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Project structure

This chapter provides a high level overview of the Astrea project to make it easier to navigate, build, and use.

CMake projects and dependencies

The GitHub repository contains the main CMake-based project with several core components:

  • ./astrea

    • header-only project containing the whole Astrea astrodynamics library
    • ./astrea/CMakeLists.txt file is the entry point for library users

    • depends on the following external libraries:

  • .

    • project used as an entry point for library development and CI/CD
    • it wraps ./astrea project together with usage examples and tests

    • additionally to the dependencies of ./astrea project, it uses:

  • ./scripts

    • Build automation, coverage reporting, and development utility scripts

Important: Library users should use the astrea/ directory as entry point

Top level CMakeLists.txt file should primarily be used by Astrea developers and contributors as an entry point for the project's development. We want to ensure that everyone will build ALL the code correctly before pushing a commit.

This is why our project has two main entry points:

  • ./CMakeLists.txt is to be used by project developers to build ALL the project code with restrictive compilation flags and comprehensive testing,
  • ./astrea/CMakeLists.txt contains the pure library definition and should be used by customers that prefer to use CMake's add_subdirectory() to handle the dependencies.

Core Components

The Astrea library provides the following major components:

flowchart TD
    astrea --- astro["astro<br/>(Astrodynamics Core)"]
    astrea --- trace["trace<br/>(Access Analysis)"]
    astrea --- snapshot["snapshot<br/>(Live Satellite Database)"]

    astro --- math["math<br/>(Mathematical Utilities)"]
    astro --- units["units<br/>(Physical Units)"]
    astro --- utilities["utilities<br/>(General Utilities)"]

    trace --- astro["astro<br/>(Astrodynamics Core)"]
    trace --- snapshot["snapshot<br/>(Live Satellite Database)"]
Component CMake Target Contents
astro astrea::astro Core astrodynamics: frames, propagation, time, orbital states
math astrea::math Mathematical utilities
units astrea::units Unit definitions and simple utilities
utilities astrea::utils General purpose utilities and algorithms
trace astrea::trace Access analysis: calculation of access, gap, and interference times with statistics
snapshot astrea::snapshot Spacetrack integrated databasing for real-time orbital data

Header files

All of the project's header files can be found in the astrea/... subdirectory.

Core astrodynamics library (astrea/astro/)

  • astrea/astro/astro.hpp contains the entire astrodynamics framework,
  • astrea/astro/astro.fwd.hpp provides forward declarations for faster compilation,
  • astrea/astro/astro.macros.hpp contains utility macros for the library,

Frames and coordinate systems

  • astrea/astro/frames/... provides coordinate frame definitions and transformations:
    • Fixed frames (ICRF, ITRF, etc.)
    • Dynamic frames (True of Date, Mean of Date, etc.)
    • Topocentric frames (SEZ, NED, etc.)
    • Custom user-defined frames

Orbital mechanics

  • astrea/astro/state/... provides orbital state representations:
    • Cartesian position and velocity
    • Classical orbital elements (Keplerian)
    • Equinoctial elements
    • Modified equinoctial elements
    • Delaunay elements
  • astrea/astro/propagation/... provides propagation algorithms:
    • Analytical propagators (Kepler, J2, etc.)
    • Numerical integrators (RK4, RK45, etc.)
    • Force model framework
    • Event detection during propagation

Celestial mechanics

  • astrea/astro/systems/... provides celestial body definitions:
    • Solar system planets and moons
    • Gravitational parameters
    • Physical and orbital characteristics
    • SPICE integration for ephemerides

Time systems

  • astrea/astro/time/... provides time system utilities:
    • Julian Date conversions
    • UTC, TT, TAI, GPS time
    • Time scale transformations
    • Leap second handling

Platform and mission analysis

  • astrea/astro/platforms/... provides spacecraft and mission modeling:
    • Spacecraft definitions with mass, area, and other properties
    • Access analysis and coverage calculations
    • Link budget and communication analysis
    • Attitude representations and kinematics

Supporting libraries

Mathematical utilities (astrea/math/)

  • Unit-aware mathematical functions optimized for astrodynamics
  • Vector and matrix operations with compile-time dimension checking
  • Numerical analysis algorithms (root finding, interpolation, etc.)
  • Statistics and filtering utilities for orbital determination

Units integration (astrea/units/)

  • Extensions to mp-units for aerospace-specific quantities
  • Custom unit definitions for astrodynamics (Earth radii, gravitational parameters, etc.)
  • Unit-aware I/O and serialization
  • Integration with legacy astrodynamics unit conventions

General utilities (astrea/utilities/)

  • Data structure utilities and containers
  • String processing and formatting for aerospace data
  • File I/O utilities for common astrodynamics file formats
  • Configuration and settings management

Access analysis (astrea/trace/)

  • Access time calculation between spacecraft, ground stations, and targets
  • Gap analysis for communication windows and coverage periods
  • Interference detection and modeling for multi-platform scenarios
  • Statistical analysis of access patterns and coverage metrics
  • Link budget integration with access calculations
  • Revisit time analysis for Earth observation missions
  • Coverage area analysis and visualization tools
  • Real-time access prediction and event scheduling

Data persistence (astrea/snapshot/)

  • Serialization for orbital states and spacecraft data
  • Binary and text format support
  • Version-compatible data persistence
  • Efficient storage for large datasets
Tip: Improving compile times

astrea/astro/astro.hpp might be expensive to compile in every translation unit. Consider including only the specific headers you need from the astrea/astro/... subdirectories for faster compilation.