( McNeese Everest Speed of Sound )

Columbia Scientific Balloon Facility

Palestine,Tx May 2008

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Team Members• Mukesh Wagle - Team Leader

• Sovit Poudel - Team Acquisitions Officer

• Parash Maharjan - Computer Specialist

• Dilip Roshan Das - Payload Structural Engineer

• Sunit Pradhan - Team Scientific Research Specialist

• David Hughes - Team Assistant

• Charles McAdon – Team Assistant

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The Sound of Titan: inspiration for MESS

• On 14th January 2005 the Huygens probe landed on the surface of Titan, Saturn’s largest moon.

• As part of Surface Science Package (SSP) was the Acoustic Properties Instrument-Velocimeter (API-V): a senser aimed to measure the speed of sound in a hydrocarbon sea or lake, should Huygens land in a liquid.

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• As Huygens landed on a solid surface only atmospheric measurements were made.

• These are among the few measurements of the speed of sound made in a remote planetary atmosphere.

• The speed of sound in a non-ideal gas, such as Titan’s lower atmosphere, is dependent upon composition, temperature and pressure.

The Sound of Titan: inspiration for MESS

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Alien Sounds• Using the speed of sound, pressure, and

temperature measurements from Huygens it is possible to estimate the methane content of Titan’s atmosphere below 11 km, given some simple initial constraints.

http___www.sciencedirect.com_science__ob=MImg&_imagekey=B6WGF-4N5CXK1-3-1&_cdi=6821&_user=6996916&_orig=&_coverDate=08%2F31%2F2007&_sk=998109997&view=c&wchp=dGLbVzW-zSkzk&md5=e333f3104ff9be0618c15617fb70cfd2&ie=_sdarticle

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Scientific Goal• The velocity of sounds depends on several physical parameters

that are both independent of chemical composition (like the temperature of the gas), density and bulk modulus of the medium, that are characteristic of the particular chemical composition of the medium. Consequently, the speed of sound could be used to determine (if environmental parameters like the temperature of the gas are known) the precise combination of individual gases present in the medium.

• We will use similar methods to determine the chemical composition of the Earth‘s atmosphere even if it is a well known quantity. This is in the following of the spirit of the LA-ACES program that invites the students’ teams to pretend they are exploring the Earth as a space mission would when it explores another world.

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• We are going to use our data from the speed of sound as a function of altitude to set limits on the chemical composition of the atmosphere as if it was an unknown alien planet.

• We are going to use a method based on Bayesian analysis as in the article:

Speed of sound measurements and the methane abundance in Titan’s atmosphere

A. Hagermann a, , P.D. Rosenberg a, M.C. Towner a, J.R.C. Garry ∗b, H. Svedhemc, M.R. Leese a, B. Hathi a, R.D. Lorenza,d,1, J.C. Zarnecki a

The Sound of Titan: inspiration for MESS

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Technical Goal

• Measure the changes in the velocity of sound as a function of altitude and compare those changes with theory based on standard atmosphere model and ideal gas relationship between velocity and temperature.

• Record sound at a sampling rate of 96000 Hz• Survivability of payload electronic equipment• Structural integrity of the payload box

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Velocity of Sound in the Atmosphere• The velocity of sound depends on atmospheric conditions;

the most important factor is the temperature. Air pressure has almost no effect on the velocity. In an ideal gas approximation, since pressure and density both contribute to sound velocity equally, the two effects cancel out, leaving only the effect of temperature. Sound usually travels slowly at higher altitude due to lower temperature (but speeds up in the stratosphere due to heating within the ozone layer). Humidity has a small, but measurable effect on the speed. Sound travels slightly (0.1%-0.6%) faster in humid air. The approximate speed of sound in 0% humidity (dry air), at temperature near 0 °C, can be calculated by using the following formula:

331.3 (0.6 ) /airv T m s Where T is the temperature in degrees Celsius.

At sea level, at a temperature of 21 °C (70 °F) and under normal atmospheric conditions, the speed of sound is 344 m/s .

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Velocity of Sound in the Atmosphere

Altitude Temperature m·s-1 km·h-1 mph knots

Sea level 15 °C (59 °F) 340 1225 761 661

11 000 m−20 000 m(Cruising altitude of commercial jets,and first supersonic flight)

-57 °C (-70 °F) 295 1062 660 573

29 000 m (Flight of X-43A)LA-ACES max altitude

-48 °C (-53 °F) 301 1083 673 585

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0 50 100 150 200 250280

300

320

340V

soun

d (m

/s)

Altitude (1000 feets)0 50 100 150 200 250

-100

-50

0

50

Tem

pera

ture

(C

elsi

us)

Velocity of Sound in the Atmosphere

Velocity and Temperature vs Altitude

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Velocity of Sound in the Atmosphere

