Problems with Tim Kopra space suit caused earlier termination of spacewalk.
This spacewalk should be as usual successful for 100%, but technical issues caused that Tim Kopra and Tim Peake were ordered to come back to Quest airlock. Main objective, removing and reinstalling Sequential Shunt Unit - SSU, was accomplished, life and health of both astronauts were not in danger in any moment of the mission.
Problems started after spotting by Tim Kopra small amount of water inside his helmet. It was small bubble, but due the safety reasons both astronauts returned to Quest airlock and whole lasting 4 hours 43 minutes spacewalk was ended at 19:31 GMT. Commander Scott Kelly assisted Kopra and Peake during removing their spacesuits and examined both suits to find any potential source of leakage. After checking special absorbing tissues which were worn by astronauts, he discovered that one worn by Tim Kopra has little moisture on places covering arms and wrists. He compared it to same absorbing suit which was worn by Tim Peake and also on this one little moisture was spotted around wrists. Further examination of water bags utilized by Astronauts also was not explaining presence of water - this one which was used by Kopra was empty, but astronaut confirmed that he just drunk all water during exhausting work on SSU. Both suits were photographed by Commander Scott Kelly and pictures will be send to Earth for further technical analysis. Whole situation is similar to spacewalk performed by Chris Cassidy (NASA) and Luca Parmitano (ASI-ESA) (171 spacewalk on ISS and third under Expedition 36) on 16 July 2013. After one hour in space, Luca Parmitano spotted significant amount of water in helmet and EVA was also terminated after 1 hour 32 minutes. Smaller leakage was spotted in same suit by Parmitano on 9 July 2013 during previous 169th spacewalk. According to NASA reason was valve from water tank. While Italian astronaut was kneeling he probably pressed tank with chest and accidentally open valve with chin. This time it could just happened again but for full explanation we are force to wait for NASA statement.
On picture above: Tim Kopra in Sokol space suit just before launch.