130,432 research outputs found
Correlation and orbit determination of space objects based on sparse optical data
No full textWhile building up a catalogue of Earth-orbiting objects, the available optical observations are typically sparse. In this case, no orbit determination is possible without previous correlation of observations obtained at different times. This correlation step is the most computationally intensive, and becomes more and more difficult as the number of objects to be discovered increases. In this paper, we tested two different algorithms, and the related prototype software, recently developed to solve the correlation problem for objects in geostationary orbit (GEO). The algorithms allow the accurate orbit determination by full least-squares solutions with all six orbital elements. The presence of a significant subpopulation of high area-to-mass ratio objects in the GEO region, strongly affected by non-gravitational perturbations, required to solve also for dynamical parameters describing these effects, that is to fit between six and eight free parameters for each orbit.
The validation was based upon a set of real data, acquired from the European Space Agency (ESA) Space Debris Telescope (ESASDT) at the Teide Observatory (Canary Islands). We proved that it is possible to assemble a set of sparse observations into a set of objects with orbits. This would allow a survey strategy covering the region of interest in the sky just once per night. As a result, it would be possible to significantly reduce the requirements for a future telescope network, with respect to what would have been required with the previously known algorithms for correlation and orbit determination
Innovative methods of correlation and orbit determination for space debris
No full textSUMMARY We propose two algorithms to provide a full preliminary orbit of an Earth-orbiting object with a number of observations lower than the classical methods, such as those by Laplace and Gauss. The first one is the Virtual debris algorithm, based upon the admissible region, that is the set of the unknown quantities corresponding to possible orbits for a given observation for objects in Earth orbit (as opposed to both interplanetary orbits and ballistic ones). A similar method has already been successfully used in recent years for the asteroidal case. The second algorithm uses the integrals of the geocentric 2-body motion, which must have the same values at the times of the different observations for a common orbit to exist. We also discuss how to account for the perturbations of the 2-body motion, e.g., the effect
Correlation of space debris observations by the virtual debris algorithm
No full textThe main problem in the orbit determination of the space debris population is the correlation of independently observed tracklets, that are sets of observations over a short time. The information contained in such data are not sufficient for a complete determination of an orbit, thus we need to find two or more tracklets belonging to the same physical object and an orbit fitting all the observations. In this paper we will show how to use the admissible region tool to generate a set of virtual objects (Virtual Debris) which can be used as alternate preliminary orbits and as starting points for a recursive procedure of correlation. We shall focus on optical observations of GEO showing some preliminary results testing the 2007 data by the ESA Optical Ground Station (OGS) at Teide Observatory (Canary Islands), after an astrometric reduction performed by University of Bern
Orbit determination with the two-body integrals. II
No full textInternational audienceThe first integrals of the Kepler problem are used to compute preliminary orbits starting from two short observed arcs of a celestial body, which may be obtained either by optical or by radar observations. We write polynomial equations for this problem, which can be solved using the powerful tools of computational Algebra. An algorithm to decide if the of two short arcs is successful, i.e. if they belong to the same observed body, is proposed and tested numerically. This paper continues the research started in Gronchi et al. (Celest. Mech. Dyn. Astron. 107(3):299-318, 2010), where the angular momentum and the energy integrals were used. The use of a suitable component of the Laplace-Lenz vector in place of the energy turns out to be convenient, in fact the degree of the resulting system is reduced to less than half
Innovative observing strategy and orbit determination for Low Earth Orbit Space Debris
No full textWe present the results of a large scale simulation, reproducing the
behavior of a data center for the build-up and maintenance of a
complete catalog of space debris in the upper part of the low Earth
orbits region (LEO). The purpose is to determine the performances of
a network of advanced optical sensors, through the use of the newest
correlation and orbit determination algorithms. This network is
foreseen for implementation in a Space Situational Awareness system,
such as the future European one. The conclusion is that it is
possible to use a network of optical sensors to build up a catalog
containing more than 98\% of the objects with perigee height between
1100 and 2000 km, which would be observable by a reference radar
system selected as comparison. It is also possible to maintain such
a catalog within the accuracy requirements motivated by collision
avoidance, and to detect catastrophic fragmentation events. The
obtained results depend upon specific assumptions on the sensor and
on the software technologie
MeSH term explosion and author rank improve expert recommendations
No full textInformation overload is an often-cited phenomenon that reduces the productivity, efficiency and efficacy of scientists. One challenge for scientists is to find appropriate collaborators in their research. The literature describes various solutions to the problem of expertise location, but most current approaches do not appear to be very suitable for expert recommendations in biomedical research. In this study, we present the development and initial evaluation of a vector space model-based algorithm to calculate researcher similarity using four inputs: 1) MeSH terms of publications; 2) MeSH terms and author rank; 3) exploded MeSH terms; and 4) exploded MeSH terms and author rank. We developed and evaluated the algorithm using a data set of 17,525 authors and their 22,542 papers. On average, our algorithms correctly predicted 2.5 of the top 5/10 coauthors of individual scientists. Exploded MeSH and author rank outperformed all other algorithms in accuracy, followed closely by MeSH and author rank. Our results show that the accuracy of MeSH term-based matching can be enhanced with other metadata such as author rank
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Optimization of Space Surveillance Resources by Innovative Preliminary Orbit Methods
No full textThe number and performance of the sensors to be used
for a survey is a function of the minimum number of observations
required to determine an orbit. This is critical
for the definition of the sensor network and the observation
planning.
Our goal is to obtain an orbit with a smaller number of
observations with respect to the classical methods, such
as Gauss/Laplace. In the context of space debris surveys,
the goal is a full 6-elements orbit from just 2 tracklets,
which could be obtained with only 2 exposures. The information
contained in a tracklet can be summarized in a
4-dimensional vector called attributable, thus two tracklets
are enough for the orbit determination problem to be
over-determined.
We have proposed an algorithm based upon the integrals
of the 2-body problem. We outline the equations and
the solution methods which are used in our implementation.
We report on the results of a validation test, based
upon the processing of one year of data from ESA Optical
Ground Station. We conclude that the method is
very effective and can be used to find correlations between
tracklets, to be confirmed with additional correlations,
thus providing a catalog of full 6-elements orbits
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