Satellite Configuration

Satellites are the basic unit of agent in the environment. Four things must be specified in subclasses of Satellite:

The observation_spec, which defines the satellite’s observation.
The action_spec, which defines the satellite’s actions.
The dyn_type, which selects the underlying dynamics model used in simulation.
The fsw_type, which selects the underlying flight software model.

A very simple satellite is defined below:

[1]:

from bsk_rl import sats, act, obs, scene, data, SatelliteTasking
from bsk_rl.sim import dyn, fsw
import numpy as np

from Basilisk.architecture import bskLogging
bskLogging.setDefaultLogLevel(bskLogging.BSK_WARNING)


class SimpleSatellite(sats.Satellite):
    observation_spec = [obs.Time()]  # Passed as list of instantiated classes
    action_spec = [act.Drift()]
    dyn_type = dyn.BasicDynamicsModel  # Passed as a type
    fsw_type = fsw.BasicFSWModel

Setting Satellite Parameters

Without instantiating the satellite, parameters that can be set in the various models can be inspected.

[2]:

SimpleSatellite.default_sat_args()

[2]:

{'hs_min': 0.0,
 'maxCounterValue': 4,
 'thrMinFireTime': 0.02,
 'desatAttitude': 'sun',
 'controlAxes_B': [1, 0, 0, 0, 1, 0, 0, 0, 1],
 'thrForceSign': 1,
 'K': 7.0,
 'Ki': -1,
 'P': 35.0,
 'utc_init': 'this value will be set by the world model',
 'batteryStorageCapacity': 288000.0,
 'storedCharge_Init': <function bsk_rl.sim.dyn.base.BasicDynamicsModel.<lambda>()>,
 'disturbance_vector': None,
 'dragCoeff': 2.2,
 'basePowerDraw': 0.0,
 'wheelSpeeds': <function bsk_rl.sim.dyn.base.BasicDynamicsModel.<lambda>()>,
 'maxWheelSpeed': inf,
 'u_max': 0.2,
 'rwBasePower': 0.4,
 'rwMechToElecEfficiency': 0.0,
 'rwElecToMechEfficiency': 0.5,
 'panelArea': 1.0,
 'panelEfficiency': 0.2,
 'nHat_B': array([ 0,  0, -1]),
 'mass': 330,
 'width': 1.38,
 'depth': 1.04,
 'height': 1.58,
 'sigma_init': <function bsk_rl.sim.dyn.base.BasicDynamicsModel.<lambda>()>,
 'omega_init': <function bsk_rl.sim.dyn.base.BasicDynamicsModel.<lambda>()>,
 'rN': None,
 'vN': None,
 'oe': <function bsk_rl.utils.orbital.random_orbit(i: Optional[float] = None, a: Optional[float] = 6871, e: float = 0, Omega: Optional[float] = None, omega: Optional[float] = None, f: Optional[float] = None, alt: float = None, r_body: float = 6371) -> Basilisk.utilities.orbitalMotion.ClassicElements>,
 'mu': 398600436000000.0,
 'thrusterPowerDraw': 0.0}

These parameters can be overriden when instantiating the satellite through the sat_args argument.

[3]:

sat = SimpleSatellite(
    name="SimpleSat-1",
    sat_args=dict(
        mass=300,  # Setting a constant value
        dragCoeff=lambda: np.random.uniform(2.0, 2.4),  # Setting a randomized value
    ),
)

Each time the simulation is reset, all of the function-based randomizers are called.

