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Defining ‘Outer Space’

As with a number of space law terms, the space treaties do not provide a definition of outer space. While for the most part a common-sense approach works there are times when it leads to a lack of certainty and clarity. However, generally speaking this has not really been an issue but it worth examining, especially as the rise of suborbital flights, spaceplanes and commercial human spaceflight could potentially cause some issue. In this post I’ll touch on some of the issues, and the two ‘approaches’ that could be used to define and delimit space. It is a more complex topic than can be dealt with in one post so will be something to which I return.

SPACE not Space

Seems fairly simple right?

Air vs Space

While space law, to some extent, ‘grew out’ of aviation law (and indeed many space law programmes today are still part of a broader aviation law course, or institute; see McGill, Leiden and Nebraska, Mississippi [see comment below] for three prominent examples) there are some fundamental differences. The biggest difference between the aviation and space regimes is sovereignty. States retain complete sovereign jurisdiction over the airspace above their territory. There is no formal upper limit to this jurisdiction, although customary law has effectively established that the lowest possible orbit is the upper limit to this jurisdiction, not only owing to the widespread acceptance of the freedom of access and use of Outer Space in UN General Assembly Resolution 1962 and Article I of the Outer Space Treaty but also to the practice of now over 60 years of satellite operations without consistent objection by states. By contrast, the exercise of territorial sovereignty in outer space is prohibited and all states enjoy the freedom of access and use to all areas of ‘Outer Space, the Moon and other celestial bodies.’

There are also differences in the workings of things like liability and registration and while the details of those differences aren’t particularly relevant to this discussion the fact that they exist is. All space objects have to go through airspace in order to get to outer space (at least until we start manufacturing space objects in outer space) and therefore there is the potential for a clash between the air and space legal and regulatory regimes. For most space objects this isn’t much of an issue because they cannot be defined as aircraft, which unlike space object does have a definition[1], which is essentially an object that uses wings to generate lift[2] (a traditional rocket by contract simply uses sheer thrust to provide lift). However, spaceplanes could be classed as both space objects (because they are ‘launched’ into outer space, although that does raise a question as to what constitutes a launch if the spaceplane takes off from a runway for example…) and aircraft. This wouldn’t necessarily apply to spaceplanes launched shuttle style, however the Chicago Convention says ‘can’ not ‘does’, so it could still apply. It is the ‘rise’ of spaceplanes and the ‘dawning’ age of commercial spaceflight that has led to a renewal of calls for an agreed definition and delimitation of outer space. However, this isn’t a new discussion, the Legal Subcommittee of the Committee on the Peaceful Uses of Outer Space have been discussing this issue for many years, and far from agreeing on a definition of outer space they can’t even agree on the need for a definition. There are generally two approaches put forth as a ‘solution’ to the question of the definition and delimitation of outer space: the spatial approach and the functional approach.


If those wings ‘can’ provide lift then this is an aircraft and a space object

Spatial Approach

The spatial approach would see the establishment of a clear boundary, so this would be to state that outer space begins at say 100km above sea level (the von Karman line).[3] So any activity below that line takes place in airspace which is subject to all the rules and regulations applicable to the air law regime (including national sovereignty) and that any activity that takes place above that line takes place in outer space and is therefore subject to the rules and regulations governing space activities. However, that could mean that certain space objects would be subject to air law while flying to and from outer space, which may be unworkable and/or undesirable.

Functional Approach

The functional approach doesn’t set a specific boundary but rather looks at the nature of the activity. So if you’re launching a satellite into low earth orbit then that is a space activity, whereas if you’re flying from London to Singapore that’s an air activity even if you’re using a spaceplane and have an apogee (highest point of a flight) of over 100 km. Obviously this still leaves room for debate and argument over what constitutes which but it avoids forcing states to give up ‘sovereignty’ over the ‘airspace’ above whatever line you would otherwise choose in the spatial approach, which is a real, if absurd, fear that states have.

Concluding Thoughts

As mentioned before this is not a new topic, it is one that has been under discussion since the dawn of the space age, and there is not only disagreement about the definition of outer space but even the need for a definition. Personally, I favour the functional approach as it provides flexibility, is probably more politically viable and conforms with existing practice (plus the clash of regimes only really applies to spaceplanes, and perhaps suborbital flights) But I’m not sure we need a formal definition or delimitation of outer space. As is frequently said by the United States and a few other countries at the working group at COPUOS on this very topic, the space law regime has worked well for 50+ years without a definition. However, commercial spaceflight, particularly spaceplanes and suborbital flights, will potentially raise some issues, and I will look to explore these in more details in later posts.


[2]“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.” Chicago Convention, Annex 7

[3]The von Karman line is meant to be above the point at which you can use the atmosphere to generate atmospheric lift and thus need to travel at orbital speeds in order to remain ‘airborne’, it is often referred to as the boundary between air and space and is accepted by the World Air Sports Federation as the boundary between air and space but has no legal effect. Although Australia did set 100km as the upper limit to their airspace in their Space Activities Act 1998. Though at the most recent session of the Legal Subcommittee of COPUOS (April 2017) the Australian delegate did try to downplay the significance of this vis-à-vis the definition and delimitation of outer space.

It is also worth noting that other altitudes are used, the US Air Force, for example, awarded ‘astronaut badges’ to several X-15 pilots who flew above 80km (although these days eligibility requires flight above 100km)

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