A Salute to Spirit   
       
   June 3, 2011: At NASA, missions are expected to go the extra mile.   
       
   The Voyagers are, perhaps, the best known example. Launched in the 1970s to   
   explore the outer planets, the iconic spacecraft have zoomed far beyond their   
   original targets to the edge of interstellar space itself, 9 billion miles   
   from Earth and still making discoveries. Pioneer 10 and 11, Ulysses,   
   Stardust-NEXT, Deep Impact, and others have similar track records. It has   
   become almost routine for superbly-engineered probes to wrap up their prime   
   missions, then travel a few million (or billion) bonus miles for extra science.   
   [...]   
   Click to view a video tribute to Spirit. [YouTube] Against this backdrop of   
   sweeping overachievement, we pause to salute a robot that might never move   
   another inch.   
       
   Well done, Spirit.   
       
   "For the past 7 years, Spirit has been on a journey as extraordinary as any   
   mission in NASA history," says Mars Exploration Rover project manager John   
   Callas of JPL. "But now it may be time to say thanks and farewell."   
       
   NASA hasn't heard from Spirit in more than a year, and on May 25th, 2011, the   
   agency sent a final transmission in its series of attempts to regain contact.   
   [...]   
   The trouble began in April 2009 when the rover trundled into a sandtrap in a   
   place called "Troy," breaking through an apparently safe crust into soft sand   
   below. Stuck in place, Spirit couldn't turn its solar panels squarely toward   
   the sun; at the same time, dust accumulated on the panels, reducing sunlight   
   even more. These impediments curtailed power just when Spirit needed power   
   most, during the deep freeze of an approaching Martian winter.   
       
   "Where Spirit is, winter temperatures drop as low as -130 C, far colder than   
   any place on Earth," says Callas. "Without sufficient electricity to power   
   internal heaters and warm critical systems, Spirit went into hibernation."   
       
   NASA has used Deep Space Network antennas and two of the agency's Mars   
   orbiters to try to reestablish contact--but no luck. Whether the rover is   
   damaged or merely "sleeping," no one can say, but most engineers believe the   
   possibility of contact is now extremely remote.   
   [...]   
   A Martian sunset photographed by Spirit in 2005. [more]   
       
   Spirit landed on Mars on Jan. 4, 2004, for a mission designed to last merely   
   three months. After quickly accomplishing its primary science goals, the rover   
   went on to work for almost six more years. In all, Spirit has traveled almost   
   8 km, explored several large craters, scrutinized thousands of rocks, scraped   
   off topsoil to reveal hidden minerals, photographed Martian dust devils and   
   sunsets, observed the moons of Mars, and took the first picture of Earth in   
   the night sky of another planet. Bonus-time, indeed.   
       
   Asked to name Spirit's top scientific discoveries, Callas lists three:   
       
   (1) Evidence of ancient hot springs. "This came about because of the failure   
   of one of Spirit's wheels," he recalls. "Two years into the mission, the right   
   front wheel stopped working--we're still not sure why. Spirit had to drag it   
   along, cutting a furrow in the ground. This revealed deposits of amorphous   
   silica widely thought to have formed in hydro-thermal systems. Apparently,   
   Mars once had water and the energy to warm it. We might never have found this   
   if not for the serendipity of the broken wheel."   
   [...]   
   The Comanche Outcrop on Mars suggests a hospitable environment for life in the   
   distant past. [more] (2) Evidence of a thick atmosphere and "sweet" water.   
   Today the atmosphere of Mars is so thin, most life as we know it couldn't   
   survive there. Spirit's discovery of carbonates at the Comanche Outcrop is   
   compelling evidence that it wasn't always so.   
       
   Callas explains: "The carbonates Spirit found formed in surface water that   
   could only exist with a thick atmosphere sitting on top of it to prevent rapid   
   evaporation. Moreover, the chemistry of the carbonates tells us that the water   
   wasn't acidic like other ancient water on Mars." Life would have liked this   
   place, billions of years ago.   
       
   (3) Evidence of an active water cycle. The first thing Spirit did when it got   
   stuck at Troy was to try to break free. Spirit's spinning wheels churned up   
   the soil, uncovering sulfates. "These minerals appear to have come in contact   
   with water perhaps as recently as a million years ago," says Callas. In   
   geological terms, that's very recent, suggesting an active water cycle on the   
   Red Planet.   
       
   Alone, any one of these discoveries would have been considered a resounding   
   success by the mission's original planners in the 1990s. All three, plus   
   others not listed, place Spirit squarely atop the pantheon of NASA's great   
   overachievers.   
   [...]   
   This may be the last thing that Spirit ever saw--a panorama at Gusev crater   
   before the rover's 4th Martian winter. [more]   
       
   Meanwhile, Spirit's twin rover Opportunity is halfway across the red planet,   
   still going strong.   
       
   "Opportunity is in good health," says Callas. "The rover is about to log 30 km   
   of distance since landing in 2004. We never dreamed of such a trek when the   
   mission began. And years of additional service appear possible."   
       
   He cautions that Mars is a dangerous place, and the rover itself is in its   
   senior years. At any moment, Opportunity could be engulfed in a storm, fall in   
   a sandtrap, or simply break down due to old age.   
       
   When one of these things inevitably happens, Opportunity will join Spirit as a   
   silent monument to grit, luck, intelligence . and oh so many extra miles.   
       
       
   Author: Dr. Tony Phillips | Credit: Science@NASA   
       
   More Information   
   Mars Exploration Rovers -- home page   
       
   A Salute to Spirit -- ScienceCast video   
       
   A Heartfelt Goodbye to a Spirited Mars Rover -- by John Callas   
       
   NASA Spirit Rover Completes Mission on Mars -- press release   
       
       
   Regards,   
       
   Roger   
      
   --- D'Bridge 3.61   
    * Origin: NCS BBS (1:3828/7)