On the eve of the second excursion outside the International Space Station within the span of a week, the Expedition 36 crew completed final preparations Wednesday for that spacewalk while continuing to support a number of research and maintenance tasks.

Flight Engineers Fyodor Yurchikhin and Alexander Misurkin completed a final timeline review of the tasks they will perform during Thursday's spacewalk.

During their excursion slated to last about six hours, the two cosmonauts will replace a laser communications experiment with a new platform for a small optical camera system, move a foot restraint and inspect several sites for the origin of a wayward antenna cover observed by Flight Engineer Chris Cassidy on Monday.

This will be the 173rd spacewalk in support of space station assembly and maintenance, the 8th in Yurchikhin's career and the third for Misurkin. Both cosmonauts will wear blue-striped Orlan spacesuits outfitted with helmet cameras.

Their previous excursion outside the station, a 7-hour, 29-minute marathon on Aug. 16 focusing on preparations for the future arrival of the "Nauka" Multipurpose Laboratory Module, was the longest spacewalk in history conducted by a pair of Russian cosmonauts.

NASA Television coverage of the spacewalk will begin at 7 a.m. Thursday, with hatch opening expected at 7:40 a.m.

Meanwhile, Flight Engineer Chris Cassidy began his workday removing and replacing multifiltration units inside the Water Recovery System. Part of the station's overall Environmental Control and Life Support System, the station's Water Recovery System recycles condensation and urine into drinkable water, reducing the amount of fresh water that must be sent to the crew aboard resupply ships.

Afterward, Cassidy performed an ultrasound on Flight Engineer Luca Parmitano for the Spinal Ultrasound investigation. Medical researchers have observed that astronauts grow up to three percent taller during their long duration missions aboard the station and return to their normal height when back on Earth.

The Spinal Ultrasound investigation seeks to understand the mechanism and impact of this change while advancing medical imaging technology by testing a smaller and more-portable ultrasound device aboard the station.

With an eye toward the return to Earth in three weeks, Cassidy joined Misurkin and Commander Pavel Vinogradov for a fit check of the "Kazbek" seat liners of their Soyuz TMA-08M spacecraft they will ride home in for a parachute-assisted landing on the steppe of Kazakhstan on the morning of Sept. 11, local time.

Flight Engineer Karen Nyberg spent part of her day in the Japanese Kibo module setting up a commercial payload. She also replaced a rope on the Advanced Resistive Exercise Device, or ARED, one of several exercise devices the station's residents can use for their daily two-hour exercise regimen to combat the loss of muscle mass and bone density experienced by long-duration crews.

Parmitano exchanged a test sample cartridge in the Solidification and Quench Furnace for another round of data collection. This metallurgical research furnace provides three heater zones to ensure accurate temperature profiles and maintain a sample's required temperature variations throughout the solidification process.

It's just one part of the Materials Science Research Rack, which allows for the on-orbit study of a variety of materials -- including metals, ceramics, semi-conductor crystals and glasses.

The station's residents also had several opportunities throughout the day to photograph the Earth below as part of the ongoing Crew Earth Observations program.

These photographs, such as the image of wildfires raging through central Idaho that was captured by the crew on Sunday, are made available to researchers studying dynamic events on Earth and published online at the Gateway to Astronaut Photography of Earth for public use.