Shuttle's rate of descent ```Name: N/A Status: N/A Age: N/A Location: N/A Country: N/A Date: N/A ``` Question: When the shuttle burns out of orbit, What is its rate of descent? During daylight hours, at what altitude does it become a naked eye object? Replies: I have watched a shuttle land. I saw the next shuttle that went up after the "Challenger" disaster land at Edwards Air Force Base in California. You *hear* the shuttle before you see it: it produces a characteristic double sonic boom as it crosses the California coast. Then everybody looks for it --- in those days typically thousands of people turned out for each landing --- and it takes about 3 or 4 minutes from when it is spotted until it lands, which is much quicker than if you were watching airplanes at the airport, because the shuttle lands faster than a jet and glides downward at a much steeper angle. The outside limit on seeing far-away objects is the resolution of your eye --- how small a thing can you make out? As a rough estimate, you can see something L feet long at a distance of D = 1720 * L/x feet away, if you can resolve something x seconds of arc across. To estimate how big x is for you, look at craters on the moon or a bird flying across it: the moon is 30 seconds of arc across, what fraction of the moon would an object have to be for you to recognize it? If you can make out things 1/5 the size of the moon, x = 6 and you can see 100 foot objects (the size of the shuttle) 30,000 feet away. But the problem with the shuttle is not the outside limit, but *finding* the thing in the sky. If you have ever watched a child's balloon rise up in a clear sky, taken your eyes off it for a moment and then tried to find it again you know what I mean. It helps that the shuttle is black (from below) but normally it is not spotted until it is well within the outside limit. christopher grayce Click here to return to the Physics Archives

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