paseos 0.2.0
A package which simulates the space environment for operating multiple spacecraft.
Requires Python: >=3.8

## PASEOS - PAseos Simulates the Environment for Operating multiple Spacecraft

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![Alt Text](resources/images/sat_gif.gif)

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</p>

Disclaimer: This project is currently under development. Use at your own risk.

<!-- TABLE OF CONTENTS -->
<details open="open">
  <summary>Table of Contents</summary>
  <ol>
    <li><a href="#about-the-project">About the Project</a></li>
    <li><a href="#paseos-space-environment-simulation">PASEOS space environment simulation</a></li>
    <li><a href="#installation">Installation</a></li>
    <li><a href="#examples">Examples</a></li>
    <ul>
    <li><a href="#actors">Actors</a></li>
    <ul>
    <li><a href="#create-a-paseos-actor">Create a PASEOS actor</a></li>
    <li><a href="#local-and-known-actors">Local and Known Actors</a></li>
    </ul>
    <li><a href="#physical-models">Physical Models</a></li>
    <ul>
    <li><a href="#set-an-orbit-for-a-paseos-spacecraftactor">Set an orbit for a PASEOS SpacecraftActor</a></li>
    <li><a href="#how-to-add-a-communication-device">How to add a communication device</a></li>
    <li><a href="#how-to-add-a-power-device">How to add a power device</a></li>
    <li><a href="#thermal-modelling">Thermal Modelling</a></li>
    <li><a href="#radiation-modelling">Radiation Modelling</a></li>
    <li><a href="#custom-modelling">Custom Modelling</a></li>
    <li><a href="#simulation-settings">Custom Central Bodies</a></li>
    </ul>
    <li><a href="#simulation-settings">Simulation Settings</a></li>
    <ul>
    <li><a href="#initializing-paseos">Initializing PASEOS</a></li>
    <li><a href="#using-the-cfg">Using the cfg</a></li>
    <li><a href="#faster-than-real-time-execution">Faster than real-time execution</a></li>
    <li><a href="#event-based-mode">Event-based mode</a></li>
    </ul>
    <li><a href="#activities">Activities</a></li>
    <ul>
    <li><a href="#simple-activity">Simple Activity</a></li>
    <li><a href="#activities-with-inputs-and-outputs">Activities with Inputs and Outputs</a></li>
    <li><a href="#constraint-function">Constraint Function</a></li>
    <li><a href="#on-termination-function">On-termination Function</a></li>
    </ul>
    <li><a href="#utilities">Utilities</a></li>
    <ul>
    <li><a href="#visualization">Visualization</a></li>
    <li><a href="#monitoring-simulation-status">Monitoring Simulation Status</a></li>
    <li><a href="#writing-simulation-results-to-a-file">Writing Simulation Results to a File</a></li>
    </ul>
    <li><a href="#wrapping-other-software-and-tools">Wrapping Other Software and Tools</a></li>
    <ul>
    <li><a href="#via-activities">Via Activities</a></li>
    <li><a href="#via-constraint-functions">Via Constraint Functions</a></li>
    <li><a href="#via-custom-properties">Via Custom Properties</a></li>
    </ul>
    </ul>
    <li><a href="#glossary">Glossary</a></li>
    <ul>
    <li><a href="#physical-model-parameters">Physical Model Parameters</a></li>
    </ul>
    <li><a href="#contributing">Contributing</a></li>
    <li><a href="#license">License</a></li>
    <li><a href="#contact">Contact</a></li>
  </ol>
</details>

## About the project

PASEOS is a `Python` module that simulates the environment to operate multiple spacecraft. In particular, PASEOS offers the user some utilities to run their own [activities](#activity) by taking into account both operational and onboard (e.g. limited-power-budget, radiation, and thermal effects) constraints. <br> PASEOS is designed to be:

- **open-source**: the source code of PASEOS is available under a GPL license.
- **fully decentralised**: one instance of PASEOS shall be executed in every node, i.e. individual spacecraft (actor), of the emulated spacecraft. Each instance of PASEOS is responsible for handling the user [activities](#activity) executed on that node (the local actor) while keeping track of the status of the other nodes. In this way, the design of PASEOS is completely decentralised and independent of the number of nodes of the constellation. Because of that, both single-node and multi-node scenarios are possible.
- **application-agnostic**: each user operation that has to be executed on a node is modelled as an [activity](#activity). The user is only required to provide the code to run and some parameters (e.g., power consumption) for each [activity](#activity). Thus, activities can be any code the user wants to simulate running on a spacecraft and thereby PASEOS is completely application-agnostic. Conceivable applications range from modelling constellations to training machine learning methods.

<br> The project is being developed by $\Phi$[-lab@Sweden](https://www.ai.se/en/data-factory/f-lab-sweden) in the frame of a collaboration between [AI Sweden](https://www.ai.se/en/) and the [European Space Agency](https://www.esa.int/) to explore distributed edge learning for space applications. For more information on PASEOS and $\Phi$-lab@Sweden, please take a look at the recording of the $\Phi$-lab@Sweden [kick-off event](https://www.youtube.com/watch?v=KuFRCcNxLgo&t=2365s).

## PASEOS space environment simulation

![Alt Text](resources/images/PASEOS_constraints.png)
PASEOS allows simulating the effect of onboard and operational constraints on user-registered [activities](#activity). The image above showcases the different phenomena considered (or to be implemented) in PASEOS.

## Installation

### pip / conda

The recommended way to install PASEOS is via [conda](https://docs.conda.io/en/latest/) / [mamba](https://github.com/conda-forge/miniforge#mambaforge) using

```

conda install paseos -c conda-forge

```

Alternatively, on Linux you can install via `pip` using

```

pip install paseos

```

The pip version requires `Python 3.8.16` due to [pykep's limited support of pip](https://esa.github.io/pykep/installation.html). 

### Building from source

To build from source, first of all clone the [GitHub](https://github.com/aidotse/PASEOS.git) repository as follows ([Git](https://git-scm.com/) required):

```
git clone https://github.com/aidotse/PASEOS.git
```

To install PASEOS you can use [conda](https://docs.conda.io/en/latest/) as follows:

```
cd PASEOS
conda env create -f environment.yml
```

This will create a new conda environment called `PASEOS` and install the required software packages.
To activate the new environment, you can use:

```
conda activate paseos
```

Alternatively, you can install PASEOS by using [pip](https://www.pypy.org/) as follows:

```
cd PASEOS
pip install -e .
```

### Using Docker

Two [Docker](https://www.docker.com/) images are available:
* [paseos](https://hub.docker.com/r/gabrielemeoni/paseos): corresponding to the latest release.
* [paseos-nightly](https://hub.docker.com/r/gabrielemeoni/paseos-nightly): based on the latest commit on the branch `main`. 

