The space shuttle and its seven astronauts are delivering the $1 billion lab on behalf of Japan. They will install the lab, with help from the space station's three residents, tomorrow.
It is named Kibo, Japanese for hope, and is 11.3 metres long and weighs more than 14,515 kg.
Shuttle commander Mark Kelly and his crew also have a new pump for the space station's malfunctioning toilet. The Russian-built toilet broke a week ago, and space officials are hopeful that this pump, from a different manufacturing batch than the spares on board, will get it working normally.
Before parking at the space station, Kelly was going to guide Discovery through a slow backflip so the station residents could photograph the shuttle's underside.
It is one of the safety measures put in place by NASA after the 2003 Columbia accident to check for launch damage.
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On Sunday, the astronauts performed a cursory wing inspection using their ship's 15 1/4-metre robot arm. They surveyed the upper edges of the wings, beaming down the camera images to ground controllers, but could not check the lower edges of the wings and the nose cap because they lacked the proper laser tools.
Their laser-tipped inspection boom is at the space station, left there by the previous shuttle crew in March. They will retrieve it and, after they depart, perform a full survey.