Orbits Learning Objective to Explain How Objects Travel in an Orbit

Total Page:16

File Type:pdf, Size:1020Kb

Orbits Learning Objective to Explain How Objects Travel in an Orbit KS3 Space Lesson 5: Orbits Learning Objective To explain how objects travel in an orbit. Success Criteria • To define what an orbit is. • To describe the difference between a natural satellite and a humanly- constructed satellite. • To investigate the relationship between time period and radius of an orbit. Target: 10 Points 1 Point 2 Points2 Points 3 Points 3 Points SunWhat is at the centre of ourMercury, List Venus, the planets Earth, in orderOur planet Explainhas an atmospherewhy there is whichlife on Solar System? Mars, startingJupiter, Saturn,from the centrecontains of the theEarth correct but mixturenot on other of gases to UranusSolar and System Neptune. and travellingsustain life.planets This is duein our to Solar System. outwards. photosynthesis and the production of oxygen. Earth is at just the right distance from the Sun which allows water to exist as a liquid on its surface. Which is the largest planet? Explain why Pluto is no longer Explain why no other Jupiter Pluto isdescribed now known as a as planet. a Other planetsplanets are too or galaxiesfar away have from dwarf planet. It is much Earth for mannedbeen explored spacecraft by humans.to get to. smaller than the other Other galaxies are much too far away. planets in our solar system and has an orbit on a different plain. Which planet is closest to What is a light year? Describe, in one paragraph, theMercury Sun? The distance light travels A day (24 hours)the difference is the time between taken for in a year. In a year, light the Earth todays, spin months once on and its axis. years. A can travel around 10 year (365 days) is the time taken for the trillion km. Earth to orbit the Sun. A month (approximately 28 days) is the time it takes for the moon to orbit the Earth. Orbits An orbit is a curved path that an object takes around another object. An object that orbits another object is called a satellite. A satellite orbits an object when its speed is balanced by the object’s gravitational force. There are natural satellites, for There are humanly-constructed example: satellites, for example: • The Earth’s moon. • communication satellites • The planets orbiting the Sun. • navigation satellites • GPS satellites • polar satellites Orbits This image is computer generated by NASA. It shows all of the objects in Earth’s orbit that were being tracked in 2005. Only around 5% of these dots are functional satellites and the rest are debris. Image by [Wikimedia.org] is licensed under CC BY 2.0 There is a ring of objects around 35,786km above the Earth’s equator. They are in geostationary orbit. These satellites travel in the same direction and at the same rate as Earth is spinning. From Earth, these satellites look like they are standing still because they are always above the same place on Earth. The animation shows a satellite in geostationary orbit. Orbits The other common type of orbit is made by a polar satellite. Polar-orbiting satellites travel north to south, crossing over both poles. Their orbit is fixed in space so as they travel, the Earth rotates inside their orbit. This means these satellites are able to scan the entire surface of the Earth in a day. Polar satellites: useful if you want to scan the entire Earth. Geostationary satellites: useful if you want to bounce signals to and from them because you will always know where they are. Types of Satellites Put the different satellites into the correct columns in the table. Natural Satellites Humanly-Constructed Satellites Geostationary Polar Mars communications weather forecasting Earth’s moon GPS military observations Halley’s comet TV Earth’s moon Halley’s comet Mars military observation satellites communications satellites navigation (GPS) satellite weather forecasting satellites TV satellites Keywords Write definitions for these keywords. An orbit: a curved path that an object takes around another object. A satellite: an object that orbits around another object. Sketch a quick diagram of a satellite in orbit around Earth. Can you name the type of orbit you have drawn? geostationary orbit polar orbit Investigating Orbits Method 1. Find a clear space in the room, away from other people and any obstacles. 2. Measure the length of string attached to your bung and check it is 100cm long. 3. Time how long it takes to swing the bung around your head once and record the result. 4. Repeat for 80cm, 60cm, 40cm and 20cm lengths of string. How could we improve this investigation? Investigating Orbits Method 1. Find a clear space in the room, away from other people and any obstacles. 