63 research outputs found
Angles-only navigation to a non-cooperative satellite using relative orbital elements
No full textThis 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. © 2012 by Gabriella Gaias, Simone D'Amico, Jean-Sebastien Ardaens
A Far Range Image Processing Method for Autonomous Tracking of an Uncooperative Target
No full textThis paper proposes an image processing method for far range rendezvous. A target spacecraft at distances up to ~km is tracked from camera images. The method is based on linking bright, connected sets of pixels over sequences of images. Stars and the target spacecraft are identified by using a star catalog and performing motion segmentation. The algorithm is illustrated in detail and
%the visibility of stars and of the target are analyzed which is a prerequisite to perform far range image processing. Further,
results of a flight experiment called ARGON are presented. The experiment took place in the extended phase of the PRISMA mission. The image processing method was employed and a successful rendezvous from ~km to ~km was accomplished using optical navigation
Fast Angles-Only Initial Relative Orbit Determination for Onboard Application
No full textThis 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
Design Challenges and Safety Concept for the AVANTI Experiment
No full textAVANTI is a formation-flight experiment involving two noncooperative satellites. After a brief overview of the challenges that experiment design and scenario induce, this paper presents the safety concept retained to guarantee the safety of the formation. The peculiarity of the proposed approach is that it does not rely on the continuous availability of tracking data of the client spacecraft but rather exploits the concept of passive safety of special relative trajectories. To this end, the formation safety criterion based on the minimum distance normal to the flight direction
has been extended in order to be applicable also to drifting relative orbits, resulting from non-vanishing relative semi-major axis encountered during a rendezvous or produced by the action of the differential aerodynamic drag
Flight Demonstration of Spaceborne Real-Time Angles-Only Navigation to a Noncooperative Target in Low Earth Orbit
No full textThe paper presents the flight performance of the onboard vision-based navigation software employed during the AVANTI experiment. Two autonomous rendezvous to a noncooperative object have been performed in orbit, first from 13 km to 1 km separation, then from 3 km to 50 m. Despite the poor visibility conditions and the strong orbit perturbations encountered at low altitude, the onboard filter was able to support the onboard guidance and control algorithms with accurate and reliable relative state estimation, enabling thus a safe and smooth approach
A numerical approach to the problem of angles-only initial relative orbit determination in low earth orbit
No full textA practical and effective numerical method is presented, aiming at solving the problem of initial relative orbit determination using solely line-of-sight measurements. The proposed approach exploits the small discrepancies which can be observed between a linear and a more advanced relative motion model. The method consists in systematically performing a series of least-squares adjustments at varying intersatellite distances in the vicinity of a family of collinear solutions coming from the linear theory. The solution presenting the smallest fitting residuals is then selected. The investigations specifically focus on the rendezvous in low Earth near-circular orbit with a noncooperative target. The objective is to determine the relative state of the formation using only bearing observations when the spacecraft are separated by a few dozen kilometers without any a priori additional information. The method is validated with flight data coming from the ARGON (2012) and AVANTI (2016) experiments. Both cases demonstrate that an observation time span of a few maneuver-free orbits is enough to compute a solution which can compete with Two-Line Elements in terms of accuracy
Angles-Only Relative Navigation Activities during AVANTI
No full textThis contribution addresses the realization of angles-only relative navigation systems as means to approach noncooperative target objects flying in low Earth orbits. Based on the recent in-flight experience collected during the AVANTI (Autonomous Vision Approach Navigation and Target Identification) demonstration, a critical comparison between spaceborne and ground-based design philosophies is drawn. Focus is given on the motivations behind the choice of the employed techniques, as well as on the consequent attainable performances. A pure vision-based angles-only approach, in fact, represents an appealing strategy for future on-orbit servicing and debris removal missions, since it requires simply a passive camera as sensing instrument. However, this comes at the cost of a weakly observable relative orbit determination problem, which demands special care, especially during autonomous operations.
For the first time in space applications, AVANTI demonstrated the capability to autonomously navigate towards a fully noncooperative target satellite in low Earth orbit making use of angles-only measurements from 50km to circa 50m of inter-satellite separation range. Within AVANTI, the DLR Earth-observation BIROS spacecraft performed far- to mid-range proximity operations with respect to the BEESAT-4 one-unit CubeSat (Berlin Technical University), released in orbit on the 9th of September 2016, by means of a single picosatellite launcher device. To meet these goals, AVANTI employed the star-tracker embarked on BIROS as far-range camera to take images of portions of the sky and autonomously carried out onboard the following activities: image processing and target identification to provide the angles-measurements of the line-of-sight to the target; real-time relative navigation using an extended Kalman filter and computation of the required impulsive maneuvers' profile to perform a rendezvous in a safe, fuel efficient manner.
