In the frame of recent GNSS Evolution studies, Airbus is investigating the use of non-navigation hosted payloads on future Galileo satellites that could both contribute to an improvement of the system itself but also offer benefits to the scientific community.

The presentation will focus on the definition of system concepts related to various experimental payloads, including: Radiation and Plasma Monitoring Unit, Magnetometer, Accelerometer, VLBI Transmitter, Advanced Laser Retro-Reflector, Quantum Communication Payload.

For each of the mention payloads the study comprises a definition of the mission objectives for both Galileo and the scientific community, an assessment of the expected benefits and of the impact they would have on the satellite and ground segment design. Furthermore, aspects like the estimated complexity, cost and technology readiness are also taken into account.

In anticipation of the presentation content, the following potential scientific uses of the various experimental payloads considered are provided next.

Radiation and Plasma Monitoring Unit: Through sampling and collection of radiation environment data and plasma data, this unit allows the characterization of the main threat coming from relativistic electrons, like ionising and non-ionising dose and internal charging. This data can be useful for the scientific community for global Space Environment and Space Weather research purposes.

Magnetometer: it shall provide visibility of the Earth’s magnetic field for the solar geomagnetic field interaction and its related impact on satellites. Also this payload can serve for Space Weather research purposes.

Accelerometer: This unit would sense the non-gravitational or surface forces acting on the satellites as e.g. solar radiation pressure (SRP), Earth albedo and thermal radiation. With the new gravity field models provided by GRACE and GOCE missions, non-conservative forces represent the main source for systematic POD biases, especially for satellites with a big area to mass ratio as that of GNSS satellites. These systematic orbit biases have a direct impact on the estimates of all relevant geodetic and geophysical parameters retrieved from GNSS data and have a crucial impact on the way to realize a highly accurate and very stable global terrestrial reference frame.

Active LRR: Scientific products derived using SLR and LLR data include precise geocentric positions and motions of ground stations, satellite orbits, components of Earth’s gravity field and their temporal variations, Earth Orientation Parameters (EOP).

VLBI Transmitter: This transmitter shall be useful for the scientific community for global geodesy, geodynamics and reference frames research purposes thanks to the possibility to provide uncorrelated measurements.

Quantum Communication Payload: this technology could be used for various purposes, among which the implementation of a Quantum Key Distribution demonstrator seems to be the most attractive one. Secure key distribution is one of the fundamental tasks in information science and technology. The principles of quantum mechanics can make two remote users share identical private keys. Since the first quantum key distribution (QKD) protocol, the Bennett-Brassard-1984 (BB84) protocol, tremendous developments have been made to bring the theory to reality.

A usual point of critique concerning the quality and accuracy of the International Terrestrial Reference Frame (ITRF) is that the different space geodetic techniques are connected primarily on the ground at co-location stations. It is suspected that difficulties to accurately determine the geometrical relation of the reference points of the co-located space geodetic instruments are the main limiting factor for the co-locations on the ground. Therefore, since several years ideas have been developed to complement the co-locations on ground by additional co-locations in space. To some extend this can be achieved already today by Satellite Laser Ranging (SLR) measurements to Global Navigation Satellite System (GNSS) satellites, which at least link SLR and GNSS on ground and in space. However, connecting GNSS and Very Long Baseline Interferometry (VLBI) in space requires direct VLBI-observations of GNSS signals. This is not possible with neither the legacy VLBI system, nor the next generation VLBI system, called VGOS (VLBI Global Observing System), that is currently in its deployment phase. The reason is that the GNSS frequencies are in L band and thus not observable with neither the S/X VLBI systems covering 2 and 8 GHz, or the broadband VGOS systems covering 3-15 GHz. Nevertheless, a number of simulation studies have been performed during the last years that demonstrate the conceptual performance and value of VLBI observations of GNSS satellites. Additionally, a number of observation sessions using astronomical L band systems have been performed. These simulation studies and L-band observations are reviewed and discussed in the presentation. Furthermore, a proposal is presented to equip next-generation Galileo satellites with signals that allow observations with VGOS telescopes.

Gamma ray bursts (GRB) are caused by extremely energetic events in the very distant universe such as hypernovae or collisions of neutron stars. They have durations from seconds to minutes and cover the entire electromagnetic spectrum. GRBs caused by merging neutron stars are particularly interesting as these objects generate gravitational waves that can be observed by gravitational wave detectors that recently opened a new observing window. The challenge is the rapid identification and accurate localization of these objects in the sky, allowing to observe these exotic but transient objects with a multitude of other ground- and satellite-based astronomical measurement techniques and to eventually understand the physical conditions and processes involved.
Precise localization of gamma-ray bursts in the sky can be performed by triangulation based on travel time differences of gamma ray pulses measured by spatially distributed detectors. A GNSS constellation like Galileo is thus the ideal host system for such detectors for three reasons: 1) Several tens of satellites form a constellation with large inter-satellite distances, 2) the satellite orbits are very well known in real time, 3) the satellites are equipped with highly stable clocks.
This presentation gives a short overview into astrophysical background of GRBs, to detectors for gamma ray flashes, and to existing GRB missions. We propose a concept to equip the Galileo satellites with GRB detectors to enhance the constellation with the capabilities of a fundamental astrophysics observatory supporting gravitational wave research.

The 2nd generation of the European GNSS “Galileo” considers the potential use of ISLs for ranging and communications with an initial solution based on an RF microwave link. The paper will present a solution for such ISL based on optical terminals from Thales Alenia Space and ranging technology from CSEM. A preliminary design for such a terminal will be presented together with first results of breadboard. The outlook for the potential development path and the possible integration of QKD capabilities will be given.

The Time Transfer by Laser Link project (T2L2) on-board the Jason 2 satellite demonstrated the achievement of time transfer between remote clocks using the laser telemetry technology and the International Laser Ranging Service (ILRS) network during its nine years of operation. T2L2 has shown ground to ground time transfer in common-view with 140 ps expanded uncertainty (coverage factor k=2). The direct comparison with other space-based time transfer technique in the microwave regime, like GPS, has also shown agreement at 100 ps level, well below the GPS uncertainty. After a review of the T2L2 results, the presentation will present the possible evolutions of the T2L2 instrument and the interests for its use on Galileo and other GNSS satellites.