Rosetta all set for Mars swing-by

Rosetta, the European Space Agency’s (ESA) spacecraft en route to comet 67P Churyumov Gerasimenko, is gearing up for a swing-by of Mars on 25th February 2007, which will help set it on the correct path to its final destination.

On arrival in 2014 Rosetta will home in towards the comet’s nucleus before deploying a lander onto its surface to make in situ measurements. As the oldest and most primitive bodies in the solar system comets provide the key to unlocking the secrets of our Universe. Comets have remained unchanged in comparison to other bodies within our solar system and provide the earliest record of materials in a pristine form.

UK scientists from 10 institutions are involved in the instruments on both the Rosetta orbiter and lander – some of which will be operating during the flyby. UK industry is also heavily involved in the mission, having provided key components, including the mission control system (SciSys UK Ltd) and the orbit control and propulsion system (EADS Astrium, UK). SciSys staff will be closely monitoring events at ESA’s European Space Operations Centre (ESOC) in Germany where the manoeuvre is being co-ordinated.

Launched in March 2004 the three tonne spacecraft could not be sent on its correct trajectory by the launcher and so on its journey it will make a series of planned gravity assist manoeuvres past the Earth and Mars.

Professor Keith Mason, CEO of the Particle Physics and Astronomy Research Council (PPARC) said, “With Rosetta now 3 years into its epic 10 year journey this flyby is an important milestone for the spacecraft. Not only will it help set it on its correct path but it provides a further opportunity to find out more about Mars from a different perspective.”

Rosetta’s closest approach to Mars will be made at 0153 GMT on 25th February 2007, 1090 days since launch.The distance from Rosetta to the surface of Mars will be around 250 km, and at its closest approach the spacecraft will be travelling at around 10.1 km/s (~36,400 kph ~22,700 mph) relative to the centre of Mars.

During the swing by there will be a 25 minute period when Rosetta is passing through the shadow of Mars, and during this time it will be impossible to generate power using the spacecraft’s vast solar arrays (which span 32 metres from tip to tip). To cope with this the orbiter will be placed in “eclipse mode”, and no science operations will take place onboard for approximately 3 hours around close approach. Rosetta will be able to view the planet Mars to either side of this ‘blackout’ .

The Rosetta lander, Philae, can be powered independently from the orbiter, and some instruments will be taking scientific measurements during the entire close approach. Professor Ian Wright from the Open University is lead investigator on Ptolemy, an instrument on the lander. He said, “Rosetta’s close vicinity to Mars will provide an excellent opportunity to take a close look at the planet. It also means that some of Rosetta’s instruments, including the mass spectrometer built at the OU, will be able to be calibrated allowing us to check that they are operating correctly.”

Professor Andrew Coates from UCL’s Mullard Space Science Laboratory, who is a co-investigator on both Rosetta and ESA’s Mars Express which continues to orbit the planet, adds, “Rosetta will use its imaging system and imaging spectrometers to gather data about the surface and atmosphere of Mars and its chemical composition. It will also collect data about the atmosphere’s interaction with the solar wind and the Martian radiation environment, and image the two natural satellites of Mars, Phobos and Deimos. All this data will complement the continuing work of Mars Express.”

Imperial College London leads the team which operates the Rosetta Plasma Consortium (RPC). Chris Carr from the team explains, “All five sensors of the RPC will be operating near-continuously for 2 days both before and after the Mars encounter. Rosetta passes so close to the planet that it will actually fly through the ionosphere – though unfortunately this coincides with the critical eclipse period where the instruments have to be temporarily shut-down. Elsewhere though, one of the RPC sensors, the ‘Ion Composition Analyser’, has a unique opportunity to do simultaneous measurements with its identical twin instrument on the Mars Express spacecraft.”

The RSI (Radio Science Investigation) team, with participation from Cardiff University, plans to gain information on the Martian ionosphere through changes to the radio signals both before and after Rosetta disappears behind the planet.

This Mars swing-by is the second such manoeuvre that Rosetta has made following on from an Earth swing-by in March 2005. A further Earth swing-by will take place later this year on 13th November followed by a final Earth swing-by in November 2009.

From Particle Physics & Astronomy Research Council


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