Directions 2021: GLONASS on the verge of a new decade

By Yury Urlichich, first deputy director general of Roscosmos State Space Corporation
Sergey Karutin, designer general of GLONASS
Nikolay Testoedov, director general, Information Satellite Systems JSC
Sergey Koblov, director general, Central Research Institute of Machine Building JSC

The year 2020 heralds the end of another 10-year stage of development of the Russian GLObal NAvigation Satellite System (GLONASS). Reconstruction of our orbital constellation, started in 2006, is bearing its fruit. Today, it is hard to imagine one’s daily life without the continuous artificial radio-navigation field provided to users globally by the GLONASS orbital constellation since 2011.

GLONASS signals are employed to perform a wide range of tasks, such as

• Saving lives in road accidents
• Air, ground and naval traffic monitoring and control
• Network synchronization of mobile cellular communications
• Monitoring and enabling the energy grid, road travel, agricultural equipment operation, and more.

Our orbital constellation is built upon a base of second-generation spacecraft (SC) — Glonass-M SC — that was developed in 2003 and has demonstrated outstanding operational capacity: 14 SC are already operating well beyond their expected lifetimes, and four SC celebrate their 13th birthday in orbit this year. Activities focused on improving GLONASS accuracy have not stopped for a single day.

If we go back to 2014, the SC-based ranging offset (which specialists refer as equivalent ranging deviation) was 1.4 m. We managed to achieve 0.9 m offset on Jan. 30, 2020, and during the same week the offset did not exceed 1.15 m. Furthermore, the penultimate series-produced Glonass-M SC (Cosmos-2545), which was launched on March 30, demonstrated basic service ranging accuracy of 0.38 m on a daily interval and 0.63 m accuracy on the “best week” interval.

Glonass-K No. 15 was launched into orbit on Oct. 25. (Photo: Roscosmos)

It was Glonass-M SC development that enabled users around the world to gain access to the first dual-frequency navigation service, which is necessary for decreasing the effects of the ionosphere on navigation accuracy.

The third generation of GLONASS SC — Glonass-K  — was successfully launched from the Plesetsk launch site on Oct. 25. This SC will provide users with a broader range of capabilities — and a more accurate and informative signal in the L3 frequency band. Further gradual rejuvenation of the GLONASS constellation will ensure the ever-improving quality of our navigation services.

Two Glonass-K2 SC are planned for the launch campaign in 2021, and all the experience accumulated during the development of third-generation GLONASS SC (Glonass-K) will be implemented in the fourth-generation SС. Glonass -K2 is a unique SC: It will provide users with five navigation signals, its accuracy will be within 0.3–0.5 m, and its assured expected lifetime will be at least 10 years.

High-Orbit Space Complex

GLONASS developers remain focused on user requirements. Recent surveys show a growing demand for high-quality navigation services in difficult conditions where the SC is visible at more than 25° above the horizon. To satisfy these needs with the implementation of new CDMA signals, development of the GLONASS High-Orbit Space Complex (HOSC) will begin in 2021. Its first SC will be launched in 2025, and complete deployment of the constellation including six SC in three or six planes will be finished by the end of 2027.

As a result, the accuracy and availability of navigation in difficult conditions will improve in the Eastern Hemisphere. But the major anticipated outcome of the HOSC implementation is assured two-fold coverage of the Northeastern segment of the globe with high-accuracy differential navigation data by GLONASS and other GNSS.

HOSC implementation will ensure 25% navigation accuracy improvement over the Eastern hemisphere. Glonass-K SC will be used as a base platform for HASC deployment due to its excellent record.

Ground Control at the Titov Main Test Space Center established a stable telemetry connection with the new satellite shortly after launch. (Photo: Roscosmos)

User Interface Harmony

One of the most important tasks for the year 2020 is harmonization of the GLONASS user interface. As we already mentioned, the signal propagation environment has a strong effect on navigation accuracy; therefore, new issues of GLONASS Interface Control Documents (ICD) are being prepared for publication.

We anticipate that GLONASS end-user accuracy improvement will be achieved through introducing additional information into reserve bits of navigation frames, including relevant parameters of an ionospheric model.

The ICD will contain operating methods with parameters of the ionospheric model and definite recommendations designed for compensation of ionospheric delays by both single-frequency and dual-frequency receivers, as well as generalized methods for compensating for tropospheric delays.

Changes in the ICD concerning FDMA and CDMA signals will ensure backward compatibility and uninterrupted operation for the existing range of user navigation equipment.