Carolin Frueh

Multiple-Object Space Surveillance Tracking Using Finite-Set Statistics

The dynamic tracking of objects is, in general, concerned with state estimation using imperfect data. Multiple object tracking adds the difficulty of encountering unknown associations between the collected data and the objects. State estimation of objects necessitates the prediction of uncertainty through nonlinear (in the general case) dynamical systems and the processing of nonlinear (in the general case) measurement data in order to provide corrections that refine the system uncertainty, where the uncertainty may be non-Gaussian in nature. The sensors, which provide the measurement data, are imperfect with possible misdetections, false alarms, and noise-affected data. The resulting measurements are inherently unassociated upon reception. In this paper, a Bayesian method for tracking an arbitrary, but known, number of objects is developed. The method is based on finite-set statistics coupled with finite mixture model representations of the multiobject probability density function. Instead of relying on ...

The Puzzling Case of the Deep-Space Debris WT1190F: A Test Bed for Advanced SSA Techniques

We report on somewhat unique photometric and spectroscopic observations of the deep-space debris WT1190F, which entered Earth atmosphere off the Sri Lanka coast, last 2015 November 13. This striking case has been imposing to the worldwide SSA community as an outstanding opportunity to effectively assess origin and physical nature of such extemporary impactors and appraise their potential threat for Earth. Our observations indicate for WT1190F an absolute magnitude R = 32.45 ± 0.31, with a flat dependence on the phase angle, and slope 0.007 ± 0.002 mag deg−1. The detected short-timescale variability suggests a “four-facet” geometry, with the body likely spinning with a period P = 2.9114 ± 0.0009 s. In the BVRI color domain, WT1190F closely resembled the Planck deep-space probe, a feature that points to an anthropic origin of the object. This match, together with a depressed reflectance around 4000 and 8500 A may be suggestive of a “grey” (aluminized) surface texture. An analysis is in progress to assess the two prevailing candidates to WT1190F’s identity, namely the Athena II upper stage of the Lunar Prospector mission, and the ascent stage of the Apollo 10 lunar module (LEM LM-4) “Snoopy”, by comparing observations with the synthetic photometry from accurate mock-up modeling and reflectance rendering.

A spherical co-ordinate space parameterisation for orbit estimation

An interesting challenge in orbital estimation problems for space surveillance using optical sensors is that, since both the orbital mechanics and the sensor observation process are non-linear, the standard filtering solutions such as Kalman filters are inapplicable and lead to divergent results. Naïve particle filtering solutions also fail since they require many particles to accurately represent the posterior distribution. However, since the sensor observation noise is modelled as a multivariate Gaussian distribution, it may be expected that the same single-object probability distributions, once projected into the augmented sensor space (a full spherical frame centred on the sensor), assume a simpler form that can be approximated by a multivariate Gaussian distribution. In this paper, a sequential Monte Carlo filter is proposed for the orbital object estimation problem, which exploits the structure of the measurement likelihood probability by introducing a proposal distribution based on a linear Kalman filter update.

A Light Curve Simulation of The Apollo Lunar Ascent Module

According two observations that were made in 2013, an yet unknown object (later designated as WT1190F) was believed to impact Earth 2 years later in the morning of November 11th 2016 at a speed of 11 km/s. During the event, astrometric signature of the object was obtained from Loiano, Italy and DEIMOS, Spain. As a primary candidate, generating the light curve of the the long last Apollo 10 Lunar ascent module (call sign Snoopy) is useful in terms of examining the confidence level of the candidate. This paper proposes a combined approach of light curve simulation, which includes the model construction using Solidworks, further characterization of model using MeshLab, and ray tracing code to generate final results. Although the observed photometric data for object in near space is usually limited to fewer data points depending on the specific setup and observation condition, the simulation procedure proposed in this article does not suffer from these uncertainties.

Heuristic and Optimized Sensor Tasking Observation Strategies with Exemplification for Geosynchronous Objects

With the new space fence technology, the catalog of known space objects is expected to increase to the order of 100,000 objects. Objects need to be initially detected, and sufficient observations need to be collected to allow for a first orbit determination. Furthermore, the objects have to be reobserved regularly, to keep them in the catalog, because the position uncertainty of the objects increases over time, due to unmodeled dynamic effects. Only a small number of ground-based and even fewer space-based sensors are currently available that are able to collect observations, compared to the large number of objects that need to be observed. This makes efficient sensor tasking, which takes into account the realistic ramifications of the problem, crucial in building up and maintaining a precise and accurate catalog of space objects. The time-varying sensor performance and specific sensor constraints are influenced by the sensor location and observational environmental effects, sensor hardware, processing software, and observation modes. This paper shows a new method of solving sensor tasking as an optimization problem translating the heuristic principles that have been successfully applied in sensor tasking of actual space situational awareness networks in a rigorous mathematical framework. A computationally fast near-optimal solution is presented, outperforming traditional heuristic sensor tasking methods. Applications of the methodology are shown via the example of the geosynchronous objects listed in the US Strategic Command two-line element catalog. The results are compared to state-of-the-art observation strategies.

Novel Multi-Object Filtering Approach for Space Situational Awareness

Surveillance activities with ground-based assets in the context of space situational awareness are particularly challenging. The observation process is indeed hindered by short observation arcs, li...

Space-Object Charging and Its Effect on Orbit Evolution

With the increasing number of uncontrolled objects in the space environment surrounding Earth, it has become important to keep track of the orbits of these objects so as to avoid collisions with ac...

The observing campaign on the deep-space debris WT1190F as a test case for short-warning NEO impacts

Abstract On 2015 November 13, the small artificial object designated WT1190F entered the Earth atmosphere above the Indian Ocean offshore Sri Lanka after being discovered as a possible new asteroid only a few weeks earlier. At ESA’s SSA-NEO Coordination Centre we took advantage of this opportunity to organize a ground-based observational campaign, using WT1190F as a test case for a possible similar future event involving a natural asteroidal body.