The punch line to this story is that backup transmitter hasn't been used since 1981.
About two weeks ago, October 16, Voyager 1 put itself into a safe mode after receiving a transmission from its mission control via the Deep Space Network commanding the satellite to turn on one of its heaters. Because it takes just about a full day for radio transmission to get to the satellite and another full day before the response is known, they found out on October 18 that Voyager failed to respond.
According to a post from NASA, it took a little while to discover that Voyager had switched off its primary X-band transmitter and switched over to its secondary S-band radio transmitter, which uses less power.
Then, on Oct. 19, communication appeared to stop entirely. The flight team suspected that Voyager 1’s fault protection system was triggered twice more and that it turned off the X-band transmitter and switched to a second radio transmitter called the S-band. While the S-band uses less power, Voyager 1 had not used it to communicate with Earth since 1981. It uses a different frequency than the X-band transmitters signal [and] is significantly fainter. The flight team was not certain the S-band could be detected at Earth due to the spacecraft’s distance, but engineers with the Deep Space Network were able to find it.
While the first thought might be to turn the X-band transmitter on, the Voyager team is more cautious than that, wanting to understand what caused the fault protection system to trigger and switch the transmitters.
[T]he team sent a command on Oct. 22 to confirm the S-band transmitter is working. The team is now working to gather information that will help them figure out what happened and return Voyager 1 to normal operations.
Two days later on the 24th, the team was finally able to connect with the elderly
spacecraft, now in the 47th year of its four year mission. Voyagers 1 and 2 (a
few weeks older than 1) are the only man-made objects to reach and operate in
interstellar space. Their advanced age has meant an increase in the
frequency and complexity of technical issues and new challenges for the
mission engineering team. Which has met those challenges so far.
How do you hear a signal from a low power transmitter that's 23 light hours, that is, 16 billion miles
away? A high gain antenna. This the Deep Space Network antenna in Canberra,Australia. With a diameter of 70 meters, or 230 feet, the DSN stations are the three
most sensitive radio receiving stations on Earth. Image credi: NASA/JPL-Caltech
