The idea of a space station was very old and existed only in the imagination. But in the 1940s, the international community showed interest in building such a structure in space to conduct different experiments that are unable to be performed here on Earth.

As the Space Age began, the Space community proposed various spacecraft designs. In 1969, the first space station was built by combining two Russian Soyuz vehicles in space. On January 25, 1984, President Ronald Reagan asked NASA to make an international space station within ten years. The construction of the ISS began in 1998. It took ten years and more than 30 missions to set up the systems.

Five space agencies representing 15 different countries took part in the construction of the ISS. These space agencies include NASA (United States), Roscosmos (Russia), JAXA (Japan), ESA (Europe), and CSA (Canada). The first mission, to send material for the ISS construction, was launched in November 1998. In the year 2000, the first crew visited the space station and stayed there for several months. In 10 years, the space station was completed. However, as we progress with technology, scientists were making more useful and new devices to attach to the ISS to perform further research.

The International Space Station (ISS) is the most expensive object humans have ever built. It cost 150 billion USD. But why was there a need to spend so much money on a space station?

NASA ISS Mission statement

“The primary objective of the ISS is to support scientific research and other activities requiring the unique attributes of humans in space.”

The idea was to build a space station to perform experiments and observations, which we cannot do here on Earth. Different experiments such as those that need to be performed in zero gravity or space were motivations for building such a giant laboratory. Scientists can carry long time experiments there, even for decades. Humans have been thinking about visiting other planets. The space station was the first platform to experience traveling and living life in space. In the future, ISS can be used as a transit point for various missions to go to the moon, Mars, or other objects in the Solar System or beyond.

The International Space Station was built in 10 years, with more than 30 missions, to deliver different segments. The ISS construction started on November 20, 1998, when the first segment of ISS was launched. Zarya, the first module of the International Space Station, provided electrical power, storage, propulsion, and guidance to the ISS during the initial stage of assembly. Now, it is only used for storage.

The next segment was the first U.S built component, named Unity. It was launched on December 4, 1998. It links the Russian and U.S modules together, and it is where the crew eat meals.

Finally, on November 2, 2000, the first crew was sent to ISS. Two Russian astronauts with a U.S commander lived there for several months. After that, different ISS segments were sent in various missions like the U.S Lab module, ESA’s Columbus laboratory, Japanese Kibo laboratory module, etc. Its main construction was completed in 2011, but as the technology improved and new experiments were designed, the ISS continues to evolve with modified components.

The International Space Station is orbiting the Earth in Lower Earth Orbit (LEO). LEO usually has a maximum altitude of 2,000 km and a minimum of 160 km from the Earth’s surface. It has an orbital period of 128 minutes or less, which means that it takes 128 minutes or less to complete a round of the orbit. The International Space Station is 250 miles above Earth’s surface and moves at 28,000 km per hour. The high speed of the satellite is due to its orbit. But why is the ISS in LEO? Why not in higher orbits, as there are already some satellites there? Well, there are pretty good reasons for the station to be in LEO. The International Space Station is below the inner Van Allen radiation belt to avoid the threats by the radiation belt. In LEO, it is easy for supply vehicles to go there. Another reason for placing it in LEO was that it is higher than the upper atmosphere so that the air drag will be minimized. The need to re-boost the orbit will also be reduced.

Van Allen Radiation belt is a zone of very high energy particles that comes from the Sun in the form of the solar wind. When these high energetic particles come in contact with Earth’s magnetic field, it creates a layer of these highly energetic particles. There are two such layers around Earth but other temporary layers can also form. If ISS would be in this radiation belt, the high energetic particles of this belt can provide heavy damage to the space station and destroy it. To avoid this, ISS is kept below the radiation belt.

As we know, ISS was built to perform different science experiments, which we are unable to perform here on Earth. Astronauts are living there for two decades, and they have conducted nearly 3,000 experiments. Experiments related to various fields are done on the ISS, including Astrobiology, astronomy, physical sciences, materials science, space weather, meteorology, and human research, including space medicine and the life sciences. One of the famous experiments performed on the ISS is the Alpha Magnetic Spectrometer (AMS), which aimed to detect Dark Matter, a challenging physics problem. Research done on ISS helped to conclude that microbes such as extremophiles can handle the space’s extreme conditions. Extremophiles, famously known as the Immortal Animals.

Researches related to medical fields have improved our understanding of how space weather influences humans during long space travels and what we can do to avoid those dangers. Recently, in an August 2020 report, scientists confirmed that bacteria from Earth survived the extreme temperature of outer space for three years, which led scientists to have faith in a hypothesis called Panspermia. This hypothesis states that life exists throughout the universe, distributed in various ways, including space dust, meteoroids, asteroids, comets, planetoids, contaminated spacecraft, etc. These are only a few examples of what scientists do on the International Space Stations. Many experiments were only possible to conduct on ISS and revolutionized our understanding of the cosmos.

