Astronaut Falling Infinitely: Gravity Exists in Space

　A spacewalk where they float like a ballon. Outer space is far away from the earth and is not affected by the earth's gravity.

　That's what you might think, but the Earth's gravity is still firmly attached to space.

　Gravity is inversely proportional to the square of the distance. The higher you are, the weaker the Earth's gravity becomes.

　It is true that gravity is weaker in space than on Earth.

　The International Space Station (ISS), an experimental facility where Japanese astronauts also work, is located at an altitude of 400 km, about the distance between Tokyo to Osaka.

　The gravity acting on the ISS is about 90% of that on Earth. The ISS is also subject to sufficient gravity, and just like objects on Earth, the Earth is constantly pulling on it.

　The ISS is still floating in space.

　That's because the ISS itself is moving at high speed.

　The ISS is moving at a speed of 28,000 km per hour. The centrifugal force in the (←) direction and the gravity force in the (↓) direction are subtracted, causing it to fall diagonally in the (↙) direction.

　However, because the point (Land Point) where it will fall is outside the Earth, it cannot fall (Land) forever and continues to move along the circular shape of the Earth.

　Due to this circular motion phenomenon, the ISS continues to fall diagonally forward, but does not appear to be falling and continues to orbit the Earth.

　Inside the ISS, which continues to fall, there is Zero Gravity and people and objects float. This is the same principle as when your body feels lighter for a moment on an amusement park's ride or in an elevator.

　If the centrifugal force (←) is smaller than the gravity (↓), the ISS will fall to Earth. If it is larger, it will leave Earth's orbit and fly away forever.

　The altitude and speed of the ISS are determined by taking into account the balance with gravity.

　Although the ISS is far away, it can actually be seen with the naked eye.

　The exact date and time are published on the Internet, so why not come and see the ISS with your own eyes?

　The same principle applies to geostationary satellites such as the familiar Himawari weather forecast satellite. Geostationary satellites rotate once a day in accordance with the rotation of the Earth. They are called geostationary satellites because they are always stationary when viewed from the ground.

　Both the ISS and geostationary satellites move at high speeds that are impossible on Earth.

　This is possible because the air in space is thinner than on Earth. If the air density was the same as on Earth, the objects would disappear quickly due to friction with the air.

　Both the ISS and geostationary satellites move in a circular motion when viewed from the Earth's perspective, but from a more macroscopic perspective, the Earth is also constantly falling toward the Sun.

　The speed at which the Earth orbits the Sun once a year is balanced with the gravity of the Sun, allowing the Earth to continue rotating without falling into the Sun.

　Space development has been heating up in recent years, but with the development comes the drawbacks.

　One of the problems is the rapid increase in artificial satellites. As of 2021, the total number is 12,000. In recent years, more than 1,000 satellites have been launched per year.

　Satellites in space are basically launched and never released. Many satellites collide with each other, and the ones that deteriorate fall to Earth and into the ocean. It's the same as illegally dumping waste in the ocean.

　By the way, where is the boundary between Space and Earth?

　The air layer (the atmosphere) that covers the Earth becomes thinner as the altitude increase. If we define space as a vacuum (or near-vacuum) state, then it would be about 100 km above the surface, and anything above that would be Space.

　Space development began in modern times, but the (宇宙) (mean to space) word itself has existed since ancient China.

　It is recorded in the Zhuangzi, a record of the words of the philosopher Chuang-tzu from the 3rd century BC.

　(宇) represents the space in front, behind, left, right, up, and down, and (宙) represents the time in past, present, and future. It is a word that expresses infinite space and time, in other words, the entire heaven and earth.