CGSIC Bulletin: Updated GPS-III Satellite Timing Group Delay, Phase Center and Inter-Signal Bias Correction Data

Lockheed Martin Space has released updates to the GPS III SV01 (SVN74) thru SV04 (SVN77) antenna phase center offsets of the L1, L2 and L5 signals for the Earth Coverage (EC) antenna deck. These values are predicted with respect to the Space Vehicle center of mass at the end of year one on-orbit. Additionally, Lockheed Martin Space has released initial antenna phase center offset, Timing Group Delay (TGD), and Inter-Signal Correction (ISC) values for SV05 (SVN78). The TGD and ISC values for SVN 78 were measured at the factory.

GPS Technical References (

The phase center, timing group delay and inter-signal bias data for SVN-78 included in this new release provides additional information that supplements the antenna gain pattern data previously available.

The phase center offset data locates the electrical center of the GPS transmit antenna. This data set also includes the inter-signal corrections as measured in the factory.  The modernized satellites provide multiple civil signals in addition to the legacy L1 C/A signal, enabling robust dual-frequency or triple-frequency receiver tracking. These techniques can, for example, help eliminate ranging errors due to ionospheric path delays.  But proper operation of a multi-frequency receiver requires accommodation of inter-signal biases that arise from differences in the transmit time of each signal type.