Jump to content

Kármán line

From Wikipedia, the free encyclopedia
(Redirected fromKarman Line)
ForThe Kármán Line,the British drama short film, see§ In popular culture.
Earth's atmosphere photographed from theInternational Space Station.The orange and green line ofairglowis at roughly the altitude of the Kármán line.[1]

TheKármán line(orvon Kármán line/vɒnˈkɑːrmɑːn/)[2]is a conventional definition of theedge of space.It is not universally accepted. The international record-keeping bodyFAI(Fédération aéronautique internationale) defines the Kármán line at an altitude of 100 kilometres (54 nautical miles; 62 miles; 330,000 feet) abovemean sea level.

While named afterTheodore von Kármán,who calculated a theoretical limit of altitude for airplane flight at 83.8 km (52.1 mi) above Earth, the later established Kármán line is more general and has no distinct physical significance, in that there is a rather gradual difference between the characteristics of the atmosphere at the line, and experts disagreeing on defining a distinct boundary where the atmosphere ends and space begins. It lies well above the altitude reachable by conventional airplanes orhigh-altitude balloons,and is approximately where satellites, even on very eccentric trajectories, willdecaybefore completing a single orbit.

The Kármán line is mainly used for legal and regulatory purposes of differentiating betweenaircraftandspacecraft,which are then subject to different jurisdictions and legislations. Whileinternational lawdoes not define the edge of space, or the limit of national airspace,[3][4]most international organizations and regulatory agencies (including the United Nations) accept the FAI's Kármán line definition or something close to it.[5]As defined by the FAI, the Kármán line was established in the 1960s.[6]Various countries and entities define space's boundary differently for various purposes.[7][3][8]

Definition

[edit]
A dark blue shaded diagram subdivided by horizontal lines, with the names of the five atmospheric regions arranged along the left. From bottom to top, the troposphere section shows Mount Everest and an airplane icon, the stratosphere displays a weather balloon, the mesosphere shows meteors, and the thermosphere includes an aurora and the Space Station. At the top, the exosphere shows only stars.
The layers of Earth's atmosphere with the Kármán line indicated (not to scale)[9]

The FAI uses the term Kármán line to define the boundary between aeronautics and astronautics:[6]

  • Aeronautics:For FAI purposes, aerial activity, including all air sports, within 100 km of Earth's surface.
  • Astronautics:For FAI purposes, activity more than 100 km above Earth's surface.

Interpretations of the definition

[edit]

The expressions "edge of space"or" near space "are often used (by, for instance, the FAI in some of their publications)[10]to refer to a region below the boundary of Outer Space, which is often meant to include substantially lower regions as well. Thus, certainballoonorairplaneflights might be described as "reaching the edge of space". In such statements, "reaching the edge of space" merely refers to going higher than average aeronautical vehicles commonly would.[11][12]

There is still no international legal definition of the demarcation between a country's air space and outer space.[13]In 1963,Andrew G. Haleydiscussed the Kármán line in his bookSpace Law and Government.[14]In a chapter on the limits of nationalsovereignty,he made a survey of major writers' opinions.[14]: 82–96 He indicated the inherent imprecision of the Line:

The line represents ameanormedianmeasurement. It is comparable to such measures used in the law asmean sea level,meanderline,tideline; but it is more complex than these. In arriving at the von Kármán jurisdictional line, myriad factors must be considered – other than the factor of aerodynamic lift. These factors have been discussed in a very large body of literature and by a score or more of commentators. They include the physical constitution of theair;the biological and physiological viability; and still other factors which logically join to establish a point at which air no longer exists and at whichairspaceends.[14]: 78, 9 

Kármán's comments

[edit]

In the final chapter of his autobiography, Kármán addresses the issue of the edge ofouter space:

Where space begins... can actually be determined by the speed of the space vehicle and its altitude above the Earth. Consider, for instance, the record flight of CaptainIven Carl Kincheloe Jr.in anX-2 rocket plane.Kincheloe flew 2000 miles per hour (3,200 km/h) at 126,000 feet (38,500 m), or 24 miles up. At this altitude and speed,aerodynamic liftstill carries 98 percent of the weight of the plane, and only two percent is carried by inertia, orKepler force,as space scientists call it. But at 300,000 feet (91,440 m) or 57 miles up, this relationship is reversed because there is no longer any air to contribute lift: only inertia prevails. This is certainly a physical boundary, whereaerodynamicsstops andastronauticsbegins, and so I thought why should it not also be a jurisdictional boundary?Andrew G. Haleyhas termed it the Kármán Jurisdictional Line. Below this line, space belongs to each country. Above this level there would be free space.[15]

