The Experts below are selected from a list of 243 Experts worldwide ranked by ideXlab platform
Kip S. Thorne - One of the best experts on this subject based on the ideXlab platform.
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gravitational waves from a compact star in a circular inspiral Orbit in the Equatorial plane of a massive spinning black hole as observed by lisa
Physical Review D, 2000Co-Authors: L S Finn, Kip S. ThorneAbstract:Results are presented from high-precision computations of the Orbital evolution and emitted gravitational waves for a stellar-mass object spiraling into a massive black hole in a slowly shrinking, circular, Equatorial Orbit. The focus of these computations is inspiral near the innermost stable circular Orbit (isco)—more particularly, on Orbits for which the angular velocity Ω is 0.03≲Ω/Ωisco 10 at r0=1 Gpc during the last year of inspiral. The hole’s spin a has a factor of ∼10 influence on the range of M (at fixed μ) for which S/N>10, and the presence or absence of a white-dwarf–binary background has a factor of ∼3 influence. A comparison with predicted event rates shows strong promise for detecting these waves, but not beyond about 1 Gpc if the inspiraling object is a white dwarf or neutron star. This argues for a modest lowering of LISA’s noise floor. A brief discussion is given of the prospects for extracting information from the observed waves.
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Transition from inspiral to plunge for a compact body in a circular Equatorial Orbit around a massive, spinning black hole
Physical Review D, 2000Co-Authors: Amos Ori, Kip S. ThorneAbstract:There are three regimes of gravitational-radiation-reaction-induced inspiral for a compact body with mass μ, in a circular, Equatorial Orbit around a Kerr black hole with mass M≫μ: (i) the adiabatic inspiral regime, in which the body gradually descends through a sequence of circular, geodesic Orbits; (ii) a transition regime, near the innermost stable circular Orbit (isco); (iii) the plunge regime, in which the body travels on a geodesic from slightly below the isco into the hole’s horizon. This paper gives an analytic treatment of the transition regime and shows that, with some luck, gravitational waves from the transition might be measurable by the space-based LISA mission.
Ahmad Sabirin Arshad - One of the best experts on this subject based on the ideXlab platform.
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Medium-sized aperture camera for Earth observation
International Conference on Space Optics — ICSO 2004, 2017Co-Authors: Eugene D. Kim, Young-wan Choi, Myung-seok Kang, Ee-eul Kim, Ho-soon Yang, Ad. Aziz Ad. Rasheed, Ahmad Sabirin ArshadAbstract:Satrec Initiative and ATSB have been developing a medium-sized aperture camera (MAC) for an earth observation payload on a small satellite. Developed as a push-broom type high-resolution camera, the camera has one panchromatic and four multispectral channels. The panchromatic channel has 2.5m, and multispectral channels have 5m of ground sampling distances at a nominal altitude of 685km. The 300mm-aperture Cassegrain telescope contains two aspheric mirrors and two spherical correction lenses. With a philosophy of building a simple and cost-effective camera, the mirrors incorporate no light-weighting, and the linear CCDs are mounted on a single PCB with no beam splitters. MAC is the main payload of RazakSAT to be launched in 2005. RazakSAT is a 180kg satellite including MAC, designed to provide high-resolution imagery of 20km swath width on a near Equatorial Orbit (NEqO). The mission objective is to demonstrate the capability of a high-resolution remote sensing satellite system on a near Equatorial Orbit. This paper describes the overview of the MAC and RarakSAT programmes, and presents the current development status of MAC focusing on key optical aspects of Qualification Model.
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Medium-sized aperture camera for Earth observation from space
Earth Observing Systems IX, 2004Co-Authors: Eugene D. Kim, Young-wan Choi, Myung-seok Kang, Ee-eul Kim, Ho-soon Yang, Abdul Aziz Abdul Rasheed, Ahmad Sabirin ArshadAbstract:Medium-sized Aperture Camera (MAC) for earth observation on a small satellite is being developed by Satrec Initiative and ATSB. Designed as a cost-effective high-resolution camera, this push-broom type camera has 1 panchromatic and 4 multispectral channels using all-CCDs-in-one focal plane, and it does not split the channels by prisms. The panchromatic channel has 2.5m, and multispectral channels have 5m of ground sampling distance at a nominal altitude of 685km. The 300mm modified Ritchey-Chretien telescope contains two aspheric mirrors and two spherical correction lenses. MAC is the main payload of RazakSAT (formerly known as MACSAT) to be launched in 2005. RazakSAT is a 180kg (including MAC) small satellite, designed to provide high-resolution imagery of 20km swath width on a near Equatorial Orbit (NEqO). The mission objective is to demonstrate the capability of a high-resolution small remote sensing satellite system on a near Equatorial Orbit. This paper describes the status report on the development of the MAC Qualification Model and technical issues.
Scott A. Hughes - One of the best experts on this subject based on the ideXlab platform.
