DOCSLIB.ORG

Perturbations in Lower Uranian Orbit Review

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Perturbations in Lower Uranian Orbit Review Perturbations in Lower Uranian Orbit Review a project presented to The Faculty of the Department of Aerospace Engineering San José State University in partial fulfillment of the requirements for the degree Master of Science in Aerospace Engineering by Zaid Karajeh December 2017 approved by Dr. Jeanine Hunter Faculty Advisor Perturbations in Lower Uranian orbit Review Karajeh Z.1 San Jose State University, San Jose, California, 95116 Uranus is almost a mystery to many of the scientists and engineers on Earth today. Its existence has been known for centuries, yet the planet has been largely unexplored and thus misunderstood. This paper describes two methods for sending a spacecraft from Earth to Uranus. First, a simple Hohmann transfer from LEO to LUO. Second, a flyby assist at Jupiter via two Hohmann transfers. The results of this paper describe why a flyby assist is the ideal option for a mission to Uranus and how it optimizes the Delta V requirement, in comparison to the more expensive single Hohmann. This paper also describes the tradeoff for conducting a flyby maneuver. The methods used to produce these results are explained in detail. The N-body analysis portion of this investigation also found that propagation did occur on the a spacecraft, the size of Voyager 2. The MATLAB script developed for this analysis has been verified and the results are acceptable. Nomenclature � = semi-major axis � = eccentricity �� = standard gravitational parameter � = mass � = radius �! = distance to apoapsis �! = distance to periapsis � = time � = velocity �! = hyperbolic excess velocity ∀ = volume of a sphere � = asymptote angle � = aim radius � = phase angle � = density � = period of orbit � = angular velocity I. Introduction Uranus is often over looked as a planet of interest. Its distance from the Earth has played a pivotal role in the prevention of further research into the Ice Giant. Although no one planet in our Solar System should be considered more important than the others, it is often seen that planets like Mars and Saturn are higher points of focus. Uranus is unique in that its irregular orbit, polar locations, and rings could provide a better insight on the history of our solar system. Further investigation into the planet will help provide a basis for possible future missions. Investigation into the nature of Uranus and the nature of natural satellites currently orbiting the Ice Giant will help determine if Oranocentric flight will be possible. II. Objective The general objective of this paper is to provide a basis for future missions to Uranus. This research will be observed in two major parts. Firstly, a discussion will be presented on the topology and history of Uranus, its rings, moons, and atmosphere. A description will be presented on the determination of a launch window, trajectory, and delta V budget necessary to propel a satellite from Earth Parking Orbit 1 Masters Student, Department of Aerospace Engineering, 1 Washington Square, San Jose, CA,95192, Student. 1 San Jose State University to Lower Uranian Orbit (LUO). Secondly, this research will investigate the gravitational perturbations produced on the space vehicle due to the rings of the Ice Giant; this will be described through the development of an N-Body model. III. Background A. History Sir William Herschel first discovered Uranus in the late 18th Century with a home-made telescope. At the time of its discovery, Uranus was deliberated as different celestial bodies ranging from a star to a comet. When Herschel had confirmed the body as a plant of our solar system, he and other astronomers failed to recognize its rings. In 1977, James Elliot, Edward Dunham, and Jessica Mink initially found a total of nine rings in orbit around Uranus via occultation. In 1986 when Voyager flew by Uranus, it had discovered two additional rings. Finally, in 2005, Hubble detected the last two rings of the Ice Giant totaling thirteen. There have been virtually no missions dictated toward the research of Uranus. As it stands, we have never sent any satellites to Uranus, with the exception of the Voyager 2 flyby. This paper and the research provided will potentially outline the necessary information needed to sustain a satellites orbit to LUO. B. General Topology The topology of Uranus is unique in that it is the only planet in the solar system that exhibits a tilted axis of rotation. Uranus faces a 97.7-degree axial tilt with retrograde rotation. Most planets in the solar system exhibit an almost 0 degree axial tilt; this becomes interesting for the development and design of a mission