Galileo OS SIS ICD.indd - GSA - Europa

5. Message Data Contents
This section describes the data items above mentioned. Semantics, formats and other
characteristics are provided for all items to be transmitted inside frames.
5.1. Navigation Data
The navigation data contain all the parameters that enable the user to perform
positioning service. They are stored on board each satellite with a validity duration and
broadcast world-wide by all the satellites of the Galileo constellation. The 4 types of
data needed to perform positioning:
5.1.1. Ephemeris
● Ephemeris which are needed to indicate the position of the satellite to the user
receiver
● Time and clock correction parameters which are needed to compute pseudo-range
● Service parameters which are needed to identify the set of navigation data, satellites,
and indicators of the signal health
● Almanac which are needed to indicate the position of all the satellites in the
constellation with a reduced accuracy
The ephemeris for each Galileo satellite is composed of 16 parameters, which are:
● 6 keplerian parameters
● 6 harmonic coeffi cients
● 1 orbit inclination rate correction parameter
● 1 LAN rate correction parameter
● 1 mean motion correction parameter, and
● 1 reference time parameter t 0e for the ephemeris data set
The ephemeris for each Galileo satellite is according to the characteristics stated in
Table 61.
Parameter Defi nition Bits Scale
factor
44 © European Union 2010
Document subject to terms of use and disclaimers p. ii-iii
OD SIS ICD, Issue 1, February 2010
Unit
M 0 Mean anomaly at reference time 32* 2 -31 semi-circles**
∆n Mean motion difference from computed value 16* 2 -43 semi-circles/s**
e Eccentricity 32 2 -33 N/A
A 1/2 Square root of the semi-major axis 32 2 -19 meters1/2
Ω 0
Longitude of ascending node of orbital plane
at weekly epoch
32* 2 -31 semi-circles**
i 0 Inclination angle at reference time 32* 2 -31 semi-circles**
ω Argument of perigee 32* 2 -31 semi-circles**