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 2.1 (or above) libraries at
runtime.

External dependencies
Runtime component
This component is required to compile and run Orekit:
Test-time component
This component is required for testing purpose only:
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, BDT, IRNSS ...)
- transparent handling of leap seconds
- support for CCSDS time code standards
Geometry
- frames hierarchy supporting fixed and time-dependent (or
telemetry-dependent) frames
- predefined frames (EME2000/J2000, ICRF, GCRF, all ITRF from 1988 to 2014
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
- computation of Dilution Of Precision (DOP) with respect to GNSS
constellations
- projection of sensor Field Of View footprint on ground for any FoV shape
Spacecraft state
- cartesian, elliptical Keplerian, circular and equinoctial parameters,
with non-Keplerian derivatives if available
- Two-Line Elements (TLE)
- 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
- configurable low thrust maneuver model based on detectors
- propulsion models intended to be used with maneuver class
- user-friendly interface for the maneuver triggers
Propagation
- analytical propagation models
- Kepler
- Eckstein-Heschler
- Brouwer-Lyddane with Warren Phipps' correction for the
critical inclination of 63.4° and the perturbative
acceleration due to atmospheric drag
- SDP4/SGP4 with 2006 corrections
- GNSS: GPS, QZSS, Galileo, GLONASS, Beidou, IRNSS and SBAS
- numerical propagators
- central attraction
- gravity models including time-dependent like trends and pulsations
(automatic reading of ICGEM (new Eigen models), SHM (old Eigen
models), EGM and GRGS gravity field files formats, even compressed)
- atmospheric drag
- 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 (including Lense-Thirring and De Sitter corrections)
- Earth's albedo and infrared
- multiple maneuvers
- empirical accelerations to account for the unmodeled forces
- state of the art ODE integrators (adaptive stepsize with error
control, continuous output, switching functions, G-stop, step
normalization ...)
- serialization mechanism to store complete results on persistent
storage for later use
- propagation in non-inertial frames (e.g. for Lagrange point halo
orbits)
- semi-analytical propagation model (DSST) with customizable force models
- central attraction
- gravity models
- atmospheric drag
- third body attraction
- radiation pressure with eclipse
- computation of Jacobians with respect to orbital parameters and
selected force models parameters
- trajectories around Lagragian points using CR3BP model
- tabulated ephemerides
- file based
- memory based
- integration based
- Taylor-algebra (or any other real field) version of most of the above
propagators, with all force models, events detection, orbits types,
coordinates types and frames allowing high order uncertainties and
derivatives computation or very fast Monte-Carlo analyzes
- unified interface above analytical/numerical/tabulated propagators for
easy switch from coarse analysis to fine simulation with one line change
- all propagators can manage the time loop by themselves and handle callback
functions (called step handlers) from the calling application at each time step
- step handlers can be called at discrete time at regular time steps, which are
independent of propagator time steps
- step handlers can be called with interpolators valid throughout one propagator
time step, which can have varying sizes
- step handlers can be switched off completely, when only final state is desired
- special step handlers are provided for a posteriori ephemeris generation: 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 analytical model, even if it really is a numerically propagated one, which
is ideal for search and iterative algorithms
- several step handlers can be used simultaneously, so it is possible to have a fine
grained fixed time step to log state in a huge file, and have at the same time a
coarse grained time step to display progress for user at a more human-friendly rate,
this feature can also be used for debugging purpose, by setting up a temporary
step handler alongside the operational ones
- 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, optionally considering
refraction)
- date and on-the-fly resetting countdown
- date interval with parameter-driven boundaries
- latitude, longitude, altitude crossing
- latitude, longitude extremum
- elevation extremum
- moving target detection (with optional radius) 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 zones traversal
- inter-satellites direct view
- ground at night
- impulse maneuvers occurrence
- geomagnetic intensity
- 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)
- events filtering based on their direction (for example to detect only
eclipse entries and not eclipse exits)
- events filtering based on an external enabling function (for example to
detect events only during selected orbits and not others)
- events combination with boolean operators
- ability to run several propagators in parallel and manage their states
simultaneously throughout propagation
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
- specific law for GNSS satellites: GPS (block IIA, block IIF, block
IIF), GLONASS, GALILEO, BEIDOU (GEO, IGSO, MEO)
- loading of CCSDS Attitude Data Messages (both AEM, and APM types are supported)