If you want to install PASEOS using Docker, access the desired repository and follow the provided instructions. 

## Examples

The next examples will introduce you to the use of PASEOS.

Comprehensive, self-contained examples can also be found in the `examples` folder where you can find an example on:

* Modelling and analysing a large constellation with PASEOS
* Modelling distributed learning on heterogeneous data in a constellation
* Using PASEOS with MPI to run PASEOS on supercomputers
* Using PASEOS to model the task of onboard satellite volcanic eruptions detection
* An example showing how total ionizing dose could be considered using a PASEOS [custom property](#customproperty)

The following are small snippets on specific topics.

### Actors

#### Create a PASEOS actor

The code snippet below shows how to create a PASEOS [actor](#actor) named **mySat** of type [SpacecraftActor](#spacecraftactor). [pykep](https://esa.github.io/pykep/) is used to define the satellite [epoch](<https://en.wikipedia.org/wiki/Epoch_(astronomy)>) in format [mjd2000](https://en.wikipedia.org/wiki/Julian_day) format. <br>
[actors](#actor) are created by using an `ActorBuilder`. The latter is used to define the [actor](#actor) `scaffold` that includes the [actor](#actor) minimal properties. In this way, [actors](#actor) are built in a modular fashion that enables their use also for non-space applications.

```py

import pykep as pk
from paseos import ActorBuilder, SpacecraftActor

# Define an actor of type SpacecraftActor of name mySat
sat_actor = ActorBuilder.get_actor_scaffold(name="mySat",
                                       actor_type=SpacecraftActor,
                                       epoch=pk.epoch(0))


```

#### Local and Known Actors

Once you have instantiated a [PASEOS simulation](#initializing-paseos) you can add other PASEOS [actors](#actor) ([Known actors](#known-actors)) to the simulation. You can use this, e.g., to study communications between actors and to automatically monitor communication windows.<br>
The next code snippet will add both a [SpacecraftActor](#spacecraftactor) and a [GroundstationActor](#ground-stationactor) (`other_sat`). An orbit is set for `other_sat`, which is placed around Earth at position `(x,y,z)=(-10000,0,0)` and velocity `(vx,vy,vz)=(0,-8000,0)` at epoch `epoch=pk.epoch(0)`.
The latter (`grndStation`) will be placed at coordinates `(lat,lon)=(79.002723, 14.642972)` and elevation of 0 m. <br> You cannot add a power device and an orbit to a `GroundstationActor`.

```py
import pykep as pk
import paseos
from paseos import ActorBuilder, SpacecraftActor, GroundstationActor
# Define the local actor as a SpacecraftActor of name mySat and its orbit
local_actor = ActorBuilder.get_actor_scaffold(name="mySat",
                                       actor_type=SpacecraftActor,
                                       epoch=pk.epoch(0))

ActorBuilder.set_orbit(
    actor=local_actor,
    position=[10000000, 0, 0],
    velocity=[0, 8000.0, 0],
    epoch=pk.epoch(0),
    central_body=pk.planet.jpl_lp("earth"),  # use Earth from pykep
)

# Initialize PASEOS simulation
sim = paseos.init_sim(local_actor)

# Create another SpacecraftActor
other_spacraft_actor = ActorBuilder.get_actor_scaffold(name="other_sat",
                                      actor_type=SpacecraftActor,
                                      epoch=pk.epoch(0))

# Let's set the orbit of other_spacraft_actor.
ActorBuilder.set_orbit(actor=other_spacraft_actor,
                       position=[-10000000, 0, 0],
                       velocity=[0, -8000.0, 0],
                       epoch=pk.epoch(0), central_body=earth)

#Create GroundstationActor
grndStation = GroundstationActor(name="grndStation", epoch=pk.epoch(0))

#Set the ground station at lat lon 79.002723 / 14.642972
# and its elevation 0m
ActorBuilder.set_ground_station_location(grndStation,
                                         latitude=79.002723,
                                         longitude=14.642972,
                                         elevation=0)

# Adding other_spacraft_actor to PASEOS.
sim.add_known_actor(other_spacraft_actor)

# Adding grndStation to PASEOS.
sim.add_known_actor(grndStation)
```

### Physical Models

#### Set an orbit for a PASEOS SpacecraftActor

Once you have defined a [SpacecraftActor](#spacecraftactor), you can assign a [Keplerian orbit](https://en.wikipedia.org/wiki/Kepler_orbit) or use [SGP4 (Earth orbit only)](https://en.wikipedia.org/wiki/Simplified_perturbations_models). 

##### Keplerian Orbit

To this aim, you need to define the central body the [SpacecraftActor](#spacecraftactor) is orbiting around and specify its position and velocity (in the central body's [inertial frame](https://en.wikipedia.org/wiki/Inertial_frame_of_reference)) and an epoch. In this case, we will use `Earth` as a central body.

```py
import pykep as pk
from paseos import ActorBuilder, SpacecraftActor
# Define an actor of type SpacecraftActor of name mySat
sat_actor = ActorBuilder.get_actor_scaffold(name="mySat",
                                       actor_type=SpacecraftActor,
                                       epoch=pk.epoch(0))

# Define the central body as Earth by using pykep APIs.
earth = pk.planet.jpl_lp("earth")

# Let's set the orbit of sat_actor.
ActorBuilder.set_orbit(actor=sat_actor,
                       position=[10000000, 0, 0],
                       velocity=[0, 8000.0, 0],
                       epoch=pk.epoch(0), central_body=earth)
```

##### SGP4 / Two-line element (TLE) 

For using SGP4 / [Two-line element (TLE)](https://en.wikipedia.org/wiki/Two-line_element_set) you need to specify the TLE of the [SpacecraftActor](#spacecraftactor). In this case, we will use the TLE of the [Sentinel-2A](https://en.wikipedia.org/wiki/Sentinel-2) satellite from [celestrak](https://celestrak.com/).

```py
from paseos import ActorBuilder, SpacecraftActor
# Define an actor of type SpacecraftActor
sat_actor = ActorBuilder.get_actor_scaffold(name="Sentinel-2A",
                                       actor_type=SpacecraftActor,
                                       epoch=pk.epoch(0))

# Specify your TLE
line1 = "1 40697U 15028A   23188.15862373  .00000171  00000+0  81941-4 0  9994"
line2 = "2 40697  98.5695 262.3977 0001349  91.8221 268.3116 14.30817084419867"

# Set the orbit of the actor
ActorBuilder.set_TLE(sat_actor, line1, line2)
```

##### Custom Propagators

You can define any kind of function you would like to determine actor positions and velocities. This allows integrating more sophisticated propagators such as [orekit](https://www.orekit.org/). A dedicated example on this topic can be found in the `examples` folder.

