Required Field Of View Research Articles

A Robust Observation, Planning, and Control Pipeline for Autonomous Rendezvous with Tumbling Targets.

Accumulating space debris edges the space domain ever closer to cascading Kessler syndrome, a chain reaction of debris generation that could dramatically inhibit the practical use of space. Meanwhile, a growing number of retired satellites, particularly in higher orbits like geostationary orbit, remain nearly functional except for minor but critical malfunctions or fuel depletion. Servicing these ailing satellites and cleaning up “high-value” space debris remains a formidable challenge, but active interception of these targets with autonomous repair and deorbit spacecraft is inching closer toward reality as shown through a variety of rendezvous demonstration missions. However, some practical challenges are still unsolved and undemonstrated. Devoid of station-keeping ability, space debris and fuel-depleted satellites often enter uncontrolled tumbles on-orbit. In order to perform on-orbit servicing or active debris removal, docking spacecraft (the “Chaser”) must account for the tumbling motion of these targets (the “Target”), which is oftentimes not known a priori. Accounting for the tumbling dynamics of the Target, the Chaser spacecraft must have an algorithmic approach to identifying the state of the Target’s tumble, then use this information to produce useful motion planning and control. Furthermore, careful consideration of the inherent uncertainty of any maneuvers must be accounted for in order to provide guarantees on system performance. This study proposes the complete pipeline of rendezvous with such a Target, starting from a standoff estimation point to a mating point fixed in the rotating Target’s body frame. A novel visual estimation algorithm is applied using a 3D time-of-flight camera to perform remote standoff estimation of the Target’s rotational state and its principal axes of rotation. A novel motion planning algorithm is employed, making use of offline simulation of potential Target tumble types to produce a look-up table that is parsed on-orbit using the estimation data. This nonlinear programming-based algorithm accounts for known Target geometry and important practical constraints such as field of view requirements, producing a motion plan in the Target’s rotating body frame. Meanwhile, an uncertainty characterization method is demonstrated which propagates uncertainty in the Target’s tumble uncertainty to provide disturbance bounds on the motion plan’s reference trajectory in the inertial frame. Finally, this uncertainty bound is provided to a robust tube model predictive controller, which provides tube-based robustness guarantees on the system’s ability to follow the reference trajectory translationally. The combination and interfaces of these methods are shown, and some of the practical implications of their use on a planned demonstration on NASA’s Astrobee free-flyer are additionally discussed. Simulation results of each of the components individually and in a complete case study example of the full pipeline are presented as the study prepares to move toward demonstration on the International Space Station.

Compensation for Blur Requires Increase in Field of View and Viewing Time.

Spatial resolution is an important factor for human pattern recognition. In particular, low resolution (blur) is a defining characteristic of low vision. Here, we examined spatial (field of view) and temporal (stimulus duration) requirements for blurry object recognition. The spatial resolution of an image such as letter or face, was manipulated with a low-pass filter. In experiment 1, studying spatial requirement, observers viewed a fixed-size object through a window of varying sizes, which was repositioned until object identification (moving window paradigm). Field of view requirement, quantified as the number of “views” (window repositions) for correct recognition, was obtained for three blur levels, including no blur. In experiment 2, studying temporal requirement, we determined threshold viewing time, the stimulus duration yielding criterion recognition accuracy, at six blur levels, including no blur. For letter and face recognition, we found blur significantly increased the number of views, suggesting a larger field of view is required to recognize blurry objects. We also found blur significantly increased threshold viewing time, suggesting longer temporal integration is necessary to recognize blurry objects. The temporal integration reflects the tradeoff between stimulus intensity and time. While humans excel at recognizing blurry objects, our findings suggest compensating for blur requires increased field of view and viewing time. The need for larger spatial and longer temporal integration for recognizing blurry objects may further challenge object recognition in low vision. Thus, interactions between blur and field of view should be considered for developing low vision rehabilitation or assistive aids.