Velocity and Percentage Diff (with respect to the ground) vs Altitude

0 50 100 150 200 250295

300

305

310

315

320

325

330

335

340

Altitude (1000 feets)

V s

ound

(m

/s)

B LayerTroposphereTropopauseStratosphereStratopauseMesosphere

0 50 100 150 200 2500

2

4

6

8

10

12

14

Altitude (1000 feets)

V s

ound

Per

cent

age

Diff

eren

ce %

B LayerTroposphereTropopauseStratosphereStratopauseMesosphere

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MESS experiment to measure sound’s velocity

According to the standard wave relationship between velocity, wavelength and frequency,

v fIf we produce a wave with fixed frequency, a change in velocity will result in a change in wavelength. Measuring the wavelengthwill allow us to calculate the change in the velocity of sound.We can measure the wavelength of the wave with a simple experimental setup.

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Speaker

Microphone 1Left channel

Microphone 2Right channelx 33 cm

PMC LinearDigital RecorderStereo HQ (96000 Hz Sampling Frequency)

There is an arrival time LAG between the two microphone, that we can use to measure the wavelength of the sound wave. The distance between the microphone and the speaker should be farther than at least one wave length. to have the microphones in the radiation zone.

Sound with a simple sinusoidal signalWith a fixed frequency of 1920 Hz

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Mathematical model of the sound amplitude recorded by the microphones.

1 sin( )y A t

2 sin( )y A t k x

2

k

If we set the origin at the first microphone the sound wave amplitude can be described as:

At the same instant of time the amplitude at the second microphone will be

With some simple math tricks we can extract the value k from the data(and therefore measure the wavelength).

Where:

2 f

Distance between the microphones

wave number

where

Frequency of thespeaker’s sound wave

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Math used to extract the velocity from our data(if you are interested)

1 2 2 sin( )cos( )2 2

k x k xy y A t

sin sin 2sin( )cos( )2 2

siny C x

Start with adding the two signals and using the trig identity:

___ 22

2

Cy

We obtain:

Constant

So the sum of the two signals is a simple sine function with frequency f.For any given sine function:

It is well know that:

Then in our case we have that:

and

and finally

2

k

then

v f

21 2( )

cos( )2 2

y yk x

A

21 1 2( )2

cos ( )2

y yk

x A

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Results from our experiment (room temperature, 21 Celsius, sea level)

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500 Hz

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The data points represent values of the measured speed of sound as a function of time (averages over 0.25 seconds) with errors bars with widths of one standard deviation (1.5 % of average value). The green line is the theoretical value expected for the given temperature of 23 degree Celsius.

The result of our tests

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The data samples are taken over each period. The average value is shifted with respect to the theoretical value (represented by the star). This is a relatively small systematic error (5 % from expected value ) due to the uncertainty of the orientation of the sound source center at the speaker. Considering this as a calibration issue, we have changed our effective distance to compensate for this systematic error.

The Gaussian behavior of the noise in our data

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Mission Operations• The recorder and the player will be turned on

and data will be stored in the memory of the recorder.

• All components will be placed properly inside the box and sealed.

• The digital recorder will actually begin collecting data about 15 minutes before the launch. We will use stop watch or voice commands (launch!, increased noise from freefalling, box landing) to synchronize our data with the altitude information.

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Payload Design

• The main part of the payload is the Digital Recorder and Player.

• Olympus LS-10 player will produce the sinusoidal control sound wave.

• Two microphones will record sound.

• A speaker will emit the sound waves during the whole experiment.

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System Design

A digital recorder will be connected in stereo to the microphones. A player will produce the sinusoidal wave through a speaker attached on the side of the box.

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Thermal Design

• Insulating Materials were used in the inner compartments of the payload to reduce heat loss.

• Also, tests performed on the box found that it is quite resistive to temperature change when covered in aluminum foil and a reflective tape.

• We did some experiments operating our payload in a freezer at -80oC for extended period(about 35 minutes) without encountering any problems.

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Data Acquisition and Analysis• Data will be recorded to the Digital Voice

Recorder.

• Sampling Frequency will be 96,000 Hz.

• The player will be able to record and store over 2. 5(?) hours of high quality sound

• A 4GB memory card will be used to store the data.

• The data will be extracted via USB onto our computers.

• Data will be analyzed using MatLab.

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Budget

Expense Budget

Box Structure $ 10

Recorders (2X) $ 800

Speaker (Sony T-30) $ 25

Microphones $ 25

Batteries (AAA, AA) $ 12

Tape, glue, straw, insulation $ 10

Miscellaneous $ 5

________________________________

Total $ 877

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Budget Cont.

Weight Budget Compromisation

Our weight per area calculation meets Federal Aviation Administration standards requirements of 8 ounces per sq. inch. However we could not have it within 500 gm due to the long structure of the box and relatively heavier recorders.

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Special Thanks . . .

• Dr. Santostasi Giovanni

• LA-ACES Organizers

• NASA Employees