Add or remove a subobject of a chain or constellation or compute access for a chain
Chains <ObjectPath> {ChainOption} [<Parameters>]
The Chains command adds or removes the specified object to/from the end of the chain or constellation. {ChainOption} can be:
| {ChainOption} | <Parameters> | Description |
|---|---|---|
| Add | <TruncObjectPath> | Add the specified subobject to a chain or constellation. The subobject must be part of the current scenario. |
| Remove | <TruncObjectPath> | Remove the specified subobject from a
chain or constellation. Remember that access calculations for a
chain are performed for the objects in the chain in the order they
are entered, removing an object in a chain will impact access
calculations.
Hint: The Remove {ChainOption} doesn't remove the object from the scenario. To remove the object from the scenario use the Unload Connect command. |
| Compute | N/A | Computes access for the chain. |
| AutoRecompute | On | Automatically recompute access for the
chain when a change occurs to any object in the chain.
Note: This option applies only to changes made via the GUI. |
| Off | Do not automatically recompute access. | |
| SetComputeTime | {TimeOption} | Define the time period used to calculate accesses. See table below for valid {TimeOption} values. |
| ClearAccesses | N/A | Remove all chain accesses. |
| AccessIntervalsFile | {On | Off | "<Filename>"} | Specify a file into which Chain strand access intervals will be saved. If On is specified a Filename must already be defined or the command will Nack. |
| AdvComputeOptions | {AdvOptions} | Turn on or off and set parameters for light time delay and event detection and step size control in access calculations. See following table for details of {AdvOptions}. |
Note: When modifying a Chain via Connect the Chain will not automatically recompute. The Chains Compute command must be used to recompute following any sequence of Add, Remove, SetComputeTime or AdvComputeOptions commands.
{TimeOption} can be:
| {TimeOption} | Description |
|---|---|
| UseObjects | The time period set for the objects in the chain is used to compute access. For facilities, places and targets, the time is the scenario time period. |
| UseScenario | The scenario time period is used to calculate accesses. |
| UserSpecified {TimeInterval} | Specify the Start and Stop times used
for access calculations.
For valid {TimeInterval} values see Time Options. |
The following table describes the options for event detection and step size control. Any or all options can be included on the command line.
| {AdvOptions} | <Parameters> | Description |
|---|---|---|
| UseLightTimeDelay | {On | Off} | Turn on or off the use of light time delay in access calculations. |
| EventsBasedOnSamples | {On | Off} | Turn EventsBasedOnSamples On to determine access intervals simply based on the samples without doing any extra sub-sampling. |
| TimeConvergence | <Value> | Set the time tolerance used during
event detection. Event times will be determined to within this
specified tolerance. <Value> is entered in Connect Time units
and must be between 1.0e-9 and 315576000.0 seconds.
EventsBasedOnSamples must be set to Off for this value to have any effect. |
| AbsValueConvergence | <Value> | Set the criterion used for convergence
for values near 0. <Value> must be between 1e-30 and 1e30
EventsBasedOnSamples must be set to Off for this value to have any effect. |
| RelValueConvergence | <Value> | An event is said to be detected when a
constraint value's relative difference compared to the previous
sample is within this tolerance. <Value> must be between 0.0
and 1.0
EventsBasedOnSamples must be set to Off for this value to have any effect. |
| MaxStepSize | <Value> | Sets the maximum sampling step size
used in access computations when computing the chain. <Value>
is entered in Connect Time units and must be between 1.0e-5 and
315576000.0 seconds.
When this value is entered Step Size Control will be set to use a variable step to choose samples. |
| MinStepSize | <Value> | Sets the minimum sampling step size
used in access computations when computing the chain. <Value>
is entered in Connect Time units and must be between 1.0e-5 and
315576000.0 seconds.
When this value is entered Step Size Control will be set to use a variable step to choose samples. |
| FixedSampleStep | <Value> | Enter a step size value to control the
step size used in Access sampling. <Value> is entered in
Connect time units and must be between 1.0e-5 and 315576000.0
seconds.
When this value is entered Step Size Control will be set to use a fixed step to choose samples. |
| FixedStepTimeBound | <Value> | Enter a value control the alignment of
samples with a UTC time grid. <Value> is entered in Connect
time units and must be between 0.0 and 86400.0 seconds.
When this value is entered Step Size Control will be set to use a fixed step to choose samples. |
| MaxGoodLTDelay | <Value> | Set the allowable light time delay for the chain strands. <Value> is entered in Connect Time units and must be greater than 0.0001 seconds. |
To add the Shuttle satellite to the chain testChain1:
Chains */Chain/testChain1 Add Satellite/Shuttle
To remove the TDRS_East satellite from the TDRSChain in the current scenario:
Chains */Chain/TDRSChain Remove Satellite/TDRS_East
To use Chain1's time period for access calculations:
Chains */Chain/Chain1 SetComputeTime UseObjects
To use the scenario time period for chain access calculations:
Chains */Chain/Chain1 SetComputeTime UseScenario
To consider only the specified portion of Chain1's time period for access calculations:
Chains */Chain/Chain1 SetComputeTime UserSpecified "14 Oct 2003 02:00:00.00" "14 Oct 2003 06:30:00.00"
To save strand accesses for the RtChain chain to the file AccessChain1.int:
Chains */Chain/RtChain AccessIntervalsFile "c:\STKUser\AccessChain1.int"
To no longer save the RtChain chain strand accesses to a file:
Chains */Chain/RtChain AccessIntervalsFile Off
To set the time tolerance to be used during event detection:
Chains */Chain/RtChain AdvComputeOptions EventsBasedOnSamples Off TimeConvergence 0.55
To compute accesses for the Chain:
Chains */Chain/RtChain Compute
If activated, Connect returns an acknowledgement message.
This command belongs to the following group(s):
10
STK Programming Interface 11.0.1