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COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-2

Objectives and Approach

• Instructor:

– Bruce Elbert, President, Application Technology Strategy, Inc.

– Hughes Satellite, 1972 - 1999

– BEE, City Univ. of NY, MSEE, Univ. of Md., MBA, Pepperdine Univ.

– Contact: tel +1 (310) 918-1728, email bruce@applicationstrategy.com

• Objectives:

– Develop a systems engineering approach for satellite communications

– Explain the techniques and tools used to design commercial communications payloads

– Provide the framework for the overall system and ground segment

• Approach:

– Blend the theoretical with the practical

– Provide both the big picture and a detailed view

– Interact and exchange concepts and methodologies

COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-3

Course Outline

• Comm Payloads and Service Requirements

• Systems Engineering to Meet Service Requirements

• Bent-pipe Repeater Design

• Spacecraft Antenna Design and Performance

• Comm Payload Performance Budgeting

• On-board Digital Processor Technology

• Multi-beam Antennas

• RF Interference and Spectrum Management

• Ground Segment Selection and Optimization

• Earth Station and User Terminal Tradeoffs

• Performance and Capacity Assessment

• Satellite System Verification Methodology

Satellite System Definitions

VSATs or other user terminals

Space segment

Ground segment

TT&C earth station

Satellite

control

center

Hub or gateway earth station

COPYRIGHT © 1997 • BRUCE R. ELBERT

(satellite operator)

(network operator or user)

COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-5

Kepler’s Laws of Planetary Motion

• First Law: The orbit of each planet is an ellipse, with the Sun at one focus.

• Second Law: The line joining the planet and the Sun sweeps out equal areas in equal times.

• Third Law: The square of the period of a planet is proportional to the cube of its mean distance from the Sun.

v

h

P = 1.659 10-4 (6378 + h)3/2

minutes

COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-6

Earth Satellite Orbit Options

Orbit definition Altitude range, km Period, hrs

• Low earth orbit (LEO) 150 - 1,000 1.5 - 1.8

• Medium earth orbit (MEO) 5,000 - 10,000 3.5 - 6

• Geosynchronous earth orbit 36,000 24

– Inclined

– Geostationary earth orbit (GEO)

LEO

MEO

GEO

COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-7 COPYRIGHT © 2000 • BRUCE R. ELBERT

Plasma sheet

Polar wind

Plasma sphere

Polar

cusp

Bow shock

Magnetosheath

Magnetopause

Solar wind

Van Allen Belts

Space Environment

COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-8

Radiation Dose vs. Altitude (5 mil Al thickness)

0 2000 4000 6000 8000 10000

10

103

105

107

109

Dose,

Rads/yr

Altitude, km

COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-9

Orbit Period and Delay vs. Altitude

0

5

10

15

20

25

0 10000 20000 30000 40000

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

0 500 1000

LEO

Altitude, km Altitude, km

Hours

7.5 75 150 225 270

Delay, ms

COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-10

LEO Constellation for Iridium

• 66 satellites

• 6 polar orbits

• Inter-satellite links

Iridium Spacecraft (Motorola and Lockheed-Martin)

PD-1-01-11

PD-1-12

http://www.faqs.org/sec-filings/100602/Iridium-

Communications-Inc_8-K/dex992.htm

GEO Orbit “Slot” for Domestic Service

COPYRIGHT © 1999 – 2001 • BRUCE R. ELBERT

• 24 hour orbit requires stationkeeping operations – Maintain orbit in equatorial plane (N/S stationkeeping)

– Compensate for east-west drift and eccentricity

– Satellite service defined by antenna beam coverage

• Lifetime determined by stationkeeping fuel reserve

PD-1-01-13

COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-14

Antenna Beam Options

Area Coverage Multiple Spot Beams

GW

GW

GW

GW

GW

GW

COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-15

Star and Mesh Topologies

Hub

Remote

Remote

Remote Remote

Remote

Remote

Peer

node

Peer

node

Peer

node

Peer

node

Control

In either topology, links can be established on demand or fixed

Large-capacity GEO Spacecraft

PD-1-01-16

Boeing 702

15 kW

4700 kg at launch

SS/Loral 1300S

19 kW

6200 kg at launch

EADS Astrium

14 kW

6000 kg at launch

LM A 2100 AX

3600 kg at launch

Major Satellite Components

• Payload subsystems

– Repeater (receivers, multiplexers, amplifiers, processing and switching)

