Challenges in the system engineering of a Precise Timing Facility for NavIC

At the heart of the NavIC/IRNSS ground segment is the IRNSS Network Timing (IRNWT) facility, a precise timing facility (PTF), responsible for the generation, maintenance and dissemination of the IRNSS system time. This paper dwells on the challenges in the system engineering of such a complex system. A PTF has two major applications namely metrological timekeeping and navigation timekeeping for precise orbit determination and time synchronization (OD&TS). These two different objectives in turn translate to two different sets of requirements such as long-term frequency stability and accuracy for metrological timekeeping, while short and medium term frequency stability and high availability of timescale for navigation. At first, these high level requirements need to be translated to a comprehensive design with minute level operational and performance specifications. The design needs to ensure high availability of the system by creating an ensemble of different kinds of atomic clocks while at the same time maintain frequency stability and optimization for various noise processes dominant at different averaging intervals. The design also need to ensure accuracy of the generated timescale with respect to a desired reference such as UTC needs to be ensured with regular time transfers either by Common-view or Two-way satellite time and frequency transfer. In the next step, the design is implemented with the appropriate selection of hardware and software elements. The system engineering of a PTF thus involves varied and multi-disciplinary facets such as selection of atomic clocks, development of ensemble algorithms, steering the generated timescale signal to the desired reference, monitoring and control of all the hardware and software involved and designing of facility including appropriate environmental conditions. The next step is the verification and validation of the realized system. This step needs to ensure that the system is tested for a sufficiently long period of times to assess both short term and long term performance of the system before it is declared operational. Three such systems have now been made operational in India for NavIC. Copyright © 2019 by ISTRAC/ISRO. Permission granted to INCOSE to publish and use.