INTERNATIONAL Space Station flight controllers yesterday began the delicate task of unfurling the outpost's new solar power wings, which two spacewalking astronauts installed during the first major task of shuttle Atlantis' 13-day flight.
Stretching the twin panels to their full 240ft length was expected to take some hours - the wings had been folded for more than six years and mission managers were worried they might stick together as they unfurl.
Construction of the International Space Station had been on hold for three and a half years while NASA recovered from the 2003 destruction of the space shuttle Columbia. The US space agency resumed building the $100-billion project in 2006 and has three years to finish 12 flights needed to complete the outpost before the last space shuttles are retired.
NASA also would like to fly two station resupply missions and make a final servicing call to the Hubble space telescope before the shuttles are mothballed.
The additional power provided by the new solar panels will pave the way for NASA to install laboratory modules built by the European Space Agency and Japan this year and in 2008.
The Atlantis astronauts, who were asleep when ground controllers sent the commands to begin deploying the panels, were expected to take over the job of extending the wings and adjusting tension reels if the folds stick.
"There are a number of things that we'll be watching for," said James Reilly, one of the astronauts, in a pre-flight interview.
Mr Reilly and John Olivas installed the beam holding the solar wings during a six-hour, 15-minute spacewalk on Monday. After the wings are extended, astronauts Patrick Forrester and Steven Swanson will undertake the mission's second spacewalk today to set up a rotary joint so they can track the Sun.
Part of an older wing must be retracted before the joint can rotate. The last shuttle crew faced a similar task and ended up having to make an unplanned spacewalk to coax the jammed wing back into its storage box by hitting it.
Anticipating similar problems, flight directors loaded Atlantis with extra fuel and supplies to keep the shuttle in orbit beyond its originally planned 11-day flight.
Even before getting to that point in the mission, NASA decided on Monday to extend it an extra two days and add a fourth spacewalk to fix a potential problem with a thermal blanket sticking up from one of the shuttle's engine pods.
Since Columbia, NASA has been scrupulous about checking for and fixing problems with shuttle heat shields, which protect the ships and their crew from the 3,000F (1,649C) temperatures of the plunge through the atmosphere prior to landing.
Columbia's wing had been hit by a piece of fuel tank insulation that fell off during the launch, puncturing a reinforced carbon heat panel. The shuttle was torn apart as it flew over Texas on its way to the landing site, killing all seven of its crew members.
Atlantis is now due back at the Kennedy Space Center in Florida on 21 June.