In short, you need to define a propagator function that returns the position and velocity of the actor at a given time. The function shall take the current epoch as arguments. You can then set the propagator function with

```py
import pykep as pk
from paseos import ActorBuilder, SpacecraftActor
# Create a SpacecraftActor
starting_epoch = pk.epoch(42)
my_sat = ActorBuilder.get_actor_scaffold(
    name="my_sat", actor_type=SpacecraftActor, epoch=starting_epoch
)

# Define a custom propagator function that just returns a sinus position
def my_propagator(epoch: pk.epoch):
  position,velocity = your_external_propagator(epoch)
  return position,velocity

# Set the custom propagator
ActorBuilder.set_custom_orbit(my_sat, my_propagator, starting_epoch)
```

##### Accessing the orbit
You can access the orbit of a [SpacecraftActor](#spacecraftactor) with

```py
# Position, velocity and altitude can be accessed like this
t0 = pk.epoch("2022-06-16 00:00:00.000") # Define the time (epoch)
print(sat_actor.get_position(t0)) 
print(sat_actor.get_position_velocity(t0))
print(sat_actor.get_altitude(t0))
```


#### How to add a communication device

The following code snippet shows how to add a communication device to a [SpacecraftActors] (#spacecraftactor). A communication device is needed to model the communication between [SpacecraftActors] (#spacecraftactor) or a [SpacecraftActor](#spacecraftactor) and [GroundstationActor](#ground-stationactor). Currently, given the maximum transmission data rate of a communication device, PASEOS calculates the maximum data that can be transmitted by multiplying the transmission data rate by the length of the communication window. The latter is calculated by taking the period for which two actors are in line-of-sight into account.

```py
import pykep as pk
from paseos import ActorBuilder, SpacecraftActor
# Define an actor of type SpacecraftActor of name mySat
sat_actor = ActorBuilder.get_actor_scaffold(name="mySat",
                                       actor_type=SpacecraftActor,
                                       epoch=pk.epoch(0))
# Add a communication device
ActorBuilder.add_comm_device(actor=sat_actor,
                             # Communication device name
                             device_name="my_communication_device",
                             # Bandwidth in kbps.
                             bandwidth_in_kbps=100000)
```

#### How to add a power device

The following code snippet shows how to add a power device to a [SpacecraftActor](#spacecraftactor).
Moreover, PASEOS assumes that the battery will be charged by solar panels, which will provide energy thanks to the incoming solar radiation when the spacecraft is not eclipsed. Charging and discharging happens automatically during [activities](#activity).

```py
import pykep as pk
import paseos
from paseos import ActorBuilder, SpacecraftActor
# Define an actor of type SpacecraftActor of name mySat
sat_actor = ActorBuilder.get_actor_scaffold(name="mySat",
                                       actor_type=SpacecraftActor,
                                       epoch=pk.epoch(0))
# Add a power device
ActorBuilder.set_power_devices(actor=sat_actor,
                               battery_level_in_Ws=100, # current level
                               max_battery_level_in_Ws=2000,
                               charging_rate_in_W=10,
                               power_device_type=paseos.PowerDeviceType.SolarPanel)
```

Alternatively to the default `paseos.PowerDeviceType.SolarPanel` you can also use `paseos.PowerDeviceType.RTG`. The only difference at the moment is that [RTGs](https://en.wikipedia.org/wiki/Radioisotope_thermoelectric_generator) also charge in eclipse.

Note that at the moment only one power device is supported. Adding another will override the existing one.

You can check the battery's state of charge and level in Ws with:

```py
print(my_actor.state_of_charge)
print(my_actor.battery_level_in_Ws)
```

#### Thermal Modelling

To model thermal constraints on spacecraft we utilize a model inspired by the one-node model described in [Martínez - Spacecraft Thermal Modelling and Test](http://imartinez.etsiae.upm.es/~isidoro/tc3/Spacecraft%20Thermal%20Modelling%20and%20Testing.pdf). Thus, we model the change in temperature as

$$mc \, \frac{dT}{dt} = \dot{Q}_{solar} + \dot{Q}_{albedo} + \dot{Q}_{central_body_IR} - \dot{Q}_{dissipated} + \dot{Q}_{activity}.$$

This means your spacecraft will heat up due to being in sunlight, albedo reflections, infrared radiation emitted by the central body as well as due to power consumption of activities. It will cool down due to heat dissipation.

The model is only available for a [SpacecraftActor](#spacecraftactor) and (like all the physical models) only evaluated for the [local actor](#local-actor).

The following parameters have to be specified for this:

- Spacecraft mass [kg], initial temperature [K], emissive area (for heat dissipation) and thermal capacity [J / (kg * K)]
- Spacecraft absorptance of Sun light, infrared light. [0 to 1]
- Spacecraft area [m^2] facing Sun and central body, respectively
- Solar irradiance in this orbit [W] (defaults to 1360W)
- Central body surface temperature [k] (defaults to 288K)
- Central body emissivity and reflectance [0 to 1] (defaults to 0.6 and 0.3)
- Ratio of power converted to heat (defaults to 0.5)

To use it, simply equip your [SpacecraftActor](#spacecraftactor) with a thermal model with:

```py
from paseos import SpacecraftActor, ActorBuilder
my_actor = ActorBuilder.get_actor_scaffold("my_actor", SpacecraftActor, pk.epoch(0))
ActorBuilder.set_thermal_model(
    actor=my_actor,
    actor_mass=50.0, # Setting mass to 50kg
    actor_initial_temperature_in_K=273.15, # Setting initial temperature to 0°C
    actor_sun_absorptance=1.0, # Depending on material, define absorptance
    actor_infrared_absorptance=1.0, # Depending on material, define absorptance
    actor_sun_facing_area=1.0, # Area in m2
    actor_central_body_facing_area=1.0, # Area in m2
    actor_emissive_area=1.0, # Area in m2
    actor_thermal_capacity=1000, # Capacity in J / (kg * K)
    # ... leaving out default valued parameters, see docs for details
)
```

The model is evaluated automatically during [activities](#activity). You can check the spacecraft temperature with:

```py
print(my_actor.temperature_in_K)
```

At the moment, only one thermal model per actor is supported. Setting a second will override the old one.

