NASA astronauts grappled with a loose jetpack designed to bring them back to safety should they float away from the ISS and into space, but in the end successfully made crucial repairs to the International Space Station. The out-of-this-world drama had Mike Fossum helping fellow space walker Piers Sellers secure the jetpack before they completed their work preparing the ISS for future shuttle missions.

During the spacewalk the Sellers' jetpack became loose when the left hook had come unlocked, prompting Fossum to tie the jetpack to Sellers' spacesuit with a tether. Later, Discovery pilot Mark Kelly radioed that Sellers' right latch had come loose as well. Sellers was told to stop moving until they figured out a plan. Sellers shuffled around the ISS to meet Fossum, who was installing the replacement part of the railcar, and latched the right side to secure Sellers' jetpack to the spacesuit.

The two Discovey crew members replaced a key system that sends power and commands to a railcar attached to the station's truss -  the backbone to the station which supports its power-generating solar arrays. In December 2005, a cable was accidentally cut on one of two systems and send commands to the railcar and power it. Although the device can operate with just one system, NASA prefers both systems are working. "If we didn't get this successfully changed and checked out, then we couldn't proceed with the next mission, which is right on our heels," says ISS lead flight director Rick LaBrode.

Sellers stayed up on the truss to help Fossum install the replacement part for the rail car. "This is a day when ingenuity and persistence paid off, and flexibility," Fossum said back in the shuttle. The pair has one more spacewalk on Wednesday which will aim to test repair equipment for the shuttle's heat shield.

The lead spacewalk officer, Tomas Gonzales-Torressaid the jetpack was in no danger of coming off but jostling up against the railcar system may have loosened them.

View Video: [Spacewalk]

The second of three spacewalks for the STS-121 mission was done last yesterday, July 10. To stow a spare cooling system pump and replace a broken cable reel for the ISS' Mobile Transporter, STS-121 spacewalkers Piers Sellers and Michael Fossum spent seven hours outside the station. The tasks will give NASA the green signal for a precisely choreographed series of 16 space shuttle missions (STS-121 included) that will complete the orbital laboratory and man it with six full-time astronauts.

August 28 will see the launch of NASA's first ISS construction mission since 2002 and it will deliver a pair of new solar panel wings and the massive truss mast to the orbital library. And to continue the orbital ISS construction effort, NASA also hopes to launch in December the STS-116 aboard Discovery.

Although the spacewalk was successful, it was not without complexities. Lead ISS flight director for NASA's STS-121 mission Rick LaBrode shared that the astronauts needed to work through stuck bolts, a stubborn spring that prevented initial attempts to install the new cable reel, and a lot of bumping - all of which made the task more complicated.

Tomas Gonzalez-Torres, lead spacewalker officer for the STS-121 mission however said that he wasn't worried at all; adding that he had a crew who can handle the job. "I couldn’t have asked for a better crew. These guys were fantastic," shares Gonzalez-Torres.