SP3 Ephemeris File
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The SP3Ephemeris object provides functionalities for reading and writing SP3 Ephemeris data to and from a SP3 Ephemeris file. This is an ASCII file of Precise Ephemeris SP3 files conforming to the Ephemeris SP3 standard.
SP3 ephemeris files (also known as "Precise Ephemeris") contain data records for the orbit and clock states for the entire GPS constellation. There are two versions of the format, Version A and Version C. FreeFlyer has the ability to read and write both versions. The data records are nominally provided at 15 minute intervals, the time system of the file is GPS time, and the reference frame for the orbit data is Earth-Centered-Earth-Fixed (ECEF). FreeFlyer automatically converts between ECEF and MJ2000 when reading and writing SP3EphemerisFiles.
More information on the SP3 format can be found in several locations. Two example references are provided below:
Additionally, historical SP3EphemerisFiles can be downloaded from multiple sources; two examples are provided below:
The NGA site provides position and velocity data in Version A of the SP3 format. There are two separate sets of SP3 files provided on the NGA site; one for the center of mass of the vehicle, and one set for the Antenna Phase Center of the vehicle. The SOPAC site provides position-only data in Version C of the SP3 format under the "Products" Data Type.
An example of the format of a SP3 file (Version C) is given below.