Life and survival in deep space
Rosetta's deep space odyssey will comprise lengthy periods of inactivity, punctuated by relatively short spells of intense activity – the encounters with Mars, Earth and asteroids.
Ensuring that the spacecraft survives the hazards of travelling through deep space for more than ten years is therefore one of the great challenges of the Rosetta mission.
For much of the outward journey, the spacecraft will be placed in 'hibernation' in order to limit consumption of power and fuel, and to minimise operating costs. At such times, the spacecraft spins once per minute while it faces the Sun, so that its solar panels can receive as much sunlight as possible.
Almost all of the electrical systems are switched off, with the exception of the radio receivers, command decoders and power supply.
Instructions from the ground take up to 50 minutes to reach the spacecraft and so Rosetta must have the 'intelligence' to look after itself. This is done by its on-board computers, whose tasks include data management and attitude and orbit control.
In case any problems arise during the lengthy cruise, back-up systems have been added to ensure that the spacecraft can remain operational during critical mission phases.
Hot and cold
Temperature control was a major headache for the designers of the Rosetta spacecraft. Near the Sun, overheating has to be prevented by using radiators to dissipate surplus heat into space. In the outer Solar System, the hardware and scientific instruments must be kept warm (especially when in hibernation) to ensure their survival.
This is achieved by using heaters located at strategic points (e.g. fuel tanks, pipework and thrusters), placing louvres over the radiators, and wrapping the spacecraft in multi-layered insulation blankets to cut down on heat losses.
Rosetta will be the first space mission to journey beyond the main asteroid belt and rely solely on solar cells for power generation, rather than the traditional radio-isotope thermal generators.
The new solar-cell technology used on the orbiter's two giant solar panels allows it to operate over 800 million kilometres from the Sun, where sunlight levels are only 4% those on Earth.
Hundreds of thousands of specially developed, non-reflective, silicon cells generate up to 8700 Watts in the inner Solar System and around 400 Watts for the deep-space comet encounter.
Last update: 1 November 2004