to the Ice Giant. If a satellite were to travel along plane of the solar system, or ecliptic plane, into oranocentric orbit it would face a polar orbit; it important to note that Uranus is 0.773 degrees inclined to the ecliptic. Unlike other planets in the solar system, Uranus’ poles can face extreme exposure to the sun due to the abnormal orientation of the planet. For the purposes of this paper, the mission will intend for LUO flight in polar orbit as to stay aligned with the ecliptic plane. Uranus also experiences an eighty-four year heliocentric orbit; this means it also faces seasonal changes once every estimated twenty-one years. When Voyager 2 passed the south pole of Uranus in 1986, scientists failed to recognize at the time that the reason for its lackluster appearance was due to lack of solar exposure. The Southern Hemisphere, at the time, was in the midst of winter. As will be discussed in more depth in the coming sections, Uranus has thirteen rings and twenty-seven moons with some moons embedded within particular rings. The estimated Perihelion of Uranus is 2,735,569,00 km whereas its Aphelion is 3,006,390,000 km. For the purposes of sustaining lower orbit flight, the atmosphere was also investigated; the constituents of the atmosphere are as follows, 82.5% hydrogen (H2), 15.2% Helium (He), and 2.3% Methane (CH4) as well as various trace compounds. The table attached provides additional information on the general topology of Uranus. Table 1. General Orbit Information on Uranus. Semimajor axis 25,559E6 km Semiminor axis 24,973E6 km Volume 5.914E13 km^3 Average density 1270 kg/m^3 Gravitational Acceleration 8.69 m/s^2 Rings 13 rings Moons 27 observed Sol 17 Earth hours 42 minutes Angular velocity at equator 9315 km/hr Rotation Retrograde Sidereal Period 83.74 Earth years 2 San Jose State University Orbital Velocity 6.83 km/s Perihelion 2,735,569,00 km Aphelion 3,006,390,000 km Orbital eccentricity 0.04717 Orbital inclination to the eliptic 0.77 degrees Obliquity (inclination of equator to Orbit) 97.77 degrees C. Rings Uranus’ rings contain a history of their own. Because of the nature of their orbit around the planet, scientists believe that the rings of Uranus formed much later. There are currently thirteen known rings of Uranus, Zeta, 6,5,4, Alpha, Beta, Eta, Gamma, Delta, Lambda, Epsilon, Mu, and Nu. The table below provides information on the distances between the rings and the surface of Uranus. Table 2. Distances and Eccentricities of the Rings of Uranus. Rings Distance from surface to inner edge Approximate width Eccentricity 1986U2R (also called Zeta) 38,000 km 2,500 km - 6 41,837 km 1.5 km 0.001 5 42,235 km 2 km 0.0019 4 42,571 km 2.5 km 0.001 Alpha 44,718 km 4-10 km 0.0008 Beta 45,661 km 5-11 km 0.0004 Eta 47,179 km 1.6 km - Gamma 47,626 km 1-4 km 0.0001 Delta 48,303 km 3-7 km - Lambda 50,024 km 2 km - Epsilon 51,149 km 20-96 km 0.0079 Rings Distance from surface to inner edge Approximate width Eccentricity R/2003 U 2 3,800 km (Mu) 67,300 km 0 R/2003 U 1 97,700 km 17,000 km (Nu) 0 There does seem to be a difficulty in understanding what the rings are actually composed of. What is known is that the inner eleven rings of Uranus, the dark rings, are composed of dark ice. The outer two rings, the bright red rings, are composed of dust on the scale of micrometers. The objects populating the inner rings are on the magnitude of one to ten meters in size. There is much deliberation and speculation as to what the rings are composed of in terms of object size, density, and material composition. The rings of the planet are nearly circular in shape, as displayed by their eccentricities. D. Moons There are currently twenty-seven known moons of Uranus. Each moon is named after a character created by William Shakespeare or Edgar Allen Poe. The moons, with their distances from the center of 3 San Jose State University Uranus, are listed in table 3 from closest to farthest. The moons Portia and Mab are embedded in the rings Nu and Mu respectively. The other moons orbit Uranus between the rings, with the exception of Miranda which orbits outside the farthest ring, Mab. With that said, the moons of Uranus also exhibit inclination angles to the Uranian plane. Table 3. Moons and their distances from the center of Uranus. Distance Moons (Km) Cordelia 49,752 Ophelia 53,764 Bianca 59,165 Cressida 61,767 Desdemona 62,659 Juliet 64,630 Portia 66,097 Rosalind 69,927 Cupid 74,800 Belinda 75,255 Perdita 76,420 Puck 86,004 Mab 97,734 Miranda 129,390 Ariel 191,020 Umbriel 266,300 Titania 435,910 Oberon 583,520 Francisco 4,276,000 Caliban 7,231,000 Stephano 8,004,000 Trinculo 8,504,000 Sycorax 12,179,000 Margaret 14,345,000 Prospero 16,256,000 Setebos 17,418,000 Ferdinand 20,901,000 E.
