ISS Astronauts Spacewalk completes urgent repair job

This April 23, 2014 NASA TV image shows International Space Station(ISS) astronauts Rick Mastracchio (L) and Steve Swanson (R) preparing for a spacewalk.

Credit: NASA

Spacewalking astronauts easily replaced a dead computer outside the International Space Station on Wednesday and got their orbiting home back up to full strength.

The two Americans on board, Rick Mastracchio and Steven Swanson, hustled through the urgent repair job, swapping out the computers well within an hour. The new one tested fine.

"Excellent work, gentlemen," Mission Control radioed.

The removed computer, a critical backup, failed nearly two weeks ago. The prime computer has been working perfectly, but NASA wanted to install a fresh spare as soon as possible.

Mission Control waited until after the arrival of a capsule full of fresh supplies Sunday.

Replacing the computer—a compact 50-pound (22-kilogram) box—involved just three bolts, hardly anything for a spacewalking chore.

Engineers do not know why the original failed. Mission Control asked the spacewalkers to keep an eye out for any damage that might explain the breakdown. Nothing jumped out.

Flight controllers were trying to load software into the spare computer on April 11, but it failed to activate.

That set into motion a frenzy of ground meetings and tests to fix the problem.

NASA feared that if the primary computer went down as well, the entire space station would be in jeopardy.

These two computers—the primary and backup—control the pointing of the solar wings and radiators, as well as the movement of the robot-arm rail cart.

It was the first failure of one of dozens of so-called MDMs, or multiplexer-demultiplexers, in and outside the space station.

Mission Control kept the spacewalk short and straight-to-the-point; it lasted a mere one hour and 36 minutes.

All routine spacewalks by U.S. station crew have been on hold since last summer's near-drowning by a spacewalking astronaut.

His helmet filled with water from the cooling system of the suit, and NASA is continuing to investigate the problem.

NASA hopes to reuse the bad computer, once it's inspected indoors by the astronauts and updated.

Their mission accomplished, Rick Mastracchio and Steven Swanson exchanged a few jokes and laughs as they got ready to go back inside.

"My arms are too short for a selfie," Mastracchio said with a chuckle, his camera pointed at himself.

SpaceX Falcon 9 Launch: Dragon Preparations Continue

International Space Station Program officials and representatives of SpaceX decided Saturday to continue preparations for the launch of the Falcon 9 rocket and the Dragon cargo craft to the space station.

The launch is slated for Monday 14th April from Launch Complex 40 at the Cape Canaveral Air Force Station, Fla.

The launch will go ahead despite the failure Friday of a backup MDM computer communications component that provides redundancy for commanding the Mobile Transporter rail car on the truss of the station. 

A final decision on whether to launch Dragon Monday will not be made until another status meeting is conducted Sunday morning.

NASA has rescheduled its SpaceX prelaunch briefing allow for operational reviews in the morning.

It now will be held at 1 p.m. EDT at the agency's Kennedy Space Center in Florida. For updates on the schedule of events for Sunday, call the Kennedy News Center recording at 321-867-2525.

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 x 14.9 x 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.

A reboost of the station using the ISS Progress 53 thrusters was conducted Saturday as planned and placed the laboratory at the correct altitude for Soyuz crew landing and launch operations in May.