Document created: 29 December 03
Air University Review, May-June
1973
What is the definition of outer space? Or, more specifically, what is the difference between national air space and outer space? The air space over each national territory is subject to that country’s sovereign control. In outer space, claims of national sovereignty have been prohibited. How is one to be distinguished from the other? The question has received much attention in recent years, and many proposals on how it might be resolved have been put forward. A great deal has also been written on the subject, and several publications of the United Nations have discussed it at some length. As yet, no consensus has emerged. However, the progress of technology may make some solution more urgent in coming years. An arbitrary decision may be the only feasible answer.
National sovereignty over air space is a primary feature of the international agreements regarding aviation. The Convention on the Regulation of Aerial Navigation, signed in Paris on 13 October 1919, provided in Article I that “. . . .every Power has complete and exclusive sovereignty over the air space above its territory.” The basic agreement governing postwar civil aviation, namely, the Convention on International Civil Aviation, signed at Chicago on 7 December 1944, reiterates the same principle, in virtually identical language.
In direct contrast, claims of exclusive national sovereignty in outer space are prohibited by international agreement. The Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space, including the Moon and Other Celestial Bodies, was concluded in 1967 under the aegis of the United Nations. Article II provides that:
Outer space, including the Moon and other celestial bodies, is not subject to national appropriation by claim of sovereignty, by means of use or occupation or by any other means.
International agreements are also developing rules of law for outer space. The Outer Space Treaty itself (Article IV, paragraph 1) pledges the signatories “not to place in orbit around the Earth any objects carrying nuclear weapons or any other kinds of weapons of mass destruction, install such weapons on celestial bodies, or station weapons in outer space in any other manner.” It also bans military bases, weapons testing, and military maneuvers from celestial bodies. The 1963 limited test-ban treaty prohibited nuclear explosions in outer space, as well as in the atmosphere and under water. In 1968, the Agreement on the Rescue of Astronauts, the Return of Astronauts and the Return of Objects Launched in Outer Space was concluded. A convention dealing with liability for damage caused by objects launched into outer space is also being negotiated.
The actual practice of nations also indicates a difference between national air space and outer space. Hundreds of objects have now been launched into orbit around the earth; in recent years no nation has protested such passage over its territory as violating its sovereignty. In fact, no nation has explicitly reserved its position concerning the passage over its territory of a space object of another country. On the other hand, no nation has been willing to limit its air space to a specific height; to do so would define the upward extent of its sovereignty and, implicitly or explicitly, the lower limit of what it considered to be outer space.
There are two general schools of thought regarding the need for and desirability of arriving soon at a clear line of demarcation between air space and outer space. One approach cites the need to delimit the legally binding obligations regarding the activities and authority of nations in outer space and air space, respectively. Without such a demarcation, it is contended, there will arise, as technology advances, disputes regarding the extent and nature of the obligations nations have assumed in the international agreements related to outer space. Similarly, without agreed definitions, a nation could assert claims of sovereignty that would interfere with space activities desired by many other countries.
The other approach argues that there is no evidence that a demarcation line is needed and that to set one now would be premature and possibly counterproductive. The proponents of this point of view call attention to the rapid pace of space technology and the practical uncertainties regarding the characteristics of feasible and desirable space activities. Trying to set a boundary now, they feel, would risk getting it too high or defined in a way that might turn out to be detrimental to future space activities. (Implicit in this viewpoint, there seems to be the expectation that the later agreement is reached, the more likely the boundary is to be set lower than it would be at present.) Those who endorse a cautious approach note that the lack of specific agreement has not led to any international difficulties and does not seem likely to. They also suggest that the effort to establish a definitive boundary could, itself, lead to controversy and confusion, as has happened in regard to the demarcation between territorial waters and the high seas.
Why not simply set the dividing line between air and outer space at the upper limit of the atmosphere? That would probably be one of the first questions by a layman. Furthermore, the international conventions that regulate aircraft seem to suggest this concept in their use of such terms as “air,” “atmosphere” and “atmospheric” space. The practical difficulty, however, is that the earth’s atmosphere does not end abruptly; it gradually transforms into outer space. Some estimates place the altitude at which air space ceases well beyond the orbits of some existing earth satellites. In fact, there is no scientific agreement on the altitude at which air space ceases.
A scientifically more sophisticated proposal might be to use the characteristics of the atmosphere to determine an appropriate dividing line between air and outer space. Suggestions have been made to establish the demarcation on the basis of differentiation between the several layers into which scientists divide the atmosphere.
The troposphere, the layer nearest the surface of the earth, extends up to about 9 to l0½ miles at the equator and 6 to 7 miles at the poles. It is the layer in which weather phenomena occur, and it is the field of operation for conventional aviation. The troposphere contains three-fourths of all the air surrounding the earth.
Most of the rest of the air in the atmosphere is contained in the next layer, called the stratosphere. It is above the weather and is reached only by the most advanced aircraft and research balloons. Its upper limit is about 25 miles. The troposphere and stratosphere contain about 99.7 percent of the air.
