Forced-Motion Circumnavigation RPO Sequence
The Forced-Motion Circumnavigation (FMC) RPO sequence places a chase satellite in an FMC.
First, the sequence moves the chase satellite from its current position to the starting point of the FMC. You can accomplish this via a set of forced-motion waypoints that by default move the chase satellite in a near-straight line along the path connecting current relative position to the start position of the FMC. If you prefer a simple hop instead of a series of waypoints, then set the Way_MaxDegrees parameter to a large value (>180 deg). Astrogator then uses a simple hop to the FMC start.
Second, the sequence maintains the FMC for the number of revolutions you specify.
The degrees of freedom in the FMC are:
- size
- orientation
- translation
- time ratio
You can vary these parameters to achieve many different FMC configurations. The figure below shows a relative z-offset orbit using this sequence.
Sequence parameters
| Option | Description |
|---|---|
| Circumnav_Radius | Enter the radius of the force motion circle. |
| NumPoints | Enter as an integer the number of points in the FMC per revolution. |
| FMC_NumRevs | Enter as a double the number of revolutions to persist in the FMC. |
| Transfer_Duration | Enter the transfer time from current position to the start of the FMC. |
| Initial_Offset_Angle | Enter the initial offset angle from the zenith direction (from +RBar). The angle is measured counterclockwise from zenith. Valid angles are +180 to -180 degrees. |
| CrossTrack_InTrackRotation | Enter the rotation angle of the FMC about the intrack axis. Valid angles are +180 to -180 degrees. |
| CrossTrack_RadialRotation | Enter the rotation angle of the FMC about the radial axes. Valid angles are +90 to -90 degrees. |
| Radial_Offset | Enter, in distance units, the radial translation of the FMC from the target. |
| InTrack_Offset | Enter, in distance units, the in-track translation of the FMC from the target. |
| CrossTrack_Offset | Enter, in distance units, the cross-track translation of the FMC from the target. |
| Way_MaxDegrees | Enter the maximum degrees between hops for the forced motion part that connects the current position to the start of the FMC. |
| Engine_Name | Enter, as a string, the name of the finite maneuver engine model. |
| Maneuver_Type | Select the type of maneuver, "Impulsive" or "Finite," from the drop-down list. |
| WhoAmI | Enter, as a string, the name of the current satellite. |
| Time_Compression_Ratio | Enter, as a double, the time ratio as compared to real time. To complete an FMC in half a revolution, enter a value of two. To take two revolutions to complete an FMC, enter a value of 0.5. |
| ThisSequence | Enter, as a string, the name of this sequence. This is nominally FMCircumnav, but if you insert the sequence multiple times in the MCS, Astrogator adds a monotonically increasing number on the end of the name each time (FMCircumnav1, FMCircumnav2, etc.). |