The backup radio transmitter has remained dormant for about 43 years.
The interstellar explorer experienced a brief pause in communications after putting itself in a protective state to conserve power. This was triggered by a command sent on Oct. 16 instructing the spacecraft to turn on one of its heaters.
On Oct 18th it was discovered by the mission ops team that the spacecraft had turned off its primary X-band radio transmitter and instead switched over to its secondary S-band radio transmitter, which uses less power. This is believed to be in response to the fault management system being triggered.
“The transmitter shut-off seems to have been prompted by the spacecraft’s fault protection system, which autonomously responds to onboard issues,” NASA officials said in the statement.
On Oct 19th, Voyager 1’s fault protection system is believed to have been triggered twice more, ultimately causing it to switch to the S-band radio transmitter, which, prior to that date, hadn’t been used since 1981.
The spacecraft’s fault management system is believed to have been triggered twice more, ultimately causing it to switch to the S-band radio transmitter, which, prior to that date, hadn’t been used since 1981.
Fault management systems software may be triggered into a false positive if hackers are able to trick the spacecrafts’ fault management system by creating a false situation that would put the system into a safe state. In a deep space mission, such as Voyager, it could be possible to upload malicious software while the spacecraft is still within easy communications (pre or post launch) reach that was timed to become active while in deep space.
Source: Voyager 1 spacecraft phones home with transmitter that hasn’t been used since 1981 | Space