The International Space Station has just marked a significant anniversary. Here's what life inside is like

This article was originally published in March 2021 and updated in November 2023.

If you are aged 23 or younger, you have never lived without humans circling our planet on the International Space Station (ISS).

Astronauts first boarded the ISS on 2 November 2000, when NASA's William M Shepherd along Russia’s Yuri P Gidzenko and Sergei K Krikalev arrived for a four-month stay.

Their main task on what is known as Expedition 1 was to set up the station's life support and communications systems, helping ISS maintain its orbit 400 kilometres above Earth at a speed of 28,000 kilometres an hour – that means it gets around the planet once every 90 minutes.

Humans have been in space ever since. But what is life like on the ISS, and what have the astronauts who have worked there achieved?

The ISS is a giant research facility where various experiments are underway at any given time, looking at everything from biology to technology, with implications for life in space and on Earth.

They include growing food in microgravity at the two Vegetable Production System (Veggie) plant growth units on board, and in the more sophisticated Advanced Plant Habitat growth chamber.

Being able to grow food in space could be an important part of planning longer space journeys and, in 2015, astronauts grew and ate their first space-grown salad.

NASA says: “The Veggie concept is a simple, low-power system to grow fresh, nutritious food for our astronauts to supplement their diet and use as a tool to support relaxation and recreation.”

Other experiments have more down-to-earth implications and benefits for the rest of humanity. Prolonged periods in a microgravity environment can lead to loss of bone and muscle strength.

How this occurs and how it can be reversed is helping inform treatments for people living with chronic conditions like osteoporosis or whose muscles are affected by conditions that limit their mobility.

The ISS is also one of three main space platforms used to study climate change. It is fitted with numerous devices that observe Earth, and astronauts also take regular photos of our planet from the space station.

The ISS sees the sun rise and set 16 times each day, and this vantage point gives it the ability to collect unique information. "It is a fundamentally different data set than most other remote sensing instruments collect on free-flying satellites,” says William Stefanov, Manager of the Exploration Science Office at NASA’s Johnson Space Center in Houston.

The World Economic Forum's Global Future Council on Space examines the role of space technologies in getting to net zero in its white paper, Space and Net Zero.

"More than 50% of essential climate variables are measurable only from space," it says. "Many satellites measure different weather, climate change and other properties of Earth, providing data on greenhouse gas emissions and insight into the consequences for all aspects of climate."

When they’re not working on research, the astronauts have a regular checklist of maintenance tasks around the ISS to work through.

The crew gets a daily update from Mission Control on activities they need to complete. That includes checking the life support systems are functioning properly, carrying out regular cleaning procedures and performing software updates.

There are lots of regular activities we take for granted that, on the ISS, are more complicated, such as personal hygiene. Microgravity makes using a toilet a major undertaking. There are leg restraints to keep the astronaut seated securely and an arrangement of fans and vacuum pumps to dispose of waste matter quickly and safely.

Free-floating droplets of water can be hazardous on the ISS, as they could find their way into sensitive equipment and cause problems. The same is true of small particles too, and that has implications for eating in space.

Here on terra firma, we routinely sprinkle salt and pepper onto our meals. Nothing sprinkles in a simple downward direction in space, though, and the risks of tiny grains of pepper and salt getting lodged somewhere they shouldn’t are high. So, they are available in liquid form instead.

The crew of the ISS gets three meals a day and some of the food they eat is no different from what they might enjoy back home. Fruit, for example, and brownies too are available in their natural forms. Other food is stored dry and has to be mixed with water before it is cooked; there is an oven on the ISS, but there are no refrigerators.

There is also plenty of free time and a range of non-research activities for the crew. In 2013, the Canadian astronaut Chris Hadfield recorded himself playing and singing a version of David Bowie’s song Space Oddity, which has been viewed almost 49 million times on YouTube.

Astronauts regularly share stories and photos via social media, keeping in touch with space-watchers far below. They also take part in educational sessions via video, discussing science and space with school students around the world.

The ISS is the third brightest object in the night sky and clearly visible when there’s no cloud cover. It moves much faster than anything else you are likely to see up there, too. While a typical aeroplane travels at around 965 km/h, the ISS moves at 28,000 km/h. Unlike a plane, there are no flashing lights on the ISS and it travels in a perfectly straight line.

The best time to see it is shortly before or after sunrise or sunset. That’s because it is still reflecting the sun’s rays from its elevated orbit, which makes it easier to see.