Update 12:13 p.m. EDT: NASA reports Swanson and Mastracchio have successfully completed the spacewalk and replaced the unresponsive MDM at 11:32 a.m. EDT.

Update 10:32 a.m. EDT: Swanson and Mastracchio have removed the faulty backup MDM.


NASA astronauts Steve Swanson and Rick Mastracchio will perform a 2 1/2-hour International Space Station spacewalk on Wednesday. The NASA live stream of the event begins at 8:30 a.m. EDT and the ISS Expedition 39 crew members will work to replace a faulty computer located on the exterior of the space station.



Swanson and Mastracchio will replace the unresponsive backup multiplexer-demultiplexer (MDM). NASA discovered the problem on April 11, and the backup MDM supports several robotic systems aboard the ISS. According to NASA, the MDM "provides redundancy for commanding the Mobile Transporter rail car on the truss of the station." The Mobile Transporter is part of the docking procedure that attaches spacecraft to the space station. For Swanson, it will be his fifth spacewalk, and it will be the ninth for Mastracchio.

The recent SpaceX ISS commercial resupply mission could have been delayed by the unresponsive MDM, but NASA went ahead with the launch and the spacecraft reached the ISS on Easter. There are 45 MDMs located throughout the space station and the backup MDM that failed has been attached to the ISS for more than 10 years.

According to NASA, the faulty backup MDM is located on the S0 truss, on top of the Destiny laboratory module. On Monday, the Expedition 39 crew spent the day unpacking the cargo from the Dragon spacecraft. The T-Cell Activation in Aging science experiment, which studies immune system depression in microgravity, was among the first items unloaded from the spacecraft.

On Tuesday, ISS Expedition 39 commander Koichi Wakata, from the Japan Aerospace Exploration Agency, met with Swanson and Mastracchio and discussed Wednesday's ISS spacewalk. Prior to the spacewalk, the ISS Progess 53 resupply spacecraft, which is currently docked at the ISS, will detach from the Zvezda service module, located on the Russian side of the space station. The cargo spacecraft will spend two days in space, traveling no farther than 311 miles away from the ISS, before reattaching on Friday, notes NASA.

The NASA International Space Station spacewalk is scheduled for 9:20 a.m. EDT and the live stream can be viewed below.

Live streaming video by Ustream