DOCSLIB.ORG

Tracking Techniques for Inclined Orbit Satellites

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Tracking Techniques for Inclined Orbit Satellites TRACKING TECHNIQUES FOR INCUNED ORBIT SATELLITES KHALID S. KHAN Andrew Corporation, Richardson, Tx 75081 July 10, 1990 ABSTRACT coincides with the equatorial plane of the planet Earth. The revolution period Some of the international and domestic of an object with respect to earth is communication satellites have been directly proportional to the distance placed in the inclined orbit. This between the object and the planet Earth. decision is receiving wide support The period of rotation of an object in within the telecommunications industry. a geosynchronous orbit matches that of A satellite in an inclined orbit is the earth, and the object looks expected to operate an additional five stationary. years. These additional operating capabilities of a satellite mean more Kepler's laws govern the rotation of an revenue for the owners and less object in an orbit. They also explain the transponder cost for the users. nature of the curve (orbit), the revolution period, and the height of the This paper discusses and furnishes geosynchronous orbit. current information pertinent to satellite maneuvering in the inclined Kepler's first law' is given by the orbit along with various tracking following equation2: techniques needed to access an inclined orbit satellite. It also suggests a c= R (1) hybrid tracking technique for an 1 + E cos 0 inclined orbit satellite. where : = GENERAL c motion of the curve R = parameter of the second order The destruction of the space shuttle in E = eccentricity mid air coupled with the loss of a few 8 = central angle satellites and launching rockets have been blamed for the current Forgeosynchronous orbit, themotionof difficulties of the satellite industry. the curve 'cl equals to the parameters On the other hand, satellite RF of the second order 'R. ' This condition electronics life and reliability have occurs when the eccentricity 'E' of the increased from approximately seven curve equals to zero. years to almost twelve years. COMSAT has proposed a new scheme, called Similarly, Kepler'sthirdlawdealswith COMSAT Maneuver', to fully maximize the the revolution period of an object in return on its investment. This space. This law is mathematically maneuver is being examined as a described below: technique to offset the problems associated with satellite industry. The ,2 = 4x2 x3 (2) IL fundamental principle of this technique : is to conserve fuel and thus extend the where life of a satellite. T = revolution period p = Kepler's constant GEOSYNCHRONOUS ORBIT = 398 ,513.52 km3/sec2 = Most of the Western commercial x Semi-major axis of elliptical communication satellites are located in orbit and the value of a circular orbit called 'Geosynchronous p = Orbit.' The plane of this orbit GM 14.6.1. 0364 CH2831-619010000-0364$1 .OO 0 1990 IEEE where : .................. G = Universal qravitational constant .................. = 6.67 * 10’ km3/kg/sec2 ....... ....... = h ....... ....... M Mass of planet Earth W W ....... = 5.977 * kg cc ....... 0 ....... ....... and 0W ....... v ....... x=r+H W ....... ....... where : 03 ....... ....... r = Radius of the earth c 0.00 = 6,370 km ....... ....... ‘4 ....... ....... = H Altitude of a satellite W ....... ....... moving in a circular orbit != J ....... ....... _J t-W ....... ....... By substituting the values of x in ....... ....... v, equation (2), it becomes as follow: ~ ....... ....... = + H)3 ,2 4r * (r (3) -5.00 lJ -0.50 -I0.50 Similarly, the velocity of an object SATELLITE LONGITUDE(DEGREE) DIURNAL MOVEMENT OF AN INCLINED ORBIT SATELLITE orbiting in geosynchronous circle can OVER A 7 DAY PERIOD be determined by the equation given below: FIGURE 2.0 satellite revolution period as well as v = J gm/a (4) the velocity. This inclined orbit is an I0’ 7 54 J 1 10 7 5 1 3 2 I 10.23 &5 7 10.21 A5 7 ‘0‘23 45 7 IC ALTITUDE h(km) FIGURE I’ RELAllON 3ETWEfN ALTIIUDI. REVOLUllON PERIOD AND ORBITAL VELOCITY OF A SATELLITE FIGURE 1.0 TIME IN YEAR5 PERFORMANCE PROFILE OF A SYNCHRONOUS ORBIT 5CLAR ARE FIGURE 3.0 Equations (l), (3), and (4) are the founding pillars of a geosynchronous out growth of the geosynchronous orbit orbit. Figure 1.0 shows graphically where inclination is approximately 0.85’ equations (3) and (4). To attain the per year, and this new orbit is called an revolution period of an approximately ‘Inclined Orbit.’ The orbital motion 24 hours, a suitable height of 22,236 starts small and increases with time. The miles was selected for satellites. inclined orbit tends toward an elliptical shape over a period of time, and the If the eccentricity is gradually major axis of this orbit is toward a increased from zero to one then the north-south direction. orbit tends toward an elliptical shape. This change triggers the changes in the There are several benefits in leaving the 14.6.2. 0365 satellite in the inclined orbit: link with the satellite. The communication between the earth station a. To use as a storage orbit and the inclined orbit satellite has the b. To save the expense of replacing following significant drawbacks: satellites c. To provide back-up to primary a. Degradation in the performance of satellites satellite components and equipment d. To provide additional service and after a period of seven years revenue b. Antenna beamwidth c. Extension of orbital inclination of GRAVITATIONAL DISTURBANCES the satellite d. Geographical location ofthe station Disturbing forces such as the gravitational attraction of the sun and Satellite EIRP (Effective Isotropic moon, the radiation pressure of the Radiated Power) , flux density and the G/T sun, and the earth's gravitational (Gain to Total system Temperature) tend field constantly cause a satellite to to decrease over time. This is also true move from its assigned position. The with the solar power supply. Figure 3.0 activity of keeping the satellite in shows a typical depletion of solar array the allocated position is ' called poweroveraperiodof seven years. This llstationkeeping.l*The stationkeeping reduction of satellite power supply requires the satellite to produce its capabilities has some impact on the own power. The propellant fuel which performancedegradation ofthe satellite provides this power is sufficient for parameters. approximately seven years. For continued operation beyond this period, Generally, smaller antennas with larger one of the following alternatives must beamwidth do not require tracking when be implemented: accessing a geosynchronous satellite. This condition is not true for larger a. Carry more fuel in the spacecraft. antennas which wish to track inclined This proposition will increase the orbit satellites. Thisdrawback requires weight of the spacecraft and may frequent periodic corrections in the increase the cost for launching. earth station antenna look angle. b. Curtail some of the satellite The larger inclination of a satellite stationkeeping activities which poses greater problems forthe accessing will have the least impact on the ground station because the movement of characteristics of the satellite. thesatellite is not in synchronization with the movement of the earth. Please INCLINED ORBIT SATELLITE see equation 4.0. It is financially economical and Other parameters, as such, polarization technically feasible to curtail some of isolation and satellite beam coverage the stationkeeping activities. Most drastically change. domestic satellite vendors have opted for east-west stationkeeping only. To offset these problems a stringent There are two basic reasons for this tracking requirement is needed. decision (a) compliance with the FCC rules and (1)) reduction of up to 96% in Someofthe following international and satellite fuel, which is in limited domestic satellites presently orbitring in supply. The deletion of north-south the inclined orbit are INTELSAT stationkeeping activity approximately satellites at 338.5' E and 177' E, two months prior to the end of the GSTAR 111, EUTELSAT F1 at 16' E t>tc. seven years operational period allows the satellite to drift in a figure I8l SATELLITE TRACKING shape. Figure 2 depicts a week of satellite path3 in an inclined orbit. As the satellites started crowding the geosynchronous orbit, trackingbecame an SATELLITE PARAMETERS essential element of an earth station equipped with fairly large-sized Movement of a satellite in the inclined antennas. The decision to incorporate orbit poses problems to an earth tracking into an earth station is station in establishing a communication contingent upon antenna half-power 14.6.3. 