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Astronauts on the International Space Station performed complex robotic maneuvers Sunday to unload a new spare parts container from the shuttle Endeavour.

The platform, which holds replacements for vital space station systems, is set to be unpacked Monday during the second of five spacewalks planned for Endeavour's STS-127 mission.

Shuttle commander Mark Polansky and pilot Doug Hurley manipulated the shuttle's robotic arm to grab the container out of Endeavour's cargo bay and move it into a temporary stowage spot on the end of the station's robotic arm.

"It's basically a platform and attached to the platform are three very large pieces of equipment," Polansky said in a preflight interview. "If required at some point in the future, it's basically a hot spare ready to go on orbit."

Inside the container are a new set of new batteries to provide power for the station when it is facing away from the sun, a spare antenna for a space-to-ground communications system and an engine for a cargo transporter system that rides along the station's backbone-like truss.

"We will be changing the batteries on the P-6 solar array, six large batteries that each weigh around 300, 350 pounds, the size of small refrigerators," said mission specialist Dave Wolf in a preflight interview. "That's the oldest solar array system on the space station so we'll rejuvenate that solar array system."

Mission specialists Tim Kopra and Koichi Wakata spent their time in the Japanese Kibo laboratory, calibrating the Japanese robotic arm there. Wakata also worked to replace some broken parts on a resistance exercise machine on the station.

The seven astronauts of the space shuttle Endeavour's STS-127 crew are on the third day of their docked mission at the station.

The rest of the crew spent Sunday making preparations for the next day's spacewalk, including configuring the spacesuits and tools that will be needed.

The day was slightly less hectic than it might have been, since mission managers determined a focused inspection of Endeavour's heat shield was not necessary. This precaution is an option if NASA needs more data to decide if a shuttle is safe to return home through Earth's atmosphere.

"Flight day five was where we had planned a focused inspection if required preflight," said lead station flight director Holly Ridings. "That is not required and so are going to move some of the robotic activities that were planned for flight day six a little bit forward."

Though mission managers have not officially cleared Endeavour for re-entry, they think they have enough information to make the decision from the first detailed inspection the astronauts conducted, as well as a series of photographs taken by station astronauts as Endeavour approached on Friday.