[4]:

sat.generate_sat_args()  # Called by the environment on reset()
sat.sat_args

[4]:

{'hs_min': 0.0,
 'maxCounterValue': 4,
 'thrMinFireTime': 0.02,
 'desatAttitude': 'sun',
 'controlAxes_B': [1, 0, 0, 0, 1, 0, 0, 0, 1],
 'thrForceSign': 1,
 'K': 7.0,
 'Ki': -1,
 'P': 35.0,
 'utc_init': 'this value will be set by the world model',
 'batteryStorageCapacity': 288000.0,
 'storedCharge_Init': 163143.33183958015,
 'disturbance_vector': None,
 'dragCoeff': 2.3538247309548956,
 'basePowerDraw': 0.0,
 'wheelSpeeds': array([ -473.17579263,   808.95683539, -1198.9659229 ]),
 'maxWheelSpeed': inf,
 'u_max': 0.2,
 'rwBasePower': 0.4,
 'rwMechToElecEfficiency': 0.0,
 'rwElecToMechEfficiency': 0.5,
 'panelArea': 1.0,
 'panelEfficiency': 0.2,
 'nHat_B': array([ 0,  0, -1]),
 'mass': 300,
 'width': 1.38,
 'depth': 1.04,
 'height': 1.58,
 'sigma_init': array([0.22038354, 0.87014395, 0.31116082]),
 'omega_init': array([ 8.34516648e-05,  4.00495587e-05, -5.79661993e-05]),
 'rN': None,
 'vN': None,
 'oe': <Basilisk.utilities.orbitalMotion.ClassicElements at 0x7fe5d3175e50>,
 'mu': 398600436000000.0,
 'thrusterPowerDraw': 0.0}

As a result, each episode will have different randomized parameters:

[5]:

for _ in range(3):
    sat.generate_sat_args()  # Called by the environment on reset()
    print("New value of dragCoeff:", sat.sat_args["dragCoeff"])

New value of dragCoeff: 2.372603023150659
New value of dragCoeff: 2.0273358785169853
New value of dragCoeff: 2.106391069342978

The Observation Specification

A variety of observation elements are available for satellites. Full documentation can be found here, but some commonly used elements are explored below.

Info: In these examples, obs_type=dict is passed to the Satellite constructor so that the observation is human readable. While some RL libraries support dictionary-based observations, the default return type - the numpy array format - is more typically used.

Satellite Properties

The most common type of observations is introspective; i.e. what is my current state? Any @property in the dyn_type or fsw_type of the satellite can be accessed using SatProperties.

[6]:

class SatPropsSatellite(sats.Satellite):
    observation_spec = [
        obs.SatProperties(
            # At a minimum, specify the property to observe
            dict(prop="wheel_speeds"),
            # You can specify the module to use for the observation, but it is not necessary
            # if only one module has for the property
            dict(prop="battery_charge_fraction", module="dynamics"),
            # Properties can be normalized by some constant. This is generally desirable
            # for RL algorithms to keep values around [-1, 1].
            dict(prop="r_BN_P", norm=7e6),
        )
    ]
    action_spec = [act.Drift()]
    dyn_type = dyn.BasicDynamicsModel
    fsw_type = fsw.BasicFSWModel

env = SatelliteTasking(
    satellite=SatPropsSatellite("PropSat-1", {}, obs_type=dict),
    log_level="CRITICAL",
)
observation, _ = env.reset()
observation

[6]:

{'sat_props': {'wheel_speeds': array([126.48306929,  44.98973063, 109.53523606]),
  'battery_charge_fraction': 0.41234591614388755,
  'r_BN_P_normd': array([-0.35512527,  0.43688692, -0.8040512 ])}}

In some cases, you may want to access a bespoke property that is not natively implemented in a model. To do that, simply extend the model with your desired property.

[7]:

class BespokeFSWModel(fsw.BasicFSWModel):
    @property
    def meaning_of_life(self):
        return 42

class BespokeSatPropsSatellite(sats.Satellite):
    observation_spec = [
        obs.SatProperties(dict(prop="meaning_of_life"))
    ]
    action_spec = [act.Drift()]
    dyn_type = dyn.BasicDynamicsModel
    fsw_type = BespokeFSWModel

env = SatelliteTasking(
    satellite=BespokeSatPropsSatellite("BespokeSat-1", {}, obs_type=dict),
    log_level="CRITICAL",
)
observation, _ = env.reset()
observation

[7]:

{'sat_props': {'meaning_of_life': 42.0}}

Alternatively, define the property with a function that takes the satellite object as an argument.

