Voyager 1 Is About to Reach One Light-Day From Earth

Fading power, delayed signals

Talking to the spacecraft is hard. A radio signal takes 24 hours to reach Voyager 1 and another 24 to come back, so engineers must work patiently to keep its systems running.

The probe is powered by three radioisotope thermoelectric generators, nuclear batteries that convert heat from the decay of plutonium-238 into electricity. At launch they delivered about 470 W; today the figure is around 215 W. They lose roughly 4 W per year, so NASA has to ration energy carefully. Eight of the ten science instruments installed at launch have already been switched off, leaving two active.

According to NASA forecasts, Voyager 1 will have to shut down its last science instrument in the 2030s. A more serious problem could come in 2036, when the power reserve may be too small to maintain radio contact with Earth. That would probably end the decades-long mission, although the probe itself will keep travelling through interstellar space.

A mission of firsts

Voyager 1 launched on 5 September 1977 from Cape Canaveral in Florida, only days after its twin, Voyager 2. It flew past Jupiter in March 1979 and Saturn in November 1980, sending back thousands of images, including the discovery of active volcanoes on Jupiter's moon Io. On 25 August 2012 it crossed the heliopause, becoming the first human-made object to enter interstellar space.

Onboard is also the Golden Record, a gold-plated copper disc about 30 cm across. It holds 115 images, greetings in 55 languages, sounds of Earth and about 90 minutes of music, from Bach, Beethoven and Mozart to Chuck Berry, plus messages from US President Jimmy Carter and UN Secretary-General Kurt Waldheim. Instructions on the casing explain how to play it and locate Earth relative to selected pulsars.