#### Radiation Modelling
PASEOS models three types of radiation effects.
1. Data corruption due to single event upsets which a event rate $r_d$.
2. Unexpected software faults leading to a random interruption of [activities](#activity) with a Poisson-distributed event rate $r_i$ per second
3. Device failures with a Poisson-distributed event rate $r_f$ per second, which can be imputed mostly to single event latch-ups
   
You can add a radiation model affecting the operations of the devices you are interested in with

```py
    from paseos import SpacecraftActor, ActorBuilder
    my_actor = ActorBuilder.get_actor_scaffold("my_actor", SpacecraftActor, pk.epoch(0))
    ActorBuilder.set_radiation_model(
        actor=my_actor,
        data_corruption_events_per_s=r_d,
        restart_events_per_s=r_i,
        failure_events_per_s=r_f,
    )
```

You can set any of the event rates to 0 to disable that part. Only [SpacecraftActors](#spacecraftactor) support radiation models. You can find out if your actor has failed with

```py
my_actor.is_dead
```

Interrupted [activities](#activity) will return as if a [constraint function](#constraint-function) was no longer satisfied.

To get a binary mask to model data corruption on the [local actor](#local-actor) you can call

```py
mask = paseos_instance.model_data_corruption(data_shape=your_data_shape,
                                             exposure_time_in_s=your_time)
```

#### Custom Modelling

Beyond the default supported physical quantities (power, thermal, etc.) it possible to model any type of parameter by using custom properties. These are defined by a name, an update function and an initial value. The initial value is used to initialize the property. As for the other physical models, you can specify an update rate via the `cfg.sim.dt` [cfg parameter](#using-the-cfg).

Custom properties are automatically logged in the [operations monitor](##monitoring-simulation-status).
Below is a simple example tracking actor altitude.

```py
import pykep as pk
from paseos import ActorBuilder, SpacecraftActor

# Define the local actor as a SpacecraftActor of name mySat and some orbit
local_actor = ActorBuilder.get_actor_scaffold(
    name="mySat", actor_type=SpacecraftActor, epoch=pk.epoch(0)
)

ActorBuilder.set_orbit(
    actor=local_actor,
    position=[10000000, 0, 0],
    velocity=[0, 8000.0, 0],
    epoch=pk.epoch(0),
    central_body=pk.planet.jpl_lp("earth"),  # use Earth from pykep
)


# Define the update function for the custom property
# PASEOS will always pass you the actor, the time step and the current power consumption
# The function shall return the new value of the custom property
def update_function(actor, dt, power_consumption):
    return actor.get_altitude()  # get current altitude


# Add the custom property to the actor, defining name, update fn and initial value
ActorBuilder.add_custom_property(
    actor=local_actor,
    property_name="altitude",
    update_function=update_function,
    initial_value=local_actor.get_altitude(),
)

# One can easily access the property at any point with
print(local_actor.get_custom_property("altitude"))
```

#### Custom Central Bodies

In most examples here you will see Earth via the pykep API being used as a spherical, central body for Keplerian orbits. For Keplerian orbits around spherical bodies, you can simply use pykep with an type of [pykep planet](https://esa.github.io/pykep/documentation/planets.html) just as the above examples used Earth. E.g.

```py
import pykep as pk
from paseos import ActorBuilder, SpacecraftActor
# Define an actor of type SpacecraftActor of name mySat
sat_actor = ActorBuilder.get_actor_scaffold(name="mySat",
                                       actor_type=SpacecraftActor,
                                       epoch=pk.epoch(0))

# Define the central body as Mars by using pykep APIs.
mars = pk.planet.jpl_lp("mars")

# Let's set the orbit of sat_actor.
ActorBuilder.set_orbit(actor=sat_actor,
                       position=[10000000, 1, 1],
                       velocity=[1, 1000.0, 1],
                       epoch=pk.epoch(0), 
                       central_body=mars)
```

However, you can also use any other central body defined via a mesh. This is especially useful in conjunction with [custom propagators](#custom-propagators). To use a custom central body, you need to define a mesh and add it to the simulation configuration. The following example shows how to do this for the comet 67P/Churyumov–Gerasimenko.

We assume `polyhedral_propagator` to be a custom propagator as explained in [Custom Propagators](#custom-propagators).

To correctly compute eclipses, we also need to know the orbit of the custom central body around the Sun. In this case we use the [orbital elements](https://en.wikipedia.org/wiki/Orbital_elements) one [can find online for 67P/Churyumov–Gerasimenko](https://en.wikipedia.org/wiki/67P/Churyumov–Gerasimenko).

```py
import pykep as pk
from paseos import ActorBuilder, SpacecraftActor

# Define the epoch and orbital elements
epoch = pk.epoch(2460000.5, "jd")
elements = (3.457 * pk.AU, 0.64989, 3.8719 * pk.DEG2RAD, 36.33 * pk.DEG2RAD, 22.15 * pk.DEG2RAD, 73.57 * pk.DEG2RAD)

# Create a planet object from pykep for 67P
comet = pk.planet.keplerian(epoch, elements, pk.MU_SUN, 666.19868, 2000, 2000, "67P")

# Load the 67P mesh with pickle
with open(mesh_path, "rb") as f:
    mesh_points, mesh_triangles = pickle.load(f)
    mesh_points = np.array(mesh_points)
    mesh_triangles = np.array(mesh_triangles)

# Define local actor
my_sat = ActorBuilder.get_actor_scaffold("my_sat", SpacecraftActor, epoch=epoch)

# Set the custom propagator
ActorBuilder.set_custom_orbit(my_sat, polyhedral_propagator, epoch)

# Set the mesh
ActorBuilder.set_central_body(my_sat, comet, (mesh_points, mesh_triangles))

# Below computations will now use the mesh instead spherical approximations
print(my_sat.is_in_eclipse())
print(my_sat.is_in_line_of_sight(some_other_actor))

# You could even specify a rotation of the central body.
# Set a rotation period of 1 second around the z axis
ActorBuilder.set_central_body(
    my_sat,
    comet,
    (mesh_points, mesh_triangles),
    rotation_declination=90,
    rotation_right_ascension=0,
    rotation_period=1,
)

```

This is particularly useful if you want to use a central body that is not included in pykep or if you want to use a central body that is not a planet (e.g. an asteroid).

