Great day for Intelsat! The Galaxy-15 bird, which stopped responding to ground commands last April 5th and was drifting across the "Orbital Parking Slots" of other satellites, is now responding to ground commands.
This was first thought to have been caused by a solar-flare event, but subsequent ground testing (and a LOT of head scratching!) has determined it was caused by an ESD event. "ESD" stands for "Electro Static Discharge", the same thing that happens when you shuffle across the carpet, grab a door knob or other grounded item, and get zapped. Actually, the other object doesn't have to be grounded, just at a lower electrical potential than you are, and current will flow.
The breakthrough was caused when the satellite's inertial wheels (a method of stabilizing the space craft....think big gyroscope) had absorbed all the momentum they could absorb, and could no longer keep the spacecraft properly oriented with respect to the Earth and the Sun. With the solar panels now pointing away from the sun and not generated any power, the batteries became depleted to the point that the onboard computer caused a reset of all the systems on the satellite, which cleared the fault, and allowed the satellite to begin functioning normally, and respond to ground commands again.
They were very lucky that the ESD event apparently didn't do any permanent damage, like blowing out a bunch of stuff, but instead caused a certain part of the onboard computer to lock-up and ignore ground commands. Once it reset itself and cleared the fault it started operating again.
Intelsat Galaxy-15 Returns To Service
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