Improved orbit predictions using two-line elements

The density of orbital space debris constitutes an increasing environmental challenge. There are three ways to alleviate the problem: debris mitigation, debris removal and collision avoidance. This paper addresses collision avoidance, by describing a method that contributes to achieving a requisite increase in orbit prediction accuracy. Batch least-squares differential correction is applied to the publicly available two-line element (TLE) catalog of space objects. Using a high-precision numerical propagator, we fit an orbit to state vectors derived from successive TLEs. We then propagate the fitted orbit further forward in time. These predictions are compared to precision ephemeris data derived from the International Laser Ranging Service (ILRS) for several satellites, including objects in the congested sun-synchronous orbital region. The method leads to a predicted range error that increases at a typical rate of 100 meters per day, approximately a 10-fold improvement over TLE's propagated with their associated analytic propagator (SGP4). Corresponding improvements for debris trajectories could potentially provide initial conjunction analysis sufficiently accurate for an operationally viable collision avoidance system. We discuss additional optimization and the computational requirements for applying all-on-all conjunction analysis to the whole TLE catalog, present and near future. Finally, we outline a scheme for debris-debris collision avoidance that may become practicable given these developments.Comment: Submitted to Advances in Space Research. 13 pages, 4 figure

Application of attributables to the correlation of surveillance radar measurements.

Space surveillance by radar is especially used for the low Earth orbit to maintain a database, also calledcatalogue, of objects on orbit. Among others, surveillance radars which are constantly scanning a region ofinterest in the sky are used for this purpose. The detections from such a radar which cannot be assigned toan already known catalogue object might not contain enough information to obtain a reliable initial orbitfor a new catalogue entry from a single measured pass, also called tracklet. Instead, two tracklets can becombined to improve the quality of the initial orbit which leads to the correlation problem. This means thatit has to be tested whether two tracklets belong to the same object and an initial orbit has to be derivedby combining the tracklets. A common approach to condense the information in the tracklet is fitting themwith so-called attributables. Because radar observations include different types of observables, the fitting ofthese attributables has to be considered as an important part of the entire correlation process. This paperanalyses the effect of the attributable fitting considering the achieved accuracy and influence on the trackletcorrelation. A new singularity-free coordinate system is introduced, which improves the results of the fittingand correlation. Finally, a test on a simulated survey scenario introduces two additional filters to remove falsepositive correlations. It is shown that the attributable-based approach can be applied successfully to trackletsof up to three minutes length with different detection frequencie

A Temporal Map in Geostationary Orbit: The Cover Etching on the EchoStar XVI Artifact

Geostationary satellites are unique among orbital spacecraft in that they experience no appreciable atmospheric drag. After concluding their respective missions, geostationary spacecraft remain in orbit virtually in perpetuity. As such, they represent some of human civilization's longest lasting artifacts. With this in mind, the EchoStar XVI satellite, to be launched in fall 2012, will play host to a time capsule intended as a message for the deep future. Inspired in part by the Pioneer Plaque and Voyager Golden Records, the EchoStar XVI Artifact is a pair of gold-plated aluminum jackets housing a small silicon disc containing one hundred photographs. The Cover Etching, the subject of this paper, is etched onto one of the two jackets. It is a temporal map consisting of a star chart, pulsar timings, and other information describing the epoch from which EchoStar XVI came. The pulsar sample consists of 13 rapidly rotating objects, 5 of which are especially stable, having spin periods < 10 ms and extremely small spindown rates. In this paper, we discuss our approach to the time map etched onto the cover and the scientific data shown on it; and we speculate on the uses that future scientists may have for its data. The other portions of the EchoStar XVI Artifact will be discussed elsewhere.Comment: Accepted for publication in Astronomical Journa

