European Space Agency astronaut Thomas Pesquet and NASA crewmate Shane Kimbrough geared up for a complex spacewalk outside the International Space Station early Wednesday to install the first of six new solar wings intended to boost the lab’s power back to factory fresh levels.
Floating in the station’s Quest airlock, the astronauts, both veteran spacewalkers, were expected to switch their suits to battery power around 8 a.m. EDT to officially kick off the year’s seventh spacewalk, the 239th excursion devoted to station assembly and maintenance since construction began in 1998.
For identification, Pesquet, call sign EV-1, will be wearing a suit with red stripes and using helmet camera No. 20. Kimbrough, EV-2, will be using an unmarked suit and using helmetcam 18. They also are equipped with a high definition helmet cameras.
The spacewalk is the first of two needed to install a pair of ISS roll-out solar arrays — iROSAs — on the far left end of the space station’s main power truss. Both excursions were timed to make sure the station is in Earth’s shadow and out of direct sunlight when the new arrays are plugged into the lab’s solar power system.
“The big problem is that we’ve got giant solar arrays that will be generating power when we’re in daylight,” said Kieth Johnson, the lead spacewalk officer. “And we are disconnecting one of those cables that if we were in daylight would be sending a lot of power through it.
“And so because of that, we plan our EVAs (spacewalks) and we time it so that when they get to that electrical connector, we do it at night, and we make sure it’s not generating any power whatsoever.”
Delivered to the station aboard a SpaceX cargo ship earlier this month, the iROSA blankets were designed to be mounted on fixtures that were assembled like Tinker Toys and bolted to the base of the existing port 6, or P6, solar wings during two spacewalks last March by other astronauts.
The space station is equipped with eight solar wings in all, four on each side of the truss, feeding up to 120 kilowatts of power into eight circuits. The two P6 arrays, installed in 2000, are the oldest on the station, supplying electricity to power channels 2B and 4B.
Wednesday’s spacewalk was devoted to attaching the first iROSA wing to the existing P6/2B array while a spacewalk Sunday will focus on the P6/4B array. The iROSA panels will each generate more than 20 kilowatts of power.
The first half of Wednesday’s outing was devoted to simply moving the first 750-pound iROSA out to the far left end of the power truss, a procedure that required Pesquet and Kimbrough to manually hand the rolled-up array back and forth as they inch their way outward toward the left-most P6 truss segment.
Once mounted on its support fixture, the first iROSA was to be unfurled just in front of the existing 112-foot-long P6/2B array. The new array, tilted out by about 10 degrees, will extend 63 feet when fully unfurled.
Unlike the station’s original solar arrays, which were deployed using complex motor-driven self-assembling trusses, the iROSA wings feature carbon composite struts on either side that are rolled up and locked in place for launch. One the locks are released, the pent-up “strain energy” is enough to unroll the blankets to their full length.
While the iROSA will block the sun for a portion of the existing solar wing, they will generate a combined power level matching the output of the original arrays when they were first deployed 20 years ago.
“The new arrays are installed on top, over in front of the existing solar arrays,” said Dana Weigel, deputy manager of the space station program at the Johnson Space Center in Houston. “The exposed portion of the old arrays will still be generating power in parallel with the new arrays.
“Those new iROSA arrays have solar cells on them that are more efficient than our original cells, they have a higher energy density, and together in combination, they generate more power than what our original array when it was new.”
Unlike the original arrays, the iROSA wings cannot be rolled up once released. They simply have to work.
“We do not have any planned contingency workarounds to fix anything just yet,” Johnson said. “But you know NASA. If something happens, we’re going to stop and look at where it is, we’re going to take pictures, we’re going to analyze what’s going on and we’ll come up with a plan to fix it.”
Pesquet and Kimbrough plan to venture back outside Sunday to install the second iROSA on the P6/4B solar wing. The remaining four iROSAs will be installed next year.
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