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Strong-field tidal distortions of rotating black holes: Formalism and results for circular, Equatorial Orbits
Physical Review D, 2014Co-Authors: Stephen O'sullivan, Scott A. HughesAbstract:Tidal coupling between members of a compact binary system can have an interesting and important influence on that binary's dynamical inspiral. Tidal coupling also distorts the binary's members, changing them (at lowest order) from spheres to ellipsoids. At least in the limit of fluid bodies and Newtonian gravity, there are simple connections between the geometry of the distorted ellipsoid and the impact of tides on the Orbit's evolution. In this paper, we develop tools for investigating tidal distortions of rapidly rotating black holes using techniques that are good for strong-field, fast-motion binary Orbits. We use black hole perturbation theory, so our results assume extreme mass ratios. We develop tools to compute the distortion to a black hole's curvature for any spin parameter, and for tidal fields arising from any bound Orbit, in the frequency domain. We also develop tools to visualize the horizon's distortion for black hole spin $a/M \le \sqrt{3}/2$ (leaving the more complicated $a/M > \sqrt{3}/2$ case to a future analysis). We then study how a Kerr black hole's event horizon is distorted by a small body in a circular, Equatorial Orbit. We find that the connection between the geometry of tidal distortion and the Orbit's evolution is not as simple as in the Newtonian limit.
Craig A. Kluever - One of the best experts on this subject based on the ideXlab platform.
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Rapid Evaluation of Low-Thrust Transfers from Elliptical Orbits to Geostationary Orbit
Journal of Spacecraft and Rockets, 2020Co-Authors: Mason J. Kelchner, Craig A. KlueverAbstract:Low-thrust Orbit transfers to geostationary Equatorial Orbit (GEO) will likely use a combination of chemical and electrical propulsion stages to strike a balance between transit time, minimal power...
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designing transfers to geostationary Orbit using combined chemical electric propulsion
Journal of Spacecraft and Rockets, 2015Co-Authors: Craig A. KlueverAbstract:Although it is clear that electric propulsion can deliver more payload mass when compared to conventional chemical propulsion, near-term transfers to geostationary-Equatorial Orbit will likely use both propulsion modes in order to reduce the transfer time. Determining the best starting Orbit for the subsequent electric-propulsion phase is the key to computing time-constrained maximum-payload transfers to geostationary Orbit. Numerical optimization methods are used to determine the unique optimal starting Orbit for a given low-thrust velocity increment ΔV to be performed by the electric-propulsion stage. This approach yields a purely analytical algorithm that can determine spacecraft mass requirements for a desired electric propulsion system and desired transfer time. Numerical examples are presented in order to demonstrate how this tool can be used to rapidly perform trade studies for transfers that use chemical and electric propulsion stages.
H. Matsuoka - One of the best experts on this subject based on the ideXlab platform.
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Comparative benefits of a low Equatorial Orbit microwave solar power satellite (SPS) operational demonstrator
2008 IEEE International RF and Microwave Conference, 2008Co-Authors: P. Collins, H. MatsuokaAbstract:The paper discusses the potential advantages of operating a microwave power-generating solar power satellite demonstrator in low Equatorial Orbit. Advantages include being able to deliver power to receiving antennas in a dozen countries around the equator many times/day, and enabling progressive growth to become a large scale system, including geo-stationary satellites. Solar power satellites operating at progressively higher altitudes can deliver power to cities at progressively higher latitudes: within 24 degrees of the equator there is potential demand for several hundred GW of power. Planning an international conference to discuss such a project is recommended.
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Low Equatorial Orbit pilot plant is on the critical path to commercial space-based solar power supply
2004 Asia-Pacific Radio Science Conference 2004. Proceedings., 1Co-Authors: P. Collins, H. MatsuokaAbstract:Summary form only given. Over the past 35 years, research has progressed on many aspects of space-based solar power supply to Earth. However, cumulative funding of this research remains several orders of magnitude less than that of other energy sources, including terrestrial solar power systems. In addition, a power pilot plant has not yet been built and operated; yet until a pilot plant is built, it will not be possible to fully evaluate the system's potential to become a major, environmentally benign source of electric power during the 21st century. Work in Japan on space-based solar power supply to Earth began in 1980. As expertise in the subject grew, the SPS Working Group was established at the Institute of Space and Astronautical Science (ISAS) to coordinate a number of projects. Among these, the project that grew into the largest single coordinated body of work concerning space-based solar power in Japan was the design of a 10 MW pilot plant satellite for operation in low Equatorial Orbit. This project, which became known as "SPS 2000", was first described in detail in 1991 by Professors Makoto Nagatomo and Kiyohiko Itoh in a paper at the "SPS91" international conference in Paris. That paper established a set of guidelines for the project, which included that the system should supply power to consumers, in order to generate real user feedback. As a related part of the project, the authors received a series of grants from the Japanese Ministry of Education and Science to visit countries near the equator to research the possibility of siting rectennae (rectifying antennae) in their territory and deliver microwave power from space for local use. These countries welcomed the proposal, and are keen to see the project realised. In addition, the project has received praise in many expert reports around the world. To date, a major conclusion of the technical work on the SPS 2000 satellite design is that the main technical challenge seems to be the robotic assembly in Orbit. Unless there is some potential for human intervention in the event of problems it is very difficult to have confidence that the 200 ton satellite, carrying some 10 hectares of solar cells could deploy itself automatically without problems. Studies on space-based solar power have reached the stage at which production and operation of a pilot plant is now the most appropriate next step. However, space agencies in USA, Europe and Japan decline to fund this work, since energy policy is not their responsibility. The decision to minimise funding of space-based solar power research to date is thus not a considered conclusion of targeted policy studies, but a by-product of government institutional arrangements whereby energy policy and space technology are controlled by separate branches of government. There is an urgent need for this governmental obstacle to be removed, and for a space-based solar power pilot plant to be put into operation.