Orbital Debris-Debris Collision Avoidance

We focus on preventing collisions between debris and debris, for which there is no current, effective mitigation strategy. We investigate the feasibility of using a medium-powered (5 kW) ground-based laser combined with a ground-based telescope to prevent collisions between debris objects in low-Earth orbit (LEO). The scheme utilizes photon pressure alone as a means to perturb the orbit of a debris object. Applied over multiple engagements, this alters the debris orbit sufficiently to reduce the risk of an upcoming conjunction. We employ standard assumptions for atmospheric conditions and the resulting beam propagation. Using case studies designed to represent the properties (e.g. area and mass) of the current debris population, we show that one could significantly reduce the risk of nearly half of all catastrophic collisions involving debris using only one such laser/telescope facility. We speculate on whether this could mitigate the debris fragmentation rate such that it falls below the natural debris re-entry rate due to atmospheric drag, and thus whether continuous long-term operation could entirely mitigate the Kessler syndrome in LEO, without need for relatively expensive active debris removal.Comment: 13 pages, 8 figures. Accepted for publication in Advances in Space Researc

Re-entry prediction of spent rocket bodies in GTO

Spent upper stages are bodies consisting of components likely to survive re-entry, for example propellant tanks. Therefore, the re-entry of upper stages might be associated with high on-ground casualty risk. This paper presents a tool for re-entry prediction of spent rocket bodies in GTO based exclusively on Two Line Element set (TLE) data. TLE analysis and filtering, spacecraft parameters estimation, and combined state and parameters estimation are the main building blocks of the tool. The performance of the tool is assessed by computing the accuracy of the re-entry prediction of 92 GTO objects, which re-entered in the past 50 years

Processing two line element sets to facilitate re-entry prediction of spent rocket bodies from geostationary transfer orbit

Predicting the re-entry of space objects enables the risk they pose to the ground population to be managed. The more accurate the re-entry forecast, the more cost-efficient risk mitigation measures can be put in place. However, at present, the only publicly available ephemerides (two line element sets, TLEs) should not be used for accurate re-entry prediction directly. They may contain erroneous state vectors, which need to be filtered out. Also, the object’s physical parameters (ballistic and solar radiation pressure coefficients) need to be estimated to enable accurate propagation. These estimates are only valid between events that change object’s physical properties, e.g. collisions and fragmentations. Thus, these events need to be identified amongst the TLEs. This paper presents the TLE analysis methodology, which enables outlying TLEs and space events to be identified. It is then demonstrated how various TLE filtering stages improve the accuracy of the TLE-based re-entry prediction

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

Astrometry24.NET – precise astrometry for SST and NEO

Astrometry24.NET (A24N) is the first openly available online tool for precise astrometry of astronomical objects able to provide an astrometric solution for both point sources as well as streaks left by non-sidereal moving objects (satellites and space debris or NearEarth Objects - NEOs). A24N is accessible by the end user through three interfaces a) a web browser with modern, responsive UI, b) a cross-platform Command Line Interface (CLI) and c) programmatically through a RESTful API. It makes use of state-of-the-art IT technologies and specifically developed detection and analysis algorithms, utilizing cloud premises, which allow for inexpensive Service Level Agreement (SLA) up to 99.9%. Processing is available on-demand, with optimized load balancing, depending on the actual usage. The architecture of the system, catalogue support, and the astrometric engine behind A24N are first described, followed by the description of the dedicated web portal, built on top of Sybilla Technologies AstroDrive engine, which enables the user to easily upload, store, search, view and manipulate their data. We show the results obtained by the service from synthetic and real data sets. NEO data from ESA Optical Ground Station (OGS) were used, reduced with A24N, Astrometrica and compared (as ground truth) with ephemerides provided from JPL Horizons. For the simulated data tests, a dedicated synthetic frames generator has been developed, which allows one to reproduce all major error sources and isolate their effect. A24N has been tried and tested on a number of data sets from various observatories, including the ESA OGS and the Test Bed Telescope (TBT) in Spain, as well as observatories belonging to the Open University (UK), Nicolaus Copernicus Astronomical Center of the Polish Academy of Sciences (Poland), Max Planck Institute for Extraterrestrial Physics (Germany, COG), Mt. Suhora Observatory of the Pedagogical University in Cracow (Poland), and Comenius University (Slovakia). Long-term monitoring of the COG sensor accuracy, precision and offset has been conducted, as well as observations of Geostationary Orbit (GEO) drifters to test the algorithms and architecture in the production environment. The results of the campaign are presented