Method and apparatus for non-coherent navigation using low frame rate telemetry

A method for obtaining measurements on a spacecraft at intervals that are shorter than the telemetry frame duration and that may be precisely time tagged on the ground and used in the determination of two-way Doppler measurements comprising the steps of:

• including, on-board a spacecraft, a divider clock frequency that is synchronous with a clock frequency used to generate telemetry frames;
• dividing said divider clock frequency to produce a divider cycle time;
• resetting said divider at the start of each telemetry frame;
• producing a divider output at the end of each divider cycle time if the divider cycle time is not first reset by the start of a telemetry frame;
• combining, using a logical OR function, said divider output with a telemetry frame start input to produce a navigation counter trigger;
• employing said navigation counter trigger to enable multiple samples of navigation counter values to be transmitted in a single telemetry frame.

An apparatus for obtaining measurements on a spacecraft at intervals that are shorter than the telemetry frame duration and that may be precisely time tagged on the ground and used in the determination of two-way Doppler measurements comprising:

• a divider that receives a divider clock frequency that is synchronous with a clock frequency used to generate telemetry frames;
• a reset, operatively connected to said divider, for resetting said divider at the start of a telemetry frame;
• a logical OR gate for comparing an output of said divider with a telemetry frame start input;
• and
• navigation counters that are triggered by an output from said OR gate;
• wherein said counters, upon being triggered by said output from said OR gate, produce navigation counter values that are used to compute said Doppler measurements.