High energy electron radiography system design and simulation study of beam angle-position correlation and aperture effect on the images

A beam line dedicated to high-energy electron radiography experimental research with linear achromat and imaging lens systems has been designed. The field of view requirement on the target and the beam angle-position correlation correction can be achieved by fine-tuning the fields of the quadrupoles used in the achromat in combination with already existing six quadrupoles before the achromat. The radiography system is designed by fully considering the space limitation of the laboratory and the beam diagnostics devices. Two kinds of imaging lens system, a quadruplet and an octuplet system are integrated into one beam line with the same object plane and image plane but with different magnification factor. The beam angle-position correlation on the target required by the imaging lens system and the aperture effect on the images are studied with particle tracking simulation. It is shown that the aperture position is also correlated to the beam angle-position on the target. With matched beam on the target, corresponding aperture position and suitable aperture radius, clear pictures can be imaged by both lens systems. The aperture is very important for the imaging. The details of the beam optical requirements, optimized parameters and the simulation results are presented.

Dynamical Modelling of FORMOSAT-7 NB-Satellite Multibody System

Many space vehicles assume their final configuration after an initial deployment phase. During this phase, one part of the vehicle moves with respect to another part as the configuration evolves from its initial to its final form. Presence of a mobile solar array attached to the satellite bus with a controlled hinge leads to significant complication of the satellite dynamics. A mathematical model as well as corresponding software is necessary for numerical investigation of the satellite arbitrary movements. To combine the computational advantages- the non-working constraint forces and torques do not appear, and the resulting equation set is of minimum dimension- comparative studies suggested that some related generalization of Lagrange's form of d'Alembert's principle most closely meet these needs. For FORMOSAT-7 NSPO built satellite, in order to accommodate the field of view requirements originated mainly from the mission payload, a spacecraft bus attached with single leaf of solar array configuration is designed. The asymmetric configuration constitutes a two body dynamics problem, not one whole rigid body case. In this paper, the FORMOSAT-7 NB-satellite attitude dynamics modelling formulation is managed pragmatically. Its final expression of equations of motion derived systematically through the general dynamical equations of motion based on Lagrange's form of d'Alembert's principle and expressed in terms of kinematics variables, velocity and angular velocity coefficients, and generalized forces is presented meticulously. Finally, the equations of motion are validated through cases of numerical simulations.

Low radiation dose ECG-gated chest CT angiography on a 256-slice multidetector CT scanner

Computed tomography angiography (CTA) of the thorax other than cardiac CTA, is utilized for a multitude of conditions and ranges in application from a diagnostic test, to presurgical planning and postsurgical follow-up. Helical CTA without electrocardiogram (ECG) gating has been routinely utilized for the evaluation of thoracic vasculature. However, its applicability can be limited in the evaluation of the thoracic aorta and pulmonary vasculature because of the artifacts resulting from cardiac motion. Traditional retrospective ECG-gated helical scans address this issue but at the price of a high radiation dose to the patient. In this paper we review CTA dose reduction strategies for non-coronary indications, examine field of view requirements, and discuss breath hold challenges for ECG-gated acquisitions. In addition, we present clinical examples performed using low-dose prospective gating technique for evaluation of the aorta acquired on a 256-slice multidetector computed tomography system.

Field of View Requirements for Deployable Training Systems: Effect of Field of View on Roll Control

Maintaining training proficiency during long combat deployments has become an important issue in recent years, and therefore the requirement for deployable training devices has also increased in importance. These training systems must not only deliver high fidelity, but must meet stringent requirements for reduced size for transportability and ease of set-up and operation. We describe an experiment examining the effect of reduced field of view on the control of a roll disturbance. Results indicated that, for control of roll angle, there was little change in performance for fields of view greater than 40 degrees. This finding provides evidence that field of view may be reduced in deployable systems without adversely affecting training effectiveness, at least for some essential capabilities.

Telescope field of view requirements for star recognition.

An experimental study was conducted by Hughes Aircraft Company to determine telescope field of view requirements for human recognition of navigation stars. The study was conducted at the Griffith Park Planetarium in Los Angeles. Four Air Force navigators viewed the night sky projected on the planetarium dome through a simulated telescope. The subjects had control of telescope azimuth and elevation. The telescope had unity power fields of view ranging between 10 and 45 degrees. The subjects were required to identify and acquire any one of the 35 major navigation stars. The results revealed a significant inverse relationship between field of view size and navigation star acquisition-identification time. Identification errors also varied inversely as a function of field of view size, and mean acquisition-identification times were significantly different between subjects. The minimum field of view required for rapid, accurate star identification-acquisition was established to be between 25 and 30 degrees.