The largest threat to the VIM is the spacecrafts' waning power supplies. The two spacecraft are powered by Radioisotope Thermoelectric Generators, and due to the natural radioactive decay of their Plutonium fuel source, occasionally have to shut down certain various scientific instruments due to a lack of power. Gyroscopic systems will likely be shut down in roughly 2010 for both spacecraft.

This is unfortunate, as two spacecraft use this system to make slight course corrections and maintain steady communications with Earth. NASA's engineers are confident, however, that they will be able to continue to communicate, as they don't plan to shut down the probes until roughly 2020, at which point the VIM will end.

The shut down sequences and more information on this can be found here near the bottom of the page.

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