(CNN) -- In the aftermath of Tuesday's tear of a space station solar array during deployment, NASA has recast its spacewalk plans for the remainder of Discovery's stay at the international space station.
A solar array ripped as it was being unfurled by astronauts aboard the space station on Tuesday.
A spacewalk planned for Thursday to inspect a balky rotary joint on the station has been indefinitely postponed in favor of prepping for a Friday spacewalk to attempt to fix the ripped array, which engineers think is structurally unstable in its current position.
"Given the fact that we could potentially damage this array if we leave it in this configuration, and if we damage it enough we could potentially not have it available for the life of the program, this then becomes our priority," said space station program manager Mike Suffradini.
Astronauts moved the "P6" solar array during spacewalks Sunday and Tuesday from a temporary location on top of the station to a permanent home on the station's main girder. Watch spacewalker describe exciting moments »
The wings of the array, which fold like an accordion, had been retracted for the move. At the end of the day Tuesday, astronauts were in the process of re-extending the wings to make them fully functional again. One side extended as planned, but astronauts stopped the process while they were extending the other half when they noticed a 2½-foot tear.
That side of the array is about 80 percent deployed. It is still generating electricity.
Neither the ripped array nor the malfunctioning rotary joint pose any safety issues for the crew, but both will need to be fixed before the full complement of new modules and laboratories from the European and Japanese space agencies can be installed on the station next year. Right now, power generation on the station is sufficient to meet requirements, though neither set of solar arrays can rotate and track the sun as designed.
Mission controllers are still planning exactly what astronauts Scott Parazynski and Doug Wheelock will do on the next spacewalk, but some details are emerging. Engineers briefed the crew on the developing plan on Wednesday.
"Right now, the crew on orbit is kind of wrapping their brains around this new option that we've thrown out there," said lead space station flight director Derek Hassmann. "It's not really very far outside our scope of experience and I'm comfortable it is something we are going to be able to put together and finish up."
The spacewalk is planned for Friday, with an option to slip to Saturday if extra time is needed. Program managers are pushing for Friday, as it leaves them an option to extend Discovery's mission one day and schedule a follow-on spacewalk Sunday if needed. If the teams are not ready to go on Friday, a Saturday spacewalk would have no follow-on options and the shuttle would land November 7 as scheduled.
The P6 array is located on the far end of the station's main girder, and it is very difficult to access. The plan is for veteran astronaut Scott Parazynski to stand on the tip of the Orbital Boom Sensor System, or OBSS, which would be attached as an extension to the space station robotic arm. The OBSS is typically used as an extension of the space shuttle robotic arm to inspect the shuttle's wings and nose cap for damage. Prior tests have shown the OBSS is stable enough as a work platform to support an astronaut if necessary.
Once Parazynski is on the OBSS, astronaut Dan Tani will robotically maneuver him up near the damage site on the array. He will then reach out and use a wire fashioned as a kind of "cufflink" to hold the ripped panels in the array together and provide the needed structural support to pull it out to its full length.
He might need to cut the guide wire where the panels are snagged in order to straighten them out. He will need to be careful not to touch the array itself, which has electricity flowing through it.
Spacewalker Doug Wheelock would be positioned in a good vantage point at the base of the array to provide verbal cues to the robotics team as they adjust Parazynski's positioning, and to reel in the snipped guide wire.
There are risks associated with the spacewalk. If the OBSS is damaged, the Discovery astronauts may not be able to use it to evaluate the shuttle's heat shield during a routine late inspection before landing, looking for any damage caused by micrometeoroids or orbital debris while the shuttle has been in space. Sensors on Discovery's wings have picked up at least one impact since the shuttle has been docked at the station, though flight controllers think it is unlikely that it did any damage.
Engineers on the ground are investigating ways to use the shuttle's robotic arm to do the inspection, but there are some areas on the vehicle that the robotic arm can't reach. E-mail to a friend
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