The Strange Way Fluids Slosh on the International Space Station   
       
   Jan. 30, 2015:  The next time you pour yourself a glass of water, pause before   
   you drink it. First, swirl the clear liquid around the glass.  Gently slosh it   
   back and forth. Tap the glass on the tabletop, and watch the patterns that   
   form on the surface.   
       
   Now imagine the same exercise... in zero gravity.  Would the waves and ripples   
   look the same?  Would the liquid slosh more, or less?  Faster, or slower?   
       
   NASA engineers spend a surprising amount of time asking themselves these same   
   questions.   
       
   http://tinyurl.com/mxefbuq   
       
   A new ScienceCast video explores the strange ways fluids bubble, froth, and   
   slosh on the International SPace Station.  Play it!   
       
   Their interest centers not on water glasses, but rather on fuel tanks. NASA's   
   most powerful rockets use liquid fuel, and when these rockets blast off, the   
   propellants slosh around.   
       
   Scientists have a good idea how liquids slosh in normal Earth gravity where   
   the weight and viscosity of the liquid rule its dynamics.  Deep space is   
   different, however.  Weightless propellants are guided by surface tension and   
   capillary effects.  Far from Earth, they could slosh and froth in unexpected   
   ways.   
       
   "Modern computer models try to predict how liquid moves inside a propellant   
   tank," says Brandon Marsell of NASA's Fluid Group at the Kennedy Space Center.   
   "Most of the models we have were validated under 1 g conditions on Earth. None   
   have been validated in microgravity."   
       
   Enter the SPHERES-Slosh experiment.   
       
   "The International Space Station provides the perfect environment to conduct   
   liquid behavior studies in microgravity," says the principal investigator,   
   Paul Schallhorn also at Kennedy.  "So we have designed an experiment that   
   simulates how rocket fuels move around inside their tanks."   
       
   Built by Professor Dan Kirk and colleagues at the Florida Institute of   
   Technology, SPHERES-Slosh is, essentially, a fluid chamber grappled by a pair   
   of bowling ball-sized robots. The two SPHERES (a product of the Space Systems   
   Laboratory at MIT) were already onboard the space station when the Slosh   
   chamber arrived in February 2014. Together, the robots move the chamber back   
   and forth to mimic common spacecraft maneuvers such as the "BBQ roll",   
   attitude adjustments, and engine shut-downs.   
       
   In 2014, astronauts supervised the robots as they made three test runs using   
   chambers 20% and 40% filled with fluid-much like a partially-spent fuel tank.     
   "We use water mixed with a bit of green food coloring," says Schallhorn.   
       
   Why water? "For one thing, it is a safe fluid for the space station.  Water is   
   on the approved list of fluids we can send to the station," he explains.   
   "Also, its viscosity is similar to hydrazine, a propellant used by satellites;   
   and its density is similar to liquid oxygen, an important cryogenic   
   propellant."   
       
   During the experiments, which can last as long as six hours, cameras, gyros   
   and accelerometers record the motions of the water.   
       
   "We are getting great data," says Marsell. "So far," he says, "our computer   
   models on Earth have done a good job predicting wave motions inside the   
   chamber."   
       
   But there is a mystery...   
       
   "It has to do with bubbles," says Schallhorn. "The way bubbles form and   
   interact inside the chamber is surprising-and not predicted by our models. We   
   were taken off guard with what we saw in the data."   
       
   The bubbling and frothing of shaken fuels is cutting-edge research in fluid   
   dynamics, and SPHERE-Slosh is showing that it may be very important.   
       
   Jacob Roth of the Fluids Group at KSC adds, "this is something we plan to   
   investigate further. Who knows? It might just shake up our understanding of   
   fluids in space."   
       
   Credits:   
       
   Production editor: Dr. Tony Phillips | Credit: Science@NASA   
       
       
   Regards,   
       
   Roger   
      
   --- D'Bridge 3.99   
    * Origin: NCS BBS - Houma, LoUiSiAna (1:3828/7)