### VARIATION OF DENSITY WITH EXTREME ALTITUDE

The formula in the previous sections and the tabulated data below give accurate predictions for an ideal atmosphere in the lower portions near the earth's surface, the troposphere and the lower stratosphere. This covers the first 20km which is where almost all aviation takes place. For variations in density beyond this level to the edge of space, where continuous gas behaviour no longer applies, a rough approximation can be used by assuming there is a logarithmic decay from sea level to the edge of space.

where **h** is
the altitude in kilometers.

__High Altitude Density
Approximation__

While this estimate is rather crude for small changes over the atmosphere near the earth's surface, it is a simple way to estimate density effects for drag on launch vehicles that will rapidly go from surface to orbital altitudes of 200 to 300km or more.