baudrunner's space: Voyager 1 is very far away
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Tuesday, January 22, 2008

Voyager 1 is very far away

Considering that the nearest star to our sun is about four light-years distant one might be tempted to believe that the Voyager 1 spacecraft launched in 1977 is still very close to home, since it 'only' takes about nine and a half hours for its radio signal to reach us travelling at light-speed. It takes a fairly substantial receiving antenna system to detect the signal produced by its twenty watt transmitter. By the time the signal reaches Earth it has become so faint that its power is just about equal to the power of a digital watch battery divided by twenty billion.

Obviously the sun can't be relied upon to produce the solar energy required to power that twenty watt transmitter since it is about five thousand times fainter to Voyager 1 than it is to us here. Its energy is generated by a radioisotope thermal electric generator (RTG). It is based on the principle that a radioactive source such as plutonium (with a half-life of 24,100 years for 239Pu) generates heat as it decays naturally. The thermal energy can be directly converted to electricity by using thermocouples, which are similar to batteries but in which the temperature difference between two types of semiconductors which can conduct electricity connected in a closed circuit induces a voltage difference of potential which naturally results in current flow.

Now, it's silly to get worked up over the potential hazard to the environment that a space craft carrying an RTG flying into unknown space more than ten billion kilometers away could conceivably represent, isn't it? Isn't it...?

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