38,818 research outputs found
The Instability Transition for the Restricted 3-Body Problem. III. The Lyapunov Exponent Criterion
We establish a criterion for the stability of planetary orbits in stellar
binary systems by using Lyapunov exponents and power spectra for the special
case of the circular restricted 3-body problem (CR3BP). The centerpiece of our
method is the concept of Lyapunov exponents, which are incorporated into the
analysis of orbital stability by integrating the Jacobian of the CR3BP and
orthogonalizing the tangent vectors via a well-established algorithm originally
developed by Wolf et al. The criterion for orbital stability based on the
Lyapunov exponents is independently verified by using power spectra. The
obtained results are compared to results presented in the two previous papers
of this series. It is shown that the maximum Lyapunov exponent can be used as
an indicator for chaotic behaviour of planetary orbits, which is consistent
with previous applications of this method, particularly studies for the Solar
System. The chaotic behaviour corresponds to either orbital stability or
instability, and it depends solely on the mass ratio of the binary components
and the initial distance ratio of the planet relative to the stellar separation
distance. Our theoretical results allow us to link the study of planetary
orbital stability to chaos theory noting that there is a large array of
literature on the properties and significance of Lyapunov exponents. Although
our results are given for the special case of the CR3BP, we expect that it may
be possible to augment the proposed Lyapunov exponent criterion to studies of
planets in generalized stellar binary systems, which is strongly motivated by
existing observational results as well as results expected from ongoing and
future planet search missions.Comment: 10 pages, 8 figures, 3 tables; accepted by Astronomy and Astrophysic
Nulling interferometry: impact of exozodiacal clouds on the performance of future life-finding space missions
Earth-sized planets around nearby stars are being detected for the first time
by ground-based radial velocity and space-based transit surveys. This milestone
is opening the path towards the definition of missions able to directly detect
the light from these planets, with the identification of bio-signatures as one
of the main objectives. In that respect, both ESA and NASA have identified
nulling interferometry as one of the most promising techniques. The ability to
study distant planets will however depend on exozodiacal dust clouds
surrounding the target stars. In this paper, we assess the impact of
exozodiacal dust clouds on the performance of an infrared nulling
interferometer in the Emma X-array configuration. For the nominal mission
architecture with 2-m aperture telescopes, we found that point-symmetric
exozodiacal dust discs about 100 times denser than the solar zodiacal cloud can
be tolerated in order to survey at least 150 targets during the mission
lifetime. Considering modeled resonant structures created by an Earth-like
planet orbiting at 1 AU around a Sun-like star, we show that the tolerable dust
density for planet detection goes down to about 15 times the solar zodiacal
density for face-on systems and decreases with the disc inclination. The upper
limits on the tolerable exozodiacal dust density derived in this study must be
considered as rather pessimistic, but still give a realistic estimation of the
typical sensitivity that we will need to reach on exozodiacal discs in order to
prepare the scientific programme of future Earth-like planet characterisation
missions.Comment: 17 pages, accepted for publication in A&
The Case for Combining a Large Low-Band Very High Frequency Transmitter With Multiple Receiving Arrays for Geospace Research: A Geospace Radar
We argue that combining a high‐power, large‐aperture radar transmitter with several large‐aperture receiving arrays to make a geospace radar—a radar capable of probing near‐Earth space from the upper troposphere through to the solar corona—would transform geospace research. We review the emergence of incoherent scatter radar in the 1960s as an agent that unified early, pioneering research in geospace in a common theoretical, experimental, and instrumental framework, and we suggest that a geospace radar would have a similar effect on future developments in space weather research. We then discuss recent developments in radio‐array technology that could be exploited in the development of a geospace radar with new or substantially improved capabilities compared to the radars in use presently. A number of applications for a geospace radar with the new and improved capabilities are reviewed including studies of meteor echoes, mesospheric and stratospheric turbulence, ionospheric flows, plasmaspheric and ionospheric irregularities, and reflection from the solar corona and coronal mass ejections. We conclude with a summary of technical requirements
