Step Three: Transmission of Tones Begins
About 20:15 PST [04:15 GMT], Spirit will begin transmitting tones back to Earth that indicate the spacecraft's status. A low-gain antenna on the spacecraft's backshell begins transmitting simple "tones" (sustained radio frequencies coded to report the spacecraft's status). These tones give Spirit a way to keep communicating after the cruise stage is jettisoned. A dictionary of about 100 possible tones can provide information such as whether the cruise stage has separated, whether the parachute opens, and whether the deceleration rate is within the expected range.
From here on out, it’s gets very busy for the next half hour.

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