## 2 Materials and Methods
### LRNTS Configuration  
In Earth-based surveying, for each site, a control network is developed prior to further positioning works. The control network is designed in such a way as to spread over the whole site to avoid any extrapolation coming from a coordinate frame definition, which could jeopardize positioning accuracy. It is implemented as a set of stable, fixed points or facilities. Characteristic points of objects that are to be placed at the site are connected to the control network points with relative measurements, such as distances, angles, or coordinate differences. Consequently, both control networks and objects' points' coordinates share the same coordinate system.  
The core of this research is developing a methodology that will allow real-time centimeter positioning accuracy throughout large areas of the Moon's surface. The targeted accuracy should be:  
* available in real-time;
* homogeneous throughout the whole area of interest;
* independent of the size or the shape of a construction/exploration site;
* replicable elsewhere (other solar system bodies).  
A solution presented in this paper suggests placing a set of transceivers along the crater rim, forming a system that would act like any GNSS cosmic segment. LRNTS distinctions from GNSS are summarized in three items:  
Figure 1: Lunar South Pole.  
* LRNTS is a ground-based system;
* it consists of transceivers instead of transmitters;
* it is self-adjustable.  
LRNTS is implemented as a coordinate frame materialized by a set of transceivers located along a crater rim. Each transceiver acts, at the same time, as a transmitter and a receiver. As the transmitter, it broadcasts GNSS-compatible signals to other transceivers (and also inside the crater), while, as the receiver, it receives navigation messages from other transceivers. In that way, LRNTS can adjust the crater coordinate frame only by mutual measurements between LRNTS sites, unless tight fitting into the Moon reference system is needed. Self-calibration of LRNTS is performed via an iterative adjustment of measurements acquired mutually between the LRNTS nodes. One of the tested configurations analyzed in this paper, which is elaborated in detail later, is schematically represented in Figure 2. Blue dots represent LRNTS nodes, while black lines indicate established connections between the nodes. The intention is to provide as much visibility as possible between the transceivers. However, due to crater topography, not all baselines could be established.  
Following the Lunar surface exploration objectives elaborated in [44], LRNTS is designed to act as a foundation positioning tool for all human and robotic missions in phases 1-3 of the Lunar surface exploration operation concept. The behavior of equipment exposed to harsh Lunar conditions can be tested against real conditions in three different environments: controlled indoor lab, virtual simulation, or outdoor analogue testing [45]. The operation of LRNTS transceivers will follow recommendations from [46], stated for robotic missions supporting the installation and maintenance of a permanent human Lunar base. Since solar power is seen as the most appropriate power source for Moon applications, microgrids can be used for powering all the facilities and vehicles in an area of interest [47].  
The navigation system presented in this paper represents a solution for extra-terrestrial positioning applications where there are no satellite navigation systems available yet. Specially, because of existing data for the Moon topography, its explorations so far, and current interests for its further utilization, this paper suggests a pseudosatellite-based regional Lunar navigation system, which makes positioning activities on the Lunar surface much more precise. In addition to that, it is economic and self-sustainable, with no need for real-time monitoring.