2. Measure the length of string attached to your bung and check it is 100cm long. 3. Time how long it takes to swing the bung around10 times your around head your once head.and record Divide the the result.measurement by 10 and record the result. 4. Repeat forthree 80cm, times 60cm, and 40cm calculate and 20cm an average. lengths of string. 5. Repeat for 80cm, 60cm, 40cm and 20cm lengths of string. Keywords AHow result do iswe accuraterepeatable calculateif the itif isthe average? close original to the experimenter true value. repeats the investigation using the Addsame up method the three and measurementsequipment and gets and the divide same the results. total by three. How could we improve the accuracy of this investigation? How will we know if our results are repeatable? Time how long it takes to swing the bung 10 times around your head. Divide the measurementRepeat three times by 10 and and calculate record the an result. average. Investigating Orbits Length of Time for 10 Orbits (s) Average Time Average Time for String for 10 Orbits (s) One Orbit (s) (cm) Repeat 1 Repeat 2 Repeat 3 100 7.00 6.70 6.78 6.83 0.68 80 6.13 6.08 6.03 6.08 0.61 60 5.21 5.38 5.66 5.42 0.54 40 3.71 4.11 3.72 3.85 0.39 20 2.14 2.40 2.29 2.28 0.23 What is the relationship between the length of the string and the time taken to orbit? As the length of the string decreases, the time taken for the object to orbit decreases. Planet Orbits Planet Orbit Time (days) Velocity (m/s) Mercury 88 47.4 Venus 225 35.0 Earth 365 29.8 Mars 687 24.1 Jupiter 4331 13.1 Saturn 10 747 9.7 Uranus 30 589 6.8 Neptune 59 800 5.4 UseThink the back results to your from investigation. your investigation At which to predictlength did what the will bung happen spin theto the fastest? orbit time of the planets as they get further from the Sun. Predict what will happen to the velocity of the orbits as the planets get further from theAs the Sun. planets get further from the Sun, the time taken to orbit increases. As the planets get further from the Sun, the velocity decreases. Extension There is a ring of objects around 35,786km above the Earth’s equator. They are in geostationary orbit. These satellites travel in the same direction and at the same rate as the Earth is spinning. From Earth, these satellites look like they are standing still because they are always above the same place on Earth. Why do all geostationary satellites need to be at the same height above Earth? The distance above the Earth affects the time an orbit takes. To orbit the Earth in the time it takes for the Earth to rotate once, this distance needs to be 35,786km. Image by [Wikimedia.org] is licensed under CC BY 2.0 Escape the Room! Answer the following questions to gain the code, allowing you to leave the classroom. 1. Neptune is the 8 th planet from the Sun. 2. There are 4 letters in the name of the Earth’s natural satellite. (moon) 3. The time it takes for the Earth to orbit the Sun is 365 days. Leaving Code: 8 , 4 , 3 , 6 , 5 , .
Recommended publications
  • 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]
  • 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]
  • 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]
  • Sun-Synchronous Satellites
    Topic: Sun-synchronous Satellites Course: Remote Sensing and GIS (CC-11) M.A. Geography (Sem.-3) By Dr. Md. Nazim Professor, Department of Geography Patna College, Patna University Lecture-3 Concept: Orbits and their Types: Any object that moves around the Earth has an orbit. An orbit is the path that a satellite follows as it revolves round the Earth. The plane in which a satellite always moves is called the orbital plane and the time taken for completing one orbit is called orbital period. Orbit is defined by the following three factors: 1. Shape of the orbit, which can be either circular or elliptical depending upon the eccentricity that gives the shape of the orbit, 2. Altitude of the orbit which remains constant for a circular orbit but changes continuously for an elliptical orbit, and 3. Angle that an orbital plane makes with the equator. Depending upon the angle between the orbital plane and equator, orbits can be categorised into three types - equatorial, inclined and polar orbits. Different orbits serve different purposes. Each has its own advantages and disadvantages. There are several types of orbits: 1. Polar 2. Sunsynchronous and 3. Geosynchronous Field of View (FOV) is the total view angle of the camera, which defines the swath. When a satellite revolves around the Earth, the sensor observes a certain portion of the Earth’s surface. Swath or swath width is the area (strip of land of Earth surface) which a sensor observes during its orbital motion. Swaths vary from one sensor to another but are generally higher for space borne sensors (ranging between tens and hundreds of kilometers wide) in comparison to airborne sensors.
