NASA Eyes Fourth Spacewalk for Discovery Shuttle Crew (SPACE.com)

15.12.2006 03:48 Space - Source: Yahoo space

HOUSTON --

NASA flight controllers are discussing the possibility of a fourth spacewalk for two Discovery shuttle astronauts to complete the furling of a stubborn solar array outside the International Space Station (ISS), mission managers said late Wednesday.

Kirk Shireman, NASA's deputy ISS program manager, said Discovery's STS-116 astronauts will proceed with their mission's final two spacewalks to overhaul the space station's power grid this week as planned, with any additional extravehicular activities (EVAs) to come no earlier than the third outing on Saturday and most likely later, if at all.

The discussion here at NASA's Johnson Space Center and elsewhere stems from the partial retraction of one of two wing-like solar arrays on the station's Port 6 (P6) truss on Wednesday [image]. While the array can stay as is until at least April 2007 without hindering ISS operations, flight controllers are studying their options while Discovery's seven astronauts are on hand to assist the station's Expedition 14 crew.

"You do not want to rush into a fix of a problem that just occurred," John Curry, NASA's lead ISS flight director for Discovery's STS-116 mission, which is also known as 12A.1 on the station side. "We can, in this particular configuration, execute every task that is assigned to the 12A.1 joint mission."

ISS and Discovery astronauts retracted the 115-foot (35-meter) P6 array just over halfway to clear space over the station's Port 3/Port 4 (P3/P4) solar wings and allow a massive rotational joint to turn the latter power plant to track the Sun. An unmarred retract process would have taken 11 minutes, but because of folding and guide wire issues the chore ran more than six hours [image].

Swarms of engineers, solar array specialists and flight controllers are going over options to complete the afflicted array's retraction.

NASA officials said potential approaches include: a fourth STS-116 spacewalk, a later spacewalk for the station's Expedition 14 crew, and even no spacewalk at all, with troubleshooting efforts originating from consoles within the ISS.

A fourth STS-116 spacewalk, if ultimately chosen, would call for Discovery astronauts Robert Curbeam and Christer Fuglesang to perform any needed repairs.

The two astronauts are due to rewire half of the space station's power system later today during the second spacewalk of their mission, and could be called upon to perform a fourth, non-solar array, spacewalk in the event the tricky ISS electrical and cooling system work not go as planned, NASA officials have said.

Flight controllers asked ISS Expedition 14 commander Michael Lopez-Alegria and Discovery commander Mark Polansky their views on a possible fourth spacewalk on Flight Days 9 or 10 of the STS-116 flight late Wednesday. The astronauts, who were completing the mission's Flight Day 5, replied that they would wait until discussions on the matter progressed further along.

Any additional spacewalk during NASA's STS-116 shuttle mission to the ISS would require the spacecraft's crew to remain docked at the orbital laboratory at least one extra day, but no more since the mission is set to run 12 days, Shireman said.

Shireman stressed that today's spacewalk, and a similar ISS rewiring job set for Saturday, are vital and complicated tasks that must be completed before any decision is made on adding more work to an already jam-packed mission.

"We've made no decision about conducting an EVA Four on this flight," he said, adding the matter should be decided in the next few days.

Wednesday's array difficulties did not prevent several key milestones in the space station's construction, including the pressurization of a station cooling system loop with 300 pounds (139 kilograms) of ammonia coolant and the successful Sun-tracking rotation of the P3/P4 solar arrays.