premise: But he said the space walkers would be asked to "go out and take a look at the solar array for us."
  National Aeronautics and Space Administration officials decided to abandon, at least for the moment, attempts to unblock the stuck array and may require a fourth space walk to fold it away.
  Space shuttle Discovery and ISS astronauts on Wednesday only managed to fold the stubborn array half-way by remote control, and NASA engineers on Friday tried to determine why it remained stuck after repeated attempts at activation.
  At one point, NASA engineers in Houston asked German astronaut Thomas Reiter to exercise vigorously for 30 seconds on the ISS's training machine, hoping his vibrations would cause the panels of the stubborn array to fold all the way.
  Reiter, who after a five-month stay on the ISS will be replaced by Discovery astronaut Williams, tried several times to shake the array into action.
   Why was German astronaut Thomas Reiter instructed to exercise vigorously on the ISS's training machine?
hypothesis: a fourth space walk to fold it away