[8]:

class CustomSatPropsSatellite(sats.Satellite):
    observation_spec = [
        obs.SatProperties(dict(prop="meaning_of_life", fn=lambda sat: 42))
    ]
    action_spec = [act.Drift()]
    dyn_type = dyn.BasicDynamicsModel
    fsw_type = fsw.BasicFSWModel

env = SatelliteTasking(
    satellite=CustomSatPropsSatellite("BespokeSat-1", {}, obs_type=dict),
    log_level="CRITICAL",
)
observation, _ = env.reset()
observation

[8]:

{'sat_props': {'meaning_of_life': 42.0}}

Opportunity Properties

Another common input to the observation is information about upcoming locations that are being accessed by the satellite. Currently, these include ground stations for downlink and targets for imaging, but OpportunityProperties will work with any location added by add_location_for_access_checking. In these examples,

[9]:

class OppPropsSatellite(sats.ImagingSatellite):
    observation_spec = [
        obs.OpportunityProperties(
            # Properties can be added by some default names
            dict(prop="priority"),
            # They can also be normalized
            dict(prop="opportunity_open", norm=5700.0),
            # Or they can be specified by an arbitrary function
            dict(fn=lambda sat, opp: opp["r_LP_P"] + 42),
            n_ahead_observe=3,
        )
    ]
    action_spec = [act.Drift()]
    dyn_type = dyn.ImagingDynModel
    fsw_type = fsw.ImagingFSWModel

env = SatelliteTasking(
    satellite=OppPropsSatellite("OppSat-1", {}, obs_type=dict),
    scenario=scene.UniformTargets(1000),
    rewarder=data.UniqueImageReward(),
    log_level="CRITICAL",
)
observation, _ = env.reset()
observation

[9]:

{'target': {'target_0': {'priority': 0.819144367651575,
   'opportunity_open_normd': 0.021598580040357227,
   'prop_2': array([ 115323.64040117, 2923815.33143642, 5667394.65693138])},
  'target_1': {'priority': 0.6320574465135106,
   'opportunity_open_normd': 0.028104719621529252,
   'prop_2': array([  46261.20914523, 3078805.50912813, 5585711.65795746])},
  'target_2': {'priority': 0.6886746498597007,
   'opportunity_open_normd': 0.02783806823690282,
   'prop_2': array([-301588.13484356, 2799865.48314278, 5722858.982331  ])}}}

Navigating the Observation

Usually, multiple observation types need to be composed to sufficiently represent the environment for the learning agent. Simply add multiple observations to the observation specification list to combine them in the observation.

[10]:

class ComposedObsSatellite(sats.Satellite):
    observation_spec = [
        obs.Eclipse(),
        obs.SatProperties(dict(prop="battery_charge_fraction"))
    ]
    action_spec = [act.Drift()]
    dyn_type = dyn.BasicDynamicsModel
    fsw_type = fsw.BasicFSWModel

env = SatelliteTasking(
    satellite=ComposedObsSatellite("PropSat-1", {}, obs_type=dict),
    log_level="CRITICAL",
)
observation, _ = env.reset()
observation

[10]:

{'eclipse': [np.float64(4260.0), np.float64(720.0)],
 'sat_props': {'battery_charge_fraction': 0.8142833896409211}}

A few useful functions exist for inspecting the observation. The observation_space property of the satellite and the environment return a Gym observation space to describe the observation. In the single agent SatelliteTasking environment, these are the same.

Info: Here, we return to the ndarray default observation type.

[11]:

env = SatelliteTasking(
    satellite=ComposedObsSatellite("PropSat-1", {}),
    log_level="CRITICAL",
)
(env.observation_space, env.unwrapped.satellite.observation_space)

[11]:

(Box(-1e+16, 1e+16, (3,), float64), Box(-1e+16, 1e+16, (3,), float64))

With the flattened-vector type observation, it can be hard for the user to relate elements to specific observations.

[12]:

observation, _ = env.reset()
observation

[12]:

array([4.41000000e+03, 5.58000000e+03, 5.82705118e-01])

The observation_description property can help the user understand what elements are present in the observation.

