orbit.constellation — Constellation Module

Description

This module allows initialization of constellation (i.e. collection of satellites) from the respective model parameters. The orbits of the satellites in the constellation can also be generated. Currently only Walker-Delta constellation [1] is supported.

Factory method pattern is used for initializing the constellation object [2]. Users may additionally define their own constellation classes adherent to the same interface functions (from_dict(.), to_dict(.), generate_orbits(.), __eq__(.)) as in the in-built constellation classes.

References

1. Space Mission Analysis and Design, 3rd ed, Section 7.6, Pg 194, 195.

2. https://realpython.com/factory-method-python/#supporting-additional-formats

Examples

1. Working with a Walker Delta Constellation.

   from orbitpy.constellation import ConstellationFactory
   
   factory = ConstellationFactory()
   specs = {"@type": 'Walker Delta Constellation', "date":{"@type": "JULIAN_DATE_UT1", "jd":2459270.75}, "numberSatellites": 2, "numberPlanes": 1,
                     "relativeSpacing": 1, "alt": 500, "ecc": 0.001, "inc": 45, "aop": 135, "@id": "abc"}
   wd_model = factory.get_constellation_model(specs) # initialization
   print(wd_model.generate_orbits())
   
   >> [OrbitState.from_dict({'date': {'@type': 'JULIAN_DATE_UT1', 'jd': 2459270.75}, 'state': {'@type': 'CARTESIAN_EARTH_CENTERED_INERTIAL', 'x': -4858.713737315466, 'y': 3435.629431500001, 'z': 3435.6294315, 'vx': -5.388312480793739, 'vy': -3.8101122943213612, 'vz': -3.810112294321361}, '@id': 'abc_11'}),
       OrbitState.from_dict({'date': {'@type': 'JULIAN_DATE_UT1', 'jd': 2459270.75}, 'state': {'@type': 'CARTESIAN_EARTH_CENTERED_INERTIAL', 'x': 4868.440891944725, 'y': -3442.5075685000006, 'z': -3442.5075685, 'vx': 5.377546621691256, 'vy': 3.8024996823446955, 'vz': 3.8024996823446946}, '@id': 'abc_12'})]
   

   from orbitpy.constellation import ConstellationFactory
   from orbitpy.util import OrbitState
   
   date =  OrbitState.date_from_dict({"@type": "JULIAN_DATE_UT1", "jd":2459270.75})
   wd_model = WalkerDeltaConstellation( date=date, numberSatellites=2, numberPlanes=1, relativeSpacing=1, alt=500, ecc=0.001, inc=45, aop=135, _id="abc")
   print(wd_model.generate_orbits())
   
   >> [OrbitState.from_dict({'date': {'@type': 'JULIAN_DATE_UT1', 'jd': 2459270.75}, 'state': {'@type': 'CARTESIAN_EARTH_CENTERED_INERTIAL', 'x': -4858.713737315466, 'y': 3435.629431500001, 'z': 3435.6294315, 'vx': -5.388312480793739, 'vy': -3.8101122943213612, 'vz': -3.810112294321361}, '@id': 'abc_11'}),
       OrbitState.from_dict({'date': {'@type': 'JULIAN_DATE_UT1', 'jd': 2459270.75}, 'state': {'@type': 'CARTESIAN_EARTH_CENTERED_INERTIAL', 'x': 4868.440891944725, 'y': -3442.5075685000006, 'z': -3442.5075685, 'vx': 5.377546621691256, 'vy': 3.8024996823446955, 'vz': 3.8024996823446946}, '@id': 'abc_12'})]
   

2. Working with a custom constellation.

   Register and initialize a constellation object NewConstellation2021 with the label New Constellation 2021. The constellation consists of only 1 satellite with all Keplerian elements equal to 0 except the altitude which is supplied by the user.

   import propcov
   from orbitpy.util import OrbitState
   from orbitpy.constellation import ConstellationFactory
   
   class NewConstellation2021():
      def __init__(self, alt):
         self.alt = alt
   
      @staticmethod
      def from_dict(d):
         return NewConstellation2021(alt = d.get('alt', 0))
   
      def __eq__(self, other):
         if(isinstance(self, other.__class__)):
               return (self.alt==other.alt)
         else:
               return NotImplemented
   
      def generate_orbits(self):
   
         orbits = []
         date = propcov.AbsoluteDate()
         state_dict = {"@type":"KEPLERIAN_EARTH_CENTERED_INERTIAL",  "sma": 6378 + self.alt, "ecc": 0, "inc": 0, "raan": 0, "aop": 0, "ta": 0}
         state = OrbitState.state_from_dict(state_dict)
         orbits.append(OrbitState(date, state, 0))
   
         return orbits
   
   factory = ConstellationFactory()
   factory.register_constellation_model('New Constellation 2021', NewConstellation2021) # register user defined constellation
   specs = {'@type': 'New Constellation 2021', 'alt': 700}
   const1 = factory.get_constellation_model(specs) # initialization of the constellation object const1
   print(const1.generate_orbits())
   
   >> [OrbitState.from_dict({'date': {'@type': 'JULIAN_DATE_UT1', 'jd': 2459270.75}, 'state': {'@type': 'CARTESIAN_EARTH_CENTERED_INERTIAL', 'x': -4858.713737315466, 'y': 3435.629431500001, 'z': 3435.6294315, 'vx': -5.388312480793739, 'vy': -3.8101122943213612, 'vz': -3.810112294321361}, '@id': 'abc_11'}), OrbitState.from_dict({'date': {'@type': 'JULIAN_DATE_UT1', 'jd': 2459270.75}, 'state': {'@type': 'CARTESIAN_EARTH_CENTERED_INERTIAL', 'x': 4868.440891944725, 'y': -3442.5075685000006, 'z': -3442.5075685, 'vx': 5.377546621691256, 'vy': 3.8024996823446955, 'vz': 3.8024996823446946}, '@id': 'abc_12'})]
   

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