Step

Top  Previous  Next

Description


The Step command advances the state of a Spacecraft, GroundVehicle, or Formation object forward or backwards in time. The epoch to which a Spacecraft or GroundVehicle is stepped is determined by the vehicle's Propagator or by a user-specified end condition. For more information, see the Stepping the Spacecraft, GroundVehicle Propagators, Lists and Formations guides.

 

 

Syntax


Spacecraft Object

// Step a Spacecraft for 2 days

While (mySpacecraft.ElaspedTime < TIMESPAN(2 days));
    Step mySpacecraft;
    Update myViewWindow;
End;
 

// Step a Spacecraft to various end conditions
Step mySpacecraft to (myVariable1 >= myVariable2);
Step mySpacecraft to (mySpacecraft.OrbitApogee);

 
Step mySpacecraft to (mySpacecraft.Epoch == TIMESPAN(25167.5 days));

Step mySpacecraft to (mySpacecraft.EpochText == "Mar 24 2024 06:00:00.000");

Step mySpacecraft to (mySpacecraft.Epoch == "Mar 24 2024 06:00:00.000".ParseCalendarDate());

 
Step mySpacecraft to (mySpacecraft.EarthShadow == 1 and mySpacecraft.ElaspedTime > TIMESPAN(2 days));
Step mySpacecraft to (mySpacecraft.EarthShadow == 1 or mySpacecraft.ElaspedTime > TIMESPAN(2 days));

 

// Step a List of Spacecraft or Formation

Step mySpacecraftList;

Step myFormation;

 

// Step a Spacecraft that is an element in a List of Spacecraft or Formation

Step mySpacecraftList[0];

Step myFormation[0];

 

GroundVehicle Object

// Step a GroundVehicle for 2 days

While (myGroundVehicle.ElaspedTime < TIMESPAN(2 days));
    Step myGroundVehicle;
    Update myViewWindow;
End;

 

// Step a List of GroundVehicles

Step myGroundVehicleList;

 

// Step a GroundVehicle that is an element in a List of GroundVehicles

Step myGroundVehicleList[0];

 

Note: The WhileStepping and Step to commands are not currently supported for the GroundVehicle object.

 

Note: As of FreeFlyer 7.3, the default timing precision mode is nanosecond precision mode. For older Mission Plans that have not yet been converted from millisecond precision mode, the syntax for working with epochs and calendar date/time strings is different. A few samples are shown below; see the timing precision mode page for more information.

 

// Step a Spacecraft to various end conditions in millisecond precision mode
Step mySpacecraft to (mySpacecraft.Epoch == 25167.5);

Step mySpacecraft to (mySpacecraft.Epoch == "Mar 24 2024 06:00:00.000".EpochScan());

Step mySpacecraft to (mySpacecraft.EarthShadow == 1 and mySpacecraft.ElapsedDays > 2);

 

 

Details


It is possible to test for multiple logical conditions using the "and" and "or" operators.

The Step command can depend on an unlimited number of conditional statements. Possible relational conditions are:

o<, <=, >, >=, ==, !=

Additional conditional syntax supported in millisecond timing precision mode only:

ois, not, very, somewhat, almost, usually (used with FuzzySet object only)

o= (equivalent to ==)

o~= (equivalent to !=)

The "Step to" syntax allows the propagator to proceed forwards or backwards in time in order to achieve the specified goals.

oIf the optional "to ..." clause is not used, the step size is determined by the Spacecraft Propagator.

oSee the Stepping the Spacecraft guide's section on stop-propagation properties and methods for more information on the available predefined end conditions.

An entire Formation or List of Spacecraft may be Stepped, or any individual element of the Formation/List may be Stepped using array indices.

The WhileStepping command allows the user to execute arbitrary FreeFlyer script at every internal step of a propagation.

The Spacecraft.Step(), Formation.Step(), Spacecraft.StepToEpoch(), Spacecraft.StepToNode(), and Spacecraft.StepToApsis() methods can also be used in place of a Step command.

 

 

Command Editor


What to Step

Specifies the Spacecraft or Formation to propagate

 

Step to condition?

Propagate will proceed forwards or backwards in time in order to achieve the specified goal

See syntax examples above for more information

 

Script

Displays the FreeFlyer Script that is generated by the editor

 

Description

Displays descriptions of the editor and its fields

Description text changes as the mouse pointer moves over the different fields within the editor

 

 

 

See Also


Lists

Formations

Stepping the Spacecraft

GroundVehicle Propagators

Stepping the Spacecraft

WhileStepping Command

List of Stop-Propagation Properties and Methods

Spacecraft Properties and Methods

GroundVehicle Properties and Methods

Formation Properties and Methods