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IT 284 Unit 8 Seminar

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Navigation

* Stars at fixed locations (celestial sphere)

Stars at fixed locations could be used to locate position on the earth

The octant and sextant

Astrolabe (~400) Octant (1731) Sextant (1759)

McGraw-Hill & US Space Command

What Stars Tell Us

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Every Celestial Body has a Ground Point - GP

Sextant AngleGP

GP

Nautical Almanac had GP for all times every day

McGraw-Hill & US Space Command

Taking a Sight

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What Time is it?

What Angle is it?

What Body are we Looking at?

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Sextant Measures Angles - Nothing More!

McGraw-Hill & US Space Command

• Sir Isaac Newton1643-1727, London, England

– Laws of Motion– Universal Law of Gravity

• Johannes Kepler1571-1630, Regensburg, Germany– Three Laws of Planetary

Motion

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Newton & Kepler’s study of our UniverseLaid the Foundation of Orbital Mechanics

Johannes KeplerSir Isaac Newton

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Laws of Planetary Motion

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Law of Planetary Motion

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McGraw-Hill & US Space Command

Law of Planetary Motion

• Ratio of the squares of the revolutionary periods for two planets is equal to the ratio of the cubes of their semimajor axes.

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Orbits – The Big Picture

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• Orbits are “racetracks” that satellites “drive” around Earth• A satellite’s orbit is fixed in space• The Earth rotates under the orbit• But the satellite’s orbital plane stays fixed

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Figure 17.13 Satellite orbits

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Space MissionsOperating Satellites on Orbit

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Boeing 702 Expanded View

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Basic Elements of a Satellite

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Payload

+Vehicle or “Bus”

=

Satellite

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Satellite Subsystems

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PowerTo Operate in

Space

ThermalHeating & Cooling

StructuralTo Protect the Satellite Communications

To Operate the Satellite

Attitude Determination and Control

To control positioning

Navigation, Guidance and Control

To safely maneuver in space

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Operating Satellite ConstellationsYou need Ground Processing and

Communications Links!

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The Space EnvironmentA Tough Place to Operate!

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Orbital Maneuvers

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• Perturbations alter an Orbit:Atmospheric Drag – “Scraping” the Earth’s atmosphereEarth Oblateness -- Causes north/south wandering of GEO satellitesSolar Effects – Radiation, particle discharge, geo-magnetic stormsThird Body Affects – Gravitational pull

• Maneuvers are required to maintain an orbit

VLunar Gravity

Earth Gravity

Solar Gravity

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Figure 17.14 Satellite categories

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Figure 17.15 Satellite orbit altitudes

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Figure 17.17 Triangulation

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Figure 17.18 GPS

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Global Positioning SystemGlobal Positioning System

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GPS CONSTELLATION

• Precise worldwide position, speed, and time • 6 orbital planes• 4 satellites in each plane• 24 satellite constellation• Medium Earth Orbit (12,500 miles from Earth)

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Geodetic Datum

• Defines the size and shape of the earth• Origin and orientation of the coordinate

systems• Branch of mathematics dating back to

Babylonian times (3500 BC)• Types include Horizontal, Vertical and

Complete

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Figure 17.20 Iridium constellation

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Satellite ConstellationsSatellite Constellations

• Iridium – First LEO Satellite communications system• 66 satellite constellation (plus 14 spares)• Provides worldwide phone coverage

Iridium Low Earth Orbit Constellation

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What is Handover?

• Leo Satellites circulate the Earth at a constant speed.

• Coverage area of a LEO satellite changes continuously.

• Handover is necessary between end-satellites.

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Iridium Network

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Iridium Network (cont.)

• 4.8 kbps voice, 2.4 Kbps data• TDMA• 80 channels /beam• 3168 beams globally (2150 active beams)• Dual mode user handset• User-Satellite Link = L-Band• Gateway-Satellite Link = Ka-Band• Inter-Satellite Link = Ka-Band

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