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Redefining the Kármán Line: Drawing the Boundary for Outer Space

Redefining the Kármán Line: Drawing the Boundary for Outer Space

Earth observation from the International Space Station (Courtesy of NASA)

Our time is a time for crossing boundaries.
— Pranav Mistry

At the end of 2018, Virgin Galactic made space tourism headlines with its spacecraft, SpaceShipTwo, reaching “Outer Space” for the very first time. I put Outer Space in quotes because a debate quickly ensued on whether SpaceShipTwo actually reached Outer Space. By achieving an altitude of 82.68 km (51.37 miles), some are arguing that Virgin Galactic did not reach Outer Space given that the widely-used boundary, the Karman Line, is set at 100 km (62.14 miles). Looking into this issue, I discovered that there isn’t a universally-accepted demarcation line for the beginning of Outer Space.

In this post, I provide an in-depth look at the line for Outer Space. First, I examine the geopolitical reasons behind the absence of an Outer Space boundary. Then, I summarize the leading positions on where the Outer Space line should be drawn. Finally, using an amalgamation of these perspectives, I propose my own demarcation line for Outer Space: treating the altitude of 80 km above sea level as the boundary, and, for geopolitical reasons, establishing—what I like to call—a “Transitionary Outer Space Zone” (“TOS Zone”) between the altitudes of 80 km to 100 km that is similar in concept to the “Exclusive Economic Zone” as a part of the Law of the Sea.

The Non-Outer Space Line: Omission by Purpose

The United Nation Committee on the Peaceful Uses of Outer Space (UNCOPUOS) has tried numerous times to create a “definition and delimitation of Outer Space.” While nations such as Australia, Kazakhstan, and Denmark have officially recognized an altitude of 100 km as the beginning of Outer Space, UNCOPUOS acknowledged that “there is a lack of political will to negotiate and agree on a boundary at the international level.”

Specifically, the United States has strenuously rejected all efforts in creating a demarcation line for Outer Space; America’s 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.” For United States, with air superiority second to none, there is a logical reason why not having a boundary is useful. Without an internationally-accepted legal definition for the beginning of Outer Space, the U.S. military is provided the unfettered ability to navigate the air space above any nation as long as its planes are “high enough.” With the lack of a boundary, it is hard for any foreign country to demand America to stop these activities as no one can definitely prove where “high enough” starts.

But, the basic tenet behind this intentional omission might be falling apart in this new space age. As commercial entities develop their capabilities in reaching altitudes that were once reachable only by government or government-affiliated entities, the need for a boundary grows. Without a line defining where Outer Space begins, uncertainties related to jurisdiction, policy, and liability could cause legal headache and impede further progress in many Outer Space related industries.

The Unofficial Gold Standard: Kármán Line

With the need for a demarcation line growing, the first candidate that many look to is the Karman Line: 100 kilometers or about 62 miles above sea level. Currently, this is the official boundary of Outer Space used by the World Air Sports Federation—or Federation Aeronautique Internationale (“FAI”). This is the world’s leading governing body for air sports who also maintains various world records for aerospace and spaceflight activities.

The FAI’s demarcation line is named after Theodore Von Karman, a Hungarian-American engineer and physicist. Through his aerospace research, Karman discovered that at a certain altitude, the atmosphere becomes so thin that the speed needed (forward thrust) to keep the object in the air (lift) is close to or greater than the orbital speed (related to free fall) at that altitude. At that level, centrifugal forces would take over and the object would stay in the air due to free fall rather than forward thrust. In other words, at this altitude, orbital mechanics (e.g., free fall) is more important than aerodynamic operations (e.g., lift).

Karman calculated this altitude to be 83.8 kilometers or about 52 miles above sea level. While Karman was not trying to define the boundary of Outer Space via his research, this result was eventually adapted by many, including the FAI, as the foundation for where Outer Space should start. Instead of using 83.8 kilometer, FAI decided in 1960 to use the easier to remember and more round number of 100 kilometers as the altitude that separates astronautics operations from aerospace activities. Thus, the 100 km “Karman Line” was born.

The Other Perspective: The Case for the 80 km Line

However, the FAI recently announced that it is looking to “change” the Karman Line. One likely candidate is an altitude of 80 kilometers, or about 50 miles, above sea level; this change would likely garner significant support.

First, there’s precedent for the 80 km boundary line. The United States Air Force awards astronaut badge to any military personnel who have flown or served on “a powered vehicle designed for flight above 50 miles from the earth’s surface.” NASA and Federal Aviation Administration appear to do the same.

Furthermore, as discussed earlier, Karman found that 83.3 kilometers is the altitude where free fall is more important than lift. This level, at about 52 miles, is much closer to the 80km/~50 miles boundary than the currently recognized Karman Line. If we are going to call this altitude the “Karman Line,” then it’s only fair that we should at least modify the boundary to a level that is closer to the actual altitude that Karman, the person the line is named after, found through his research.

A Side Perspective: The Mission’s Intention

Another perspective, supported by Thomas Gangale, that has garnered some interest recently is to define Outer Space by the intention of the object rather than by an altitude. Under this perspective, Gangale argues that it is the planned destination of the airborne object that should define its classification as a spacecraft or aircraft. Even if the object does not reach Outer Space or a certain altitude, if its plans were to go to Outer Space, it would still be a spacecraft. Hence, if such a launch were to fail, the resulting legal liabilities would be determined through space-related rules and regulations rather than the ones governing airplane operations.

However, by making it subjective and based on the intention of the object, this perspective actually blurs the line and introduces additional ambiguity. For instance, it could lead to individuals abusing the system by outwardly stating intentions of reaching Outer Space even when if it is not their actual goal. When we turn our legal regime strictly on only subjective distinctions, we incentivize entities to choose the legal regime most favorable for them and create a policing problem: other than clear-cut cases, no one can ever prove with certainty whether an object is meant to be a spacecraft or an aircraft.