Darwin -— an experimental astronomy mission to search for extrasolar planets
As a response to ESA call for mission concepts for its Cosmic Vision 2015–2025 plan, we propose a mission called Darwin. Its primary goal is the study of terrestrial extrasolar planets and the search for life on them. In this paper, we describe different characteristics of the instrument
Early Dynamical Evolution of the Solar System: Pinning Down the Initial Condition of the Nice Model
In the recent years, the "Nice" model of solar system formation has attained
an unprecedented level of success in reproducing much of the observed orbital
architecture of the solar system by evolving the planets to their current
locations from a more compact configuration. Within the context of this model,
the formation of the classical Kuiper belt requires a phase during which the
ice giants have a high eccentricity. An outstanding question of this model is
the initial configuration from which the Solar System started out. Recent work
has shown that multi-resonant initial conditions can serve as good candidates,
as they naturally prevent vigorous type-II migration. In this paper, we use
analytical arguments, as well as self-consistent numerical N-body simulations
to identify fully-resonant initial conditions, whose dynamical evolution is
characterized by an eccentric phase of the ice-giants, as well as planetary
scattering. We find a total of eight such initial conditions. Four of these
primordial states are compatible with the canonical "Nice" model, while the
others imply slightly different evolutions. The results presented here should
prove useful in further development of a comprehensive model for solar system
formation.Comment: 10 pages, 8 figures, 4 tables. Accepted to the Astrophysical Journal
Power Quality Enhancement in Hybrid Photovoltaic-Battery System based on three–Level Inverter associated with DC bus Voltage Control
This modest paper presents a study on the energy quality produced by a hybrid system consisting of a Photovoltaic (PV) power source connected to a battery. A three-level inverter was used in the system studied for the purpose of improving the quality of energy injected into the grid and decreasing the Total Harmonic Distortion (THD). A Maximum Power Point Tracking (MPPT) algorithm based on a Fuzzy Logic Controller (FLC) is used for the purpose of ensuring optimal production of photovoltaic energy. In addition, another FLC controller is used to ensure DC bus stabilization. The considered system was implemented in the Matlab /SimPowerSystems environment. The results show the effectiveness of the proposed inverter at three levels in improving the quality of energy injected from the system into the grid.Peer reviewedFinal Published versio
Structural Design Concepts for a Multi-Megawatt Solar Electric Propulsion (SEP) Spacecraft
As a part of the Space Exploratory Initiative (SEI), NASA-Lewis is studying Solar Electric Propulsion (SEP) spacecraft to be used as a cargo transport vehicle to Mars. Two preliminary structural design concepts are offered for SEP spacecraft: a split blanket array configuration, and a ring structure. The split blanket configuration is an expansion of the photovoltaic solar array design proposed for Space Station Freedom and consists of eight independent solar blankets stretched and supported from a central mast. The ring structural concept is a circular design with the solar blanket stretched inside a ring. This concept uses a central mast with guy wires to provide additional support to the ring. The two design concepts are presented, then compared by performing stability, normal modes, and forced response analyses for varying levels of blanket and guy wire preloads. The ring structure configuration is shown to be advantageous because it is much stiffer, more stable, and deflects less under loading than the split blanket concept
Nonlinear Control of a DC MicroGrid for the Integration of Photovoltaic Panels
New connection constraints for the power network (Grid Codes) require more
flexible and reliable systems, with robust solutions to cope with uncertainties
and intermittence from renewable energy sources (renewables), such as
photovoltaic arrays. The interconnection of such renewables with storage
systems through a Direct Current (DC) MicroGrid can fulfill these requirements.
A "Plug and Play" approach based on the "System of Systems" philosophy using
distributed control methodologies is developed in the present work. This
approach allows to interconnect a number of elements to a DC MicroGrid as power
sources like photovoltaic arrays, storage systems in different time scales like
batteries and supercapacitors, and loads like electric vehicles and the main AC
grid. The proposed scheme can easily be scalable to a much larger number of
elements.Comment: arXiv admin note: text overlap with arXiv:1607.0848
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