Two space shuttle astronauts scaling the outside of the International Space Station ran into some trouble Tuesday with a mix-up in cables and a lost part, a U. S. space agency spokesman said. Their mission to finish hooking up a billion-dollar robotic arm was supposed to last six and a half hours but stretched to nearly eight. First, there were problems with the cables Canadian Chris Hadfield and American Scott Parazynski were connecting to power and control the 18-metre-long Canadarm2, which they installed outside the station Sunday. 'The reserve power supply of the robot arm didn't work at first, but it ran just fine after we sorted a couple of cables, 'the National Aeronautics and Space Administration(NASA)spokesman said. Then, as the spacewalkers were dismantling an unnecessary antenna from the station, Hadfield lost his grip on a connector part. NASA officials feared the part could get stuck somewhere in the workings of the station or visiting space shuttles and cause some disruptions, so as a precaution, Hadfield and Parazynski searched for it, but they had to give up, ending the chase unsuccessfully. However, the main aim of the spacewalk was accomplished. Power and data connections were made to a port that is anchoring the robotic ann to the station. The arm is crucial to the future work on the coristruction site in space. Canadam2 will literally lend a hand in building the station. The 18-metre crane has appendages at both ends that will allow it to grasp other ports that will be added to the station so eventually it will be able to crawl hand-over-hand like an inch worm along the station' s outside walls. But for now, that job was being left to spacewalkers like Hadfield and Parazynski. Until 'Big Ann' is fully functional, outside work on the station can only be done by visiting shuttle astronauts using the shuttles' own robotic arms. Big Ann's first big test will come Wednesday, when it is to hand its own 1, 360-kilogram delivery pallet to the shuttle Endeavour's robotic arm so it can be stowed in the shuttle's cargo bay for return to Earth. Meanwhile, the eight space travelers who remained inside the station and shuttle Tuesday were kept busy unpacking about 2 tonnes of supplies and scientific equipment from a cargo module delivered by Endeavour. Over the next several days, the module will be unloaded, then repacked with trash from the space station for Endeavour's return to Earth, planned for Monday. The station's three-member crew was getting the first visitors of its four-month mission, which began last month. They are the second crew to inhabit the station, an international project by the United States, Russia, Europe, Canada and Japan. Its construction is planned for completion in 2006. What is crucial to the future work on the construction site in space?