"Congratulations on a successful launch & docking Soyuz 46S crew - see you soon!" said British astronaut Tim Peake in a tweet with a photo of the Soyuz vehicle approaching the space station.
15 years ago this week, the International Space Station accommodated its first crew members. Now, 180 months later, the orbiting outpost has not been uncrewed since, playing host to over 220 astronauts, cosmonauts and fee-paying space tourists.
Here are just a few of the highs and lows of humanity's most ambitious international endeavor in space.
PHOTOS: 'Space Invader' Found on International Space Station
The space station awaiting NASA astronaut William Shepherd, center, and cosmonauts Yuri Gidzenko, left, and Sergei Krikalev, right, 15 years ago wasn’t the first outpost to orbit Earth, nor the first to host residents from the United States and its former Cold War foe, Russia. But unlike NASA’s 1970s-era Skylab and the series of Soviet stations that ended in 2001 with Mir, the International Space Station, or ISS, was a joint program from the get-go.PHOTOS: Meet the Space Station's Resupply Fleet
Assembly began on Nov. 20, 1998 with Russia launching the Zarya control module, pictured here in the center with the shorter solar panel wings. Three space shuttle missions followed to install the Unity connecting node (located at the bottom in this image), deliver supplies and prepare the station for the arrival of the Russian-launched Zvezda service module, at top, with a Russian Progress cargo ship attached. Two more space shuttle missions followed with more equipment and supplies before the first station crew blasted off aboard a Russian Soyuz rocket on Oct. 31, 2000. The crew arrived at the station two days later to begin a 4.5 month-long mission.PHOTO: Enormous Red Sprites Seen From Space
The first station crew, known as Expedition One, hosted two visiting crews of space shuttle astronauts and added the U.S. Destiny laboratory module to the growing outpost before their replacements arrived aboard another space shuttle mission on March 10, 2001. That handover marked the first in an unbroken string of crew rotations that have kept the station permanently staffed for 15 years. The current station crew, led by NASA astronaut Scott Kelly, is Expedition 45.PHOTOS: Space Station Astronauts Log One Million Photos
During their 167-day flight, the Expedition Two crew, comprised of Russian cosmonaut Yury Usachev and NASA astronauts Susan Helms and James Voss, became de facto space ambassadors when Russia insisted on flying a privately paying tourist. NASA vehemently objected to Dennis Tito, an American businessman, flying with the Russian taxi crew delivering a fresh Soyuz capsule to the station. NASA said it was too early in the station’s ongoing development for non-professional astronauts, but in the end, Russia, which was charging Tito some $20 million for the trip, prevailed. Tito, left in above image, spent six days aboard the station. Since then, six other passengers have paid upwards of $40 million to visit the station. One tourist, Microsoft co-founder Charles Simonyi, flew twice.PHOTOS: Urban Planning: Cities Seen From Space
Station assembly continued at a steady pace until Feb. 1, 2003, when shuttle Columbia, on a rare, non-space station research flight, broke apart during its return to Earth, killing seven astronauts. Shuttle flights were immediately suspended, shifting sole responsibility for keeping the station staffed to Russia. The shuttle returned to flight in July 2005, but was grounded again for another year for more modifications. The STS-107 Columbia crew, left to right from top, David Brown, pilot William McCool, payload commander Michael Anderson, Kalpana Chawla, commander Rick Husband, Laurel Clark and Israeli astronaut Ilan Ramon.PHOTOS: Epic Aurora Photos From the Space Station
Heeding the advice of the Columbia accident investigation board, NASA decided to retire its remaining three space shuttles once construction of the space station was finished. After 21 post-Columbia shuttle missions to the station, plus one last servicing call to the Hubble Space Telescope, NASA grounded the fleet. Shuttle Atlantis, pictured above, completed the last flight on July 21, 2011. On the second to last mission, sister ship Endeavour delivered the station’s premier science experiment, a multi-national $2 billion particle detector known as the Alpha Magnetic Spectrometer. With the shuttles out of service, NASA again was dependent on Russia to fly crews to the station.PHOTOS: Inside Atlantis' Final Space Station Mission
As part of its post-shuttle planning, NASA embarked on a controversial, cost-cutting program to purchase flight services, rather than build and operate its own spaceships, for transportation to and from the station. Ultimately, two companies, Space Exploration Technologies, or SpaceX, and Orbital Sciences, which has since merged with another firm and is now known as Orbital ATK, began making cargo runs to the station. SpaceX got there first, with a test run in May 2012, pictured above. Astronauts aboard the station use a robotic arm to snare the capsule from orbit and berth it to the station. NASA also has given launch contracts and financial support to SpaceX and Boeing to fly station crew as well.PHOTOS: Meet the Space Station's Resupply Fleet
