Science & Tech

 Space Laboratory: ISS

The International Space Station (ISS) is the largest man-made object built outside the Earth. The activities on the ISS, which moves an average of 400 km above the Earth's surface, are carried out in cooperation with the US, Russian, European, Japanese and Canadian space agencies.

The ISS has experimental modules and equipment that allow scientific experiments to be conducted in different areas. So why was it necessary to conduct experiments on a spacecraft orbiting the Earth?

All living things and objects on Earth are pulled towards the centre of the Earth by the Earth's gravity. Researchers who want to eliminate the role of this effect on scientific research are conducting experiments in environments where the effects of gravity are minimized - called weightless environments.

What is a Weightless Environment?

First, let's focus on what exactly is meant by the term weightless environment. Imagine that you stand on a scale to measure your mass. Gravity pulls you towards the center of the Earth. The scale prevents you from accelerating towards the center of the Earth. You apply a force equal to your weight on the scale. The scale also applies an equal but opposite force on your body. Your weight acting on the scale is what allows the scale to measure your mass. Now imagine that you put a weight on the scale and let it fall freely in space. You cannot read any value on the scale. Because the weight and the scale do not exert any force on each other while accelerating towards the center of the Earth under the influence of gravity.

 In the theory of general relativity, movements made "only" under the influence of gravity are called "free motion". Freely moving objects do not feel any force on them, even if they are accelerating under the influence of gravity. Weightless environment experiments are experiments conducted under conditions where objects can move freely under gravity and where their movements under the influence of gravity are not obstructed by other objects.

 It is difficult to create an ideal weightless environment. However, conditions close to ideal can be approached in various environments. For example, there are two separate "free fall" facilities at NASA Lewis Research Center. Experimental equipment is released from various heights inside an air friction shield in these facilities. Since they are not in contact with the shield they are in, they move relatively freely. Before being stopped by air cushions located under the towers, the experimental equipment falls for 5.2 seconds in the 132-meter-high facility and for 2.3 seconds in the 24-meter-high facility. The facility that allows objects to remain in a weightless environment for the longest time on Earth is located in Japan. Experimental equipment falls freely for approximately 10 seconds in a 490-meter-high shaft located in an old coal mine.

Weightless environment experiments are also conducted with airplanes. With parabolic planes, a weightless environment can be experienced for 15-25 seconds at approximately 10 kilometers above the Earth. Similarly, weightless environment experiments can be conducted with sounding rockets that move in a parabolic motion. These rockets, which can reach much higher altitudes than planes, fall freely for a few minutes before re-entering the atmosphere and starting to feel air friction.

There are space laboratories specifically established for weightless environment experiments that orbit the Earth. Weightless environment experiments that continue for very long periods can be conducted at the International Space Station, established in cooperation with the US, Russia, Canada, Japan and European space agencies, and at China's Tiangong Space Station.

Let's say once again that all of these facilities, vehicles and laboratories are actually under the influence of the Earth's strong gravitational pull. The acceleration of gravity on Earth is approximately 9.8 m/s. Even in space stations that orbit at an altitude of approximately 400 kilometers, this value drops to only 8.7 m/s². The degree to which these environments are weightless is proportional to the degree to which they can fall freely. For example, the force experienced by experimental equipment in parabolic airplanes is one percent of the gravitational force experienced on Earth. In sounding rockets that leave the atmosphere, this value drops to one hundred thousandth. The force experienced in space laboratories is almost zero.

Advantages of Experimenting on the International Space Station

A weightless environment affects many scientific processes. For example, bone density decreases in space. It is thought that the reason for this situation is the slowdown in the formation of osteoblast cells responsible for bone formation due to the decrease in the load acting on the bones in weightless conditions. Plant growth processes are also affected by gravity. Experiments conducted on the ISS show that the growth direction of plant roots and stems becomes irregular in weightless conditions.

There are also changes in the functioning of physical and chemical processes in a weightless environment. For example, surface tension, adhesion and cohesion forces become decisive in the movement of fluids. In addition, convection, one of the ways heat is spread on Earth, does not occur in a weightless environment.

Although substances with different densities on Earth separate according to density differences, they can mix homogeneously in a weightless environment. For example, while a water-oil mixture forms a separate heterogeneous mixture on Earth, it can mix homogeneously on the ISS.

Thanks to these unique effects of the weightless environment on physical processes, materials with superior functional properties can be developed. For example, single crystal materials, which are critical materials in the field of aviation and space, can be successfully produced in weightless conditions.

In addition, experiments conducted on the ISS can determine the reactions of living beings, electronic devices, and materials to weightless conditions in space, high-energy radiation, and temperature changes.

Experiment Modules and Equipment on the International Space Station

Scientific research is conducted on the ISS in five main categories: physics, life sciences, remote sensing, technology, and education.

In the modules where scientific research is conducted on the ISS, standard-sized units are used so that equipment can be easily placed and replaced. These units are called international standard payload racks (ISPR).

Kibo

Kibo, one of the modules where scientific experiments are conducted on the ISS, was established by Japan. Kibo, the largest module on the ISS, consists of four main components. The PM module is the environment where astronauts conduct experiments, and the pressure, temperature and humidity conditions inside are similar to those on Earth. The EF module, which is directly exposed to outer space conditions, can conduct experiments on the long-term effects of open space conditions. The logistics module stores experimental equipment, samples and other support equipment. In addition to the equipment used to conduct experiments, the Kibo module also contains a robotic arm. The robotic arm is used to transport experimental equipment as well as to place small satellites such as cube satellites into orbit.

Destiny

Established by the US in 2001, Destiny is the first scientific laboratory module of the ISS. The Destiny module has a diameter of 4.2 m and a length of 8.5 m. There is an observation window in the Destiny module. There is also a closed experimental cabin that allows astronauts to work safely with samples during scientific experiments. This equipment, called the Weightless Environment Scientific Experiment Cabin (MSG), conducts research in the fields of material science, biotechnology, fluid dynamics, and crystal growth.

columbus

Columbus, the third experimental module on the ISS, was built by ESA. The 4.5 m diameter and 6.9 m long laboratory was sent into space in 2008 and installed on the ISS. The Columbus module includes the Biolab, where studies on microorganisms, cells and tissue samples are conducted; the European Physiology Module, where the effects of weightlessness on human physiology are studied; and the Fluid Science Laboratory, where the properties of fluids in weightlessness are studied. Columbus also has two components that are directly exposed to outer space conditions.

Nauka

Nauka, the Russian experimental module, was launched in 2021 and installed on the ISS. The 13-meter-long module has a mass of approximately 20 tons. The Nauka module has an ESA robotic arm on it.