Technical considerations

[edit]

An atmosphere does not abruptly end at any given height but becomes progressively less dense with altitude. Also, depending on how the various layers that make up the space around theEarthare defined (and depending on whether these layers are considered part of the actual atmosphere), the definition of the edge of space could vary considerably: If one were to consider thethermosphereandexospherepart of the atmosphere and not of space, one might have to extend the boundary of space to at least 10,000 km (6,200 miles) above sea level. The Kármán line thus is a largely arbitrary definition based on some technical considerations.

An aircraft can stay aloft only by constantly traveling forward relative to the air (rather than the ground), so that the wings can generate aerodynamic lift. The thinner the air, the faster the plane must go to generate enough lift to stay up.[16]At very high speeds, centrifugal force (Kepler force) contributes to maintaining altitude. This is the virtual force that keeps satellites in circular orbit without any aerodynamic lift.

As altitude increases and air density decreases, the speed to generate enough aerodynamic lift to support the aircraft weight increases until the speed becomes so high that the centrifugal force contribution becomes significant. At a high enough altitude, the centrifugal force will dominate over the lift force and the aircraft would become effectively an orbiting spacecraft instead of an aircraft supported by aerodynamic lift.

In 1956, von Kármán presented a paper in which he discussed aerothermal limits to flight. The faster aircraft fly, the more heat they would generate due toaerodynamic heatingfrom friction with the atmosphere andadiabatic processes.Based on the currentstate of the art,he calculated the speeds and altitudes at which continuous flight was possible—fast enough that enough lift would be generated and slow enough that the vehicle would not overheat.[17]The chart included an inflection point at around 275,000 feet (52.08 mi; 83.82 km), above which the minimum speed would place the vehicle intoorbit.[18][19]

The term "Kármán line" was invented byAndrew G. Haleyin a 1959 paper,[20]based on the chart in von Kármán's 1956 paper, but Haley acknowledged that the 275,000 feet (52.08 mi; 83.82 km) limit was theoretical and would change as technology improved, as the minimum speed in von Kármán's calculations was based on the speed-to-weight ratio of current aircraft, namely theBell X-2,and the maximum speed based on current cooling technologies and heat-resistant materials.[18]Haley also cited other technical considerations for that altitude, as it was approximately the altitude limit for anairbreathing jet enginebased on current technology. In the same 1959 paper, Haley also referred to 295,000 feet (55.9 mi; 90 km) as the "von Kármán Line", which was the lowest altitude at whichfree-radicalatomic oxygenoccurred.[18]

Alternatives to the FAI definition

[edit]
Atmospheric gasses scatter the blue wavelengths, thus giving the Earth a blue arc. As the altitude increases the atmosphere decreases such that by several criteria it ceases to exist. Optically the atmospheric halo here gradually fades into the blackness of space.

TheU.S. Armed Forcesdefinition of anastronautis a person who has flown higher than 50 miles (80 km)above mean sea level,approximately the line between themesosphereand thethermosphere.NASAformerly used the FAI's 100-kilometre (62-mile) figure, though this was changed in 2005 to eliminate any inconsistency between military personnel and civilians flying in the same vehicle.[21]Three veteran NASAX-15pilots (John B. McKay,William H. DanaandJoseph Albert Walker) were retroactively (twoposthumously) awarded theirastronaut wings,as they had flown between 90 km (56 miles) and 108 km (67 miles) during the 1960s, but at the time had not been recognized as astronauts.[11]The latter altitude, achieved twice by Walker, exceeds the modern international definition of the boundary of space.

The United StatesFederal Aviation Administrationalso recognizes this line as a space boundary:[22]

Suborbital Flight: Suborbital spaceflight occurs when a spacecraft reaches space but its velocity is such that it cannot achieve orbit. Many people believe that in order to achieve spaceflight, a spacecraft must reach an altitude higher than 100 kilometers (62 miles) above sea level.

