# A Lunar-Orbiting Satellite Constellation for Wireless Energy Supply
## 2 State of the Art Models
The infrastructure required for MPT, such as microwave transmitters, receivers, and antennas, is relatively less expensive. However, the costs can vary depending on the scale and complexity of the MPT system. Lastly, in terms of mass, LPT systems typically have a smaller physical footprint and lower mass compared to MPT systems. This is due to the narrow beam of laser transmission, which requires a smaller receiving area. Laser transmitters and receivers can be more compact in size, and the absence of large antennas further contributes to reduced mass requirements. The historical milestones of WPT using microwaves are further explored in [11]. The paper delves into the details of transmitters and receiving components, including rectennas, a technology that was invented several decades ago [12] but is still under development and has a relatively low technological readiness level (TRL). The basic principle behind MPT is the conversion of electrical energy into microwave energy. This microwave energy is subsequently transmitted to a receiving antenna, where it is reconverted back into electrical energy. The efficiency of this process depends on the frequency of the electromagnetic waves used for the transmission, as well as the distance between the transmitting and receiving antennas. This technology is of great interest in the search for a solution to space-based solar power for the Earth [13], and one of the major challenges in its development is the potential health risks [14] associated with exposure to high levels of microwave radiation. The topic of LPT is addressed in [15], where it is concluded that \"all studies so far essentially concluded that there were no principal technical showstoppers to the concept. On the other hand, with each redesign cycle based on new technology, the total mass in orbit, cost and complexity of the entire system decreased substantially, indicating a remaining potential for further improvements\". The basic principle behind LPT is similar to that of MPT. Electrical energy powers a laser which converts it into electromagnetic energy, which is then transmitted to a receiving station to be converted back into electrical energy. Because laser radiation can be focused into very narrow beams, this technology has the potential to be much more efficient over very long distances compared to other methods of WPT for the same amount of power transmitted. This leads to one of the major challenges for the system, which is the implementation of a very accurate pointing system (with sub-arcsecond accuracy) to allow pointing such a narrow beam over hundreds or thousands of kilometers. The other crucial challenge comes from the need for high-power lasers which generally have an efficiency of at most 50-60%. This means that the satellite must have onboard a highly performant thermal management system to dissipate heat generated by the laser. In [16] two different WPT systems are compared as methods to send energy to the lunar surface. The location of future research sites on the lunar polar regions has raised the overarching problem of how to supply continuous power to the lunar bases located at the poles. Continuous sustainable power is one of the many challenges in establishing a permanent lunar outpost. The laser system has an overall lower efficiency, but is worth investigating after comparing the cost and mass of the system, both space- and Moon-segments. An overview of the research in Europe on WPT can be found in [17], where a project from JAXA to create the microwave-based space solar power system (M-SSPS) to send power to Earth is also mentioned. Space-based solar power is the concept of collecting solar power in outer space with satellites and distributing it to Earth. The idea is similar to the one developed in this paper but focuses on the use of microwave radiation for terrestrial applications. The research nevertheless demonstrates how the topic of WPT is fundamental for our future towards the exploitation of more clean energy resources.