- exporting of attitude ephemeris in CCSDS AEM file format
Orbit determination
- batch least squares fitting
- optimizers choice (Levenberg-Marquardt or Gauss-Newton)
- decomposition algorithms choice (QR, LU, SVD, Cholesky)
- choice between forming normal equations or not
- sequential batch least squares
- sequential Gauss-Newton optimizer
- decomposition algorithms choice (QR, LU, SVD, Cholesky)
- possibility to use an initial covariance matrix
- Kalman filtering
- customizable process noise matrices providers
- time dependent process noise provider
- implementation of the Extended Semi-analytical Kalman Filter (ESKF)
- parameters estimation
- orbital parameters estimation (or only a subset if desired)
- force model parameters estimation (drag coefficients, radiation
pressure coefficients, central attraction, maneuver thrust, flow
rate or start/stop epoch)
- measurements parameters estimation (biases, satellite clock offset,
station clock offset, station position, pole motion and rate, prime
meridian correction and rate, total zenith delay in tropospheric
correction)
- can be used with numerical, DSST, SDP4/SGP4,
Eckstein-Hechler, Brouwer-Lyddane, or Keplerian propagators
- multi-satellites orbit determination
- initial orbit determination methods (Gibbs, Gooding, Lambert and Laplace)
- ground stations displacements due to solid tides
- ground stations displacements due to ocean loading (based on Onsala
Space Observatory files in BLQ format)
- several predefined measurements
- range
- range rate (one way and two ways)
- turn-around range
- azimuth/elevation
- right ascension/declination
- position-velocity
- position
- inter-satellites range (one way and two way)
- inter-satellites GNSS phase
- GNSS code
- GNSS phase with integer ambiguity resolution and wind-up effect
- multiplexed
- possibility to add custom measurements
- loading of ILRS CRD laser ranging measurements file
- several predefined modifiers
- tropospheric effects
- ionospheric effects
- clock relativistic effects
- station offsets
- biases
- delays
- Antenna Phase Center
- Shapiro relativistic effect
- possibility to add custom measurement modifiers (even for predefined
events)
- possibility to parse CCSDS Tracking Data Message files
- measurements generation
- with measurements feasibility triggered by regular event detectors
(ground visibility, ground at night, sunlit satellite, inter
satellites direct view, boolean combination...)
- with measurement scheduling as fixed step streams (optionally
aligned with round UTC time)
- with measurement scheduling as high rate bursts rest periods
(optionally aligned with round UTC time)
- possibility to customize measurement scheduling
GNSS
- computation of Dilution Of Precision
- loading of ANTEX antenna models file
- loading of RINEX observation files (version 2 and version 3)
- loading of RINEX navigation files (version 3)
- support for Hatanaka compact RINEX format
- loading of RINEX clock files (version 2 and version 3)
- parsing of IGS SSR messages for all constellations (version 1)
- parsing of RTCM messages
- implementation of Ntrip protocol
- loading of SINEX station file
Orbit file handling
- loading of SP3 orbit files (versions a to d)
- loading of CCSDS Orbit Data Messages (OPM, OEM, OMM and OCM types are supported,
in both KVN and XML formats, standalone or in combined NDM)
- loading of SEM and YUMA files for GPS constellation
- exporting of ephemeris in CCSDS OEM file format
- loading of ILRS CPF orbit files
Earth models
- atmospheric models (DTM2000, Jacchia-Bowman 2008, NRL MSISE 2000,
Harris-Priester and simple exponential models), and Marshall solar
Activity Future Estimation, optionally with lift component
- support for CSSI space weather data
- tropospheric delay (modified Saastamoinen, estimated, fixed)
- tropospheric mapping functions (Vienna 1, Vienna 3, Global, Niell)
- tropospheric refraction correction angle (Recommendation ITU-R P.834-7
and Saemundssen's formula quoted by Meeus)
- tropospheric models for laser ranging (Marini-Murray, Mendes-Pavlis)
- Klobuchar ionospheric model (including parsing α and β coefficients from
University of Bern Astronomical Institute files)
- Global Ionospheric Map (GIM) model
- NeQuick ionospheric model
- VTEC estimated ionospheric model with Single Layer Model (SLM) ionospheric mapping function
- Global Pression and Temperature models (GPT and GPT2)
- geomagnetic field (WMM, IGRF)
- geoid model from any gravity field
- displacement of ground points due to tides
- tessellation of zones of interest as tiles
- sampling of zones of interest as grids of points
Customizable data loading
- loading by exploring folders hierarchy on local disk
- loading from explicit lists of files on local disk
- loading from classpath
- loading from network (even through internet proxies)
- support for zip archives
- automatic decompression of gzip compressed (.gz) files upon loading
- automatic decompression of Unix compressed (.Z) files upon loading
- automatic decompression of Hatanaka compressed files upon loading
- plugin mechanism to add filtering like custom decompression algorithms,
deciphering or monitoring
- plugin mechanism to delegate loading to user defined database or data
access library
- possibility to have different data context
(a way to separate sets of EOP, leap seconds, etc)
Localized in several languages
- Danish
- English
- French
- Galician
- German
- Greek
- Italian
- Norwegian
- Romanian
- Spanish