Two US astronauts have successfully hooked up 40 electrical connections between the first two pieces of the International Space Station, allowing power and data to flow from one side to the other.

To Nasa's surprise, Monday's critical wiring job took less time than expected.

Jerry Ross and James Newman completed the job four hours into their planned six-and-a-half hour spacewalk, the first of three scheduled for this week.

About an hour-and-a-half later, flight controllers turned on the power inside the fledgling station. Electricity to the cables had been shut off before the spacewalk, for the astronauts' safety.

Ross worked non-stop from the end of Endeavour's 50-foot (15-metre) robot arm, starting at the bottom with the American-made Unity module.

He attached jumper cables there before being hoisted more than 40 feet (12 metres) to the Russian-built Zarya stacked on top.

"Jerry, How's the view?" Newman called out from below. "Fantastic if I had time to look," Ross replied.

Ross and Newman left the shuttle Endeavour's airlock and began their walk shortly before 2230 (GMT)/1730 (EST).

The two modules have been successfully joined

Most of the cables on the International Space Station will run along the outside of the structure, avoiding the chaotic tangle that ran through the corridors of the Russian Mir station and hindered hatch closings in emergencies.

In a pre-flight interview, Ross said: "The first EVA (extra vehicular activity) is by far the most critical one.

"It's the one that is required to hook together the elements of the station that are up there and to permit us to start activating the US-built parts of that station."

Ross and Newman have two other spacewalks planned for the 12-day mission.

"How's the view?"

Falling is not a problem in weightlessness, but working seven storeys above the safe haven of the shuttle could be.

Frank Culbertson, Operations Manager for the space station programme, said: "They may be the most difficult EVAs ever performed. But they will get even harder."

More than 1,100 hours of spacewalks will be required during the construction phase of the station's 10- to 15-year life - more than in the entire history of human space flight.

The space station became a reality on Sunday as the first two components were brought together in orbit by Endeavour's crew.

In time, more than 100 space station components will be assembled in orbit in one of the most ambitious and expensive engineering feats ever undertaken.

Sixteen nations are involved in the $60bn project, which will require more than 40 manned missions and hundreds of hours of high-risk space walks during the construction phase.

Endeavour's six-member crew will enter the station on Thursday, finding it much like the unfinished interior of a new home.