Brussels, 15 Oct 2002
How can you be prepared for any eventuality when you are aiming to go where no-one has gone before? Some challenge, and one that European Space Agency (ESA) scientists will have to overcome on three occasions in upcoming missions to land 'space probes' on alien worlds.
The dangers facing any attempt to land a craft in space are numerous. From the extreme demands of atmospheric entry to unpredictable and hostile weather conditions, scientists have to prepare for all eventualities in the hope of successfully delivering these expensive and one time probes to their intended destinations.
One such probe is Huygens, currently en-route to Titan, Saturn's largest moon, aboard the spacecraft Cassini. It has been built to withstand temperatures of 18,000 degrees Celsius, three times the heat of the Sun's surface, to enable it to penetrate Titan's dense atmosphere.
This would seem sufficient, but as Jean-Pierre Lebreton explains, the Huygens team are taking nothing for granted. 'Things will get interesting once Cassini draws close to Saturn. If we find the atmospheric density is different from what we expected, we could consider slightly changing the angle at which Huygens enters to protect it from overheating or the parachute deploying wrongly.'
The team in charge of the ESA's Rosetta lander, which aims to be the first manmade object to land on a comet (Comet Wirtanen 2011), have also prepared for a number of contingencies. They have no idea what the terrain of the comet will be like, so on touchdown two harpoons will be used to anchor the probe to the surface, be it rock, ice or snow.
Self-adjusting landing gear will then ensure that the craft remains upright, even on a slope. As if one were needed, a further challenge will be the comet's lack of any gravity - in order to remain 'landed', the probe's feet will have to drill themselves into the ground.
Weather conditions represent the greatest concern for scientists on the Beagle 2 Mars Express lander project. They have chosen a rendezvous date that should ensure that Beagle 2 avoids any of Mars' planet wide dust storms, but the high risk of strong lateral winds has led the team to chose a landing site that is extremely large and flat to give it the best chance of a safe touchdown.
Ground based research can help to give scientists an idea of the challenges they will face during these landings. Data from previous missions, if they exist, can also add to their knowledge, and, as with the Cassini mission, even data gathered in the days and hours before touchdown can allow for some last-minute adjustments. But the key to successfully landing manmade probes in alien environments is planning for every possible eventuality, as all three ESA teams have tried to do. And even then, all of them will be hoping for that final ingredient to ensure a smooth mission, a bit of good luck.
For further information, please consult the following web address: http://www.esa.int