McGraw-Hill & US Space Command 2
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
4
What Time is it?
What Angle is it?
What Body are we Looking at?
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2
3
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
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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McGraw-Hill & US Space Command
Orbits – The Big Picture
9
• 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
McGraw-Hill & US Space Command
Space MissionsOperating Satellites on Orbit
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Boeing 702 Expanded View
McGraw-Hill & US Space Command
Basic Elements of a Satellite
12
Payload
+Vehicle or “Bus”
=
Satellite
McGraw-Hill & US Space Command
Satellite Subsystems
13
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
McGraw-Hill & US Space Command
Operating Satellite ConstellationsYou need Ground Processing and
Communications Links!
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McGraw-Hill & US Space Command
Orbital Maneuvers
16
• 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
McGraw-Hill & US Space Command
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)
McGraw-Hill & US Space Command
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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McGraw-Hill & US Space Command 24
Satellite ConstellationsSatellite Constellations
• Iridium – First LEO Satellite communications system• 66 satellite constellation (plus 14 spares)• Provides worldwide phone coverage
Iridium Low Earth Orbit Constellation
McGraw-Hill & US Space Command
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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