New Horizons has set the speed record for spaceflight, and is racing toward pluto and will make it in record time. However, its RTG doesn't have the longevity o

New Horizons has set the speed record for spaceflight, and is racing toward pluto and will make it in record time. However, its RTG doesn't have the longevity of Voyager's, so New Horizons won't last nearly as long. NH does have an extended mission, but nothing will match the voyagers': the stars and planets -- literally -- aligned, and it's an opportunity that will probably never come again.