Works byJonathan McDowell(Harvard-Smithsonian Center for Astrophysics)[23]andThomas Gangale(University of Nebraska-Lincoln) in 2018[18][24]advocate that the demarcation of space should be at 80 km (50 miles; 260,000 feet), citing as evidence von Kármán's original notes and calculations (which concluded the boundary should be 270,000 ft), confirmation that orbiting objects can survive multiple perigees at altitudes around 80 to 90 km, plus functional, cultural, physical, technological, mathematical, and historical factors.[3][25]More precisely, the paper summarizes:

To summarize, the lowest possible sustained circular orbits are at of order 125 km altitude, but elliptical orbits with perigees at 100 km can survive for long periods. In contrast, Earth satellites with perigees below 80 km are highly unlikely to complete their next orbit. It is noteworthy that meteors (travelling much more quickly) usually disintegrate in the 70–100 km altitude range, adding to the evidence that this is the region where the atmosphere becomes important.

These findings prompted the FAI to propose holding a joint conference with theInternational Astronautical Federation(IAF) in 2019 to "fully explore" the issue.[10]

Another definition proposed ininternational lawdiscussions defines the lower boundary of space as the lowest perigee attainable by an orbiting space vehicle, but does not specify an altitude.[26]This is the definition adopted by the U.S. military.[27]: 13 Due to atmospheric drag, the lowest altitude at which an object in a circular orbit can complete at least one full revolution without propulsion is approximately 150 km (93 miles),[28]whereas an object can maintain anelliptic orbitwithperigeeas low as about 90 km (56 miles) without propulsion.[citation needed]The U.S. government is resisting efforts to specify a precise regulatory boundary.[29][30]

For other planets

[edit]

While the Kármán line is defined for Earth only, several scientists have estimated the corresponding figures forMarsandVenus.Isidoro Martínez arrived at 80 km (50 miles) and 250 km (160 miles) high, respectively,[31]while Nicolas Bérend arrived at 113 km (70 miles) and 303 km (188 miles).[32]

[edit]

In 2014, Oscar Sharp directedThe Kármán Line,a British live-action drama short film starringOlivia Colmanas Sarah, a wife and mother who suddenly starts levitating until she slowly and eventually crosses the eponymous Kármán line and into outer space.[33]

See also

[edit]

