jmskip
commented
2 days ago There is no universally accepted definition of where space begins. NASA does not define it. The Kármán line, an imaginary and somewhat arbitrary boundary approximately 62 miles (100 kilometers) above sea level, is considered by many to be where space begins. At this altitude, there's no appreciable air to breathe or scatter light, so the sky appears black instead of blue. The US FAA (https://www.faa.gov/space/human_spaceflight), while also not defining where space begins, recognizes "any flight crew or space flight participant who is on an FAA-licensed launch or reentry vehicle and reaches 50 statute miles above the surface of the Earth" by listing their name on the FAA Commercial Human Space Flight Recognition web page (https://www.faa.gov/space/human_spaceflight/recognition/).
(Here's a link that directly addresses the issue: https://www.space.com/42733-virgin-galactic-space-claim-relies-on-karman-line.html)
I propose the following terms:
o Parabolic flight - a flight within the Earth's atmosphere where an aircraft describes a series of parabolic arcs lasting on the order of tens of seconds to simulate microgravity
o Suborbital space flight - a flight in which a vehicle, launched from either the ground or from an aircraft, has a trajectory which carries it above a substantial part of the Earth's atmosphere but does not reach orbit. The occupants and/or contents experience a period (typically minutes) of microgravity by virtue of being in free fall.
NASA's definition doesn't specify a point of delimitation between Earth's atmosphere and space. However, the Kármán line, an imaginary boundary about 62 miles (100 kilometers) above sea level, is generally accepted as the place where space begins. At this altitude, there's no appreciable air to breathe or scatter light, so the sky appears black instead of blue.