orbital.c File Reference

Function relating to the use of Keplerian orbital elements. More...

Functions
int	novas_orbit_native_posvel (double jd_tdb, const novas_orbital *restrict orbit, double *restrict pos, double *restrict vel)
	Calculates a rectangular equatorial position and velocity vector for the given orbital elements for the specified time of observation, in the native coordinate system in which the orbital is defined (e.g.
int	novas_orbit_posvel (double jd_tdb, const novas_orbital *restrict orbit, enum novas_accuracy accuracy, double *restrict pos, double *restrict vel)
	Calculates a rectangular equatorial position and velocity vector for the given orbital elements for the specified time of observation.
int	novas_set_orbsys_pole (enum novas_reference_system type, double ra, double dec, novas_orbital_system *restrict sys)
	Sets the orientation of an orbital system using the RA and DEC coordinates of the pole of the Laplace (or else equatorial) plane relative to which the orbital elements are defined.

Detailed Description

Function relating to the use of Keplerian orbital elements.

For example, the IAU Minor Planet Center publishes up-to-date Keplerial orbital elements for all asteroids, comets, and Near-Earth Objects (NEOs) regularly. On short timescales these can provide accurate positions for such objects, that are as good as, or comparable to, the ephemeris data provided by NASA JPL.

For newly discovered objects, the MPC orbital elements may be the only source, or the most accurate source, of position information.

To use Keplerian orbital elements with SuperNOVAS, simply define the orbital parameters in a novas_orbital structure. By default heliocentric orbits are assumed, but you may also define orbitals around other bodies, such as a major planet, by defining the body (or barycenter) that is at the center of the orbital, and the orientation of the orbital system (w.r.t. the ecliptic or equator of date) with novas_set_orbsys_pole(). E.g.:

novas_orbital orb = NOVAS_ORBIT_INIT;
 
orb.a = ...    // [AU] semi-major axis
...            // populate the rest of the orbital parameters.
 
// Set Jupiter as the orbital center
orb.system.center = NOVAS_JUPITER_INIT;
 
// Set the orientation by defining the RA/Dec of the orbital pole, say in ICRS
novas_set_orbsys_pole(NOVAS_ICRS, ra_pole, dec_pole, &orb.system);

Once the orbital is defined, you can use it to define a generic object via make_orbital_object() to enable the the same astrometric calculations as for ephemeris sources, e.g.:

object source;
 
// Let's say the orbital is that for Callisto, so we set the source name
// and NAIF ID number (504) accordingly.
make_orbital_object("Callisto", 504, &orb, &source);

Or, you can calculate geometric orbital positions and velocities directly via novas_orbit_posvel(), while novas_orbit_native_posvel() will do the same, but in the native coordinate system in which the orbital is defined.

Date

Created on Mar 6, 2025

Author

Attila Kovacs

Since

1.2

See also

novas_orbital, make_orbital_object()

ephemeris.c

Function Documentation

novas_orbit_native_posvel()

int novas_orbit_native_posvel	(	double	jd_tdb,
		const novas_orbital *restrict	orbit,
		double *restrict	pos,
		double *restrict	vel )

Calculates a rectangular equatorial position and velocity vector for the given orbital elements for the specified time of observation, in the native coordinate system in which the orbital is defined (e.g.

ecliptic for heliocentric orbitals).

REFERENCES:

1. E.M. Standish and J.G. Williams 1992.
2. https://ssd.jpl.nasa.gov/planets/approx_pos.html
3. https://en.wikipedia.org/wiki/Orbital_elements
4. https://orbitalofficial.com/
5. https://downloads.rene-schwarz.com/download/M001-Keplerian_Orbit_Elements_to_Cartesian_State_Vectors.pdf

Parameters

	jd_tdb	[day] Barycentric Dynamic Time (TDB) based Julian date
	orbit	Orbital parameters
[out]	pos	[AU] Output ICRS equatorial position vector around orbital center, or NULL if not required.
[out]	vel	[AU/day] Output ICRS velocity vector rel. to orbital center, in the native system of the orbital, or NULL if not required. 0 if successful, or else -1 if the orbital parameters are NULL, or if the position and velocity output vectors are the same or the orbital system is ill defined (errno set to EINVAL), or if the calculation did not converge (errno set to ECANCELED).

Author

Attila Kovacs

Since

1.4

See also

novas_geom_posvel(), ephemeris(), make_orbital_object()

References TWOPI.

novas_orbit_posvel()

int novas_orbit_posvel	(	double	jd_tdb,
		const novas_orbital *restrict	orbit,
		enum novas_accuracy	accuracy,
		double *restrict	pos,
		double *restrict	vel )

Calculates a rectangular equatorial position and velocity vector for the given orbital elements for the specified time of observation.

REFERENCES:

1. E.M. Standish and J.G. Williams 1992.
2. https://ssd.jpl.nasa.gov/planets/approx_pos.html
3. https://en.wikipedia.org/wiki/Orbital_elements
4. https://orbitalofficial.com/
5. https://downloads.rene-schwarz.com/download/M001-Keplerian_Orbit_Elements_to_Cartesian_State_Vectors.pdf

Parameters

	jd_tdb	[day] Barycentric Dynamic Time (TDB) based Julian date
	orbit	Orbital parameters
	accuracy	NOVAS_FULL_ACCURACY (0) or NOVAS_REDUCED_ACCURACY (1).
[out]	pos	[AU] Output ICRS equatorial position vector around orbital center, or NULL if not required.
[out]	vel	[AU/day] Output ICRS equatorial velocity vector rel. to orbital center, or NULL if not required.

Returns

0 if successful, or else -1 if the orbital parameters are NULL, or if the position and velocity output vectors are the same or the orbital system is ill defined (errno set to EINVAL), or if the calculation did not converge (errno set to ECANCELED).

Author

Attila Kovacs

Since

1.2

See also

novas_geom_posvel(), ephemeris(), make_orbital_object()

References novas_orbit_native_posvel().

novas_set_orbsys_pole()

int novas_set_orbsys_pole	(	enum novas_reference_system	type,
		double	ra,
		double	dec,
		novas_orbital_system *restrict	sys )

Sets the orientation of an orbital system using the RA and DEC coordinates of the pole of the Laplace (or else equatorial) plane relative to which the orbital elements are defined.

Orbital parameters of planetary satellites normally include the R.A. and declination of the pole of the local Laplace plane in which the Keplerian orbital elements are referenced.

The system will become referenced to the equatorial plane, the relative obliquity is set to (90° - dec), while the argument of the ascending node ('Omega') is set to (90° + ra).

NOTES:

1. You should not expect much precision from the long-range orbital approximations for planetary satellites. For applications that require precision at any level, you should rely on appropriate ephemerides, or else on up-to-date short-term orbital elements.

Parameters

	type	Coordinate reference system in which ra and dec are defined (e.g. NOVAS_GCRS).
	ra	[h] the R.A. of the pole of the oribtal reference plane.
	dec	[deg] the declination of the pole of the oribtal reference plane.
[out]	sys	Orbital system

Returns

0 if successful, or else -1 (errno will be set to EINVAL) if the output sys pointer is NULL.

Author

Attila Kovacs

Since

1.2

See also

make_orbital_object()

References NOVAS_EQUATORIAL_PLANE, and NOVAS_TIRS.