adam-assist

---

Table of Contents

• Installation
• Usage
  • Propagating Orbits
  • Generating Ephemerides

Overview

adam-assist is a pluggable propagator class for the adam-core package that uses ASSIST for propagating orbits.

Installation

pip install adam-assist

Usage

Propagating Orbits

Here we initialize a set of adam_core.orbit.Orbit objects from the JPL Small Bodies Database and propagate them using the AdamAssistPropagator class. You can manually initialize the orbits as well.

from adam_core.orbits.query.sbdb import query_sbdb
from adam_core.time import Timestamp
from adam_assist import ASSISTPropagator

# Query the JPL Small Bodies Database for a set of orbits
sbdb_orbits = query_sbdb(["2020 AV2", "A919 FB", "1993 SB"])
times = Timestamp.from_mjd([60000, 60365, 60730], scale="tdb")


propagator = ASSISTPropagator()

propagated = propagator.propagate_orbits(sbdb_orbits, times)

Of course you can define your own orbits as well.

import pyarrow as pa
from adam_core.orbits import Orbit
from adam_core.coordinates import CartesianCoordinates, Origin
from adam_core.time import Timestamp
from adam_assist import ASSISTPropagator

# Define an orbit
orbits = Orbit.from_kwargs(
  orbit_id=["1", "2", "3"],
  coordinates=CartesianCoordinates.from_kwargs(
    # use realistic cartesian coords in AU and AU/day
    x=[-1.0, 0.0, 1.0],
    y=[-1.0, 0.0, 1.0],
    z=[-1.0, 0.0, 1.0],
    vx=[-0.1, 0.0, 0.1],
    vy=[-0.1, 0.0, 0.1],
    vz=[-0.1, 0.0, 0.1],
    time=Timestamp.from_mjd([60000, 60365, 60730], scale="tdb"),
    origin=Origin.from_kwargs(code=pa.repeat("SUN", 3)),
    frame="eliptic"
  ),
)

propagator = ASSISTPropagator()

propagated = propagator.propagate_orbits(orbits)

Generating Ephemerides

The ASSISTPropagator class uses the adam-core default ephemeris generator to generate ephemerides from the ASSIST propagated orbits. The default ephemeris generator accounts for light travel time and aberration. See adam_core.propagator.propagator.EphemerisMixin for implementation details.

from adam_core.orbits.query.sbdb import query_sbdb
from adam_core.time import Timestamp
from adam_core.observers import Observers
from adam_assist import ASSISTPropagator

# Query the JPL Small Bodies Database for a set of orbits
sbdb_orbits = query_sbdb(["2020 AV2", "A919 FB", "1993 SB"])
times = Timestamp.from_mjd([60000, 60365, 60730], scale="utc")
observers = Observers.from_code("399", times)
propagator = ASSISTPropagator()

ephemerides = propagator.generate_ephemeris(sbdb_orbits, observers)

Configuration

When initializing the ASSISTPropagator, you can configure several parameters that control the integration. These parameters are passed directly to REBOUND's IAS15 integrator. The IAS15 integrator is a high accuracy integrator that uses adaptive timestepping to maintain precision while optimizing performance.

• min_dt: Minimum timestep for the integrator (default: 1e-12 days)
• initial_dt: Initial timestep for the integrator (default: 0.001 days)
• epsilon: Controls the adaptive timestep behavior (default: 1e-6)
• adaptive_mode: Controls the adaptive timestep behavior (default: 1)

These parameters are passed directly to REBOUND's IAS15 integrator. The IAS15 integrator is a high accuracy integrator that uses adaptive timestepping to maintain precision while optimizing performance.

Example:

propagator = ASSISTPropagator(
  min_dt=1e-12,
  initial_dt=0.0001,
  epsilon=1e-6,
  adaptive_mode=1
)

When initializing the ASSISTPropagator, you can configure several parameters that control the integration. These parameters are passed directly to REBOUND's IAS15 integrator. The IAS15 integrator is a high accuracy integrator that uses adaptive timestepping to maintain precision while optimizing performance.

Default SPK Files

The asteroids SPK file sb441-n16.bsp contains the 16 largest asteroids in the solar system. They are listed here by number for reference:

1 Ceres 3 Juno 4 Vesta 7 Iris 10 Hygiea 15 Eunomia 16 Psyche 31 Euphrosyne 52 Europa 65 Cybele 70 Panopaea 87 Sylvia 88 Thisbe 107 Camilla 511 Davida 704 Interamnia