1,382 research outputs found
Precise Orbit Determination of CubeSats
CubeSats are faced with some limitations, mainly due to the limited onboard power and the quality of the onboard sensors. These limitations significantly reduce CubeSats' applicability in space missions requiring high orbital accuracy. This thesis first investigates the limitations in the precise orbit determination of CubeSats and next develops algorithms and remedies to reach high orbital and clock accuracies. The outputs would help in increasing CubeSats' applicability in future space missions
Past, Present and Future of a Habitable Earth
This perspective of this book views Earth's various layers as a whole system, and tries to understand how to achieve harmony and sustainable development between human society and nature, with the theme of " habitability of the Earth." This book is one effort at providing an overview of some of the recent exciting advances Chinese geoscientists have made. It is the concerted team effort of a group of researchers from diverse backgrounds to generalize their vision for Earth science in the next 10 years. The book is intended for scholars, administrators of the Science and Technology policy department, and science research funding agencies. This is an open access book
Past, Present and Future of a Habitable Earth
This perspective of this book views Earth's various layers as a whole system, and tries to understand how to achieve harmony and sustainable development between human society and nature, with the theme of " habitability of the Earth." This book is one effort at providing an overview of some of the recent exciting advances Chinese geoscientists have made. It is the concerted team effort of a group of researchers from diverse backgrounds to generalize their vision for Earth science in the next 10 years. The book is intended for scholars, administrators of the Science and Technology policy department, and science research funding agencies. This is an open access book
Understanding space weather to shield society: A global road map for 2015-2025 commissioned by COSPAR and ILWS
There is a growing appreciation that the environmental conditions that we
call space weather impact the technological infrastructure that powers the
coupled economies around the world. With that comes the need to better shield
society against space weather by improving forecasts, environmental
specifications, and infrastructure design. [...] advanced understanding of
space weather requires a coordinated international approach to effectively
provide awareness of the processes within the Sun-Earth system through
observation-driven models. This roadmap prioritizes the scientific focus areas
and research infrastructure that are needed to significantly advance our
understanding of space weather of all intensities and of its implications for
society. Advancement of the existing system observatory through the addition of
small to moderate state-of-the-art capabilities designed to fill observational
gaps will enable significant advances. Such a strategy requires urgent action:
key instrumentation needs to be sustained, and action needs to be taken before
core capabilities are lost in the aging ensemble. We recommend advances through
priority focus (1) on observation-based modeling throughout the Sun-Earth
system, (2) on forecasts more than 12 hrs ahead of the magnetic structure of
incoming coronal mass ejections, (3) on understanding the geospace response to
variable solar-wind stresses that lead to intense geomagnetically-induced
currents and ionospheric and radiation storms, and (4) on developing a
comprehensive specification of space climate, including the characterization of
extreme space storms to guide resilient and robust engineering of technological
infrastructures. The roadmap clusters its implementation recommendations by
formulating three action pathways, and outlines needed instrumentation and
research programs and infrastructure for each of these. [...]Comment: In press for Advances of Space Research: an international roadmap on
the science of space weather, commissioned by COSPAR and ILWS (63 pages and 4
figures
BDS GNSS for Earth Observation
For millennia, human communities have wondered about the possibility of observing
phenomena in their surroundings, and in particular those affecting the Earth on which they live.
More generally, it can be conceptually defined as Earth observation (EO) and is the collection of
information about the biological, chemical and physical systems of planet Earth. It can be undertaken
through sensors in direct contact with the ground or airborne platforms (such as weather balloons and
stations) or remote-sensing technologies. However, the definition of EO has only become significant
in the last 50 years, since it has been possible to send artificial satellites out of Earthâs orbit.
Referring strictly to civil applications, satellites of this type were initially designed to provide
satellite images; later, their purpose expanded to include the study of information on land
characteristics, growing vegetation, crops, and environmental pollution. The data collected are used
for several purposes, including the identification of natural resources and the production of accurate
cartography. Satellite observations can cover the land, the atmosphere, and the oceans.
Remote-sensing satellites may be equipped with passive instrumentation such as infrared or
cameras for imaging the visible or active instrumentation such as radar. Generally, such satellites are
non-geostationary satellites, i.e., they move at a certain speed along orbits inclined with respect to the
Earthâs equatorial plane, often in polar orbit, at low or medium altitude, Low Earth Orbit (LEO) and
Medium Earth Orbit (MEO), thus covering the entire Earthâs surface in a certain scan time (properly
called âtemporal resolutionâ), i.e., in a certain number of orbits around the Earth.
