Help Shape the Future of Space Exploration

Join The Planetary Society Now Join Now!

Join our eNewsletter for updates & action alerts

   Please leave this field empty
Blogs

Headshot of Emily Lakdawalla

Planetary Radio Q and A: Boom-boom!

Posted by Emily Lakdawalla

22-09-2009 17:11 CDT

Topics:

This week's Planetary Radio is the second of two with Robert Zubrin. On "Questions and Answers" I answered my own question:When Space Shuttle Discovery landed at Edwards Air Force Base, I stood outside to listen for its boom. I was surprised to hear a boom-boom. Why, I wondered, does the Shuttle make a double sonic boom?

I found explanations of the answer online here and here, as well as a neat Youtube video of a cracking double-boom, accompanied by NASA TV footage, here (embedded below).

The reason for there being any sonic boom is because the Shuttle is outrunning its own noise. Sound travels through the air as pressure waves. When an aircraft moves faster than the expansion speed of those waves, the wavefronts pile up in a cone shape that expands aftward, much like the wake of a speedboat. The overlapping wavefronts reinforce each other and manifest as a big, sharp pressure wave, resulting in the boom sound.

Supersonic aircraft actually create many bow waves from all of their little protuberances, but all the little waves usually merge to form two big ones. One sonic boom is created at the nose of the aircraft. The second boom is created behind the aircraft, where air rushes in to fill the void left by the aircraft's passage. The air can only flow in so fast, though. The faster the aircraft is traveling, the farther behind it the second boom is. If the aircraft is moving relatively slowly, just over the speed of sound, we usually hear only one bang. But if the aircraft is moving more quickly and the two sonic booms are separated by more than a tenth of a second, we'll hear it as two separate booms.

 
See other posts from September 2009

 

Or read more blog entries about:

Comments:

Leave a Comment:

You must be logged in to submit a comment. Log in now.
Facebook Twitter Email RSS AddThis

Blog Search

LightSail - Flight by Light

Support LightSail!

In 2016, The Planetary Society’s LightSail program will take the technology a step further.

I want to help!

Featured Images

Philae's landing site in 3D

Hayabusa-2 spacecraft
Curiosity in-situ science targets at Confidence Hills, sols 758-771
The Confidence Hills work area at the edge of Pahrump Hills outcrop, Curiosity sol 777
More Images

Featured Video

View Larger »

Space in Images

Pretty pictures and
awe-inspiring science.

See More

Join the New Millennium Committee

Let’s invent the future together!

Become a Member

Connect With Us

Facebook! Twitter! Google+ and more…
Continue the conversation with our online community!