    [Show full text]
  • Rockets and Space Travel
    Rockets and Space Travel ASTR 101 10/15/2018 1 Rockets and Space travel • Airplane: – glides in air, burns fuels in air. • Rocket: – travels in empty space, – has to carry both fuel and the oxidizer Rocket pushed (for example liquid oxygen and hydrogen). upward • The chemical reaction (burning) between the fuel and the oxidizer generates a large volume of hot exhaust gases which is expelled through a nozzle at a high gas velocity. pushed downward • What moves a rocket forward is the thrust exerted on the rocket by escaping hot gas. according to the Newton’s third law: “for every action there is an equal and opposite reaction” – Rocket pushes exhaust gases out – Exhaust gas pushes the rocket in the opposite direction. Like air rushing from a balloon pushes the balloon forward 2 There are several types of rocket engines: Solid fuel rocket engines: – The fuel and the oxidizer in solid form are premixed and stored in the combustion chamber. • for example: gunpowder (charcoal and potassium solid fuel nitrate earliest type), or aluminum power and mixture ammonium perchlorate( type of a modern rocket fuel). – Once ignited mixture burns and produce hot gases, which combustion escape though a nozzle at the end of the chamber chamber producing the thrust. They are: nozzle – simple, – relatively inexpensive – produce a larger thrust – but lacks controllability • can't be turned off once the burn starts, it goes until all of fuel is used up. 3 • Liquid fuel rocket : – The Fuel and oxidizer (usually liquid Oxygen) are in liquid form, stored in separate tanks. – Fuel and the oxidizer are injected into the combustion chamber by mechanical pumps where they are combined fuel and burned.
    [Show full text]
  • SATELLITES ORBIT ELEMENTS : EPHEMERIS, Keplerian ELEMENTS, STATE VECTORS
    www.myreaders.info www.myreaders.info Return to Website SATELLITES ORBIT ELEMENTS : EPHEMERIS, Keplerian ELEMENTS, STATE VECTORS RC Chakraborty (Retd), Former Director, DRDO, Delhi & Visiting Professor, JUET, Guna, www.myreaders.info, [email protected], www.myreaders.info/html/orbital_mechanics.html, Revised Dec. 16, 2015 (This is Sec. 5, pp 164 - 192, of Orbital Mechanics - Model & Simulation Software (OM-MSS), Sec 1 to 10, pp 1 - 402.) OM-MSS Page 164 OM-MSS Section - 5 -------------------------------------------------------------------------------------------------------43 www.myreaders.info SATELLITES ORBIT ELEMENTS : EPHEMERIS, Keplerian ELEMENTS, STATE VECTORS Satellite Ephemeris is Expressed either by 'Keplerian elements' or by 'State Vectors', that uniquely identify a specific orbit. A satellite is an object that moves around a larger object. Thousands of Satellites launched into orbit around Earth. First, look into the Preliminaries about 'Satellite Orbit', before moving to Satellite Ephemeris data and conversion utilities of the OM-MSS software. (a) Satellite : An artificial object, intentionally placed into orbit. Thousands of Satellites have been launched into orbit around Earth. A few Satellites called Space Probes have been placed into orbit around Moon, Mercury, Venus, Mars, Jupiter, Saturn, etc. The Motion of a Satellite is a direct consequence of the Gravity of a body (earth), around which the satellite travels without any propulsion. The Moon is the Earth's only natural Satellite, moves around Earth in the same kind of orbit. (b) Earth Gravity and Satellite Motion : As satellite move around Earth, it is pulled in by the gravitational force (centripetal) of the Earth. Contrary to this pull, the rotating motion of satellite around Earth has an associated force (centrifugal) which pushes it away from the Earth.
    [Show 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.
    [Show full text]
  • The UCS Satellite Database
    UCS Satellite Database User’s Manual 1-1-17 The UCS Satellite Database The UCS Satellite Database is a listing of active satellites currently in orbit around the Earth. It is available as both a downloadable Excel file and in a tab-delimited text format, and in a version (tab-delimited text) in which the "Name" column contains only the official name of the satellite in the case of government and military satellites, and the most commonly used name in the case of commercial and civil satellites. The database is updated roughly quarterly. Our intent in producing the Database is to create a research tool by collecting open-source information on active satellites and presenting it in a format that can be easily manipulated for research and analysis. The Database includes basic information about the satellites and their orbits, but does not contain the detailed information necessary to locate individual satellites. The UCS Satellite Database can be accessed at www.ucsusa.org/satellite_database. Using the Database The Database is free and its use is unrestricted. We request that its use be acknowledged and referenced in written materials. References should include the version of the Database that was used, which is indicated by the name of the Excel file, and a link to or URL for the webpage www.ucsusa.org/satellite_database. We welcome corrections, additions, and suggestions. These can be emailed to the Database manager at [email protected] If you would like to be notified when updated versions of the Database are completed, please send an email request to this address.
