# Clock

The Clock attribute of a Satellite object lets you set
spacecraft clock parameters and define those clock
parameters that are to be simulated/estimated. Currently this clock
attribute is only used in the modeling of TDRS 3L Doppler
measurements.

Settings |

Parameter |
Description |

Enabled |
Enables the use/simulation/estimation of clock parameters.
Other clock parameters are only exposed when Enabled is set to
true. |

Estimate |
Defines the clock parameters to be simulated/estimated. See
table below. |

ClockControls |
See table below. |

ClockUncertainty |
See table below. |

OrbitClockCorrelations |
6x3 matrix defining initial orbit/clock cross correlations.
Orbit is {R, I, C, Rdot, Idot, Cdot}.. Clock is {phase, frequency,
aging} |

## Estimate

The following combinations of clock parameters can be
simulated/estimated:

- {phase, frequency} (the default)
- {phase, frequency, aging}
- {frequency}
- {frequency, aging}

where phase is the current time, frequency is the first derivative
of phase, and aging is the second derivative. Thus, aging
represents a long term constant rate of change in frequency and a
corresponding quadratic change in phase.
Estimate |

Parameter |
Description |

Phase |
= true, enables clock phase |

Freq |
= true, enables clock fractional frequency |

Aging |
= true , enables clock aging |

## Clock Controls

The following are the clock controls properties:

ClockControls Properties |

Property |
Description |

PhaseBias |
Clock phase (time) offset estimate at state creation time
. |

FreqBias |
Clock frequency offset estimate at state creation time. This is
a fractional frequency, units are sec/sec. |

AgingBias |
Clock aging offset estimate at state creation time. |

A0 |
Frequency-modulated (FM) clock white noise statistic. |

Aminus1 |
FM clock flicker noise statistic (not currently modeled). |

Aminus2 |
FM clock random walk statistic. |

AgingWN |
FM clock drift statistic. |

## Clock Uncertainty

The following are the clock uncertainty properties:

ClockUncertainty Properties |

Property |
Description |

Phase_sigma |
Uncertainty associated with the phase bias estimate at the
initial filter time. Used to initialize the covariance. |

Freq_sigma |
Uncertainty associated with the frequency bias estimate at the
initial filter time. Used to initialize the covariance. |

Aging_sigma |
Uncertainty associated with the aging bias estimate at the
initial filter time. Used to initialize the covariance. |

PhaseFreq_correlation
PhaseAging_correlation
FreqAging_correlation |
Cross-correlations among the above attributes. |

ODTK 6.5