Likeany big machine, the huge International Space Station requires dailymaintenance repairs to keep flying in space. But every now and then somethingbig or critical ? like the recent cooling system trouble ? pops up to shine aspotlight on the $100 billion space station, which has been continuously mannedby astronauts for nearly 10 years.
Halfof the spacestation's cooling system shut down late Saturday when a circuit breakertripped 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 afflictedcooling system line ? called Loop A.
Butwhile astronauts regularly work through smaller glitches on the space station,critical or seriousmalfunctions are relatively rare. The space station has been underconstruction since 1998. It is currently home to six people and has a maintruss as long as a football field.
Here'sa look, by no means comprehensive, at some recent notable malfunctions duringthe space station's 10 years in orbit:
Russiandocking system glitch
Themost recent notable glitch at the space station occurred in early July, when anunmanned Russian cargo ship sailed completely past the International SpaceStation instead of docking at the outpost as planned.
TheProgress 38 cargo ship was flying on autopilot as designed on July 2 when itunexpectedly aborted the docking attempt and missedthe space station. Russian engineers suspect interference between thespacecraft's Kurs automated docking system and a space station system thatallows cosmonauts to take remote control of the Progress spacecraft caused the abort.
Thesolution? Simply turn off the remote control system on the space station. Thestation crew did that and on July 4 the Progress 38 parked itself at theorbiting lab as planned.
Coolingsystem valve woes
Thespace station's Loop A cooling system has seen some glitches before. InApril, a stuck valve sent NASA engineers scrambling to come up with a fix whilethe space shuttle Discovery was docked at the orbiting lab.
Atthe time, NASA engineers were considering an emergency spacewalk to either fix or replace the faulty Loop A valve. The valve controlled the flowof nitrogen, which is used to pressurize the cooling system plumbing ahead ofthe liquid ammonia flow.
Engineersdidn't immediately fix the valve, but after studyingthe space malfunction exhaustively they did decide the glitch didn't posean immediate problem. The crew of Endeavour did not have to perform an extraspacewalk and were able to depart the space station in mid-April as planned.
Spacepotty and space urine recycler
Thespace station's toilets and related life support equipment have also had theirshare of troubles.
Inrecent years, the space station's high-tech toilet has had several glitches dueto faulty pumps and other problems. Most recently, one of two spacetoilets on the station flooded in July 2009 because of a faulty separatorpump and control panel.
Thereare currently two bathrooms on the International Space Station to handlerestroom needs for its six-person crew.
Relatedto the space toilet issues are glitches in the station's urine recyclingsystem, which is part of a larger water purification system. A spinningcentrifuge-like component has been the culprit for most of the malfunctions andrequired replacement in 2008 and 2009.
Thespace 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'satmosphere. The system, and its Russian counterpart Elektron, have experiencedbreakdowns from time to time and been repaired.
Smokysmells and leaks
Airleaks and smoke-like smells have both popped up on the space station in oneform or another.
InJanuary 2004, slow airleak that perplexed NASA for weeks sent astronauts hunting through thespace station for its cause. After checking several different systems, aflexible hose used as a makeshift handhold near a window was identified as itscause and repaired.
In2006, a small leak of toxic potassium hydroxide in the space station's RussianElektron oxygen generator, which overheated a connected rubber seal to create asmoke-like smell that set off a brief fire scare on the space station. Openflames are not allowed on the space station because of such a fire risk.
Aftersome investigation, astronauts traced the smell to the Elektron unit anddiscovered the leak, which they carefully cleaned up.
Anunrelated smoky smell in a space station spacesuit later prompted a brief banon U.S. spacewalks until it could be addressed. That ban was lifted after a fewdays once the suit was cleaned.
Witha spacecraft as complex as the International Space Station, computer problemscan border on nightmarish.
Thereare literally dozens of laptop computers linked together to control variousspace station systems and from time-to-time Russian and American machines havefailed or suffered hiccups.