    [Show full text]
  • Remote Sensing I: Basics
    Remote Sensing I: Basics Kelly M. Brunt Earth System Science Interdisciplinary Center, University of Maryland Cryospheric Science Laboratory, NASA Goddard Space Flight Center [email protected] (Based on Nick Barrand’s UAF Summer School in Glaciology 2014 lecture) ROUGH Outline: Electromagnetic Radiation Electromagnetic Spectrum NASA Satellites and the Electromagnetic Spectrum Passive & Active instruments Types of Survey Methods Types of Orbits Resolution Platforms & Sensors (Speaker’s bias: NASA, lidar, and Antarctica…) Electromagnetic Radiation - Energy derived from oscillating magnetic and electrostatic fields - Properties include wavelength (, in m) and frequency (, in Hz) related to (speed of light, 299,792,458 m/s) by: Wikipedia Electromagnetic Radiation Electromagnetic Spectrum NASA (increasing frequency…) Electromagnetic Radiation Electromagnetic Spectrum NASA (increasing wavelength…) Radiation in the Atmosphere NASA Cryosphere Specular: Smooth surface; energy reflected in 1 direction (e.g., sea ice lead) Diffuse: Rough surface; energy reflected in many directions (e.g., pressure ridges) Nick Barrand, UAF Summer School in Glaciology, 2014 NASA Earth-orbiting Satellites (‘observatory’ or ‘bus’) NASA Satellite, observatory, or bus: everything (i.e., instrument, thrust, power, and navigation components…) e.g., Terra Instrument: the part making the measurement; often satellites have suites of instruments e.g., ASTER, MODIS (on satellite Terra) NASA Earth-orbiting Satellites (‘observatory’ or ‘bus’) Radio & Optical; weather Optical;
    [Show full text]
  • Chapter 11 Satellite Orbits
    CHAPTER 11 SATELLITE ORBITS 11.1 Orbital Mechanics Newton's laws of motion provide the basis for the orbital mechanics. Newton's three laws are briefly (a) the law of inertia which states that a body at rest remains at rest and a body in motion remains in motion unless acted upon by a force, (b) force equals the rate of change of momentum for a body, and (c) the law of equal but opposite forces. For a two body system comprising of the earth and a much smaller object such as a satellite, the motion of the body in the central gravitational field can be written → → dv / dt = -GM r / r3 → where v is the velocity of the body in its orbit, G is the universal gravitational constant (6.67 x 10**11 N m**2/kg**2), M is the mass of the earth, and r is position vector from the centre of mass of the system (assumed to be at the centre of the earth). The radial part of this equation has the more explicit form m d2r/dt2 - mrω2 = -GMm/r2 where ω is the angular velocity and m is the satellite mass. The second term on the left side of the equation is often referred to as the centrifugal force The total energy of the body in its orbit is a constant and is given by the sum of the kinetic and potential energies E = 1/2 m [(dr/dt)2 + r2ω2] - mMG/r . The angular momentum is also conserved so that L = mωr2 , which allows us to rewrite the energy E = 1/2 m (dr/dt)2 + L2/(2mr2) - mMG/r .
    [Show full text]
  • Determining and Evaluating the Hydrological Signal in Polar Motion Excitation from Gravity Field Models Obtained from Kinematic Orbits of LEO Satellites
    remote sensing Article Determining and Evaluating the Hydrological Signal in Polar Motion Excitation from Gravity Field Models Obtained from Kinematic Orbits of LEO Satellites Justyna Sliwi´ ´nska* and Jolanta Nastula Space Research Centre, Polish Academy of Sciences, 00-716 Warsaw, Poland * Correspondence: [email protected] Received: 27 June 2019; Accepted: 27 July 2019; Published: 30 July 2019 Abstract: This study evaluates the gravity field solutions based on high-low satellite-to-satellite tracking (hl-SST) of low-Earth-orbit (LEO) satellites: GRACE, Swarm, TerraSAR-X, TanDEM-X, MetOp-A, MetOp-B, and Jason 2, by converting them into hydrological polar motion excitation functions (or hydrological angular momentum (HAM)). The resulting HAM series are compared with the residuals of observed polar motion excitation (geodetic residuals, GAO) derived from precise geodetic measurements, and the HAM obtained from the GRACE ITSG 2018 solution. The findings indicate a large impact of orbital altitude and inclination on the accuracy of derived HAM. The HAM series obtained from Swarm data are found to be the most consistent with GAO. Visible differences are found in HAM obtained from GRACE and Swarm orbits and provided by different processing centres. The main reasons for such differences are likely to be different processing approaches and background models. The findings of this study provide important information on alternative data sets that may be used to provide continuous polar motion excitation observations, of which the Swarm solution provided by the Astronomical Institute, Czech Academy of Sciences, is the most accurate. However, further analysis is needed to determine which processing algorithms are most appropriate to obtain the best correspondence with GAO.
    [Show full text]