ADVANTAGE - Advanced Technologies for Navigation and Geodesy

Kepler constellation

The project ADVANTAGE (Advanced Technologies for Navigation and Geodesy), supported by the Helmholtz-Gemeinschaft Deutscher Forschungszentren e.V. (Helmholtz Association of German Research Centers), investigates cutting-edge technologies for the advancement of satellite navigation and space geodesy.

The introduction of optical frequency references, atom interferometry, as well as of optical ranging and communications, creates new opportunities for systems based on time and frequency dissemination. The project investigates innovative architectures for a future satellite system that fully exploits the benefits of each of the aforementioned technologies. The architecture shall be based on a satellite constellation, named Kepler, divided into two segments: twenty-four Medium-Earth-Orbit (MEO) satellites and at least four Low-Earth-Orbits (LEO) satellites. MEO satellites shall be equipped with laser-stabilized cavities, characterized by Allan deviations down to 1e-14 and beyond for short integration time intervals, whereas LEO satellites shall be equipped with stable optical references (e.g. Iodine-based optical clocks). Optical terminals placed on each satellite will allow inter-satellite links (ILS), enabling tight intra- and inter-plane synchronization across the whole constellation, and providing absolute (sub-mm) inter-satellite ranging.
The envisioned architecture allows creating a reference system for position and time of unequalled performance, while at the same time reducing the need for an extensive ground infrastructure for both navigation and geodetic applications.

Precise orbits will be derived from a combination of inter-satellite and ground measurements with an improvement by at least one order of magnitude over current frameworks. These will form the basis for time and frequency transfer via two-way optical links. The optical references in space, inter-connected via optical links, shall provide an ultra-stable time standard amongst the satellites. This ultra-stable time in the optical domain will then be converted to radio frequencies using frequency combs, and transferred to ground receivers using classic, albeit modernized, radio navigation signals.

The proposed architecture will form the basis of an extremely robust and stable time scale, available globally and continuously. The potential impact of the system under development extends from satellite navigation and time dissemination, to the definition of precise geodetic reference frames and satellite geodesy applications, such as gravity field sensing and modeling, Earth observation missions, sea level monitoring, atmospheric sensing.

The project results will influence the future evolution of satellite navigation in general and of the European GNSS system in particular. The results shall be transferred both to the academic world and to industries to ensure the utilization of the most promising options in future systems and applications.

The Institute of Communications and Navigation at DLR contributes in ADVANTAGE to the design and development of:

Systems Engineering and Architecture. System engineering defines and refines the architecture against the goal of developing technologies for a system supporting navigation, geodesy and time keeping; ensures that external influences present on navigation satellites are not masking the benefit of the new technologies; design the satellite functional architecture embedding all envisioned new technologies; studies solutions for a continuous and robust navigation infrastructure in support of final user.
Time and frequency synchronization subsystem. Strategies for a tight synchronization of the constellation elements are investigated to reliably realize a synchronous broadcasting of RF signals via the satellite navigation payloads.
Terminals for optical inter-satellite links. Three types of optical terminals are designed, aiming at a) linking coplanar MEO satellites, b) establishing MEO-to-LEO satellites links and c) establishing LEO-to-MEO satellite links. All connections are designed as bi-directional links with ranging and time/frequency transfer capabilities.
Demonstration of the ranging and communication system: design, prototype implementation, system integration and tests. An essential component of the project is to build-up selected subsystems in the laboratory, both with the goal of understanding the implementation aspects and in supporting their adoption in future Galileo generations. A first integration of these technologies in an optical time transfer experiment is being developed, aiming at demonstrating time and frequency transfer between two remote clocks using a free-space optical link in a laboratory environment.

Partners

Institute of Communications and Navigation, German Aerospace Center (DLR), Oberpfaffenhofen
Institute of Space Systems, German Aerospace Center (DLR), Bremen (Optical Frequency References and Clocks)
The Helmholtz Centre Potsdam - GFZ German Research Centre for Geosciences (Exploitation and Science)

Funded by