... its oscillator, which allows it to accept a wide range of frequencies, had quit, essentially shrinking the target for transmissions from Earth. Assuming a much narrower bandwidth, and manually subtracting the Doppler effect, they recalibrated their signal. It worked — but to this day, the same calculation must precede every command.
IIRC from an old SciAm article, the temperature of the spacecraft's electronics is also taken into account when doing this calculation.