0366 beamwidth, satellite orbit and cost. Step tracking systems equipped with The signal strength of a Trajectory Algorithm (TEA) are being used transmit/receive carrier depends upon to track an inclined orbit satellite. The the alignment of antenna beamwidth with TEA approach takes into consideration respect to the satellite. Therefore, it INTELSAT's eleven parameters along with becomes necessary to implement a some additional parameters. tracking system if the antenna has a narrow beamwidth. Program tracking, an accurate way to follow a satellite at Ku-band frequency, The simplest form of a tracking system is a suitable technique for above could be a mechanical driver that moves mentioned case c which requires the antenna boresight axis in a plane. prediction and computation of all Determination of the required movement physical effects acting on the satellite could be achieved in three ways: !a) with respect to time. Pre-determined receive the satellite signal during satellite positions are furnished by entire communication period, (b) track Telemetry Tracking and Control station to the satellite when it is needed, and the transponder users. (c) beam an earth station toward a satellite based upon pre-determined A simple program tracker is not capable position. of peaking an inclined orbit satellite. A program tracking system must be devised In first category, Monopulse tracking, to take into consideration of parameters an expensive technique, utilizes a real similar to INTELSAT's Ephemeris data. The time nulling process with Automatic Ephemeris data may be different for non- Gain Control.
Load more

Recommended publications
  • Analysis of Perturbations and Station-Keeping Requirements in Highly-Inclined Geosynchronous Orbits
    ANALYSIS OF PERTURBATIONS AND STATION-KEEPING REQUIREMENTS IN HIGHLY-INCLINED GEOSYNCHRONOUS ORBITS Elena Fantino(1), Roberto Flores(2), Alessio Di Salvo(3), and Marilena Di Carlo(4) (1)Space Studies Institute of Catalonia (IEEC), Polytechnic University of Catalonia (UPC), E.T.S.E.I.A.T., Colom 11, 08222 Terrassa (Spain), [email protected] (2)International Center for Numerical Methods in Engineering (CIMNE), Polytechnic University of Catalonia (UPC), Building C1, Campus Norte, UPC, Gran Capitan,´ s/n, 08034 Barcelona (Spain) (3)NEXT Ingegneria dei Sistemi S.p.A., Space Innovation System Unit, Via A. Noale 345/b, 00155 Roma (Italy), [email protected] (4)Department of Mechanical and Aerospace Engineering, University of Strathclyde, 75 Montrose Street, Glasgow G1 1XJ (United Kingdom), [email protected] Abstract: There is a demand for communications services at high latitudes that is not well served by conventional geostationary satellites. Alternatives using low-altitude orbits require too large constellations. Other options are the Molniya and Tundra families (critically-inclined, eccentric orbits with the apogee at high latitudes). In this work we have considered derivatives of the Tundra type with different inclinations and eccentricities. By means of a high-precision model of the terrestrial gravity field and the most relevant environmental perturbations, we have studied the evolution of these orbits during a period of two years. The effects of the different perturbations on the constellation ground track (which is more important for coverage than the orbital elements themselves) have been identified. We show that, in order to maintain the ground track unchanged, the most important parameters are the orbital period and the argument of the perigee.
