Mars - MGExcavator at Mars pole

After a fortuitous landing close to the ice-covered north pole of Mars, the NASA Phoenix lander is operating as a remotely controlled digging machine. On board the platform are two German items of equipment: a camera and a detector for the analysis of soil samples

PhoenixMarsLander Bild (Standa

Mars Lander Phoenix auf der Oberfläche des Roten Planeten (C) NASA Image  


On 25 May 2008 Phoenix landed close to the north pole of the Red Planet after long preparations and with assistance from other space probes that are currently circling Mars. Everything was set to go as planned, and in the event it did. "The landing was unbelievably smooth," Dr. Horst Uwe Keller told FLUG REVUE. The scientist at the Max Planck Institute of Solar System Research (MPS) in Katlenburg-Lindau played a significant role in the development of the German camera which is attached to the 2.35 metre long robotic arm of the lander. "We simulated the most impossible scenarios for the descent of the lander," he said, "but fortunately none of them occurred. So, for example, we had assumed that the signal would fail for several minutes during the descent phase. That would actually have been quite normal, but as it turned out we received signs of life from the lander without interruption. It was fantastic!"

Not a single fault occurred during the flight, landing or the work on the surface of Mars to date. The landing site was just one-third of a degree off the horizontal. Still, the atmosphere of Mars is a lot thinner than the Earth’s, so that despite the big parachute there can be problems with braking retardation. On the other hand this time NASA did not use any airbags for the last leg of the descent, but twelve retrorockets which functioned impeccably instead.

For Keller and his three German scientist colleagues, who are currently working at the control centre in the USA, Phoenix counts as a quick mission. For example, it is quite different from Cassini, the outbound flight of which stretched over several years, and the probe is still sending back images today. The Rosetta comet probe mission, which is not scheduled to reach its destination until 2014, will take even longer. Dr. Keller and his cameras are involved in everything. Many years of work have gone into their development. "At the moment six of my cameras are flying through space," says Keller proudly, "two of them on the US probe Dawn."

The collaboration between NASA and MPS dates back over twenty years: in March 1986, a camera from Katlenburg photographed the core of the Giotto comet for the first time. Since then NASA has come to rely on cameras and imaging detectors from Germany. Thus, the proposal for the Mission Mars Pathfinder came from MPS, and later Keller developed the camera for the Mars Polar Lander.

The Mars Polar Lander was supposed to touch down at the south pole of Mars in December 1999 and perform tasks similar to those being carried out by Phoenix today. But contact was lost after entry into the Mars atmosphere and was never restored, so that it is assumed that the space probe was dashed to pieces on the surface of Mars. Moreover, this same fate befell almost half of all previous Mars missions which ended in failure for a variety of reasons, starting with the Mars Climate Orbiter in September 1999. But NASA did not give up and launched the Discovery programme of Mars exploration, under which a relatively low-cost space probe, a rover or a lander should be sent to our planetary neighbour roughly every two years. The requirement for strict cost control was imposed after the billion dollar Mars Observer was lost in August 1993, a bitter blow for NASA.

The Mars Surveyor, for which Keller had also contributed a camera, was now due to fly in 2001. In actual fact the research programme for that year envisaged two space probes, a lander with rover and an orbiter. The latter was launched under the name of Mars Odyssey, but the first was never deployed for cost reasons. Just as the lander was approaching completion, it was mothballed along with Keller’s camera.

Nevertheless, the valuable landing device was later retrieved from the hangar and modified to incorporate the latest knowledge. In this way the Phoenix rose from the ashes. The German camera was the only component that did not need to be modified or replaced: it still worked perfectly after almost ten years, as extensive testing proved. The specialists from MPS also supplied a detector for the optical microscope, to be used to examine particles from the soil samples. So today, as the excavator blade digs down up to a metre into the cold soil of Mars, the high-tech camera weighing only 415 grams supplies images of the stratification of Mars soil with an incredible resolution of 50 micrometres, about the thickness of a human hair. The scientists are hoping to find traces of water ice half a metre down. "Between now and August we are fully occupied," reports Dr Keller. "We are working here according to Mars days, which are about 40 minutes longer than days on the Earth. So every three days our life rhythm shifts by two hours."

All the work must completed by the time the Mars winter arrivee. The work on this little mission, which is meeting with strong public interest, has to be carried out quickly and accurately. At present the temperatures encountered at the landing site, known as the "Green Valley", is "mild", ranging from -73ºC to -33ºC. But at the end of the year the sun will disappear below the horizon and the Mars winter will embrace the earthly explorer with icy claws. It is hardly to be hoped that it will be possible to revive Phoenix next spring after such a frost attack. For this reason three terrestrial teams are working around the clock on the ongoing programme. The first analyses the data and imagery, the second prepares the commands for the next lot of work, and the third makes strategic decisions on the research work over the next four to five days.

Every two hours the lander is awoken by radio command and receives fresh commands or exports the results of its work to the relay stations in Mars orbit, from where they are transmitted to Earth. "It is a very complex programme, under which every move has to be exactly right," says Dr Keller. "In this way we are hoping to have completed the core mission programme after just one and a half months." What comes after that will not be obligatory, but a bonus. Every extra day will bring new discoveries – assuming that no faults develop. But for his camera, Dr Keller would put his hand in the fire.
by Matthias Gründer

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