Spacecraft Lifetime

If only my laptop or mp3 battery would last that long... We must be able to learn something from this.

The two Voyager spacecraft continue to operate, with some loss in subsystem redundancy, but still capable of returning science data from a full complement of VIM science instruments. Both spacecraft also have adequate electrical power and attitude control propellant to continue operating until around 2020 when the available electrical power will no longer support science instrument operation. At this time science data return and spacecraft operations will end.

Spacecraft electrical power is supplied by Radioisotope Thermoelectric Generators (RTGs) that provided approximately 470 w of 30 volt DC power at launch. Due to the natural radioactive decay of the Plutonium fuel source, the electrical energy provided by the RTGs is continually declining. At the beginning of 2001, the power generated by Voyager 1 had dropped to 315 w and to 319 w for Voyager 2. Both of these power levels represent better performance than the pre-launch predictions, which included a conservative degradation model for the bi-metallic thermocouples used to convert thermal energy into electrical energy. As the electrical power becomes less and less, power loads on the spacecraft must be turned off in order to avoid having demand exceed supply. As loads are turned off spacecraft capabilities are eliminated. The following table identifies the year when specific capabilities will end as a result of the available electrical power limitations.

* Limited by ability to capture 1.4 kbps data using a 70m/34m antenna array
In order to maximize the duration of the fields and particles data acquisition capability, the first spacecraft loads to be turned off are instrument heaters on the scan platform. As these heaters are turned off the UVS, which is mounted on the scan platform, cools down until the point is reached when it can no longer function.

Termination of gyro operations ends the capability to calibrate the magnetometer instrument with magnetometer roll manoeuvres (MAGROLs). These manoeuvres are performed 6 times a year, on each spacecraft, and consist of a spacecraft attitude manoeuvre of 10 successive 360 degree turns about the roll axis. Data from a MAGROL allow the spacecraft magnetic field to be determined and subtracted from the magnetometer science data. This is important since the spacecraft magnetic field is larger than as the solar magnetic field being measured. The termination of gyro operations also means an end to the attitude manoeuvres used to check the combined calibration of the Sun Sensor and the High Gain Antenna pointing direction for maintaining communications with the ground.

Instrument power sharing limits the number of science instruments that can be on at any given time. This instrument power sharing will continue until the available power will no longer support any instrument operation. At that time the Voyager Interstellar Mission will end.