# Summary of Lunar Constellation Navigation and Orbit Determination Technology
## 2 Current Status of Lunar Relay Navigation Satellite Networks
### U.S. Lunar Navigation and Communication Plan  
1. LunaNet  
As the National Aeronautics and Space Administration (NASA) continues to explore the Moon and the solar system, the demand for powerful interstellar communication and navigation systems is also increasing [17]. To meet this growing demand, NASA is developing LunaNet, a flexible and expendable lunar navigation and communication system architecture that can provide network, positioning, navigation and timing (PNT) as well as scientific services to lunar exploration users [10]. With the LunaNet system, lunar probes or astronauts can access networks just like people on Earth. Each communication link can be connected to a larger network, allowing data transmission between any devices on the network. The system architecture will offer users three services: network services, positioning, navigation and timing services, and scientific utilization services. After utilizing LunaNet, users will encounter an operational environment similar to Earth users. To provide the required navigation capabilities to lunar missions, LunaNet will provide the following data:  
1. Universal stable time and frequency reference source for achieving time synchronization between all elements of the entire network;
2. Key measurement information obtained from each observable communication link, such as radiance or optimization;
3. Observability of GNSS signals;
4. Angle measurement of stars and celestial bodies for determining relative positions;
5. Images of surface features nearby for relative terrain navigation;
6. Broadcasting signals that transmit navigation data throughout the lunar environment, similar to GPS signals on Earth. The LunaNet architecture is open, expandable, and interoperable. Lunar exploration missions can either be components or users of the LunaNet infrastructure, or even play both roles simultaneously. To satisfy future needs, NASA is exploring spacecraft designs including lunar relay satellites and small satellite constellations to expand the LunaNet infrastructure. These relay satellites or small satellites can carry payloads that provide PNT-related basic functions, such as ranging equipment, autonomous navigation processors, broadcast beacons and time reference source/distribution modules. 2. CommStar-1  
On 9 January 2024, NASA once again postponed its manned lunar landing mission. The \"Artemis 2\" and \"Artemis 3\" missions will be postponed to September 2025 and September 2026 respectively, and one of the key technologies is high-speed communications between the Earth and the Moon. A new company called CommStar Space Communications has announced a plan to launch CommStar-1, a hybrid data relay satellite that can be used as private communications infrastructure for space missions. The CommStar-1 relay infrastructure will be designed as a hybrid system for radio frequency and optical (laser) communications. CommStar-1 will be a larger communication platform than anything else currently considered for missions on the lunar surface or in orbits around the Moon, capable of receiving and relaying signals between satellites and the Earth from its access points in the cislunar service area. CommStar-1 will provide active and always-on advanced data services at a distance of more than 362,102 km (225,000 miles) from the Earth, while its general location will be closer to the Moon. The goal is to establish a space-based Cislunar Network Access Point (C-NAP), operating in a stable and diverse orbit, as a hybrid space-based platform (Earth-Moon, Moon) and a hybrid data communications relay to Earth. CommStar Space Communication hopes to use the new communications satellite as the primary communications infrastructure to serve the anticipated needs of government and commercial agencies from a low Earth orbit to the Moon and eventually beyond. CommStar-1 is designed to be the first satellite in a similar system. The specific design goals are as follows:  
1. Receive/distribute radio frequency and optical (laser) communications from the Moon, Earth, and cislunar space;
2.