Sunday, November 30, 2008

Shuttle Landed at Edwards!




So this morning I arrived at my desk at UCLA and popped open a web browser to see a CNN article that said that the Shuttle Endeavour would be landing at Edwards Air Force base today at 4:25 pm Pacific time. As it was only about 10:30 am when I got in, I briefly entertained the idea of driving the 2 hours up to Edwards to see the landing. The shuttles are scheduled to be retired from service in 2010, and Edwards landings don't happen all that often, maybe once a year, so this could possibly be the last shuttle landing in California ever. I spent 20 minutes looking around online and reading about viewing locations, before I went to NASA.gov and found that CNN had got the times wrong: It would be landing at 4:25 EASTERN time, 1:25 pm pacific. Thanks CNN. And yes it was their mistake, not me misreading the numbers, as I had kept that browser page open and compared it with the NASA site. Serves me right for trusting CNN on details. Oh well.

I did get a shuttle-related treat anyway, though. I had heard anecdotally that you can hear the double-sonic booms from the Shuttle as it passes over the L.A. area on its way to Edwards. But I'd never heard it firsthand in L.A.. I remember back in college, when I worked at EarthKAM, wondering if we'd hear the booms in San Diego, but we never did. I guessed, at the time, that the shuttle was simply to high and too far away from our location on the ground to be able to hear it unless you are right under it. I know it also depends on whether the shuttle is approaching Edwards on an ascending (south to north) or descending (north to south) section of its orbit, as it will be coming in farther north if it's on a descending track.

Anyway, I expected I might be able to hear a soft double-boom if I went outside at the right time. So at 1:15 pm, when the NASA TV announcer said the shuttle was at an altitude of 20 miles and only 137 miles from the Edwards runway (which put the shuttle right over the coast, right around Oxnard) I walked outside onto the roof and listened. I waited for about 5 minutes, figuring that it would take less time than that for the shuttle to pass the area on its way to Edwards, as it was going about Mach 2.5 (~2000 mph). I waited and looked upward, listening. Nothing. A tad disappointed but not too surprised, I walked back toward the door, and was about 2 steps from going back in side when. . .

BOOM-BOOM!

It was unmistakable, and much louder than I had been expecting! I walked down the hall to see if my friend had heard it from his office, but he wasn't there. I then thought to call my friend Phil, who lives in Downey to the southeast. He had the same idea, apparently, as my phone was ringing and I answered to hear his voice: "My house just shook!". Next came a text message from Regan, who was in the valley. She had heard the booms, which she said were so lound it sounded "like a bomb went off". Curious, I texted my sister and called my mom, who both reported hearing the booms clearly all the way in San Diego. Apparently, everyone else in the Southern CA area heard it as well, according to the OC Register and LAist.

From the timing and from listening to the NASA TV broadcast, I gather the shuttle was somewhere between 15 and 18 miles (80,000 ft and 95,000 ft) in altitude when I heard the boom. So, since sound travels around 700 mph at sea level (~11.5 miles per minute), it makes some sense that Endeavour's shock wave took a couple of minutes to reach me. As the shuttle flew right over L.A., I guess I shouldn't be surprised that I could hear it. . . but I am impressed that my family in San Diego, another 150 miles south, could hear it so clearly!

3 comments:

Ryan said...

Hey David! Very cool! I heard the sonic boom also and thought it was an earthquake! It is amazing that it is such a force that we hear it so loudly. Soo.. do the astronauts actually hear it inside the shuttle, or not?

Regan said...
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David said...

The astronauts don't hear it inside the shuttle. The "boom" we hear is a shockwave, a wave of increased pressure and air density, moving over us where we stand on the ground. The thing creating the shockwave is the shuttle itself. It's sort of like a ship moving through the water, leaving a wake in its path. The difference is that the shuttle is moving faster than the speed of sound, that is, faster than the individual air molecules can get out of its way, so they pile up in front of it. A better analogy is to try the following: put a piece of paper on the table and press down on it with your finger. Your finger represents the shuttle and the paper represents the air. Now, while still pressing down, push forward and watch how the paper "piles up" in front of and to the sides of your finger. As your finger moves along, the wave travels with it, and it moves past stationary objects on the paper (like the people letting the shockwave pass them by). But your finger never crosses the wave. In the same way, the shuttle itself never crosses the shockwave, so the astronauts never hear the sonic boom.