Realtime coverage of U.S. EVA-20 (P6 coolant radiator bypass)

CBS News

03:20 PM EDT, 11/01/12: Spacewalk ends

Akihiko Hoshide hands a camera to Sunita Williams just before floating back inside the airlock of the International Space Station to close out a six-hour 38-minute spacewalk (Credit: NASA TV)
Space station commander Sunita Williams and Japanese astronaut Akihiko Hoshide returned to the Quest airlock module and began repressurizing the compartment at 3:07 p.m. EDT (GMT-4), officially ending a successful six-hour 38-minute spacewalk to bypass a suspect solar array radiator.

This was the 166th spacewalk devoted to station assembly and maintenance since construction began in 1998 and the fifth this year. One hundred and nine astronauts, cosmonauts and international partners have now logged 1,049 hours and 01 minute of space station EVA time, or 43.7 days.

With today's spacewalk, Williams, a former Navy helicopter pilot, moves up to No. 5 on the list of most experienced spacewalkers with 50 hours and 40 minutes of EVA time during seven excursions. Hoshide now has 21 hours and 23 minutes of spacewalk time during three EVAs.

Williams and Hoshide successfully reconfigured ammonia coolant lines to bypass a presumed leak in a radiator used to cool electrical components in one of the space station's solar array modules. A spare radiator then was successfully deployed to take over cooling.

Flight controllers plan to monitor the system for several weeks to determine if the leak is still present. If there are no signs of a leak, they will know the problem was, in fact, in the bypassed radiator. In that case, managers could elect to simply use the spare radiator indefinitely. If the leak is still there, engineers will know it's somewhere else in the system. In that case, another spacewalk likely will be required at some point to replace a pump module.

But switching to the spare radiator effectively tapped an additional reservoir of ammonia and even with a leak, the coolant system should be able to operate for nearly a year, giving engineers time to come up with a solution.

02:00 PM EDT, 11/01/12: Spare radiator deployed in successful cooling system bypass

After successfully reconfiguring ammonia coolant lines to bypass a suspect solar array radiator, space station commander Sunita Williams and Japanese astronaut Akihiko Hoshide stood by while flight controllers sent commands to deploy a spare radiator to take over cooling the electronics supporting one of the lab's far left-side solar panels.

A spare radiator can be seen extending to the right of the station's main power truss after spacewalkers successfully bypassed a radiator that is believed to have a leak. The suspect radiator is the one visible on the left at the far end of the power truss. (Credit: NASA TV)
"Stand by for deploy," astronaut Mike Fincke radioed the spacewalkers from mission control.

A few moments later, the articulating panel began unfolding, extending directly away from the bypassed radiator on the other side of the station's power truss.

"I see motion," Williams radioed as the radiator began extending. It took the panel several minutes to fully deploy, but there were no problems and flight controllers were pleased with the result.

"Suni and Aki, our heartfelt congratulations to you and the entire team," Fincke called from Houston. "We've accomplished just about everything we set out to do today."

"And a big huge congratulations to you guys on the ground for putting this together," Williams replied. "It's nice to see it deployed again."

"Yeah, we've got smiles all around," Fincke said.

The successful bypass surgery will help engineers pinpoint the source of a small ammonia leak, believed to be in a coolant line snaking through a radiator shared by two left-side solar panels. That radiator will still be used for the coolant system supporting electrical channel 4B, but the ammonia cooling channel 2B components is now flowing through the spare radiator.

The spare was used early in station assembly, before the port 6, or P6, arrays (channels 2B and 4B) were moved to their permanent location on the end of the station's 357-foot-long power truss. With the spare taking over for the channel 2B radiator loop, engineers should be able to determine whether the leak was, in fact, in the original radiator.

If so, they may elect to simply use the spare radiator indefinitely. If the leak is still present, however -- and it may take several weeks to find out -- engineers will know it is somewhere else in the system and a second spacewalk may be needed down the road. But by switching to the spare radiator, the system can operate normally for another year or so, even with a leak.

Earlier, Williams and Hoshide re-positioned two ammonia jumpers and activated a valve to divert coolant into the spare radiator and isolate the suspect cooling panel. That work went fairly smoothly, although Williams had problems attaching devices used to add rigidity to the coolant line quick-disconnect fittings. She got all but one installed before the crew focused on getting the spare radiator deployed.

