Nova Zhang
The Space Shuttle Atlantis broke the sound barrier upon re-entering Earth's atmosphere, creating sonic booms that were heard over Los Angeles. This phenomenon occurs when a speeding aircraft pushes air molecules aside, forming shock waves that result in a loud noise. Virgin Galactic's SpaceShipTwo also broke the sound barrier during a rocket-powered test flight, paving the way for space tourism. SpaceX rockets have been observed to break the sound barrier and generate sonic booms during their descent as well. These sonic booms can be heard as double booms due to the shock waves formed at both the nose and tail of the spacecraft.
| Characteristics | Values |
|---|---|
| Speed | Three or four times the speed of sound, or up to 2,800 mph |
| Sonic booms | Two |
| Shock waves | One at the nose and one at the tail |
| Sound | Distinctive double booms |
| Sound intensity | Louder in canyon areas |
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What You'll Learn
Sonic booms
The phenomenon of sonic booms was observed during the flight of Virgin Galactic's SpaceShipTwo in 2013. The private space plane broke the sound barrier during a test run after being released by its "mothership", WhiteKnightTwo. This event marked a significant milestone in the company's journey towards space tourism.
Additionally, residents of Los Angeles experienced sonic booms from a space shuttle returning to Earth. The shuttle Atlantis created twin sonic booms as it passed over the city, startling residents who were already on edge due to a recent earthquake. The distinct double booms were caused by the shuttle's length, measuring 122 feet, which resulted in a slight delay between the nose and tail sounds.
Furthermore, the Space Shuttle Atlantis broke the sound barrier upon re-entry, as recorded in Naples, Florida. Sonic booms can be influenced by the environment, with NASA officials noting that they sound louder in canyon areas due to reverberations. The absence of clouds can also intensify the sound, as there are fewer elements to muffle the noise.
It is worth noting that aircraft are designed to minimize the occurrence of sonic booms during cruising speeds due to the rapid increase in drag associated with supersonic expansion fans. However, at transonic speeds, which range from Mach 0.8 to 1.2, aircraft can still exhibit dramatic condensation effects, especially when humidity is close to saturation.
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Shock waves
When an aircraft travels faster than the speed of sound, it creates a series of pressure waves in front of and behind it. These pressure waves are known as shock waves, and they travel at the speed of sound. As the aircraft's speed increases, the waves are forced together and eventually merge into a single shock wave, which we hear as a sonic boom. This boom is not a one-time occurrence when an object breaks the sound barrier but will follow any object travelling faster than the speed of sound.
The sonic boom can sound like an explosion or a thunderclap to the human ear. The power or volume of the shock wave depends on the quantity of air being accelerated and the size and shape of the aircraft. The strongest sonic boom ever recorded was 7,000 Pa (144 psf), which did not cause injury to researchers who were exposed to it. However, there is a probability that a sonic boom of sufficient strength could cause minor damage to structures, such as shattering glass.
The creation of a shockwave is inescapable if the aircraft generates aerodynamic lift. However, some theoretical aircraft designs do not appear to create sonic booms, such as the Busemann biplane. Additionally, the shape of the aircraft can influence the strength of the sonic boom, with careful shaping potentially reducing the nuisance of the boom to the point that overland supersonic flight becomes feasible.
The shockwaves are created by micro shocks as the aircraft passes through the air. Not every section of the plane creates a shock wave simultaneously. Some parts that are hitting the air head-on will break the sound barrier first, while others that are swept back or smoother will only create a shock wave at faster speeds. Right before the frontal cone of the plane breaks the sound barrier, the plane is buffeted by widespread tiny shocks occurring randomly. After breaking the sound barrier, the frontal cone shock wave envelops the rest of the plane, causing the micro shocks to disappear.
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Vapour cones
As an aircraft approaches transonic speed, the airflow around it experiences dramatic variations in temperature and pressure. When the aircraft breaches the transonic barrier, vapour cones become visible. These cones are created by a sudden drop in air pressure and temperature, which causes water vapour in the trailing air to condense. The vapour cone appears as a cone-shaped cloud that fans out from the aircraft.
The development of the vapour cone is dependent on the shock and expansion of waves that ripple through the air. When an aircraft transitions from subsonic to supersonic speed, a shock wave is created, leading to a rapid increase in pressure and temperature around the aircraft. This is followed by an equally rapid decrease in pressure and temperature behind the shock wave, creating an expansion zone that enables the formation of the vapour cone. The Prandtl-Glauert singularity theory explains this phenomenon, describing how the compressibility of air is crucial as an object nears Mach 1.
The temperature, pressure, and aircraft speed all influence the resulting vapour effects. Higher altitudes, with colder temperatures and lower pressure, can enhance the formation of vapour cones. Additionally, the humidity level in the air also plays a role, as condensation effects are more likely when the humidity is closer to saturation. The size and visibility of the vapour cone can vary depending on the dew point, with lower dew points facilitating more impressive vapour displays.
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Supersonic speed
The speed of sound, often referred to as Mach 1, is approximately 767 miles per hour (mph) or 1,235 kilometres per hour (km/h) at sea level. However, it varies with altitude and temperature. To break the sound barrier means to exceed this speed, entering the realm of supersonic flight.
Space shuttles, such as the Atlantis, have been known to break the sound barrier during their re-entry into the Earth's atmosphere. In one instance, the Atlantis created twin sonic booms as it passed over Los Angeles, California, during its descent. The length of the shuttle, about 122 feet, caused a distinct double boom, with a brief gap between the nose and tail sounds.
Achieving supersonic speed is not limited to space shuttles. Private space tourism companies like Virgin Galactic have also broken the sound barrier with their spacecraft. In 2013, Virgin Galactic's SpaceShipTwo conducted a successful rocket-powered test flight, reaching supersonic speeds.
It's worth noting that supersonic flight has unique characteristics. For instance, at supersonic speeds, air behaves differently, with compression and expansion causing condensation effects, especially in humid conditions. Additionally, the shape of the aircraft and aerodynamics play a crucial role in achieving and maintaining supersonic speeds.
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Transonic speed
The term "transonic" was coined by NACA director Hugh Dryden and Theodore von Kármán to describe flight across the speed of sound. The exact range of transonic speeds depends on the object's critical Mach number, which is influenced by factors such as temperature. As objects approach the speed of sound, the airflow around them becomes highly unstable, with air moving faster than sound over some parts of the object while slower in other parts. This causes a rapid increase in drag, which can be mitigated through the use of swept wings or wasp-waist fuselages. Most modern jet-powered aircraft are engineered to operate at transonic airspeeds.
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Frequently asked questions
Yes, a space shuttle can break the sound barrier. Sonic booms are created when a speeding aircraft pushes aside air molecules in its path, forming shock waves.
According to Air Force Lt. Col. Curtis Brown, a space shuttle can travel at three or four times the speed of sound, or up to 2,800 mph.
Sonic booms are the loud noises created when a speeding aircraft pushes air molecules aside, forming shock waves. When a small military jet breaks the sound barrier, twin sonic booms are heard in quick succession, creating one loud sound.
