Weak GNSS signal navigation for lunar exploration missions

Weak-signal GNSS navigation could potentially increase the robustness, flexibility and autonomy of the navigation architectures for future lunar exploration missions. GNSS reception during the various phases of such a mission suffers from very low signal levels, partial visibility of the GNSS sources and unfavourable geometry, actually making use of the spill over of the beams around the Earth mask. The objective of a recent ESA study was to evaluate the challenges of such a navigation solution using GPS and future Galileo signals with carrier to noise density ratio levels as low as 10 to 15 dBHz. The inves¬tigated mission phases included transfer orbit, low lunar orbits, lunar ascent and descent as well as surface operation and navigation at the Lagrange points L1 and L2.