Data Provider Groups | Data Provider Elements
Modified Equinoctial Elements
Modified Equinoctial elements differ from the Equinoctial elements by using the the semilatus rectum (usually denoted by p) instead of the semimajor axis (a) and by using the the true longitude instead of the mean longitude. The elements are valid for elliptic, parabolic, and hyperbolic orbits.Due to the method of computation, element rates will not be consistent with finite differencing of the element values for cases where the velocity is not the true time derivative of the acceleration; for this reason, these values will not be reported for the J2, J4 and SGP4 propagators.
Available for these objects: Satellite
Type: Time-varying data.
Availability: Reports | Graphs | Dynamic Displays | Strip Charts
Data Provider Groups
Data can be requested in a variety of coordinate systems, where the origin of the coordinate system is the object's central body. The available coordinate systems depend on the object's central body. Nominally, the systems Fixed, Inertial, J2000, TrueOfDate, and MeanOfDate are supported, although some central bodies (notably the Earth and Sun) have more.The following lists the systems available for Earth.
| Name | Description |
|---|---|
| ICRF | International Celestial Reference Frame. The ICRF axes are defined as the inertial (i.e., kinematically non-rotating) axes associated with a general relativity frame centered at the solar system barycenter (often called the BCRF). |
| MeanOfDate | The mean equator mean equinox coordinate system evaluated at the requested time. |
| MeanOfEpoch | The mean equator mean equinox coordinate system evaluated at the epoch of the object. |
| TrueOfDate | The true equator true equinox coordinate system evaluated at the requested time. |
| TrueOfEpoch | The true equator true equinox coordinate system evaluated at the epoch of the object. |
| B1950 | The mean equator mean equinox coordinate system evaluated at the beginning of the Besselian year 1950 (31 December 1949 22:09:46.866 = JD 2433282.4234591). |
| TEMEOfEpoch | The true equator mean equinox coordinate system evaluated at the epoch of the object. |
| TEMEOfDate | The true equator mean equinox coordinate system evaluated at the requested time. |
| AlignmentAtEpoch | The nonrotating coordinate system coincident with the Fixed system evaluated at the object's coordinate reference epoch. |
| J2000 | The mean equator mean equinox coordinate system evaluated at the J2000.0 epoch (2000 January 1.5 TDB = JD 2451545.0 TDB). |
Data Provider Elements
| Name | Dimension | Type | Description |
|---|---|---|---|
| Time | Date | Real Number or Text | Time. |
| Semilatus Rectum | Distance | Real Number | The semilatus rectum p is defined by p=a*(1-e^2) where, a is the semimajor axis |
| e * sin(omegaBar) | Unitless | Real Number | h = eccentricity * sin(right_ascension_of_the_ascending_node + argument_of_periapse). Equinoctial elements h and k together describe the shape of the orbit and the location of the periapse. |
| e * cos(omegaBar) | Unitless | Real Number | k = eccentricity * cos(right_ascension_of_the_ascending_node + argument_of_periapse). Equinoctial elements h and k together describe the shape of the orbit and the location of the periapse. |
| tan(i/2) * sin(raan) | Unitless | Real Number | p = tan(inclination/2) * sin(right_ascension_of_the_ascending_node). Equinoctial elements p and q together describe the orientation of the orbit plane. Retrograde orbits have a singularity at zero inclination, and posigrade orbits have a singularity at 180 deg inclination. |
| tan(i/2) * cos(raan) | Unitless | Real Number | q = tan(inclination/2) * cos(right_ascension_of_the_ascending_node). Equinoctial elements p and q together describe the orientation of the orbit plane. Retrograde orbits have a singularity at zero inclination, and posigrade orbits have a singularity at 180 deg inclination. |
| True Longitude | Longitude | Real Number or Text | The sum of the right ascension of the ascending node, the argument of periapsis, and the true anomaly. The Calc Object allows a choice of element type (Osculating elements, Kozai-Izsak Mean elements, Brouwer-Lyddane Mean elements using only short period terms, and Brouwer-Lyddane Mean elements using both short and long period terms). The default is osculating. The Calc Object allows a choice of coordinate systems. The default is Earth Centered Inertial. |
| Direction | Unitless | Text | The type of equinoctial elements. Retrograde has its singularity at an inclination of 0 deg. Posigrade has its singularity at an inclination of 180 deg. |
| Semilatus Rectum Rate | Rate | Real Number or Text | Rate of change of p. Computed by applying the variation of parameters equations of motion to the perturbative acceleration. |
| e * sin(omegaBar) Rate | Unitless Per Time | Real Number or Text | Rate of change of h. Computed by applying the variation of parameters equations of motion to the perturbative acceleration. |
| e * cos(omegaBar) Rate | Unitless Per Time | Real Number or Text | Rate of change of k. Computed by applying the variation of parameters equations of motion to the perturbative acceleration. |
| tan(i/2) * sin(raan) Rate | Unitless Per Time | Real Number or Text | Rate of change of p. Computed by applying the variation of parameters equations of motion to the perturbative acceleration. |
| tan(i/2) * cos(raan) Rate | Unitless Per Time | Real Number or Text | Rate of change of q. Computed by applying the variation of parameters equations of motion to the perturbative acceleration. |
| True Longitude Rate | AngleRate | Real Number or Text | The rate of change of the true longitude. Accounts for the total acceleration (i.e., including the two-body acceleration). |
| True Longitude Perturb Rate | AngleRate | Real Number or Text | The perturbative rate of change of the true longitude. Accounts only for the perturbative acceleration (i.e., the acceleration without the inclusion of the two-body acceleration). |