A laboratory that orbits Earth
The International Space Station, or ISS, is a large research laboratory circling Earth at roughly 400 kilometers up. It was built in pieces by space agencies from the United States, Russia, Europe, Japan and Canada, and has been continuously occupied since November 2000. It is about the size of a football field when counting its solar arrays, and the pressurized living and working space is comparable to a large house. A typical crew is around six or seven people, who usually stay for about six months, though some missions are shorter or longer.
The station travels at roughly 7.7 kilometers per second, so it circles Earth about every 90 minutes, a consequence of the physics described in how a rocket reaches orbit. That means the crew sees about 16 sunrises and 16 sunsets in each 24-hour day.
Why everything floats
Astronauts float because they are in continuous free fall. Gravity at the station’s altitude is still around 90 percent as strong as at the surface, but the station and everything inside it are falling around Earth together, so nothing presses against anything else. Scientists call this microgravity.
This changes ordinary tasks. Objects drift away unless fastened. Handrails, foot loops and Velcro are everywhere. Liquids form floating blobs. Crumbs and dust float into the air and eyes, so food and the cabin environment are managed accordingly. Astronauts move by gently pushing off surfaces, since a hard push sends them across the module.
The daily schedule
Station time is set to Coordinated Universal Time (UTC) because crews come from different countries and the sun cycle outside is meaningless. A typical day starts with waking up, a quick wash, breakfast and a planning conference with teams on the ground. The workday is mostly scheduled, with time for science experiments, maintenance and repairs, and communication with mission control. The crew typically works for about eight hours or more on weekdays, with lighter weekends. Crews also make time for calls with family and sometimes to the public.
Sleeping
There is no up or down, so astronauts sleep in sleeping bags attached to a wall in small private compartments or in alcoves. Bags are tethered because a loose sleeper would drift into equipment. Some say that sleep feels unusual without the sensation of weight, and arms tend to float up in front of the body. Light from frequent sunrises is blocked with covers, and sleep quality can vary between individuals.
Eating and drinking
Food is mostly packaged. Some meals are dehydrated and rehydrated with hot water, and others are ready to eat in pouches or cans. Sticky foods are easier to handle than crumbly ones. Salt and pepper are used in liquid form because loose grains would float. Drinks are sipped from sealed pouches with straws. Fresh items, such as fruit, arrive on supply ships and are usually eaten quickly. Crews often eat together, and meals are an important social time.
The sense of taste can feel muted in orbit, which some astronauts attribute to fluids shifting toward the head. This is one of the many ways the human body responds to spaceflight, and individual experiences vary.
Exercise
Without gravity to push against, muscles and bones lose strength more quickly than normal. To limit this, astronauts exercise about two hours a day using a treadmill, a stationary bike and a resistance machine, all designed to work in microgravity and often with harnesses or restraints. Even so, bone density and muscle mass can drop during long stays, and crews follow structured rehabilitation after returning to Earth. Other known effects include fluid shifting toward the head, changes in vision for some people, and temporary problems with balance on return. Researchers study these effects to understand health on long missions and also on Earth. This information is general; the medical details for any individual are managed by flight surgeons.
Washing and the bathroom
There are no showers. Astronauts clean up using wet towels and rinseless soap, and they wash hair with a small amount of no-rinse shampoo. Clothes are worn for a few days and then discarded, since laundry is not practical. The toilet uses airflow, instead of gravity, to pull waste away, and users strap themselves in. Used air is filtered.
Water is precious because every liter has to be launched from Earth or recycled. The station’s systems capture moisture from the air, and recycle wastewater, including urine, into drinking water. This mirrors natural processes like the water cycle on a small scale, and it is a key technology for future long missions. Electricity comes from large solar panels, and batteries supply power while the station is in Earth’s shadow.
Work and science
The main reason for the station is research. Experiments cover human health, biology, materials, fluids and combustion, which behave differently without gravity. Others use the station’s position to observe Earth or space. Crew members run experiments, take samples, perform maintenance and sometimes act as test subjects themselves. Researchers on the ground design many of the experiments and receive the data.
Occasionally, astronauts go outside for a spacewalk to repair equipment or install new hardware. Each takes careful planning, since they wear pressurized suits, use safety tethers and work for several hours. Cargo ships, some robotic, deliver supplies and carry back samples.
Staying well mentally
Living in a small group of people in an enclosed space for months presents psychological challenges. The crew has regular contact with ground teams, scheduled time off, hobbies, and views of Earth that many describe as a highlight. Mission planners pay attention to workload, privacy, sleep and group dynamics. As with physical health, these topics are the subject of ongoing research, and findings may not apply to everyone.
Why it matters
The station shows how people can live and work away from Earth for extended periods, and it provides practical experience for future journeys. Its lessons about recycling, health and teamwork also apply to long trips, such as a journey to Mars. At some point the station is expected to be retired and replaced by other platforms, with its schedule determined by the participating agencies.