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  ISS 51: Contingency EVA to replace failed MDM

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Author Topic:   ISS 51: Contingency EVA to replace failed MDM
Robert Pearlman
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Posts: 42988
From: Houston, TX
Registered: Nov 1999

posted 05-20-2017 05:43 PM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
NASA update
International Space Station managers will meet Sunday morning to discuss a forward plan for dealing with the apparent failure of one of two fully redundant multiplexer-demultiplexer (MDM) data relay boxes on the S0 truss of the complex.

External MDM-1 apparently failed at 1:13 p.m. Central time Saturday. Multiple attempts by flight controllers to restore power to the relay box have not been successful. Troubleshooting efforts are continuing. The Expedition 51 crew was informed of the apparent failure and is not in any danger. The MDMs on the truss control the functionality of the station’s solar arrays and radiators among other equipment, and provide power to a variety of other station components.

Because the two MDMs have full redundancy, the apparent loss of MDM-1 has had no impact on station operations.

Robert Pearlman
Editor

Posts: 42988
From: Houston, TX
Registered: Nov 1999

posted 05-21-2017 11:59 AM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
NASA update
International Space Station Program managers met Sunday and gave approval for a contingency spacewalk no earlier than Tuesday [May 23] by two Expedition 51 crewmembers to change out a multiplexer-demultiplexer (MDM) data relay box on the S0 truss that failed on Saturday morning. The cause of the MDM failure is not known. A final decision on a firm date for the spacewalk and who will conduct the spacewalk will be made later in the day Sunday.

The data relay box is one of two fully redundant systems housed in the truss that control the functionality of radiators, solar arrays, cooling loops and other station hardware. The other MDM in the truss is functioning perfectly, providing uninterrupted telemetry routing to the station's systems. The crew has never been in any danger and the MDM failure, believed to be internal to the box itself, has had no impact on station activities.

On Sunday, shortly before managers met to discuss the forward plan for dealing with the failed MDM, station commander Peggy Whitson of NASA prepared a spare data relay box and tested components installed in the replacement. She reported that the spare MDM was ready to be brought outside to replace the failed unit. Back on March 30, Whitson and Expedition 50 commander Shane Kimbrough of NASA conducted a spacewalk to install the MDM with upgraded software that failed Saturday.

A similar MDM replacement spacewalk was conducted in April 2014 by Expedition 39 crewmembers Steve Swanson and Rick Mastracchio.

The spacewalk will last about two hours in duration to replace the failed box. No other tasks are planned for the excursion. It will be the sixth spacewalk conducted from the Quest airlock this year.

Robert Pearlman
Editor

Posts: 42988
From: Houston, TX
Registered: Nov 1999

posted 05-21-2017 06:54 PM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
NASA update
After a review of spacewalk preparations and crew readiness throughout the day Sunday, the decision was made to press ahead with the spacewalk on Tuesday. It will be conducted by Expedition 51 Commander Peggy Whitson and Flight Engineer Jack Fischer of NASA.

A similar MDM replacement spacewalk was conducted in April 2014 by Expedition 39 crewmembers Steve Swanson and Rick Mastracchio of NASA.

Tuesday's spacewalk will last about two hours in duration to replace the failed box. An additional task was added for Fischer to install a pair of wireless communications antennas on the Destiny Lab while Whitson replaces the failed data relay box. The antenna installation task was originally planned for the last spacewalk on May 12.

The contingency spacewalk will be the 201st in support of space station assembly and maintenance and the sixth conducted from the Quest airlock this year.

This will be the 10th spacewalk in Whitson's career and the second for Fischer. Whitson will be designated as extravehicular crewmember 1 (EV 1) and will wear the suit with the red stripes. Fischer will be extravehicular crewmember 2 (EV 2) and will wear the suit with no stripes.

Tuesday's spacewalk is expected to begin around 8 a.m. EDT, or earlier, if the crew is running ahead of schedule with its spacewalking preparations. NASA Television coverage will begin at 6:30 a.m.

Robert Pearlman
Editor

Posts: 42988
From: Houston, TX
Registered: Nov 1999

posted 05-23-2017 09:44 AM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
NASA update
Expedition 51 Commander Peggy Whitson and Flight Engineer Jack Fischer of NASA concluded their spacewalk at 10:06 a.m. EDT [1406 GMT on Tuesday (May 23)]. During the spacewalk, which lasted two hours and 46 minutes, the two astronauts successfully replaced a computer relay box, and installed a pair of antennas on station to enhance wireless communication for future spacewalks.

Spacewalkers have now spent a total of 1,250 hours and 41 minutes working outside the station during 201 spacewalks in support of assembly and maintenance of the orbiting laboratory. This was the 10th spacewalk for Whitson, who moves into third place all-time for cumulative spacewalking time, and the second for Fischer.

All times are CT (US)

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