## Chuck Yeager, the First Man to Break the Sound Barrier has Died. He was 97

On Dec.7th, 2020, World War II flying ace and legendary test pilot General Chuck Yeager passed away while in hospital in Los Angeles. He was 97 years of age and is survived by his second wife, Victoria Yeager (nee Victoria Scott D’Angelo), and his three children, Susan, Don, and Sharon. Yeager is interred at Arlington National Cemetery outside of Washington D.C. with full military honors.

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## How Fast is Mach One?

Within the realm of physics, there are certain barriers that human beings have come to recognize. The most well-known is the speed of light, the maximum speed at which all conventional matter and all forms of information in the Universe can travel. This is a barrier that humanity may never be able to push past, mainly because doing so violate one of the most fundamental laws of physics – Einstein’s Theory of General Relativity.

But what about the speed of sound? This is another barrier in physics, but one which humanity has been able to break (several times over in fact). And when it comes to breaking this barrier, scientists use what is known as a Mach Number to represent the flow boundary past the local speed of sound. In other words, pushing past the sound barrier is defined as Mach 1. So how fast do you have to be going to do that?

## Definition:

When we hear the term Mach 1 it is easy to assume it is the speed of sound through Earth’s atmosphere. However this term is more loaded than you might think. The truth is that a Mach Number is a ratio rather than an actual direct measurement of speed. And this ratio is due to the fact that the speed of sound varies from one location to the next, owing to differences in temperature and air density.

Mathematically, this can be defined as M = u/c, where M is the Mach number, u is the local flow velocity with respect to the boundaries (i.e. the speed of the object moving through the medium), and c is the speed of sound in that particular medium (i.e. local atmosphere, water, etc).

When the speed of sound is broken, this results in what is known as a “sonic boom”. This is the loud, cracking sound that is associated with the shock waves that are created by an object traveling faster than the local speed of sound. Examples range an aircraft breaking the sound barrier to miniature booms caused by bullets flying by, or the crack of a bullwhip.

## Speed of Sound:

Basically, the speed of sound is the distance traveled in a certain amount of time by a sound wave as it propagates through an elastic medium. As already noted, this is not a universal value, but comes down to the composition of the medium and the conditions of that medium.  When we talk of the speed of sound, we refer to the speed of sound in Earth’s atmosphere. But even that is subject to variation.

However, scientists tend to rely on the speed of sound as measured in dry air (i.e. low humidity) and at a temperature of 20 °C (68 °F) as the standard. Under these conditions, the local speed of sound is 343 meters per second (1,235 km/h; 767 mph) – or 1 kilometer in 2.91 s and 1 mile in 4.69 s.

## Classifications:

As with most ratios, there are approximations and categories that are used to measure the speed of the object in relation to the sound barrier. This gives us the categories of subsonic, transonic, supersonic, and hypersonic. This categorization system is often used to classify aircraft or spacecraft, the minimum requirement being that most of the craft classified have the ability to approach or exceed the speed of sound.

For aircraft or any object that flies at a speed below the sound barrier, the classification of subsonic applies. This category includes most commuter jets and small commercial aircraft, though some exceptions have been noted (i.e. supersonic commercial jets like the Concorde).

Since these craft never meet or exceed the speed of sound, they will have a Mach number that is less than one and therefore expressed in decimal form – i.e. less than Mach 0.8 (273 m/s; 980 km/h; 609 mph). Typically, these aircraft are propeller-driven and tend to have high aspect-ratio (slender) wings and rounded features.

The designation of transonic applies to a condition of flight where a range of airflow velocities exist around and past the aircraft. These speeds are concurrently below, at, and above the speed of sound, ranging from Mach 0.8 to 1.2 (273-409 m/s; 980-1,470 km/h; 609-914 mph). Transonic aircraft nearly always have swept wings, causing the delay of drag-divergence, and are driven by jet engines.

The next category is supersonic aircraft. These are craft that can move beyond the compression of air that is the “sound barrier.” These craft generally have a Mach number of between 1 and 5 (410–1,702 m/s; 1,470–6,126 km/h; 915-3,806 mph). Aircraft designed to fly at supersonic speeds show large differences in their aerodynamic design because of the radical differences in the behavior of flows above Mach 1.

These include sharp edges, thin wing sections, and tail stabilizers (aka. fins) or canards (forewings) that are capable of adjusting. Craft that typically have this designation include modern fighter jets, spy planes (like the SR-71 Blackbird) and the aforementioned Concorde.

The last category is hypersonic, which applies to aircraft that can exceed the speed of Mach 5 and can achieve speeds as high as Mach 10 (1,702–3,403 m/s; 6,126–12,251 km/h; 3,806–7,680 mph). Very few aircraft can move at such speeds, and tend to be rocket-powered (like the X-15), scramjets (like the X-43, or HyperX), or spacecraft that are in the process of leaving Earth’s atmosphere.

Another example is objects entering the Earth’s atmosphere. These can take the form of spacecraft performing re-entry, or meteorites that have passed through and broken up in Earth’s atmosphere. For example, the meteor that entered the skies above the above the small town of Chelyabinsk, Russia, in February of 2013 was traveling at a speed of about 19.16 ± 0.15 km/s (68,436 – 69,516 km/h; 42,524 – 43,195 mph).

