CAPE CANAVERAL, Fla. -- Two orbital electricians started work outside the International Space Station a bit early Saturday, aiming to hook up handrails and string power cables on the $1.4 billion U.S. Destiny science laboratory.
Running about 30 minutes ahead of schedule, astronauts Daniel Barry and Patrick Forrester set out on their second sortie of the week at 9:42 a.m. EDT (1342 GMT) as shuttle Discovery and the station soared high above South America.
Floating within Discovery's expansive cargo bay, the astronauts gathered up four bulky bags containing handrails and cables before heading off to a work site two stories above their shuttle mothership.
Said Barry: "I feel like I'm on a Christmas shopping spree."
Shuttle skipper Scott Horowitz, doubling as a crane operator, hoisted the two astronauts up to the bus-sized lab with Discovery's 50-foot (15-meter) robot arm.
The first order of business there: Installing 11 handrails on the starboard and port side of the Destiny lab. Shaped something like bathroom towel bars, the metal rails will provide handholds that future spacewalkers can use to get from one end of the 28-foot (8.5-meter) lab to the other.
Two 45-foot (13.6-meter) power cables then were to be strung along the handrails. The electrical lines will provide back-up power sources for critical heaters on a station truss segment that is to be launched to the outpost aboard shuttle Atlantis next February.Equipped with sensitive electronics boxes, the so-called S-0 truss will be mounted to the outpost near the Destiny lab, forming the core of a skeletal backbone that eventually will stretch 356 feet (108 meters) from end to end.
Heaters on the truss must be hooked up to a power source to avoid damaging internal electronics, and the electrical lines will provide spacewalking astronauts with a second method of doing just that.
The cables only would be used if primary electrical lines on the truss for some reason could not be connected.
Coming on the heels of an initial spacewalk Thursday, the second sortie started amid a moderate geomagnetic storm that created higher-than-normal cosmic radiation levels in low Earth orbit.
Triggered by a coronal mass ejection on the backside of the sun Tuesday, the radiation storm struck the planet's magnetosphere Friday, creating a flux of high-energy protons 1000 times higher than normal.
The start and end of Thursday's spacewalk was purposely timed to steer clear of an area over the South Atlantic Ocean where astronauts typically are exposed to elevated levels of cosmic radiation.
Sidestepping the so-called South Atlantic Anomaly enabled NASA flight directors to avoid exposing the spacewalkers to cosmic radiation levels any higher than those within the protective confines of the shuttle's crew cabin.
The joined shuttle-station complex had just passed beyond the western edge of the same area when Barry and Forrester drifted outside the outpost Saturday.
Launched Aug. 10 from Kennedy Space Center, Discovery and its crew of four astronauts ferried new station commander Frank Culbertson and his two Russian cosmonaut colleagues -- Vladimir Dezhurov and Mikhail Turin -- to the outpost for a four-month research mission.
Outgoing station commander Yuri Usachev and two U.S. flight engineers -- Susan Helms and Jim Voss -- will return to Earth aboard Discovery after a 167-day stay in orbit.
With that trio in tow, the shuttle is due to depart the station Monday, heading off on a two-day voyage back to NASA's coastal Florida spaceport. Landing remains scheduled for 12:48 p.m. EDT (1648 GMT) Wednesday.
Culbertson and his crew will remain in space until Dec. 9.
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