I set up an elevation detector which seems to work perfectly. For Validation I set up the same detector in GMAT. The issue is, that the GMAT detector detects 6 events, whereas my detector only detects 4 events. Those 6 events consist of the 4 events, and two additional events. Those 2 additional events have a remarkably shorter contact duration, compared to the rest of the events.
Therefore my question is, if there’s something like a minimum time span for elevation detection events in Orekit?
Yes, it is a general feature for all events detector, it is called maxCheckInterval.
In older versions of Orekit/Hipparchus, it used to be a single double value (a time in seconds for Orekit). In newer versions of the library, it can be an AdaptableInterval. The goal of this check is to first separate events before a full-blown root-finding algorithm is run. If this setting is too large, then pairs of events could be missed if they are close enough. The AdaptableInterval feature has been added especially with ElevationDetector in mind, in order to allow close events to be detected but not paying a too large overhead when the satellite is far below horizon. There is a special ElevationDetectionAdaptableIntervalFactory factory for this case.