1,167 research outputs found
DISCUS - The Deep Interior Scanning CubeSat mission to a rubble pile near-Earth asteroid
We have performed an initial stage conceptual design study for the Deep
Interior Scanning CubeSat (DISCUS), a tandem 6U CubeSat carrying a bistatic
radar as main payload. DISCUS will be operated either as an independent mission
or accompanying a larger one. It is designed to determine the internal
macroporosity of a 260-600 m diameter Near Earth Asteroid (NEA) from a few
kilometers distance. The main goal will be to achieve a global penetration with
a low-frequency signal as well as to analyze the scattering strength for
various different penetration depths and measurement positions. Moreover, the
measurements will be inverted through a computed radar tomography (CRT)
approach. The scientific data provided by DISCUS would bring more knowledge of
the internal configuration of rubble pile asteroids and their collisional
evolution in the Solar System. It would also advance the design of future
asteroid deflection concepts. We aim at a single-unit (1U) radar design
equipped with a half-wavelength dipole antenna. The radar will utilize a
stepped-frequency modulation technique the baseline of which was developed for
ESA's technology projects GINGER and PIRA. The radar measurements will be used
for CRT and shape reconstruction. The CubeSat will also be equipped with an
optical camera system and laser altimeter to sup- port navigation and shape
reconstruction. We provide the details of the measurement methods to be applied
along with the requirements derived of the known characteristics of rubble pile
asteroids.Comment: Submitted to Advances in Space Researc
3D Reconstruction of Small Solar System Bodies using Rendered and Compressed Images
Synthetic image generation and reconstruction of Small Solar System Bodies and the influence of compression is becoming an important study topic because of the advent of small spacecraft in deep space missions. Most of these missions are fly-by scenarios, for example in the Comet Interceptor mission. Due to limited data budgets of small satellite missions, maximising scientific return requires investigating effects of lossy compression. A preliminary simulation pipeline had been developed that uses physics-based rendering in combination with procedural terrain generation to overcome limitations of currently used methods for image rendering like the Hapke model. The rendered Small Solar System Body images are combined with a star background and photometrically calibrated to represent realistic imagery. Subsequently, a Structure-from-Motion pipeline reconstructs three-dimensional models from the rendered images. In this work, the preliminary simulation pipeline was developed further into the Space Imaging Simulator for Proximity Operations software package and a compression package was added. The compression package was used to investigate effects of lossy compression on reconstructed models and the possible amount of data reduction of lossy compression to lossless compression. Several scenarios with varying fly-by distances ranging from 50 km to 400 km and body sizes of 1 km and 10 km were simulated and compressed with lossless and several quality levels of lossy compression using PNG and JPEG 2000 respectively. It was found that low compression ratios introduce artefacts resembling random noise while high compression ratios remove surface features. The random noise artefacts introduced by low compression ratios frequently increased the number of vertices and faces of the reconstructed three-dimensional model
ADAM: a general method for using various data types in asteroid reconstruction
We introduce ADAM, the All-Data Asteroid Modelling algorithm. ADAM is simple
and universal since it handles all disk-resolved data types (adaptive optics or
other images, interferometry, and range-Doppler radar data) in a uniform manner
via the 2D Fourier transform, enabling fast convergence in model optimization.
The resolved data can be combined with disk-integrated data (photometry). In
the reconstruction process, the difference between each data type is only a few
code lines defining the particular generalized projection from 3D onto a 2D
image plane. Occultation timings can be included as sparse silhouettes, and
thermal infrared data are efficiently handled with an approximate algorithm
that is sufficient in practice due to the dominance of the high-contrast
(boundary) pixels over the low-contrast (interior) ones. This is of particular
importance to the raw ALMA data that can be directly handled by ADAM without
having to construct the standard image. We study the reliability of the
inversion by using the independent shape supports of function series and
control-point surfaces. When other data are lacking, one can carry out fast
nonconvex lightcurve-only inversion, but any shape models resulting from it
should only be taken as illustrative global-scale ones.Comment: 11 pages, submitted to A&
Asteroid Models from Multiple Data Sources
In the past decade, hundreds of asteroid shape models have been derived using
the lightcurve inversion method. At the same time, a new framework of 3-D shape
modeling based on the combined analysis of widely different data sources such
as optical lightcurves, disk-resolved images, stellar occultation timings,
mid-infrared thermal radiometry, optical interferometry, and radar
delay-Doppler data, has been developed. This multi-data approach allows the
determination of most of the physical and surface properties of asteroids in a
single, coherent inversion, with spectacular results. We review the main
results of asteroid lightcurve inversion and also recent advances in multi-data
modeling. We show that models based on remote sensing data were confirmed by
spacecraft encounters with asteroids, and we discuss how the multiplication of
highly detailed 3-D models will help to refine our general knowledge of the
asteroid population. The physical and surface properties of asteroids, i.e.,
their spin, 3-D shape, density, thermal inertia, surface roughness, are among
the least known of all asteroid properties. Apart for the albedo and diameter,
we have access to the whole picture for only a few hundreds of asteroids. These
quantities are nevertheless very important to understand as they affect the
non-gravitational Yarkovsky effect responsible for meteorite delivery to Earth,
or the bulk composition and internal structure of asteroids.Comment: chapter that will appear in a Space Science Series book Asteroids I
Evidence for a meteoritic origin of the September 15, 2007, Carancas crater
On September 15th, 2007, around 11:45 local time in Peru, near the Bolivian border, the
atmospheric entry of a meteoroid produced bright lights in the sky and intense detonations. Soon after,
a crater was discovered south of Lake Titicaca. These events have been detected by the Bolivian
seismic network and two infrasound arrays operating for the Comprehensive Nuclear-Test-Ban Treaty
Organization, situated at about 80 and 1620 km from the crater. The localization and origin time
computed with the seismic records are consistent with the reported impact. The entry elevation and
azimuthal angles of the trajectory are estimated from the observed signal time sequences and backazimuths.
From the crater diameter and the airwave amplitudes, the kinetic energy, mass and
explosive energy are calculated. Using the estimated velocity of the meteoroid and similarity criteria
between orbital elements, an association with possible parent asteroids is attempted. The favorable
setting of this event provides a unique opportunity to evaluate physical and kinematic parameters of
the object that generated the first actual terrestrial meteorite impact seismically recorded
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