    [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]
  • Small Satellites in Inclined Orbits to Increase Observation Capability Feasibility Analysis
    International Journal of Pure and Applied Mathematics Volume 118 No. 17 2018, 273-287 ISSN: 1311-8080 (printed version); ISSN: 1314-3395 (on-line version) url: http://www.ijpam.eu Special Issue ijpam.eu Small Satellites in Inclined Orbits to Increase Observation Capability Feasibility Analysis DVA Raghava Murthy1, V Kesava Raju2, T.Ramanjappa3, Ritu Karidhal4, Vijayasree Mallikarjuna Kande5, G Ravi chandra Babu6 and A Arunachalam7 1 7 Earth Observations System, ISRO Headquarters, Bengaluru, Karnataka India [email protected] 2 4 5 6ISRO Satellite Centre, Bengaluru, Karnataka, India 3SK University, Ananthapur, Andhra Pradesh, India January 6, 2018 Abstract Over the period of past four decades, Remote Sensing data products and services have been effectively utilized to showcase varieties of applications in many areas of re- sources inventory and monitoring. There are several satel- lite systems in operation today and they operate from Po- lar Orbit and Geosynchronous Orbit, collect the imagery and non-imagery data and provide them to user community for various applications in the areas of natural resources management, urban planning and infrastructure develop- ment, weather forecasting and disaster management sup- port. Quality of information derived from Remote Sensing imagery are strongly influenced by spatial, spectral, radio- metric & temporal resolutions as well as by angular & po- larimetric signatures. As per the conventional approach of 1 273 International Journal of Pure and Applied Mathematics Special Issue having Remote Sensing satellites in near Polar Sun syn- chronous orbit, the temporal resolution, i.e. the frequency with which an area can be frequently observed, is basically defined by the swath of the sensor and distance between the paths.
    [Show full text]
  • Open Rosen Thesis.Pdf
    THE PENNSYLVANIA STATE UNIVERSITY SCHREYER HONORS COLLEGE DEPARTMENT OF AEROSPACE ENGINEERING END OF LIFE DISPOSAL OF SATELLITES IN HIGHLY ELLIPTICAL ORBITS MITCHELL ROSEN SPRING 2019 A thesis submitted in partial fulfillment of the requirements for a baccalaureate degree in Aerospace Engineering with honors in Aerospace Engineering Reviewed and approved* by the following: Dr. David Spencer Professor of Aerospace Engineering Thesis Supervisor Dr. Mark Maughmer Professor of Aerospace Engineering Honors Adviser * Signatures are on file in the Schreyer Honors College. i ABSTRACT Highly elliptical orbits allow for coverage of large parts of the Earth through a single satellite, simplifying communications in the globe’s northern reaches. These orbits are able to avoid drastic changes to the argument of periapse by using a critical inclination (63.4°) that cancels out the first level of the geopotential forces. However, this allows the next level of geopotential forces to take over, quickly de-orbiting satellites. Thus, a balance between the rate of change of the argument of periapse and the lifetime of the orbit is necessitated. This thesis sets out to find that balance. It is determined that an orbit with an inclination of 62.5° strikes that balance best. While this orbit is optimal off of the critical inclination, it is still near enough that to allow for potential use of inclination changes as a deorbiting method. Satellites are deorbited when the propellant remaining is enough to perform such a maneuver, and nothing more; therefore, the less change in velocity necessary for to deorbit, the better. Following the determination of an ideal highly elliptical orbit, the different methods of inclination change is tested against the usual method for deorbiting a satellite, an apoapse burn to lower the periapse, to find the most propellant- efficient method.
    [Show full text]
  • Single Axis Tracking with the RC1500B the Apparent Motion Of
    Single Axis Tracking with the RC1500B The apparent motion of an inclined orbit satellite appears as a narrow figure 8 pattern aligned perpendicular to the geo-stationary satellite arc. As the inclination of the satellite increases both the height and the width of the figure 8 pattern increase. The single axis tracker can follow the long dimension of the figure 8 but cannot compensate for the width of the figure 8 pattern. A paper (available on our web site - http://www.researchconcepts.com/Files/track_wp.pdf) describes the height and width of the figure 8 pattern as a function of the inclination of the satellite’s orbit. Note that the inclination of the satellite increases with time. The maximum rate of increase is approximately 0.9 degrees per year. As the inclination increases, the width of the figure 8 pattern will also increase. This has two implications for system performance. One, the maximum signal loss due to antenna misalignment will increase with time, and two, the antenna must have range a of motion sufficient to accommodate the greatest satellite inclination that will be encountered. Many people feel that single axis tracking is viable for antenna’s up to 3.8 meters at C band and 2.4 meters at Ku band. Implicit in this is the fact that the inclination of most commercial satellites is not allowed to exceed 5 degrees. This assumption should be verified before a system is fielded. A single axis tracking system must be in precise mechanical alignment to minimize loss due to the mount’s inability to compensate for the width of the figure eight pattern.
