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  ISS 39: Backup MDM computer not responding

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Author Topic:   ISS 39: Backup MDM computer not responding
Robert Pearlman
Editor

Posts: 29470
From: Houston, TX
Registered: Nov 1999

posted 04-11-2014 09:50 PM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
NASA update
Backup computer not responding to commands

The Mission Control team at NASA's Johnson Space Center in Houston confirmed Friday night (April 11) that a backup computer on the exterior of the International Space Station called a Multiplexer-Demultiplexer (MDM) is not responding to commands.

The station's MDM computers control some systems associated with robotics aboard the space station. The primary MDM operating aboard the space station is functioning normally and there is no immediate impact to space station operations. The computer outage does not pose a risk to the six crew members aboard the space station.

ISS teams are assessing next steps to attempt to bring the computer back online or replace it. Replacing the backup MDM, if needed, would require a spacewalk.

Robert Pearlman
Editor

Posts: 29470
From: Houston, TX
Registered: Nov 1999

posted 04-12-2014 12:36 PM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
NASA update
NASA plans spacewalk to replace failed router

NASA flight controllers and engineers are laying out a timeline for a contingency spacewalk required to replace a failed backup computer component on the outside of the International Space Station. No date for the spacewalk has been scheduled.

Such a spacewalk is one of the so-called "Big 12" that station crews train to execute for the loss of a critical component on the complex.

The component, called a multiplexer demultiplexer (MDM) is one of more than a dozen housed on the truss of the station that routes computer commands to various systems on the outpost. The failure Friday to a box called EXT-2, a backup box to a prime component in the S0 truss that measures 10.5 by 14.9 by 16.4 inches and weighs 50.8 pounds, occurred during a routine health check of the device.

The prime multiplexer continues to operate flawlessly, and there has been no impact to station operations. The crew was informed of the problem and is in no danger, continuing its normal complement of research work and routine maintenance.

Robert Pearlman
Editor

Posts: 29470
From: Houston, TX
Registered: Nov 1999

posted 04-13-2014 12:11 PM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
NASA update
Contingency spacewalk no earlier than April 22

Preparations are underway for a contingency spacewalk by two of the International Space Station's Expedition 39 crew members no earlier than April 22 to replace a failed backup computer command relay box with a spare housed inside the station.

Mission managers approved a plan for the preparation of two of the U.S. spacesuits on the station and the replacement of a fan pump separator on one of the suits prior to the spacewalk. That work will begin immediately.

The station crew will also be readying the spare relay box for its staging in the Quest airlock prior to the spacewalk.

The problem with the failed box, which measures 10.5 by 14.9 by 16.4 inches (26.7 by 37.8 by 41.7 cm) and weighs 50.8 pounds (23 kg), occurred during a routine health check of the device. The prime multiplexer demultiplexer (MDM) continues to operate normally.

This pair of MDMs provide commanding to the station's external cooling system, Solar Alpha Rotary joints, Mobile Transporter rail car and insight into other truss systems.

Robert Pearlman
Editor

Posts: 29470
From: Houston, TX
Registered: Nov 1999

posted 04-16-2014 11:02 AM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
Astronauts prep for spacewalk to replace relay box

Astronauts on the International Space Station's Expedition 39 crew focused Tuesday (April 15) on preparing for a contingency spacewalk to be conducted in the next week or so.

Rick Mastracchio and Steve Swanson spent their day preparing for the 2.5-hour spacewalk to replace the failed multiplexer demultiplexer (MDM).

The backup computer relay system, located in the S0 truss, assists in providing insight into the truss systems, the operation of the external cooling loops, the operations of the Solar Alpha Rotary joints and the Mobile Transporter rail car.

Swanson performed a full end-to-end checkout of his spacesuit with its new fan separator pump installed. During the checkout, a cranky CO2 sensor was discovered and is now being investigated.

Mastracchio, meanwhile, gathered and configured the tools he and Swanson will use during the excursion.

Swanson and Mastracchio also participated in an on-board training session for the spacesuit "life jacket," known as the Simplified Aid For EVA Rescue, or SAFER. Should a spacewalker become untethered during a spacewalk and begin floating away from the space station, the small nitrogen-jet thrusters of SAFER would propel the astronaut back to safety.

The two NASA astronauts joined up with station commander Koichi Wakata for an audio conference with ground team that is finalizing procedures for the spacewalk.

Wakata assisted with spacewalk preparations, completing a flush of the water inside the cooling loops of the spacesuits and the airlock.

The date of the spacewalk is contingent on when a SpaceX resupply mission launches.

If SpaceX launches Friday (April 18), the spacewalk will be conducted Wednesday (April 23). If SpaceX launches Saturday, the contingency spacewalk moves earlier to Sunday (April 20).

Robert Pearlman
Editor

Posts: 29470
From: Houston, TX
Registered: Nov 1999

posted 04-23-2014 10:39 AM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
Spacewalkers replace failed backup computer

Astronauts Steve Swanson and Rick Mastracchio stepped outside the International Space Station for a short spacewalk to replace a failed backup computer on Wednesday (April 23).

The two began the extravehicular activity (EVA, or spacewalk) at 8:56 a.m. CDT (1356 GMT) and ended the excursion at 10:32 a.m. (1532 GMT) for an elapsed time of one hour and 36 minutes.

The computer, known as a multiplexer-demultiplexer (MDM), ceased responding to flight controllers' commands on April 11 after a routine health check by Mission Control in Houston. While the primary MDM continued to function, space station managers ordered Wednesday's spacewalk to ensure redundancy on critical systems.

The computer outage did not pose a risk to the six crew members aboard the space station.

Swanson and Mastracchio worked on the S0 truss, which is where the backup MDM is mounted. The truss is located above the Destiny laboratory module and forms the center of the station's backbone.

The MDM provides telemetry and commands to the truss systems, including the rotary joints for the station's solar arrays and the mobile transporter rail car that rides along the truss structure.

The two spacewalkers successfully removed the failed computer from the S0 truss where it has been located since the truss was delivered in April 2002 and installed a spare MDM that was stored inside the Destiny lab since being delivered aboard space shuttle Endeavour in April 2001. The station houses a total 45 MDMs, 24 internally and 21 externally.

All times are CT (US)

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