The Rosetta orbiter - spacecraft design

Rosetta is a large aluminium box with dimensions 2.8 x 2.1 x 2.0 metres. The scientific instruments are mounted on the 'top' of the box (Payload Support Module) while the subsystems are on the 'base' (Bus Support Module).

On one side of the orbiter is a 2.2-metre diameter communications dish – the steerable high-gain antenna. The lander is attached to the opposite face.

Two enormous solar panel 'wings' extend from the other sides. These wings, each 32 square metres in area, have a total span of about 32 metres tip to tip. Each of them comprises five panels, and both may be rotated through +/-180 degrees to catch the maximum amount of sunlight.

In the vicinity of Comet 67P/Churyumov-Gerasimenko, the scientific instruments almost always point towards the comet, while the antennae and solar arrays point towards the Sun and Earth (at large distances, they are more or less in the same direction).

In contrast, the orbiter’s side and back panels are in shade for most of the mission. Since these panels receive little sunlight, they are an ideal location for the spacecraft’s radiators and louvres. They will also face away from the comet, so damage from comet dust will also be minimised.

Propulsion

At the heart of the orbiter is the main propulsion system. Mounted around a vertical thrust tube are two large propellant tanks, the upper one containing fuel, and the lower one containing the oxidiser.

The orbiter also carries 24 thrusters for trajectory and attitude control. Each of these thrusters pushes the spacecraft with a force of 10 Newtons, about the same as experienced by someone holding a large bag of apples. Over half the launch weight of the entire spacecraft is taken up by propellant.

An international enterprise

Rosetta’s industrial team involves more than 50 contractors from 14 European countries and the United States. The prime spacecraft contractor is Astrium Germany. Major subcontractors are Astrium UK (spacecraft platform), Astrium France (spacecraft avionics) and Alenia Spazio (assembly, integration and verification).