Is Mach Number Unique to Aircraft Only?
When we hear the word "Mach", we immediately think of pointy-nosed fighter jets tearing through the sky or legendary Concorde passenger planes. This pairing is very natural as the aviation industry is the area where the Mach number is most commonly used and heard. However, the objects that push aerodynamic limits are not only aircraft with wings.
If the speed of a moving object approaches or exceeds the speed of sound in the medium it passes through; whether it is an airplane, a spacecraft, a rocket, a bullet, or a wheeled car, the Mach number comes into play in engineering calculations. To convert and make sense of these speeds in different areas into the units you use, you can always keep our Mach Number Calculator tool handy.
Space Exploration and Atmospheric Entry: Extreme Mach Speeds
When space shuttles, orbital vehicles like the International Space Station (ISS), or interplanetary exploration probes are moving in the vacuum of space, the "Mach" number is not mentioned. Because there is no air in space, therefore there is no concept of the speed of sound. Speeds in space are expressed as absolute speeds like kilometers/second (For example, the orbital speed of the ISS is about 7.66 km/s).
However, the situation completely changes when a spacecraft enters the atmosphere to return to Earth. The spacecraft hits the upper layers of the atmosphere (thermosphere and mesosphere) at an extremely high speed. From this point on, because there is air around it, the vehicle's speed begins to be expressed in Mach.
- Atmospheric Entry Speed: When a space shuttle enters the Earth's atmosphere, its speed is generally around Mach 25 (25 times the speed of sound, about 28,000 km/h).
- Plasma Shield: At this incredible Mach speed, the air in front of the shuttle cannot find time to escape and scatter to the sides. The air compresses so violently that the temperature rises to thousands of degrees, and the molecules ionize to form a "plasma" layer around the shuttle. (This is why radios cut out for a few minutes during reentry).
- Deceleration: The spacecraft must use drag intentionally to reduce its speed from Mach 25 to subsonic speeds where it can deploy its parachutes.
Mach in Ballistics and Weapons Technologies
In military engineering and ballistic science, although the speeds of bullets, howitzers, or missiles are generally expressed as muzzle velocity (meters/second), the Mach number is still used when calculating the drag they are subjected to along the path they travel in the air.
- Bullets: The speed of a bullet fired from a modern infantry rifle (e.g., 5.56 mm caliber) is approximately 900 m/s. This corresponds to a speed of about Mach 2.6 at sea level. Because the bullet travels faster than the speed of sound, the sound it makes (sonic boom crack) while traveling in the air until it hits the target is not heard; the sound comes after the target is hit or the bullet passes.
- Cruise Missiles: Traditional cruise missiles like the Tomahawk fly low to avoid radar detection and are generally at subsonic (Mach 0.7 - 0.8) speeds. However, today's advanced Hypersonic Cruise Missiles can maneuver at speeds of Mach 5 and above within the atmosphere, leaving air defense systems helpless.
Traveling Faster Than Sound on Land: Automotive Records
Going faster than the speed of sound on wheels is much harder than doing it with an airplane. Because you don't just have to cut through the air, you also have to deal with the reflections of shock waves coming from the ground surface and the friction of the tires with the surface.
ThrustSSC (Super Sonic Car), designed by British engineers, managed to overcome this seemingly impossible obstacle in the Black Rock Desert in the USA in 1997. This vehicle, which had two massive fighter jet engines on it, exceeded the speed of sound on a one-mile-long course on the ground.
- The record speed reached by the vehicle was registered as 1.228 km/h.
- At the desert temperature of that day (remember that the speed of sound changes with temperature), this value meant a speed of Mach 1.016 reached on land, and it took the title of the first official supersonic land vehicle in history. A massive sonic boom occurred as the car passed.
How Can We Imagine These Speeds?
When you hear on television that a missile is flying at Mach 3, or a space shuttle is entering the atmosphere at Mach 25, you might wonder what this means in km/h compared to the speed you go on the highway in your car. When reading such news or watching popular science documentaries, you can use our Mach Number Calculator tool to draw a clear picture in your mind. By entering the Mach value and the assumed temperature, you can instantly see the km/h equivalents of these mind-blowing speeds.