With two new supply lines to the station, NASA was happily back making cargo runs to the station until launch accidents temporarily grounded both firms. Pictured above, an Orbital Antares rocket, carrying a Cygnus cargo ship, exploded minutes after liftoff from the Mid-Atlantic Regional Spaceport on Wallops Island, Virginia, on Oct. 28, 2014. The company plans to resume flights on a new version of Antares in 2016. Meanwhile, Orbital has purchased two rides for Cygnus capsules on United Launch Alliance Atlas rockets. SpaceX, which also flies commercial satellites on its Falcon 9 rockets, had a launch accident on June 28, 2015, during its seventh resupply run to the station. SpaceX is planning to resume flights in December, though its next station cargo flight is not expected until January at the earliest.PHOTOS: 'Space Invader' Found on International Space Station
Despite launch accidents, political turmoil and financial concerns, the 15-nation station partnership has endured and become a model for future international programs to send astronauts and cosmonauts farther into space. In March, NASA and Russia began the first of what is expected to be series of year-long missions in an attempt to learn more about how spaceflight impacts the human body and mind. NASA astronaut Scott Kelly, pictured above, and Russian cosmonaut Mikhail Kornienko are serving as the first subjects, work that scientists hope will pave the way for three-year missions to Mars.PHOTOS: Inside the First 100 Days of a Year in Space
A Russian Soyuz rocket launched a joint U.S.-Russian crew to the International Space Station Friday (March 18), a space team that includes an astronaut aiming to break an American spaceflight record recently set by NASA's year-in-space astronaut Scott Kelly.
American astronaut Jeff Williams of NASA and cosmonauts Oleg Skripochka and Aleksey Ovchinin of Russia's Federal Space Agency (Roscosmos) launched toward the space station at 5:26 p.m. EDT (2126 GMT) from the Baikonur Cosmodrome in Kazakhstan. The trio, riding in a Soyuz space capsule, arrived at the space station after a 6-hour journey, with their spacecraft docking at 11:09 p.m. EDT (0309 GMT on March 19), according to a NASA update. [Watch tonight's Soyuz launch in this video replay]
Finally, at 12:55 a.m. EDT Saturday (0455 GMT), the two crews opened the hatches between the Soyuz and space station, allowing the three new crewmembers to join American astronaut Tim Kopra, British astronaut Tim Peake and Russian cosmonaut Yuri Malenchenko in the giant orbiting lab.
"In four windows I can see the Earth," one of the cosmonauts told Mission Control as they rose.
The six-month space station stay will be Ovchinin's first flight to space and Skripochka's second, but Williams is a spaceflight and space station veteran. Williams is visiting the station for a fourth time; his first time was more than 15 years ago via the space shuttle Atlantis while the station was still under construction. While he's in space, he will break Scott Kelly's new record of the most cumulative time in space by an American.
By the end of Kelly's recent near-yearlong mission (he landed March 1), the astronaut racked up a lifetime total of 520 days in space. On this new mission, Williams, who is making a record third long-duration stay on space station, should reach 534 cumulative days once he returns to Earth in six months. He will have spent time in space with at least 50 other space explorers, Williams said.
"The first time I was there before Expedition 1, and I was there in Expedition 13, about halfway through the assembly [of the International Space Station]. And the last time was Expeditions 21 and 22, right at the end of the assembly," Williams told Space.com in a video interview during a break from training in February. "I plan on taking the opportunity to refresh the world on what an adventure it's been building the space station, and what an achievement it's been in terms of human accomplishments in the history of human exploration."
Next week, an Orbital ATK Cygnus cargo spacecraft will launch to the station, bringing supplies, spacewalking gear and new experiments for the six crewmembers to conduct. During the expedition, the crewmembers will look into spaceflight's effect on the musculoskeletal system, how tablets dissolve in microgravity and the effectiveness of extra-small exercise equipment, NASA said in a mission summary. (The three new arrivals will stay on for both Expedition 47 and Expedition 48.)
When not occupied by experiments or exercise, Williams will be taking the opportunity to add to his (already substantial) space photography, seeking out alternate views of places he's seen over his 15 years of spaceflight.
"I do have a long list of targets that I want to try to get again, maybe in a different way, catch in different lighting conditions," he told Space.com. "The equipment we have on board now is far advanced from what it was before, when I was there last, particularly for night photography. So I want to try to add to my collection some good night photography."
More from SPACE.com:
Cosmic Quiz: Do You Know the International Space Station?
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Russia's Manned Soyuz Space Capsule Explained (Infographic)