloy end fittings and deployment mechanisms. The radial booms will be deployed mainly by the centrifugal force developed by the spinning spacecraft, while the antenna booms are driven by redundant springs.