Once the satellite is in service, operations and maintenance kicks in – in the form of constant monitoring and adjustment of:
- The satellite’s position in its orbital box;
- The satellite’s attitude, or orientation of the satellite in orbit to ensure it is pointing at the earth;
- Orbital debris and collision risks;
- Payload performance – adjusting beam power levels and gain states; and
- Overall condition – power, thermal, propulsion, etc.
Additionally, every day, multiple days’ worth of commands are uploaded to the satellite, protecting against a scenario where the ground control center might be offline due to a natural disaster or other event. In such an event, the satellite can autonomously function for a period of time, allowing for the control capability to be re-established. In other words, the satellite won’t fall out of the sky if the ground control capability is interrupted or lost.
Every satellite, over its lifetime will experience anomalies or failures on orbit. These can range from rather minor issues, such as losing a number of solar array cells to major satellite malfunctions. Fortunately, significant anomalies are exceedingly rare. Because we can’t go up and fix a satellite once it’s in orbit, satellites are designed to be incredibly robust and fault tolerant in an extraordinarily unforgiving environment. The majority of commercial communications satellites exceed their intended lifetimes, which are usually on the order of 15 years or so.
A satellite’s end of life is generally determined either by remaining fuel or general state of functionality. International guidelines call for satellite operators to reserve enough fuel to “de-orbit” – or boost a satellite to a graveyard orbit approximately 300km above the geostationary belt. By removing an old satellite from the increasingly valuable geostationary arc, we are preventing the accumulation of debris in the form of old, unused satellites. End of life may also occur if the satellite’s payload or control electronics degrade to the point where continued, reliable functionality is in doubt.
Once in the graveyard orbit, there are a number of safety precautions operators commit to including:
- Turning off the payload to cease Radio Frequency (RF) transmissions;
- Spinning down reaction wheels;
- Venting any remaining fuel, oxidizer or helium pressurant out of the tanks. This helps to prevent a debris producing explosion if the satellite was to be struck by micrometeoites or other space debris;
- Pointing the solar arrays away from the sun to prevent any further battery charging;
- Disabling battery charging;
- Shutting down telemetry transmitters; and
- Shutting down command receivers. At this point, the satellite’s life has ended. Depending on the satellite, end of life could occur as much as 20 – 25 years after launch, and up to 30 years from the time design work started.
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