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Raumfahrt - 2. ISS-Spacewalk (EVA-25) erfolgreiche Reparatur von Ammoniak Kühlschleifen

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22.12.2013

Space Station Crew Removes Ammonia Pump; Next Spacewalk Set for Tuesday

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Expedition 38 Flight Engineers Rick Mastracchio and Mike Hopkins wrapped up a 5-hour, 28-minute spacewalk outside the International Space Station at 12:29 p.m. EST Saturday, completing the first in a series of excursions aimed at replacing a degraded ammonia pump module associated with one of the station's two external cooling loops that keeps both internal and external equipment cool.

 

A second spacewalk to install a replacement pump module, originally planned for Monday, is now scheduled for Tuesday.

The extra day will allow time for the crew to resize a spare spacesuit on the space station for use by Mastracchio. During repressurization of the station's airlock following the spacewalk, a spacesuit configuration issue put the suit Mastracchio was wearing in question for the next excursion.-- specifically whether water entered into the suit's sublimator inside the airlock. The flight control team at NASA's Johnson Space Center in Houston decided to switch to a backup suit for the next spacewalk.

This issue is not related to the spacesuit water leak that was seen during a July spacewalk by European Space Agency astronaut Luca Parmitano and NASA's Chris Cassidy. Both Mastracchio and Hopkins reported dry conditions repeatedly throughout Saturday's activities and the two were never in danger.

NASA Television coverage of Tuesday's spacewalk will begin at 6:15 a.m. EST. The spacewalk scheduled to begin at 7:10 a.m.

During Saturday’s spacewalk, the two astronauts focused on removing a degraded pump module from Loop A of the station’s external Active Thermal Control System. That pump module encountered a problem Dec. 11 when an internal valve stuck in an incorrect position, causing temperatures in the station’s cooling lines to drop.

After exiting the Quest airlock Saturday, Hopkins made his way out to the worksite at center of the Starboard 1 truss segment. Mastracchio meanwhile attached himself to a foot restraint at the end of the station’s 57-foot robotic arm so that Flight Engineer Koichi Wakata, the robotics operator for the spacewalks, could fly Mastracchio to the worksite and position him for his various tasks.

The two spacewalkers first spent some time demating four ammonia fluid line “quick disconnects” from the pump module.

Once the four fluid lines were disconnected, Mastracchio and Hopkins worked to attach the fluid lines to a pump module jumper box, which allows the ammonia to reach the system’s plumbing in the ammonia and nitrogen tanks to keep it in a liquid state.

Afterward the spacewalkers installed a generic thermal cover over the pump module jumper and ammonia fluid lines.

With the spacewalk proceeding well ahead of schedule, Mission Control in Houston informed Mastracchio and Hopkins that they could press ahead with the first task originally planned for Monday’s spacewalk –removing the degraded pump module from the starboard truss and attaching it to a stowage location on the Payload Orbital Replacement Unit Accommodation (POA) on the station’s railcar, or Mobile Base System.

While Hopkins set up the POA and an adjustable grapple fixture, Mastracchio removed the five electrical connectors from the pump module and unfastened the module from the truss.   

With Mastracchio holding the 780-pound pump while he was attached to the end of the robotic arm, Wakata guided the arm to attach the module to the grapple fixture and activated the snares to hold it in place.

Mastracchio now holds 43 hours and 58 minutes of spacewalking time during seven spacewalks, and Hopkins now holds 5 hours and 28 minutes during one spacewalk.

Saturday’s spacewalk was the 175th in support of space station assembly and maintenance.

Quelle: NASA

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Update: 23.12.2013

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ISS-Crew bereitet sich für 2.Spacewalk vor um Pumpe zu ersetzen

Two Expedition 38 crew members are set to head out of the Quest airlock Tuesday for the second in a series of spacewalks to replace a degraded ammonia pump module on the International Space Station’s starboard truss.

Flight Engineers Rick Mastracchio and Mike Hopkins, who completed a 5-hour, 28-minute spacewalk Saturday to remove the faulty pump module from the starboard truss, spent their Monday preparing for the Christmas eve excursion slated to begin at 7:10 a.m. EST. The two spacewalkers will retrieve a spare pump module from an external stowage platform and install it in the currently vacated slot to restore full cooling capability for the complex. The pump module removed by Mastracchio and Hopkins Saturday encountered a problem Dec. 11 with its internal flow control valve, causing temperatures in the station’s cooling lines to drop.

