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Forum:Space Shuttles - Space Station
Topic:ISS 35: US EVA to diagnose P6 truss coolant leak
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The crew is not in danger, and the station continues to operate normally otherwise. Work is underway to reroute power channels to maintain full operation of the systems normally controlled by the solar array that is cooled by the suspect loop.

Expedition 35's Chris Cassidy and Tom Marshburn began preparing for the possible spacewalk to inspect the area it appears the leak is originating from, and potentially make repairs to the leaking ammonia cooling loop. Station managers are meeting this morning and will meet again tonight to discuss procedures and timeline work for a spacewalk, if approved.

Working in the Quest airlock, astronauts Cassidy and Marshburn checked out the U.S. spacesuits they would wear if a spacewalk is approved, and Expedition 35 Commander Chris Hadfield began preparing to assist as the "intravehicular" crewmember, or spacewalk choreographer.

Cassidy and Marshburn have each conducted three spacewalks, all on the STS-127 mission to the ISS in 2009. They collaborated on two of those spacewalks.

Late Thursday morning, the Expedition 35 crew reported seeing small white flakes floating away from an area of the station’s P6 truss structure. The crew used handheld cameras and Mission Control used external television cameras to gain additional imagery in an attempt to narrow down the leak’s location. The crew’s reports, along with imagery and data received by flight controllers in Mission Control in Houston, confirmed that the rate of the ammonia leaking from this section of the cooling system increased.

Ammonia is used to cool the station’s power channels that provide electricity to station systems. Each solar array has its own independent cooling loop. This ammonia loop is the same one that spacewalkers attempted to troubleshoot a leak on during a spacewalk on Nov. 1, 2012.

It is not yet known whether this increased ammonia flow is from the same leak, which at the time was not visible. It is anticipated that the 2B power channel, which is one of eight power channels to supply electricity for station systems, will be depleted of ammonia coolant by late this morning and will be shut down.

HeadshotWon't this EVA be a bit more dicey than usual? Isn't ammonia highly toxic?

Since the leak rate has increased significantly, the two astronauts will have to be very cautious to avoid getting their suits contaminated by this stuff. Does anyone know what provisions are aboard the ISS for de-contaminating an EVA suit should the worst happen?

Robert PearlmanThis is not the first time spacewalking astronauts have been exposed to leaking ammonia.

As such there are procedures that they follow that includes budgeting time in the spacewalk for the astronauts to "bake" their spacesuits in the sun to let the ammonia boil off before reentering the airlock and for additional inspections of their suits before re-pressurizing.

The space station crew also staged additional breathing masks near the Quest airlock this morning in the unlikely scenario ammonia flakes or contaminated suits made it inside.

HeadshotI know that ISS astronauts have worked with ammonia leaks before. From what I have been reading today, however, the leak rate this time is far greater than previous incidents and the risk of serious suit contamination is also higher.

Hopefully this will be a non-issue by Saturday evening.

Robert PearlmanThere is a news briefing on the spacewalk scheduled for 3 p.m. CDT during which I am sure the question of ammonia contamination will be addressed (and if not, I'll ask about the increased risk, if there is any, either during the conference or after it ends).

Update: Here is what chief flight director Norm Knight said about the ammonia precautions for Saturday's spacewalk:

They are going to do a visual inspection. We know there is ammonia in the area... so they will do a visual inspection of each other to make sure there is no ammonia ice on their suits. Once they have concluded that they are clean, that starts a bake out timer. We do that to make sure we have adequate time for any hidden ammonia that might be on the suits to evaporate. On a rough order of magnitude, 30 to 45 minutes is required for that bake out time.

That clock starts and they will begin their transit back to the airlock, down the P6 truss. Once they get in the airlock, they will hook up on umbilicals, they will repress the airlock to 5 psi and perform a test... a simple way of detecting of how much ammonia might be in the atmosphere at that 5 psi level. And based on that we'll make a determination if there is contamination or not. If consumables permit, they may do a second test. We don't anticipate that to be required.

Robert PearlmancollectSPACE
Astronauts performing 'precedent-setting' unplanned spacewalk

Astronaut Tom Marshburn was planning to spend Saturday (May 11) packing for home. After five months in space, his ride back to Earth is set to leave the International Space Station (ISS) in just a couple of days.