Load more

Recommended publications
  • The Utilization of Halo Orbit§ in Advanced Lunar Operation§
    NASA TECHNICAL NOTE NASA TN 0-6365 VI *o M *o d a THE UTILIZATION OF HALO ORBIT§ IN ADVANCED LUNAR OPERATION§ by Robert W. Fmqcbar Godddrd Spctce Flight Center P Greenbelt, Md. 20771 NATIONAL AERONAUTICS AND SPACE ADMINISTRATION WASHINGTON, D. C. JULY 1971 1. Report No. 2. Government Accession No. 3. Recipient's Catalog No. NASA TN D-6365 5. Report Date Jul;v 1971. 6. Performing Organization Code 8. Performing Organization Report No, G-1025 10. Work Unit No. Goddard Space Flight Center 11. Contract or Grant No. Greenbelt, Maryland 20 771 13. Type of Report and Period Covered 2. Sponsoring Agency Name and Address Technical Note J National Aeronautics and Space Administration Washington, D. C. 20546 14. Sponsoring Agency Code 5. Supplementary Notes 6. Abstract Flight mechanics and control problems associated with the stationing of space- craft in halo orbits about the translunar libration point are discussed in some detail. Practical procedures for the implementation of the control techniques are described, and it is shown that these procedures can be carried out with very small AV costs. The possibility of using a relay satellite in.a halo orbit to obtain a continuous com- munications link between the earth and the far side of the moon is also discussed. Several advantages of this type of lunar far-side data link over more conventional relay-satellite systems are cited. It is shown that, with a halo relay satellite, it would be possible to continuously control an unmanned lunar roving vehicle on the moon's far side. Backside tracking of lunar orbiters could also be realized.
    [Show full text]
  • AAS 13-250 Hohmann Spiral Transfer with Inclination Change Performed
    AAS 13-250 Hohmann Spiral Transfer With Inclination Change Performed By Low-Thrust System Steven Owens1 and Malcolm Macdonald2 This paper investigates the Hohmann Spiral Transfer (HST), an orbit transfer method previously developed by the authors incorporating both high and low- thrust propulsion systems, using the low-thrust system to perform an inclination change as well as orbit transfer. The HST is similar to the bi-elliptic transfer as the high-thrust system is first used to propel the spacecraft beyond the target where it is used again to circularize at an intermediate orbit. The low-thrust system is then activated and, while maintaining this orbit altitude, used to change the orbit inclination to suit the mission specification. The low-thrust system is then used again to reduce the spacecraft altitude by spiraling in-toward the target orbit. An analytical analysis of the HST utilizing the low-thrust system for the inclination change is performed which allows a critical specific impulse ratio to be derived determining the point at which the HST consumes the same amount of fuel as the Hohmann transfer. A critical ratio is found for both a circular and elliptical initial orbit. These equations are validated by a numerical approach before being compared to the HST utilizing the high-thrust system to perform the inclination change. An additional critical ratio comparing the HST utilizing the low-thrust system for the inclination change with its high-thrust counterpart is derived and by using these three critical ratios together, it can be determined when each transfer offers the lowest fuel mass consumption.