During repressurization of the Quest airlock at the conclusion of Saturday’s spacewalk, a spacesuit configuration issue put Mastracchio’s suit in question for the second spacewalk. A small amount of water entered the suit’s sublimator -- the cooling system of the suit itself -- after the two astronauts had already hooked themselves up to airlock umbilicals. As a result, flight controllers decided to switch to a backup suit for Mastracchio for the next spacewalk.

This issue is not related to the spacesuit water leak that was seen during a July spacewalk by European Space Agency astronaut Luca Parmitano and NASA's Chris Cassidy. Both Mastracchio and Hopkins reported dry conditions repeatedly throughout Saturday's activities and the two were never in danger.

Mastracchio and Hopkins resized other suits in the Quest airlock Sunday while allowing the suit Mastracchio wore Saturday to dry out.  That spacesuit will be returned to service in a future spacewalk.

After preparing spacewalking tools and configuring the crew equipment lock of the Quest airlock Monday, the two NASA astronauts joined up with Flight Engineer Koichi Wakata of the Japan Aerospace Exploration Agency to review the spacewalk’s procedures.  Wakata will again be in control of the station’s robotic arm, Canadarm2, this time with Hopkins attached to the foot restraint at the end of the 57-foot arm.

During Tuesday’s spacewalk Mastracchio and Hopkins will retrieve the spare pump module from External Stowage Platform 3 and install it in the slot that is now empty through the removal of the degraded pump Saturday. After the spacewalkers complete five electrical connections and four fluid connections, activation of the pump will restore full dual-loop cooling capability for the station.

Mastracchio will be wearing a suit marked with red stripes. Hopkins will wear a suit with no stripes.  This will be the 176th spacewalk in support of space station assembly and maintenance. It also will be the second Christmas eve spacewalk conducted in history.  Fourteen years ago, space shuttle Discovery astronauts Steve Smith and John Grunsfeld conducted an 8-hour, 8-minute spacewalk to install upgrades and new insulation on the Hubble Space Telescope.

If the spacewalk goes as expected Tuesday, all of the pump replacement work should be completed with just two spacewalks. The degraded pump, removed during Saturday’s spacewalk, will remain on the Payload Orbital Replacement Unit Accommodation (POA) on the station’s railcar, or Mobile Base System.  According to flight controllers, the degraded pump can remain on the POA until at least next June, based on a thermal analysis by the ground control team.

The completion of the spacewalk will clear the way for Commander Oleg Kotov and Flight Engineer Sergey Ryazanskiy to conduct their own spacewalk Friday out of the Pirs docking compartment to install a pair of high-fidelity cameras on the Zvezda service module and to refresh several experiment packages on the exterior of the Russian segment of the station.

Flight Engineer Mikhail Tyurin assisted Kotov and Ryazanskiy on Monday with a “dry run” of the spacewalk as the two cosmonauts donned their Russian Orlan spacesuits and entered Pirs to test their suits.

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Flight Engineer Rick Mastracchio works outside the International Space Station during Saturday's spacewalk to remove a degraded ammonia pump.

Quelle: NASA

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Update: 24.12.2013

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Vorbereitungen für 2.Spacewalk

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Quelle: NASA-TV-LIVE

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Update: 17.30 MEZ

Astronauts Conduct ISS Pump Replacement Spacewalk

Expedition 38 Flight Engineers Rick Mastracchio and Mike Hopkins are conducting the second in a series of spacewalks to replace a degraded ammonia pump module on the International Space Station’s starboard truss. The spacewalk officially began at 6:53 a.m. EST and is scheduled to run about 6 hours and 30 minutes.

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LIVE Spacewalk-2

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Update: 25.12.2013

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Spacewalkers beenden entscheidende Raumstation ISS Reparaturen rechtzeitig zu Weihnachten

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Nearly two weeks after a faulty coolant valve crippled the International Space Station, two NASA astronauts took on a rare Christmas Eve spacewalk to get things back to normal.

During Tuesday's seven-hour, 30-minute repair operation, spacewalkers Rick Mastracchio and Mike Hopkins installed a refrigerator-sized coolant pump module with an assist from Japanese astronaut Koichi Wakata, who operated the 58-foot-long (18-meter-long) robotic arm from inside the space station.