Williams was asked to make a final attempt before wrapping things up. The spool positioning devices, or SPDs, are not required for the system to operate, but the added rigidity can help prevent leaks in the quick-disconnect fittings.

11:35 AM EDT, 11/01/12: Ammonia coolant line jumpers connected

Astronaut Sunita Williams has successfully repositioned two ammonia line jumpers, bypassing a section of a solar array coolant loop inside a radiator that is believed to have a leak. The ammonia can now flow through a spare radiator that will be extended later in the spacewalk.

"Very good news," astronaut Mike Fincke radioed from mission control after Williams engaged a fourth and final quick-disconnect fitting. "We're now flowing ammonia through both jumpers. Everything is looking good."

The primary goal of the spacewalk is to bypass a suspect radiator used to control temperatures in the electronics associated with one of the space station's far left-side solar arrays. Engineers suspect a leak in the radiator and the spacewalkers are in the process of bypassing that part of the coolant loop, diverting ammonia into a spare, still-stowed radiator that was used during the early stages of station assembly.

Japanese spacewalker Akihiko Hoshide is removing a protective shroud from the spare radiator to clear the way for its extension. Williams, meanwhile, is attempting to install spool positioning devices, or SPDs, on the ammonia line quick-disconnect fittings to help increase their rigidity. Williams initially ran into an interference issue with one of the SPDs, but she eventually worked it into place.

Flight controllers then came up with a plan to use wire ties to secure the remaining SPDs. The SPDs are not required, but flight controllers want them installed if possible as an aid to preventing leakage through the fittings.

"You've been outside for about three hours, you're doing super duper on the timeline, we're very happy down here," Fincke radioed.

10:25 AM EDT, 11/01/12: Spacewalkers work to connect bypass jumpers; drive coolant isolation valve

Two hours into a planned 6.5-hour spacewalk, station commander Sunita Williams and Japanese astronaut Akihiko Hoshide, working at the far left end of the station's 357-foot-long solar array truss, are reconfiguring ammonia line jumpers to isolate one of two coolant loops in a radiator used to control temperatures in the P6 solar array module.

Station commander Sunita Williams and Akihiko Hoshide work at the far left end of the International Space Station's solar array truss to reconfigure ammonia coolant lines. (Credit: NASA TV)
The P6 module features independent coolant loops for electrical channels 2B and 4B and a small leak is present somewhere in the 2B system. Engineers suspect it is in the radiator. Williams and Hoshide are reconfiguring jumpers to divert ammonia used to cool channel 2B components into a spare radiator, isolating the 2B loop in the original radiator.

The astronauts had no problems during the initial stages of the spacewalk and Williams reported there were no signs of leakage or any other problems with the ammonia line quick-disconnect fittings.

"Both sides look fine, there is no evidence of any leakage, the O-rings looks good. It looks great," she reported. "No issues at all."

She finished about half the required steps in the jumper reconfiguration before running into problems attaching a spool positioning device, or SPD, to one of the jumpers. The SPDs are used to prevent leakage through quick-disconnect fittings.

While flight controllers evaluated alternative procedures, the astronauts turned their attention to driving a valve to block the flow of channel 2B ammonia into the original radiator. They reported seeing a few flakes of frozen ammonia float out as the valve was driven closed with a power tool, but that was expected and posed no problems for the spacewalkers.

"I think there were probably seven or eight flakes, they were probably 2-millimeter-size pieces, maybe smaller," Williams said. "I saw them fly out. Nothing stuck to me as far as I can tell."

"Maybe one or two hit my helmet," Hoshide reported.

Hoshide then moved to a spare, still-stowed radiator to remove a protective shroud. The radiator will be extended later in the spacewalk to provide cooling for channel 2B components. Williams, meanwhile, is going back to the quick-disconnect fittings to continue the required jumper/SPD reconfiguration.

08:45 AM EDT, 11/01/12: Spacewalk begins

Editor's note: Portions of the following story (electrical system background) were posted last week, after a news briefing to discuss the goals of today's spacewalk.

Floating in the Quest airlock module, Expedition 33 commander Sunita Williams and Japanese astronaut Akihiko Hoshide switched their spacesuits to battery power at 8:29 a.m. EDT (GMT-4) to kick off a planned six-and-a-half-hour spacewalk to bypass a suspect solar array radiator that may be the source of an ammonia coolant leak.

