Where is Outer Space?

I did not make it to the Galloway Symposium in December 2018 because of a travel conflict. I clearly missed an excellent presentation on scientific considerations of where outer space is.  Dr. Jonathan McDowell of the Harvard-Smithsonian Center for Astrophysics presented his paper The Edge of Space: Revisiting the Von Karman Line.  Looking at the inner edge of space from historical, physical and technological viewpoints, he proposes 80 kilometers as a more appropriate boundary than the currently popular 100 km Von Karman line.

In his presentation at the Galloway, he prepared some excellent slides (with cool pictures) laying out the history and logic for his proposal.  In the slides, he concludes that:

1) Elliptical orbit satellites can sustain perigees of 80-90 km but not 70 km

2) Lifting vehicles (airplanes, balloons) can operate up to 50 km or so but not 55 km

3) The effective Karman line (gravity force = aerodynamic force)is between 65 and 90 km depending on time, latitude and satellite properties, and is about 77 km for the ‘most typical’ values

4) The natural physical boundary region is the mesosphere from 50 to (85-100) km or so. The stratopause is at about 50 km, the mesopause varies with time and latitude

Reijnen’s “mesospace”, Sgobba’s “near space”, Pelton’s “protozone” should therefore be located in the physical mesosphere

The USAF were right! 80 km (50 miles) is a good dividing line, perhaps with a transitional protozone or ‘mesozone’ underneath it extending from 50 or 65 km to 80 or 90 km.

I propose that – for *scientific* purposes:

Geodetic heights up to 50 km are ‘air’

Geodetic heights above 80 km are ‘space’

Geodetic heights from 50 to 80 km are the ‘protozone’ or ‘mesozone’

Check it out.