    [Show full text]
  • Astrodynamics
    Politecnico di Torino SEEDS SpacE Exploration and Development Systems Astrodynamics II Edition 2006 - 07 - Ver. 2.0.1 Author: Guido Colasurdo Dipartimento di Energetica Teacher: Giulio Avanzini Dipartimento di Ingegneria Aeronautica e Spaziale e-mail: [email protected] Contents 1 Two–Body Orbital Mechanics 1 1.1 BirthofAstrodynamics: Kepler’sLaws. ......... 1 1.2 Newton’sLawsofMotion ............................ ... 2 1.3 Newton’s Law of Universal Gravitation . ......... 3 1.4 The n–BodyProblem ................................. 4 1.5 Equation of Motion in the Two-Body Problem . ....... 5 1.6 PotentialEnergy ................................. ... 6 1.7 ConstantsoftheMotion . .. .. .. .. .. .. .. .. .... 7 1.8 TrajectoryEquation .............................. .... 8 1.9 ConicSections ................................... 8 1.10 Relating Energy and Semi-major Axis . ........ 9 2 Two-Dimensional Analysis of Motion 11 2.1 ReferenceFrames................................. 11 2.2 Velocity and acceleration components . ......... 12 2.3 First-Order Scalar Equations of Motion . ......... 12 2.4 PerifocalReferenceFrame . ...... 13 2.5 FlightPathAngle ................................. 14 2.6 EllipticalOrbits................................ ..... 15 2.6.1 Geometry of an Elliptical Orbit . ..... 15 2.6.2 Period of an Elliptical Orbit . ..... 16 2.7 Time–of–Flight on the Elliptical Orbit . .......... 16 2.8 Extensiontohyperbolaandparabola. ........ 18 2.9 Circular and Escape Velocity, Hyperbolic Excess Speed . .............. 18 2.10 CosmicVelocities
    [Show full text]
  • Optimisation of Propellant Consumption for Power Limited Rockets
    Delft University of Technology Faculty Electrical Engineering, Mathematics and Computer Science Delft Institute of Applied Mathematics Optimisation of Propellant Consumption for Power Limited Rockets. What Role do Power Limited Rockets have in Future Spaceflight Missions? (Dutch title: Optimaliseren van brandstofverbruik voor vermogen gelimiteerde raketten. De rol van deze raketten in toekomstige ruimtevlucht missies. ) A thesis submitted to the Delft Institute of Applied Mathematics as part to obtain the degree of BACHELOR OF SCIENCE in APPLIED MATHEMATICS by NATHALIE OUDHOF Delft, the Netherlands December 2017 Copyright c 2017 by Nathalie Oudhof. All rights reserved. BSc thesis APPLIED MATHEMATICS \ Optimisation of Propellant Consumption for Power Limited Rockets What Role do Power Limite Rockets have in Future Spaceflight Missions?" (Dutch title: \Optimaliseren van brandstofverbruik voor vermogen gelimiteerde raketten De rol van deze raketten in toekomstige ruimtevlucht missies.)" NATHALIE OUDHOF Delft University of Technology Supervisor Dr. P.M. Visser Other members of the committee Dr.ir. W.G.M. Groenevelt Drs. E.M. van Elderen 21 December, 2017 Delft Abstract In this thesis we look at the most cost-effective trajectory for power limited rockets, i.e. the trajectory which costs the least amount of propellant. First some background information as well as the differences between thrust limited and power limited rockets will be discussed. Then the optimal trajectory for thrust limited rockets, the Hohmann Transfer Orbit, will be explained. Using Optimal Control Theory, the optimal trajectory for power limited rockets can be found. Three trajectories will be discussed: Low Earth Orbit to Geostationary Earth Orbit, Earth to Mars and Earth to Saturn. After this we compare the propellant use of the thrust limited rockets for these trajectories with the power limited rockets.
