How do astronauts eat and defecate in space? The science behind daily life on the ISS

Space travel demands more than just technical skill and physical fitness, it requires astronauts to adapt their most basic routines to a weightless environment. Even basic tasks like eating a meal or using the toilet require engineering solutions. Indian astronaut Shubhanshu Shukla, currently aboard the ISS, recently while talking to Prime Minister Narendra Modi revealed how he shared traditional Indian desserts such as gajar ka halwa and aamras with his fellow crew members. These dishes were prepared and packaged by ISRO and DRDO in dehydrated form, reconstituted on board. But how exactly do astronauts actually eat and defecate in microgravity? Here's a factual look at how these essential routines are managed hundreds of kilometres above Earth.

Eating on the International Space Station (ISS) requires specially designed processes due to the absence of gravity. Without gravity, food and liquids float, so astronauts rely on sealed packaging, magnetic trays, and Velcro-attached cutlery to manage their meals. Meals are mostly thermostabilised or freeze-dried, and rehydrated with a water dispenser before consumption. Food is heated in warm-air ovens.

Astronauts anchor themselves using footholds during meals. Each person has a food tray with fastened packets and cutlery. Bread is avoided to prevent crumbs; tortillas are used instead. Drinks like tea and juice are delivered in pouches with straws fitted with one-way valves to prevent floating liquids.

Astronauts select meals months in advance. Diets are reviewed by nutritionists to maintain muscle mass and bone health. Requirements include higher calcium and vitamin D, and reduced sodium intake. According to NASA, meals range from pasta and chicken to snacks like nuts and dried fruits, 's Johnson Space Center

In microgravity, astronauts use a vacuum toilet system that relies on suction instead of gravity. They strap themselves in place. Waste is pulled into sealed containers using airflow. A camera assists with alignment.

Urine is collected via a funnel system and processed by the Urine Processor Assembly, which recycles over 98 per cent of water back into drinking supply. Solid waste is sealed, stored, and loaded onto cargo craft. Most is incinerated during re-entry into Earth’s atmosphere.

As missions become longer, including lunar bases and Mars trips, space agencies are experimenting with growing crops and microalgae aboard spacecraft. Shukla is participating in ISRO experiments involving seed growth and algae cultivation aboard the ISS, aimed at developing sustainable food sources in space.