But instead of getting ready for his return, Marshburn and his fellow flight engineer Chris Cassidy are making a last-minute spacewalk in hopes of finding and fixing a coolant leak in the orbiting outpost's main power system.

The contingency spacewalk is the latest in a long but still relatively-rare record of unplanned extravehicular activities (or EVAs) carried out by NASA astronauts. Under normal circumstances, the U.S. space agency prepares its crew members and ground teams to conduct spacewalks with the benefit of weeks of planning and months of training.

Saturday's spacewalk was devised and scheduled in less than two days.

"From purely a station perspective, during an increment, I would say this is precedent-setting," Norm Knight, NASA's chief flight director, said Friday in a press briefing.

Robert Pearlman
Spacewalk to troubleshoot ammonia leak begins

Expedition 35 crew members Chris Cassidy and Tom Marshburn began an unplanned spacewalk outside the International Space Station (ISS) on Saturday (May 11) at 7:44 a.m. CDT (1244 GMT) to inspect and possibly replace a pump controller box on the outpost's far port truss (P6) suspected of leaking ammonia coolant.

A leak of ammonia coolant from the area near or at the location of a Pump and Flow Control Subassembly was detected on Thursday (May 9), prompting engineers and flight controllers to begin plans to support the unscheduled spacewalk.

The device contains the mechanical systems that drive the cooling functions for the port truss.

The P6 truss was launched to the station as the oldest component of the station’s backbone aboard the space shuttle Endeavour on the STS-97 mission in November 2000. It was relocated from its original installation position to the far left side of the space station during the STS-120 mission in October/November 2007.

The spacewalk is the 168th in support of the assembly and maintenance of the space station and the third for both Cassidy and Marshburn, who conducted two spacewalks together during the STS-127 mission in July 2009.

Cassidy is designated as extravehicular crew member 1 (EV-1), whose spacesuit is distinguished by red stripes. Marshburn is EV-2, and is wearing a suit with no stripes.

Expedition 35 commander Chris Hadfield with the Canadian Space Agency is serving as the intravehicular crew member, choreographing the spacewalkers tasks outside.

HeadshotDoes anyone know how many more spare ammonia pumps the ISS has?

Can the old pump be returned to Earth, say aboard a Dragon, for evaluation?

Robert PearlmanIf I recall from yesterday's briefing correctly, there are two additional pumps aboard.

The removed pump cannot be returned to Earth. As ISS program manager Michael Suffredini explained, it might fit back through the airlock but as it is suspected as leaking ammonia, there is no way he would ever bring that inside the space station. (To return it to Earth on Dragon, it would need to come inside as there is no access to the pressurized capsule otherwise.)

Robert Pearlman
Astronauts complete spacewalk to repair leak

Expedition 35 flight engineers Chris Cassidy and Tom Marshburn completed Saturday's (May 11) unplanned spacewalk at 1:14 p.m. CDT (1814 GMT) to inspect and replace a pump controller box on the International Space Station's far port truss (P6) leaking ammonia coolant. The pair began the spacewalk at 8:44 a.m.

A little more than two-and-a-half hours into the spacewalk, Cassidy and Marshburn removed the 260-pound pump controller box from the P6 truss and replaced it with a spare that had been stowed nearby on the port-side truss, or backbone of the station. Mission Control ran the new pump while the spacewalkers watched for any ammonia snowflakes, but so far there have been no new signs of a leak.

Long-term monitoring of the pump will be required to determine whether the pump replacement has fixed the leak.

Jay ChladekThe only way I "might" see them allowing the box inside to be returned on a Dragon would be if there was a way to open up EVERY internal line in the thing to space and let the ammonia boil off for a long time, but if there is no sure fire way to tell if there is any trace of ammonia left inside it, forget it.

Another way I could see "possibly" doing it would be if a Dragon was capable of being depressurized and having its CBM hatch opened outside when not docked. But it would have to be linked to the station with the SSRMS and having a pair of spacewalking astronauts manhandling the bad pump inside. Plus, there would need to be some way to secure the pump inside the Dragon without having an EMU wearing astronaut enter it.

Look at the bright side though, it beats having to track down glycol leaks INSIDE a station, as what began happening with Mir in the mid-1990s.

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