References

[edit]
  1. ^"Airglow Over the Indian Ocean".NASA Earth Observatory. 2020-10-08.Retrieved2024-04-20.
  2. ^"von-karman".Dictionary Unabridged(Online). n.d.
  3. ^abcVoosen, Paul (2018-07-24)."Outer space may have just gotten a bit closer".Science.doi:10.1126/science.aau8822.S2CID126154837.RetrievedApril 1,2019.
  4. ^Harwood, William;"Richard Branson and Virgin Galactic complete successful space flight",CBS News,2021-07-12
  5. ^"The Kármán Line: Where does space begin?".5 March 2021.
  6. ^abSanz Fernández de Córdoba, Dr. S. (2004-06-24)."The 100 km Boundary for Astronautics".Fédération aéronautique internationale.Retrieved28 December2020.
  7. ^Drake, Nadia(2018-12-20)."Where, exactly, is the edge of space? It depends on who you ask".National Geographic.Archived fromthe originalon March 4, 2021.Retrieved2021-07-14.
  8. ^"Air Force Guidance Memorandum to AFMAN 11-402"(PDF).Department of the Air Force.2021-05-27.RetrievedJuly 13,2021.
  9. ^Layers of the Atmosphere,National Weather Service JetStream – Online School for Weather
  10. ^ab"Statement about the Karman Line".Fédération aéronautique internationale (World Air Sports Federation).2018-11-30.RetrievedApril 1,2019.
  11. ^abLevine, Jay (2005-10-21)."A long-overdue tribute".NASA.Retrieved2006-10-30.
  12. ^"World Book @ NASA".NASA. Archived fromthe originalon May 4, 2009.Retrieved2006-10-18.
  13. ^International Law: A Dictionary,by Boleslaw Adam Boczek; Scarecrow Press, 2005; page 239: "The issue whether it is possible or useful to establish a legal boundary between airspace and outer space has been debated in the doctrine for quite a long time.… no agreement exists on a fixed airspace – outer space boundary…"
  14. ^abcHaley, Andrew G.;(1963)Space Law and Government,Appleton-Century-Crofts
  15. ^von Kármán, Theodore;Edson, Lee (1967).The Wind and Beyond,p. 343
  16. ^Benson, Tom, ed. (2014-06-12)."The Lift Equation".Glenn Research Center.National Aeronautics and Space Administration.Archived fromthe originalon 2015-03-17.Retrieved2015-03-14.
  17. ^Theodore von Kármán,Aerodynamic Heating – The Temperature Barrier in Aeronautics,PROC. HIGH-TEMPERATURE SYMPOSIUM, BERKELEY, CALIFORNIA (1956).
  18. ^abcdGangale, Thomas (2017)."The Non Kármán Line: An Urban Legend of the Space Age"(PDF).Journal of Space Law.41(2): 155. Archived fromthe original(PDF)on 24 May 2021.
  19. ^Grush, Loren (2018-12-13)."Why defining the boundary of space may be crucial for the future of spaceflight".The Verge.RetrievedApril 1,2019.
  20. ^Andrew G. Haley,Space Exploration: The Problems of Today, Tomorrow and in the Future,2 PROC. ON THE L. OF OUTER SPACE 49 (1959).
  21. ^Jenkins, Dennis R. (2005-10-21)."NASA – Schneider walks the Walk [A word about the definition of space]".nasa.gov.NASA.Retrieved19 October2018.
  22. ^"Space: Commercial Space Transportation Licenses: Human Spaceflight (also referred to as crewed spaceflight)",[US] Federal Aviation Administration, 2021-03-16
  23. ^McDowell, Jonathan C.(2018)."The edge of space: Revisiting the Karman Line".Acta Astronautica.151:668–677.arXiv:1807.07894.Bibcode:2018AcAau.151..668M.doi:10.1016/j.actaastro.2018.07.003.
  24. ^Gangale, Thomas (2018).How High the Sky? The Definition and Delimitation of Outer Space and Territorial Airspace in International Law.Studies in Space Law. Vol. 13. Leiden, The Netherlands:Koninklijke Brill NV.doi:10.1163/9789004366022.ISBN978-90-04-36602-2.S2CID135092905.
  25. ^Specktor, Brandon (2018-07-25)."The Edge of Space Just Crept 12 Miles Closer to Earth".Live Science.RetrievedApril 1,2019.
  26. ^"Space Environment and Orbital Mechanics".Army Space Reference Text.United States Army.2000. Archived fromthe originalon April 18, 2012.RetrievedApril 24,2012.Where Space Begins:There is no formal definition of where space begins. International law, based on a review of current treaties, conventions, agreements and tradition, defines the lower boundary of space as the lowest perigee attainable by an orbiting space vehicle. A specific altitude is not mentioned. By international law standards aircraft, missiles and rockets flying over a country are considered to be in its national airspace, regardless of altitude. Orbiting spacecraft are considered to be in space, regardless of altitude.
    U.S. definition:The U.S. government defines space in the same terms as international law.
  27. ^National Security Space Institutein conjunction withU.S. Army Command and General Staff College(2006).U.S. Military Space Reference Text.National Security Space Institute.RetrievedApril 1,2019– viaHomeland Security Digital Library.
  28. ^Lal, Bhavya; Nightingale, Emily (November 5, 2014).Where is Space? And Why Does That Matter?(PDF).Space Traffic Management Conference. Aerospace.csis.org. p. 6.
  29. ^King, Matthew T. (2016)."Sovereignty's Gray Area: The Delimitation of Air and Space in the Context of Aerospace Vehicles and the Use of Force".Journal of Air Law and Commerce.81(3): 377–497 [p. 432].
  30. ^"Delegation of the U.S., Statement on the Definition and Delimitation of Outer Space and the Character and Utilization of the Geostationary Orbit, to the Comm. on the Peaceful Uses of Outer Space, Legal Subcomm. of Its Fortieth Session (Apr. 2–13, 2001)".Archivedfrom the original on 2020-03-28.Retrieved2019-11-21.With respect to the question of the definition and delimitation of outer space, we have examined this issue carefully and have listened to the various statements delivered at this session. Our position continues to be that defining or delimiting outer space is not necessary. No legal or practical problems have arisen in the absence of such a definition. On the contrary, the differing legal regimes applicable in respect of airspace and outer space have operated well in their respective spheres. The lack of a definition or delimitation of outer space has not impeded the development of activities in either sphere.
  31. ^Martínez, Isidoro;Space EnvironmentArchived2021-07-09 at theWayback Machine,2021
  32. ^A variant of the Kármán line theory facilitating the identification of a precise altitude boundary. International Astronautical Congress 2022,Nicolas Bérend, Sep 2022, Paris, France.HAL Id:hal-03798830
  33. ^Larson, Sarah (7 May 2015)."The Screening Room:" The Kármán Line "".The New Yorker.
[edit]
Retrieved from "https://en.wikipedia.org/w/index.php?title=Kármán_line&oldid=1238583238"