A third layer, called the mesosphere, extends to about 50 miles, and beyond that is the ionosphere. The latter is sparsely occupied by gas particles, less dense than the most complete vacuum that can be achieved on earth. The upper limit of the ionosphere is not defined.
The major difficulty in trying to define a boundary by utilizing the characteristics of the atmosphere is the lack of uniform criteria. The physical characteristics of the atmosphere and of the various layers can be judged by a variety of criteria, such as the composition of the gases, their densities and their temperatures. These properties are not uniform at a certain altitude. They can also vary with solar activity, time of day, season, region, and other circumstances. The boundaries between the layers of the atmosphere are thus not precise, uniform in height above the earth, or constant. Nor is it possible, because of the variance in the properties of the atmosphere, to arrive at any other boundary between air and outer space that would be precise, uniform, and constant.
The layman, faced with these scientific difficulties, might suggest using the characteristics of aircraft flight to arrive at an adequate boundary. Surely, he might think, we can define the height at which aircraft can actually fly, and everything above that could be considered outer space. The Council of the International Civil Aviation Organization (ICAO) defines an aircraft as “any machine that can derive support in the atmosphere from the reactions of the air other than the reactions of the air against the earth’s surface.” The maximum altitude at which a machine can derive support from the reactions of the air is presently estimated at about twenty one miles by the ICAO Secretariat.
One of the most widely discussed proposals for a demarcation between air space and outer space is that it be established at the altitude where aerodynamic lift yields to centrifugal force, what is known as the “Von Kármán line.” To accomplish aerial flight, weight equals aerodynamic lift plus centrifugal force. Aerodynamic lift decreases with altitude because of the decreasing density of the air. Beyond zero airlift, centrifugal force takes over.
This approach also involves several difficulties that seem to preclude a uniform and constant boundary. The theoretical limit of the height of air flight may increase as the result of such developments as improved cooling techniques or more heat-resistant materials. The aerodynamical forces also vary with the character and speed of the specific object involved. Moreover, the density of the atmosphere itself is not constant but is subject to a variety of fluctuations, as already noted.
If an approach based on the characteristics of the atmosphere and aircraft is not adequate, how about tackling the problem from the other side, that of outer space? For instance, could not outer space be defined as everything beyond the lowest point (perigee) of an orbiting satellite? At a certain altitude, the earth’s atmosphere is too dense for an artificial satellite to stay in orbit. The lowest perigee approach would have the advantages of being in accord with existing practices in orbiting satellites and with the attitudes of countries toward objects in earth orbit.
The International Law Association (not an intergovernmental body) did adopt in 1968 a definition of outer space as the space beyond the lowest perigee reached by any satellite placed in orbit before 27 January 1967, the date on which the Outer Space Treaty was opened for signature. The Association, however, added that this definition was without prejudice to the possibility of including later any part of the space below that perigee.
The association’s added qualification indicates one of the difficulties in this approach. The perigee of a durable satellite orbit at present is about 95 to 100 miles. However, improvements in space flight technology, such as orbiting with continuing rocket thrust, may lower this perigee to 70-75 miles. That large an element of legal uncertainty would hardly be compatible with a definition seeking to determine national sovereignty over air space. Another problem with this definition involved the practical questions of who determined precisely the lowest perigee of a satellite before 27 January 1967 and whether it was an active satellite or a piece of space debris.
More generally, this approach also fails to provide a precise and continuing boundary because, scientifically speaking, no precise altitude can be determined as the single lowest possible perigee of any artificial satellite. Such a determination would depend on the characteristics of the object and the atmosphere; and these vary, as already noted in connection with aircraft.
To try to meet these difficulties, a number of other approaches have been
suggested. All, however, seem to involve shortcomings of their own or do not
solve all the problems that we have noted. One suggestion has been to set the
boundary at the point where the gravitational pull of the earth ceases, this
approach deriving from the idea that a nation’s sovereignty need only extend to
the height from which an object can be dropped on its territory. However,
gravity ceases very gradually at remote heights; it is not possible to indicate
an exact altitude where a boundary could be drawn based on the earth’s
attraction. And, even if one were feasible, it would probably be much too high;
one calculation, for instance, indicates that the earth’s attraction in
relation to the moon is dominant up to some 205,000 miles, and much farther in
relation to the sun. A further practical difficulty is that the gravitational
effect of the earth depends on the escape velocity of the object, which, of
course, can vary.
Another approach tries to overcome the difficulties in defining the outer limit of the atmosphere by proposing an intermediate zone between air space and outer space. It has been noted that, as a practical matter, there exists a buffer zone between, on the one hand, the highest altitudes reached by balloons and aircraft and, on the other hand, the lowest altitude at which satellites remain in orbit without any means of propulsion. Details vary, but generally this proposal suggests an appropriate international regime in this area, between the national sovereignty of air space and the freedom of outer space. One immediate difficulty with this approach is that the present intermediate zone is likely to narrow with technological developments and may well disappear entirely. More basically, the proposal still does not solve the difficulties we have noted above in finding uniform and constant criteria that would make possible precise dividing lines between the zones.