In other words, the meteorite was traveling between Mach 55 and 56 when it hit our atmosphere! Given its tremendous speed, when the meteor reached the skies above Chelyabinsk, it created a sonic boom so powerful that it caused extensive damage to thousand of building in six cities across the region. This damage, which included a lot of exploding windows, resulted in 1,500 people being injured.

So how fast is Mach One? The short answer is that it depends on where you are. But in general, it is a speed that exceeds about 1200 km/h or 750 mph. If you’re capable of going this fast, you will be breaking the sound barrier, and people for miles around will be hearing about it!

We have written many interesting articles about sound here Universe Today. Here’s What is Sound?, What is the Fastest Jet in the World?, What is Air Resistance?, and What Does NASA Sound Like?

For more information, check out NASA’s Article about the Mach Number, and here’s a link to a lesson about the Mach Number.

We’ve recorded an episode of Astronomy Cast all about the space shuttle. Listen here, Episode 127: The US Space Shuttle.

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## NASA Astronaut Scott Kelly Sets US Record for Most Time in Space – At the ‘Speed of Sound’: Video

Video Caption: See NASA astronaut Scott Kelly’s extraterrestrial exploits as he breaks US record for time in space in this music video set to the song ‘Speed of Sound’ by Coldplay. Credit: NASA/Coldplay

NASA astronaut Scott Kelly has just broken the American record for most time spent in space – at 383 days and counting – as part of his groundbreaking yearlong mission living aboard the International Space Station (ISS), where he currently serves as station commander.

See Kelly break the US spaceflight endurance record on the ISS at the “SPEED OF SOUND” in the beautifully space themed music video (above) set to the worldwide hit song by rock band Coldplay.

The video recounts a flurry of highlights from the yearlong space station mission with his partner, Russian cosmonaut Mikahail Kornienko, and the rest of the rotating cast of international crewmates.

On October 16, 2015, Kelly surpassed the US time in space record of 382 days previously held by NASA astronaut Mike Fincke.

The ‘1 Year ISS mission’ is aimed at conducting research to explore the impact of long term stays in space on the human body and aid NASA’s long term plans for a human ‘Journey to Mars’ in the 2030s.

“Records are meant to be broken. Look fwd to one of my colleagues surpassing my end 500+ days on our #JourneyToMars!’ Kelly tweeted from the ISS about his record breaking achievement.

As of today, October 20, Kelly has reached the 206 day mark aboard the ISS, of his planned 342 days in space. He’s now about a month past the half way mark.

In addition to his scientific research, Kelly has been a prolific photographer of all things space – including natural wonders and natural disasters like Hurricane Joaquin.

Here’s his newly released photo titled ‘Earth Art From Australia.’

See the NASA graphic herein showing the US astronauts who have accumulated the most spaceflight experience to date.

Kelly accumulated his time in space during multiple spaceflights. Altogether this is his fourth mission and second long duration stay aboard the ISS. This flight also marks his second stint as station commander – as a member of the current Expedition 45 crew.

To be sure, Kelly is not merely passing Fincke’s record days but actually smashing through it by many months because he still has a long way to go until he returns home to Earth.

At the conclusion of his yearlong mission when he plummets back home in a Russian Soyuz capsule – along with Kornienko – on March 2, 2016, he will have compiled 522 total days living in space.

Kelly will also become the first American to spend a year in space, a feat previously achieved by only four Russian cosmonauts – all in the 1980s and 1990s aboard Russia’s Mir space station.

Next week on Thursday, Oct. 29, Kelly will break another American record for the single-longest spaceflight.

“On Oct. 29 on his 216th consecutive day in space, he will surpass astronaut Michael Lopez-Alegria’s record for the single-longest spaceflight by an American. Lopez-Alegria spent 215 days in space as commander of the Expedition 14 crew in 2006.”

Kelly and Kornienko are spending a year aboard the ISS, “testing the limits of human research, space exploration and the human spirit,” says NASA officials.

The pair launched to the ISS in March 2015 along with Russian cosmonaut Gennady Padalka. He recently returned to Earth in September 2015 after setting the record for most time spent in space by any Earthling – with an accumulated total of 879 days living and working in space.

During their 342 days in space, Kelly and Kornienko are specifically “participating in studies in space that provide new insights into how the human body adjusts to weightlessness, isolation, radiation and stress of long-duration spaceflight. Kelly’s twin brother, former astronaut Mark Kelly, will participate in parallel twin studies on Earth to help scientists compare the effects on the body and mind in space.”

“The investigations in progress on the space station will help scientists better understand how to protect astronauts as they travel into deep space and eventually on missions to the Red Planet. The strong U.S.-Russian collaboration during the one-year mission is an example of the global cooperation aboard the space station that is a blueprint for international partnerships to advance shared goals in space exploration. Strengthening international partnerships will be key in taking humans deeper into the solar system,” according to NASA.

Kelly and the crew are also surely looking forward to the arrival of the Orbital ATK resupply ship carrying science experiments, provisions, spare parts, food and other goodies after it blasts off from Florida on Dec. 3 – detailed in my story here.

Stay tuned here for Ken’s continuing Earth and planetary science and human spaceflight news.