    [Show full text]
  • Arxiv:1505.07033V2 [Astro-Ph.IM] 4 Sep 2015
    September 7, 2015 0:46 manuscript Journal of Astronomical Instrumentation c World Scientific Publishing Company A CUBESAT FOR CALIBRATING GROUND-BASED AND SUB-ORBITAL MILLIMETER-WAVE POLARIMETERS (CALSAT) Bradley R. Johnson1, Clement J. Vourch2, Timothy D. Drysdale2, Andrew Kalman3, Steve Fujikawa4, Brian Keating5 and Jon Kaufman5 1Department of Physics, Columbia University, New York, NY 10027, USA 2School of Engineering, University of Glasgow, Glasgow, Scotland G12 8QQ, UK 3Pumpkin, Inc., San Francisco, CA 94112, USA 4Maryland Aerospace Inc., Crofton, MD 21114, USA 5Department of Physics, University of California, San Diego, CA 92093-0424, USA Received (to be inserted by publisher); Revised (to be inserted by publisher); Accepted (to be inserted by publisher); We describe a low-cost, open-access, CubeSat-based calibration instrument that is designed to support ground- based and sub-orbital experiments searching for various polarization signals in the cosmic microwave background (CMB). All modern CMB polarization experiments require a robust calibration program that will allow the effects of instrument-induced signals to be mitigated during data analysis. A bright, compact, and linearly polarized astrophysical source with polarization properties known to adequate precision does not exist. Therefore, we designed a space-based millimeter-wave calibration instrument, called CalSat, to serve as an open-access calibrator, and this paper describes the results of our design study. The calibration source on board CalSat is composed of five \tones" with one each at 47.1, 80.0, 140, 249 and 309 GHz. The five tones we chose are well matched to (i) the observation windows in the atmospheric transmittance spectra, (ii) the spectral bands commonly used in polarimeters by the CMB community, and (iii) The Amateur Satellite Service bands in the Table of Frequency Allocations used by the Federal Communications Commission.
    [Show full text]
  • A Strategy for the Eigenvector Perturbations of the Reynolds Stress Tensor in the Context of Uncertainty Quantification
    Center for Turbulence Research 425 Proceedings of the Summer Program 2016 A strategy for the eigenvector perturbations of the Reynolds stress tensor in the context of uncertainty quantification By R. L. Thompsony, L. E. B. Sampaio, W. Edeling, A. A. Mishra AND G. Iaccarino In spite of increasing progress in high fidelity turbulent simulation avenues like Di- rect Numerical Simulation (DNS) and Large Eddy Simulation (LES), Reynolds-Averaged Navier-Stokes (RANS) models remain the predominant numerical recourse to study com- plex engineering turbulent flows. In this scenario, it is imperative to provide reliable estimates for the uncertainty in RANS predictions. In the recent past, an uncertainty estimation framework relying on perturbations to the modeled Reynolds stress tensor has been widely applied with satisfactory results. Many of these investigations focus on perturbing only the Reynolds stress eigenvalues in the Barycentric map, thus ensuring realizability. However, these restrictions apply to the eigenvalues of that tensor only, leav- ing the eigenvectors free of any limiting condition. In the present work, we propose the use of the Reynolds stress transport equation as a constraint for the eigenvector pertur- bations of the Reynolds stress anisotropy tensor once the eigenvalues of this tensor are perturbed. We apply this methodology to a convex channel and show that the ensuing eigenvector perturbations are a more accurate measure of uncertainty when compared with a pure eigenvalue perturbation. 1. Introduction Turbulent flows are present in a wide number of engineering design problems. Due to the disparate character of such flows, predictive methods must be robust, so as to be easily applicable for most of these cases, yet possessing a high degree of accuracy in each.
    [Show full text]
  • Up, Up, and Away by James J
    www.astrosociety.org/uitc No. 34 - Spring 1996 © 1996, Astronomical Society of the Pacific, 390 Ashton Avenue, San Francisco, CA 94112. Up, Up, and Away by James J. Secosky, Bloomfield Central School and George Musser, Astronomical Society of the Pacific Want to take a tour of space? Then just flip around the channels on cable TV. Weather Channel forecasts, CNN newscasts, ESPN sportscasts: They all depend on satellites in Earth orbit. Or call your friends on Mauritius, Madagascar, or Maui: A satellite will relay your voice. Worried about the ozone hole over Antarctica or mass graves in Bosnia? Orbital outposts are keeping watch. The challenge these days is finding something that doesn't involve satellites in one way or other. And satellites are just one perk of the Space Age. Farther afield, robotic space probes have examined all the planets except Pluto, leading to a revolution in the Earth sciences -- from studies of plate tectonics to models of global warming -- now that scientists can compare our world to its planetary siblings. Over 300 people from 26 countries have gone into space, including the 24 astronauts who went on or near the Moon. Who knows how many will go in the next hundred years? In short, space travel has become a part of our lives. But what goes on behind the scenes? It turns out that satellites and spaceships depend on some of the most basic concepts of physics. So space travel isn't just fun to think about; it is a firm grounding in many of the principles that govern our world and our universe.
