Overview

The Orekit library aims at providing efficient low level components for the development of flight dynamics applications.

Orekit, a pure Java library, depends only on the Java Standard Edition version 8 (or above) and Hipparchus version 1.0 (or above) libraries at runtime.

External dependencies

Runtime component

This component is required to compile and run Orekit:

• Copyright © Hipparchus project
  License: Apache License, version 2.0
  Reference: https://www.hipparchus.org/

Test-time component

This component is required for testing purpose only:

• JUnit 4
  Copyright © Erich Gamma and Kent Beck
  License: Common Public License, version 1.0
  Reference: http://www.junit.org/

Design & Implementation

General concepts

As a a low level library, Orekit aims at being used in very different contexts which cannot be foreseen, from quick studies up to critical operations.

The main driving goals for the development of Orekit are:

• validation
• robustness
• maintainability
• efficiency

These goals lead to design and coding guidelines including:

• comprehensive test suite for high level of coverage
• automated checking tools for robustness
• consistent coding style for readable, clear and well documented code
• wide use of immutable objects for efficiency

Packages

Orekit is made of twelve packages shown in the following diagram.

Features

Time

• high accuracy absolute dates
• time scales (TAI, UTC, UT1, GPS, TT, TCG, TDB, TCB, GMST, GST, GLONASS, QZSS ...)
• transparent handling of leap seconds

Geometry

• frames hierarchy supporting fixed and time-dependent (or telemetry-dependent) frames
• predefined frames (EME2000/J2000, ICRF, GCRF, ITRF93, ITRF97, ITRF2000, ITRF2005, ITRF2008 and intermediate frames, TOD, MOD, GTOD and TEME frames, Veis, topocentric, tnw and qsw local orbital frames, Moon, Sun, planets, solar system barycenter, Earth-Moon barycenter, ecliptic)
• user extensible (used operationally in real time with a set of about 60 frames on several spacecraft)
• transparent handling of IERS Earth Orientation Parameters (for both new CIO-based frames following IERS 2010 conventions and old equinox-based frames)
• transparent handling of JPL DE 4xx (405, 406 and more recent) and INPOP ephemerides
• transforms including kinematic combination effects
• composite transforms reduction and caching for efficiency
• extensible central body shapes models (with predefined spherical and ellipsoidic shapes)
• cartesian and geodesic coordinates, kinematics

Spacecraft state

• Cartesian, Keplerian (including hyperbolic), circular and equinoctial parameters
• Two-Line Elements
• transparent conversion between all parameters
• automatic binding with frames
• attitude state and derivative
• Jacobians
• mass management
• user-defined associated state (for example battery status, or higher order derivatives, or anything else)

Maneuvers

• analytical models for small maneuvers without propagation
• impulse maneuvers for any propagator type
• continuous maneuvers for numerical propagator type

Propagation

• analytical propagation models:
  • Kepler
  • Eckstein-Heschler
  • SDP4/SGP4 with 2006 corrections
• numerical propagation with:
  • customizable force models:
    • central attraction
    • gravity models including time-dependent trends and pilsations (automatic reading of ICGEM (new Eigen models), SHM (old Eigen models), EGM and GRGS gravity field files formats, even compressed)
    • atmospheric drag (DTM2000, Jacchia-Bowman 2006, Harris-Priester and simple exponential models) and Marshall solar Activity Future Estimation
    • third body attraction (with data for Sun, Moon and all solar systems planets)
    • radiation pressure with eclipses
    • solid tides, with or without solid pole tide
    • ocean tides, with or without ocean pole tide
    • general relativity
    • multiple maneuvers
  • state of the art ODE integrators (adaptive stepsize with error control, continuous output, switching functions, G-stop, step normalization ...)
  • computation of Jacobians with respect to orbital parameters and selected force models parameters
  • serialization mechanism to store complete results on persistent storage for later use
• semi-analytical propagation based on Draper Semianalytic Satellite Theory (DSST) with customizable force models:
  • central body with full gravity model
  • third body attraction
  • atmospheric drag
  • radiation pressure with eclipses
• tabulated ephemerides:
  • file based
  • memory based
  • integration based
• specialized GPS propagation, using SEM or YUMA files
• unified interface above analytical/numerical/semianalytical/tabulated propagators for easy switch from coarse analysis to fine simulation with one line change
• all propagators can be used in several different modes:
  • slave mode: propagator is driven by calling application
  • master mode: propagator drives application callback functions
  • ephemeris generation mode: all intermediate results are stored during propagation and provided back to the application which can navigate at will through them, effectively using the propagated orbit as if it was an analytical model, even if it really is a numerically propagated one, which is ideal for search and iterative algorithms
• handling of discrete events during integration (models changes, G-stop, simple notifications ...)
• predefined discrete events:
  • eclipse (both umbra and penumbra)
  • ascending and descending node crossing
  • anomaly, latitude argument or longitude argument crossings, with either true, eccentric or mean angles
  • apogee and perigee crossing
  • alignment with some body in the orbital plane (with customizable threshold angle)
  • angular separation thresholds crossing between spacecraft and a beacon (typically the Sun) as seen from an observer (typically a ground station)
  • raising/setting with respect to a ground location (with customizable triggering elevation and ground mask)
  • date
  • latitude, longitude, altitude crossing
  • latitude, longitude extremum
  • elevation extremum
  • anomaly, latitude argument, or longitude argument crossings, either true, mean or eccentric
  • moving target detection in spacecraft sensor Field Of View (any shape, with special case for circular)
  • spacecraft detection in ground based Field Of View (any shape)
  • sensor Field Of View (any shape) overlapping complex geographic zone
  • complex geographic zone traversal
  • impulse maneuvers occurrence
• possibility of slightly shifting events in time (for example to switch from solar pointing mode to something else a few minutes before eclipse entry and reverting to solar pointing mode a few minutes after eclipse exit)
• possibility of filtering events based on their direction (for example to detect only eclipse entries and not eclipse exits)
• possibility of filtering events based on an external enabling function (for example to detect events only during selected orbits and not others)

Attitude

• extensible attitude evolution models
• predefined laws:
  • central body related attitude (nadir pointing, center pointing, target pointing, yaw compensation, yaw-steering)
  • orbit referenced attitudes (LOF aligned, offset on all axes)
  • space referenced attitudes (inertial, celestial body-pointed, spin-stabilized)
  • tabulated attitudes, either respective to inertial frame or respective to Local Orbital frames

Orbit determination

• batch least squares fitting of orbit
• several predefined measurements
• range
• range rate
• azimuth
• elevation
• position-velocity
• possibility to add custom measurements
• several predefined modifiers
• tropospheric effects
• ionospheric effects
• station offsets
• biases
• delays
• possibility to add custom measurement modifiers (even for predefined events)

Orbit file handling

• loading of SP3-a and SP3-c orbit files
• loading of CCSDS Orbit Data Messages (both OPM, OEM, and OMM types are supported)

Earth models

• tropospheric delay (modified Saastamoinen)
• tropospheric refraction correction angle (Recommendation ITU-R P.834-7 and Saemundssen's formula quoted by Meeus)
• geomagnetic field (WMM, IGRF)
• geoid model from any gravity field
• tessellation of zones of interest as tiles
• sampling of zones of interest as grids of points

Customizable data loading

• loading from local disk
• loading from classpath
• loading from network (even through internet proxies)
• support for zip archives
• support from gzip compressed files
• plugin mechanism to delegate loading to user defined database or data access library

Localized in several languages

• English
• French
• Galician
• German
• Greek
• Italian
• Norwegian
• Romanian
• Spanish