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  • Closing In On Mars
    Posted by Guy Norris 8:45 PM on May 25, 2008

     1.40pm PDT, NASA JPL. 

    Tensions are running high here at JPL in Pasadena, Calif. as the Phoenix Mars Lander accelerates towards the Martian surface. The spacecraft is now well within the planet’s gravity well and within the next three hours will reach 12,700 mph as it approaches the Martian atmosphere. “It will take 8 hours to get to 12,700 mph and just seven minutes to get to zero miles per hour” says JPL Phoenix program manager Barry Goldstein referring to the aero-breaking, parachute and thruster-aided descent phase.


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    The acceleration curve as Phoenix closes in on the Red Planet



    The mission control team has decided to “wave off the last update, and all we can do now is wait and watch,” says Goldstein. The latest navigation predictions puts the landing well within the ‘3 sigma’ 99% probability ellipse landing zone, determined to be the safest area of flat ground in the artic region. One concern was a “small rather diffuse rock pile” in the predicted landing area. However, controllers believe the chances of landing on top of the 6ft high hillock are extremely low. “There was a lot of agony over a 0.1% probability, but our last solution showed things were looking good,” Goldstein says.


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     The small 'rock pile' can be made out in the upper mid-section to the left of the center of the predicted landing zone in the blue ellipse.



    Close up images of the landing zone taken by the Mars Reconnaissance Orbiter show the surface to be covered with small polygonal patterns – a classic micro-feature of Earth’s permafrost regions known as ‘tundra polygons.’ Measuring around 15ft across, project chief investigator Peter Smith says “we hope we can get into a trough between the polygons and understand the difference between the two.” Smith also hopes the lander will be within imaging range of small rocks that would provide visible clues to the erosional and climatic history of the planet.


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    Smith (left) and Goldstein in front of a computer simulation of what all hope becomes reality in a few hours


    The expected landing is targeted for 4.53pm PDT, and first indications of a successful touchdown (or not) will be available for around 15 minutes due to the time it takes for the signal to travel the 171 million miles (275 kilometers) between Mars and Earth. The first images are not expected until 7 to 7.15pm PDT. “We’re extremely hopeful” says Goldstein who adds that he “ran out of fingers and toes” estimating the number of events that must successfully take place during the final descent phase. At a minimum these include 26 ‘pyro’ (pyrotechnic) events and 12 descent thrust actuations, not to mention the millions of instructions in the flight control processor.

    Tags: os99, Mars, Phoenix Mars Lander, NASA, JPL

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