The peculiarity of the AVANTI demonstration compared to the formation-flying missions flown so far in low Earth orbit is that it was confronted to an incontrovertible noncooperative scenario. Although BEESAT-4 embarks a Phoenix GPS receiver, in fact, such device was not yet commissioned and, therefore, not operating by the time when AVANTI took place. Radar-tracking observations could not be used when the satellites were separated by less than 5 km, due to the impossibility to distinguish the signals emitted from the two spacecraft. Two-line elements, which generally are not accurate enough to support close-range proximity operations, are also affected by the same problem at close range. Thus, the only observations available during AVANTI were the pictures collected by BIROS's star-tracker, and consequently, the only way to monitor and cross-evaluate the behavior of the spaceborne solution was to re-process such measurements a-posteriori on-ground. Contrary to the onboard unit, the ground-based navigation system could benefit from the availability of calibrated maneuvers from GPS-based precise absolute orbit determination, and, of course, from the presence of man in-the-loop. In addition, alternative image processing and filter techniques (i.e., iterative and/or batch schemes) could be employed, given the lack of real-time and computational resources constraints.
Regarding both spaceborne and ground-based navigation systems, AVANTI capitalizes the experience already collected in 2012 using the PRISMA formation flying testbed. At that time, the so-called ARGON (Advanced Rendezvous demonstration using GPS and Optical Navigation) experiment had already tackled the problem of angle-only relative navigation by making a ground-in-the-loop approach to a target using optical methods. With respect to such achievements, AVANTI demanded an increased level of complexity to cope with a more challenging mission scenario. Contrary to ARGON which, thanks to the dusk-dawn orbit of PRISMA, benefited from optimal illumination conditions, AVANTI experienced frequent and extended interruptions of visual tracking.
Such irregular visibility conditions derive by the fact that the target and chaser spacecraft are eclipsed by Earth during a large part of their orbit and on the other hand the camera becomes blinded by the Sun during another large part of the orbit. In addition, BIROS flies at a low altitude (500 km) inducing a strong unknown differential drag which has to be estimated as part of the orbit determination. Combined with the fact that the picosatellite is a tiny object and that the problem is weakly observable, these constraints make the angles-only relative orbit determination very challenging.
Despite all the aforementioned difficulties, flight data show that the filter design retained for AVANTI was perfectly suited for the needs of the experiment. Two approaches have been performed autonomously: from 13 km to 1 km (Nov 19-23, 2016) and from 3 km to 30 m (Nov 25-28, 2016). Initialized from the ground with a reasonably good guess of the relative state, the filter was able to support the onboard controller with a navigation solution accurate at the meter level in the lateral direction and to about 10% of the inter-satellite separation in the boresight direction.
Considering different stages of experiment commissioning, and phases with rising levels of autonomy, almost two months of flight data support the proposed analysis. Indeed AVANTI demonstrated the viability of the angles-only navigation approach in a general, and thus extremely representative, orbit scenario. Nevertheless, the Authors shed light on critical points still deserving improvements and propose a critical assessment of the performances achievable in flight
Spaceborne autonomous vision-based navigation system for AVANTI
No full textA 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
Flight Demonstration of Autonomous Noncooperative Rendezvous in Low Earth Orbit
No full textThis paper presents ultimate design, implementation, and in-flight performance of the spaceborne guidance navigation and control system which enabled the Autonomous Vision Approach Navigation and Target Identification (AVANTI) experiment; a flight demonstration developed by the German Space Operations Center (GSOC) of the German Aerospace Center (DLR) and carried out in November 2016. Designed to prove the viability to perform far- to mid-range proximity operations with respect to a noncooperative flying object using only optical angle measurements, AVANTI realized the first autonomous vision-based rendezvous to a passive target spacecraft in low Earth orbit. Within this experiment, the DLR Earth-observation BIROS satellite approached down to less than 50 m of inter-satellite distance the BEESAT-4 CubeSat, previously released in orbit by BIROS itself. To this end, a dedicated spaceborne formation-
flying system carried out relative navigation and maneuver planning tasks. Moreover, it took over BIROS orientation and maneuvering capabilities to steer the spacecraft along a passively safe rendezvous trajectory. During AVANTI, the images taken by BIROS constituted the only source of relative navigation information. In the absence of external, independent, and precise navigation data of the target satellite, AVANTI performances have been assessed against the ground-based post-facto reprocessing of the images collected in flight
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