    [Show full text]
  • Mission Design for the Lunar Reconnaissance Orbiter
    AAS 07-057 Mission Design for the Lunar Reconnaissance Orbiter Mark Beckman Goddard Space Flight Center, Code 595 29th ANNUAL AAS GUIDANCE AND CONTROL CONFERENCE February 4-8, 2006 Sponsored by Breckenridge, Colorado Rocky Mountain Section AAS Publications Office, P.O. Box 28130 - San Diego, California 92198 AAS-07-057 MISSION DESIGN FOR THE LUNAR RECONNAISSANCE ORBITER † Mark Beckman The Lunar Reconnaissance Orbiter (LRO) will be the first mission under NASA’s Vision for Space Exploration. LRO will fly in a low 50 km mean altitude lunar polar orbit. LRO will utilize a direct minimum energy lunar transfer and have a launch window of three days every two weeks. The launch window is defined by lunar orbit beta angle at times of extreme lighting conditions. This paper will define the LRO launch window and the science and engineering constraints that drive it. After lunar orbit insertion, LRO will be placed into a commissioning orbit for up to 60 days. This commissioning orbit will be a low altitude quasi-frozen orbit that minimizes stationkeeping costs during commissioning phase. LRO will use a repeating stationkeeping cycle with a pair of maneuvers every lunar sidereal period. The stationkeeping algorithm will bound LRO altitude, maintain ground station contact during maneuvers, and equally distribute periselene between northern and southern hemispheres. Orbit determination for LRO will be at the 50 m level with updated lunar gravity models. This paper will address the quasi-frozen orbit design, stationkeeping algorithms and low lunar orbit determination. INTRODUCTION The Lunar Reconnaissance Orbiter (LRO) is the first of the Lunar Precursor Robotic Program’s (LPRP) missions to the moon.
    [Show full text]
  • Spacecraft Guidance Techniques for Maximizing Mission Success
    Utah State University DigitalCommons@USU All Graduate Theses and Dissertations Graduate Studies 5-2014 Spacecraft Guidance Techniques for Maximizing Mission Success Shane B. Robinson Utah State University Follow this and additional works at: https://digitalcommons.usu.edu/etd Part of the Mechanical Engineering Commons Recommended Citation Robinson, Shane B., "Spacecraft Guidance Techniques for Maximizing Mission Success" (2014). All Graduate Theses and Dissertations. 2175. https://digitalcommons.usu.edu/etd/2175 This Dissertation is brought to you for free and open access by the Graduate Studies at DigitalCommons@USU. It has been accepted for inclusion in All Graduate Theses and Dissertations by an authorized administrator of DigitalCommons@USU. For more information, please contact [email protected]. SPACECRAFT GUIDANCE TECHNIQUES FOR MAXIMIZING MISSION SUCCESS by Shane B. Robinson A dissertation submitted in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY in Mechanical Engineering Approved: Dr. David K. Geller Dr. Jacob H. Gunther Major Professor Committee Member Dr. Warren F. Phillips Dr. Charles M. Swenson Committee Member Committee Member Dr. Stephen A. Whitmore Dr. Mark R. McLellan Committee Member Vice President for Research and Dean of the School of Graduate Studies UTAH STATE UNIVERSITY Logan, Utah 2013 [This page intentionally left blank] iii Copyright c Shane B. Robinson 2013 All Rights Reserved [This page intentionally left blank] v Abstract Spacecraft Guidance Techniques for Maximizing Mission Success by Shane B. Robinson, Doctor of Philosophy Utah State University, 2013 Major Professor: Dr. David K. Geller Department: Mechanical and Aerospace Engineering Traditional spacecraft guidance techniques have the objective of deterministically min- imizing fuel consumption.
