Target Specification Commands

target … end_target
target
   platform ...
   libration_point ...
   eci_position ...
   eci_state ...
   offset ...
   position_offset ...
   velocity_offset ...
   offset_time ...
   lag_time ...
end_target

These commands specify the target of a targeting-class orbital maneuver (Target, Intercept, and Rendezvous). When specifying a target, one selects both a base target, and an optional offset from that base target.

Base Target Commands

platform <string-value>

Use the platform with the given name as the base target.

libration_point <system> <point>

Use the given libration point of the given system as the base target. Allowed values of the system are:

  • earth_moon - This will select a point with the Earth as the primary, and the Moon as the secondary object.

  • sun_earth - This will select a point with the Sun as the primary, and the Earth as the secondary object.

  • sun_jupiter - This will select a point with the Sun as the primary, and Jupiter as the secondary object.

The allowed values for the point are:

  • l1 - The L1 point. This is on the line connecting the primary and secondary, and between the two objects.

  • l2 - The L2 point. This is on the line connecting the primary and secondary, and beyond the secondary object.

  • l3 - The L3 point. This is on the line connecting the primary and secondary, and on the opposite side of the primary as the secondary.

  • l4 - The L4 point. This is one of the equilateral points, and is ahead of the secondary in the direction of orbit.

  • l5 - The L5 point. This is one of the equilateral points, and is behind the secondary in the direction of orbit.

eci_position <x-position> <y-position> <z-position> <length-units>

Use the given ECI position as the base target. This is equivalent to eci_state with a velocity of zero.

eci_state <x-position> <y-position> <z-position> <length-units> <x-velocity> <y-velocity> <z-velocity> <speed-units>

Use the given ECI position and velocity as the base target.

Note

This command only has an effect for a Rendezvous maneuver; it is ignored for Target and Intercept.

Offset Commands

offset <frame> <x-offset> <y-offset> <z-offset> <length-units>
position_offset <frame> <x-offset> <y-offset> <z-offset> <length-units>

Specify a position offset from the specified base target, expressed in the given frame. The available frame options are:

  • ric - The RIC frame uses an x-axis (Radial) along the target’s position vector, a z-axis (Cross-track) along the target’s orbital angular momentum, and a y-axis (In-track) completing the right-handed frame.

  • ntw - The NTW frame uses an x-axis along the target’s velocity vector, a z-axis perpendicular to x and in the same plane as the target’s nadir vector, and a y-axis completing the right-handed frame.

If both a position_offset and velocity_offset are provided, the same frame need not be used for both.

For example, an offset of offset ntw 20 0 0 meters would be 20 meters ahead of the target in its direction of motion.

Note

This command is useful for maneuvering around targets for proximity operations.

Note

The command offset may be deprecated in the future, so it is suggested to use position_offset.

velocity_offset <frame> <x_offset> <y_offset> <z_offset> <speed-units>

Specify a velocity offset from the specified base target, expressed in the given frame. The available frame options are:

  • ric - The RIC frame uses an x-axis (Radial) along the target’s position vector, a z-axis (Cross-track) along the target’s orbital angular momentum, and a y-axis (In-track) completing the right-handed frame.

  • ntw - The NTW frame uses an x-axis along the target’s velocity vector, a z-axis perpendicular to x and in the same plane as the target’s nadir vector, and a y-axis completing the right-handed frame.

If both a position_offset and velocity_offset are provided, the same frame need not be used for both.

Note

This command only has an effect for the Rendezvous maneuver, and it is ignored for Target and Intercept.

offset_time <time-value>

For targets that have a kinematic offset (at least one of position_offset or velocity_offset is provided), also specifying an offset_time will indicate at what time after the end of the maneuver that the provided kinematic offset will be achieved. For example, this command can be used to target a state such that 1 hour after the maneuver the maneuvering platform will attain the given target.

Note

If a non-zero offset_time is provided, but there is no non-zero kinematic offset, this command will have no effect.

Note

This command can be combined with lag_time, but the combined effect can be non-intuitive.

lag_time <time-value>

Specify a lag time for the target. If a lag time is specified, the actual target will be advanced by the specified time along its motion relative to where the targeting operation is aimed. For example, the performer of a Rendezvous maneuver that has a lag_time specified will achieve an orbit that follows along the orbit of the target platform, but will be the given time behind the target in its orbit.

Note

This command can be combined with offset_time, but the combined effect can be non-intuitive.