A new pair of solar wings and two massive trusses are packed and ready to rocket into orbit aboard NASA's shuttle Atlantis this week to become the latest additions to the International Space Station (ISS).

Weighing in at more than 17.5 tons, the hefty Boeing-designed Starboard 3/Starboard 4 (S3/S4) truss segments and solar arrays are the first new components bound for the ISS this year, and are vital for the station to support new international laboratory modules during upcoming shuttle flights.

"It's the heaviest payload for the space station yet," Chuck Hardison, Boeing's ISS site manager at NASA's Kennedy Space Center in Florida, told SPACE.com.

Atlantis' seven-astronaut STS-117 crew, commanded by veteran shuttle flyer Rick Sturckow, is set to launch towards the ISS the evening of June 8 to begin the two-day trek to the orbital laboratory. The S3/S4 truss is expected to be installed over the course of three spacewalks during the planned 11-day mission.

Power-ful payload

The 35,678-pound (16,183-kilogram) station trusses and solar arrays outweigh their portside counterparts – the Port 3/Port 4 elements launched in September 2006 – by about 701 pounds (317 kilograms). Together, the two new starboard solar wings are expected to unfurl to a wingspan of about 240 feet (73 meters) and generate a total of 66 kilowatts, or enough to power 30 homes, NASA officials said.

"So that's our primary payload," Atlantis shuttle pilot Lee Archambault said in NASA interview. "That's our goal, to install this and have it up and operating by the time we leave."

Less than 1,000 pounds (453 kilograms) of other cargo, spacewalking tools and supplies will ride up to the ISS inside Atlantis' middeck. Tucked among that cargo are a Russian-built Sokol spacesuit and Soyuz spacecraft seat liner for ISS Expedition 15 flight engineer Clayton Anderson, who will launch aboard Atlantis and relieve NASA astronaut Sunita Williams as station crewmember.

The $367.3 million S3/S4 element is an integrated pair of aluminum trusses that measure almost 45 feet (13 meters) long, more than 16 feet (4.8 meters) wide and 15 feet (4.5 meters) high.

Once the STS-117 crew arrives at the ISS aboard Atlantis, the astronauts will pluck the S3/S4 segment out of the shuttle's payload bay for later installation on the space station's starboard side. The segment's hexagonal S3 piece attaches to the station's Starboard 1 (S1) truss – a Starboard 2 element was dropped from the station during an earlier redesign – and connects to the S4 truss via a rotary joint that allows the outboard solar arrays to turn like a paddle wheel to track the Sun.

The new starboard solar wings are the third of four arrays planned for the ISS. The older Port 6 solar arrays stand half-furled above the station while the most recent addition of P3/P4 lends the station its current off-kilter look. During the STS-117 mission, starboard-reaching Port 6 array will also be folded away to give the space station a more symmetrical appearance.

"[W]e'll be balancing out the station with the solar arrays on that side," said STS-117 spacewalker Jim Reilly in a NASA interview.

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