NASA set to conduct emergency spacewalk

Two NASA astronauts aboard the International Space Station (ISS) are set to conduct an emergency spacewalk tomorrow to replace a failed data relay box that controls some of the key hardware on the orbital outpost.
Expedition 51 Commander Peggy Whitson and Flight Engineer Jack Fischer will change out a multiplexer-demultiplexer (MDM) data relay box on the S0 truss that failed last week. The cause of the MDM failure is not known.
ISS programme managers decided to press ahead with the spacewalk after a review of preparations and crew readiness on Sunday.
The data relay box is one of two 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, NASA said.

Whitson has prepared a spare data relay box and tested components installed in the replacement. She has reported that the spare MDM was ready to be brought outside to replace the failed unit.
Whitson and Expedition 50 commander Shane Kimbrough had conducted a spacewalk to install the same MDM with upgraded software on March 30.

A similar MDM replacement spacewalk was conducted in April 2014 by Expedition 39 crewmembers Steve Swanson and Rick Mastracchio.
Tomorrow's spacewalk is expected to begin around 8 am EDT (5:30 pm IST) will last about two hours in duration to replace the failed box.
Fischer will also 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.