N.B. `get_altitude` computes the altitude above [0,0,0] in the central body's frame, thus is not affected by the central body's rotation or mesh.
N.B. #2 Any custom central body still has to orbit the Sun for PASEOS to function correctly.

### Simulation Settings

#### Initializing PASEOS

We will now show how to create an instance of PASEOS. An instance of PASEOS shall be bounded to one PASEOS [actor](#actor) that we call [local actor](#local-actor). Please, notice that an orbit shall be placed for a [SpacecraftActor](#spacecraftactor) before being added to a PASEOS instance. <br>

#### How to instantiate PASEOS

```py
import pykep as pk
import paseos
from paseos import ActorBuilder, SpacecraftActor
# Define the local actor as a SpacecraftActor of name mySat and its orbit
local_actor = ActorBuilder.get_actor_scaffold(name="mySat",
                                       actor_type=SpacecraftActor,
                                       epoch=pk.epoch(0))
ActorBuilder.set_orbit(
    actor=local_actor,
    position=[10000000, 0, 0],
    velocity=[0, 8000.0, 0],
    epoch=pk.epoch(0),
    central_body=pk.planet.jpl_lp("earth"),  # use Earth from pykep
)

# initialize PASEOS simulation
sim = paseos.init_sim(local_actor)
```

For each actor you wish to model, you can create a PASEOS instance. Running multiple instances on the same machine / thread is supported.

#### Using the cfg

When you instantiate PASEOS as shown in [Initializing PASEOS](#initializing-paseos), a PASEOS instance is created by using the default configuration. However, sometimes it is useful to use a custom configuration.

The next code snippet will show how to start the PASEOS simulation with a time different from `pk.epoch(0)` (MJD2000) by loading a custom configuration.

```py
import pykep as pk
import paseos
from paseos import ActorBuilder, SpacecraftActor

#Define today as pykep epoch (16-06-22)
#please, refer to https://esa.github.io/pykep/documentation/core.html#pykep.epoch
today = pk.epoch_from_string('2022-06-16 00:00:00.000')

# Define the local actor as a SpacecraftActor of name mySat
# pk.epoch is set to today
local_actor = ActorBuilder.get_actor_scaffold(name="mySat",
                                       actor_type=SpacecraftActor,
                                       epoch=today)

# Let's set the orbit of local_actor.
# pk.epoch is set to today
ActorBuilder.set_orbit(
    actor=local_actor,
    position=[10000000, 0, 0],
    velocity=[0, 8000.0, 0],
    epoch=pk.epoch(0),
    central_body=pk.planet.jpl_lp("earth"),  # use Earth from pykep
)

# Loading cfg to modify defaults
cfg=load_default_cfg()
# Set simulation starting time by converting epoch to seconds
cfg.sim.start_time=today.mjd2000 * pk.DAY2SEC
# initialize PASEOS simulation
sim = paseos.init_sim(local_actor)
```

You can access the current simulation time (seconds since the start) and the current epoch like this:

```py
time_since_start_in_s = sim.simulation_time
current_epoch = sim.local_time
```

#### Faster than real-time execution

In some cases, you may be interested to simulate your spacecraft operating for an extended period. By default, PASEOS operates in real-time, thus this would take a lot of time. However, you can increase the rate of time passing (i.e. the spacecraft moving, power being charged / consumed etc.) using the `time_multiplier` parameter. Set it as follows when initializing PASEOS.

```py

cfg = load_default_cfg() # loading cfg to modify defaults
cfg.sim.time_multiplier = 10 # setting the parameter so that in 1s real time, paseos models 10s having passed
paseos_instance = paseos.init_sim(my_local_actor, cfg) # initialize paseos instance

```

#### Event-based mode

Alternatively, you can rely on an event-based mode where PASEOS will simulate the physical constraints for an amount of time. The below code shows how to run PASEOS for a fixed amount of time or until an event interrupts it.

```py
    import pykep as pk
    import paseos
    from paseos import ActorBuilder, SpacecraftActor

    # Define the central body as Earth by using pykep APIs.
    earth = pk.planet.jpl_lp("earth")

    # Define a satellite with some orbit and simple power model
    local_actor = ActorBuilder.get_actor_scaffold("MySat", SpacecraftActor, pk.epoch(0))
    ActorBuilder.set_orbit(local_actor, [10000000, 0, 0], [0, 8000.0, 0], pk.epoch(0), earth)
    ActorBuilder.set_power_devices(local_actor, 500, 1000, 1)

    # Abort when sat is at 10% battery
    def constraint_func():
        return local_actor.state_of_charge > 0.1

    # Set some settings to control evaluation of the constraint
    cfg = load_default_cfg()  # loading cfg to modify defaults
    cfg.sim.dt = 0.1  # setting timestep of physical models (power, thermal, ...)
    cfg.sim.activity_timestep = 1.0  # how often constraint func is evaluated
    sim = paseos.init_sim(local_actor, cfg) # Init simulation

    # Advance for a long time, will interrupt much sooner due to constraint function
    sim.advance_time(3600, 10, constraint_function=constraint_func)
```

### Activities

#### Simple activity

PASEOS enables the user to register their [activities](#activity) that will be executed on the `local actor`. This is an alternative to the [event-based mode](#event-based-mode)

To register an activity, it is first necessary to define an asynchronous [activity function](#activity-function). The following code snippet shows how to create a simple [activity function](#activity-function) `activity_function_A` that prints "Hello Universe!". Then, it waits for 0.1 s before concluding the activity. <br> When you register an [activity](#activity), you need to specify the power consumption associated to the activity.

```py
#Activity function
async def activity_function_A(args):
  print("Hello Universe!")
  await asyncio.sleep(0.1) #Await is needed inside an async function.
```