    [Show full text]
  • Habitability of Planets on Eccentric Orbits: Limits of the Mean Flux Approximation
    A&A 591, A106 (2016) Astronomy DOI: 10.1051/0004-6361/201628073 & c ESO 2016 Astrophysics Habitability of planets on eccentric orbits: Limits of the mean flux approximation Emeline Bolmont1, Anne-Sophie Libert1, Jeremy Leconte2; 3; 4, and Franck Selsis5; 6 1 NaXys, Department of Mathematics, University of Namur, 8 Rempart de la Vierge, 5000 Namur, Belgium e-mail: [email protected] 2 Canadian Institute for Theoretical Astrophysics, 60st St George Street, University of Toronto, Toronto, ON, M5S3H8, Canada 3 Banting Fellow 4 Center for Planetary Sciences, Department of Physical & Environmental Sciences, University of Toronto Scarborough, Toronto, ON, M1C 1A4, Canada 5 Univ. Bordeaux, LAB, UMR 5804, 33270 Floirac, France 6 CNRS, LAB, UMR 5804, 33270 Floirac, France Received 4 January 2016 / Accepted 28 April 2016 ABSTRACT Unlike the Earth, which has a small orbital eccentricity, some exoplanets discovered in the insolation habitable zone (HZ) have high orbital eccentricities (e.g., up to an eccentricity of ∼0.97 for HD 20782 b). This raises the question of whether these planets have surface conditions favorable to liquid water. In order to assess the habitability of an eccentric planet, the mean flux approximation is often used. It states that a planet on an eccentric orbit is called habitable if it receives on average a flux compatible with the presence of surface liquid water. However, because the planets experience important insolation variations over one orbit and even spend some time outside the HZ for high eccentricities, the question of their habitability might not be as straightforward. We performed a set of simulations using the global climate model LMDZ to explore the limits of the mean flux approximation when varying the luminosity of the host star and the eccentricity of the planet.
    [Show full text]
  • Richard Dalbello Vice President, Legal and Government Affairs Intelsat General
    Commercial Management of the Space Environment Richard DalBello Vice President, Legal and Government Affairs Intelsat General The commercial satellite industry has billions of dollars of assets in space and relies on this unique environment for the development and growth of its business. As a result, safety and the sustainment of the space environment are two of the satellite industry‘s highest priorities. In this paper I would like to provide a quick survey of past and current industry space traffic control practices and to discuss a few key initiatives that the industry is developing in this area. Background The commercial satellite industry has been providing essential space services for almost as long as humans have been exploring space. Over the decades, this industry has played an active role in developing technology, worked collaboratively to set standards, and partnered with government to develop successful international regulatory regimes. Success in both commercial and government space programs has meant that new demands are being placed on the space environment. This has resulted in orbital crowding, an increase in space debris, and greater demand for limited frequency resources. The successful management of these issues will require a strong partnership between government and industry and the careful, experience-based expansion of international law and diplomacy. Throughout the years, the satellite industry has never taken for granted the remarkable environment in which it works. Industry has invested heavily in technology and sought out the best and brightest minds to allow the full, but sustainable exploitation of the space environment. Where problems have arisen, such as space debris or electronic interference, industry has taken 1 the initiative to deploy new technologies and adopt new practices to minimize negative consequences.
    [Show full text]
  • 1961Apj. . .133. .6575 PHYSICAL and ORBITAL BEHAVIOR OF
    .6575 PHYSICAL AND ORBITAL BEHAVIOR OF COMETS* .133. Roy E. Squires University of California, Davis, California, and the Aerojet-General Corporation, Sacramento, California 1961ApJ. AND DaVid B. Beard University of California, Davis, California Received August 11, I960; revised October 14, 1960 ABSTRACT As a comet approaches perihelion and the surface facing the sun is warmed, there is evaporation of the surface material in the solar direction The effect of this unidirectional rapid mass loss on the orbits of the parabolic comets has been investigated, and the resulting corrections to the observed aphelion distances, a, and eccentricities have been calculated. Comet surface temperature has been calculated as a function of solar distance, and estimates have been made of the masses and radii of cometary nuclei. It was found that parabolic comets with perihelia of 1 a u. may experience an apparent shift in 1/a of as much as +0.0005 au-1 and that the apparent shift in 1/a is positive for every comet, thereby increas- ing the apparent orbital eccentricity over the true eccentricity in all cases. For a comet with a perihelion of 1 a u , the correction to the observed eccentricity may be as much as —0.0005. The comet surface tem- perature at 1 a.u. is roughly 180° K, and representative values for the masses and radii of cometary nuclei are 6 X 10" gm and 300 meters. I. INTRODUCTION Since most comets are observed to move in nearly parabolic orbits, questions concern- ing their origin and whether or not they are permanent members of the solar system are not clearly resolved.
    [Show full text]