VLS ProcessControl Properties 
Property 
Description 
Generate 
If true and the parent filter setting ProcessControl.EnableVLS
is also true, the VLS will be executed in conjunction with the
Filter execution. 
Formulation 
The VLS is constructed as an array of fixed epoch smoothers
with epochs placed on selected filter nodes. Select the fixed epoch
formulation to be used within the VLS:
 Frazer  maps observation residuals from the current filter
epoch back to the fixed epoch associated with the smoothed
estimate. This form is very computationally efficient since it does
not require any matrix inversion operations.
 CarltonRauch  maps filter state corrections from the current
filter epoch back to the fixed epoch associated with the smoothed
estimate. This form does require matrix inversions but may be more
numerically stable than the Frazer form under certain
conditions.

UseMaximumLag 
Use a maximum lag completion criterion for the fixed epoch
smoother estimates. The lag is defined as the time between the
epoch of the fixed epoch smoother and the current filter epoch. It
is recommended to always use the maximum lag completion criterion
to avoid the possibility of the fixed epoch smoother estimate never
reaching completion. 
MaximumLag 
Fixed epoch smoother estimates are considered to be complete
when this amount of time has elapsed between the epoch of the fixed
epoch smoother and the current filter epoch when the fixed epoch
smoother estimate and UseMaximumLag is set to true. 
UseCovarianceReduction 
Use a covariance reduction completion criterion for the fixed
epoch smoother estimates. The covariance reduction of the fixed
epoch smoother estimate is measured as largest relative change in a
diagonal element of the smoothed state error covariance
matrix. 
MinimumCovarianceReduction 
Fixed epoch smoother estimates are considered to be complete
when the covariance reduction associated with N consecutive
accepted measurements are all below this threshold. Covariance
reduction is measured as largest relative change in a diagonal
element of the smoothed state error covariance matrix. A covariance
reduction of 0.001 would therefore mean that the largest relative
change in a diagonal element would be 0.1%. The value of N is set
via the attribute NumMeasForCovarianceReduction. 
NumMeasForCovarianceReduction 
The number of consecutive accepted measurements for which the
MinimumCovarianceReduction threshold must be satisfied in order for
a fixed epoch smoother estimate to be considered complete. 
MinimumOutputSpacing 
Specify the minimum desired time between smoothed states for
output. The VLS can produce output on any node where filter output
is available, but is not required to produce output on all nodes.
Specify a value of zero to produce output on all filter nodes. If a
value greater than zero is specified, then filter nodes are skipped
to produce the desired minimum spacing. Additional nodes are not
introduced to achieve the exact spacing specified. Maneuver times
(instant maneuver centroid times and finite maneuver start and stop
times) will always be included even if they violate the specified
minimum output spacing. 
OutputFullHistory 
If false: the VLS output will consist of the results from fixed
epoch smoothers which have met at least one of the specified
convergence criteria. The output will terminate at the first node
which does not meet any of the convergence criteria.
If true: the VLS output will consist of the results from all
fixed epoch smoothers regardless of if they have met any of the
specified convergence criteria. The output will terminate at the
end time of the filter.

OrbitTypeDivergenceCheck 
Enables a divergence monitoring check which warns the operator
if the smoother and filter orbit states represent different types
of orbits (one elliptical orbit and one hyperbolic orbit). By
default, this check is enabled. Certain situations, such as a
transition between a closed orbit and an escape trajectory, will
benefit by the disabling of this check for smoothing operations.
Note that smoothing operations are not suspended under this check
as they are for the fixed interval smoother. This is due to the
fact that smoothed ephemeris points in the VLS are generated
independently of one another allowing the VLS to recover from
locally divergent conditions. 