Saturday, May 23, 2009

Space Shuttle Reentry "Emission"

Space Shuttle and trailing hot gas plume during entry

If you add molecules of nitric oxide (one oxygen and one nitrogen, chemical symbol = NO) in the stratosphere at altitudes greater than about 20 km, the result is ozone depletion. One way to generate NO molecules to air is to heat it to about 2500 deg centigrade at which point nitrogen and in the air react to form nitric oxide (that is, NO).
Air can be heated to this temperature by the friction around a Space Shuttle during entry (or reentry). (BTW it is not really "friction" heating, but that is another post.) That is why the Space Shuttle has those tiles, to protect it from the very hot air that surrounds the vehicle during reentry and forms the glowing plume behind it. So the Shuttle for practical purposes the Shuttle is an "NO emitter" during reentry.

Almost three decades ago two guys Park and Raish (1980) did a quick calculation and estimated that the Space Shuttle generates approximately 0.02 kilotons of NO in the upper stratosphere during each entry as air heats up in the hot tail (see picture above) behind the Shuttle.

This is interesting of course because this NO will react with and destroy some ozone. This is also bad because ozone destruction, in general, is bad. So it is interesting that simply by returning to earth, the Space Shuttle causes ozone depletion.

Very roughly this is equivalent to the mass of total NO emitted by the jet engines of a Concorde supersonic transport during half a dozen or so transatlantic flights. (The Concorde does not fly anymore by the way.) I point this out so that you can put the Space Shuttle reentry NO production during reentry into some context by comparing it to another source of NO molecules that scientists worry about, supersonic transports. Park and Raish did not calculate the ozone destruction caused by a Shuttle reentry. A different model would be needed to do that.

I wonder a few things here:

1. The Park and Raish work was done over a quarter of century ago. Would the result be different using up to date calculations and models?

2. How does the ozone depletion from Shuttle entry compare to the depletion from Shuttle launch? The emissions from the big solid rockets likely cause more ozone depletion but I wonder how much more?

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