    [Show full text]
  • Measurement Techniques and New Technologies for Satellite Monitoring
    Report ITU-R SM.2424-0 (06/2018) Measurement techniques and new technologies for satellite monitoring SM Series Spectrum management ii Rep. ITU-R SM.2424-0 Foreword The role of the Radiocommunication Sector is to ensure the rational, equitable, efficient and economical use of the radio- frequency spectrum by all radiocommunication services, including satellite services, and carry out studies without limit of frequency range on the basis of which Recommendations are adopted. The regulatory and policy functions of the Radiocommunication Sector are performed by World and Regional Radiocommunication Conferences and Radiocommunication Assemblies supported by Study Groups. Policy on Intellectual Property Right (IPR) ITU-R policy on IPR is described in the Common Patent Policy for ITU-T/ITU-R/ISO/IEC referenced in Annex 1 of Resolution ITU-R 1. Forms to be used for the submission of patent statements and licensing declarations by patent holders are available from http://www.itu.int/ITU-R/go/patents/en where the Guidelines for Implementation of the Common Patent Policy for ITU-T/ITU-R/ISO/IEC and the ITU-R patent information database can also be found. Series of ITU-R Reports (Also available online at http://www.itu.int/publ/R-REP/en) Series Title BO Satellite delivery BR Recording for production, archival and play-out; film for television BS Broadcasting service (sound) BT Broadcasting service (television) F Fixed service M Mobile, radiodetermination, amateur and related satellite services P Radiowave propagation RA Radio astronomy RS Remote sensing systems S Fixed-satellite service SA Space applications and meteorology SF Frequency sharing and coordination between fixed-satellite and fixed service systems SM Spectrum management Note: This ITU-R Report was approved in English by the Study Group under the procedure detailed in Resolution ITU-R 1.
    [Show full text]
  • P.Roceedings
    Source of Acquisiti on NASA Contractor/Grantee .P .ROCEEDINGS , . -. -. fi.t.... ~ I I I -- -_ .. - T & D [] 0 FIFTH 0 0 S T A T IISPACEI E S CONGRESS COCOA BEACH, FLORIDA I - , , ',- MARCH 11,12,13,14,1968 ~ / 5i: .3 1/, ! ..?t~b , .~ I - , I FOREWORD Each' spring the Canaveral Council of Technical Societies sponsors a symposium devoted to the' accomplishments of oU,r space programs and plans for future activities. These pro­ ceedings provide a permanent record of the papers presented at our Fifth Space Congress held in Cocoa Beach, Florida, March 11 - 14, 1968. The Fifth Space Congress theme, "Our Goals in Space Operations ~ ', was, chosen to provide a forum for engineers and scientists to express individual and corporate views on where our nation should be heading in space operation. The papers presented herein depict the broad and varied views of the industrial organizations and government agencies involved in space activities. We believe that these proceedings will provide technical stimulation and serve as a valuable reference for the scientists and engineers working in our space program. On behalf of the Canaveral Council of Teclmical SOCieties, I wish to express our appreciation to the authors who prepared and presented papers at the Fifth Space Congress. M~/?~~~- EDWARDP. W~ General Chairman Fifth Space Congress • I I TABLE OF CONTENTS (Continued) Session Pages Elliptic Capture Orbits for Missions to the Near Planets by F . G. Casal/B. L. Swenson/ A. C. Mascy of Moffett Field, Calif . .............................................................................. 25.3.1-8 A Venus Lander Probe for Manned Fly-By Missions by P.
