It is generally accepted that at some point the territorial airspace of states ends and outer space begins. An Old Danish proverb tells us “Great lords have long hands, but they do not reach to Heaven.” At the dawn of the Space Age in 1957 it became relevant to codify a law of outer space and not long after the launch of Sputnik the United Nations established the Committee on the Peaceful Uses of Outer Space (COPUOS). In 1959 this committee was made permanent.
COPUOS' job is “To review, as appropriate, the area of international co-operation, and to study practical and feasible means for giving effect to programmes in the peaceful uses of outer space which could appropriately be undertaken under United Nations auspices” and “To study the nature of legal problems which may arise from the exploration of outer space” (Resolution 1472). They do not deal with military issues, nor do they regulate the geostationary orbit approximately 35 000 kilometers above the equator as it is controlled by the International Telecommunications Union.
As the space race picked up speed, the General Assembly of the United Nations declared outer space “the common heritage of mankind” in 1963.  The declaration was unanimously approved and the principles stated in it forms the framework of all later treaties:
- “The exploration and use of outer space shall be carried on for the benefit and in the interests of all mankind.
- Outer space and celestial bodies are free for exploration and use by all States on a basis of equality and in accordance with international law.
- Outer space and celestial bodies are not subject to national appropriation by claim of sovereignty, by means of use or occupation, or by any other means.
- The activities of States in the exploration and use of outer space shall be carried on in accordance with international law…in the interest of maintaining international peace and security and promoting international co-operation and understanding.
- States bear international responsibility for national activities in outer space…
- In the exploration and use of outer space, States shall be guided by the principle of co-operation and mutual assistance and shall conduct all their activities in outer space with due regard for the corresponding interests of other States…
- The State on whose registry an object launched into outer space is carried shall retain jurisdiction and control over such object, and any personnel thereon, while in outer space. Ownership of objects launched into outer space, and of their component parts, is not affected by their passage through outer space or by their return to the earth. Such objects or component parts found beyond the limits of the State of registry shall be returned to that State, which shall furnish identifying data upon request prior to return.
- Each State which launches or procures the launching of an object into outer space, and each State from whose territory or facility an object is launched, is internationally liable for damage to a foreign State or to its natural or juridical persons by such object or its component parts on the earth, in air space, or in outer space.
- States shall regard astronauts as envoys of mankind in outer space, and shall render to them all possible assistance in the event of accident, distress, or emergency landing on the territory of a foreign State or on the high seas. Astronauts who make such a landing shall be safely and promptly returned to the State of registry of their space vehicle.”
In 1967 these principles were reitereated in the Outer Space Treaty. Furthermore, article IV of the OST prohibits weapons of mass destruction in orbit or in any other way installed in outer space, and the militarization of the Moon or other celestial bodies. Activities that harms the environment was also prohibited (article IX).
Several treaties dealing with the specifics of the principles above exists, but there are still many ambiguities in space law. For one, the question of jurisdiction has not been solved, nor is there any agreement on where precisely the national airspace stops and outer space begins. Still, the reason why the law of outer space is not further developed is that at this point in time it simply doesn't need to be. When we get to rocket cars and commercial space stations the law of outer space have progressed as well.
(This is part of my personal quest (study) on international and humanitarian law)