ISS Anniversary: Here’s How (And Why) Humans Have Lived in Space For Over Two Decades

Happy birthday, ISS.
Maia Mulko
Exterior views of the ISS Source: NARA

The first components of the International Space Station (ISS) were launched on November 20, 1998, roughly 12 years after the first Soviet MIR-2 module was launched and a full 25 years after Skylab

The ISS took 10 years and more than 30 missions to assemble. It is the result of unprecedented scientific and engineering collaboration among five space agencies representing 21 countries: NASA (United States of America), Roscosmos (Russia), JAXA (Japan), CSA (Canada), and ESA (16 EU countries and the UK).

With fully-equipped laboratories and advanced life support systems powered by solar arrays, the ISS has space for up to seven crew members to live and work, conducting many kinds of research in low Earth orbit. 

Let’s explore (and celebrate) one of the most impressive pieces of engineering ever created.

What is a modular space station?

The ISS is a modular space station. This means that it’s made of several pressurized modules (currently 16). These were launched at different times in the ISS' history. 

ISS blueprint
Source: Daniel Molybdenum/Flickr

The first modules – the Russian-built Zarya ("Sunrise") cargo block, and the U.S.-built Unity connecting node – were launched in 1998. On Dec. 6, the STS-88 crew captured Zarya and mated it with Unity inside the shuttle's payload bay. Despite never having been in the same hemisphere, the two pieces mated together perfectly.

However, these first two modules lacked a long-term life support system and that’s why the ISS wasn’t occupied until 2000. By that time the Zvezda Service Module had been added. This provided station living quarters, life support systems, electrical power distribution, data processing systems, flight control systems, propulsion systems, communications systems, and a docking port, and served as the early cornerstone for the first human habitation of the station.

Zvezda was followed soon after by the first sections of the Integrated Truss Structure. This has a total of 11 segments that act as attachment points for solar arrays, thermal control radiators, and external payloads as well as electrical and cooling utility lines and the Mobile Transporter rails. 

The Nauka ("Science") Multipurpose Laboratory Module, launched July 21, 2021, is the latest module of the ISS. It serves as a science facility, docking port, and spacewalk airlock for future operations. There are also plans to add at least one more module to the ISS. 

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What is the purpose of the ISS?

The main purpose of the ISS is as a base to conduct scientific research in the fields of astronomy, astrobiology, meteorology, chemistry, space weather, space medicine, and more. 

For that, it contains seven research or laboratory modules: Columbus (ESA), Destiny (NASA), Rassvet and Poisk (Russian Mini-Research Module 1 and 2 respectively), Kibo (Japanese Experiment Module), and Nauka (Multipurpose Laboratory Module). Besides the labs, the ISS also has additional scientific hardware located at different points around the station. 

Materials Science Research Rack
Materials Science Research Rack. Source: NASA/Flickr

Around 3,000 scientific studies or experiments have been performed on the ISS. Science aboard the ISS has blossomed as astronauts have devoted more time to research. Many of these studies aim at identifying the effects of microgravity on the human body and how materials behave in space.

Ultimately, many of these studies could help pave the way for humans to travel and reside in space for a long time without suffering from muscle atrophy and bone loss — some of the most common health problems related to weightlessness. In fact, the ISS crew members must exercise for about two hours each day to avoid these issues. This is why the ISS is equipped with a space-adapted treadmill, a stationary bike, and weightlifting equipment. 

Other studies focus on Earth’s atmosphere and on the Sun’s cosmic rays. The ISS crew has also conducted research on cosmic dust, dark matter, and antimatter in the universe, among many others

Life on the ISS

Life on the ISS is possible thanks to advanced life support systems providing air, water, and food. 

Most of the oxygen used on the ISS is generated through electrolysis, a process in which electricity from the station's solar panels is used to split water into hydrogen gas and oxygen gas. The oxygen is released into the spacecraft’s atmosphere so that astronauts can breathe. Exhaled carbon dioxide is removed using zeolite, a sponge-like material that absorbs CO2. 

But where does the water come from? It would be too difficult and expensive to take water from the Earth to the ISS. Consider that at least 4000 gallons of water per year would be needed to sustain a four-people crew (and there’s room for seven in the ISS). So it’s more practical to produce it up there, or rather, reuse it. 

The ISS's Water Reclamation System (WRS) takes water from the astronauts’ urine, as well as from humidity and condensation on the station, and purifies it to turn it into potable water.  Some water is also shipped from the Earth to the station to ensure that there's enough "fresh" water being mixed in for the crew. 

The crew uses this water to produce oxygen, drink, and wash. There are no showers on the ISS because water doesn’t fall down in microgravity. Instead, the astronauts use liquid soap, water, and rinseless shampoo. They squeeze liquid soap and water from pouches onto their skin and towels to wipe off the excess water. 

As for food, it is brought to the ISS from Earth as pre-prepared meals in zip lock bags and cans. The astronauts have microwaves and convection ovens to cook with. Much of the food is dehydrated so that it doesn’t spoil or become contaminated. But astronauts also have some fresh foods (mainly fruits and vegetables) refrigerated in the spacecraft. Their food supplies are usually re-stocked by an automated transfer vehicle every two months. 

The ISS crew can also make coffee using a space-adapted coffee machine called ISSpresso. They also have access to tea, lemonade, and orange juice. They must drink it all with a straw though, as the liquids would float away from a glass.

JAXA space food ramen
JAXA ramen. Source: Tnk3a/Wikimedia Commons

After the astronauts eat and drink, they may want to go to the bathroom. Due to microgravity conditions, they must fasten themselves to the toilet. To keep waste from floating off, the ISS toilet has a suction fan that sucks the waste away. 

As for sleeping, the astronauts of the ISS wrap themselves in sleeping bags in small crew cabins. Each crew cabin is just big enough for one person. Given that laying down on a bed is not possible in microgravity, they simply doze off while floating in the sleeping pod. Some astronauts mimic the sensation of pressure from blankets using bungee cords or Velcro their heads to a cushion to get the feeling of lying on a pillow.

How long will the ISS stay in low Earth orbit?

Although the ISS is still working properly, NASA plans on retiring it by the end of the decade. One plan is for private companies to build new space stations. According to NASA’s Director of Commercial Spaceflight, Phil McAlister, NASA envisions being, "just one of many users instead of the primary sponsor and infrastructure supporter," for these new space stations.

This way, NASA could save up to $1 billion dollars every year. It could use this money to fund missions to the Moon, Mars, and perhaps further.

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