NASA commentator Rob Navias said the new module passed an initial pressure test. "We have a pump that is alive and well," he reported on NASA TV.

The only other time NASA conducted a spacewalk on Christmas Eve was during a Hubble repair operation in 1999. The timing lent a holiday spirit to Tuesday's proceedings. "It's like Christmas morning, opening up a little present here," Mastracchio joked as he checked his tools.

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Two and a half hours into the job, Hopkins stood at the end of the robotic arm and steadied the 780-pound (355-kilogram) pump module as it was swung into position for installation. "Mike Hopkins taking a special sleigh ride on this Christmas Eve," Navias observed.

The spacewalk didn't always go as smoothly as Santa's rounds, however: After the astronauts slid the boxy apparatus into place and secured it with bolts, they had some trouble switching the cooling system's fluid lines. They had to tap and pry at one of the interim fluid-line connections to free it up, and in the process they set off a mini-blizzard of toxic ammonia "snowflakes."

The snowflakes dissipated, and all the proper connections were eventually made. But the astronauts reported that some of the frozen ammonia got onto their spacesuits. As a result, they had to take some extra time to let the chemicals "bake out" from their suits before ending the spacewalk.

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Essential role
Tuesday's spacewalk followed up on Saturday's operation to remove the faulty pump module. A valve inside that module failed on Dec. 11, forcing one of the station's two ammonia coolant loops to go offline.

The cooling system plays an essential role in keeping the onboard electronics from overheating. When the first loop failed, NASA had to shut down non-essential systems and switch other systems over to the second loop, reducing the station's safety margin in the process. If the other loop had failed, that could have forced the six-man crew to abandon the station.

A similar pump module switch-out required three difficult spacewalks in 2010, but only two were needed this time around, in part because of the lessons learned three years earlier. The astronauts who were involved in those 2010 spacewalks, Doug Wheelock and Tracy Caldwell Dyson, were on hand at Mission Control in Houston to lend advice. 

When the repairs were made, Wheelock told the crew, "It's the best Christmas ever."

"Merry Christmas to everybody," Hopkins replied. "It took a couple of licks to get 'er done, but we got it."

Worries about water
Safety concerns added some extra twists to the past week's repair operation: In July, Italian astronaut Luca Parmitano almost drowned when water from his spacesuit cooling system backed up into his helmet. The crew overhauled the spacesuits, and NASA pronounced them "clean" — but as a precaution, the helmets were equipped with absorbent pads and emergency snorkels.

Neither Mastracchio and Hopkins reported any helmet problems on Saturday or on Tuesday.

After Saturday's 5.5-hour spacewalk, Mastracchio mistakenly flipped a switch on his suit that may have sent water to a different cooling device known as a sublimator. In a worst-case scenario, that could have caused the device to freeze up during the next spacewalk.

As a result, Mastracchio's suit was set aside to dry out, Hopkins' suit was resized to fit Mastracchio, and a backup suit was fitted for Hopkins' use. The switch required an extra day of preparation — which is why the follow-up spacewalk took place on Tuesday instead of Monday, as originally scheduled.

Getting back to normal
If further tests confirm that Tuesday's repairs were successful, operations could return to normal over the next few days. NASA also could go ahead with a cargo resupply mission that had to be postponed due to the cooling system problem. The launch of Orbital Sciences' Cygnus cargo capsule is now scheduled for Jan. 7.

The station is currently at its maximum capacity of six live-aboard spacefliers. In addition to Mastracchio, Hopkins and Wakata, three Russians round out the crew: Oleg Kotov, Sergey Ryazanskiy and Mikhail Tyurin.

Kotov and Ryazanskiy are planning a spacewalk of their own on Friday, to install new equipment on the station's Russian segment.

Quelle: NBC-News

NASA astronaut Rick Mastracchio participates in the first Expedition 38 spacewalk designed to troubleshoot a faulty coolant pump on the International Space Station.
Image Credit: 
NASA
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Following two spacewalks to replace a degraded pump module on the truss, or backbone, of the International Space Station, flight controllers in the Mission Control Center at NASA's Johnson Space Center in Houston successfully restarted the new pump Tuesday night.

The pump module controls the flow of ammonia through cooling loops and radiators outside the space station, and, combined with water-based cooling loops inside the station, removes excess heat into the vacuum of space.