    [Show full text]
  • Computing GPS Satellite Velocity and Acceleration from the Broadcast
    Computing GPS Satellite Velocity and Acceleration from the Broadcast Navigation Message Blair F. Thompson , Steven W. Lewis , Steven A. Brown Lt. Colonel, 42d Combat Training Squadron, Peterson Air Force Base, Colorado Todd M. Scott Command Chief Master Sergeant, 310th Space Wing, Schriever Air Force Base, Colorado ABSTRACT We present an extension to the Global Positioning System (GPS) broadcast navigation message user equations for computing GPS space vehicle (SV) velocity and acceleration. Although similar extensions have been published (e.g., Remondi,1 Zhang J.,2 Zhang W.3), the extension presented herein includes a distinct kinematic method for computing SV acceleration which significantly reduces the complexity of the equations and improves the mean magnitude results by approximately one order of magnitude by including oblate Earth perturbation effects. Additionally, detailed anal- yses and validation results using multiple days of precise ephemeris data and multiple broadcast navigation messages are presented. Improvements in the equations for computing SV position are also included, removing ambiguity and redundancy in the existing user equations. The recommended changes make the user equations more complete and more suitable for implementation in a wide variety of programming languages employed by GPS users. Furthermore, relativistic SV clock error rate computation is enabled by the recommended equations. A complete, stand-alone table of the equations in the format and notation of the GPS interface specification4 is provided, along with benchmark test cases to simplify implementation and verification. 1 j INTRODUCTION Basic positioning of a Global Positioning System (GPS) receiver requires accurate modeling of the location of the antenna phase center of four or more orbiting space vehicles (SV) in view.
    [Show full text]
  • This Article Presents the Rudiments of Constellation Design to Familiarize
    This articlepresents the rudiments ofconstellation design to familiarize the reader with some of this field’smethods, issues, and concerns. Two exotic constellations are under consideration for various missions. The traveling-salesman problem The need for satellite constellationsis a natural outgrowth of the need for global communica- tions and intelligence gathering. A single satel- lite can only observea spherical cap regionof the Earth (as illustrated in Figure l), called the in- stantaneous nadir-pointing coverage circle (also tational harmonics,produce an array of constel- referred to as a footprint) of the satellite. The lations with specific propertiesto support Various coverage circle’s area,A, is a function of altitude, mission constraints. Akey point is that constella- h, and the Earth’s radius,R (6,378.14 km), tion design isnot the mere repetitionof a satellite orbit as a template. A(h)= 2a2(1 - COS 0)= 2d2h/(R + h), (1) The aggregate of satellites andorbits presents a totally new systemsproblem with a combina- which is always smaller than the hemisphere’s torial growth in complexity for the most ele- area, 2d2.Hence, we can get a quick estimate mentary analysis questions. The fundamental of the lower boundfor the number, N, of satel- performance metric is constellation geometric- lites with altitude, h, required to provide instan- coverage statistics.Ergodic theory, the multires- taneous global coverageby dividing the Earth’s olution visual calculus, and dynamical systems surface byA(h): theory are some new approachesto constellation design problems. New infrastructures and new N > 4d2/ A(h) = 2 + 2Wh. (2) paradigms willfurther develop this technology. The importance of communications satellite Although Equation 2 is not a tight estimate, it constellations cannot be overstated.
