Six crew members will ride Atlantis on the 15th shuttle mission to the space station. Photo: NASA

After a frustrating summer of work to fix potentially dangerous fuel line cracks, NASA is gearing up to resume shuttle flights Wednesday with launch of the Atlantis on a critical mission to deliver a 14-ton section of the international space station's main solar array truss.

Commander Jeffrey Ashby, pilot Pamela Melroy, flight engineer Sandra Magnus, cosmonaut Fyodor Yurchikhin and spacewalkers Piers Sellers and David Wolf, a Mir veteran, are scheduled to blast off on the 111th shuttle mission between 2 p.m. and 6 p.m. EDT (1800-2200 GMT) Wednesday.

As with all station flights, launch will be timed to coincide with the moment Earth's rotation carries pad 39B into the plane of the target's orbit. But in keeping with NASA's post Sept. 11 security procedures, the exact launch time will not be revealed until 24 hours before liftoff.

Whenever Atlantis finally takes off, armchair astronauts will enjoy a spectacular new view of the climb to space from a camera mounted on the side of the shuttle's external tank. Looking down on the orbiter and its twin solid-fuel boosters, the camera will run from launch through external tank separation after Atlantis reaches space.

"We're hoping on this flight to get some interesting, new and unique video," said lead flight director Phil Engelauf. "We will for the first time be mounting a public affairs camera on the external tank looking aft down the stack through launch.

"That camera will be activated about (15) minutes before launch and should operate through MECO (main engine cutoff) plus about six minutes," he said. "We haven't tried this before, but you've seen these kind of photographs on expendable launches in the past. This will be the first time we've tried it with the shuttle and we've very optimistic about getting some pretty dramatic video going up hill."

This will be the view seen live during Atlantis' launch.

If all goes well, Ashby will guide Atlantis to a docking with the space station one day 20 hours after launch, between 9:38 a.m. and 1:38 p.m. on Oct. 4. Awaiting their arrival will be Expedition 5 commander Valery Korzun, Sergei Treschev and NASA biochemist Peggy Whitson.

The station's fifth full-time crew, Korzun and company were launched to the outpost June 5 aboard the shuttle Endeavour. They are scheduled to return to Earth around Nov. 20 to close out a 167-day voyage. The station has been continuously manned for 691 days as of Sept. 24.

The primary goal of Atlantis' flight is to deliver and install the first starboard side - S1 - outboard solar array truss segment, a massive 45-foot-long, 15-foot-wide component massing 28,776 pounds.

When completed, the station's nine-segment solar array truss will stretch 330 feet and carry two huge sets of solar panels on each end. Radiators inboard of the solar arrays will dissipate the heat generated by the station's electronic systems.

The central element of the truss, a $600 million component known as S0, was attached to the top of the U.S. laboratory module Destiny during a shuttle flight in April.

The S1 truss fills most of Atlantis' payload bay. Photo: NASA

The Boeing-built $390 million S1 segment aboard Atlantis is the first outboard section. A virtually identical segment, known as P1, will be attached to the port, or left side of the central S0 truss during the next shuttle visit in November.

S1 is scheduled for attachment to S0 the day after Atlantis docks with the station. Whitson and Magnus, operating the station's Canadarm2 space crane, plan to pull S1 from the shuttle's cargo bay and to carefully position it so a powerful, remotely operated claw at the end of S0 can engage a capture bar on the near end of S1.

After the claw pulls the two segments together, motorized bolts at the four corners of the truss interface will drive in to lock the two segments firmly together.

While the attachment process is winding up, Wolf and Sellers will exit the station's Quest airlock module for the first of three planned spacewalks to connect electrical cables, ammonia coolant lines and data links between S1 and S0 and to install fittings to prevent fluid line connectors from sticking together. During the first spacewalk, however,Wolf and Sellers will focus on making critical electrical connections and deploying a new S-band antenna.

"I think the tasks being performed on these EVAs are comparable to what we've done on other missions," said station flight director Andrew Algate. "Many of the tasks are similar. We're hooking up ammonia QDs (quick-disconnect fittings), which we've done before, we're mating electrical umbilicals, all the tasks we're doing on these EVAs have been done on previous missions."

Even so, no one takes the work lightly.

"We don't want to cause any damage out there," Wolf said. "We need to be very careful. It's a delicate, in some ways, space station. Lots of antennas, no-touch areas, so we'll be very cognizant of those."

S1 and P1 will provide the cooling needed for the space station's electrical systems. The two truss segments each feature three huge folding radiator arrays made up of eight panels each that will extend 75 feet into space to dissipate up to 72,000 watts of heat, enough to cool eight 2,000-square-foot homes.

S1 and P1 house independent computers to operate and monitor internal systems, ammonia tanks, pump assemblies and nitrogen pressurization systems for the coolant loops. Each segment features 15 miles of electrical wiring, a third of a mile of fiber optic cabling and 426 feet of stainless steel tubing to route ammonia coolant between the radiators and heat exchangers mounted on S0 and elsewhere.

The STS-112 crew patch depicts the addition of S1. Photo: NASA

S1 also features an S-band antenna and electronic gear to provide a redundant satellite communications path to the ground, a video system that will aid in future assembly operations and a small cart that future spacewalkers can use to move equipment and tools to different work sites.

Heat rejection is provided by two independent ammonia coolant loops. The extendable radiator wings are mounted at right angles to a rectangular framework that can be rotated through 105 degrees to point the radiators toward the cold of deep space.

"It's hard to convey in words what we're really doing," said station program manager Bill Gerstenmaier. "The thing that's challenging about this is this is the first time we've ever attached two truss segments together.

"Then you have all the connectors and fluid lines that have to be mated between the two truss pieces," he added. "Then there's all the electrical stuff, there are new computers out there that have to interface with the other computers on the station, so we had to get that software synched up.

"There's now a thermal rotary joint. This thing rotates and all the ammonia has to flow through this rotating joint (to and from the radiators) and that's a very complex mechanical design. Overall, it's almost mind boggling what we're doing putting this thing together."

If all goes well, Atlantis will return to Earth Oct. 13. Two weeks later, on Oct. 28, the Russians plan to launch a fresh Soyuz lifeboat to the lab complex. The two-man taxi crew will return to Earth Nov. 7 aboard the Soyuz currently docked to the station.

Soyuz spacecraft are certified for six months in space and they must be periodically replaced.

The taxi crew's departure will clear the way for the year's final shuttle mission, launch of Endeavour on Nov. 10 to deliver the P1 solar array truss segment.

"I anticipate that there will be a lot of great moments," Ashby said in a NASA interview. "I think the two greatest things for me will be when we dock and first open the hatch and greet our friends that are there on board the space station. I know that's a very, very memorable moment.

"And, the second one that I know will be very special is when we undock and start to fly around and look back on the space station with S1 attached and realize that we've successfully completed our little part of the construction of space station."

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