The question is simple, the answer is less. While billionaires Richard Branson and Jeff Bezos both claimed to have reached space on their respective flights on July 11 and 20, the question of where Earth’s atmosphere ends and space begins does not tolerate a formal answer. “The definition, or rather the international ‘norm’ when talking about space, is 100 km, but the limit of space is not a registered definition – as the kilogram can be”, reveals Christophe Bonnal, CNES engineer and launch vehicle expert.
He explains that there is no clear definition, “which is quite surprising since we have been talking about outer space since the 1950s in all the texts. What is implied is that it is the zone that lies above the atmosphere, but even there it is not very clear: when we observe the different layers of the atmosphere, we realize that at more than 10,000 km in the exosphere there is still a little atmosphere, although it is very tenuous, so there is no physico-chemical boundary.”
Space – and its limits – have been debated for decades. At the beginning of astronautics, “the science of navigation in space”, according to the definition of Larousse, there was a rivalry between the United States and the Soviet Union, which used different units of calculation (nautical mile, statute mile, kilometer), which has contributed to a show confusion. An engineer and physicist born in Budapest in 1881, naturalized American, contributed greatly to refining this definition: Theodore von Kármán, who gave his name to the limit currently recognized by the International Aeronautical Federation (FAI).
“It is a rather ‘elegant’ solution”, explains Christophe Bonnal: “as long as there is enough atmosphere to sustain the aircraft, we are still in the atmosphere. The higher we go, the less dense the air is, it is therefore necessary to increase the speed (to generate the phenomenon of lift which enables the plane to sustain itself, ed. note). The limit is about 7,800m/s, which is equivalent to 30,000 km/h , or the orbital speed, and at that point , it there’s no point in having wings”. Furthermore, as Christophe Bonnal points out, “within the various space agencies, after the work done on the re-entry of rockets into the atmosphere, it is considered that there is a limit of 120 km below which already the effects of atmosphere”. The altitude has been rounded to 100 km for greater clarity and adopted by the FAI and the vast majority of space actors.
A boundary that is subject to interpretation
The US Army, FAA (Federal Aviation Authority), and NASA, on the other hand, set the space limit to 50 miles (80 km), allowing Richard Branson to receive his astronaut “wings” upon returning from his flight. “He has actually reached space according to the definition of the US Air Force, but he has to specify it, moreover he says ‘the Virgin astronauts'”, states the CNES engineer, who continues: “the plane designed by Richard Branson cannot exceed 85 -86 km, because the engine has to be cut off too early, to avoid vibrations, so he would either have to develop a new engine, which would waste his time, or make do with what he has, and therefore ‘cheat’ in a certain way”.
“Jean-François Clervoy says that when he carried out his first mission aboard the American shuttle, past the 90 km line, his colleagues turned to him and told him: ‘that’s it, you’re an astronaut'”, reports Christophe Bonnal.
Not all space tourists will be astronauts
As for whether space tourists can qualify as astronauts, the engineer tempers: “If we consider the root of the word astronaut, it is ‘one who navigates between the stars’, and therefore is in orbit and does not make a launch to climb four minutes to 100 km and then fall back to the same place”.
The FAA has also updated its criteria for defining an astronaut in a document published on July 20: thus, it is necessary to “meet requirements regarding the qualification and training of flight crews”; has flown more than 80 km above the earth’s surface as a flight crew; “has demonstrated that he performed activities during the flight that were essential to public safety or that contributed to the safety of manned spaceflight”. The stated goal is to “maintain the prestige of astronaut wings” – knowing that, at least for now, it’s a US rule that hasn’t (yet) been adopted by the FAI.
Therefore, if passengers on Blue Origin and Virgin Galactic flights should not be able to claim the title of astronaut under the new FAA definition, neither should future passengers on flights aboard Crew Dragon. : Elon Musk aims to offer three-day trips in orbit, or about forty laps around the Earth. Called Inspiration4, the mission is currently scheduled for September 2021.
This article originally appeared on Business Insider France
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