On Monday, the International Space Station (ISS) marked 25 years since the first module was launched 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.
Across a quarter of a century, the orbital outpost has hosted 273 people from 21 countries, with the visitors working on more than 3,000 research and educational investigations.
To mark the station’s 25th birthday, here are 11 FAQs about the ISS:
How big is the ISS?
NASA describes it as “larger 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 sleeping quarters, 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 kph), orbiting Earth every 90 minutes. This means the crew aboard the station experiences 16 sunrises and sunsets every day. Some of these have been captured in amazing time-lapses.
How long do astronauts stay aboard the station?
Astronauts usually stay for about six months, though a few come for a shorter period of time while others stay much longer. In October 2023, Frank Rubio returned to Earth after spending 371 days in space — the longest period of time spent in orbit by a NASA astronaut. His mission was originally scheduled to last for six months but an issue with his spacecraft saw it extended to more than a year.
What’s the largest number of people to have stayed on the ISS at one time?
The station usually hosts around six people, but a couple of times it’s had as many as 13 on board. This is usually due to crew changeovers so doesn’t usually last too long.
From where on the ISS can you get the best views of Earth?
Thanks to its seven windows, the station’s Cupola module offers unparalleled views of Earth. It’s where astronauts often go during their time off. Some grab a camera and record what they see. French astronaut Thomas Pesquet, for example, always carefully researches what part of the world the ISS will be passing over at any given time so that he can get the best shots.
Has the station ever been in any danger?
Yes. With so much space junk orbiting Earth, there’s always a risk of a piece of it hitting the facility. It’s out of the way of most of it, but if a large piece is spotted coming its way, ground controllers can alter the facility’s orbit to steer clear of it. In 2021, the astronauts were ordered to seek refuge in their spacecraft for a short time when a cloud of debris was believed to be heading its way. Thankfully, the ISS avoided any damage and everyone on board could carry on 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 easy to spot the station as it passes overhead at an altitude of about 250 miles.
How do astronauts use the bathroom?
Astronauts always say that this is the question that they get asked the most. As you can imagine, such a task can not be performed in the usual way due to the microgravity conditions. To ensure a mess-free visit to the bathroom, engineers designed a special contraption that uses a suction tube for urine (which is filtered and recycled for drinking water) and a small space for depositing solid waste. For a closer look at how the ISS toilet works, check out this explainer.
Will the ISS stay in orbit for another 25 years?
Sadly not. Its aging design means that it’s getting harder and costlier 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 as it enters Earth’s atmosphere.
So, will that be it for long-duration stays in space?
Certainly not. NASA is already partnering with private firms to build new space stations to carry on from where the ISS left off. One of those companies 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 staying aboard its own space station in low-Earth orbit, and NASA has plans to build a base on the moon for long stays by astronauts.
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