Looking back at 25 years of the ISS

The US-built Unity node docked with the Russian-built Zarya module on December 6, 1998.


Wednesday marks the 25th anniversary of the International Space Station’s (ISS) physical assembly in orbit. On December 6, 1998, the crew aboard the space shuttle Endeavor attached the US-built Unity node to the Russian-built Zarya module, kicking off the modular construction of the ISS. A quarter century later, we look back at the milestones and breakthroughs from one of humanity’s most impressive marvels of engineering and international cooperation.

The ISS, which orbits the Earth 16 times every 24 hours at a speed of five miles per second, has been inhabited by researchers for over 23 years. It’s the product of five space agencies from 15 countries. NASA, Roscosmos (Russia’s national space agency), ESA (European Space Agency), JAXA (Japan Aerospace Exploration Agency) and CSA (Canadian Space Agency) have contributed to the station’s assembly and operation.

From ink to orbit

Its official journey began in the early 1990s when the United States’ Freedom (ordered by President Ronald Reagan in 1984) and Russia’s Mir-2 space station projects were in danger of (literally) never getting off the ground. Freedom was in jeopardy primarily due to a lack of Congressional funding amid rising costs, while Mir-2 was on the brink partially because of financial hardships following the collapse of the Soviet Union.

On September 2, 1993, the two nations, each needing an international ally to forge ahead, signed an agreement to combine their programs and collaborate on a joint mission that would have seemed wildly implausible a few years earlier. US Vice President Al Gore and Russian Prime Minister Viktor Chernomyrdin inked the pact, marking the formal conception of the cosmic laboratory we know today as the ISS.

Russian Prime Minister Viktor Chernomyrdin (R) and U.S. Vice President Al Gore appear at a press conference, 16 December 1993. The U.S. and Russia signed a series of space and investment agreements, including one making Russia a partner in the international space station project. Vice President also criticized nationalist leader Vladimir Zhirinovsky, saying
US Vice President Al Gore (left) and Russian Prime Minister Viktor Chernomyrdin in 1993 (VITALY ARMAND via Getty Images)

The following years included a design overhaul to fold Russian technology into America’s existing Freedom plans, a milestone 1995 docking of NASA’s Atlantis to Russia’s Mir station (epitomizing the fruit of the once-far-fetched collaboration), the addition of funding and cooperation from Europe, Canada and Japan in 1996 and Russia’s launch of Zarya a month before the ISS assembly began. That all led to the day 25 years ago when the two nations’ space tech linked together, sounding the death knell for the Cold War-era space race.

The first crewed mission began on November 2, 2000, when NASA astronaut Bill Shepherd and cosmonauts Yuri Gidzenko and Sergei Krikalev stepped onboard. The inaugural crew spent four months in space, laying the groundwork for subsequent crews. (The record for the most time living and working in space was set by Peggy Whitson, who celebrated 665 days aboard the ISS in 2017.)

ISS inaugural crew of Yuri P. Gidzenko (left) William M. Shepherd (center), and Sergei K. Krikalev.
ISS inaugural crew of Yuri P. Gidzenko (left) William M. Shepherd (center), and Sergei K. Krikalev. (NASA)

The US Lab Module linked to the station in February 2001, expanding the station’s onboard living space by 41 percent. Four years later, Congress named the US portion a national laboratory. Far more than a symbolic gesture (although it was also that), the designation opened the door to funding and research from a much more comprehensive array of institutions, including universities, other government agencies and private businesses. In 2008, laboratories from Europe and Japan joined the ISS.

The ISS’s construction and expansion from 1998 to 2010 amassed around 900,000 pounds of modules. The station contains about $100 billion worth of gear spinning around the globe.

Research and breakthroughs

Photo taken aboard the ISS during its initial assembly. A module sits upright at center with the Earth behind it.
Photo taken aboard the ISS during its initial assembly. A module sits upright at center with the Earth behind it. (NASA)

During the ISS’s more than 100,000 orbits of the Earth, it has ushered breakthroughs in areas ranging from disease research to bodily changes from microgravity.

