“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 Satellite & Data Communication for Air Cadets

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

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.

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

UK Space Primer

Scope The Space EnvironmentThe Space Environment OrbitsOrbits LaunchLaunch The Global Positioning SystemThe Global Positioning System The Principles of Data CommunicationThe Principles of Data Communication The Types & Roles of Mobile CommunicationThe Types & Roles of Mobile Communication SummarySummary QuestionsQuestions

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

Space Characteristics No geographical boundaries Freedom of movement Unique characteristics

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

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

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

Orbits - Definition of Terms

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

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

Common Orbits LEO MEO GEO HEO 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 ~800-40,000 km 11 HRS 58 MIN ~26,000-8,000 KPH Orbit size determines time for one orbit Orbit size and shape also determines the speed Earth NOT to scale !

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)

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

LEO Orbit – 2D Ground Trace

Sun-Synchronous Orbits Near-Polar, 97°-99° InclinationNear-Polar, 97°-99° Inclination km km

LEO Sun-Synchronous Orbit 2D Ground Trace

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

Geostationary

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

HEO

HEO 2D Ground Trace

Orbital Example – Earth Fixed

Orbital Pertubations

Atmosphere Orbital Decay Effect of the Atmosphere Height (km) Life 2002 weeks yrs Myrs

Effect of the Earth’s Shape TOP VIEW SIDE VIEW 15m15m7.5m 7.5m EQUATOR km km N Pole

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’.

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

Persistence………

…….versus Resolution

Orbital Requirements LEO Coverage Dwell Time Revisit Time Resolution & Power Requirements GEO c.70 0

Achieving Orbit

Initial Launch Direct ascent into low altitude orbit

Data Table Earth Gravitational Force Mass of EarthRadius of EarthOrbital HeightOrbital VelocityOrbital Period Energy Required to Achieve Orbit 6.67E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E+07

Hohman Transfer Orbit Initial Orbit Transfer Orbit Final Orbit

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:

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:

Skynet 5A Launch Simulation

42 The Global Positioning System (GPS)

2 nd USAF Space Operations Squadron

System Description 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 Space Segment Control Segment User Segment

SPACE SEGMENT

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

Orbital Planes The GPS Constellation utilises the Medium Earth Orbit

CONTROL SEGMENT

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

Navigation data MCS Monitor station Ground antenna Telemetry Commands Navigation data uploads Control Segment

USER SEGMENT

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

GPS Military Missions Navigation Position, Velocity and Time Worldwide Any weather Any time Time Users calculate GPS time GPS time will be within 1000ns of UTC Time transfer to within 100ns of UTC Synchronizes digital communications 53

GPS Position To determine a GPS position: Distance to satellites Satellite orbit/position Earth’s shape Coordinate reference framework 54

GPS Solution 55

GPS Solution c = speed of light (3x10 8 m/s) t t,1, t t,2, t t,3, t t,4 = times that GPS satellites 1, 2, 3, and 4, transmitted their signals. These times are provided to the receiver as part of the information that is transmitted t r,1, t r,2, t r,3, t r,4 = times that the signals from GPS satellites 1, 2, 3, and 4, are received according to the inaccurate GPS receiver’s clock x 1, y 1, z 1 = coordinates of GPS satellite 1. These coordinates are provided to the receiver as part of the information that is transmitted Similar meaning for x 2, y 2, z 2, etc. The receiver solves these equations simultaneously to determine x, y, z, and t c

Coordinate Frames 57

Position Derivation GPS receivers determine position Cartesian Co-ordinates (X,Y,Z) WGS-84 Ellipsoid Cartesian Co-ordinates are translated Local datum (ie. OSGB-36) Cartesian Co-ordinates are transformed Latitude, Longitude, and Elevation Elevation is determined with reference to: Ellipsoid, Geoid, or Mean Sea Level 58

Local Mapping Datum A Map Datum is a coordinate reference system consisting of unique and invariable coordinates which are based on an ellipsoid/geoid model over a portion of the earth. 59 NAD 27 ED 50 ED 79 Tokyo Indian Bngldsh OSGB 36

Introduction to SATCOM

Satellite Communication Systems Communication Satellites are used to relay information from one point to another. They enable long range communications at high data rates by overcoming The line of sight limitation of traditional communications like VHF and UHF. The low data rate capacity of traditional long range communication i.e. HF. SATCOM is used for both voice and data communications and is extremely important for both the military and commercial world (just think Sky TV), as well as society as a whole (the Global Commons) SATCOM does not require landline point to point connection. Very useful for Military operations Very useful for work in areas of low/no infrastructure, including disaster relief.

1962 – Telstar

Categories Frequency Transponder Type Orbit

Frequency Applications for frequency allocations are ratified by the International Telecommunications Union (ITU) NATO frequency allocations for Military Communication Satellites are: UplinkDownlink UHF MHz MHz SHF GHz GHz EHF GHz GHz S Band for Command, Control and Telemetry of satellites

Frequency Bands DesignationFrequency (Uplink/Downlink) UHF MHz/ MHzMilitary L-Band1.6GHz/1.5GHz S-Band2.5GHz C-Band6GHz/4GHz X-Band (SHF) GHz/ GHzMilitary Ku-Band14GHz/12GHz Ka-Band30GHz/20GHz EHF GHz/ GHzMilitary

Beamwidth Beamwidth for a 1 metre SATCOM antenna BandFrequencyDegrees UHF300MHz60 SHF8.0 GHz2.5 EHF40.0GHz0.5 D

UHF Characteristics Mature Technology Relatively Cheap Low Data Rates Low Gain Antennas Good Adverse Weather Performance Limited Anti-Jam Capability Poor Performance in Nuclear Environment

SHF/X-Band Characteristics Mature Technology Inexpensive Higher Data Rates than UHF Higher Gain Antennas suitable for Spot Beams Adequate Adverse Weather Performance Some Anti-Jam Capability Some Performance in Nuclear Environment

EHF & Ku/Ka Characteristics Less Mature Technology than SHF and UHF Expensive Higher Data Rates Very High Gain Antennas for Small Spot Beams Very Poor Adverse Weather Performance Good Anti-Jam Capability *Good Performance in Nuclear Environment * UK – US MoU

Categories Frequency Transponder Type Orbit

Transparent Transponders DOWNLINK UPLINK SATELLITE POWER AMPLIFIER FREQUENCY CONVERTER RECEIVER & LOW NOISE AMPLIFIER

Reconstituting Transponders RECODED DOWNLINK CODED UPLINK SATELLITE POWER AMPLIFIER DECODER & LOW NOISE AMPLIFIER RECODER & FREQUENCY UP-CONVERTER FREQUENCY DOWN- CONVERTER

Store Dump Transponders DOWNLINK UPLINK SATELLITE FREQUENCY UP-CONVERTER & POWER AMPLIFIER FREQUENCY DOWN- CONVERTER RECEIVER & LOW NOISE AMPLIFIER DATA STORAGE SYSTEM

Categories Frequency Transponder Type Orbit

SATCOM Orbits Most SATCOMs are in Geosynchronous Orbit Most of these are in GEO Stationary orbits. Some SATCOM systems reside in Low Earth Orbit (LEO) For example IRIDIUM. Useful for global coverage including the polar regions.