Papers by Thomas Schildknecht
To better characterize and model optical data acquired from ground-based telescopes, the Optical ... more To better characterize and model optical data acquired from ground-based telescopes, the Optical Measurements Center (OMC) at NASA/JSC attempts to emulate illumination conditions seen in space using equipment and techniques that parallel telescopic observations and source-target-sensor orientations. Equipment in the OMC includes a 75-watt Xenon arc lamp, used as a solar simulator; a Santa Barbara Instrument Group CCD camera with
While building up a catalog of Earth orbiting objects, if the available optical observations are ... more 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 nongravitational 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.
Acta Astronautica, 2006
Two thousand seven hundred and ninety uncorrelated targets brighter than magnitude 18.5 were dete... more Two thousand seven hundred and ninety uncorrelated targets brighter than magnitude 18.5 were detected by the European Space Agency (ESA) 1-m space debris telescope at Tenerife during more than 1000 observation hours between February 2001 and December 2004. The ...
Since more than a decade the Astronomical Institute of the University of Bern (AIUB) is investiga... more Since more than a decade the Astronomical Institute of the University of Bern (AIUB) is investigating the small-size space debris environment in high-altitude orbit regions. Originally the efforts concentrated on statistical optical surveys with the primary goal to derive fluxes as input data for statistical environment models. It became, however, obvious that important characteristics of the debris population could not be determined by this technique. The sparse surveys did not yield orbital elements for the debris objects, and it was very difficult to assess the total number of objects for a given region. One essential task of the space debris research is to find and understand the sources of debris, which in turn will enable to devise efficient mitigation measures - a prerequisite for the sustainable use of outer space. In order to understand the nature and eventually the origin of small-size debris objects, observations allowing to derive orbital parameters and physical characteristics like size, shape and material are required. This paper discusses the AIUB activities to build-up and maintain an orbit catalogue of small-size debris. AIUB uses its dedicated 0.3m robotic telescope ZimSMART-2 to constantly survey the GEO, the GTO and the MEO region. The data from this telescope is fused with observations from AIUB's 1-meter ZIMLAT telescope and ESA's 1-meter telescope in Tenerife and shared with international partners. The resulting catalogue of orbital elements enables physical characterization of the debris objects trough photometry, light curve and reflectance spectroscopy observations.
An unexpected space debris population with the unique property of a very high area-to-mass
ratio ... more 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 data.
Key words: methods: data analysis – Catalogues – celestial mechanics – ephemeredes –
minor planets, asteroids: individual: space debris.
Advances in Space Research, 2008
A new population of uncatalogued objects in geosynchronous Earth orbits (GEO), with a mean motion... more A new population of uncatalogued objects in geosynchronous Earth orbits (GEO), with a mean motion of about 1 rev/day and eccentricities up to 0.6, has been identified recently. The first observations of this new type of objects were acquired in the framework of the European Space Agency's (ESA) search for space debris in GEO and the geostationary transfer orbit (GTO) using the ESA 1-m telescope on Tenerife. Earlier studies have postulated that the perturbations due to the solar radiation pressure can lead to such large eccentricities for GEO objects with a high area-to-mass ratio (A/M). The simulations showed that the eccentricities of GEO objects with large A/M exhibit periodic variations with periods of about one year and amplitudes depending on the value of A/M. The findings of these studies could be confirmed by observations from the ESA 1-m telescope on Tenerife.
Advances in Space Research, 2003
For centuries orbit determination in Celestial Mechanics was a synonym for the determination of s... more For centuries orbit determination in Celestial Mechanics was a synonym for the determination of six so-called Keplerian elements of the orbit of a minor planet or a comet based on a short series of (three or more) astrometric places observed from one or more observatories on ...
