An unpiloted Russian Progress resupply craft undocked Tuesday from the International Space Station to set the stage for the arrival of a new Progress cargo vehicle on Sept. 10.

The ISS Progress 38 cargo craft, loaded with trash and other items for disposal, undocked from the aft end of the station’s Zvezda service module at 7:22 a.m. EDT. Russian flight controllers will conduct thruster tests with the Progress to gather engineering data before sending it to a fiery descent Monday over the Pacific Ocean.

The ISS Progress 38 cargo craft undocked from the aft end of the International Space Station's Zvezda service module Tuesday at 7:22 a.m. EDT. The Expedition 24 crew members had loaded Progress 38 with trash and other discarded items for disposal and burn-up over the Pacific Ocean. The cargo ship will undergo thruster firing tests to gather data for Russian flight controllers before it is deorbited Monday, Sept. 6 to burn up in the Earth’s atmosphere.

The unmanned ISS Progress 39 cargo craft will launch Sept. 8 and automatically dock and resupply the station crew Sept. 10.

The ISS Progress 38 cargo craft currently docked with the International Space Station will undock from the aft end of the Zvezda service module on Tuesday. Progress 38 will be deorbited and re-enter the Earth’s atmosphere on Sept. 6. The Expedition 24 crew members have been loading the Progress 38 with trash and other discarded items for disposal and burn up over the Pacific Ocean. The unmanned Progress 39 cargo craft will automatically dock and resupply the station crew on Sept. 10.

Science was the order of the day Tuesday aboard the International Space Station as the Expedition 24 crew catches up on research and experiments put on hold during the weeks recovering from the failure of an ammonia pump module in the complex’s thermal control system on July 31.

Watch the EVA live at http://www.nasa.gov/multimedia/nasatv/index.html

Expedition 24 Flight Engineers Doug Wheelock and Tracy Caldwell Dyson switched their spacesuits to battery power at 7:19 a.m. EDT, signaling the start of the first of two spacewalks that will focus on removing the ammonia pump module that failed last Saturday and putting its replacement in place.

The repair tasks, which include removing the failed pump module from the S1 Truss and retrieving a spare from an external stowage platform, are expected to take about 6.5 to 7 hours. They are scheduled to complete installation and activation of the new pump module during the second spacewalk planned for Wednesday at 6:55 a.m.

NASA International Space Station managers have delayed two spacewalks to replace a faulty cooling system component to Saturday and Wednesday.

Saturday's spacewalk now is officially scheduled to begin at 6:55 a.m. EDT, and will be followed by a second spacewalk Wednesday to complete replacement of the ammonia pump module that failed last Saturday.

Teams of flight controllers, engineers, and spacewalk and robotics experts have made significant progress in preparing for the spacewalk, but need an additional day to finish working out all the details.

The additional time to prepare for the first spacewalk allows for the final procedures to be uplinked late today and gives the station crew one full day to review the plans that have been developed by Mission Control. Managers also moved the second spacewalk to Wednesday to give the crew additional time to rest and prepare.

NASA has decided to wait until Friday to conduct a spacewalk to replace a failed ammonia pump module on the International Space Station.

Mission managers, program managers, flight controllers, engineers, astronauts and spacewalk experts made the decision Monday evening after continuing to analyze and refine engineering requirements, and reviewing the results of an underwater practice session.

Expedition 24 astronauts Doug Wheelock and Tracy Caldwell Dyson currently are scheduled to start the repairs on the station's starboard truss Friday. Fellow astronauts Cady Coleman and Suni Williams spent the afternoon in the Johnson Space Center's Neutral Buoyancy Laboratory practicing underwater the tasks needed to restore the cooling loop over the course of two spacewalks.

The members of the International Space Station's Expedition 24 crew shifted their sleep schedule Monday in preparation for their mission's first spacewalk, waking up at about 2:40 p.m. EDT.

Flight Engineers Fyodor Yurchikhin, a veteran of three spacewalks in 2007 during Expedition 15, and Mikhail Kornienko, a spacewalk rookie, will perform the six-hour spacewalk. The pair will exit the Pirs docking compartment and work outside the Zarya and Zvezda modules. The Pirs Docking Compartment hatch is slated to open at 11:45 p.m. to begin the excursion.

The pair will outfit the Rassvet module's Kurs automated rendezvous system, install cables and remove and replace a video camera. Kurs is a Russian radio telemetry system that allows automated dockings of unmanned spacecraft such as the Progress resupply vehicle. The new video camera will document the rendezvous and docking of future Automated Transfer Vehicles to the aft end of the Zvezda service module.

The altitude of the International Space Station was raised early Friday morning after the docked Progress 38 vehicle fired its thrusters for nearly 18 minutes. The reboost places the station at an altitude to support the departure of the Expedition 24 crew in September and the arrival of the Expedition 25 crew in October.

The first Expedition 24 spacewalk will begin on Monday, July 26. Russian flight engineers Mikhail Kornienko and Fyodor Yurchikhin will exit the International Space Station's Pirs docking compartment and prepare the Rassvet module for automated spacecraft dockings. The cosmonauts will install a Kurs automated rendezvous system on Rassvet allowing unmanned Russian vehicles, such as Progress resupply craft, to dock at that port.

After enjoying some time off during a light-duty weekend, the Expedition 24 crew of the International Space Station got back to work Monday, preparing for a series of upcoming spacewalks, conducting routine maintenance and working with science experiments.

Flight Engineers Mikhail Kornienko and Fyodor Yurchikhin reviewed procedures and the timeline for a spacewalk scheduled for July 26 that will outfit the recently installed Rassvet module with automated Kurs rendezvous and docking capability for approaching Russian vehicles.

Flight Engineer Doug Wheelock performed routine scrubbing on the cooling loops in the U.S. spacesuits that he and Flight Engineer Tracy Caldwell Dyson will wear during a spacewalk scheduled for August 5.