Page 40 - Winter Issue 2018
P. 40

Fr-om Sputnik to Spat.-.eX°:
60 Years of Pocket Launch
Acoustics
Caroline P. Lubert The field of rocket launch noise is 60 years old and has a lot to celebrate!
Department of Mathen[11:t{i1<::S In the Beginning
Statistics At 7.28 pm (GMT) on October 4, 1957, the Soviet Union launched a 58-cm-di-
_ _ ‘ ameter polished metal sphere into an elliptical Earth orbit at 29,000 kilometers
Iames Madmen Umvemty per hour (kph), 800 km above the Earth’s surface. The satellite was equipped with
Haflisonburg Virg?:iSaC2::(1): two pairs of external radio antennae that broadcast pulses from a one-watt, 3.5-kg
’ USA radio-transmitting unit inside the sphere. Signals were emitted on two frequen-
cies, 20.005 MHz and 40.002 MHz, spending 0.3 second at each (see bit.ly/2fSY]Nl
Email: to hear these transmissions). The successful launch of Sputnik took the world by
Lubertcp@jmu.edu surprise at a time when the USSR and the United States were both desperately
seeking to establish dominance over the new frontier, space.
Sputnik 1, where sputnik means “something that is traveling (the satellite) with a
traveler (the Earth),” was the world’s first artificial satellite. However, the language
of rockets, the launch vehicles for satellites, goes back centuries. According to the
Merriam-Webster Dictionary New Edition (2016), the first known use of the word
rocket was in 1611. Deriving from the Italian word “rocchetta” meaning distaff, a
rod used in spinning or weaving, it is defined in the Merriam-Webster Diction-
ary New Edition (2016) as “a jet engine that operates on the same principle as the
firework rocket, consists essentially of a combustion chamber and an exhaust nozzle,
carries either liquid or solid propellants which provide the fuel and oxygen needed
for combustion and thus make the engine independent of the oxygen of the air, and
is used especially for the propulsion of a missile (such as a bomb or shell) or a ve-
hicle (such as an airplane) .” Although we think of rockets as relatively new inven-
tions, the first device to use the basic principles of rocket propulsion was probably
a wooden bird, invented somewhere around 400 BC and propelled by escaping
steam using the law of action-reaction (see bit.ly/2BNOi7F).
During the early days of the Space Race, the risk of rockets exploding during or just
after liftoff was high and the technical focus was on improving rocket reliability. As
the prospect of launch failure diminished (Martinez-Val and Perez, 2009), attention
turned to other aspects of the liftoff process. At the time, very little was known about
the acoustics of rocket launches, and at 300 m from the launch pad, peak levels could
reach as much as 200 dB during liftoff (as far as 3 km from the launch pad, peaks of
140 dB, which is the threshold of pain in humans, were being observed). Such high
acoustic loads are a source of vibration, and vibroacoustic interaction can critically
affect correct operation of a rocket and its environs. Thus it was quickly realized that
even a small decrease in noise could result in a significant reduction in both risk and
cost, and the discipline of Launch Vehicle Acoustics was born.
And Then came Sputnik...
Many important breakthroughs in rocket design were made between the 16th
and 19th centuries. For example, the concept of a vehicle with multiple stages that
35 | Acnuseics Thday | Winter 2018 | volume 14, issue 4 ©2018 Acoustical Society ofAmerica. All rights reserved.























































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