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The Global Positioning System (GPS). 1. 2 nd USAF Space Operations Squadron. 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.

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Presentation Transcript
system description
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

gps satellites
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
Orbital Planes

The GPS Constellation utilises the Medium Earth Orbit

control segment1
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

gps services
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’

11

gps military missions
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

12

gps position
GPS Position

To determine a GPS position:

Distance to satellites

Satellite orbit/position

Earth’s shape

Coordinate reference framework

13

gps solution1
GPS Solution

c = speed of light (3x108m/s)

tt,1, tt,2, tt,3, tt,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

tr,1, tr,2, tr,3, tr,4= times that the signals from GPS satellites 1, 2, 3, and 4, are received according to the inaccurate GPS receiver’s clock

x1, y1, z1 = coordinates of GPS satellite 1. These coordinates are provided to the receiver as part of the information that is transmitted

Similar meaning for x2, y2, z2, etc.

The receiver solves these equations simultaneously to determine x, y, z, and tc

position derivation
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

17

local mapping datum
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.

OSGB 36

NAD 27

ED 50

ED 79

Tokyo

Indian Bngldsh

18

satellite communication systems
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.

categories
Categories

Frequency

Transponder Type

Orbit

frequency
Frequency

Applications for frequency allocations are ratified by the International Telecommunications Union (ITU)

NATO frequency allocations for Military Communication Satellites are:

Uplink Downlink

UHF 290-320MHz 240-270MHz

SHF 7.9-8.4GHz 7.2-7.75GHz

EHF 43.5-45.5GHz 20.2-21.2GHz

S Band for Command, Control and Telemetry of satellites

uhf characteristics
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
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
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

categories1
Categories

Frequency

Transponder Type

Orbit

transparent transponders
Transparent Transponders

RECEIVER &

LOW NOISE

AMPLIFIER

POWER

AMPLIFIER

FREQUENCY

CONVERTER

DOWNLINK

UPLINK

SATELLITE

reconstituting transponders
Reconstituting Transponders

POWER

AMPLIFIER

FREQUENCY

DOWN-

CONVERTER

DECODER &

LOW NOISE

AMPLIFIER

RECODER &

FREQUENCY

UP-CONVERTER

RECODED

DOWNLINK

CODED

UPLINK

SATELLITE

store dump transponders
Store Dump Transponders

FREQUENCY

UP-CONVERTER

& POWER

AMPLIFIER

RECEIVER &

LOW NOISE

AMPLIFIER

DATA

STORAGE

SYSTEM

FREQUENCY

DOWN-

CONVERTER

DOWNLINK

UPLINK

SATELLITE

categories2
Categories

Frequency

Transponder Type

Orbit

satcom orbits
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.