Directions 2016: GLONASS priorities — improved accuracy and reliability

Sergey Karutin, GLONASS designer general (left); Nikolay Testoyedov, director general, SC Information Satellite Systems (center); and Andrey Tyulin, director general, SC Russian Space Systems.

By Sergey Karutin, Nikolay Testoyedov and Andrey Tyulin

Currently, Global Navigation Satellite Systems (GNSS) are widely used in transportation, power systems, agriculture, communication, banking and the service sector. Humankind has very rapidly realized the benefits of GNSS use and therefore its dependence on the “artificial navigation field” is constantly growing. That is why at the present stage of GLONASS development, the major research and development foci include not only activities aimed at enhanced accuracy, availability and integrity of navigation, but also theoretical and practical efforts focused at ensuring resilience of navigation (interference mitigation).

These activities logically evolve from the changes GLONASS has experienced over the last decade, establishing the essential groundwork to boost the demand in its services. In 2011, the fully operational constellation of 24 GLONASS-M satellites was deployed. For the first time, civil users got the benefit of navigation signals in two frequency bands (L1 and L2) for positioning.

The GLONASS-K satellite launched the same year transmits a new navigation signal in the L3 frequency band. Its onboard atomic clocks include two Cesium and two Rubidium frequency standards. Implementation of these onboard frequency standards with long-term relative stability less than 5×10^-14 provides better accuracy without reliance on ground control. The program of onboard atomic frequency standards development also includes design of a hydrogen maser with relative daily stability of 5×10^-15 and its in-orbit validation onboard GLONASS-K satellites in 2017–2018.

Simultanesously, the high reliability of GLONASS-M satellites operating beyond their design lifetime, 1.5 times longer in some cases, led to a change in the constellation replenishment strategy. In 2012, the launch-on-demand approach was adopted for future satellites. Currently, nine GLONASS-M satellites are in ground stock, scheduled for launch in 2015–2017 timeframe.

These factors caused a three-year delay in constellation modernization and launch of new GLONASS-K satellites.
Nevertheless, in 2014 GLONASS-K No. 12 was put into orbit with the single phased antenna array for the L1/L2/L3 signals. GLONASS-M satellites No. 55–61 also have the enhanced functional capabilities due to additional L3 navigation payload. The string structure of navigation message digital information provides for a higher rate of data update in case of necessity.

We contribute to the user navigation equipment interference mitigation capabilities by developing GLONASS signals at the frequency bands different from the common frequencies accepted for GPS, Galileo and BeiDou. It is common knowledge that, in some cases, low-end personal jammers made to jam the L1 band with the center frequency of 1575.42 MHz and installed in vehicles may cause severe problems to critical infrastructure. In similar situations, use of 1600.992 MHz and 1248.02 MHz center frequencies (new GLONASS CDMA signals) allows improving the reliability of navigation.

Efforts on the global network of the radio and laser-ranging stations for precise orbit determination and time synchronization (ODTS) are also of note. Six GLONASS measuring stations have been established abroad so far. Further expansion of the network is scheduled for 2015–2016 to ensure ODTS accuracy of up to 0.1 meter in real time during the next few years.

Global use of GLONASS is impossible without international cooperation, and we pay special attention to the recommendations of the UN International Committee on GNSS. In particular, we are finalizing the GLONASS Open Services Positioning Performance Standard and developing the national GNSS Performance Monitoring and Assessment System to be used to continuously monitor quality of the GLONASS services and its compliance with the standard.