content long 18-November-2017 09:35:44

Engineering

Structure

The spin-stabilised Ulysses spacecraft has a box-type structure with two overhanging balconies and a single aluminium honeycomb equipment platform. All electronics units of the scientific instruments and spacecraft subsystems, most of the sensors and the propellant tank are mounted on this platform. The Radio-isotope Thermoelectric Generator (RTG) which provides the spacecraft's main power is mounted on an outrigger structure to minimise its radiation effects and to isolate the main subsystems and the experiments from excess heat.

Artis's impression of Ulysses

The two-section radial boom carries the two magnetometer sensors, the solar X-ray/cosmic gamma-ray burst sensors and the magnetic search-coil sensor of the wave experiment. Because of the radiation pattern of the RTG, it was necessary to have the gamma-ray sensor lying as closely as possible along the RTG centre axis. The boom design allows for this, at the same time providing the maximum boom-length consistent with a two-hinge system and also satisfying the spacecraft balance constraints in both the stowed and deployed configurations. The boom is made from carbon-fibre-reinforced plastic (CFRP) tubing 50 mm in diameter and with 1 mm wall thickness.

The electrical antennas of the URAP wave experiment consist of a pair of radially extending wire booms in the spin plane and an axial boom deployed along the orbital spin axis. The wire booms consist of 5 mm wide and 0.04 mm thick Cu-Be ribbon stowed during launch on two identical drive units. The wires were deployed to a length of 72.5 m tip-to-tip by centrifugal forces acting on tip masses after the second trajectory correction manoeuvre (TCM-2). Each wire boom has a passive tubular root damper which reduces relative motions between the boom and the spacecraft by natural material damping with a time constant of 3.5 h.

The axial boom element is formed by a pre-stressed, coilable elastic Cu-Be tube anchored in the axial-boom drive mechanism located on the rear face of the spacecraft. The boom element was deployed to a length of 7.5 m by a traction force through a set of rollers driven by a stepper motor one day after the wire booms.


Last Update: 30 November 2006

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