SP3

The Standard Product 3 (SP3) format is a standardized ASCII text format developed by the National Geodetic Survey (NGS) for the dissemination of precise satellite ephemerides and clock information. Initially designed for GPS satellites, the format has been extended to accommodate other Global Navigation Satellite Systems (GNSS), such as GLONASS and Galileo.

SP3 content and structure

Each SP3 file contains satellite positions and clock corrections at specific epochs. Optionally, satellite velocities and clock rate-of-change information can also be included.

SP3 files are consisted of a header which provides metadata, including the version of the format, the time span covered, the number of satellites, the coordinate system used, and the agency responsible for the data; and a data section which lists the satellite positions (X, Y, Z coordinates in kilometers) and clock corrections (in microseconds) for each epoch. If velocities are included, they are expressed in decimeters per second.

SP3 evolution

• SP3-a: the original version introduced to standardize GPS orbit data exchange.
• SP3-b: enhanced to support multiple satellite systems, including GLONASS.
• SP3-c: introduced further refinements, such as increased precision and additional metadata fields.
• SP3-d: the latest version, expanding the maximum number of satellites from 85 to 999, allowing unlimited comment records in the header, and increasing the maximum length of each comment record from 60 to 80 characters.

External references

For detailed specifications and guidelines, refer to the official SP3 documentation provided by the International GNSS Service (IGS):