The European Space Agency’s (ESA) Rosetta spacecraft - with Open University science on board - successfully completed a swing-by of Mars in the early hours of Sunday morning (25th February 2007). It’s an important milestone on the spacecraft’s 7.1 billion km journey to comet Churyumov Gerasimenko and it provided a unique opportunity to gather further scientific data and images from the Red Planet.
The critical gravity assist manoeuvre around Mars has helped Rosetta change direction – putting it on the correct track towards Earth its next destination planet whose gravitational energy Rosetta will exploit in November this year to gain acceleration and continue on its ten-year journey to the comet which it will reach in 2014. The OU's Dan Andrews who has worked on the mission as part of its Centre for Earth, Planetary, Space and Astronomical Research (CEPSAR) said: "A spacecraft rarely has a rocket powerful enough to send it directly to its target in one shot. So we use slingshots around the planets to steal orbital energy from them".
At its closest approach (around 2.15 GMT) Rosetta passed the surface of Mars at a distance of 250 km (155 miles) travelling at a mere 10.1 km/second relative to the centre of the planet.
During the swing by there was a 25 minute period when Rosetta passed into the shadow of Mars denying the probe the ability to generate power using its solar arrays. At this time the spacecraft was put into “eclipse mode” with no science operations taking place on the orbiter instruments.
Rosetta swings close by Mars - ESA photo
The camera onboard the lander (CIVA) provided a stunning image showing sections of the spacecraft and one of its solar arrays with Mars in the background. The photograph on the right was taken by a camera on the Philae lander on board Rosetta which will attempt to land on the comet in 2014. The Ptolemy instrument on Philae was developed by CEPSAR scientist at The Open University.
Professor Keith Mason, CEO from the Particle Physics and Astronomy Research Council (PPARC), said, “Rosetta has provided some amazing images of Mars from a completely different perspective. Data gathered during the swing-by will complement that collected by other current missions enabling us to build up a comprehensive picture of the make up of Mars.”
However, during the lead up to the closest approach and after the eclipse period the flyby presented scientists with a golden opportunity to calibrate the payload with instruments on other orbiting spacecraft such as Mars Express and Mars Reconnaissance Orbiter. Prior to the orbiter’s instruments being switched off the Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS) captured some detailed images showing the atmospheric features of Mars, including cloud systems above the North polar cap.
Professor Ian Wright from the Open University is Principal Investigator for Ptolemy, a miniaturised mass spectrometer on the lander – whose instruments were able to operate during the whole period of the close approach. He said, “This is the first time that the Philae lander has operated autonomously, completely relying on the power of its batteries. It is reassuring to know that so many miles away from home all instruments operated as is planned. This was a great rehearsal for 2014 and touch down on the comet when Philae will conduct its scientific measurements independent from the Rosetta orbiter.”
UK scientists from 10 institutions are involved in the instruments on both the Rosetta orbiter and lander. Chris Carr leads the Imperial College London team that operates the Rosetta Plasma Consortium (RPC) instruments, “Our instruments operated near continuously both sides of the flyby – allowing simultaneous measurements with its identical twin instrument on Mars Express. With Rosetta and Mars Express together, we hope to understand more about the vast and complex plasma environment around the red planet.”