ISS is a modular space station, which means more modules can be added or removed, making it a good flexible structure. There are various parts of the International Space Station. The main critical components are the

• Integrated Truss Structure
• Radiator panels,
• Other different equipment for experiments like AMS, etc.

The Integrated Truss Structure(ITS) holds the solar arrays which generate electricity from solar energy. ITS is the largest external component of ISS and it consists of ten separate segments.

Radiator panels (External Active Thermal Control System, EATCS), which are mounted on ITS, remove heat from the station and maintain an equilibrium in the ISS.

Other parts are like robotic arms, which helps in the maintenance of the station through moving supplies, equipment, and even astronauts.

There are dock ports there which help in transferring supplies and crews in the stations. There are 16 pressurized modules in the ISS. Astronauts live and work here in these modules. Zarya was the first pressurized module launched. Unity or Node 1 is cylindrical modules with six berthing location (location where other modules can be connected with Unity) to connect with other modules.

The next module is Zvezda, which is responsible for the life-supporting systems of the station. The destiny module is connecting with Unity through its berthing location. This is the modules where NASA performs different experiments. That’s why it is also called U.S Lab. Other modules are Pirs and Poisk, Quest, Harmony, Tranquility, Columbus, Kibo, Cupola, Rassvet, Leonardo, Bigelow Expandable Activity Module (BEAM), International Docking Adopter (IDA), and Bishop Airlock Module. ISS is evolving and new components are becoming part of it as are inventing new technologies and experiments for exploration purposes.

ISS is evolving, and new components are getting augmented or improved as the technology matures or the need arises.

Living in outer space is very harmful. These include exposure to harmful radiation from the Sun, the danger of space debris, the risk of losing life support systems such as cabin pressure, food, water, etc., and many other risk factors. In the making of the International Space Station, all these risks were kept in mind. That’s the reason many astronauts have visited and lived there for several months. To avoid the dangers of living in space, no astronaut lives more than six months in the ISS. But one man has made a record for spending a long time in the ISS. He is a Russian astronaut named Valery Polyakov. He spent 437 days aboard the ISS.

Astronauts on ISS, live in pressurized modules, where conditions for life are maintained such as the suitable temperature, oxygen supply, etc. Most of the oxygen on the station is generated through the process of Electrolysis of wastewater, sweat, and even urine. In this process, water is decomposed into hydrogen and oxygen with the use of electricity from the solar panels of the ISS. When electricity passes through water, it splits water into hydrogen and oxygen. This oxygen then becomes part of ISS’s atmosphere. Well, scientists are very smart and they use that hydrogen to make water again using simple chemistry. Astronauts combine this hydrogen with the carbon dioxide they breathe out and make water out of it.

Food supplies are provided from Earth through different rocket missions. Astronauts in space station have to be physically and mentally fit all the time. So, they do proper exercises there and also do medical experiments to determine how their bodies are adjusting to microgravity environments for a long period of time. All-day, they are working on different experiments and monitoring them on the ISS.

Cargo Spacecraft is the robotic spacecraft that is built to supply the necessary things like food, propellants (A chemical substance used in the production of energy or pressurized gas that is subsequently used to create the movement of a fluid or to generate propulsion of a vehicle, projectile, or other objects), and other supplies to the ISS. Russian cargo spacecraft, American, Japanese, and European space agencies have been sending the necessary ISS supplies. Now, Elon Musk’s SpaceX has also entered the game, and SpaceX is sending supplies and astronauts for NASA to the ISS. On May 30, 2020, SpaceX sent two NASA astronauts to the ISS. It was the first time when a private space agency sent astronauts into space. SpaceX has docked two spacecraft to the space station.

When astronauts get out of the spacecraft or any other space vehicle, it is called a spacewalk. The spacewalk is also called EVA, which stands for extravehicular activity. During the spacewalk, the astronauts are entirely out of the station. However, they remain closed to the station or spacecraft to avoid floating away into space accidentally. They can stay out of the vehicle for several hours during the spacewalk, depending on the job.

Russian astronaut Anatoly Solovyev holds the world record for the most spacewalks. He did 16 spacewalks and remained for a total of 82 hours out of the station. There are different reasons why do astronauts go for a spacewalk. By going on spacewalks, they can repair and fix different parts of the ISS and test new equipment. Spacewalk also helps in understanding various space behaviors and phenomena. It seems exciting, but it can be very dangerous. So, astronauts prepare themselves for hours before going for a spacewalk. These spacesuits are pressurized and filled with oxygen, which they need to breathe. They also took water with them to drink.

One of the main benefits of the oxygen in their spacesuits is that it provides astronauts to breathe pure oxygen and the astronauts get rid of the nitrogen in their bodies. This process is called Nitrogen purging. This process starts few hours before the Spacewalk. Removing nitrogen from the Astronaut body can benefit them in many ways. When astronauts are in the space station, pressure there is higher. When astronauts go for a spacewalk outside the station, the pressure there is very low. During their stay in the station, nitrogen can get dissolved into their blood and tissue and that sudden movement of astronauts from the high-pressure environment to low pressure environment cause that dissolved gas to create bubbles in their bodies and can even block blood flow. So, the absence of nitrogen prevents bubble formation. Otherwise, it will make them physically unfit and will affect the work they are doing.

