Repeat Orbit Flag

Some satellite operators will manoeuvre the satellite to keep it within the defined nominal SSO Sun Synchronous Orbit or Exact Repeat orbit. This occurs for many operational satellites (e.g. Landsat, Radarsat,Spot, etc).

Knowing this SaVoir can make assumptions for long term orbit analysis by extrapolation of the current defined orbit. This assumption is implemented through the Repeat Orbit Modifier in the Orbit section of the satellite configuration file.

When a satellite orbit is configured with the Repeat Orbit Modifier the satellite will show a little icon at the left of the satellite name. It will be a little Sun icon for Sun Synchronous orbits, or three oblique lines for Exact Repeat orbits

Repeat Orbit Modifier

The Repeat Orbit Modifier is defined in the Orbit section of the Satellites configuration file. It implies the definition of a Modifier flag and RC Repeat Cycle and CL Cycle Length parameters.

The Repeat Orbit Modifier tells the orbit propagator to handle orbit calculation as follows:

Perform all orbit propagation within the time span [Epoch, Epoch + Nominal Orbit Period], with Epoch = epoch of the state vector (TLE Two Line Elements, OSV Orbit State Vector, etc), and the Nominal Orbit Period, calculated from the RC Repeat Cycle and CL Cycle Length .
```
Nominal Orbit Period= 86400 * RC / CL
```
Any intersection calculations will be performed within the span of a single SSO Sun Synchronous Orbit cycle, and cloned for each of the subsequent cycles of the simulation period.

Error detection

If the satellite is not kept within the defined Repeat Orbit, an inconsistency will occur between the Nominal Orbit Period and the Orbit Period of the state vector.

If the difference between both periods is higher than 0.2 seconds (*) a warning will be displayed in the Scenario Pane (Sun icon with exclamation mark) and the Orbit Properties grid (Period Difference in red). In that case it is advisable to update the Satellite configuration file, removing the Repeat Orbit Modifier.

(*) The warning threshold is set to 0.2 seconds by default, but can be changed individually for every satellite, via the Period threshold parameter in the orbit properties grid