Once an activity is registered, the user shall call `perform_activity(...)` to run the registered activity.
The next snippet will showcase how to register and perform the activity `activity_A`. <br>

```py
import pykep as pk
import paseos
from paseos import ActorBuilder, SpacecraftActor
import asyncio
# Define the local actor as a SpacecraftActor of name mySat and its orbit
local_actor = ActorBuilder.get_actor_scaffold(name="mySat",
                                       actor_type=SpacecraftActor,
                                       epoch=pk.epoch(0))

ActorBuilder.set_orbit(
    actor=local_actor,
    position=[10000000, 0, 0],
    velocity=[0, 8000.0, 0],
    epoch=pk.epoch(0),
    central_body=pk.planet.jpl_lp("earth"),  # use Earth from pykep
)

# Add a power device
ActorBuilder.set_power_devices(actor=local_actor,
                               # Battery level at the start of the simulation in Ws
                               battery_level_in_Ws=100,
                               # Max battery level in Ws
                               max_battery_level_in_Ws=2000,
                               # Charging rate in W
                               charging_rate_in_W=10)

# initialize PASEOS simulation
sim = paseos.init_sim(local_actor)

#Activity function
async def activity_function_A(args):
  print("Hello Universe!")
  await asyncio.sleep(0.1) #Await is needed inside an async function.

# Register an activity that emulate event detection
sim.register_activity(
    "activity_A",
    activity_function=activity_function_A,
    power_consumption_in_watt=10
)

#Run the activity
sim.perform_activity("activity_A")
```

##### Waiting for Activities to Finish

At the moment, parallel running of multiple activities is not supported.
However, if you want to run multiple activities in a row or just wait for the existing one to finish, you can use

```py
await sim.wait_for_activity()
```

to wait until the running activity has finished.

#### Activities with Inputs and Outputs

The next code snippet will show how to register and perform activities with inputs and outputs. In particular, we will register an [activity function](#activity-function) `activity_function_with_in_and_outs` that takes an input argument and returns its value multiplied by two. Then, it waits for 0.1 s before concluding the activity. <br>
Please, notice that the output value is placed in `args[1][0]`, which is returned as reference.

```py
import pykep as pk
import paseos
from paseos import ActorBuilder, SpacecraftActor
import asyncio
# Define the local actor as a SpacecraftActor of name mySat and its orbit
local_actor = ActorBuilder.get_actor_scaffold(name="mySat",
                                       actor_type=SpacecraftActor,
                                       epoch=pk.epoch(0))

ActorBuilder.set_orbit(
    actor=local_actor,
    position=[10000000, 0, 0],
    velocity=[0, 8000.0, 0],
    epoch=pk.epoch(0),
    central_body=pk.planet.jpl_lp("earth"),  # use Earth from pykep
)

# Add a power device
ActorBuilder.set_power_devices(actor=local_actor,
                               # Battery level at the start of the simulation in Ws
                               battery_level_in_Ws=100,
                               # Max battery level in Ws
                               max_battery_level_in_Ws=2000,
                               # Charging rate in W
                               charging_rate_in_W=10)

# initialize PASEOS simulation
sim = paseos.init_sim(local_actor)

#Activity function
async def activity_function_with_in_and_outs(args):
  activity_in=args[0]
  activity_out=activity_in * 2
  args[1][0]=activity_out
  await asyncio.sleep(0.1) #Await is needed inside an async function.

# Register an activity that emulate event detection
sim.register_activity(
    "my_activity",
    activity_function=activity_function_with_in_and_outs,
    power_consumption_in_watt=10,
)

#Creatie an input variable for activity
activity_in=1

#Create a placeholder variable to contain the output of the activity function.
#It is created as a list so its first value is edited
# as reference by the activity function.
activity_out=[None]

#Run the activity
sim.perform_activity("my_activity",
                      activity_func_args=[activity_in, activity_out],
                    )
#Print return value
print("The output of the activity function is: ", activity_out[0])
```

#### Constraint Function

It is possible to associate a [constraint function](#constraint-function) with each [activity](#activity) to ensure that some particular constraints are met during the [activity](#activity) execution. When constraints are not met, the activity is interrupted. Constraints can be used, e.g., to impose power requirements, communication windows or maximum operational temperatures. <br>
The next code snippet shows how to:

- create a [constraint function](#constraint-function) (`constraint_function_A`) which returns `True` when the local actor's temperature is below ~86°C and `False` otherwise (this requires a thermal model on the actor)
- how use `constraint_function_A` to constraint our [Simple Activity](#simple-activity).

```py
import pykep as pk
import paseos
from paseos import ActorBuilder, SpacecraftActor
import asyncio
# Define the local actor as a SpacecraftActor of name mySat and its orbit
local_actor = ActorBuilder.get_actor_scaffold(name="mySat",
                                       actor_type=SpacecraftActor,
                                       epoch=pk.epoch(0))

ActorBuilder.set_orbit(
    actor=local_actor,
    position=[10000000, 0, 0],
    velocity=[0, 8000.0, 0],
    epoch=pk.epoch(0),
    central_body=pk.planet.jpl_lp("earth"),  # use Earth from pykep
)

# Add a power device
ActorBuilder.set_power_devices(actor=local_actor,
                               # Battery level at the start of the simulation in Ws
                               battery_level_in_Ws=100,
                               # Max battery level in Ws
                               max_battery_level_in_Ws=2000,
                               # Charging rate in W
                               charging_rate_in_W=10)

# initialize PASEOS simulation
sim = paseos.init_sim(local_actor)

#Activity function
async def activity_function_A(args):
  print("Hello Universe!")
  await asyncio.sleep(0.1) #Await is needed inside an async function.

#Constraint function
async def constraint_function_A(args):
  local_actor_temperature=args[0]
  return (local_actor_temperature < 350)

# Register an activity that emulate event detection
sim.register_activity(
    "activity_A_with_constraint",
    activity_function=activity_function_A,
    power_consumption_in_watt=10,
    constraint_function=constraint_function_A
)

#The constraint function is related to the operational temperature of the local actor.
operational_temperature_in_K=local_actor.temperature_in_K

#Run the activity
sim.perform_activity("activity_A_with_constraint",
                      constraint_func_args=[operational_temperature_in_K],
                    )
```

#### On-termination Function

It is also possible to define an [on-termination function](#on-termination-function) to perform some specific operations when on termination of the [activity](#activity). The next code snippet shows:

- how to create an [on-termination function](#on-termination-function) that prints "activity (activity_A_with_termination_function) ended.".
- How to associate our [on-termination function](#on-termination-function) to our [Simple Activity](#simple-activity).

