Shuttle Discovery Launches To ISS Carrying Z-1 Truss

The Space Shuttle Discovery successfully launched from Kennedy Space Center, pad 39A, at 2317 UTC (4:17 p.m. PDT) on October 11. The 7 member crew will deliver the Z-1 Truss (mounted on a Spacehab pallet), Control Moment Gyros, Pressurized Mating Adapter-3 (PMA-3) and two DDCU (Heat pipes). Flight STS-92 was launched into a 350 km (189 nmi), 51.6° orbit to rendezvous for a service and assembly mission (ISS-05-3A) with the International Space Station (ISS). This is the 100^th launch of the Space Shuttle.

During the mission the US$273 million Z-1 truss (Z for zenith port) will be secured to the top the “Unity” docking module.  Weighing in at 8,357 kg (18,424 lbm), the cube-shaped Z-1 truss is the first of 10 skeletal structures that eventually will be installed to form the station’s 108 m (356 ft) metal spine.

The Z-1 truss will house four stabilizing gyroscopes and Ku-band and S-band communication antennas. The domed-shaped gyroscopes will reduce the amount of propellant required to maintain the station’s position on orbit. The dish-shaped antennas will be used to beam voice and television communications between the station and ground control. The Z-1 truss includes a temporary mounting platform for a pair of solar power arrays planned for launch aboard a shuttle Endeavour flight later this year.

A conical 1,156 kg (2,549 lbm) Pressurized Mating Adapter (PMA 3) will be attached to the bottom of the “Unity” docking module. The US$20 million tunnel-like docking mating adapter, 2.5 meters (8 ft) in length, will serve as the primary shuttle docking port for future crews. Docking at the station’s current shuttle docking port will not be an option because the space shuttle’s tail would block installation of the two massive solar wings, which will stretch 73 m (240 ft) from end to end once deployed in orbit.

Four back-to-back Extra Vehicular Activities (EVAs), each lasting about 6.5 hours, will be undertaken on consecutive days to install the Z-1 truss and the new docking port. In addition, the communications dish will be deployed at the end of a long boom, electric power converters will be installed on the station and toolboxes will be stowed outside the outpost for future construction crews. The spacewalks will be carried out by a quartet of astronauts working in teams of two. Chiao and McArthur will perform the first and third spacewalks. Mission specialists Wisoff and Lopez-Alegria will perform the second and fourth EVAs.

A highlight of the mission will occur on the last EVA when Wisoff and Lopez-Alegria test-fly US$7 million jet backpacks that should enable astronauts to rescue themselves during EVA emergencies. A second emergency drill will be staged to see if a spacewalking construction astronaut can, if necessary, carry an unconscious partner back to the shuttle for medical attention. Wisoff and Lopez-Alegria will take turns acting as if they are suffering from an orbital version of “the bends.” The plan then is to assist the "incapacitated" spacewalker back to the shuttle airlock to ensure such a rescue could be undertaken in an actual emergency.

Once the spacewalks are concluded, Discovery’s crew will enter the space station to deliver supplies and complete electrical connections to the Z-1 truss.

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