The Juventas GNC Subsystem, Autonomous Landing on the Surface of the Binary Asteroid Dimorphos
Authors:   GMV Spain, Tres Cantos, Spain, Manuel Moreno Villa Víctor , Stancu Florin-Adrian , Ovejero Provencio Daniel , Valentin Plamadeala Andrei , Nistal Reñones Marcos , Domínguez Castillo Adalberto , Plevier Camiel , Scoubeau Mehdi , da Silva Pais Cabral Francisco 
Published: January 2024

Juventas is a deep space 6U XL CubeSat with the objective of performing a scientific and technological demonstration mission, aiming for the characterization of the binary asteroid Didymos, and its small companion Dimorphos. Juventas takes part in the Hera mission as one of the two CubeSats that will be released in the asteroid’s proximities. As experimental payload, Juventas is designed to take higher risks than his mothercraft and get closer to the asteroids, and eventually perform an autonomous landing on Dimorphos.
Juventas will be inserted into a special set of orbits, called Self-Stabilized Terminator Orbits (SSTO). The existence of this special type of in which the solar radiation pressure (SRP) perturbation cancels the gravitational pull of the central body. The high latency of the information along with the small distances to the target causes great uncertainties in the predicted CubeSat state. Hence, to prevent the asteroid from abandoning the camera’s field of view, fast onboard attitude corrections must be commanded by the GNC system to achieve continuous imaging of the asteroid.
Juventas’ GNC is designed to be able to land on the surface of Dimorphos once the radar observations from the SSTOs have been performed. The landing comprises a controlled touchdown using the autonomous GNC system and a series of uncontrolled bounces until Juventas rests on the asteroid's surface. The highly perturbed dynamics together with the small size of the target make the landing the most challenging operation that Juventas will face.
The landing of Juventas on Dimorphos presents a series of difficulties that can only be tackled by the autonomous GNC implementation. Firstly, the insertion maneuver from the SSTO has a high uncertainty due to the long turnaround times. This insertion is corrected by the GNC which allows a flexible solution for the definition of the maneuvers, being flexible to the number of maneuvers and their execution times. Each of the maneuvers employs the estimated instantaneous state estimation of the filter, using data fusion techniques that combine Image Processing of NAVCAM images for line-of-sight estimation and ranging with a laser altimeter. Consequently, braking maneuvers are performed when the estimated SC approaches the surface of Dimorphos.
The GNC is also flexible to the moment of execution of the insertion phase, being able to compute the optimal position with respect to the orbital plane to perform the maneuvers. Secondly, Juventas should land at a reduced velocity to guarantee that the CubeSat will not bounce back and escape the gravity field of Dimorphos.
This paper will include the consolidated strategies of the GNC designed for the Juventas landing strategy. The focus will be directed towards the modes and functions necessary to operate the CubeSat autonomously.