NASA astronaut Clay Anderson will toss a 1,400-pound ammonia tank off the International Space Station (ISS) July 23 along with another surplus piece of hardware, as he and Expedition 15 Commander Fyodor Yurchikhin conduct a U.S.-side extravehicular activity (EVA) that will mark the first time a Russian cosmonaut operates the station's Canadian-built robotic arm.

With cosmonaut Oleg Kotov at the controls in the U.S. Destiny laboratory module, Anderson will ride the Canadarm2 twice to a point below the space station, which controllers will turn around before the EVA so it is essentially flying backward. Each time Anderson will lean back slightly in his foot restraint, then shove the excess gear away from the ISS in a retrograde direction designed to prevent it from striking the orbiting facility on a later orbit.

For extra safety, about two hours after the two items are jettisoned controllers plan to reboost the station to the required altitude for the STS-118/13A.1 space shuttle/ISS-assembly mission scheduled for Aug. 7. That will place it above the orbit of the 212-pound flight support hardware for a video stanchion, and the much more massive early ammonia servicer (EAS). Both will be tracked from the ground until they re-enter the atmosphere -- a process that could take as long as 330 days for the EAS but much less for the smaller piece -- in case there is a possibility of "recontact" with the station.

The tracking also will let NASA give as much notice as possible before the EAS re-enters, since some of its parts are expected to reach the ground. Originally launched to replace any ammonia that leaked from a temporary station cooling system that is no longer needed, the EAS has passed its five-year on-orbit service life and a one-year extension, and must be taken off the P6 truss element before that element is relocated to the end of the main station truss in October. Its ammonia supply never was needed.

The station crew was busy July 18 configuring the Quest airlock and preparing for a dry run of the EVA July 19. In addition to jettisoning the hardware, Yurchikhin and Anderson will replace a failed remote power control module needed to provide redundancy when the station's mobile transporter is moved along the truss in preparation for the upcoming assembly mission, and clean some contamination from the main seal on the Unity node's nadir common berthing mechanism, where Anderson is scheduled to relocate the No. 3 pressurized mating adaptor after the shuttle mission to clear the way for Europe's Columbus module.

The spacewalk is planned to last about six-and-a-half hours, with get-ahead tasks programmed for the EVA crew if they finish early.