On Monday, the International Space Station (ISS) celebrated the 25th anniversary of the launch of the first module into space.
The Zarya module arrived in low Earth orbit in November 1998 and was joined by the Unity module less than a month later.
In a quarter of a century, the orbital outpost has hosted 273 people from 21 countries, with visitors working on more than 3,000 research and educational investigations.
To mark the station’s 25th anniversary, here are 11 FAQs about the ISS:
How big is the ISS?
NASA describes it as “bigger than a six-bedroom house.” The ISS actually measures 357 feet (108 meters) from end to end, which is about the size of an American football field. It includes six dormitories, three bathrooms, a gym and numerous research facilities.
How fast is the ISS traveling?
The space station travels at about 17,500 mph (28,000 km/h) and orbits the Earth every 90 minutes. This means the crew aboard the station experiences 16 sunrises and sunsets each day. Some of them were captured in stunning time-lapses.
How long do astronauts stay on board the station?
Astronauts typically stay for about six months, although some come for a shorter period while others stay much longer. In October 2023, Frank Rubio returned to Earth after spending 371 days in space – the longest time spent in orbit by a NASA astronaut. His mission was initially scheduled to last six months, but a problem with his spacecraft extended it to more than a year.
What is the maximum number of people who have stayed on the ISS at one time?
The station usually accommodates around six people, but on a few occasions it has had up to 13 on board. This is usually due to crew changes and usually doesn’t last too long.
Where on the ISS can you get the best views of Earth?
Thanks to its seven windows, the station’s Dome module offers an unrivaled view of the Earth. This is where astronauts often go in their free time. Some people take a camera and record what they see. French astronaut Thomas Pesquet, for example, always carefully researches which part of the world the ISS will fly over at any given time so he can get the best shots.
Has the station ever been in danger?
Yes. With so much space debris orbiting Earth, there is always a risk that a piece of debris could crash into the facility. Most of them are out of the way, but if a large chunk is spotted, ground controllers can change the installation’s orbit to avoid it. In 2021, astronauts were ordered to take shelter in their spacecraft for a short time when a cloud of debris was thought to be heading their way. Fortunately, the ISS avoided any damage and everyone on board was able to continue as usual.
Can you see the ISS from Earth?
Yes, and you don’t need a telescope or even binoculars to see it. You just need to know when to look up. NASA has helpfully launched an app to make it easier to locate the station as it passes overhead at an altitude of around 250 miles.
How do astronauts use the bathroom?
Astronauts always say this is the question they get asked the most. As you can imagine, such a task cannot be carried out in the usual way due to microgravity conditions. To ensure a mess-free visit to the toilet, engineers designed a special contraption that uses a suction tube for urine (which is filtered and recycled for drinking water) and a small space to deposit solid waste. For a closer look at how the ISS toilets work, check out this explainer.
Will the ISS remain in orbit for another 25 years?
Unfortunately not. Its aging design means it is becoming increasingly difficult and expensive to maintain. The current plan is to continue operating the ISS until 2030. The following year, NASA and its partners will carefully lower the orbital facility to a point where much of it will burn up upon entering Earth’s atmosphere.
So, will the same be true for long-term stays in space?
Certainly not. NASA is already partnering with private companies to build new space stations to continue where the ISS left off. One such company is SpaceX, which is working with Los Angeles-based startup Vast and could become the first to launch a new module as early as 2025. China also has taikonauts aboard its own space station in low Earth orbit, and NASA plans to build a base on the Moon for long-term astronaut stays.