The aim of the LIFELINE project was to perform a feasibility study of a Relativistic Positioning System. Nowadays, all GNSS in operation are based on Newtonian physics and rely on global reference frames fixed to Earth. Relativistic effects are treated as deviations that need to be corrected. A practical RPS would consist, for example, in a constellation of satellites, each one broadcasting not only its General Relativity coordinates (proper times or other observables) at emission but also the coordinates that it receives from the other satellites.

Current on-board orbit determination concepts are in the most cases an integral part of the satellite avionics. However, it is believed that a capability of on-board precise orbit determination would allow to develop new areas of applications. E.g. autonomous station keeping (LEO, MEO and GEO), on-board SAR processing (LEO), missions with high resolution image processing (LEO) or missions related to atmospheric sounding.For this reason, this study shall investigate the conceptual approach for an on-board precise orbit determination system which is not a part of the on-board avionics.

Currently, GNSS is the backbone of most Position, Navigation and Timing (PNT) solutions, in providing 24/7 continuous, all-weather, global coverage to an unlimited number of receiver-equipped users. There is an increasing dependency on the availability and reliability of GNSS. However, GNSS is widely known to be vulnerable to an evolving range of threats (natural and man-made, unintentional and deliberate).

The E.Inspector mission objectives are to:* Image an ESA owned space debris in its current status * Use obtained images for the verification and validation of the e.deorbit or space tug GNC sensorsFollowing a successful ESA internal CDF study, the mission is now proposed to go to phase A to be studied by industry.Several drivers make this mission design challenging:* A possible long and large (delta-V) transfer to the target* Compliance to Space Debris Mitigation guidelines from possibly high altitude* A close RDV while maintaining keep-out zones and ensuring passively safe trajectories* Tr

A GSTP Element 2 activity with France, has taken an existing product used to help signals from satellites reach underground and developed and improved it for navigation purposes.

Achievements and status:

Achievements and status:

Multi-revolution Solar Electric Propulsion (SEP) transfer from the low altitude launcher injection orbit to the final operational orbit is seriously considered or already base-lined for telecom (NeoSat, Electra, Alphabus-extension), Navigation (Galileo next generation) and Earth Observation satellites. With SMART-1 significant experience has been gained to carry out these operations by a fully ground-based approach using conventional radiometric measurements. Meanwhile the boundary conditions for such operations have changed considerably. Engine technology and characteristics have evolved.

Earth Orientation Parameters (EOP) are of fundamental importance for all ESA missions. Currently, the EOPs are obtained from an external entity the Earth Orientation and Reference Service (IERS). The goal of this activity is the development of ESA capability for the estimation and prediction of Earth Orientation Parameter in order to become independent of external services. Several aspects related to this subject topic need to be investigated and further developed.