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:

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