GEO station keeping handler

Orekit Python Wrapper usage
1

Hello! I am using the LongitudeCrossingDetector and LatitudeCrossingDetector to determine when an impulsive maneuver needs to be done for a GEO. This is working perfectly.

I set up a handler to perform a maneuver when the event occurs. Within this handler, another detector is needed to figure out when the GEO is at apogee/perigee or crossing the line of apsides. I only want this event detector working after latitude/longitude crossing was detected, but I am unsure how to do that.

Any help would be greatly appreciated!

2

You can use an EventEnablingPredicateFilter that will wrap the second detector and trigger it only based on an EnablingPredicate you will provide. This enabling predicate will simply have to hold a boolean that will be switched when the first event occurs.

3

Thank you for the suggestion @luc

So, I have used the EventEnablingPredicateFilter to wrap around the second detector with an EnablingPredicate that is set to currentState.getDate().isBefore(lastAllowedDate).

I then use this EventEnablingPredicateFilter to trigger the maneuver as follows:

maneuver = ImpulseManeuver(trigger_perigee, attitudeProvider, delta_v, 220.0)
maneuver = maneuver.of_(ApsideDetector)

This is all inside the eventOccurred method of the PythonEventHandler class I created. However, when I attempt to propagate the GEOs using the TLEPropagator I keep getting the following error message:

JavaError: <super: <class 'JavaError'>, <JavaError object>>
Java stacktrace:
java.lang.RuntimeException: NameError
at org.orekit.python.PythonEventHandler.eventOccurred(Native Method)
at org.orekit.propagation.events.AbstractDetector.eventOccurred(AbstractDetector.java:162)
at org.orekit.propagation.events.EventsLogger$LocalHandler.eventOccurred(EventsLogger.java:227)
at org.orekit.propagation.events.EventsLogger$LocalHandler.eventOccurred(EventsLogger.java:222)
at org.orekit.propagation.events.AbstractDetector.eventOccurred(AbstractDetector.java:162)
at org.orekit.propagation.events.EventState.doEvent(EventState.java:461)
at org.orekit.propagation.analytical.AbstractAnalyticalPropagator.acceptStep(AbstractAnalyticalPropagator.java:268)
at org.orekit.propagation.analytical.AbstractAnalyticalPropagator.propagate(AbstractAnalyticalPropagator.java:168)
at org.orekit.propagation.AbstractPropagator.propagate(AbstractPropagator.java:260)
at org.orekit.propagation.AbstractPropagator.getPVCoordinates(AbstractPropagator.java:265)
4

Hi,

Seems like something is going wrong in the python event handler method eventOccured - name error. If I understand you right, the exact same eventOccured method is working in another propagator?

Do you have a expected-to-work-but-don’t code to share, it is easier to spot then?

Regards
/Petrus

5

Hi @petrus.hyvonen! I have not gotten it to work yet with any propagator, I was trying to test it with the TLEPropagator as it is much faster. However, I am currently running it with the numerical propagator, but still waiting for that to finish. Here is my simplified version of the handler:

class LatitudeCrossingHandler(PythonEventHandler):

    def init(self, initialstate, target):
        pass

    def eventOccurred(self, s, T, increasing):  # impulsive inclination maneuver
        inertialFrame = FramesFactory.getEME2000()

        # need to ensure the Z axis is aligned with orbital momentum,
        # so we select an attitude aligned with LVLH Local Orbital frame
        attitudeProvider = LofOffset(inertialFrame, LOFType.LVLH)

        ascendingNodeStopper = NodeDetector(300.0, 1e-6, 100, StopOnIncreasing()) # check later, 100 madeup

        lastAllowedDate = currentState.getDate().shiftedBy(1.0 * currentState.getKeplerianPeriod()) # let maneuvers happen for 1 orbits
        predicate = currentState.getDate().isBefore(lastAllowedDate)
        trigger = EventEnablingPredicateFilter(ascendingNodeStopper, predicate)

        delta_v = Vector3D(SomeArray)  # calculate required impulsive velocity change

        maneuver = ImpulseManeuver(trigger, attitudeProvider, delta_v, 220.0)
        maneuver = maneuver.of_(NodeDetector)

        propagator.addEventDetector(maneuver)

        return Action.CONTINUE

    def resetState(self, detector, oldState):
        """Reset TimingEvent handler to given state."""
        return oldState

Cheers

Patrick

1 Like
6

Hi,

It is really hard to see without running it. One way to debug (if you are not using a debugger) is to do the return statement at different locations in the eventOccured method and try to figure out which line is giving the error. That’s narrows down the problem a bit.

7

Currently I am struggling to get the EventEnablingPredicateFilter working. It requires an EnablingPredicate but I keep getting a NotImplementedError when I try to create an instance.

I would like to have it so it only performs the ImpulseManeuver for the next couple perigee passes, where I define the predicate as:

lastAllowedDate = s.getDate().shiftedBy(3 * s.getKeplerianPeriod()) # let maneuvers happen for 3 orbits
predicate = s.getDate().isBefore(lastAllowedDate)
8

Hi @pshober, thanks for your post, it helps mee too.

What is currentState? Where is it defined?

I’m trying to convert to Python the java script

src/main/java/org/orekit/tutorials/maneuvers/ImpulseAtNode.java

that appears in the tutorials. In particular, I have troubles with its line 117:

final EnablingPredicate predicate = (state, detector, g) → state.getDate().isBefore(lastAllowedDate);

How would you translate it to Python? state, detector and g are not defined at that point of the script…

Thank you very much!
Alfredo

9

Hi,

I came across this thread while working on station keeping with the Python wrapper.
To write a predicate, a Python class must be written, and it has to inherit from the PythonEnablingPredicate class. An example can be found in this thread: ImpulseManeuver on PositionAngle with Python wrapper - #4 by petrus.hyvonen

Cheers
Clément