Precise Line-of-Sight Modelling for Angles-Only Relative Navigation

This work presents a precise analytical model to reconstruct the line-of-sight vector to a target satellite over time, as required by angles-only relative navigation systems for application to rendezvous missions. The model includes the effects of the geopotential, featuring: the analytical propagation in the mean relative orbital elements (up to second-order expansion), the analytical two-way osculating/mean orbital elements’ conversion (second-order in J 2 and up to a given degree and order of the geopotential), and a second-order mapping from the perturbed osculating elements’ set to the local orbital frame. Performances are assessed against the line-of-sight reconstructed out of the precise GPS-based positioning products of the PRISMA mission. The line-of-sight modelled over a far-range one day long scenario can be fitted against the true one presenting residuals of the order of ten arc-seconds, which is below the typical sensor noise at far-range

Angles-only Navigation to a Non-Cooperative Satellite using Relative Orbital Elements

This work addresses the design and implementation of a prototype relative navigation tool that uses camera-based measurements collected by a servicer spacecraft to perform far- range rendezvous with a non-cooperative client in low Earth orbit. The development serves the needs of future on-orbit-servicing missions planned by the German Aerospace Center. The focus of the paper is on the design of the navigation algorithms and the assessment of the expected performance and robustness under real-world operational scenarios. The tool validation is accomplished through a high-fidelity simulation environment based on the Multi-Satellite-Simulator in combination with the experience gained from actual flight data from the GPS and camera systems on-board the PRISMA mission

Fast angles-only initial relative orbit determination for onboard application

This paper presents three computationally-light algorithms to solve the initial relative orbit determination problem using line-of-sight measurements. A comparative assessment of their performance and robustness is assessed, based on real flight data from two different in-orbit experiments. The proposed algorithms are optimized for the challenging scenario of far-range noncooperative rendezvous in low Earth orbits. Accordingly, these algorithms are meant to support active debris removal missions, where a first guess solution is required to initialize the onboard relative navigation system

Spaceborne autonomous vision-based navigation system for AVANTI

A novel autonomous vision-based navigation system has been designed to support the upcoming AVANTI (Autonomous Vision Approach Navigation and Target Identification) experiment. AVANTI aims at demonstrating the fully autonomous approach to a noncooperative satellite using a simple camera in a safe and fuel-efficient manner. To that end, the pictures of the camera are first processed onboard by a target identification algorithm, which extracts line-of-sight measurements to the target spacecraft. In a second step, the measurements feed a navigation filter which provides the relative state estimate of the target to the onboard guidance module. Being embarked as autonomous embedded system, the navigation module needs to guarantee robustness and simplicity of use without sacrifying the navigation performance. The paper describes the strategy adopted for the robust target identification, relying on a kinematic identification of the target trajectory throughout a sequence of pictures. The filtering is done using an analytical model for the relative motion which considers the mean effects of the perturbations due to the Earth's equatorial bulge (J2) and the differential drag. The vision-based navigation filter has been tested and validated in a highly realistic simulation environment and using flight data from the PRISMA formation flying mission. Overall, the results show that reliable target recognition (more than 97% success) and accurate navigation performance at the meter-level can be achieved

In-orbit experience and lessons learned from the AVANTI experiment

This work addresses flight results and practical challenges of the Autonomous Vision Approach Navigation and Target Identification in-orbit demonstration. This endeavor realized a fully autonomous rendezvous to a noncooperative target in low Earth orbit, in the separation ranges between tens of kilometers to 50 m, relying exclusively on angles-only observations extracted from pictures collected by a monocular, far-range, camera system. By considering experiment commissioning and execution phases, a total of two months of in-orbit experience could be collected, making AVANTI the most authoritative benchmark for designing the first phase of the approach for future active debris removal missions. Accordingly, this work revisits how crucial design decisions revealed decisive to the success of the mission and how they impacted the obtained experiment performances. As conclusion, such lessons learned gained from the flight campaign are reshaped as design guidelines for handing over the peculiar guidance navigation and control system - referred as to AVANTI-concept - to future rendezvous missions

Angles-only relative orbit determination in low earth orbit

The paper provides an overview of the angles-only relative orbit determination activities conducted to support the Autonomous Vision Approach Navigation and Target Identification (AVANTI) experiment. This in-orbit endeavor was carried out by the German Space Operations Center (DLR/GSOC) in autumn 2016 to demonstrate the capability to perform spaceborne autonomous close-proximity operations using solely line-of-sight measurements. The images collected onboard have been reprocessed by an independent on-ground facility for precise relative orbit determination, which served as ultimate instance to monitor the formation safety and to characterize the onboard navigation and control performances. During two months, several rendezvous have been executed, generating a valuable collection of images taken at distances ranging from 50 km to only 50 m. Despite challenging experimental conditions characterized by a poor visibility and strong orbit perturbations, angles-only relative positioning products could be continuously derived throughout the whole experiment timeline, promising accuracy at the meter level during the close approaches. The results presented in the paper are complemented with former angles-only experience gained with the PRISMA satellites to better highlight the specificities induced by different orbits and satellite designs

Fast Angles-Only Initial Relative Orbit Determination for Onboard Application

This paper presents three computationally-light algorithms to solve the initial relative orbit determination problem using line-of-sight measurements. A comparative assessment of their performance and robustness is assessed, based on real flight data from two different in-orbit experiments. The proposed algorithms are optimized for the challenging scenario of far-range noncooperative rendezvous in low Earth orbits. Accordingly, these algorithms are meant to support active debris removal missions, where a first guess solution is required to initialize the onboard relative navigation system

In-flight demonstration of formation control based on relative orbital elements

The fundamental objective of the PRISMA mission is to respond to the increasing demand of autonomous formation flying and on-orbit servicing technology through the in-flight demonstration of novel guidance, navigation and control (GNC) techniques. This paper addresses one of the primary experiments conducted in the frame of the PRISMA mission to demonstrate broad autonomous formation keeping and reconfiguration capabilities on a routine basis using GPS navigation, relative orbital elements, and impulsive control. After a brief introduction of the adopted formation flying concept and its key algorithms, the paper focuses on the experiment planning, operations and its performance in orbit. The obtained results show the high readiness of the developed spaceborne GNC technology and pave the way for its adoption in future advanced multi-satellite missions for remote sensing.</p