The name of the [activity](#activity) is passed as input to the [on-termination function](#on-termination-function) to showcase to handle [on-termination function](#on-termination-function) inputs.

```py
import pykep as pk
import paseos
from paseos import ActorBuilder, SpacecraftActor
import asyncio
# Define the local actor as a SpacecraftActor of name mySat and its orbit
local_actor = ActorBuilder.get_actor_scaffold(name="mySat",
                                       actor_type=SpacecraftActor,
                                       epoch=pk.epoch(0))

ActorBuilder.set_orbit(
    actor=local_actor,
    position=[10000000, 0, 0],
    velocity=[0, 8000.0, 0],
    epoch=pk.epoch(0),
    central_body=pk.planet.jpl_lp("earth"),  # use Earth from pykep
)

# Add a power device
ActorBuilder.set_power_devices(actor=local_actor,
                               # Battery level at the start of the simulation in Ws
                               battery_level_in_Ws=100,
                               # Max battery level in Ws
                               max_battery_level_in_Ws=2000,
                               # Charging rate in W
                               charging_rate_in_W=10)

# initialize PASEOS simulation
sim = paseos.init_sim(local_actor)

#Activity function
async def activity_function_A(args):
  print("Hello Universe!")
  await asyncio.sleep(0.1) #Await is needed inside an async function.

#On-termination function
async def on_termination_function_A(args):
  #Fetching input
  activity_name=args[0]
  print("Activity ("+str(activity_name)+") ended.")

# Register an activity that emulate event detection
sim.register_activity(
    "activity_A_with_termination_function",
    activity_function=activity_function_A,
    power_consumption_in_watt=10,
    on_termination_function=on_termination_function_A
)

#The termination function input is the activity name
activity_name="activity_A_with_termination_function"

#Run the activity
sim.perform_activity("activity_A_with_termination_function",
                      termination_func_args=[activity_name],
                    )
```

### Utilities

#### Visualization

Navigate to paseos/visualization to find a jupyter notebook containing examples of how to visualize PASEOS.
Visualization can be done in interactive mode or as an animation that is saved to your disc.
In the figure below, Earth is visualized in the centre as a blue sphere with different spacecraft in orbit.
Each spacecraft has a name and if provided, a battery level and a communications device.
The local device is illustrated with white text.
In the upper-right corner, the status of the communication link between each spacecraft is shown.
Finally, the time in the lower left and lower right corners corresponds to the epoch and the PASEOS local simulation time.

![Alt Text](resources/images/animation.png)

#### Monitoring Simulation Status

You can easily track the status of a PASEOS simulation via the `monitor` which keeps track of actor status.

It allows access like this

```py
(...) # actor definition etc., see above
instance = paseos.init_sim(local_actor=my_local_actor)

(...) # running the simulation

# access tracked parameters
timesteps = instance.monitor["timesteps"]
state_of_charge = instance.monitor["state_of_charge"]
```

#### Writing Simulation Results to a File

To evaluate your results, you will likely want to track the operational parameters, such as actor battery status, currently running activity etc. of actors over the course of your simulation. By default, PASEOS will log the current actor status every 10 seconds, however you can change that rate by editing the default configuration, as explained in [How to use the cfg](#how-to-use-the-cfg). You can save the current log to a \*.csv file at any point.

```py
cfg = load_default_cfg() # loading cfg to modify defaults
cfg.io.logging_interval = 0.25  # log every 0.25 seconds
paseos_instance = paseos.init_sim(my_local_actor, cfg) # initialize paseos instance

# Performing activities, running the simulation (...)

paseos_instance.save_status_log_csv("output.csv")
```

### Wrapping Other Software and Tools

PASEOS is designed to allow easily wrapping other software and tools to, e.g., use more sophisticated models for specific aspects of interest to the user. There are three ways to do this:

* [Via Activities](#via-activities) - An [activity](#simple-activity) using an external software is registered and executed as any other [activity](#activity), e.g. to perform some computations while tracking runtime of that operation.
* [Via Constraint Functions](#via-constraint-functions) - A [constraint function](#constraint-function) using an external software. This is useful to use a more sophisticated model to check whether, e.g., a physical constraint modelled outside of PASEOS is met. 
* [Via Custom Properties](#via-custom-properties) - A [custom property](#custom-property) using an external software. This is useful to, e.g., use a more sophisticated model for a physical quantity such as total ionization dose or current channel bandwidth.

#### Via Activities

The wrapping via activities is quite straight forward. Follow the [instructions on registering and performing activities](#simple-activity) and make use of your external software inside the activity function.

```py
import my_external_software
#Activity function
async def activity_function_A(args):
  my_external_software.complex_task_to_model()
  await asyncio.sleep(0.01)
```

#### Via Constraint Functions

Inside constraint functions, external software can be used to check whether a constraint is met or not. This works both for [activity constraints](#constraint-function) and for [constraints in event-based mode](#event-based-mode). 


The constraint function should return `True` if the constraint is met and `False` otherwise.

```py
import pykep as pk
from paseos import ActorBuilder, SpacecraftActor

import my_complex_radiation_model

# Defining a local actor
local_actor = ActorBuilder.get_actor_scaffold("MySat", SpacecraftActor, pk.epoch(0))

def constraint_func():
  t = local_actor.local_time
  device_has_failed = my_complex_radiation_model.check_for_device_failure(t)
  return not device_has_failed

# Can be passed either with event-based mode, will run until constraint is not met
sim.advance_time(3600, 10, constraint_function=constraint_func)

# (...)

# or via activity constraints, will run until constraint is not met
# N.B: this is an excerpt follow the #constraint-function link for more details
sim.register_activity(
    "activity_A_with_constraint_function",
    activity_function=activity_function_A,
    power_consumption_in_watt=10,
    constraint_function=constraint_func
)
```

#### Via Custom Properties

Finally, [custom properties](#custom-modelling) can be used to wrap external software. This is useful to use a more sophisticated model for a physical quantity, e.g. one could use a simulator like [ns-3](https://www.nsnam.org/) to model the current channel bandwidth.

For more details see [custom properties](#custom-modelling).

```py
import my_channel_model

# Will be automatically called during PASEOS simulation
def update_function(actor, dt, power_consumption):
    # Get the current channel bandwidth from the external model
    channel_bandwidth = my_channel_model.get_channel_bandwidth(actor)
    return channel_bandwidth

# Add the custom property to the actor, defining name, update fn and initial value
ActorBuilder.add_custom_property(
    actor=local_actor,
    property_name="channel_bandwidth",
    update_function=update_function,
    initial_value=1000,
)

# (... run simulation)

# One can easily access the property at any point with
print(local_actor.get_custom_property("channel_bandwidth"))

```

<!-- Commented out since they are not quite up to date anymore
## System Design of PASEOS

![Alt Text](resources/images/datastructure.svg)
![Alt Text](resources/images/flowchart.svg) 
-->

## Glossary

- ### Activity

  Activity is the abstraction that PASEOS uses to keep track of specific actions performed by an [actor](#actor) upon a request from the user. >PASEOS is responsible for the execution of the activity and for updating the system status depending on the effects of the activity (e.g., by discharging the satellite battery).<br>
  When registering an activity, the user can specify a [constraint function](#constraint-function) to specify constraints to be met during the execution of the activity and an [on-termination](#on-termination) function to specify additional operations to be performed by PASEOS on termination of the activity function.

