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 Relative Orbit Determination during the AVANTI Experiment

This paper presents the key results of the angles-only relative orbit determination activities performed during the AVANTI experiment. This in-orbit endeavor was conducted by DLR in autumn 2016 and aimed at demonstrating spaceborne autonomous rendezvous to a noncooperative target using solely optical measurements. In view of the complexity of the experiment, a ground-based verification layer had been built-up to support continuously the experiment with the best possible knowledge of the formation state

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

Autonomous Navigation and Control of Formation Fliyng Spacecraft on the PRISMA Mission

In this paper in-flight results of the PRISMA on-board GPS based navigation system are presented. The onboard navigation performance is estimated through a comparison with the on-ground POD results and is evaluated in terms of accuracy requirements fulfilment and robustness in critical situations (e.g., attitude and orbit control maneuvers, large GPS data gaps). An overview is also given of the innovative and flexible PRISMA operations concept and the DLR’s PRISMA Experiment Control Center (ECC)

Integrated Solution for Rapid Development of Complex GNC Software

The paper describes the integrated software solution retained for the design and development of the AVANTI experiment, a challenging on-board autonomous formation-flying endeavour to be conducted in 2016. This solution aims at enabling rapid prototyping by providing a powerful development, validation and testing environment, able to support simultaneously the design and validation of novel Guidance, Navigation and Control algorithms, the definition and documentation of the interfaces with the ground segment, the implementation of the onboard software using space quality standards, the integration into an existing satellite bus and all related testing activities

Spaceborne Autonomous and Ground Based Relative Orbit Control for the TerraSAR-X/TanDEM-X Formation

TerraSAR-X (TSX) and TanDEM-X (TDX) are two advanced synthetic aperture radar (SAR) satellites flying in formation. SAR interferometry allows a high resolution imaging of the Earth by processing SAR images obtained from two slightly different orbits. TSX operates as a repeat-pass interferometer in the first phase of its lifetime and will be supplemented after two years by TDX in order to produce digital elevation models (DEM) with unprecedented accuracy. Such a flying formation makes indeed possible a simultaneous interferometric data acquisition characterized by highly flexible baselines with range of variations between a few hundreds meters and several kilometers [1]. TSX has been successfully launched on the 15th of June, 2007. TDX is expected to be launched on the 31st of May, 2009. A safe and robust maintenance of the formation is based on the concept of relative eccentricity/inclination (e/i) vector separation whose efficiency has already been demonstrated during the Gravity Recovery and Climate Experiment (GRACE) [2]. Here, the satellite relative motion is parameterized by mean of relative orbit elements and the key idea is to align the relative eccentricity and inclination vectors to minimize the hazard of a collision. Previous studies have already shown the pertinence of this concept and have described the way of controlling the formation using an impulsive deterministic control law [3]. Despite the completely different relative orbit control requirements, the same approach can be applied to the TSX/TDX formation. The task of TDX is to maintain the close formation configuration by actively controlling its relative motion with respect to TSX, the leader of the formation. TDX must replicate the absolute orbit keeping maneuvers executed by TSX and also compensate the natural deviation of the relative e/i vectors. In fact the relative orbital elements of the formation tend to drift because of the secular non-keplerian perturbations acting on both satellites. The goal of the ground segment is thus to regularly correct this configuration by performing small orbit correction maneuvers on TDX. The ground station contacts are limited due to the geographic position of the station and the costs for contact time. Only with a polar ground station a contact visibility is possible every orbit for LEO satellites. TSX and TDX use only the Weilheim ground station (in the southern part of Germany) during routine operations. This station allows two scheduled contact per day for the nominal orbit configuration, meaning that the satellite conditions can be checked with an interval of 12 hours. While this limitation is usually not critical for single satellite operations, the visibility constraints drive the achievable orbit control accuracy for a LEO formation if a ground based approach is chosen. Along-track position uncertainties and maneuver execution errors affect the relative motion and can be compensated only after a ground station contact