    [Show full text]
  • University of Cincinnati
    UNIVERSITY OF CINCINNATI _____________ , 20 _____ I,______________________________________________, hereby submit this as part of the requirements for the degree of: ________________________________________________ in: ________________________________________________ It is entitled: ________________________________________________ ________________________________________________ ________________________________________________ ________________________________________________ Approved by: ________________________ ________________________ ________________________ ________________________ ________________________ Use of Near-Frozen Orbits for Satellite Formation Flying A thesis submitted to the Division of Research and Advanced Studies of the University of Cincinnati in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE (M.S.) in the Department of Aerospace Engineering and Engineering Mechanics of the College of Engineering 2001 by Heidi L. Davidz B.S., The Ohio State University, 1997 Committee Chair: Dr. Trevor Williams Abstract There is growing interest in flying coordinated clusters of small spacecraft to perform missions once accomplished by single, larger spacecraft. Using these satellite clusters reduces cost, improves survivability, and increases the flexibility of the mission. One challenge in implementing these satellite clusters is maintaining the formation as it experiences orbital perturbations, most notably due to the non-spherical Earth. Certain aspects of the orbital geometry can remain virtually fixed
    [Show full text]
  • For Earth Applications
    NASA TECHNICAL NASA TM X- 71515 MEMORANDUM r- I (NASA-TM-X-71515) WIDE AREA COVERAGE N74-20536 RADAR IMAGING SATELLITE FO, EARTH APPLICATIONS (NASA) 11+- p HC $8.75 117 CSCL 22B Unclas G3/31 33463 WIDE AREA COVERAGE RADAR IMAGING SATELLITE FOR EARTH APPLICATIONS by Grady H. Stevens and James R. Ramer Lewis Research Center Cleveland, Ohio February 1974 This information is being published in prelimi- nary form in order to expedite its early release. WiDE AREA COVERAGE RADAR IMAGING SATELLITE FOR EART APPLICATIONS CONMTNTS Page I. INTRODUCTION ................................................. II. SUMMARY ....................o.............. ................ 5 III. ORBIT CONSIDERATIONS ...................... ................ 19 A. General ................. ....................... ........ 10 B. Sun-Synchronous Orbits ........................ .... 11 1. Orbit Eclipse ................................. .......14 2. Atmospheric Drag ............... 16 a. Orbit Decay ............ ....................... 16 b. Drag Compensation ................................ 20 3. Earth Coverage Patterns .............................. 24 C. Equatorial Orbits ........................................ 29 1. Orbit Eclipse ........................................ 30 2. Earth Coverage Patterns ............................. 30 3. Radiation Damage to Solar Cells .............. ....... 33 IV. RADAR CONSIDERATIONS ...................................... 36 A. General ....................... ................. ....... 36 B. Synthetic Aperture Radar ................................
    [Show full text]
  • Demonstration of the COBRA Teardrop Concept Using Two Smallsats in 8-Hour Elliptic Orbits
    SSC01-II-3 Demonstration of the COBRA Teardrop Concept Using Two Smallsats in 8-Hour Elliptic Orbits Authors/POC*: John E. Draim* Vice President, Astrodynamics and Launch Vehicles Space Resource America Corp. 1101 Pennsylvania Ave., Suite 600 Washington, D.C. 20004 Tel: (202) 756-4390 Fax: (202) 756-7441 e-mail: [email protected] Dr. Richard Inciardi Senior Vice President & General Manager, Program Operations Group Space Resource America Corp. Washington, D.C. Dr. Paul Cefola Technical Staff MIT Lincoln Laboratory Lexington, MA Dr. Ron Proulx Dr. David Carter Principal Member, Technical Staff Principal Member, Technical Staff The Charles Stark Draper Laboratory The Charles Stark Draper Laboratory Cambridge, MA Cambridge, MA ABSTRACT: Space Resource America Corporation is engaged in developing new concepts for communications satellite systems that will avoid interference with any of the Geostationary satellites and can provide a significant increase in global capacity compared with that of the GEO ring. Additionally, since all satellites in such a system are flying in formation, they will not interfere with each other. The company has filed for a series of patents on the orbital arrays, or constellations, that appear to hold the most promise in satisfying both commercial and government requirements. Each of the three active arcs of a single 8-hour satellite has a ground trace that resembles a coiled COBRA, and the orbits were so named. The acronym-like name COBRA was later amplified to “Communications Orbiting Broadband Repeating Arrays”. One of these arrays employs six 8-hour period leaning elliptical orbit satellites describing three continuous closed paths in the Northern Hemisphere.
    [Show full text]