NASA has switched off a heater on a part of the Voyager 1 probe, plunging the temperature of its one functioning instrument to below minus 110° Fahrenheit (minus 79°C) – well below the minimum temps of minus 31° Fahrenheit (minus 35° C) at which it was designed to operate.
Space boffins took the decision in order to conserve the probe's energy supply as it continues to venture beyond the edge of the solar system.
Voyager 1's ultraviolet spectrometer (UVS), a light meter which is its only working instrument, spots the presence of certain atoms or ions. This allowed it to investigate auroral activity on the planets and satellites it has passed since launch in 1979 and has even allowed it to observe supernovae. The spacecraft is now journeying beyond the 'bubble' created by the Sun's gravity and is enduring the coldest temperatures it has experienced to date.
“Scientists and mission managers will continue to monitor the spectrometer's performance,” the agency said in a canned statement. “It was very active during Voyager 1's encounters with Jupiter and Saturn, and since then an international team led by scientists in France has been analysing the spectrometer's data.”
Voyager 1 and its cargo of scientific equipment were designed to operate at temperatures as low as minus 31° Fahrenheit (minus 35° C). But NASA has had to turn down the thermostat again and again over the past 17 years in order to push Voyager 1 to keep working up to 2025 – far beyond its scheduled retirement date of 1989. It is now operating well below expected temperatures.
Since then, Voyager 1 and its companion probe Voyager 2 have been journeying further from Earth. Voyager 1 is now 11 billion miles (17.7 billion km) away from the Sun, almost 120 times as far from the Sun as Earth, with Voyager 2 trailing some two billion miles (3.2 billion km) behind. Both send data back to Earth at 160 bits/sec and 1.4 kbps for high-rate plasma wave data, via a 3.7-metre antenna.
Voyager 1's power is supplied by radioisotope thermoelectric generators that pumped out approximately 470 Watts and a 30-Volt DC supply at launch in 1977. By 2008, radioactive decay of the plutonium fuel source had caused the output to drop to 285 Watts.
In fact, this power performance is better than expected by pre-launch predictions, but NASA will continue to conserve power by turning off functions over the coming years.
NASA said it expects Voyagers 1 and 2 to be unable to power any single instrument by 2025. ®