8 unforgettable moments during the International Space Station's decades in orbit, from DNA research to making space tacos

• Over two decades, the International Space Station has been humanity's home in space.
• The orbiting laboratory was launched in 1998 and has exceeded its 15-year expected lifespan.

The International Space Station has been humanity's only inhabited outpost in space for decades.

NASA aims to keep the space station going until 2030 and beyond, even opening it up to commercial spaceflight.

Russia's space agency head announced on Tuesday that it would pull out of the aging station after 2024. But officials have since told NASA that they would like to keep cooperation going at least until they build their own space station, per Reuters. This could mean the ISS would remain a beacon of international collaboration for at least six more years, Reuters reported.

Here are eight unforgettable moments from the ISS's 24 years in space:

The landmark 'Twins Study,' which showed that living in space can change human DNA

Much of the research at the ISS is preparation to understand the effect of space exploration on humans, ahead of putting boots on the moon and Mars. NASA's groundbreaking "Twins Study" compared the health and biology of astronaut Mark Kelly to his Earth-bound identical twin, Scott Kelly.

The study, published in 2019, found that Kelly's DNA changed in space. Upon Scott's return to Earth after 340 days aboard the ISS, researchers found that his telomeres — the protective caps at the end of DNA strands — were unexpectedly longer than Mark's telomeres.

Scientists are also conducting experiments aboard the ISS to combat bone and muscle loss. According to NASA, astronauts lose between 1 and 2% of their bone density for every month spent in space.

The first observation of an unusual 'cool-flame'

During an unrelated experiment, conducted in 2012, scientists aboard the ISS were able to observe large fuel droplets of heptane extinguishing twice. While the initial burn was at the traditional higher temperature, the second time it went out, the scientists observed low-temperature, soot-free flames in steadily burning fuels for the first time.

This so-called "cool flame" flickers at about 600 degrees Celsius (about 1,120 degrees Fahrenheit), according to NASA. That's about half the temperature of a candle flame, which burns at about 1,400 degrees Celsius (2,500 degrees Fahrenheit).

The flame burns for much longer in a low-gravity environment, such as aboard the ISS, which allowed the scientists to see the flame in heptane fuel burn for the first time, according to NASA.

The discovery could help scientists use fuel more efficiently in the future, and improve fire safety on the ISS.

Astronauts send the first tweets from the ISS

In 2010, astronaut Timothy "TJ" Creamer sent the first live tweet from the International Space Station, after the space station updated to a better internet connection, which allowed astronauts access to social media.

—TJ Creamer (@Astro_TJ) January 22, 2010

This, however, was not the first tweet sent from an astronaut aboard the ISS.

Access to the internet on the space station was limited until 2010, so astronaut Mike Massimino had a tweet sent by NASA on his behalf in 2009. Massimino transmitted messages to NASA's Mission Control Center on Earth and NASA tweeted them out:

"From orbit: Launch was awesome!! I am feeling great, working hard, & enjoying the magnificent views, the adventure of a lifetime has begun," Massimo tweeted, with help from NASA.

The ISS became one of the first space tourism destinations

The first space tourist was Dennis Tito, a US millionaire who boarded the ISS on April 30, 2001, and stayed aboard for eight days.

In total, 14 people have gone to the space station as commercial spaceflight participants, the official term for space tourists, including Cirque du Soleil founder Guy Laliberté, Russian film director Klim Shipenko, actor Yulia Peresild, billionaire Yusaku Maezawa, and production assistant, Yozo Hirano.

NASA also opened ISS commercial space opportunities in recent years. In April 2022, Axiom Space, a commercial aerospace company, launched the first private mission to the ISS. "We are opening a new era in human spaceflight," Michael López-Alegría, a former NASA astronaut, who is also an Axiom executive and mission commander, said on Twitter in April. "We are taking the first step in a next generation platform initiative that's going to bring working, living, and research in space to a much broader and more international audience."

Astronauts grew plants on the ISS and made space tacos

Astronauts have successfully grown fresh food aboard the space station, in order to help NASA study plant growth in low gravity, give them fresh grub, and gain insights into how to provide future spacefarers with a sustainable, long-lasting food source. The agency says the ISS astronauts have successfully harvested three types of lettuce, radishes, and peas. In 2021, scientists aboard the ISS cultivated the chili peppers grown in space, using them, along with fajita beef and vegetables, to make the first space tacos.

Astronauts are not just growing edible plants. In 2016, astronaut Scott Kelly shared photos of his space-grown zinnia flower, making it the first flower to bloom in space.

A Russian film crew filmed the first fiction movie fully shot in space

A Russian film crew went to the ISS in October 2021 to film a full, feature-length film aboard the space station. The film follows a Russian doctor sent to the station to treat a critically ill cosmonaut.

"I'm feeling a bit sad today," actress Yulia Peresild said on Russian state TV, after landing on Earth after 12 days of filming, according to CBS News. "It seemed that 12 days would be a lot, but I did not want to leave when everything was over."

Still, there is controversy about whether this is the first fiction production filmed in space. An eight-minute movie shot by space tourist Richard Garriot, called "Apogee of Fear," took place aboard the ISS in 2008 and starred astronauts on the ISS.

An ongoing example of international cooperation in a divided world

The ISS has been a shining example of international collaboration since it launched in 1998. The station involves space agencies from the United States, Europe, Canada, and Japan, with a rotating crew of astronauts.

As of May 2022, hundreds of individuals from 20 countries have visited the ISS, according to NASA.

In July 2022, amid high tension between Russia and the US over the war in Ukraine, Russia's space agency announced its plans to pull out of the ISS after 2024, ending a decades-long partnership with NASA at the orbiting outpost. In a July 26 statement, NASA Administrator Bill Nelson said the agency has not been notified by Roscosmos of any plans to end ISS cooperation.

"NASA is committed to the safe operation of the International Space Station through 2030, and is coordinating with our partners," Nelson said in the statement, according to The New York Times. "NASA has not been made aware of decisions from any of the partners."

Dazzling views of Earth from space — including auroras and volcanic eruptions

Astronauts aboard the ISS — like the station itself — are traveling at 17,500 mph, 250 miles above the planet, and orbiting it every 90 minutes. With this vantage point, they regularly share beautiful images looking down at Earth, snapping shots of phenomena like aurora, harsh storms, volcanic eruptions, and light pollution. In a 1987 book, author Frank White coined the term "the overview effect," referring to the high astronauts report experiencing after seeing Earth from space.