August 03, 2012
Text: Helmut Hornung
Monday, 6 August, 3 p.m. local Martian time: travelling at a speed of more than 21,000 kilometres per hour a metal cone enters the top layers of the Martian atmosphere. After a few seconds the heat shield starts to glow - a meteor flares up in the sallow sky over the reddish-brown rocky desert. Less than four minutes after the entry manoeuvre the space vehicle is racing down towards the surface with the speed of a jet engine. Eleven kilometres above the surface a parachute shoots out of the capsule, shortly afterwards the front heat shield is blasted off.
Now the rover goes into action. A camera eye and descent radar continuously report data such as descent speed and position above the planned landing site back to the onboard computer. It controls the process and finally gives the command to eject the top heat shield and the parachute. Eight rocket engines ignite and bring Curiosity to within a few metres of the surface.
What follows now is unique in the history of space travel. While the landing unit hovers in the air, the rover is slowly lowered to the ground suspended from three cables. It looks as if a “celestial” crane is setting down a load. This explains why the engineers call this stage of the descent the Sky Crane. As the rover is being lowered it unfolds its six wheels. When it has made contact with the ground the vehicle releases itself, the Sky Crane shoots up into the sky before crashing down again at a safe distance from Curiosity.
Even optimists have some concerns given the complexity of the manoeuvre, which has never been done before. But this time, the NASA engineers could not resort to the tried-and-tested airbag method which had been used to successfully land the two rovers Spirit and Opportunity, for example. Weighing in at around 99 kilograms, Curiosity is simply too heavy. Moreover, the landing must proceed fully automatically. The engineers in the control centre have no chance to intervene, because Mars is almost 250 million kilometres away and the signals take 14 minutes to get there, even at the speed of light.
The rolling laboratory the size of a small car has ten scientific instruments on board which receive their energy from a radioisotope generator with 4.8 kilograms of plutonium. Two cameras (MastCams) observe their surroundings very closely, while twelve more are used for navigation. The ChemCam. is a special feature. The instrument bombards a rock, for example, with a laser beam and analyses the radiation released by the vaporisation in a spectrometer, whose sensitivity ranges from the ultraviolet through to the near infrared. One camera observes the sample area.
In addition to instruments for recording the weather or the cosmic radiation, CheMin and SAM are used particularly for the geological field research. Both experiments make it possible to accurately determine the composition of minerals. SAM measures the isotopic ratio of carbon and oxygen in a sample so that the researchers can draw conclusions about the geological history of the red planet. And more is yet to come: the ensemble of mass spectrometer, laser spectrometer and gas chromatograph can also “sniff” out organic substances and thereby find out whether the fundamental building bricks of life are present on Mars.
The choice of landing site is ideal for this: the Gale crater, named after the Australian astronomer Walter F. Gale (1865 to 1945), lies in the Elysium volcanic region and was formed at least three billion years ago in a meteorite impact. Its central mountain, Aeolus Mons, towers up to five kilometres into the sky and consists of layered rock. It is obvious that erosion processes such as wind, maybe even flowing water, were at work here and have left their mark on the ground.
Curiosity is to land at the foot of the mountain. On the pictures taken by other space probes the region appears flat. Nevertheless, the scientists hope for fascinating insights and views. Over the next two years the rover will travel around two dozen kilometres. And - if it remains in good health – it will also climb the mountain. Mars research would then have reached its peak in the truest sense of the word.