Astronaut Sunita Williams floats out of the space station's Quest airlock module to kick off a planned six-and-a-half-hour spacewalk to bypass a suspect cooling system radiator. Joining her is Japanese astronaut Akihiko Hoshide. (Credit: NASA TV)
For identification, Williams, call sign EV-1, is wearing a suit with red stripes and will be using helmet camera No. 20. Hoshide, EV-2, is wearing an unmarked suit and will be using helmet cam 18.

This is the 166th spacewalk devoted to station assembly and maintenance since construction began in 1998, the fifth this year, the seventh for Williams and the third for Hoshide. Going into U.S. EVA-20, 109 astronauts, cosmonauts and international partners had logged 43.4 days of station spacewalk time.

Assuming a full-duration spacewalk Thursday, Williams, a former military helicopter pilot, will move up to No. 5 on the list of most experienced spacewalkers with more than 50 hours of EVA time. She currently ranks 13th overall and first among female space fliers.

The goal of the excursion is to reconfigure ammonia coolant jumpers and deploy a spare radiator on the space station's far left-side solar array module in a bid to bypass a presumed leak in the photo-voltaic radiator, or PVR, normally used to cool the port 6, or P6, solar array electronics.

"We're real suspicious of the radiator, just because it kind of stretches out there and it's susceptible to micrometeoroid impacts," Mike Lammers, the NASA flight director overseeing the spacewalk, said last week. "The goal of this EVA is to isolate the PVR from the system by closing (a) disconnect. By doing that and watching the quantity that's in the radiator that's cut off from the rest of the system, we can kind of determine if that leak is in the PVR."

The lion's share of the International Space Station's electrical power comes from four sets of dual-panel solar arrays, two on the right side of a 357-foot-long truss and two on the left side. Each set of solar arrays features two 115-foot-long panels that extended in opposite directions. The Russian segment of the station taps into the U.S. power grid to supplement electricity generated by two relatively small solar panels on the Zvezda command module.

The two U.S. arrays at the far left end of the station's integrated power truss -- the P6 arrays -- feed power to electrical channels 2B and 4B. The P6 set of arrays, like its three counterparts, routes power from the solar panels directly into the station's electrical grid during daylight passes, at the same time charging dual sets of batteries that take over during orbital darkness.

The suspect coolant system radiator can be seen extending from the P6 solar array module. (Credit: NASA TV)

To keep the power generation components cool, each of the four sets of arrays uses two independent coolant loops that circulate ammonia through cold plates to carry heat out to a single shared radiator that extends from each module. The photo-voltaic radiator weighs 1,650 pounds and is made up of seven panels measuring 6 feet by 11 feet.
An extremely small leak in channel 2B's thermal control system was first noticed in 2007. But earlier this summer, the leak rate suddenly increased, leading engineers to suspect a space debris hit might have punched a tiny hole -- about the width of a human hair -- in the channel 2B ammonia line that snakes through the photo-voltaic radiator.

Left unresolved, enough ammonia could leak out over the next few months to trigger an automatic shutdown, knocking out one of the station's eight main power channels.

In a lucky break for NASA, the P6 truss segment was the first installed on the station and it came equipped with a separate cooling system used early in the station's construction. That early external thermal control system, or EETCS, was shut down, and its two radiators retracted, when the P6 segment was moved to the port side of the integrated power truss and tied into the station's main power system.

To isolate the P6 coolant system leak, Williams and Hoshide will divert ammonia coolant into the old system by operating a valve and reconfiguring jumpers at a panel of quick-disconnect fittings. One of the old radiators then will be re-extended to provide cooling to the channel 2B components.

Channel 4B cooling will continue to be provided by the PVR.

The bypass operation will buy time for engineers to track down the leak and figure out what might be done about it. If the leak is in the P6 radiator, managers could decide to simply let it leak out and use the old coolant system indefinitely for channel 2B.

If the leak is in the channel 2B pump module, a replacement unit could be installed later. But the simplest solution is to isolate the PVR and see what happens.

"What this (spacewalk) will tell us is whether the radiator is the cause of the leak," said space station Program Manager Mike Suffredini. "If it turns out the leak continues, we have a little time. When we filled this system a year ago, the result of that fill was to also fill the early ammonia system as well, so we have extra ammonia in that loop.

"So it buys us a little time. It lets us isolate the PVR to see if that's the cause. if that turns out not to be the cause, then we have to think about the next steps."