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.
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