The International Space Station, shown on Nov. 5, 2007, is being built over more than a decade, at a cost of about $150 billion Cdn. (NASA)

The International Space Station is an orbiting science lab, a multibillion-dollar construction project and the most massive artificial object ever to orbit the Earth.

The ISS is being built — piece by piece, like a massive Lego toy — over more than a decade and is expected to be completed in 2010.

In all, 16 countries are participating in construction and scientific experiments on the ISS: the United States, Russia, Canada, Japan, Brazil and — through the European Space Agency — Belgium, Denmark, France, Germany, Italy, the Netherlands, Norway, Spain, Sweden, Switzerland and the United Kingdom.

It's an enormously ambitious construction job. When completed, the station is expected to have a mass of almost 450 tonnes and a living space of 935 cubic metres, or what NASA says will be bigger than a five-bedroom house.

It won't be cheap. The European Space Agency estimates the overall cost of the space station will be nearly $150 billion by the time the station ceases regular operations in 2016.

There have been at least two astronauts on board the station since November 2000, making it the site of humanity's permanent presence in space.

American astronauts Peggy Whitson, Daniel Tani and Russian cosmonaut Yuri Malenchenko make up the current three-person crew at the station. European Space Agency astronaut Leopold Eyharts of France is set to replace Tani in February with the arrival of the space shuttle Atlantis.

Here's a look at some of the highlights from the last six missions to the space station.

Mission STS-121: July 4 to July 17, 2006: The Discovery crew didn't add any parts to the station, but they kept themselves busy replacing critical hardware needed for future assembly, and taking more photos and videos than any previous mission. The crew also moved close to 3,500 kg of supplies and equipment onto the station, including a new heat exchange for the common cabin air assembly, and an extra space suit and emergency jet pack. The crew performed three spacewalks to do maintenance and test new safety procedures. German Thomas Reiter stayed aboard the station to augment the two-person crew of Michael Lopez-Alegria and Mikhail Tyurin. Prior to Reiter's arrival, all members of the ISS crew had been either American or Russian.

Mission STS-115: Sept. 9 to Sept. 21, 2006: The space shuttle Atlantis crew delivered and installed the second port truss segment and also installed new solar arrays. The arrays were brought aboard the station and a second set of solar panels, perpendicular to the first, was installed, doubling the capacity of the orbiting laboratory. It was the first major work to the station in four years. Atlantis also counted Canadian astronaut Steve MacLean among its crew. During the mission, MacLean became the first Canadian to operate Canadarm 2 in space and the second Canadian to perform a spacewalk.

Mission STS-116: Dec. 9 to Dec. 22, 2006: The space shuttle Discovery's mission included a crew switch, the rewiring to a permanent power source and a record-breaking spacewalk. Discovery's crew delivered and installed the third port truss segment to the second port truss segment. They also replaced the temporary solar arrays with the permanent arrays brought to the station by Atlantis. Two spacewalks were required to rewire the station one side at a time. Problems arose when the old solar array failed to retract properly. American astronaut Robert Curbeam had to make an unscheduled spacewalk to manually retract a part of the array, and in the process became the first astronaut to make four spacewalks in one mission. American Suni Williams also replaced Germany's Reiter as part of the three-person crew aboard the station.

Mission STS-117: June 8 to June 22, 2007: Atlantis delivered a truss segment for the starboard side of the station holding another set of solar arrays that will eventually act as a permanent source of power for the station. The mission was extended from 11 to 13 days after damage to a thermal blanket on the space shuttle's heat shield was discovered. The mission took another unexpected turn when a bank of computers on the Russian side of the space station - which help maintain the station's correct position in orbit - crashed and had to be rebooted. Two astronauts repaired the thermal blanket and Atlantis made its way back to Earth, bringing back Williams, who set a record for the longest time in space for a woman astronaut. American astronaut Clay Anderson replaced her as part of the station's three-person crew.

Mission STS-118: Aug. 8 to Aug. 21, 2007: The space shuttle Endeavour didn't add any major pieces to the station, but astronauts completed some repair work on the station, replacing a faulty gyroscope and moving around other components on the station's exterior in preparation for a later addition to the solar array. Two astronauts in particular had memorable voyages. Saskatoon-born and Montreal-raised Dave Williams set a Canadian spacewalking record during the mission, spending 17 hours and 47 minutes outside the space station during three spacewalks. Former schoolteacher turned astronaut Barbara Morgan was also part of the Endeavour crew. Morgan had been the backup to Christa McAuliffe as part of the Teacher in Space program in 1984. The program was suspended after McAuliffe and six astronauts died when the Challenger shuttle exploded in flight in January 1986.

Mission STS-120: Oct. 23 to Nov. 7, 2007: Discovery brought the Italian-built connection module called Harmony, the first major addition to the station's living space since a Russian Soyuz rocket brought the Pirs docking compartment in 2001. The astronauts also moved a truss equipped with a solar array to its new home on the station's port side and U.S. astronaut Daniel Tani replaced Anderson as a member of the three-person crew. The mission was extended to 15 days to deal with yet another problem aboard the station – a malfunctioning rotary joint for moving the station's solar wings and a solar wing that ripped as it was unfurled. While the crew repaired the tear, fixing the malfunctioning joint would fall to the space station crew after Discovery returned to Earth.

Early assembly

Assembly of the space station began with the launch of the Zarya Control Module on Nov. 20, 1998. Zarya provided battery power, fuel storage, and a rendezvous and docking spot for space vehicles, and was mated in December 1998 with the U.S.'s Unity Node. The two pieces would join to form the young International Space Station.

Pieces were added steadily through 2002, with astronauts aboard Endeavour adding a piece of the station's backbone in November 2002. That was the last shuttle mission before the Columbia disaster, which grounded the shuttle fleet for nearly two-and-a-half years and suspended construction of the ISS.

After the Columbia disaster, five Russian Soyuz and two earlier Discovery missions visited the station, but no major additions were added.

The station was originally supposed to be completed by 2005, but the Columbia disaster and other delays have pushed that to 2010.

Canada's contribution

Canada's major contribution is known to NASA as the Space Station Remote Manipulator System, but it's better known as Canadarm 2.

Canadarm 2 is a larger and more sophisticated version of the robotic arm built for the space shuttle. Fully extended, the arm is nearly 18 metres long, three metres longer than the shuttle's arm, and can handle loads up to 116 tonnes.

The new arm also has a hand on either end so one can latch onto the space station while the other end reaches out and picks up things that it needs. Then it can let go and grab on somewhere else.

The real talent in the new design is in its ability to move around where the astronauts most need the robot arm. The Canadarm 2 can crawl along the body of the space station on its two hands, end over end like an inchworm. The outside of the station has a number of sockets where the arm can plug in. As well, the arm can be fixed to a work platform that moves on rails from one end of the station to the other.

Canada will also be contributing a smaller, two-armed robot that has finer movements than either of the arms. It's designed to take on delicate assembly jobs that are now done by astronauts on spacewalks. NASA calls it the Special Purpose Dexterous Manipulator, although it's more commonly known as Dextre or the Canada Hand, because it can be attached to one end of Canadarm 2.

Dextre will be delivered to the station aboard Endeavour, which is scheduled to launch in March 2008.

All three components - Canadarm 2, the work platform on rails and Dextre - were designed and built by MDA Space Missions, formerly Spar Aerospace, of Brampton, Ont. In January 2008, MDA announced that it would be selling its satellite and space businesses to U.S. weapons and rocket maker Alliant Techsystems of Edina, Minn., as part of a $1.325-billion cash deal. The deal must be reviewed under the Investment Canada Act before it can be approved.