[I was beginning to think NASA had gone out of business because this is the   
   first article I've received since 28 August.]   
       
   NASA Spacecraft takes GPS to New Heights   
       
   Sept. 18, 2015: As any backcountry hiker knows, Global Positioning System, or   
   GPS, trackers are crucial for navigation. But they can also be a little   
   finicky.  Units sometimes lose lock when you walk into the shadow of a canyon   
   wall, when you point the units at the ground, or even when you make a sharp   
   turn.   
       
   Now imagine a GPS system flying through the vacuum of space at 22,000 mph,   
   rapidly spinning 43,000 miles above the surface of the blue planet below.   
   Would it work?   
       
   https://www.youtube.com/watch?v=taMzKcehfGw#t=15   
       
   Turns out, the answer is yes.  NASA has developed a GPS navigation system for   
   the newly-launched MMS satellites that operates under these incredible   
   conditions.   
       
   NASA's MMS spacecraft are flying around Earth in a precise formation made   
   possible by an out-of-this-world system of GPS navigators.   
   On March 12, the four spacecraft of the Magnetospheric Multiscale (MMS)   
   mission left Earth on a mission to investigate the physics of magnetic   
   reconnection: Magnetic lines of force cross, cancel, reconnect and-Bang!   
   Magnetic energy is unleashed, with charged-particles flying off near the speed   
   of light.  This process happens in many places. It sparks solar flares on the   
   sun as well as powering magnetic storms near Earth.   
       
   Understanding how magnetic reconnection works requires the four spacecraft to   
   fly in a tight pyramid formation through Earth's magnetic field. Positioning   
   is crucial.   
       
   Speed and altitude are not the only challenges for the spacecraft's onboard   
   GPS units.  In addition, the MMS spacecraft spin; each one makes three   
   revolutions per minute.   
       
   "Spinning adds a whole new dimension to trying to figure out where you are,"   
   said Ken McCaughey, MMS GPS Navigator Product Development Lead at NASA's   
   Goddard Space Flight Center. "We have eight GPS antennas on each spacecraft.   
   As the spacecraft rotates we have an algorithm running that allows us to hand   
   off from one antenna to the next without losing the signal."   
       
   During the first month, the team compared the MMS "Navigator system" with   
   orthodox ground tracking systems and found Navigator to be even more accurate   
   than expected. At the farthest point in its orbit, some 43,500 miles away from   
   Earth, Navigator can determine the position of each spacecraft with an   
   uncertainty of better than 50 feet.   
       
   The MMS Navigator system exceeded all of the team's expectations. At the   
   farthest point of the MMS orbit of 43,500 miles, Navigator was able to receive   
   signals from the GPS satellites and perform onboard navigation solutions.  At   
   the lowest point of the MMS orbit, Navigator traveled at velocities over   
   22,000 miles per hour. In comparison, GPS satellites orbit at 12,550 miles   
   away from the earth and travel at 8,600 miles per hour, and most satellites   
   using GPS receivers are in low earth orbits at altitudes between 110 and 1,250   
   miles.   
       
   It's fair to say.the MMS GPS is far out and moving fast!   
       
   This system will be even more important during the second phase of the MMS   
   mission when the orbit will double in size and travel all the way out to   
   95,000 miles from Earth.   
       
   Thanks to this extraordinary GPS tracking, the work of understanding magnetic   
   reconnection can begin.   
       
       
   Regards,   
       
   Roger   
      
   --- D'Bridge 3.99   
    * Origin: NCS BBS - Houma, LoUiSiAna (1:3828/7)