Another thing that keeps Astronauts safe during a spacewalk is SAFER. SAFER stands for Simplified Aid for EVA Rescue. It has small jet thrusters that help astronauts fly back to the station if they are unbound and floating away from the space station.

As it is obvious from the term, microgravity means small gravity. It is when things are in a state of weightlessness. When you go away from Earth, its gravitational influence begins to decrease. On the ISS, the gravity is weaker than here on the Earth’s surface. If you weigh 100 pounds here on Earth, you will weigh 90 pounds there. As ISS is in free-fall, astronauts there are in a state of weightlessness. It means they can’t walk as we do here on Earth, but they float. But why is this the case? It’s just 250 miles above Earth, and gravity is not that weak there. Then why it doesn’t fall to Earth? Let’s understand this with a simple example.

When you throw a ball up, it will cover some distance and then due to Earth’s gravity, it will fall back, with a curved path. If you increase the speed of the ball, the ball will cover more distance and the curvature of the ball’s path will increase. Now, imagine you are standing on the top of a very high location in the world. When you keep throwing the ball with higher and higher speed, a time will come when the curve of the ball’s path will match Earth’s curvature. At this point, the ball won’t fall back to Earth. It will start orbiting around it. This is called Free-fall. The same happens with ISS. Its path’s curvature matches Earth’s curvature and it keeps orbiting the planet instead of falling. As the ISS is moving very close to Earth, it sometimes moves towards the Earth and can enter into Earth’s atmosphere.

To prevent this, thrusters are used to move the ISS upward. But in the whole journey around the Earth, astronauts feel completely weightless. Working for a long time in weightlessness can cause many problems for astronauts. That’s why they do different exercises there to maintain their fitness. Interestingly, in ISS, astronauts can move heavier objects just by pushing them with the tip of their fingers due to weightlessness. When fire burns on ISS, its flame has a round shape. Crystals can grow better as their shapes are more perfect without gravity. Though this microgravity situation is very dangerous for astronauts, it has also proven very useful for different science experiments.

Recycling is the process of making used things re-useable. It is very important in the International Space Station. We know that food, water, and other supplies are provided to the astronauts through Cargo Missions, which are very expensive. On ISS, astronauts are trained to recycle things to avoid more expenses. For example, 90% of the water on ISS is recycled. On ISS, astronauts stretch the use of water. Water is recycled from the sweat droplets and carbon dioxide of the astronauts. Water performs a double role. When it is decomposed into hydrogen and oxygen, hydrogen again takes part in the formation of water and oxygen becomes the part of ISS’s atmosphere. This is done through a process called Electrolysis, which we have discussed in detail. On ISS both water and oxygen are recycled through this technique. Another interesting thing about ISS is the recycling of plastic materials. A 3D printer on ISS, called the Fabricator, can recycle the plastic and make it re-useable. This 3D printer will use the used plastic objects and make new 3D things that astronauts need like plastic bags, plastic syringes, or custom-made wrenches, etc. These are a few examples of recycling on ISS. There are many other things that are recycled and used again on ISS such as plastic waste etc.

The communication between ISS and the Earth is very crucial. The connection between the crew on the space station and the Ground support team on the Earth makes the astronauts achieve the objectives. It is essential for different space activities like spacewalks and performing various experiments there. Astronauts live there for an extended period, so communication is necessary for the astronauts to talk to their families. There is a whole group of satellites called Tracking and Data Relay Satellites or TDRS for communication purposes, connecting the space station with the Earth. These satellites are located more than 22,000 miles above the Earth, in Geosynchronous Orbit. When an astronaut wants to communicate or transmit data to a support team on Earth, the data will be converted into radio-frequency signals. TDRS then sends these radio signals to ground-based stations. The ground-based station will then convert the radio frequency signals to readable data. The space station can connect to Earth only when the ground-based antennas are in light of sight of the station’s position. ISS completes its trip around the Earth in one and a half hours, and in this time, the station gets less than 15 minutes when it can transmit data to Earth.

The interesting question here is why we only use Radiofrequency to communicate between the space station and the Earth. The reason is that not all the frequencies can pass through the Earth’s atmosphere. Ultraviolet and other higher frequencies get absorbed by different atmosphere components. But some frequencies don’t. The most obvious one is the visible light wavelength. For the same reason, you can’t see the stars on a cloudy night sky, as the visible light gets absorbed. So the most effective one is the radio frequency for space communication. That is why astronauts on ISS use radio frequency signals to communicate with the support team on Earth. Though radio waves are effective in space communication, we can’t use the radio waves’ whole frequency range for communication purposes. Radio waves with a frequency range from 30 MHz to 30 GHz, can only be used for communication purposes.