The first remote-sensing satellites were the American NASA/USGS Landsat Program;
subsequently, the European: ENVISAT (ENVironmental SATellite), ERS (European Remote-Sensing
satellite), RapidEye, the French SPOT (Satellite Pour lâObservation de laTerre), and the Canadian
RADARSAT satellites were launched. The IKONOS, QuickBird, and GeoEye-1 satellites were
dedicated to cartography. The WorldView-1 and WorldView-2 satellites and the COSMO-SkyMed
system are more recent. The latest generation are the low payloads called Small Satellites, e.g., the
Chinese BuFeng-1 and Fengyun-3 series.
Also, Global Navigation Satellite Systems (GNSSs) have captured the attention of researchers
worldwide for a multitude of Earth monitoring and exploration applications. On the other hand,
over the past 40 years, GNSSs have become an essential part of many human activities. As is widely
noted, there are currently four fully operational GNSSs; two of these were developed for military
purposes (American NAVstar GPS and Russian GLONASS), whilst two others were developed for
civil purposes such as the Chinese BeiDou satellite navigation system (BDS) and the European
Galileo. In addition, many other regional GNSSs, such as the South Korean Regional Positioning
System (KPS), the Japanese quasi-zenital satellite system (QZSS), and the Indian Regional Navigation
Satellite System (IRNSS/NavIC), will become available in the next few years, which will have
enormous potential for scientific applications and geomatics professionals.
In addition to their traditional role of providing global positioning, navigation, and timing (PNT)
information, GNSS navigation signals are now being used in new and innovative ways. Across the
globe, new fields of scientific study are opening up to examine how signals can provide information
about the characteristics of the atmosphere and even the surfaces from which they are reflected before
being collected by a receiver.
EO researchers monitor global environmental systems using in situ and remote monitoring tools.
Their findings provide tools to support decision makers in various areas of interest, from security
to the natural environment. GNSS signals are considered an important new source of information
because they are a free, real-time, and globally available resource for the EO community
AAS/GSFC 13th International Symposium on Space Flight Dynamics
This conference proceedings preprint includes papers and abstracts presented at the 13th International Symposium on Space Flight Dynamics. Cosponsored by American Astronautical Society and the Guidance, Navigation and Control Center of the Goddard Space Flight Center, this symposium featured technical papers on a wide range of issues related to orbit-attitude prediction, determination, and control; attitude sensor calibration; attitude dynamics; and mission design
New on-board multipurpose architecture integrating modern estimation techniques for generalized GNSS based autonomous orbit navigation
This dissertation investigates a novel Multipurpose Earth Orbit Navigation System (MEONS) architecture aiming at providing a generalized GNSS based spacecraft orbit estimation kernel matching the modern navigation instance of enhanced flexibility with respect to multiple Space Service Volume (SSV) applications (Precise Orbit Determination for Earth Observation satellite, Low Thrust Low to High Autonomous Orbit Rising, formation flying relative navigation, Small Satellite Autonomous Orbit Acquisition). The possibility to address theoretical and operational solutions within a unified framework is a foundamental step for the implementation of a reusable and configurable high performance navigation capability on next generation platforms
Nonlinear Bayesian filtering based on mixture of orthogonal expansions
This dissertation addresses the problem of parameter and state estimation of nonlinear dynamical systems and its applications for satellites in Low Earth Orbits. The main focus in Bayesian filtering methods is to recursively estimate the state a posteriori probability density function conditioned on available measurements. Exact optimal solution to the nonlinear Bayesian filtering problem is intractable as it requires knowledge of infinite number of parameters. Bayes' probability distribution can be approximated by mixture of orthogonal expansion of probability density function in terms of higher order moments of the distribution. In general, better series approximations to Bayes' distribution can be achieved using higher order moment terms. However, use of such density function increases computational complexity especially for multivariate systems. Mixture of orthogonally expanded probability density functions based on lower order moment terms is suggested to approximate the Bayes' probability density function. The main novelty of this thesis is development of new Bayes' filtering algorithms based on single and mixture series using a Monte Carlo simulation approach. Furthermore, based on an earlier work by Culver [1] for an exact solution to Bayesian filtering based on Taylor series and third order orthogonal expansion of probability density function, a new filtering algorithm utilizing a mixture of orthogonal expansion for such density function is derived. In this new extension, methods to compute parameters of such finite mixture distributions are developed for optimal filtering performance. The results have shown better performances over other filtering methods such as Extended Kalman Filter and Particle Filter under sparse measurement availability. For qualitative and quantitative performance