top of page

Space: The Line Must Be Drawn…Where?

By David Manthos

Where does air space end and outer space begin? Since 1966, the United States has persistently argued that this question does not yet need to be answered. But now that vehicles and missiles capable of operating in the grey area between these domains are functional or imminent, the time has come to draw a clear line in the atmosphere.

Legally, air space and outer space are very different. The Chicago Convention of 1944 asserts that signatory states have “complete and exclusive sovereignty over the airspace above its territory.” But the Outer Space Treaty of 1967 (OST) asserts that space and celestial objects are “not subject to national appropriation” and are to be open to all nations exclusively for peaceful purposes.

The principle of freedom of international space was tentatively set a decade earlier when the Soviet Union launched the Sputnik satellite on October 4, 1957. In a memo summarizing a White House briefing on the launch, President Eisenhower’s Deputy Secretary of Defense, Donald Quarles, optimistically noted, “the Russians have in fact done us a good turn, unintentionally, in establishing the concept of freedom of international space—this seems to be generally accepted as orbital space, in which the missile is making an inoffensive passage.”

So if a line is to be drawn, where should it be? One widely-accepted boundary is the Kármán line, named for a Hungarian physicist who attempted to calculate the maximum achievable altitude for conventional aircraft. Kármán’s calculations in 1956 put the line at 83.8 km (~50 miles), but over time this imaginary line has been rounded up to 100 km (~62.5 miles). The UN Committee On the Peaceful Uses of Outer Space (COPUS) notes there are many justifications for a line drawn around 100-130 km, and that various delegations have supported such a limit over the years. On the other hand, the U.S. military and government has generally considered anyone who has reached an altitude of 50 miles (~80 km) as eligible to be recognized as an “astronaut.”

Why might the international community need to decide, finally and jointly, as a matter of law, where to draw the line?

First, there is an accelerating arms race for hypersonic weapons that can operate between 40 and 100 km above the Earth’s surface. President Trump brags about America’s “super duper” and “hydrosonic” (sic) missiles, but at least publicly the U.S. appears to be behind Russia and China’s advancement in hypersonic technology

Second, experimental manned and unmanned spacecraft including the SR-72, X-37B, a mysterious Boeing mothership, and Russian and Chinese counterparts are all systems that could fly at extreme altitudes and drop into conflict zones. Planes and missiles of this type could create international conflict simply by overflying other nations en route to a war zone. For example, if the U.S. considers 80 km to be the edge of space but Iran says 120 km is the limit, Iran could argue that they may legally target a U.S. hypersonic vehicle flying at 90 km over Iran on its approach to Afghanistan.

Third, commercial spaceflight and suborbital tourism may soon be a reality. Virgin Galactic is entering the final testing stages for its Unity spacecraft, planning to fly Sir Richard Branson as early as Q1 2021. Likewise, Spacex is proposing global commercial flights via the Starship rocket with flight times under an hour to any point on Earth. Without a clear delineation between airspace and outer space, these flights will have to seek permission to “enter” each nation’s airspace, go around uncooperative nations, or risk creating international incidents.

Arguments against drawing a line have included concerns that prematurely setting a limit may arbitrarily restrict exploration and development of new technologies. Also, the United States may have hoped in the past to maintain ambiguity about whether high-altitude surveillance craft like the U-2 and SR-71 were spy planes or spacecraft. But bear in mind the U-2 had a service ceiling around 70,000 ft (~21 km) and the SR-71 operated at 85,000+ ft (~26 km), far short of even the lowest proposed threshold.

Some functionalists suggest that U.S. resistance to explicit boundaries relates to how such a definition would impact the country’s use of intercontinental ballistic missiles (ICBM). A detailed analysis of the OST relating to ICBMs could be the subject of a much longer article, but the question whether ICBMs enter outer space is not dependent on line drawing in the atmosphere. Even in a 1967 force assessment of the Soviet nuclear arsenal, the CIA noted several Soviet missile tests achieved a rather anemic apogee of only 300 nautical miles (~550 km), compared to 700 nm (1,300 km) for a “normal ICBM.” By comparison, the International Space Station orbits at an altitude of approximately 400 km. Consequently, ICBMs unquestionably enter outer space.

While militaries with 80+ km flight capability may benefit from this legal ambiguity in order to carry out a few surprise attacks or surveillance flights, technology is rapidly catching up to this question. Whether we draw the line at 80 km as the top of the flyable atmosphere, 320 km as the lowest orbit that can be sustainably maintained by a satellite without propulsion, or somewhere in between, it is time to resolve this matter and prevent unnecessary future conflict.


bottom of page