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Home | Update | Latest Issue | Gallery | FR Profile | Datafiles | FR 9/97 NASA PATHFINDER ON TRIUMPHANT MARS MISSION by Wolfdietrich Hoeveler Very few of the planets are fascinating mankind as much as Mars, our neighbor in this solar system. Scientists have known for years that Mars with its atmosphere and water supply in ice-form would probably tolerate human life most easily of all the planets. It is no wonder that Russia and the USA have so far conducted 19 missions to research Mars. Many of them failed, others had only poor outcomes. Most often, photos were the only results. A Mars exploratory vehicle was out of question for a long time due to the high costs. Only the modern and miniaturized electronics made it possible to develop small vehicles with efficient mini-sensors and systems for data collection and transmission. Five years ago, these developments made it possible for NASA to project the relatively cheap Pathfinder mission in the frame of the so called Discovery program. Pathfinder was to cost only $150 million plus another 25 million dollars for the Mars vehicle Sojourner. Three different Mars missions were to start in the fall of last year. The first Surveyor orbiter, which took off on November 6, 1996, was the first probe on the way to the red planet, reaching it supposedly in September of this year. The Russian Mars 96 mission followed on November 16, but failed already in the launch phase. losing the German camera on board. Pathfinder, which was launched with a McDonnell Douglas Delta II on December 4, 1996, was the last of the three. 497 million kilometers were to be covered in 212 days. A last system check was accomplished on 19 June, 15 days before the landing. The software of the computer, an adapted commercial IBM 6000, was changed for the landing. Beginning on June 23, the 370 command sequences for the landing and the first ground operations were transmitted. Both, Pathfinder and Sojourner were supposed to be controllable from the earth, as well as, being able to operate on their own The actual landing phase began approximately 90 minutes before the landing with a direct ballistic entry into the Mars atmosphere with a speed of 26469 km/h. The probe was first aerodynamically slowed down. Two to three minutes after the entry, a parachute opened at an altitude of approximately six to ten kilometers. Further steps in the landing sequence included the release of the heat shield, the lowering of the actual landing vehicle on a 20-meter rope. Eight seconds before the touch-down, the airbags were inflated and shortly after the retro rockets were fired to further reduce the sinkrate to approximately 25 m/sec. At an altitude of 30 meters, Pathfinder was released from the rope and the landing vehicle landed and rolled over the ground until the standstill. As the next sequence, the three upper airbags were deflated and three petals were flipped down. The NASA team found out later that the retraction of the airbags didn't work out in the first try. These actions were accomplished in the dark since the sun rose on Mars some hours after the landing. The first photos from Mars created much enthusiasm. Still, they also revealed the first problem. Due to the not completely retracted airbags, the Mars vehicle Sojourner could not immediately start to explore the planet. The problem was solved after an extensive simulation at the NASA control center in Pasadena, California, via a radio transmission. The way was clear for Sojourner's "Tour de Mars", the photos from Pathfinder and Sojourner going around the world. German research institutes had a major contribution to two important Pathfinder sensors. APX spectrometer The APX spectrometer (Alpha Proton X-ray) is the most important sensor of the Mars vehicle Sojourner. It is designed for the analysis of the chemical compounds of the Mars surface and Mars stone in respect to the geo-chemical and climatic development of our neighboring planet. The spectrometer was supplied by the Max-Planck Institute for Chemistry in Mainz, Germany, which is also responsible for this experiment. The APX spectrometer features nine disc-like mounted radiation sources with Curiumisotop 244 which radiate alpha particles. Sojourner's sensor is able to register the interaction between the alpha particles and either the atomic kernels, the protons of the irradiated atomic kernels or the electrons which are circling the atomic kernels. This allows the sensor to determine all elements (with the exception of hydrogen and helium) which are contained in the tested material with a higher concentration of approximately 0,1 weight percent. The spectrometer can be positioned either vertically or horizontally. It is driven as close as four centimeters to the stone which is to be analyzed. A typical analysis takes approximately ten hours but may be shortened. IMP camera The photo processing system of the Pathfinder was developed with German participation also, namely by the Max-Planck Institute for Aeronomy in Katlenburg/Lindau and by the Technical University of Braunschweig. The IMP camera (Imager for Pathfinder) has two "eyes" which are 15 centimeters apart from each other and whose views cross at a distance of ten meters. Inside the camera, the light is deflected by mirrors into the heart of the sensor, a CCD sensor unit (Charge Coupled Device) with a resolution of 256 x 256 Pixels, developed by the Max-Planck Institute for Aeronomy. The big advantage of this sensor is its ability to individually transmit and process the single load packages of the photo elements. This information can then be processed by a computer into a complete picture. The IMP camera furthermore features 24 filters per "eye" which supply additional scientific data. Geologists, for example, can analyze the light reflected from stone with twelve filters, making it possible to determine the compound of the stone. Meteorologists can accomplish measurements of the atmosphere with the help of the IMP camera (aerosol concentration, as well as, wind speeds and directions). The Max-Planck Institute and the TU Braunschweig have also supplied the picture data processing programs and the data compression. From page 46 of FLUG REVUE 9/97 Home | Update | Latest Issue | Gallery | FR Profile | Datafiles | FR 9/97 Copyright 1997 by Motor-Presse Stuttgart. All rights reserved. Last updated August 5, 1997 FLUG REVUE, Ubierstr. 83, 53173 Bonn, Germany