Robotic Exploration of the Solar System (Springer Praxis Books) by Paolo Ulivi;David M. Harland

Author:Paolo Ulivi;David M. Harland
Language: eng
Format: epub
Published: 2008-09-03T04:13:00+00:00

Meanwhile, the other instruments had also been returning data. The initial runs of the gas chromatograph analyzed the composition of the atmosphere, finding it to be 95 per cent carbon dioxide, 2-3 per cent nitrogen, 12 per cent argon and less than 0.5 per cent oxygen. In 1983 some meteorites on Earth were found to contain trapped gas with the same composition and isotopic ratios, and it was realized that these came from Mars. They were called the Shergottite-Nakhlite-Chassignite (SNC) class for the areas in which the first ones were recovered - Shergotty in India (in 1865), Nakhla in Egypt (in 1911) and Chassigny in France (in 1815). Most of the members of this class are significantly younger than the age of the solar system and also of the other `mundane' meteorites, and their analysis has helped to unravel many details of the geological history of Mars. In a sense, the SNC meteorites have compensated for a long-overdue Mars Sample Return mission which, when this is finally undertaken, will probably be the single most important planetary mission.509,510 The meteorology instruments on the Viking 1 lander recorded an average pressure of just 7.7 hPa, and a temperature varying from -86°C at 5 o'clock in the morning to -31°C at 3 o'clock in the afternoon. There was a late-afternoon breeze and variable nocturnal winds, but these were far too weak to have produced either the dust deposits seen by the lander on the rocks or the `tails' downwind of craters seen from orbit, which were probably emplaced by the occasional dust storms.511 The only major failure of the lander's mission was when the seismometer refused to uncage and, being almost unusable for its intended purpose, was used to measure the extent to which the lander was shaken by wind gusts. On 22 July the robotic arm was commanded to extend 30 cm, rotate to jettison the protective cover from its scoop, and then return to its stowed position. It extended and released the cover, but jammed attempting to retract. The fault was soon realized to be the locking pin that had latched the cover, and it was decided that the arm had not extended far enough to enable the pin to fall out. As operations were planned in threeday uplink cycles, instructions to extend the arm to 35 cm and then shake the pin loose were added to the sequence that was uplinked to the lander on 25 July, and the pictures taken in support of this effort showed the pin on the ground. Images of the discarded sampler cover and locking pin were analyzed to estimate the hardness of the ground.512

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