[13]:

env.unwrapped.satellite.observation_description

[13]:

[np.str_('eclipse[0]'),
 np.str_('eclipse[1]'),
 np.str_('sat_props.battery_charge_fraction')]

The Action Specification

The action specification works similarly to observation specification. A list of actions is set in the class definition of the satellite.

[14]:

class ActionSatellite(sats.Satellite):
    observation_spec = [obs.Time()]
    action_spec = [
        # If action duration is not set, the environment max_step_duration will be used;
        # however, being explicit is always preferable
        act.Charge(duration=120.0),
        act.Desat(duration=60.0),
        # One action can be included multiple time, if different settings are desired
        act.Charge(duration=600.0,),
    ]
    dyn_type = dyn.BasicDynamicsModel
    fsw_type = fsw.BasicFSWModel

env = SatelliteTasking(
    satellite=ActionSatellite("ActSat-1", {}, obs_type=dict),
    log_level="INFO",
)
env.reset()

# Try each action; index corresponds to the order of addition
_ =env.step(0)
_ =env.step(1)
_ =env.step(2)

2025-06-20 19:57:39,227                                WARNING    Creating logger for new env on PID=5472. Old environments in process may now log times incorrectly.
2025-06-20 19:57:39,320 gym                            INFO       Resetting environment with seed=1276189173
2025-06-20 19:57:39,384 gym                            INFO       <0.00> Environment reset
2025-06-20 19:57:39,385 gym                            INFO       <0.00> === STARTING STEP ===
2025-06-20 19:57:39,385 sats.satellite.ActSat-1        INFO       <0.00> ActSat-1: action_charge tasked for 120.0 seconds
2025-06-20 19:57:39,386 sats.satellite.ActSat-1        INFO       <0.00> ActSat-1: setting timed terminal event at 120.0
2025-06-20 19:57:39,401 sats.satellite.ActSat-1        INFO       <120.00> ActSat-1: timed termination at 120.0 for action_charge
2025-06-20 19:57:39,401 data.base                      INFO       <120.00> Total reward: {}
2025-06-20 19:57:39,402 comm.communication             INFO       <120.00> Optimizing data communication between all pairs of satellites
2025-06-20 19:57:39,402 sats.satellite.ActSat-1        INFO       <120.00> ActSat-1: Satellite ActSat-1 requires retasking
2025-06-20 19:57:39,403 gym                            INFO       <120.00> Step reward: 0.0
2025-06-20 19:57:39,404 gym                            INFO       <120.00> === STARTING STEP ===
2025-06-20 19:57:39,404 sats.satellite.ActSat-1        INFO       <120.00> ActSat-1: action_desat tasked for 60.0 seconds
2025-06-20 19:57:39,405 sats.satellite.ActSat-1        INFO       <120.00> ActSat-1: setting timed terminal event at 180.0
2025-06-20 19:57:39,414 sats.satellite.ActSat-1        INFO       <180.00> ActSat-1: timed termination at 180.0 for action_desat
2025-06-20 19:57:39,414 data.base                      INFO       <180.00> Total reward: {}
2025-06-20 19:57:39,415 comm.communication             INFO       <180.00> Optimizing data communication between all pairs of satellites
2025-06-20 19:57:39,415 sats.satellite.ActSat-1        INFO       <180.00> ActSat-1: Satellite ActSat-1 requires retasking
2025-06-20 19:57:39,416 gym                            INFO       <180.00> Step reward: 0.0
2025-06-20 19:57:39,417 gym                            INFO       <180.00> === STARTING STEP ===
2025-06-20 19:57:39,417 sats.satellite.ActSat-1        INFO       <180.00> ActSat-1: action_charge tasked for 600.0 seconds
2025-06-20 19:57:39,418 sats.satellite.ActSat-1        INFO       <180.00> ActSat-1: setting timed terminal event at 780.0
2025-06-20 19:57:39,479 sats.satellite.ActSat-1        INFO       <780.00> ActSat-1: timed termination at 780.0 for action_charge
2025-06-20 19:57:39,479 data.base                      INFO       <780.00> Total reward: {}
2025-06-20 19:57:39,480 comm.communication             INFO       <780.00> Optimizing data communication between all pairs of satellites
2025-06-20 19:57:39,480 sats.satellite.ActSat-1        INFO       <780.00> ActSat-1: Satellite ActSat-1 requires retasking
2025-06-20 19:57:39,481 gym                            INFO       <780.00> Step reward: 0.0

As with the observations, properties exist to help understand the actions available.

