Astronauts on the International Space Station are conducting the longest space walk of their mission Saturday to work on repairing a damaged piece of equipment.

Two astronauts will float outside the orbital outpost for more than seven hours as they work on cleaning and lubricating a joint that turns solar panels to face the sun.

The job was made more difficult after a $100,000 tool kit drifted away from the astronauts on a previous spacewalk.

Meanwhile, engineers back on earth will try to solve a problem with a newly installed system designed to recycle astronauts' urine into drinking water.

The system shut down twice during testing on Friday.  Scientists hope they can still collect enough samples of purified urine and other waste water to bring back for analysis.

The U.S. space shuttle Endeavour is on a 15-day mission to expand and improve the International Space Station's living space.  The shuttle is scheduled to return to earth in just over a week.

The mission coincided with the 10th anniversary of the ISS.  It is said to have orbited the earth more than 57,500 time since the first component of the space station was launched in 1998.

Some information for this report provided by AP and Reuters.