Third spacewalk complete; power converters installed

McArthur installs a power regulating device during a third consecutive day of exterior work on the International Space Station

From Miles O'Brien
CNN Space Correspondent

HOUSTON, Texas (CNN) -- A pair of overqualified, overachieving electricians latched a pair of voltage regulating boxes to the International Space Station on Tuesday.

NASA spacewalkers Bill McArthur and Leroy Chiao spent nearly seven hours singing, whooping and humming their way through a long list of station construction duties.

The work may have been demanding but the surroundings were clearly sublime.

"It's just great to be here," said McArthur at one point.

"Wow, look at that sunrise," said Chaio on another occasion.

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Their work prepared the station for the installation of the outpost's huge solar arrays -- due to arrive at the world's most inaccessible construction site in December.

The fourth and final spacewalk is set to begin Thursday.

Spacewalkers Mike Lopez-Alegria and Jeff Wisoff will continue the station construction work and will test out a small emergency rocket pack designed to propel a loose astronaut back to the safety of the shuttle. They will also practice a technique for rescuing an incapacitated spacewalker.

Discovery's seven member crew is slated to spend 11 days in orbit. A Florida landing is scheduled for shortly after 2 PM ET, on Sunday, October 22.

Solar arrays due in December

The 129-pound power boxes installed on the station Tuesday will ensure that energy captured by the solar photo-voltaic cells flows evenly into the station's power grid.

In Discovery's cargo bay, Chiao takes inventory of the tools he used during a spacewalk

The first set of U.S. solar arrays will arrive on the shuttle Endeavour in December. By that time, the station should have been occupied for about a month by its first permanent crew.

That crew -- NASA's Bill Shepherd and his Russian crewmates Yuri Gidzenko and Sergei Kirkalev -- will be anxiously awaiting the arrival of those solar arrays. Until they are installed, the crew will not have access to the U.S. component of the space station -- a connecting node called Unity.

Unity's hatches will be sealed, and its heaters and lights doused, to save precious power on the space station. The problem is rooted on both sides of the Atlantic.

Batteries in the Russian components of the station continue to be a problem. Two of the batteries inside the crew living quarters -- the so-called "Zvezda" service module -- are currently not working. Batteries inside the first Russian piece of the station -- the "Zarya" space tug -- have been a concern since the module was launched in December of 1998.

Commander Brian Duffy uses an I-Max camera to film his crew on Discovery's middeck after a 6-hour-plus spacewalk

Meanwhile, some of the hardware latched onto the space station this week by the crew of Discovery is proving to be more power-hungry than anticipated. The so-called Control Motion Gyroscopes (CMGs) that are a part of the huge truss bolted onto the station on Saturday will need a warmer thermostat setting than initially thought.

Some CMGs tested in a vacuum chamber before Discovery's launch failed during expected temperature swings in space. The gyroscopes are crucial: they rotate on three axes to keep the station in its proper position without expending too much thruster fuel.

To be certain the CMGs don't fail on account of the cold, NASA engineers decided to increase the thermostat setting on their heaters. The added power drain that will result was factored into the decision to seal off "Unity" until the new solar arrays arrive.

Two spacewalks down; two new pieces in place on space station
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Discovery docks at International Space Station
October 13, 2000
Shuttle Discovery zooms in on orbiting outpost
October 12, 2000
Shuttle soars into space for 100th time
October 11, 2000
NASA scrubs 3rd attempt to launch shuttle
October 10, 2000
Wind gusts force delay of 100th shuttle flight
October 9, 2000

Shuttle Orbiter Discovery (OV-103)
NASA
Human Space Flight (HSF) - International Space Station

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