Directions 2019: High-orbit GLONASS and CDMA signal

Yury Urlichich, First Deputy Director General, Roscosmos. (Photo: Roscosmos)

By Yury Urlichich
First Deputy Director General, Roscosmos State Space Corporation

The year 2019 will bring GLONASS users many new opportunities. Improving navigation services specifically at the user level, primarily assessed in terms of signal accuracy and availability, is our primary goal. Improving navigation accuracy is based on space system development, including both the orbital constellation (space segment) and ground control segment.

CDMA Signal

A Glonass-K2 spacecraft (SC) launch followed by flight testing will be the most important event in space segment development. This SC will enable navigation not only using legacy FDMA signals available for users for more than 35 years, but simultaneously with a full row of CDMA signals in all GLONASS frequency bands: L1, L2 and L3.

Currently the major navigation error contributors are the radio signal trajectory and the user terminal receiving environment. The new signals will allow lowering the hardware-dependent SC-user ranging error by an order of magnitude, reducing the influence of signal reflections from buildings, constructions and landscape (multipath effect), thus enabling their effective use for high-precision navigation with real-time errors below 0.1 m.

We are also finalizing in 2019 the newest edition of the GLONASS Interface Control Document containing recommended models for evaluation of tropospheric and ionospheric delays. Our forecasts show two times navigation accuracy improvement for users of these models.

High-Orbit GLONASS

Improving signal availability is equally important. As large urban areas demonstrate growing use of navigation technologies, these users experience difficulties receiving signals from SC flying below the elevation angle of 25°. To provide a navigation solution in such environments, we will begin development of High-Orbit GLONASS in 2019.

High-Orbit GLONASS will consist of six SC distributed among the three orbital planes and forming two SC ground traces with 64.8° orbit inclination, eccentricity of 0.072, revolution period of 23.9 hours, geographical longitude of the ascendant angle – 60°, 120° (See figure below).

High-Orbit GLONASS — ground track in red. (Image: Roscosmos)

The new generation space segment will be populated with Glonass-B satellites designed on the proven Glonass-K platform, successfully providing services since 2012. Users will be offered the full spectrum of new CDMA signals in all three GLONASS frequency bands.

The first Glonass-B is planned for launch in 2023, with the full constellation of six SC to be deployed by the end of 2025, increasing by 25% the navigation accuracy in the Eastern hemisphere.

The satellite mass below 1,000 kg allows Angara-A5, the new Russian heavy launch vehicle, to perform a dual launch from either Plesetsk or Vostochny launch sites.

Much attention is being paid to the signal characteristics’ stability throughout the whole system lifecycle. For this purpose, ROSCOSMOS developed the GLONASS Monitoring and Performance Assessment System for civil users, including the distributed network of monitoring stations abroad, and dedicated radio telescopes capable of analyzing the navigation signal structure and power on the Earth’s surface.

Currently the planned user range error (URE) for signal in space is 1.4 m. Feb. 26, with URE of 1.13 m, became the best day of the ten-month long monitoring in 2018. Moreover, this value tends to decrease as Glonass-M satellites operating beyond their guaranteed life period are being replaced. For instance, on Nov. 3, Glonass-M satellite No. 57 launched, replacing No. 16 after almost 12 years of operation in orbit.

As already mentioned, the Glonass-K2 is planned for launch in 2019. Compared to Glonass-M and Glonass-K satellites, Mission Definition Requirements for Glonass-K2 define URE to be 0.3 m, qualitatively improving GLONASS user performance.

The new on-board frequency standard based on passive hydrogen maser (PHM) will also contribute to better performance. This PHM is undergoing its ground tests and will be installed onboard the SC by the end of the year. Its relative 24-hour stability of better than 5×10-15 ensures the required URE.