In October 2017 we will celebrate the 35th anniversary of the first GLONASS satellite launch. Since 1982, the capabilities provided by GLONASS satellites have multiplied and the system’s ground infrastructure has expanded beyond the Russian Federation.
Growing demand for satellite navigation services and increasing user requirements call for continuing modernization, which is only possible if advanced, technically complex solutions are employed, thorough efforts on design and in-orbit validation are made, and continuing dialogue with users is maintained to promptly react to their needs.
The stable operation of the third generation GLONASS-M satellites, the core of the today’s constellation, means more satellites are working beyond their design lifetime. In 2016, two single-satellite launches occurred, in February and May. Seven more satellites of this type remain in ground storage.
The reliability of on-orbit satellites forces us to develop new ground storage technologies since some satellites were manufactured more than three years ago, while the need for their launch may not arise until 2018. Therefore in the next two years the constellation will be sustained with this type of satellite.
The performance of the on-board atomic frequency standards (AFS) carried by the latest GLONASS-M satellites is considerably better than that of those carried by the first GLONASS-M satellites (see Figure 1). Their relative one-day stability has improved from 10-13 to 2.4× 10-14, contributing to smaller signal-in-space range errors (SISREs).
In February 2016, flight testing of the fourth generation GLONASS-K satellite was completed. It carries not only a cesium atomic-beam tube but a rubidium AFS for the first time in GLONASS history. The relative daily stability of this rubidium AFS is 4×10-14. As a result the SISRE for this satellite is about 1 meter.
We are also proud of the success of the passive hydrogen maser (PHM), which we have been building for almost 7 years (Figure 2). Multiyear ground tests displayed its excellent reliability and one-day stability of 5×10-15. It is expected to contribute to 0.3-meter SISRE. The PHM for flight tests measures 360×180×630 millimeters and weighs 25 kilos. Its power consumption is 54 watts. The PHM will be validated onboard the GLONASS-K2 satellite set for launch in 2018.
User Needs. On the threshold of the first GLONASS-K2 launch, new GLONASS reference documents were published in October 2016, describing the family of code-division multiple-access (CDMA) radionavigation signals. The draft GLONASS Open Service Performance Standard has been developed. The GLONASS User Information Support System continues to evolve.
The system transmitting CDMA navigation signals is referred to in four interrelated interface control documents containing general information on signals and the detailed description of signal structures and digital message data. The new signals make it possible to include 63 satellites in the constellation, not only in circular medium-Earth orbit but also on geostationary and high-Earth orbits.
The transition to the flexible string-type structure of the message data produces 2-second periodicity of integrity information delivery to users. The increased number of digits occupied by the ephemeris and clock parameters contributes to a better orbit and clock broadcast accuracy. The ephemeris broadcast precision improves from 0.4 to 0.001 meters. Time-stamp length in CDMA signal has increased to 30 bits, compared to 12 bits of frequency-division multiple-access signals.
The GLONASS Open Service Performance Standard, being drafted according to recommendations of the International Committee on Global Satellite Navigation Systems (ICG), is harmonized with the Performance Standard Template elaborated by the Working Group on Systems, Signals and Services of ICG with the active involvement of the Russian Federation.
As a result, it is also harmonized with the GPS, Galileo and BeiDou performance documents — in addition to international parameters like the horizontal and vertical availability, user positioning error (average and worst over Earth’s surface) and UTC broadcast error. The Draft Standard also includes:
- PDOP availability (PDOP availability for the worst point on the Earth’s Surface, global average);
- User Equivalent Range Error for the worst point of a satellite visibility cone (95%);
- UTC(SU)-GLONASS Time offset broadcast error (global average 95%);
- 21 healthy satellites availability;
- Per-slot availability;
- 24 healthy satellites availability;
- Continuity (probability that a healthy satellite becomes unhealthy without notification 48 hours in advance);
- Major failure probability (SIS URE of >75 meters).
GLONASS User Information Support infrastructure development is a complex program that covers establishing User Information Centers to raise awareness of all categories of users of the capabilities GLONASS provides and its guaranteed performance through www.glonass-iac.ru in Russian, English and Chinese languages.
The network of GLONASS-based navigation and information service providers is being developed. Services include satellite navigation activities, from emergency response to control of autonomous unmanned vehicles.