322 research outputs found
Orbit determination of space objects based on sparse optical data
While building up a catalog of Earth orbiting objects, if the available
optical observations are sparse, not deliberate follow ups of specific objects,
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), including the accurate orbit
determination by full least squares solutions with all six orbital elements.
Because of the presence in the GEO region of a significant subpopulation of
high area to mass objects, strongly affected by non-gravitational
perturbations, it was actually necessary to solve also for dynamical parameters
describing these effects, that is to fit between 6 and 8 free parameters for
each orbit. The validation was based upon a set of real data, acquired from the
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, starting from a sparse time distribution of
observations, which would be compatible with a survey capable of covering the
region of interest in the sky just once per night. This could result in a
significant reduction of the requirements for a future telescope network, with
respect to what would have been required with the previously known algorithm
for correlation and orbit determination.Comment: 20 pages, 8 figure
Variation of the area-to-mass ratio of high area-to-mass ratio space debris objects
An unexpected space debris population with the unique property of a very high area-to-mass ratio (HAMR) was detected in 2004 by Schildknecht and colleagues. Ever since, attempts have been made to investigate the dynamical properties of these objects further. Their orbits are heavily perturbed by the effect of direct radiation pressure, and unknown attitude motion complicates orbit prediction. The area-to-mass ratio of the objects seems to be unstable over time. Only sparse optical data are available for these objects in drift orbits. This paper makes use of optical observations of five HAMR objects, observed over several years, and investigates the variation of their area-to-mass ratio and orbital parameters. A normalized orbit determination setup is established and validated with two low- and two high-area-to-mass-ratio-objects, to ensure that comparable orbits over longer time spans are determined even with sparse optical dat
Variation of Area-to-Mass-Ratio of HAMR Space Debris Objects
An unexpected space debris population has been detected in 2004 Schildknecht
et al. (2003, 2004) with the unique properties of a very high area-to-mass
ratio (HAMR) Schildknecht et al. (2005a). Ever since it has been tried to
investigate the dynamical properties of those objects further. The orbits of
those objects are heavily perturbed by the effect of direct radiation pressure.
Unknown attitude motion complicates orbit prediction. The area-to-mass ratio of
the objects seems to be not stable over time. Only sparse optical data is
available for those objects in drift orbits. The current work uses optical
observations of five HAMR objects, observed over several years and investigates
the variation of their area-to-mass ratio and orbital parameters. A normalized
orbit determination setup has been established and validated with two low and
two of the high ratio objects, to ensure, that comparable orbits over longer
time spans are determined even with sparse optical data.Comment: 10 pages, accepted Monthly Notices of Royal Astronomical Society,
MN-11-1785-MJ.R1, The definitive version is available at
www.blackwell-synergy.co
Polarization Observables for Two-Pion Production off the Nucleon
We develop polarization observables for the processes
and , using both a helicity and hybrid helicity-transversity
basis. Such observables are crucial if processes that produce final states
consisting of a spin-1/2 baryon and two pseudoscalar mesons are to be fully
exploited for baryon spectroscopy. We derive relationships among the
observables, as well as inequalities that they must satisfy. We also discuss
the observables that must be measured in `complete' experiments, and briefly
examine the prospects for measurement of some of these observables in the near
future.Comment: 20 pages, using revtex
K*-couplings for the antidecuplet excitation
We estimate the coupling of the K* vector meson to the N-->Theta+ transition
employing unitary symmetry, vector meson dominance, and results from the GRAAL
Collaboration for eta photoproduction off the neutron. Our small numerical
value for the coupling constant is consistent with the non-observation of the
Theta+ in recent CLAS searches for its photoproduction. We also estimate the
K*-coupling for the N-->Sigma* excitation, with Sigma* being the Sigma-like
antidecuplet partner of the Theta+-baryon.Comment: 9 pages, 1 figure. Minor changes in text and abstract, references
added; version to appear in Phys. Rev.
Correlation and orbit determination of space objects based on sparse optical data
While 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 determinatio
Some Radiative Corrections to Neutrino Scattering: I Neutral Currents
With the advent of high precision neutrino scattering experiments comes the
need for improved radiative corrections. We present a phenomenological analysis
of some contributions to the production of photons in neutrino neutral current
scattering that are relevant to experiments subsuming the 1% level.Comment: 17 Pages, 7 .pdf Figure
An optical survey for space debris on highly eccentric and inclined MEO orbits
Optical surveys for space debris in high-altitude orbits have been conducted since more than ten years. Originally these efforts concentrated mainly on the geostationary region (GEO). Corresponding observation strategies, processing techniques and cataloguing approaches have been developed and successfully applied. The ESA GEO surveys, e.g., resulted in the detection of a significant population of small-size debris and later in the discovery of high area-to-mass ratio objects in GEO-like orbits. Comparably less experience
(both, in terms of practical observation and strategy definition) is available for eccentric orbits that (at least partly) are in the MEO region, in particular for the Molniya-type orbits. Different survey and follow-up strategies for searching space debris objects in highly-eccentric MEO orbits, and to acquire orbits
which are sufficiently accurate to catalog such objects and to maintain their orbits over longer time spans were developed. Simulations were performed to compare the performance of different survey and cataloguing strategies. Eventually, optical observations were conducted in the framework of an ESA study using ESA’s Space Debris Telescope (ESASDT) the 1-m Zeiss telescope located at the Optical Ground Station (OGS) at the Teide Observatory at Tenerife, Spain. Thirteen nights of surveys of Molniya-type orbits were performed between January and August 2013. Eventually 255 surveys were
performed during these thirteen nights corresponding to about 47 h of observations. In total 30 uncorrelated faint objects were discov-
ered. On average one uncorrelated object was found every 100 min of observations. Some of these objects show a considerable brightness
variation and have a high area-to-mass ratio as determined in the orbit estimation process
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