Advances in Space Research, 2008
In the framework of its space debris research activities ESA established an optical survey progra... more In the framework of its space debris research activities ESA established an optical survey program to study the space debris environment at high altitudes, in particular in the geostationary ring and in the geostationary transfer orbit region. The Astronomical Institute of the University of Bern (AIUB) performs these surveys on behalf of ESA using ESA's 1-m telescope in Tenerife. Regular observations were started in 1999 and are continued during about 120-140 nights per year. Results from these surveys revealed a substantial amount of space debris at high altitudes in the size range from 0.1 to 1 m. Several space debris populations with different dynamical properties were identified in the geostationary ring. During the searches for debris in the geostationary transfer orbit region a new population of objects in unexpected orbits, where no potential progenitors exist, was found. The orbital periods of these objects are clustered around one revolution per day; the eccentricities, however, are scattered between 0 and 0.6. By following-up some of these objects using the ESA telescope and AIUB's 1-m telescope in Zimmerwald, Switzerland, it was possible to study the properties of this new population. One spectacular finding from monitoring the orbits over time spans of days to months is the fact that these objects must have extreme area-to-mass ratios, which are by several orders of magnitudes higher than for 'normal-type' debris. This in turn supports the hypothesis that the new population actually is debris generated in or near the geostationary ring and which is in orbits with periodically varying eccentricity and inclination due to perturbations by solar radiation pressure. In order to further study the nature of these debris, multi-color and temporal photometry (light curves) were acquired with the Zimmerwald telescope. The light curves show strong variations over short time intervals, including signals typical for specular reflections. Some objects exhibit distinct periodic variations with periods ranging from 10 to several 100 s. All this is indicative for objects with complicated shapes and some highly reflective surfaces.
Advances in Space Research, 2005
The satellites of geostationary navigation overlay systems such as EGNOS (European Geostationary ... more The satellites of geostationary navigation overlay systems such as EGNOS (European Geostationary Navigation Overlay System) are equipped with single-frequency microwave transponders. The tracking data contain a GPS-like signal corresponding to the GPS C/A-code (Clear Access code) in the GPS L 1 -band of the electromagnetic spectrum. This signal is tracked by (some of the) commercially available GPS receivers and may be used for orbit determination and for the estimation of EGNOS clock corrections.
Acta Astronautica, 2010
A new population of objects with high area-to-mass ratios (AMR) in the geostationary orbit (GEO) ... more A new population of objects with high area-to-mass ratios (AMR) in the geostationary orbit (GEO) has been identified recently. The first observations of this new type of objects were acquired in the framework of the European Space Agency's (ESA) search for space debris in the GEO and the geostationary transfer orbit using ESA's 1-m telescope on Tenerife (ESASDT). Since 2005 some of the newly detected objects with high AMR have been maintained in a catalogue. In addition to the ESASDT, the 1-m telescope of the Astronomical Institute of the University of Bern (AIUB) in Zimmerwald and several instruments located in the region of the former Soviet Union have been used to acquire the observations needed to maintain the orbital elements of these objects. The data from the latter telescopes is provided to AIUB by the Keldysh Institute of Applied Mathematics (KIAM) in the framework of a collaboration.
Acta Astronautica, 2008
In the framework of ESA's space debris research program optical measurements to search for space ... more In the framework of ESA's space debris research program optical measurements to search for space debris in high-altitude orbits are performed with the ESA 1-m telescope on Tenerife. Observations have been acquired during more than 500 nights during the past 6 years. Most of the data are 'statistical' in the sense that no catalogue of orbital data for individual objects is produced but only a list of 'detections' including rough orbital information and a visual magnitude for each of these detections. Moreover due to the narrow field of view of the telescope the optical surveys provide only snapshot-like samples of the space debris environment. There is no simple relation between the observed detection rates and the number of objects.
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Papers by Thomas Schildknecht
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 data.
Key words: methods: data analysis – Catalogues – celestial mechanics – ephemeredes –
minor planets, asteroids: individual: space debris.
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 data.
Key words: methods: data analysis – Catalogues – celestial mechanics – ephemeredes –
minor planets, asteroids: individual: space debris.