Rosetta's Christmas present to Mars Express
24 December 2000On 25 December 2003, ESA's Mars Express orbiter will arrive in orbit around the Red Planet after releasing a small lander named Beagle 2 onto its rust-coloured, dusty deserts. This wonderful Christmas present for planetary scientists would not have been possible without major contributions from another ESA project - the Rosetta comet chaser.
Although both missions are due for launch in 2003, their backgrounds are very different. Mars Express is a medium-sized mission, one of the pioneers in ESA's efforts to build faster, cheaper, space science missions. Rosetta is a more ambitious, more expensive, Cornerstone mission, which will spend more than a decade travelling through the Solar System in an effort to unravel the secrets of Comet Wirtanen.
Mars Express is the first of the ESA's new "flexible" missions. With a total budget of just 150 million Euro (1996 prices), it will be built and launched for about half the cost of similar, previous missions. However, this has only been made possible by re-using existing hardware, adopting new project management practices, shortening the design and development time, and minimising launcher costs.
In particular, Mars Express is making maximum use of pre-existing "off-the-shelf" technology and hardware that has already been developed for the Rosetta Orbiter. About 60% of the technology on the Mars Express spacecraft has been "borrowed" from Rosetta (see table). This includes such vital components as the onboard computer, the low gain antenna for communication with Earth, and the gyroscopes that control the spacecraft's attitude.
Mars Express hardware items in common with Rosetta
- Command and data handling system (on-board computer)
- Transponder (transmitter and receivers in S and X band)
- Low gain antenna
- Gyroscopes and accelerometers
- Solar array drive mechanism, a motor and gearbox to rotate each array by more than one turn in each direction
- Power control unit to ensure maximum power generation by the solar array
- Power distribution unit to distribute power to all on-board consumers and avoid short circuits should one of them fail.
- Remote terminal units to interface a system, such as the sun sensor or science instruments, with the on-board computer.
- Interface unit to the on-board computer for attitude determination sensors
- Star Tracker
"What we are doing with Mars Express will affect flexible missions at the agency, which may in future be linked more closely to major missions," said Rudi Schmidt, Mars Express Project Manager. "In this way, we are able to make savings without taking big risks."
"A further advantage is that 'commonalities' with Rosetta and its payload make it possible to streamline management methods by handing over more responsibility to industry," he added.
"Rosetta will spend 11 years in deep space, travelling almost as far as the orbit of Jupiter before entering orbit around the comet's nucleus and then flying alongside the comet on its journey towards the Sun," explained John Ellwood, Rosetta's Project Manager. "Such a complex, groundbreaking mission requires the maximum reliability and the highest specifications for its components. We are delighted to be able to share these new technologies with our colleagues on Mars Express."