[15]:

env.action_space

[15]:

Discrete(3)

[16]:

env.unwrapped.satellite.action_description

[16]:

['action_charge', 'action_desat', 'action_charge']

Some actions take additional configurations, add multiple actions to the satellite, and/or have “special” features that are useful for manually interacting with the environment. For example, the imaging action can add an arbitrary number of actions corresponding to upcoming targets and process the name of a target directly instead of operating by action index.

[17]:

class ImageActSatellite(sats.ImagingSatellite):
    observation_spec = [obs.Time()]
    action_spec = [
        # Set the number of upcoming targets to consider
        act.Image(n_ahead_image=3)
    ]
    dyn_type = dyn.ImagingDynModel
    fsw_type = fsw.ImagingFSWModel

env = SatelliteTasking(
    satellite=ImageActSatellite("ActSat-2", {}),
    scenario=scene.UniformTargets(1000),
    rewarder=data.UniqueImageReward(),
    log_level="INFO",
)
env.reset()

env.unwrapped.satellite.action_description

2025-06-20 19:57:39,497                                WARNING    Creating logger for new env on PID=5472. Old environments in process may now log times incorrectly.
2025-06-20 19:57:39,499 gym                            INFO       Resetting environment with seed=1455343752
2025-06-20 19:57:39,500 scene.targets                  INFO       Generating 1000 targets
2025-06-20 19:57:39,576 gym                            INFO       <0.00> Environment reset

[17]:

['action_image_0', 'action_image_1', 'action_image_2']

Demonstrating the action overload feature, we task the satellite based on target name. While this is not part of the official Gym API, we find it useful in certain cases.

[18]:

target = env.unwrapped.satellite.find_next_opportunities(n=10)[9]["object"]
_ = env.step(target)

2025-06-20 19:57:39,582 sats.satellite.ActSat-2        INFO       <0.00> ActSat-2: Finding opportunity windows from 0.00 to 600.00 seconds
2025-06-20 19:57:39,630 sats.satellite.ActSat-2        INFO       <0.00> ActSat-2: Finding opportunity windows from 600.00 to 1200.00 seconds
2025-06-20 19:57:39,662 gym                            INFO       <0.00> === STARTING STEP ===
2025-06-20 19:57:39,662 act.discrete_actions           WARNING    <0.00> Action 'Target(tgt-358)' is not an integer. Will attempt to use compatible set_action_override method.
2025-06-20 19:57:39,663 sats.satellite.ActSat-2        INFO       <0.00> ActSat-2: Target(tgt-358) tasked for imaging
2025-06-20 19:57:39,665 sats.satellite.ActSat-2        INFO       <0.00> ActSat-2: Target(tgt-358) window enabled: 1019.9 to 1136.4
2025-06-20 19:57:39,665 sats.satellite.ActSat-2        INFO       <0.00> ActSat-2: setting timed terminal event at 1136.4
2025-06-20 19:57:39,889 sats.satellite.ActSat-2        INFO       <1022.00> ActSat-2: imaged Target(tgt-358)
2025-06-20 19:57:39,891 data.base                      INFO       <1022.00> Total reward: {'ActSat-2': 0.7276647940807758}
2025-06-20 19:57:39,892 comm.communication             INFO       <1022.00> Optimizing data communication between all pairs of satellites
2025-06-20 19:57:39,893 sats.satellite.ActSat-2        INFO       <1022.00> ActSat-2: Satellite ActSat-2 requires retasking
2025-06-20 19:57:39,894 gym                            INFO       <1022.00> Step reward: 0.7276647940807758