( BBC ) - It came like a shock to the system nearly 50 years ago on 4 October, 1957. The Soviet Union launched a beach ball-sized orbital satellite to usher in the "space age".
The act in itself proved neither particularly shocking nor threatening but what it signalled certainly was: the sense that if the Soviets could put an orbital spacecraft over our heads it could bring a nuclear missile down on our heads.
This resulted in a total reorientation of priorities in the United States and the establishment of the National Aeronautics and Space Administration (Nasa) as a focal point for space activities.
At the same time, a little-known principle critical to the safety of the entire world also resulted from Sputnik.
The Soviet satellite established the overwhelmingly critical principle of overflight in space.
This is the ability to send reconnaissance and other satellites over a foreign nation for any non-lethal purpose free from the fear of attack on them.
Orbiting reconnaissance satellites served more than virtually any other technology as a stabilising influence in the Cold War.
The ability to see what rivals were doing helped to ensure that national leaders on both sides did not make decisions based on faulty intelligence.
Both the Americans and the Soviets benefited from this capability, and the world was safer as a result, but it might have turned out another way.
In a critical document, Meeting the Threat of Surprise Attack, issued on 14 February 1955, US defence officials raised the question of international law governing territorial waters and airspace, in which individual nations controlled those regions as if they were their own soil.
That international custom allowed nations to board and confiscate vessels within territorial waters near their coastlines and to force down aircraft flying in their territorial airspace.
This has resulted in shoot-downs on occasion, as when the Soviet Union downed a Korean Air Lines Boeing 747 in 1983.
But in 1957 space as a territory had not yet been defined, and US leaders argued that it should be recognised as beyond the normal confines of territorial limits.
An opposite position, however, argued for the extension of territorial limits into space above a nation into infinity.