NASA: Spacewalk Clears Path for ISS Construction

NASA: Spacewalk Clears Path for ISS Construction
STS-121 spacewalker Michael Fossum totes a new Trailing Umbilical System (TUS) at the end of the ISS robotic arm during a July 10, 2006 spacewalk to replace a faulty station cable reel. The dark cavity seen in the ISS truss above Fossum is where he installed the new unit. (Image credit: NASA TV.)

HOUSTON - There was a lot riding on today'sspacewalkoutside the InternationalSpace Station (ISS) and two shuttle astronauts did not disappoint, NASAofficials said Monday.

"It was abig deal," Rick LaBrode, lead ISS flight director for NASA's STS-121mission, told reporters. "To get it behind us is a great feeling."

STS-121spacewalkers PiersSellers and MichaelFossum spent almost seven hours outside the ISS to stow a spare coolingsystem pump and replace a broken cable reel for the station's MobileTransporter. Both tasks will allow NASA to forge ahead with a preciselychoreographed series of 16 space shuttle missions - including STS-121 - to complete theorbital laboratory and staff it with six full-time astronauts.

"Theassembly sequence is set to proceed fast and furious here, we're only six orseven weeks away from the next mission," said Phil Engelauf, chief of NASA'sSTS-121 mission operations representative, during a briefing here at NASA'sJohnson Space Center. "Seeing how everything has worked here, we have a greenflag to press ahead."

NASA'sfirst ISS construction mission since late 2002 - STS-115 aboard the Atlantisorbiter - is slated to launch on Aug. 28 to deliver a pair of new solar panelwings and their massive truss mast to the orbital laboratory. The space agencyhopes to launch STS-116 aboard Discovery in December to continue the orbitalISS construction effort.

But much ofthat work hinged on restoring the backup power and data cable system for thestation's Mobile Transporter, which will be used to haul large ISS componentsinto position along the outpost's main truss. Today's spare pump moduleinstallation was also originally slated for the STS-116 crew, but was pushedearlier to get ahead on the many tasks needed to support the ISS.

Discovery'sSTS-121 mission is NASA's second orbiter flight since the 2003 Columbia accident and is atthe midpoint of a 13-day flight to the ISS. Sellers, Fossum and their shuttlecrewmates launchedtoward the ISS on July 4 carrying tons of supplies,a newstation astronaut and a mission to complete NASA's orbiter inspection andrepair tests before the flight is through.

"Themission is going great," Engelauf said. "The healthof the vehicle is great and we're not really working any particularproblems."

A toughspacewalk

There maybe no major problems but Discovery spacewalkers Sellers and Fossum certainlyhad their share of frustrating moments during their Monday spacewalk, whichmarked the second of three planned for their STS-121 mission.

"Wedefinitely knew it wasn't going to be simple," LaBrode said, adding that thespacewalk included many complicated tasks.

Theastronauts had to work through stuck bolts (the solution: twist the screwharder), a stubborn spring that prevented initial attempts to install the newcable reel in place, and a lot of bumping that ultimately knocked Sellers' emergencythruster system loose.

Sellers wasconnected to Discovery or the ISS with two tethers at all times, and not indanger of drifting free, but spacewalk planners were concerned the SimplifiedAid for EVA Rescue (SAFER) thruster system could separate from his spacesuit and pose a debrishazard for the orbiter or station. Fossum later reengaged the latches to lockSellers' SAFER system into its fittings.

"I wasn'tworried about the crew at all," said Tomas Gonzalez-Torres, lead spacewalkofficer for the STS-121 mission.

Gonzalez-Torressaid his STS-121 spacewalking astronauts and ground crew performed above thebar during the orbital repair, and were on schedule - and ahead at some times -through the six-hour and 47-minute activity.

"I couldn'thave asked for a better crew," Gonzalez-Torres said. "These guys werefantastic.

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Tariq Malik

Tariq is the Editor-in-Chief of and joined the team in 2001, first as an intern and staff writer, and later as an editor. He covers human spaceflight, exploration and space science, as well as skywatching and entertainment. He became's Managing Editor in 2009 and Editor-in-Chief in 2019. Before joining, Tariq was a staff reporter for The Los Angeles Times covering education and city beats in La Habra, Fullerton and Huntington Beach. In October 2022, Tariq received the Harry Kolcum Award for excellence in space reporting from the National Space Club Florida Committee. He is also an Eagle Scout (yes, he has the Space Exploration merit badge) and went to Space Camp four times as a kid and a fifth time as an adult. He has journalism degrees from the University of Southern California and New York University. You can find Tariq at and as the co-host to the This Week In Space podcast with space historian Rod Pyle on the TWiT network. To see his latest project, you can follow Tariq on Twitter @tariqjmalik.