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Name: John
Status: educator
Grade: 9-12
Location: OK
Country: USA
Date: Winter 2011-2012


Question:
My classes and I have been looking at the Red Bull/Stratos home page and discussing Felix Baumgartner's future attempt to free fall from 120,000 feet. Why is the build up of heat upon reentry not an issue, if he is expected to reach 700 plus miles per hour?



Replies:
It might be, but I am sure that has been taken into account. Here are some procedures that might be keep him from turning into a crisp. At high altitude the density of air is low so there would little resistance to avoid heating. I presume he will be outfitted with a heat resistant suit of some sort and a number of sensors to monitor temperature, pressure, and descent speed. As atmospheric pressure increases, his “jump” gear is probably fitted with devices to slow the rate of descent. I would guess the devices would be more complicated than a simple parachute, at least at high rates of fall, but some sort of “parachute” nonetheless to control his descent rate. In addition, I would guess he also has some sort of controllers to keep him from tumbling. At the high speed tumbling could be a worse issue than just speed. With some sort of foils (wings??) he could possibly move around in circles and glide at the same altitude. This would give him time to dissipate the heat. Basically, he would be a glider, dropping in a controlled spiral. He could control the “pitch” of the screw trajectory. Of course, some sort of breathing apparatus would have to be part of his apparatus.

You and your class are commended for asking a very valid problems.

Vince Calder


700 mph is not fast enough to cause a worrisome amount of heating during the short time (a few minutes) he will be falling. Also, he will be falling through extremely cold air (around -60F). It is a good question, though, because when we think of reentry, we are normally thinking of the reentry of a space vehicle, which must slow down from orbital speed (~17,000 mph).

Tim Mooney


Hi John,

The buildup of heat due to air friction is not significant in this case because Baumgartner's speed of 700 MPH is not fast enough to create significant heat. Speeds at minimum of several thousands of miles per hour are required for frictional heat to be significant.

Regards, Bob Wilson



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