Studying how proteins, cells and biological processes behave in microgravity has boosted research in Alzheimer’s, Parkinson’s, heart disease and asthma. Many of these studies wouldn’t have been possible on Earth. Meanwhile, protein crystal growth experiments have sparked advances in developing treatments for conditions including cancer, gum disease and Duchenne Muscular Dystrophy.

ISS researchers made surprising discoveries about “cool flames,” which can burn at extremely low temperatures. Nearly impossible to study outside of microgravity, the astronauts’ research has challenged our previous understanding of combustion. It may open new frontiers with internal combustion engines (ICE), allowing them to run cleaner and more efficiently.

Studies aboard the space station have contributed significantly to our knowledge of human muscle atrophy and bone loss. (ISS astronauts typically work out at least two hours daily to prevent these conditions.) Studying how prolonged time in microgravity affects muscle deterioration and recovery also applies to Earthbound patients stuck in bed for extended periods. In addition, the research can help us learn more about conditions like osteoporosis, leading to improved preventative measures and treatments. It has also helped scientists better understand broader biological changes in microgravity, which could pay dividends if or when humans colonize Mars.

Water purification systems designed to sustain astronauts over long periods have also borne fruit on Earth. ISS astronauts recycle 98 percent of their pee and sweat using highly efficient and compact systems. This has led to the technology’s use in agriculture, disaster relief and aid provision for less developed areas.

ISS astronauts studied the Bose-Einstein Condensate (BEC), a “fifth state of matter” that deviates significantly from known states like solids, liquids, gases and plasmas. In 2018, the ISS’s Cold Atom Lab produced BEC in orbit for the first time. Space’s colder temperatures and lack of gravity allow for longer observation times, helping researchers learn more about the behaviors of atoms and BECs. Not only is this crucial to quantum physics studies, it could aid in developing more advanced quantum technologies down the road.

For more detail on the ISS’s breakthroughs, NASA has a dedicated writeup from 2020.


Expanded cross-section of the ISS, showing its various parts and labels.
Expanded cross-section of the ISS, showing its various parts and labels. (NASA)

The ISS is currently scheduled for decommissioning in January 2031. (Russia currently plans to leave in 2028.) Its late 90s infrastructure is aging quickly, and the space station would grow increasingly and prohibitively expensive to maintain over the long haul. Government and commercial orbital labs will likely pick up the slack in the following years.

When its time comes, the ISS will undergo a controlled deorbit. As for what that might involve, Kirk Shireman, deputy manager of NASA’s space station program, broached the subject with in 2011. “We’ve done a lot of studies,” he said. “We have found an orbit and a change in velocity that we believe is achievable, and it creates a debris footprint that’s all in water in an unpopulated area.”

As Engadget’s Andrew Tarantola wrote about the ISS’s pending demise:

Beginning about a year before the planned decommissioning date, NASA will allow the ISS to begin degrading from its normal 240-mile high orbit and send up an uncrewed space vehicle (USV) to dock with the station and help propel it back Earthward. The ultimate crew from the ISS will evacuate just before the station hits an altitude of 115 miles, at which point the attached USV will fire its rockets in a series of deorbital burns to set the station into a capture trajectory over the Pacific Ocean.

NASA plans to guide any remaining bits into a remote area of the South Pacific Ocean. “We’ve been working on plans and update the plans periodically,” Shireman said. “We don’t want to ever be in a position where we couldn’t safely deorbit the station. It’s been a part of the program from the very beginning.”

NASA 25th-anniversary event

NASA held a live-streamed event on Wednesday to mark the quarter-century anniversary of the Zarya and Unity modules linking up. All seven STS-88 Space Shuttle Mission crew members joined NASA Associate Administrator Bob Cabana (mission commander) and ISS Program Manager Joel Montalbano to discuss the milestone.

You can watch it here: