Like any big machine, the huge International Space Station requires daily maintenance repairs to keep flying in space. But every now and then something big or critical ? like the recent cooling system trouble ? pops up to shine a spotlight on the $100 billion space station, which has been continuously manned by astronauts for nearly 10 years.
Half of the space station's cooling system shut down late Saturday when a circuit breaker tripped in a pump used to move super-cold liquid ammonia through the system. Now astronauts living aboard the station are planning two emergency spacewalks, currently set for Thursday and Sunday, to replace the pump in the afflicted cooling system line ? called Loop A.
But while astronauts regularly work through smaller glitches on the space station, critical or serious malfunctions are relatively rare. The space station has been under construction since 1998. It is currently home to six people and has a main truss as long as a football field.
Here's a look, by no means comprehensive, at some recent notable malfunctions during the space station's 10 years in orbit:
Russian docking system glitch
The most recent notable glitch at the space station occurred in early July, when an unmanned Russian cargo ship sailed completely past the International Space Station instead of docking at the outpost as planned.
The Progress 38 cargo ship was flying on autopilot as designed on July 2 when it unexpectedly aborted the docking attempt and missed the space station. Russian engineers suspect interference between the spacecraft's Kurs automated docking system and a space station system that allows cosmonauts to take remote control of the Progress spacecraft caused the abort.
The solution? Simply turn off the remote control system on the space station. The station crew did that and on July 4 the Progress 38 parked itself at the orbiting lab as planned.
Cooling system valve woes
The space station's Loop A cooling system has seen some glitches before. In April, a stuck valve sent NASA engineers scrambling to come up with a fix while the space shuttle Discovery was docked at the orbiting lab.
At the time, NASA engineers were considering an emergency spacewalk to either fix or replace the faulty Loop A valve. The valve controlled the flow of nitrogen, which is used to pressurize the cooling system plumbing ahead of the liquid ammonia flow.
Engineers didn't immediately fix the valve, but after studying the space malfunction exhaustively they did decide the glitch didn't pose an immediate problem. The crew of Endeavour did not have to perform an extra spacewalk and were able to depart the space station in mid-April as planned.
Space potty and space urine recycler
The space station's toilets and related life support equipment have also had their share of troubles.
In recent years, the space station's high-tech toilet has had several glitches due to faulty pumps and other problems. Most recently, one of two space toilets on the station flooded in July 2009 because of a faulty separator pump and control panel.
There are currently two bathrooms on the International Space Station to handle restroom needs for its six-person crew.
Related to the space toilet issues are glitches in the station's urine recycling system, which is part of a larger water purification system. A spinning centrifuge-like component has been the culprit for most of the malfunctions and required replacement in 2008 and 2009.
The space station's water recycling system is also tied into a U.S. oxygen generator, which can separate new water into hydrogen and oxygen to boost the station's atmosphere. The system, and its Russian counterpart Elektron, have experienced breakdowns from time to time and been repaired.
Smoky smells and leaks
Air leaks and smoke-like smells have both popped up on the space station in one form or another.
In January 2004, slow air leak that perplexed NASA for weeks sent astronauts hunting through the space station for its cause. After checking several different systems, a flexible hose used as a makeshift handhold near a window was identified as its cause and repaired.
In 2006, a small leak of toxic potassium hydroxide in the space station's Russian Elektron oxygen generator, which overheated a connected rubber seal to create a smoke-like smell that set off a brief fire scare on the space station. Open flames are not allowed on the space station because of such a fire risk.
After some investigation, astronauts traced the smell to the Elektron unit and discovered the leak, which they carefully cleaned up.
An unrelated smoky smell in a space station spacesuit later prompted a brief ban on U.S. spacewalks until it could be addressed. That ban was lifted after a few days once the suit was cleaned.
Major computer glitches
With a spacecraft as complex as the International Space Station, computer problems can border on nightmarish.
There are literally dozens of laptop computers linked together to control various space station systems and from time-to-time Russian and American machines have failed or suffered hiccups.
