## 1 Introduction
### Interplanetary and Lunar Nanospacecraft  
The ESTCube-LuNa concept poses several novel challenges in the field of space technology: we envision cubesat-style solutions in communications, navigation and control for operating a lunar nanospacecraft. The proposed solutions require significant development effort; however, we suggest that alternative solutions to deep space networks (DSNs) are necessary, as the current space agency DSNs are a limited resource. By going DSN-free, a much larger community of interplanetary nanospacecraft developers would open up.  
Cubesats, in fact, nanosatellites in general, are typically developed for LEO conditions, where standard solutions for communications, navigation and attitude control exist. In an effort to bring cubesats into deep space, several outstanding missions have demonstrated the applicability and challenges of the _interplanetary nanospacecraft_, whose mass is in the order of 10 kg. MarCO cubesats supported the InSight Mars mission by relaying data in real time [33]. The LICIACube cubesat imaged the Didymoss system after the DART impact of the moon Dimorphos [34]. The Hera mission will follow up Dimorphos with two deep space cubesats--Milani (ex. APEX) and Juventas [35; 36; 37]. Hayabusa-2 deployed miniature rovers--Rover-1A and Rover-1B--on Ryugu and took images of the asteroid [38].  
While orbiting the Moon, a _lunar nanospacecraft_ offers a stepping stone between the LEO and interplanetary environments. As a matter of fact, NASA's Artemis 1 Moon mission launched ten technology demonstration cubesats, some of which operated or were planned to operate independently from the main mission. However, with the increased risk associated with technology demonstration, many of the Artemis 1 cubesats did not fulfil their mission objectives, emphasising the difficulty of operating cubesats in deep space. One of the most notable of the Artemis 1 cubesats is the CAPSTONE mission, which serves as a pathfinder for cis-lunar operations and navigation for the Lunar Gateway. CAPSTONE was able to establish two-way communications with the ground [39]. Meanwhile, the ESA-supported cubesat LUMIO has been proposed to employ an inter-satellite link with a mothership in lunar orbit [40]. Either directly or via the mothership, NASA and the ESA's lunar nanospaccerrafts use DSNs, operated by agencies themselves, for communications and navigation with radio frequency (RF) ranging.  
The ESTCube-LuNa concept is designed without DSNs, which is a limited resource and will not be able to serve all future deep space-especially nanospacecraft--missions. We propose repurposing radio telescopes for high-speed communications and ranging with multiple patch antennas on the nanospacecraft. For telemetry and command, we propose an omnidirectional approach in the space segment while using Yagi-Uda antennas on the ground. ESTCube-LuNa uses visual celestial navigation for determining the nanospacecraft's position in the cis-lunar lunar system. A dedicated real-time 3D (RT3D)environment is developed for simulating the navigation world and algorithms. As opposed to RF ranging, the visual navigation solution is designed to be solved on board by employing field-programmable gate arrays (FPGAs) for image processing-detection and triangulation of the Moon, the Earth and the Sun. The visual navigation solution also provides the attitude knowledge. The attitude estimate can be improved with Sun sensors, a star tracker and an inertial measurement unit (IMU). For attitude control, we propose using miniature cubesat thrusters similar to those which have already been demonstrated in LEO [41].