Space walk under way right now - watch here

The crew of the International Space Station have a space walk under way right now. This EVA - extra-vehicular activity - is critical for the ISS - its power supply is on a knife edge.

Live broadcast by Ustream

There were two EVAs held over the last week. But on the second one, the astronauts Sunita (Suni) Williams and Akihiko Hishide had troubles when they started replacing a faulty power unit (called a Main Bus Switching Unit - MSBU), with one bolt on a replacement power supply that kept binding, preventing them from finishing the job. These units control the power from the huge solar panels - two panel per unit, meaning a big dint in the ISS power supply. They tried repeatedly to get the bolt to screw home, but it was only going  in a half turn. After eight hours and 17 minutes - the third longest EVA ever - they had to give up as they were up against the limit of certain batteries in their spacesuits.

Then to make matters worse, a few days later there was another failure that took out a third solar panel out of the eight in total. This left NASA with no option but to shut down some functions and focus on life support and control functions.

So today, they have a 6:30 hour EVA planned to try it again - this time trying to clean the threads of metal strippings and greasing up the troublesome bolt. They started at 9:00pm Canberra time, so will be going into the early hours of the morning.

You can watch here, or click over to http://www.nasa.gov/ntv

UPDATE: Success! Almost four hours into the spacewalk, and up against the "bingo" limit for abandoning the task, Suni and Akihiko completed cleaning all the metal shavings out of the bolts and the holes, lubricating them and after a couple of goes got both bolts home. Then the power unit came online and the station is back to full power. There's nothing up on the NASA website about it yet, but likely will be later today, if you want to learn all about the Toothbrush Tool and other minutiae!