How many steps are there to distinguish between "aviation" and "aerospace"?

Review expert: Qian Hang, aerospace science expert of the First Academy of China Aerospace Science and Technology Corporation

Let's clarify a common misunderstanding: aerospace is not exactly the same thing. Although the two words "aviation" and "space" are often used together, they have clear boundaries in terms of technical fields and application scope. Today, let's take a deep look at the differences between the two.

The boundary between space and the earth - the Karman line

There is no unified view internationally on the exact boundary between aviation and aerospace, but in order to establish a relatively universal standard, the International Aeronautical Federation introduced the concept of the " Kármán line ".

Before understanding the Karman lines, we must first understand the atmosphere. Scientists divide the atmosphere into five layers, including:

Troposphere (about 0-10km)

Stratosphere (about 10-50km)

Middle layer (about 50-85km)

Thermosphere (about 80-800km)

Exosphere ( 800-2000 or about 3000km )

The passenger planes we usually take fly at an altitude of 6,800-8,000 meters, near the junction of the troposphere and the stratosphere. They can stay in the air without falling, mainly relying on the lift of the air. The shape of the wing has been carefully designed, so that as long as it reaches a certain speed, it can create enough pressure difference between the upper and lower wings, thereby generating air lifting force to lift the plane up. At the "Kármán line" 100 km above the ground, the atmosphere is too thin for the plane to fly normally. Therefore, the Kármán line can be considered the dividing line between the atmosphere and space.

Karman Lines | National Geographic China

Qian Xuesen defined the scope of the three technical terms "aviation, aerospace, and astronautics" as follows: flight activities within the atmosphere are called "aviation"; flight activities outside the atmosphere and within the solar system are called "aerospace"; and activities flying out of the solar system and into the vast universe are called "astronautics."

In short, aviation refers specifically to the navigation of aircraft within the Earth's atmosphere, whether manned or not. Spaceflight refers to the navigation of spacecraft that leave the atmosphere and enter outer space, also known as space flight or space travel. With the human desire and exploration of wider space, our activities have expanded from land to ocean, and then from ocean to atmosphere, and finally broke through the atmosphere and went deep into the universe. This process is a vivid portrayal of human beings constantly expanding the boundaries of their own activities.

Flight environment and flight altitude

Aviation technology is mainly focused on the research and development of military and civilian aircraft, as well as the manufacture of air-breathing engines, etc. In contrast, aerospace technology focuses on the development of unmanned and manned spacecraft, launch vehicles and missile weapons. As typical representatives of these two technologies, aircraft and spacecraft are mainly different in terms of flight environment and flight altitude.

C919 | People's Daily

Aircraft always fly in the dense atmosphere , and their operating altitude is limited. At present, the maximum flight altitude of modern aircraft is about 30 kilometers above the ground. Even if the flight altitude of aircraft is increased in the future, it will still not be able to escape the dense atmosphere.

In contrast, a spacecraft needs to pass through the dense atmosphere, enter the nearly vacuum space, and fly according to the motion laws similar to those of natural celestial bodies. The perigee height of the spacecraft's orbit is at least 100 kilometers.

Long March 2D carrier rocket | People's Daily

For operating spacecraft, it is also crucial to study the space flight environment, which is closely related to its flight altitude from the earth.

Both the flight power unit and the working time limit aircraft use air-breathing engines to provide thrust, absorbing oxygen from the air as an oxidant, and only carrying fuel itself ; the launch and operation of spacecraft use rocket engines to provide thrust, carrying both fuel and oxidant. Air-breathing engines cannot work without air, while rocket engines have less resistance and greater effective thrust when they are out of air.

Flames gushed out from the engine | People's Daily

Air-breathing engines, including their fuel tanks, can be used multiple times with an aircraft, while launch vehicles used to launch spacecraft are currently mostly single-use. Although the solid boosters of the space shuttle can be reused 20 times after recovery, and its orbiter liquid rocket engine can be reused 50 times, the number of uses is still very small compared to the air-breathing engines used in aircraft.

The fuel used in air-breathing engines is only aviation gasoline and aviation kerosene, while the propellants used in rocket engines are diverse, including liquid, solid, and solid-liquid types.

Aircraft engine | Baidu Image

Whether it is a military or civilian aircraft, the maximum range is about 20,000 kilometers , and the longest flight time does not exceed one day and night. Its range of activities and working time are very limited, and it is mainly used for military and transportation. Although general light aircraft are widely used, the range of each activity is relatively smaller. Spacecraft can work continuously for a very long time in orbit.

Looking back at the development of China's space industry, from missile research and development to satellite launches, from the construction of the Beidou navigation system to the implementation of the lunar exploration project, each generation of astronauts has created a series of brilliant achievements that have attracted worldwide attention with their perseverance and independent innovation. Today, space activities have played a pivotal role in China's economic construction and social development, and have injected strong impetus into promoting national scientific and technological progress and industrial upgrading.