space equivalent zone (uncountable)

1. (aviation) The top of the Earth's atmosphere, from 50,000 ft (the start of the stratosphere) and up (to the edge of the exosphere at 1000 mi); where the effects of exposure to the environment on human life is similar to that of exposure to space; it being physiologically incompatible with human life.

Both the Armstrong line (63,000ft) and the Karman line (100km) lie within this zone, as does low Earth orbit (LEO) as LEO still encounters wisps of atmosphere.

• physiological efficient zone (lower than 12,500ft)
• physiological deficient zone (12,500-50,000ft)
• space zone (1000mi and up)