There have been several questions recently about the details of the definition of the Karman Line and the history of those calculations. This is not about those issues.

The question is: In practical, mission planning terms, is the Karman Line at 100km ever actually used?

I am not asking about a replacement definition for the line. Nor about alternative ideas of what the line could be. I am asking about whether having any line is useful at all.

  • $\begingroup$ It is exactly as useful as the length of "a westward climb along the eastern and northern slopes of Mount Penteli to the pass of Dionysos, and then a straight southward downhill path to Athens", which is another challenging trip which "includes a very steep initial climb" and results in a patch. $\endgroup$ – uhoh Oct 28 '18 at 6:45
  • $\begingroup$ There is a range around the Karman line. Within this range, no airplane could fly using the aerodynamical lift force and no satellite may stay in orbit longer without using thrust to fight drag. This range is just crossed by satellites inserted to orbit or reentering the atmosphere. But there is no exact definition of this range. $\endgroup$ – Uwe Oct 28 '18 at 9:36

The Karman line is used for two things:

  1. to legally separate the airspace above a country (over which the country has jurisdiction) from space (over which the country has no jurisdiction).
  2. to determine who has been "in space" and gets to be called an astronaut (but the USA uses a different definition, 80 km, to make sure the X-15 pilots were included).
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  • $\begingroup$ Not all X-15 pilots could be included by using the 80 km definition. The pilot of flight 64 Neil A. Armstrong had to wait some years for his astronaut badge. $\endgroup$ – Uwe Oct 28 '18 at 8:56
  • $\begingroup$ Armstrong may not have cared a whole lot about his X-15 astronaut badge :) $\endgroup$ – Organic Marble Oct 28 '18 at 13:26
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    $\begingroup$ The legal distinction is the most important thing about the Karman line. Launching things into another country's airspace is a very touchy subject, while satellites will necessarily fly over many countries. National airspace being legally cut off at a specific altitude is absolute necessity to make spaceflight politically possible. $\endgroup$ – SF. Oct 28 '18 at 15:12
  • $\begingroup$ There may be countries who use the 100-km-mark as the upper national airspace boundary, but I dunno of any. There is no internationally binding boundary between national space and outer space. The American FAA is using the 50-mi-mark. According to Wikipedia, the Space Shuttle flew above another country (probably Mexico) less than 50 mi high without any uproar. On the other hand, some equatorial countries declared their national airspace up to geostationary orbit (which is higher than 20,000 mi). $\endgroup$ – LoveForChrist Jun 9 at 17:59
  • $\begingroup$ @Uwe and OrganicMarble Neil Armstrong never crossed the 50-mi-mark in the X-15. His highest X-15 flight went to 207,500 ft. $\endgroup$ – LoveForChrist Jun 9 at 18:00

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