the filters have been simulated for orbit determination of a satellite through radar measurements / Global Positioning System and optical navigation for a lunar orbiter. This provides a new unified view on use of orthogonally expanded probability density functions for nonlinear Bayesian filtering based on Taylor series and Monte Carlo simulations under sparse measurements. Another new contribution of this work is analysis on impact of process noise in mathematical models of nonlinear dynamical systems. Analytical solutions for nonlinear differential equations of motion have a different level of time varying process noise. Analysis of the process noise for Low Earth Orbital models is carried out using the Gauss Legendre Differential Correction method. Furthermore, a new parameter estimation algorithm for Epicyclic orbits by Hashida and Palmer [2], based on linear least squares has been developed. The foremost contribution of this thesis is the concept of nonlinear Bayesian estimation based on mixture of orthogonal expansions to improve estimation accuracy under sparse measurements. âą.EThOS - Electronic Theses Online ServiceGBUnited Kingdo
Stability of CubeSat Clocks and Their Impacts on GNSS Radio Occultation
Global Navigation Satellite Systemsâ radio occultation (GNSS-RO) provides the upper troposphere-lower stratosphere (UTLS) vertical atmospheric profiles that are complementing radiosonde and reanalysis data. Such data are employed in the numerical weather prediction (NWP) models used to forecast global weather as well as in climate change studies. Typically, GNSS-RO operates by remotely sensing the bending angles of an occulting GNSS signal measured by larger low Earth orbit (LEO) satellites. However, these satellites are faced with complexities in their design and costs. CubeSats, on the other hand, are emerging small and cheap satellites; the low prices of building them and the advancements in their components make them favorable for the GNSS-RO. In order to be compatible with GNSS-RO requirements, the clocks of the onboard receivers that are estimated through the precise orbit determination (POD) should have short-term stabilities. This is essential to correctly time tag the excess phase observations used in the derivation of the GNSS-RO UTLS atmospheric profiles. In this study, the stabilities of estimated clocks of a set of CubeSats launched for GNSS-RO in the Spire Global constellation are rigorously analysed and evaluated in comparison to the ultra-stable oscillators (USOs) onboard the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC-2) satellites. Methods for improving their clock stabilities are proposed and tested. The results (i) show improvement of the estimated clocks at the level of several microseconds, which increases their short-term stabilities, (ii) indicate that the quality of the frequency oscillator plays a dominant role in CubeSatsâ clock instabilities, and (iii) show that CubeSatsâ derived UTLS (i.e., tropopause) atmospheric profiles are comparable to those of COSMIC-2 products and in situ radiosonde observations, which provided external validation products. Different comparisons confirm that CubeSats, even those with unstable onboard clocks, provide high-quality RO profiles, comparable to those of COSMIC-2. The proposed remedies in POD and the advancements of the COTS components, such as chip-scale atomic clocks and better onboard processing units, also present a brighter future for real-time applications that require precise orbits and stable clocks
GENESIS: Co-location of Geodetic Techniques in Space
Improving and homogenizing time and space reference systems on Earth and,
more directly, realizing the Terrestrial Reference Frame (TRF) with an accuracy
of 1mm and a long-term stability of 0.1mm/year are relevant for many scientific
and societal endeavors. The knowledge of the TRF is fundamental for Earth and
navigation sciences. For instance, quantifying sea level change strongly
depends on an accurate determination of the geocenter motion but also of the
positions of continental and island reference stations, as well as the ground
stations of tracking networks. Also, numerous applications in geophysics
require absolute millimeter precision from the reference frame, as for example
monitoring tectonic motion or crustal deformation for predicting natural
hazards. The TRF accuracy to be achieved represents the consensus of various
authorities which has enunciated geodesy requirements for Earth sciences.
Today we are still far from these ambitious accuracy and stability goals for
the realization of the TRF. However, a combination and co-location of all four
space geodetic techniques on one satellite platform can significantly
contribute to achieving these goals. This is the purpose of the GENESIS
mission, proposed as a component of the FutureNAV program of the European Space
Agency. The GENESIS platform will be a dynamic space geodetic observatory
carrying all the geodetic instruments referenced to one another through
carefully calibrated space ties. The co-location of the techniques in space
will solve the inconsistencies and biases between the different geodetic
techniques in order to reach the TRF accuracy and stability goals endorsed by
the various international authorities and the scientific community. The purpose
of this white paper is to review the state-of-the-art and explain the benefits
of the GENESIS mission in Earth sciences, navigation sciences and metrology.Comment: 31 pages, 9 figures, submitted to Earth, Planets and Space (EPS
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