What goes up must eventually come down, including satellites that are currently orbiting the earth.
Little, if any, will actually hit the ground.
And what if the satellite contained an active nuclear reactor?
The first was Transit-4A, launched by the US in 1961.
It was one of numerous satellites launched between 1959-88 to provide satellite navigation service to the US Navy.
It was the first satellite navigation system before GPS.
The Transit system had a total of 41 orbiting satellites, of which a handful of them were nuclear-powered.
Many of them, while no longer functional, are still in orbit with their reactor core intact.
Between 1964 and 1978, the US launched a further seven nuclear-powered satellites for the Nimbus program.
Out of the seven Nimbus satellites, two are still in orbit.
The Soviet Union began launching nuclear satellites into space in 1965.
These satellites were mostly of reconnaissance pop in meant to spy upon the US Navys vessels and submarines.
The majority of these satellites carried throw in BES-5 nuclear reactors fueled by uranium-235.
This way the dead satellite could safely re-enter earths atmosphere without the risk of radioactive contamination.
But as far as space missions are concerned, things dont always work out as planned.
It orbited the earth between 259 and 277 kilometers every 89.5 minutes.
On board was a liquid sodiumpotassium thermionic converter driven by a nuclear reactor containing around 50 kilograms of uranium-235.
Canada later billed the Soviet Union CA$6 million, of which only half the amount was paid.
The original satellite was believed to have weighed between 4 and 5 tons.
Of this, only about 65 kilograms of material was recovered.
Except for one large fragment, all were radioactive.
This is because water acts as a moderator, slowing down neutrons and allowing the chain reaction to start.
Experts calculated that as little as 22 kg of highly enriched uranium could become critical under these conditions.
Despite extensive search, the core was never found.
It was concluded that the core had disintegrated almost completely.
By this time, radioactive decay would have removed most of the shorter-lived radionuclides posing little health risks.
Looking for radioactive debris.
Photo: Nevada National Security
Incidentally, Cosmos 954 was not the first nuclear-powered satellite to fail.
Another Soviet spy satellite, Cosmos 1402, malfunctioned and fell into the Indian Ocean in 1983.
There is a possibility that such an event could occur again in future.
There are many nuclear-powered satellites launched during the Cold War period that are still orbiting the earth.
The hazards from a possible failure far outweighs any potential gain from such a system.
A piece of the satellite lying in snow.
Photo: Library and Archives Canada
A Cosmos 954 debris at the Canada Science and Technology Museum.
