The Moon and Mars, and the outer solar system, are the new two-tiered frontier for human and robotic space exploration. “Living, working and experimenting on ISS has given us the confidence to survive in space, to venture beyond Low-Earth Orbit (LEO). And by the time the ISS retires, LEO will just be another place where humans hang out,” he adds

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As it happens, the decommissioning of the space station comes at a time when the US National Aeronautics and Space Administration (NASA) — which oversaw its installation and will oversee its deorbiting — is readying for a new age in which its role will be vastly altered. NASA is already signing deals as a facilitator in the growing commercial space-exploration economy.

The American company Axiom has finalised a contract that will allow it to attach at least one habitable commercial module to ISS by 2026. There will eventually be four such units. After ISS’s retirement, the modules will coalesce and become the Axiom Station.

NASA has meanwhile signed agreements with US-based companies such as Blue Origin, Nanoracks and Northrop Grumman, to help design and build independent commercial space stations and space destinations.

“The agency is committed to continuing to work with industry with the goal of having one or more stations in orbit to ensure competition, lower costs, and meet the demand of NASA and other customers,” Angela Hart, manager of NASA’s Commercial Low Earth Orbit Development Program, said in January.

Why must ISS go?

It was only meant to serve for 15 years but, as with so much space technology, has exceeded expectations to last nearly 26. “It would have been nice to leave ISS out there, like an in-orbit museum, but it would disintegrate and become dangerous,” says McDowell. “It would become steadily more battered, unstable and out of control.”

Disposing it is expected to cost about $1 billion, in a delicate operation that will stretch over months.

To begin with, the space station will slowly be allowed to lose altitude. At about 200 miles above Earth’s surface, a special deorbit vehicle will attach itself and provide the final pull. ISS will then be guided towards a remote point in the Pacific Ocean, at a pace that will allow as much of the space station to burn away on re-entry as possible.

Nothing this big has ever re-entered (or exited) the atmosphere. But based on the re-entry of two other space stations, the Russian Mir in 2001 and NASA’s Skylab in 1979 (ISS is four to five times larger than these), the space agency expects the skin of the modules to blaze away first, leading the internal hardware to rapidly melt. What is most likely to survive re-entry are denser, heat-resistant components such as the scaffolding or truss sections.

Where will it go?

Space debris of this kind is typically guided to a specific remote point in the Pacific Ocean called Point Nemo, or the Oceanic Pole of Inaccessibility (because it is one of the furthest points from land; there is another in the Indian Ocean).

Nicknamed the Space Cemetery, Point Nemo sits about 2,700 km from New Zealand to the west, South America to the east and Antarctica to the south.

Bits of titanium, stainless steel, aluminium and parts containing cryogenic fuel are usually what make it to the ocean floor in this freezing stretch, says space archaeologist Alice Gorman, an associate professor at Flinders University in Adelaide. Because of its depth and remoteness, there is little to no data on what happens to these remains, or on the impact on marine life here.

But it needn’t be all bad news. “Many shipwrecks end up fostering rich marine communities,” Gorman says. “Could these rocket bodies turn into habitats for sea creatures? I like to hope they can.”

Onward

NASA, meanwhile, is already at work on its next. Gateway will be humanity’s first lunar-orbit space station. It will reportedly be crucial to the exploration of the lunar South Pole. Assembly is expected to begin in 2028.

Gateway will make it easier to plan NASA’s upcoming Artemis series of crewed orbiter and lander missions, McDowell says. “After that, it’s Mars and the outer solar system.”

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FRONTIER LEAGUE: A timeline of space stations before ISS

What came before the International Space Station? The answer is: quite a lot. ISS is about 25 years old, but we’ve had space stations for more than half a century. Who got there first? How did a space race end in Tranquillity? Take a look.

* Early musings: The idea of space stations can be traced, rather incredibly, to the mid-1800s. That’s when astronomers and physicists first began asking: Could humans get something to orbit Earth in the same way that the planets glide around the Sun?

In Russia, Konstantin Tsiolkovsky, called the father of modern space-flight, drew an outline for a “space station with a rotating section to generate artificial gravity. Such a station could be used to investigate Earth and refuel ships proceeding to other destinations, such as the moon,” writes Jay Chladek, in his 2017 book Outposts on the Frontier: A Fifty-Year History of Space Stations.

The German aerospace engineer Wernher von Braun, who worked with the Nazis during the war and became an American citizen after it, wrote in 1951 of an idea to send humans to Mars by using a space station as an assembly point for an interplanetary vessel. “Development of the space station is as inevitable as the rising of the sun; man has already poked his nose into space and he is not likely to pull it back,” he wrote, in 1952.

* MOL beginnings: When NASA was founded in 1958, it took over space exploration, which had until then been led by the US Air Force. But, amid the Cold War, the US military wasn’t taking its eye off the skies.

Plans took shape for a Manned Orbiting Laboratory (MOL), a series of 60-ft-long space stations in low-Earth orbit, to be occupied by two-man crews and built for military reconnaissance. Pilots were selected. A test flight was carried out in 1966. Then, amid budget cuts as the Vietnam War dragged on, and amid a fast-approaching 1969 deadline for a first manned mission to the Moon (by NASA), the project was abruptly ended.

Some of the spacesuits and waste-management designs would live on, when the US did launch its first space station, Skylab (1973-74). But first…

* A Soviet Salyut: In many ways, Almaz (Russian for Diamond) was the Soviet Union’s response to MOL. It was the brainchild of pioneering Soviet rocket scientist Vladimir Chelomei.

Almaz was a codename; it was officially the Orbital Piloted Station (OPS). The space station was conceived, in 1964, as a three-man orbiter that would gather intelligence with the help of a telescopic camera system and reconnaissance equipment.

Then the Apollo 11 landed on the moon. The Soviet government wanted to give Russia something as thrilling to celebrate. So, in 1970, the USSR announced that it would build a “civilian” or research-focused space station.

Salyut (Russian for Greetings) was launched in 1971. The world’s first space station was 66 ft long, or about the size of a large swimming pool.

A series of Salyuts would be sent into space over the years. The final one, Salyut 7, was launched in 1982. It held plant cultivator experiments, materials-processing furnaces, a treadmill and a bicycle that could read the user’s heart rate and other vital signs.

* Skylab: By 1965, NASA was having a bit of an identity crisis. It was clear by now that a lunar landing was well within reach. But after that, what? How would the US cement its status as a leader in space exploration?

There were calls for the organisation to devote more resources to unmanned missions and scientific research. There were also calls for it to justify and reduce its massive budgets. At the same time, NASA engineers in Alabama were looking at ways to use spent Saturn rockets. If they were left in orbit, could they be turned into a space lab that could be gradually expanded?

This seemed like an economical way to compete with the Soviet Union, which already had its Salyut in the skies.

And so it was that Skylab — a two-level orbital workshop made from a converted Saturn V launch vehicle — came about. It began the trend of student-suggested science experiments, which continue at ISS today. A key early one: could spiders spin webs in zero-gravity? It turns out they can.

* Mir:By the end of Salyut 7’s run, the world was a different place. Mikhail Gorbachev had taken the reins in a post-Cold War Russia. Peace was on the cards. Russia’s new space station, accordingly, launched in February 1986, was named Mir (Russian for Tranquillity).

Mir would be occupied for over a decade, visited by astronauts from Syria, Bulgaria, Afghanistan, France, Germany, Austria and Slovakia. An American astronaut visited in 1992. As it became clear that the two giants of space exploration could work together, a new plan took shape.

In 1993, the two countries announced plans for a revolutionary project that would be called, simply, the International Space Station.