However, that is not to say some subjectivity is not useful for defining an artificial and “invisible” line in the air. But there needs to be some objectivity that can serve as a foundation. This balance between objectivity and subjectivity is something that I tried to solve through my proposal.

My Proposal: Drawing from the Law of the Sea

After examining these leading perspectives, I believe that we need an Outer Space boundary that has an objective element and allows for certain subjective flexibility. Hence, I propose that we should set the legal boundary for Outer Space at 80 kilometers above sea level but also establish, what I like to call, a “Transitionary Outer Space Zone” (“TOS Zone”) between 80 kilometers to 100 kilometers similar to the concept of “Exclusive Economic Zone” for the Law of the Sea.

First, I believe we should revert back to the 80 km altitude line to mark the beginning of Outer Space. As discussed, objective scientific evidence demonstrates that at around the 80 km altitude, the astronautic principle of orbital velocity becomes more important than the aeronautical concept of lift for a flying object. This makes the 80 km line the perfect segue for the demarcation of Outer Space. After all, Outer Space travel is not about the calculation of atmospheric factors but rather rooted in the principles of gravitational forces (e.g., planning a free-return trajectory from the Moon or using the Hohmann transfer orbit). When a spacecraft no longer have to consider the influence of any planetary specific factors, then it must be in the realm of Outer Space. Since the science here is not exact, even if Karman calculated this altitude at 83.8 km, we can round it to the nearest round number of 80 km; this would make it more precise than the 100 km currently in place.

However, in order to get this boundary established, we also need to account for the geopolitical challenges that have inhibited the establishment of such border in the first place. By adding in a subjective element, a 20 km TOS Zone between the altitudes of 80 km and 100 km, I believe we can bring more hesitant nations onboard with this idea. Some nations are troubled by a bright-line boundary as it would restrict these nations’ abilities to operate with a certain level of impunity; it’s hard for such nation’s aerospace activities over another nation to be challenged if the former nation could use the ambiguity to argue that its activities are actually in the free-for-all realm of astronautic activities. But, if we take the concept of “Exclusive Economic Zone” from the Law of the Sea, we can have the demarcation line as well as mitigate the concerns of these nations.

Under the concept of Exclusive Economic Zone, a coastal nation-state would have exclusive “sovereign rights for the purpose of exploring and exploiting, conserving and managing the natural resources” of the zone that is within 200 nautical miles from its coastal baseline. However, within such Exclusive Economic Zones, other nations would still enjoy “the freedoms . . . of navigation and overflight . . . and other internationally lawful uses of the sea related to these freedoms, such as those associated with the operation of ships, aircraft and submarine cables and pipelines.” Hence, while a nation could claim the resources of such territory, it must allow other nations unimpeded access to this territory for lawful reasons.

We can port this concept into a demarcation zone for Outer Space by creating the TOS Zone. This zone would begin at my proposed boundary for Outer Space, 80 km, and end at the current level for the Karman Line, 100 km. In this zone, all spacecrafts have the ability to freely traverse. However, any foreign spacecraft within another nation’s TOS Zone cannot remain in a “holding pattern” or act as a “nuisance.” Prohibited activities could include: (1) aimlessly circling around and remaining in another nation’s TOS Zone without permission, (2) annoying or harassing a nation within its own TOS Zone, (3) interfering or impeding with the activities of a nation in its own TOS Zone (when this occurs, such foreign nation’s objects must give way) or (4) when technology progress to such a state: building or operating any permanent hovering airbases in another nation’s TOS Zone.

By creating the TOS Zone, we can mitigate some nations’ concerns with the establishment of an Outer Space boundary. These nations could be reassured by the fact that a certain range of altitudes is still available for every nation’s use even with the demarcation line. Nevertheless, because activities in this TOS Zone will be regulated, it would also confer certain protections for the nation underneath and guarantee that such nation’s activities will take precedent and will not experience unduly interference within its own TOS Zone.

A New Vision for Outer Space

By defining the Outer Space boundary at 80 km and adding in a 20 km Transitionary Outer Space Zone on top of that, I believe my proposal provides the air cover needed to create a legal regime that will be sustainable for both future governmental and commercial growth in the Outer Space sector. By working to define such fundamental concepts such as the demarcation of Outer Space or whether space tourists can be considered astronauts, we can start building the foundation to provide the certainty necessary for continued investment and progress in Outer Space exploration and development.


Why Defining the Boundary of Space May be Crucial for the future of Spaceflight https://www.theverge.com/2018/12/13/18130973/space-karman-line-definition-boundary-atmosphere-astronauts

Matters relating to the definition and delimitation of outer space: replies of the International Institutes of Space Law (IISL) http://www.unoosa.org/res/oosadoc/data/documents/2017/aac_105c_22017crp/aac_105c_22017crp_29_0_html/AC105_C2_2017_CRP29E.pdf

The Edge of Space: Revisiting the Karman Line https://arxiv.org/abs/1807.07894


FAI Astronautic Records Commission: 100KM Altitude Boundary for Astronautics https://www.fai.org/page/icare-boundary

Statement about the Karman Line https://www.fai.org/news/statement-about-karman-line

What’s in a name: The Definition of a “Space Object” https://www.icao.int/Meetings/SPACE2016/Presentations/1%20-%20F.%20VonDerDunk%20-%20University%20of%20Nebraska-Lincoln.pdf

Exclusive Economic Zone: http://www.un.org/depts/los/convention_agreements/texts/unclos/part5.htm

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