Three ESA missions are due to send down robotic
‘spaceprobes’ when they arrive at their alien destinations. Since these
craft will be going where no one has gone before, how can scientists be
sure what it will be like down there? How do you ensure that your
spaceprobe is prepared for anything?
Experts take every precaution to ensure that these probes
will not burn up entering an alien atmosphere, or meet a
spectacular, untimely end via a crash landing on
inhospitable terrain. These probes expect the worst.
For example, the Huygens probe, which is currently on its journey to Titan,
Saturn’s largest moon, on-board the Cassini spacecraft, can withstand
temperatures of up to 18 000°C in the shockwave in front of the heat
shield. This is about three times the Sun’s surface temperature. Why? The
heat generated as Huygens travels through Titan’s thick atmosphere will be
immense.
Jean-Pierre Lebreton, Huygens Project Scientist, says “Things will get
interesting once Cassini draws close to Saturn. We’ll get the best views
of Saturn and Titan that we ever had. We’ll also observe Titan to verify
that our models are correct. 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. However, late changes may bring new
risks.”
Scientists chose the site for the landing of the Mars Express lander,
Beagle 2, very carefully. Isidis Planitia, the chosen site, is largely flat
without too many rocks to jeopardise a safe landing. However, Mars’s
famous planetwide dust storms were taken into consideration. ” Major
dust storms are not expected to occur at the time and place of the landing.
However, there may be strong lateral winds.” says Mars Express Project
Scientist Agustin Chicarro.
ESA’s Rosetta lander, which will be the first man-made object to land
on a comet, has another set of challenges altogether. “Firstly, we don’t
know anything about how rough the surface is,” says Rosetta Project
Scientist Gerhard Schwehm. “It could be covered with fluffy snow like the
Alps or it could be hard rocks and craters. We can, however, be sure
that it will not be smooth and flat resembling parking lots.”
Scientists designed Rosetta’s landing gear to cope with most nasty
surprises as soon as it touches down on Comet Wirtanen in 2011. Two
harpoons will anchor the probe to the surface. The self-adjusting landing
gear will ensure that it stays upright, even on a slope. The lander’s feet
will drill into the ground. These devices will help counteract the fact
that there is no gravity on a comet.
Observations of Mars, Titan, and Comet Wirtanen will continue
frantically while the spacecrafts approach their final destination. In this
way, scientists will be able to make last-minute adjustments to the
timing of the landing. Information from other space missions and
ground-based observations will increase scientists’ understanding about
the targets of the missions. In Rosetta’s case, this will help to determine
the comet’s probable size and speed of rotation. These will help improve
our ‘models’ for comet behaviour. However, for Rosetta, they may come
too late. “We’ll just have to see if the models we’re using are good
enough” says Schwehm.