An effort has been made to get around all these problems of scientific definition by proposing that the exclusive sovereignty of an underlying country should extend as high as it could effectively apply its authority. This principle has often been asserted in efforts to analyze the scope and effects of the international agreements governing civil aviation. However, it has equally been challenged on the grounds it would produce unacceptable disparities, conflicts, and uncertainties. Since nations are at widely different levels of scientific and technical development, their air spaces would vary greatly. If each country were allowed to project its sovereignty upward and sideward in accord with its effective power, conflicting claims would seem highly likely to occur; and there would be no way to resolve them except naked power. The criterion of effective power would also create marked uncertainties because sovereignty would vary with the development of technology.
Another attempt to avoid the difficulties of spatial definitions proposes that a distinction be made between aeronautical and astronautical activities, rather than trying to decide on a demarcation between air space and outer space. The proponents of this approach argue that a legal definition is usually needed to permit certain activities and prohibit others. Accordingly, they feel that in regard to outer space activities, it would be better to seek this objective, not by trying to set boundaries but by defining objectives and missions for space vehicles. Their thought is that the important interests of all countries can be protected more effectively, not by putting territorial limits to national sovereignty but by legally prohibiting those actions in the course of space activities that would endanger these interests.
This approach proposes that astronautical activities should be subject to one and the same legal regulation, irrespective of the altitude at which they are carried out. It would apply to them the moment they leave the earth, in order to avoid a complicated determination of their passing from one legal status to another. This concept stems from the belief that, as the scope of international space law gradually extends, international regulation will have to approach the launching pads. The only way to preserve the logical unity of legal regulation, it is contended, is by dispensing with a demarcation in space and adopting a functional criterion.
However, there are difficulties with this approach, too. It is not always possible to distinguish precisely between space activities and other activities. Using the purpose of each activity as the criterion has been suggested; but often this could be ambiguous (e.g., an aircraft equipped with scientific instruments to observe an eclipse, or balloons bearing instruments for space observations). Moreover, the prospects of scientific and technical progress in the development of aircraft and space vehicles make the practical problem of distinguishing between them ever more complicated. Another intricate problem of potentially great scope is how nations could differentiate between space activities at low altitudes and air activities, so as to regulate each effectively and discretely.
About the only sound conclusion from a review of the various approaches to differentiating between air space and outer space is that no fully satisfactory answer is in sight. In fact, each of the approaches seems to have at least one serious defect. The problem has not been a pressing one. Indeed, the many uncertainties and potential developments in space activities have even suggested some wisdom in waiting until man’s abilities and needs in space are much better defined.
However, technology is moving on. In the not too distant future, machines
capable of flying along a ballistic trajectory are expected to orbit the earth,
fly in outer space and air space, and make soft landings on the earth. The
space shuttle, which NASA hopes to make a follow-on program to the projected
Apollo and Skylab series, apparently will be such a vehicle. Aeronautical
researchers are reported to be thinking about a hypersonic transport (HST) as a
next step after the supersonic transport, for about the year 2000. Some of the
features being considered are described as “rocket-assisted take-offs” and “space
vehicle-like bursts beyond the atmosphere followed by semi-orbital ‘free fall’
until descent.”1
Developments such as these are bringing closer the day when some formula will be needed, as a practical matter, to accommodate the differences between air space and outer space. The difficulties involved in all the approaches that have been suggested indicate that the decision may well have to be an arbitrary one. The goal obviously should be to select a boundary that seems to balance best the varying difficulties, advantages, and other pertinent considerations. Some demarcation line in the 50- to 75-mile altitude range may be the most satisfactory—or least unsatisfactory.
Fort Bragg, North Carolina
Note
1. Albert R. Karr, “The SST Is a Turtle Compared to the HST, Which May Be on the Way,” Wall Street Journal, 4 January 1971, p. 1.
Dr. Raymond J. Barrett (Ph.D., Trinity College, Ireland) is
Department of State Advisor, John F. Kennedy Center for Military Assistance,
Fort Bragg, N.C. With State, he has served in Mexico, Managua, Dublin, Cairo,
and Madrid; in the Office of Southern and East African Affairs; as Canadian
Desk Officer; as U.S. Secretary of the U.S.—Canadian Permanent Joint Board on
Defense; and as Deputy Chief, Program Staff, Office of International
Conferences. He recently served an exchange tour as Assistant Chief, Global
Plans and Policy Division, Hq USAF.
Disclaimer
The conclusions and opinions expressed in this
document are those of the author cultivated in the freedom of expression, academic
environment of Air University. They do not reflect the official position of the
U.S. Government, Department of Defense, the United States Air Force or the Air
University.
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