Marking 10 years aboard the International Space Station (photos)

This week marks the 10th anniversary of a milestone in space exploration.

Since the year 2000, the International Space Station has been continuously occupied. Constant human presence aboard the space station--an outpost one official has called the "zero gravity United Nations"--has been an unparalleled global success, from both a scientific and cultural standpoint.

More than 200 orbiting explorers have visited the space complex; 15 nations have contributed to the missions, providing modules and hardware; and more than 600 experiments have been carried out on board. The exploration outpost has served as a symbol of international cooperation and worldwide unity.

This image, taken in September 2000, shows the growing space station, which would soon expand, becoming occupied just weeks later after the Russian launch on October 31 and subsequent docking on November 2.

Donning a Russian space suit and preparing to simulate a space walk, astronaut William Shepherd gets ready for his time in orbit at the Gagarin Cosmonaut Training Center in February 2000--prior to the launch of Expedition 1 on October 31, 2000.

Posing for their final photos before launch, the Expedition 1 crew members--Commander William Shepherd; Soyuz Commander Yuri Gidzenko; and Flight Engineer Sergei Krikalev--stand alongside their Soyuz vehicle at the Baikonur Cosmodrome in Kazakhstan.

The Soyuz spacecraft lifts off from the Baikonur Cosmodrome at 10:53 a.m. on October 31, 2000. After docking with the International Space Station on November 2, 2000, Commander Shepherd, Soyuz Commander Gidzenko, and Flight Engineer Krikalev would spend 136 days, from November 2000 to March 2001, aboard the station.

In a photo taken during the first week of occupancy, cosmonaut Yuri Gidzenko, Soyuz commander for the Expedition 1 crew, is seen aboard the International Space Station. The image was among the first few still images transmitted back from the station after the crew arrived.

Emerging from a tunnel hatch aboard the ISS, and stabilizing himself for work in the Zvezda Service Module, Expedition 1 Flight Engineer Sergei Krikalev is seen floating weightless.

Equipped with a very large camera lens, cosmonaut Sergei Krikalev, Expedition 1 flight engineer, prepares to take a position in the space station's viewing portal, where he will shoot images of Earth's geography.

Wearing a Russian space suit, astronaut Mike Fincke, NASA ISS science officer and flight engineer, explores outside the walls of the space station in 2004, as part of Expedition 9.

In this photo, taken during the first week of Expedition 1's occupation of the ISS, cosmonauts Sergei Krikalev (left) and Yuri Gidzenko work in the Zvezda Service Module. The center of the Russian portion of the station, known as the Russian Orbital Segment, the Zvezda Service Module is responsible for hosting some of the station's life support systems, as well as providing living quarters for two crew members.

Looking over the Gulf of Mexico and portions of Texas, including Galveston Island and Galveston Bay.

Sergei Krikalev and Yuri Gidzenko input data into a laptop computer in the Zvezda Service Module aboard the International Space Station.

Weightless, floating through a corridor inside the Zvezda Service Module, cosmonaut Yuri Gidzenko carries a ventilator fan during routine maintenance work on the ISS systems.

A full view of the ISS, with the Caspian Sea in the background, was photographed by a crew member aboard the Space Shuttle Discovery after the undocking of the two spacecraft during Expedition 5 in 2002.

Astronaut Robert Curbeam is seen above the cargo bay of the Space Shuttle Atlantis during a space walk in 2001. The photo was taken from inside the International Space Station's Destiny Laboratory.

Standing near the hatch leading from the Unity Node into the newly attached Destiny Laboratory, cosmonaut Yuri Gidzenko poses for a picture shortly after installation of the Destiny Lab module in February 2001.

Astronauts Thomas Jones and Robert Curbeam are seen in the cargo bay of the Space Shuttle Atlantis during their third space walk, in February 2001.

Against the backdrop of an Earth desert, the Space Shuttle Atlantis is pictured shortly after its departure from the International Space Station in February 2000.

Cosmonaut Sergei Krikalev is positioned at a porthole on the Zvezda service module of the International Space Station in February 2001, as the Space Shuttle Atlantis approaches for a linkup leading to several days of joint activities between the two crews. The crew cabin and forward section of the Shuttle can be seen in the window, along with scattered clouds over the Western Pacific.

Nikolai Budarin, flight engineer for ISS Expedition 6, poses near the Potok 150MK air decontamination equipment in the Zvezda Service Module. Early evaluation of the internal environment during the first years aboard the ISS from air, water, and surface samples provided a baseline of the contaminant environment and potential health hazards. Maintaining a safe, healthy, and habitable environment on board the ISS has been one of the ongoing challenges over the years. Essential health and environmental systems are critical to life in orbit, and the ability to assess these systems--and make repairs and software updates--while simultaneously keeping everything running, is a difficult-to-master skill.

Holding a sound-level meter, Expedition 3 Mission Commander Frank Culbertson researches acoustic conditions aboard the ISS. The space station's Acoustic Measurement Program is responsible for creating spaces where crews can live, communicate, and work amid hundreds of noise-emitting instruments and systems.