OnFeb. 20, a brief maincomputer failure on the space station knocked out communications betweenthe laboratory and Mission Control for about an hour. A software glitch relatedto how data was sent to Earth from the station's European-built Columbus labwas the prime suspect.
Moresubstantial computer problems have caused some serious worry on the spacestation and on Earth.
InJune 2007, a majorfailure within the six-computer navigation and control system in charge ofthe Russian segment of the space station left the station without the use ofits Russian attitude control thrusters, Elektron oxygen generator and othersupport equipment. A carbon dioxide scrubber and other environmental controlsystems were also offline and temperatures inside the station's Russian-builtZvezda service module (where the computers are located) rose to around 80degrees Fahrenheit.
Ittook several days for Russian cosmonauts to install cables to bypass a faultyelectronics box and work around the glitch. A Russian computer crash in 2002also caused attitude control issues as well.
Americancomputers on the space station have also not been failure-free.
InApril 2001, a computer crash in the U.S. Destiny laboratory forced MissionControl to reroute communications through the shuttle Endeavour, which wasvisiting at the time. A failed hard drive in one of Destiny's three command andcontrol computers was identified as the cause and replaced.
Rippedsolar wings and jammed joints
Oneof the most dramatic International Space Station glitches in recent yearsinvolved rip in one of the orbiting lab's expansive solar arrays used to powerthe orbiting lab.
InOctober 2007, one of the space station's port side solar wings rippedwhile being unfurled by astronauts using a workstation inside the orbitinglaboratory. The malfunction forced NASA mission planners to overhaulmission plans for space shuttle Discovery astronauts, who were visiting at thetime.
Thecrew performed a daringspacewalk repair in which a spacesuit-clad astronaut patched up the rippedsolar array using fabric stitches and tools wrapped in tape to insulate themagainst the potential shock hazard of working next to a solar array.
Toreach the torn spot, spacewalking astronaut Scott Parazynski had to stand atthe end of a 50-foot (15-meter) inspection boom attached to the end of thestation's robotic arm. The boom was part of the space shuttle Discovery andused for heat shield inspections.
"Whatan accomplishment, beautiful," Parazynski said at the time. "It's astaut as a sail. Everything looks completely intact."
During thatsame Discovery shuttle mission, astronauts discovered metal shavings gumming upa huge paddlewheel-like joint that turns the space station's outboard starboardsolar arrays. The metal shavings were apparently caused by wear on the joint'smain ring.
Over thecourse of several spacewalks in November 2008, astronauts cleaned the metalshavings from the ring to help improve its performance.
When bigparts fail
The failureof big parts on the space station can be a problem as well. Some of spacestation's vital large components are the space station's control momentgyroscopes ? big spinning devices used to change the station's position inspace without the use of rocket thrusters.
The spacestation uses four control moment gyroscopes as part of its U.S.-built attitudecontrol system. They spin about 6,600 times per minute to help provide theangular momentum required to move the massive space station.
Each of thegyroscopes weighs about 600-pound (272-kilogram) and they are so large onlyNASA's space shuttles are large enough to deliver new ones, so orderingreplacements isn't easy. The space station can maintain its position with onlytwo working gyroscopes if required.
The gyroscopeshave failed several times in the past, including in 2006 and 2002, both timesbeing replaced on later space missions.
Oneunexpected space station glitch in January 2009 shookthe space station ? literally.
Theentire space station experienced an expectedly strong vibration on Jan. 14,2009. The space shudder was so strong it shook items off the walls during anotherwise routine maneuver to boost the outpost's orbit.
Russianspacecraft parked at the space station typically push the space station into ahigher orbit every now and then to keep it on course. It was during such amaneuver, a 22-second engine burn, that the odd rattle shook the space stationand astronauts.
Afteran analysis, space station mission managers said later that the shaking eventdid not damage the space station. But at the time it was a dramatic event forthe space station's crew, which was commanded by veteran NASA astronaut MichaelFincke at the time.
"Wewere definitely surprised," Fincke told SPACE.com from the spacestation Feb. 5, 2009 after the shaking event. "It's not usual during areboost 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 missioncoverage.