When folded up, the Beagle 2 lander resembles a very large pocket watch. This is the state in which it passed the long journey to Mars, attached to one side of the Mars Express spacecraft underneath the umbrella of its heat resistant shield.
Beagle 2 Lander
Five days before reaching Mars in late December 2003, a spring mechanism on board Mars Express will eject Beagle 2. The mothercraft will leave the little lander to make its own descent to the surface, powered only by the pull of the planet's gravity. The heat resistant shield will protect it as friction with the upper atmosphere slows it down. When its speed has fallen to about 1600 kmh-1, parachutes will deploy to slow it further. Finally, large gas-filled bags will inflate to protect it as it bounces to a halt on Isidis Planitia, the selected landing site.
As soon as the lander has come to a halt, the gas-filled bags will be released and the outer casing will open to reveal the inner workings. First, solar panels will unfold: they will catch sunlight to charge the batteries which will power the lander and its experiments throughout the mission. Next, a robotic arm will spring to life. Attached to the end of the arm will be Beagle's PAW (Position Adjustable Workbench) where most of the experiments are situated. The PAW's first job will be to move around so that the cameras attached to it can take in the view.
"Beagle 2 must accomplish its mission in just 180 sols (Martian days which are almost the same length as an Earth day). The first few days will be spent running pre-programmed sequences, imaging the site and running the environmental sensors, preparing for when the lander will start doing very detailed rock and soil analysis," says Mark Sims, Beagle 2 lander manager from Leicester University, United Kingdom.
Beagle 2 will land on Isidis Planitia, a large, flat sedimentary basin straddling the relatively young northern plains and ancient southern highlands, where traces of life could have been preserved. The landing site (11.6oN, 90.75oE) is at low latitude to minimise the amount of insulation (and hence mass) needed to protect the lander from the cold Martian night.
The site is not too rocky to threaten a safe landing (but rocky enough to be interesting for the experiments), has few steep slopes down which the probe may have to bounce as it lands, and is not too dusty. Isidis Planitia is at a low enough elevation to provide sufficient depth of atmosphere to allow the parachutes to brake the lander's descent.
The region seems to be a sedimentary basin where traces of life could have been preserved. "This is the best site given the landing constraints and scientific aims of Beagle 2," says John Bridges from the Natural History Museum, London who lead the landing site study.
Like the Mars Express mothercraft, the Beagle 2 probe is pioneering new methods of spacecraft project management and construction. The main engineering challenges are a consequence of the probe's mass (about 65 kg) and size (just 0.95 m in diameter). "A consequence of the low mass and small size is that we have to design the whole thing as one entity - nobody provides any boxes. We've taken the requirements and functionality and designed it as a collective system: it's a spacecraft where all the functionality is integrated together. The mass and size drive this approach," says Mark Sims, Beagle 2 project manager at Leicester University in the United Kingdom.