# What physical ways can the Kármán line be used? [closed]

I have also seen many posts on this. I understand what the line is used for legally. The Kármán plane or a plane that is most efficient at the line regardless of the shape seems not to have a specific purpose but maybe I am wrong?

I left this link below as an example on how the line might be used:

Challenging the Kármán line from above

• @uhoh fix it i think you may change it. – Muze Dec 26 '18 at 18:12
• One particular user seems to be obsessing about it, and resisting urges to take a look into an orbital mechanics book. Thus, ignorance prevails and the circle repeats itself. – AtmosphericPrisonEscape Dec 27 '18 at 0:51

For a number of reasons human reasons like giving someone astronaut wings, winning the X prize or for rules around national boundaries there is a need for a hard divider between 'space' and 'atmosphere' and the calculations for the Karman line provide a convenient mathematical way to do that. The fact that the Karman line of 100km used for most purposes is actually some distance from the ~85km point that Karman calculated is possibly telling in terms of how meaningful the value is other than it being a round number higher than aircraft can fly and lower than space craft can sensibly sustain orbit.

So the Karman line is a legal construct for space law and administration, and almost meaningless for actual engineering.

• What about for reentry? – Muze Dec 26 '18 at 18:14
• @Muze - The only real impact to re-entry is that legally you would need airspace and traffic clearance for every nation your profile crosses below 100km, so a complication in doing space operations out of smaller nations. All other engineering for heat/drag etc needs to start well above that point and be tapered in. – GremlinWranger Dec 26 '18 at 22:55
• but even that is a legal impact, not a physical one – user20636 Dec 27 '18 at 21:44

It's a pretty abstract boundary, with gradual changes either side, of no practical use.

No "line" has never[sic] found a practical use in engineering, and it has been misinterpreted by lawyers as having some physical significance it does not in fact have.

"How High the Sky?" Thomas Gangale, p. 156