[♪ INTRO] The International Space Station has enjoyed more than two decades in the sun, orbiting the Earth more than 140,000 times.

It’s brought us unrivaled space and earth science, but unfortunately, its days are numbered. Its aging technologies mean that it can’t stay in orbit forever, and NASA is starting to make plans for what happens at the end of its life, as well as what will eventually take its place.

Construction of the ISS began in 1998, and it’s been permanently inhabited since 2000. Over the last twenty years, its operation has been a collaboration between five space agencies representing fifteen countries, and it has been a testbed for unique science that couldn’t be done anywhere else. These have mostly been government initiatives, performing experiments in microgravity, studying space, studying the Earth, and monitoring the effects of space on the human body.

But this orbiting lab can’t last forever. It’s using tech that was first designed in the 1980s, so… it’s aging rapidly. At some point the ISS’s operators will have no choice but to pull the plug.

Precisely when they do that will be guided mainly by the structure’s integrity over the coming years. While many components can be repaired and replaced, the station’s primary structure can’t; things like its habitable modules, radiators, and trusses. These critical components accrue small amounts of stress every time a spacecraft docks or undocks from the station, and even when it crosses between the day and night sides of the Earth.

For instance, the service module of the ISS’s Russian segment was found to be leaking air into space back in 2019. It took until 2021 to trace the leak to microcracks in the module’s structure, probably caused by metal fatigue or micrometeorite impacts. Right now, the loss of a little air poses no danger to the crew aboard, but the cracks are a stark illustration of the aging problem.

NASA and the other space agencies have analyzed their components, and they do expect the overall structure to last until at least 2030. But they’re officially making plans for what happens next. In short, the agencies plan to deorbit the station, and crash it back into Earth, but making sure it’s done safely will take many years of careful planning.

The process starts with the station thrusting in the opposite direction to its orbital motion, so it will begin to drop towards the atmosphere. These maneuvers could start anytime between 2026 and 2028. That window actually depends on the Sun.

That’s because when the Sun is more active, the atmosphere expands, causing more drag at higher altitudes, making the station slow down quicker. And the timing of the drag-induced drop is critical. Weighing in at 420 tons, and spanning the area the size of a football field, the station will be the largest structure ever to reenter the Earth’s atmosphere.

The heat from reentry will make it partly break apart and burn up, but the size and the complexity of the structure means that some parts are very likely to make it to the surface. So the space agencies want to make very sure that those parts come down somewhere they won’t hurt anyone or cause any damage. The timing of the deorbiting burns will be carefully chosen to put the ISS on course for an uninhabited spot in the Pacific Ocean around July 2030.

This space graveyard is sometimes called Point Nemo, and is at least 2700 kilometers from the nearest landmass. That’s helpful when deorbiting giant spacecraft, since it’s never possible to hit a target straight on when your projectile is tumbling down through the entire atmosphere. But we’ve gotten pretty good at aiming for Point Nemo over the years.

The ocean floor in the area is now home to almost 300 spaceship wrecks. Among them are the pieces of the 120-tonne Mir space station, and many of the cargo capsules that regularly resupply the ISS. Soon, the ISS will join them too.

Now, it’ll take a little extra oomph to push the ISS down past the point of no return, which will be provided by docking a few extra thrusters to the station. The last missions will bring home the remaining science experiments, and of course the crew, before the ISS plunges on a collision course with Point Nemo. Losing the International Space Station will be a sad day for space research, but one of the reasons NASA wants to wait until 2030 is to allow something else to be developed that can take its place.

The agency plans to transition from a single station run by international governments, to several so-called commercial low-Earth orbit destinations, or CLDs. In other words, orbiting platforms owned and run by private companies. NASA itself intends to book time on the CLDs for its own missions.

So, as part of the transition, many of the ISS missions through the 2020s will be focused on getting these CLDs up and running. NASA already has an agreement with a company called Axiom Space to dock a module to the ISS, along with their own private crew. The idea is that this module will eventually detach and become its own standalone station, even before the ISS is decommissioned.

There are likely to be many more. So, the legacy of the International Space Station will live on. The station has outperformed every expectation, and made countless important discoveries in the last quarter century.

Even as it burns through the atmosphere, and sinks deep into the most inaccessible part of the ocean, it enables and heralds a brand new age of accessible space exploration. Thanks for watching this episode of SciShow Space. The month of March is almost over, which means you’re almost out of time to order March’s pin of the month!

This month’s pin is Pioneer 10, the 30-year solar system mission that could. This is a pre-order, meaning we’ll take all the orders we get at the end of the month and then make that many pins. And we won’t make any more, but we will get started on a new pin next month.

Orders close at the end of March, so check out the link in the description before time runs out! [♪ OUTRO]