# Verifying Mach 10+ Shocks in Shuttle Launch Exhaust

• DaveC426913
In summary: Mach number, pressure (and pressure differential), and exhaust velocity are related. The higher the exhaust velocity, the more shock diamonds will be visible.
DaveC426913
Gold Member
My friend (whom I normally trust) told me something I did not know and would like to verify.

We were watching a shuttle launch, talking about the main engines which, while much fainter than the boosters, can be seen in the right light.

http://fascinatingly.com/wp-content...-space-shuttle/lift-off-shuttle-wallpaper.jpg

He said that the pulses seen in the blue hydrazine flame from the main engines are actually supersonic shockwaves. He went on to say that you can count how many Machs the exhaust speed is by counting the pulses visible. The attached pic is cut off but in the vdieo we were watching we counted 10+ shocks, the implication being that the exhaust was in excess of Mach 10.

True?

(I had seen the pulses but assumed they were simply ... pulses, generated by some function of the engine.)

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Followup:

Well, the math works out at least...

According to Wiki, the engines can generate an exhaust velocity of 4440m/s at sea level which is ~ Mach 13.

Seriously I wished I had a place in the spaceship. When can I fly ?

DaveC426913 said:
He said that the pulses seen in the blue hydrazine flame from the main engines are actually supersonic shockwaves. He went on to say that you can count how many Machs the exhaust speed is by counting the pulses visible. The attached pic is cut off but in the vdieo we were watching we counted 10+ shocks, the implication being that the exhaust was in excess of Mach 10.

True?
The SSME's are fueled with liquid hydrogen (H2) and oxygen with the mixture rich in H2. The engines do not pulse, but what appear to be pulses are indeed reflected shock waves due to the fact that the flow is supersonic. The numbers seem reasonable, but I would recommend confirming with NASA or Pratt & Whitney Rocketdyne.

FYI -
http://www.pwrengineering.com/articles/nozzledesign.htm
http://www.pwrengineering.com/data.htm

One can see a similar pattern with the exhaust of an SR-71 when it takes off with max thrust.

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This is amazing

lonton said:
Seriously I wished I had a place in the spaceship. When can I fly ?

You have an extra \$30 million laying around? The Russians will let you fly with them for that fee.

He also said that the distinctive crackling sound that the engines make is sonic boom after sonic boom.

DaveC426913 said:
He also said that the distinctive crackling sound that the engines make is sonic boom after sonic boom.
That is essentially what is happening. The air around the exhaust plume is displaced at the speed of sound in the air. There are tremedous pressure gradients in the plume, particularly at the boundary of plume and air.

The sound pressure from miles away even is most impressive. I saw a launch a couple of years ago. No sub-woofer can reproduce the thundering sound that pounds at you. Dumbfoundingly awesome is about the the only way to describe the sensation of power.

From what I have heard, the number of shock diamonds depends not on the mach speed of the exhaust, but rather the pressure difference between the exhaust gasses and the sarounding atmosphere.

As (merely anecdotal) support, the same exhaust will produce a different number of shock diamonds at different altitudes. Also, I've seen pics of the X-1 with about 8 or 10 shock diamonds behind it, and I'm pretty sure that the exhaust from that vehicle does not exit at Mach 10.

Let's keep researching, I'm quite keen to know the truth on this one.

## 1. How do you verify Mach 10+ shocks in shuttle launch exhaust?

The verification of Mach 10+ shocks in shuttle launch exhaust is a complex process that involves both theoretical analysis and experimental testing. First, the exhaust flow is modeled using computational fluid dynamics (CFD) simulations to predict the location and strength of the shocks. Then, physical experiments are conducted using wind tunnels and high-speed cameras to validate the CFD results and accurately measure the shock characteristics.

## 2. Why is it important to verify Mach 10+ shocks in shuttle launch exhaust?

The verification of Mach 10+ shocks in shuttle launch exhaust is crucial for ensuring the safety and efficiency of space shuttle launches. These shocks can cause significant damage to the shuttle and its components if not properly accounted for in the design and operation of the launch vehicle. By verifying and understanding these shocks, engineers can make informed decisions to mitigate their effects and improve the overall performance of the shuttle.

## 3. What factors can affect the presence and strength of Mach 10+ shocks in shuttle launch exhaust?

The presence and strength of Mach 10+ shocks in shuttle launch exhaust can be influenced by a variety of factors, including the velocity and mass flow rate of the exhaust, the shape and design of the nozzle, and the atmospheric conditions. These factors can vary depending on the specific launch mission and can also be affected by other external factors, such as wind and temperature.

## 4. How do you measure and analyze Mach 10+ shocks in shuttle launch exhaust?

Measuring and analyzing Mach 10+ shocks in shuttle launch exhaust involves a combination of experimental techniques and numerical simulations. Physical experiments using high-speed cameras and pressure sensors provide direct measurements of the shock characteristics. Computational methods, such as CFD simulations, are also used to model the flow and predict the location and strength of the shocks. These results are then compared and validated to provide a comprehensive understanding of the shocks in the exhaust flow.

## 5. How can the knowledge gained from verifying Mach 10+ shocks in shuttle launch exhaust be applied to future space missions?

The knowledge gained from verifying Mach 10+ shocks in shuttle launch exhaust can be applied to future space missions in several ways. First, it can be used to improve the design and operation of launch vehicles, ensuring their safety and efficiency. Additionally, this knowledge can also be applied to other high-speed flow systems, such as supersonic aircraft, to better understand and control shock waves. Furthermore, the techniques and methods used to verify Mach 10+ shocks can also be applied to other complex fluid dynamics problems in various industries, leading to further advancements in science and technology.

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