Broadcast Ephemeris

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Frequently Asked Questions

What is broadcast ephemeris?

Broadcast ephemeris is the set of orbital parameters and clock corrections transmitted by each GNSS satellite, allowing receivers to compute the satellite's position and apply timing corrections. This page decodes and displays these parameters in real time for all constellations.

Where does the data come from?

The data is sourced from the IGS (International GNSS Service) real-time broadcast ephemeris stream BCEP00BKG0, operated by BKG Frankfurt. It aggregates navigation messages from a global network of reference stations. The stream is decoded using RTCM 3.3 messages (1019, 1020, 1042, 1043, 1044, 1045, 1046).

How often is it updated?

A persistent connection to the IGS stream provides near-continuous updates. Broadcast ephemeris refresh intervals vary by constellation: GPS every 2 hours (IS-GPS-200N), Galileo every 10 minutes (OS SIS ICD v2.2), GLONASS every 30 minutes (ICD-GLONASS L1,L2 v5.1), BeiDou every 1 hour (BDS-SIS-ICD-B1I-3.0), and QZSS every 2 hours (IS-QZSS-PNT-006).

What do the health flags mean?

Each constellation encodes health differently. GPS uses a 6-bit field: the MSB indicates LNAV data health, and the 5 LSBs encode signal component status per IS-GPS-200N Table 20-VIII. Galileo uses a 2-bit Signal Health Status (0=OK, 1=Out of Service, 2=Extended Operations, 3=In Test) per OS SIS ICD Table 84. GLONASS uses the Bn flag (0=healthy, 1=malfunction). BeiDou uses a 1-bit SatH1 flag (0=good, 1=bad). QZSS uses a 6-bit field where only the MSB indicates L1 health — lower bits encode per-signal availability (IS-QZSS-PNT-006 Table 4.1.2-5).

What does the amber "Expired" state mean?

A satellite shown in amber has a last-received ephemeris that exceeds its constellation's validity period. The data is still viewable but should not be used for positioning. Validity periods are defined by each constellation's ICD: GPS 2h, Galileo 4h, GLONASS 30min, BeiDou 1h, QZSS 2h, SBAS ~10min.

How are GPS satellite blocks determined?

GPS satellite block types (IIR, IIR-M, IIF, III) are determined from the PRN-to-block mapping published by the U.S. Coast Guard Navigation Center (NAVCEN) at navcen.uscg.gov/gps-constellation. This is a static mapping updated when new satellites are launched or decommissioned.

How are BeiDou generations determined?

BeiDou satellite generations (BDS-2/BDS-3) and orbit types (GEO/IGSO/MEO) are inferred from the PRN number ranges defined in the BDS-SIS-ICD-B1I-3.0: PRN 1-5 are BDS-2 GEO, PRN 6-10 and 16 are BDS-2 IGSO, PRN 11-14 are BDS-2 MEO, PRN 19-46 are BDS-3 MEO, and PRN 38-40 are BDS-3 IGSO.

How are Galileo generations determined?

Galileo satellites are identified as IOV (In-Orbit Validation: E11, E12, E19, E20) or FOC (Full Operational Capability: all others). E14 and E18 are FOC satellites in eccentric orbits due to a launch anomaly — they are still operational but orbit at a different altitude and eccentricity than nominal FOC satellites.

What are the QZSS satellites?

QZSS (Quasi-Zenith Satellite System) currently has 4 operational satellites. J01 (QZS-1) was the first Block I satellite, J02 (QZS-2R) and J04 (QZS-4) are Block II, and J03 (QZS-3) is in geostationary orbit. J07 (QZS-1R) is a Block II replacement for QZS-1.

What SBAS systems are shown?

The SBAS grid shows geostationary augmentation satellites from multiple systems worldwide: EGNOS (Europe, PRN 120-136), WAAS (North America, PRN 131-138), GAGAN (India, PRN 127-140), MSAS (Japan, PRN 129-137), SDCM (Russia, PRN 125-141), BDSBAS (China, PRN 130-144), and KASS (South Korea, PRN 147-148). Each PRN maps to a specific geostationary satellite.

How are GLONASS satellite types determined?

GLONASS satellite types are determined from the M field in the RTCM 1020 navigation message: M=0 indicates a legacy GLONASS satellite, M=1 indicates a GLONASS-M (modernized) satellite. GLONASS-M satellites carry additional signals and capabilities compared to the original GLONASS constellation.

What parameters are shown for each satellite?

For Keplerian constellations (GPS, Galileo, BeiDou, QZSS): orbital elements (√a, e, i₀, Ω₀, ω, M₀), perturbation corrections (Crs, Crc, Cuc, Cus, Cic, Cis), clock corrections (af₀, af₁, af₂), and constellation-specific fields like TGD, BGD, IODC, and signal health. For state-vector constellations (GLONASS, SBAS): position, velocity, acceleration, and clock parameters.