- ### Activity function

  User-defined function emulating any operation to be executed in a PASEOS by an [actor](#actor). Activity functions are necessary to register [activities](#activity). Activity functions might include data transmission, housekeeping operations, onboard data acquisition and processing, and others.

- ### Actor

  Since PASEOS is fully-decentralised, each node of a PASEOS constellation shall run an instance of PASEOS modelling all the nodes of that constellation. The abstraction of a constellation node inside a PASEOS instance is a PASEOS `actor`.

- ### Constraint function

  A constraint function is an asynchronous function that can be used by the PASEOS user to specify some constraints that shall be met during the execution of an activity.

- ### Custom Property
  
  Users can define their own physical quantity to track parameters not natively simulated by PASEOS. This is described in detail [above](#custom-modelling) and in a dedicated example notebook on modelling total ionizing dose.

- ### GroundstationActor

  `PASEOS actor` emulating a ground station.

- ### Local actor

  The `local actor` is the `actor` whose behaviour is modelled by the locally running PASEOS instance.

- ### Known actors

  In a PASEOS instance, `known actors` are all the other actors that are known to the [local actor](#local-actor).

- ### On-termination function

  An on-termination function is an asynchronous function that can be used by the PASEOS user to specify some operations to be executed on termination of the predefined PASEOS user's activity.

- ### SpacecraftActor
  PASEOS [actor](#actor) emulating a spacecraft or a satellite.

### Physical Model Parameters

Description of the physical model parameters and default values in PASEOS with indications on sensitivity of parameters and suggested ranges.

|               Name                | Datatype |                                 Description                                 |  Default   | Suggested Range | Sensitivity |
| :-------------------------------: | :------: | :-------------------------------------------------------------------------: | :--------: | :-------------: | :---------: |
|        Battery Level [Ws]         |  float   |                            Current battery level                            |     -      |       > 0       |    high     |
|    Maximum Battery Level [Ws]     |  float   |                            Maximum battery level                            |     -      |       > 0       |    high     |
|         Charging Rate [W]         |  float   |                        Charging rate of the battery                         |     -      |       > 0       |    high     |
|         Power Device Type         |   enum   |          Type of power device. Can be either "SolarPanel" or "RTG"          | SolarPanel |        -        |   medium    |
|    Data Corruption Events [Hz]    |  float   | Rate of single bit of data being corrupted, i.e. a Single Event Upset (SEU) |     -      |      >= 0       |     low     |
|        Restart Events [Hz]        |  float   |                   Rate of device restart being triggered                    |     -      |      >= 0       |   medium    |
|        Failure Events [Hz]        |  float   |    Rate of complete device failure due to a Single Event Latch-Up (SEL)     |     -      |      >= 0       |    high     |
|             Mass [kg]             |  float   |                                Actor's mass                                 |     -      |       > 0       |     low     |
|      Initial Temperature [K]      |  float   |                         Actor's initial temperature                         |     -      |      >= 0       |   medium    |
|          Sun Absorptance          |  float   |                     Actor's absorptance of solar light                      |     -      |      [0,1]      |    high     |
|       Infrared Absorptance        |  float   |                    Actor's absportance of infrared light                    |     -      |      [0,1]      |   medium    |
|      Sun-Facing Area [$m^2$]      |  float   |                         Actor's area facing the sun                         |     -      |      >= 0       |    high     |
| Central Body-Facing Area [$m^2$]  |  float   |                      Actor's area facing central body                       |     -      |      >= 0       |   medium    |
|       Emissive Area [$m^2$]       |  float   |                   Actor's area emitting (radiating) heat                    |     -      |      >= 0       |    high     |
| Thermal Capacity [$J / (kg * K)$] |  float   |                          Actor's thermal capacity                           |     -      |      >= 0       |     low     |
|     Body Solar Irradiance [W]     |  float   |                           Irradiance from the sun                           |    1360    |      >= 0       |   medium    |
|   Body Surface Temperature [K]    |  float   |                      Central body surface temperature                       |    288     |      >= 0       |     low     |
|          Body Emissivity          |  float   |                     Central body emissivity in infrared                     |    0.6     |      [0,1]      |   medium    |
|         Body Reflectance          |  float   |                    Central body reflectance of sunlight                     |    0.3     |      [0,1]      |   medium    |
|     Heat Conversion Ratio [-]     |  float   |  Conversion ratio for activities, 0 leads to know heat-up due to activity   |    0.5     |      [0,1]      |    high     |


## Contributing

The `PASEOS` project is open to contributions. To contribute, you can open an [issue](https://github.com/gomezzz/MSMatch/issues) to report a bug or to request a new feature. If you prefer discussing new ideas and applications, you can contact us via email (please, refer to [Contact](#contact)).
To contribute, please proceed as follow:

1. Fork the Project
2. Create your Feature Branch (`git checkout -b feature/AmazingFeature`)
3. Commit your Changes (`git commit -m 'Add some AmazingFeature'`)
4. Push to the Branch (`git push origin feature/AmazingFeature`)
5. Open a Pull Request

## License

Distributed under the GPL-3.0 License.

## Contact

Created by $\Phi$[-lab@Sweden](https://www.ai.se/en/data-factory/f-lab-sweden).

- Pablo Gómez - pablo.gomez at esa.int, pablo.gomez at ai.se
- Gabriele Meoni - gabriele.meoni at esa.int, g.meoni at tudelft.nl
- Johan Östman - johan.ostman at ai.se
- Vinutha Magal Shreenath - vinutha at ai.se

## Reference

If you have used `PASEOS`, please cite the following paper:
```
@article{gomez23paseos,
  author = {Gómez, Pablo and Östman, Johan and Shreenath, Vinutha Magal and Meoni, Gabriele},
  title = {{PA}seos {S}imulates the {E}nvironment for {O}perating multiple {S}pacecraft},
  journal = {arXiv:2302.02659 [cs.DC]},
  year = {2023},
}
```