Two astronauts quickly replaced a bad backup computer box and took on an extra task at the International Space Station on Wednesday during one of NASA's shortest spacewalks.
Within an hour, NASA astronaut Rick Mastracchio and Steve Swanson removed the old box, which failed to respond to commands on April 11, and installed a spare. Ground controllers reported that the new box, known as a multiplexer-demultiplexer or MDM, was working fine.
Mastracchio tucked the old box into an equipment bag and told Mission Control that he had "one MDM, slightly used."
"Nice and clean," Mission Control communicator Jeremy Hansen told the spacewalkers. "Good job."
Most spacewalks run for five or six hours, but this one lasted only an hour and 36 minutes — arguably making it NASA's shortest glitch-free operation outside the space station.
Routine but critical task
The backup box is part of a redundant system that plays a part in controlling critical equipment on the station, including the solar arrays, a robotic rail car and the external cooling system. The primary computer box is working just fine, but NASA didn't want to go without a working backup any longer than necessary.
Replacing the box is considered one of the space station's "Big 12" routine maintenance tasks. Mastracchio and Swanson have been trained in advance for such jobs.
While Mastracchio switched the boxes, Swanson cut some dangling lanyards that had been blocking the way for the space station's Dextre robotic hand. In the future, Dextre might be able to perform maintenance tasks like the computer replacement without the need for a spacewalk.
This was the ninth spacewalk for Mastracchio, and the fifth for Swanson. Even as they worked, the astronauts spared a few moments to take in the sights. At one point, Mastracchio asked Mission Control what part of the world he was flying over. When he was told it was South America, Mastracchio joked, "Sorry, I wasn't a geography major."
Toward the end of the spacewalk, Mastracchio turned his camera back toward himself and laughingly complained, "My arms are too short for a selfie."
The spacewalkers wore absorbent helmet pads on the backs of their necks, plus emergency snorkels that are at the ready inside their helmets. Those extra safety measures were put into effect last year, after Italian spacewalker Luca Parmitano nearly drowned in his helmet due to a leak in his suit's water separation system.
NASA is still investigating the issue, but mission managers think they've addressed the problem by replacing the system's components. In fact, Mastracchio wore the same suit that Parmitano used. Lingering concern about the spacesuits is the main reason why NASA wanted to keep this spacewalk short.
Wednesday's extravehicular activity went just a few minutes longer than Parmitano's spacewalk, which was aborted due to the water leak. Only a few spacewalks at the International Space Station were shorter. One was a 2004 outing that was cut short at the 14-minute mark due to an oxygen pressure problem. And then there were two "internal spacewalks," conducted inside a depressurized area of the station in 2001 and 2009. They lasted less than 20 minutes each.
Busy day for station's crew
While Mastracchio and Swanson worked outside, Japanese astronaut Koichi Wakata played a supporting role inside the station.
Meanwhile, their Russian crewmates — Mikhail Tyurin, Alexander Skvortsov and Oleg Artemyev — helped out with a previously planned test of an automated rendezvous system installed on a robotic Progress cargo ship. The Progress was undocked early Wednesday morning and took up a position about 300 miles (500 kilometers) from the station to begin two days of tests.
All this activity is going on while a freshly arrived SpaceX Dragon cargo ship is docked to a different port on the station.