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Gen William L Shelton, CinC USAF Space Command Speech to U.S. National Space Symposium, 12 Apr 11

Satellite & Data Communication for Air Cadets. “Our dependence [on space] has never been higher. In fact, it’s integrated into how we fight wars today so deeply that it is hard to imagine taking space out of the equation.”. Gen William L Shelton, CinC USAF Space Command

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Gen William L Shelton, CinC USAF Space Command Speech to U.S. National Space Symposium, 12 Apr 11

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  1. Satellite & Data Communication for Air Cadets “Our dependence [on space] has never been higher. In fact, it’s integrated into how we fight wars today so deeply that it is hard to imagine taking space out of the equation.” Gen William L Shelton, CinC USAF Space Command Speech to U.S. National Space Symposium, 12 Apr 11

  2. Unit Aim The aim of this unit is to give learners knowledge of satellite and data communication systems and networks for Air Cadets. CLASSIFICATION UNCLASSIFIED

  3. Unit Introduction This unit gives learners knowledge of satellite and data communication systems and networks that are required at ATC Senior and Master Air Cadet level. This unit introduces the principles and equipment used in satellite and data communication. It explores the types, orbits and roles and construction of satellites, and describes the basic function of a Global Positioning System. The unit also develops an understanding of types of data communications networks and mobile communication.

  4. Learning Outcomes On completion of this unit a learner should: • Know main types and roles of satellites and principles of earth orbit. • Know components and principles of a Global Positioning System • Know principles of data communication • Know types and roles of mobile communication

  5. UK Space Primer

  6. Scope • The Space Environment • Orbits • Launch • The Global Positioning System • The Principles of Data Communication • The Types & Roles of Mobile Communication • Summary • Questions

  7. The Space Environment Reference: Chapter 1; UK Space Primer 7

  8. Space Characteristics • No geographical boundaries • Freedom of movement • Unique characteristics

  9. The Boundary Between Air & Space 150km Spacecraft in orbit 100km Limit of aerodynamic control 80km US Definition 150 100 80 9

  10. The Space Environment An environment characterised by: High energy particles Fluctuating magnetic fields Variable temperatures No aerodynamic forces The laws of orbital motion 10

  11. Key Environmental Regions Magnetosphere Exosphere Thermosphere Mesosphere Ionosphere Space Weather Stratosphere Troposphere Terrestrial Weather 11

  12. Orbits - Definition of Terms

  13. Apogee and Perigee Apogee Furthest point from Earth Perigee Closest point to Earth

  14. Ground Trace A ground trace is the projection of a satellite’s 3D orbit onto the earth’s surface as a 2D representation

  15. Common Orbits ~800-40,000 km 11 HRS 58 MIN ~26,000-8,000 KPH HEO MEO GEO LEO Orbit size determines time for one orbit Orbit size and shape also determines the speed Earth NOT to scale ! 850 km 101 MINUTES 24,600 KPH ~20,830 km 11 HRS 58 MIN ~14,330 KPH ~36,160 km 23 HRS 56 MIN ~11,160 KPH

  16. Orbital Mechanics Basic Orbits Include: Low Earth Orbit (LEO), including sun-synchronous Medium Earth Orbit (MEO) Also called semi-synchronous Geosynchronous Earth Orbit (GEO) including Geostationary. Highly Elliptical Orbit (HEO) including Molniya Spacecraft obey Kepler, not Bernoulli Satellite manoeuvres require Deliberate planning Time Fuel (limited)

  17. Low-Earth Orbit (LEO) Altitude 160 – 2000 km

  18. LEO Orbit – 2D Ground Trace

  19. Sun-Synchronous Orbits • Near-Polar, 97°-99° Inclination • 760 - 860 km

  20. LEO Sun-Synchronous Orbit2D Ground Trace

  21. Medium Earth Orbits (MEO) 2D Ground Trace Period: 2 – 24hrs Average = 12 hour period Altitude: 2000 – 35786 km, Near Circular Average 20,800 km

  22. Geostationary

  23. Highly Elliptical Orbits (HEO) Apogee High Altitude Perigee Low Altitude

  24. HEO

  25. HEO 2D Ground Trace

  26. Orbital Example – Earth Fixed

  27. Orbital Pertubations

  28. Effect of the Atmosphere Atmosphere Orbital Decay

  29. Effect of the Earth’s Shape 15m N Pole 7.5m 7.5m 12 714 km EQUATOR 12 756 km TOP VIEW SIDE VIEW 15m

  30. Orbital Pertubations These are subtle but accumulative effect on an orbit Nodal regression The orbital plane effectively twists around the earth This is because of the shape of the Earth. This effect is known as Orbital Twist. Perigee Rotation This effect appears as a twisting of the satellites position relative to the Equator. Therefore, satellites need to be managed, in effect ‘flown’.

  31. Applications of Orbits LEO Earth Observation with resolution Communications MEO Missions Global Navigation Satellite Systems GEO Communications Earth Observation with persistence HEO Communications Earth Observation with persistence

  32. Persistence………

  33. …….versus Resolution

  34. Orbital Requirements GEO LEO c.700 Coverage Dwell Time Revisit Time Resolution & Power Requirements

  35. Achieving Orbit

  36. Initial Launch Direct ascent into low altitude orbit

  37. Data Table

  38. Hohman Transfer Orbit Initial Orbit Transfer Orbit Final Orbit

  39. On Orbit Manoeuvre Basics Attain initial on-orbit station. Maintain assigned position (all Geo satellites). Modify orbit to meet new mission requirements. On-board motors (“thrusters”) are fitted to modify the satellite’s orbit to:

  40. Repositioning Primarily for GEO satellites . Using fuel shortens life. Takes weeks or months to complete the manoeuvre. Takes capability away from users. Moving satellite to a higher or lower orbit:

  41. The Global Positioning System (GPS) 42

  42. 2nd USAF Space Operations Squadron

  43. System Description Space Segment • Navigational Signals • Ranging Codes • System Time • Clock Correction • Propagation Delay • Satellite Ephemeris • Satellite Health • Downlink Data • Satellite Ephemeris Data • Clock Data • Uplink Data • Satellite Ephemeris Corrections • Clock Data Corrections User Segment Control Segment

  44. SPACE SEGMENT

  45. GPS Satellites 24-satellite constellation Six orbital planes, four satellites per plane Semi-synchronous, circular orbits (~11,000 mi) 12-hr ground-repeating orbits

  46. Orbital Planes The GPS Constellation utilises the Medium Earth Orbit

  47. CONTROL SEGMENT

  48. Control Segment GPS Satellite S Band Up/ Downlink Downlink Satellite Links Satellite Links Uplink Station Master Control Station Transmit: - Navigation Data - Commands Collect Telemetry Monitor Stations Collect Range Data Monitor Navigation Services Navigation Estimation Satellite Control Systems Operation

  49. USER SEGMENT

  50. GPS Services Standard Positioning Service (SPS) Uses Coarse Acquisition Code (C/A Code) only Models Ionospheric errors Think ‘civilian GPS’ Precise Positioning Service (PPS) Uses C/A Code and Precision Code (P-Code) Calculates Ionospheric errors Has encryption capability (Y code) Think ‘Military GPS’ 52

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