Discovery...sound barrier question

Factual Questions
1

What causes the bam-bam (like someone slamming the door shut twice quickly whe the shuttle breaks the sound barrier? I have heard a few of these identical sounds when the space shuttle terminates its landing at Edwards Air Force Base. And exactly at 1:57pm today pacific coast time there it was.

I did try to search under sonic boom and the sound barrier but everything I got referred to musical groups. So in short, why 2 bams, not one or 3?

2

One sonic boom is caused by the nose, the second by the tail. For a very good explanation of sonic booms, see http://web.galcit.caltech.edu/SonicBoom/boomprimer.html

3

Bibliophage: the link you gave me explains it perfectly. Thanks for directing me there!

4

There was a thread here Photgraph(sic) sound barrier?. In it, the_nudge aka crnugent posted this link. The first link on that page is to an mpeg showing the shock wave. Check it out!