On Feb. 20, a brief main computer failure on the space station knocked out communications between the laboratory and Mission Control for about an hour. A software glitch related to how data was sent to Earth from the station's European-built Columbus lab was the prime suspect.
More substantial computer problems have caused some serious worry on the space station and on Earth.
In June 2007, a major failure within the six-computer navigation and control system in charge of the Russian segment of the space station left the station without the use of its Russian attitude control thrusters, Elektron oxygen generator and other support equipment. A carbon dioxide scrubber and other environmental control systems were also offline and temperatures inside the station's Russian-built Zvezda service module (where the computers are located) rose to around 80 degrees Fahrenheit.
It took several days for Russian cosmonauts to install cables to bypass a faulty electronics box and work around the glitch. A Russian computer crash in 2002 also caused attitude control issues as well.
American computers on the space station have also not been failure-free.
In April 2001, a computer crash in the U.S. Destiny laboratory forced Mission Control to reroute communications through the shuttle Endeavour, which was visiting at the time. A failed hard drive in one of Destiny's three command and control computers was identified as the cause and replaced.
Ripped solar wings and jammed joints
One of the most dramatic International Space Station glitches in recent years involved rip in one of the orbiting lab's expansive solar arrays used to power the orbiting lab.
In October 2007, one of the space station's port side solar wings ripped while being unfurled by astronauts using a workstation inside the orbiting laboratory. The malfunction forced NASA mission planners to overhaul mission plans for space shuttle Discovery astronauts, who were visiting at the time.
The crew performed a daring spacewalk repair in which a spacesuit-clad astronaut patched up the ripped solar array using fabric stitches and tools wrapped in tape to insulate them against the potential shock hazard of working next to a solar array.
To reach the torn spot, spacewalking astronaut Scott Parazynski had to stand at the end of a 50-foot (15-meter) inspection boom attached to the end of the station's robotic arm. The boom was part of the space shuttle Discovery and used for heat shield inspections.
"What an accomplishment, beautiful," Parazynski said at the time. "It's as taut as a sail. Everything looks completely intact."
During that same Discovery shuttle mission, astronauts discovered metal shavings gumming up a huge paddlewheel-like joint that turns the space station's outboard starboard solar arrays. The metal shavings were apparently caused by wear on the joint's main ring.
Over the course of several spacewalks in November 2008, astronauts cleaned the metal shavings from the ring to help improve its performance.
When big parts fail
The failure of big parts on the space station can be a problem as well. Some of space station's vital large components are the space station's control moment gyroscopes ? big spinning devices used to change the station's position in space without the use of rocket thrusters.
The space station uses four control moment gyroscopes as part of its U.S.-built attitude control system. They spin about 6,600 times per minute to help provide the angular momentum required to move the massive space station.
Each of the gyroscopes weighs about 600-pound (272-kilogram) and they are so large only NASA's space shuttles are large enough to deliver new ones, so ordering replacements isn't easy. The space station can maintain its position with only two working gyroscopes if required.
The gyroscopes have failed several times in the past, including in 2006 and 2002, both times being replaced on later space missions.
Shaky space station
One unexpected space station glitch in January 2009 shook the space station ? literally.
The entire space station experienced an expectedly strong vibration on Jan. 14, 2009. The space shudder was so strong it shook items off the walls during an otherwise routine maneuver to boost the outpost's orbit.
Russian spacecraft parked at the space station typically push the space station into a higher orbit every now and then to keep it on course. It was during such a maneuver, a 22-second engine burn, that the odd rattle shook the space station and astronauts.
After an analysis, space station mission managers said later that the shaking event did not damage the space station. But at the time it was a dramatic event for the space station's crew, which was commanded by veteran NASA astronaut Michael Fincke at the time.
"We were definitely surprised," Fincke told SPACE.com from the space station Feb. 5, 2009 after the shaking event. "It's not usual during a reboost to see anything come off the walls."
- Gallery - Space Station's Windows on the World
- Graphic: How Big Is the International Space Station?
- Cooling System Malfunction Highlights Space Station's Complexity
Click here for SPACE.com's complete International Space Station mission coverage.