The new pump now is considered fully functional, but it will take some time to fully reintegrate the pump and Loop A of the two-loop external cooling system. Teams at mission control are following a schedule that should allow the restored cooling loop to be fully activated and integrated into the station’s cooling system on Christmas Day, Dec. 25.

Electrical systems that depend on cooling from Loop A will be repowered or moved back from temporary support on Loop B gradually on Thursday, Friday and throughout the weekend.

Expedition 38 Flight Engineers Mike Hopkins and Rick Mastracchio removed the degraded pump module during a 5 hour, 28 minute spacewalk Saturday, Dec. 22. They retrieved a replacement pump from an external stowage platform near the end of the station’s backbone, and installed it during a 7 hour, 30 minute spacewalk on Christmas eve, Dec. 24.

Engineers at mission control sent a series of commands to the new pump module at the end of Tuesday’s spacewalk to ensure that ammonia – an excellent thermal conductor – was flowing to the new pump module. Beginning about 4:30 p.m. EST today, remote commands started the process of pressurizing the new pump. Reactivation of the pump is now complete, and it is performing its job regulating the flow and temperature of the ammonia in Loop A of the two-loop cooling system.

On Saturday, the crew had moved the old pump module to a temporary stowage platform on a rail car on the station’s mobile base system, where it can remain indefinitely.

Quelle: NASA

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Astronauts Brave Brief Ammonia Snowstorm As They Conclude Fix To Space Station

Toxic snowflakes in space were just one obstacle astronauts faced down today (Dec. 24) as they successfully replaced an ammonia pump that will, if all goes to plan, put the space station back in full service in a few hours.

“They’re just completely surrounding us now,” radioed NASA astronaut Rick Mastracchio of the ammonia flakes as the astronauts clipped four fluid lines into place on to the spare pump. NASA said the ammonia was just residual fluid and not indicative of a leak. “Some little ones, some big ones,” he added.

Within a few minutes, however, the ammonia dissipated. Some flakes did strike the spacesuits of Mastracchio and fellow NASA spacewalker Mike Hopkins, causing NASA to do a modified decontamination procedure where the astronauts stayed in a vacuum for a few extra minutes inside the airlock. (The sun’s heat bakes off ammonia over time, and the crew was outside long enough for most ammonia to dissipate, NASA said.)

The spacewalk completed with no further drama at 7 hours and 30 minutes, earning high praise for the participating astronauts from Mission Control in Houston.

“It’s the best Christmas ever,” radioed CapCom and NASA astronaut Doug Wheelock from the ground as the spacewalkers entered the International Space Station’s Quest airlock at the end of the repair job. “We got it,” Mastracchio responded.

Preliminary tests show the spare pump is working perfectly. The pump is a welcome present for the six-person Expedition 38 crew, which saw a reduction in science and backup systems for two weeks after a valve in the last pump failed, causing one of the station’s two cooling loops to shut down automatically. The loops are needed to regulate the temperatures of electronics and systems on station.

The Expedition 38 crew was so quick with the repair that they finished the job in two spacewalks instead of the planned three. The astronauts fell behind the timeline today as they struggled with some of the fluid connections to the new pump, but the final steps — putting the electrical connections in place — took just minutes. The pump was brought from another location on station today, and installed into its permanent spot to help ammonia flow through the cooling system.

Anywhere between hundreds and thousands of people at NASA and international partners scrambled to put spacewalks together to fix the cooling problem after it happened. Wheelock, himself a veteran of a tricky ammonia pump repair in 2010, communicated with the spacewalkers. Japanese astronaut Aki Hoshide filled the other CapCom slot, helping Japanese astronaut Koichi Wakata who handled robotics in orbit.

Mastracchio marked his eighth spacewalk with today’s repair while Hopkins, who rode Canadarm2 for the first time in a last-minute decision, was on his second. As with a spacewalk on Saturday (Dec. 21), the astronauts reported no helmet water leaks — comforting words for agency officials who put in new procedures and parts after an incident in July. (Mastracchio experienced a water problem during repressurization Saturday that was unrelated to the first incident, and wore a backup suit today to let the primary one dry out.)

Should the ammonia pump work as planned, this clears the way for the Russians to do a spacewalk Dec. 27 to install the Urthecast high-resolution camera that will beam live views of Earth, among other tasks. Expedition 38 has the day off tomorrow (Dec. 25), NASA TV added.

Quelle: UT






 

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