– Antennas (reflectors, feeds, feed networks, support structure and pointing mechanisms)

• Bus subsystems

– Tracking, telemetry, command and ranging (TTC&R)

– Solar panels

– Batteries

– Reaction control system (propulsion)

– Attitude and spacecraft control processing

– Thermal control and structure

PD-1-01-17

Lockheed-Martin A2100 Three-Axis Spacecraft

PD-1-01-18

Lockheed-Martin A2100 Block Diagram

PD-1-01-19

COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-20

Typical Spacecraft Mass Allocation

• Geostationary orbit

• 15 year mission

• Three axis spacecraft

• ~2000 kg total dry mass

• ~8000 watts total (EOL)

• Standard payload type

Repeater Antenna Power

TT&C ACS Propulsion

Thermal Structure Harness

COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-21

Typical Spacecraft Power Allocation

• GaAs solar cells

• Flat solar panels

• NiH2 batteries

• 15 year operation

• ~8000 watts EOL

Repeater TT&C ACS

Propulsion Power Thermal

COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-22

Satellite Size v. Capabilities

Hypothetical

class of satellite

Conceptual

number of

Transponders

General Range

of EOL Power

General Range

of Launch

Mass, kg

“Small” 24 to 36 4 to 6 kW 1500 to 2500

“Medium” 48 to 72 8 to 10 kW 3000 to 4000

“Large” 90 to 120 12 to 22 kW 4500 to 6000

COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-23

UHF L S C X Ku Ka Q V

1 10 100 GHz 0.1

Microwave

30 3

Microwave Spectrum (log scale)

COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-24

Total

attenuation

toward

zenith, dB

Propagation Effects on

Satellite Systems at

Frequencies Below 10 GHz,

NASA Publication 1108(02) 1987 Frequency, GHz

H2O

O2

O2 H20

Clear Air Attenuation

sin

w0a

a2a8A

Variation of total

attenuation as a

function of elevation

angle, >10

COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-25

ITU-DAH Rain Model

75

55

37

26

14

25

mm/hr, .01% of the time

COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-26

Elevation Angle Dependence

Rain Cell

(rain rate)

),,( FplrrfA

pl

el

el

COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-27

Rain Attenuation (temperate climate)

Availability

99.5%

98.0%

10°

20°

45°

10°

20°

45°

1 10 100

Frequency, GHz

Elevation

angle

2 4 8 20 40 80

50

40

30

20

10

0

Attenuation,

dB

COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-28

Typical Margin for Rain Fade (12 GHz)

Rain Intensity Margin region mm/hr at 99.8%

A 6 0.3

B 12 0.5

C 15 0.7

D 19 0.9

E 22 1.1

F 28 1.4

G 30 1.5

H 32 1.7

J 35 1.8

K 42 2.2

L 60 3.2

M 63 3.4

N 98 4.8

P 145 5.8

COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-29

Rain Attenuation Solutions

• Ku band (14/12 GHz) – Link margin

» Satellite EIRP

» Dish size

– Uplink power control

– Automatic Gain Control (AGC) in spacecraft

– Antenna feed blower

– Site selection (rain zone)

• Ka band (30/20 GHz)

– Link margin

» Satellite EIRP

• Spot beams

• Dynamic power

» Dish size

– Uplink power control

– AGC

– Dynamic data/coding rate

– Antenna feed blower

– Radome

– Site selection

» Rain zone

» Diversity

• Site

• Satellite

Site (Space) Diversity

D

D

PD-1-30

COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-31

Further Details on Propagation

• Ionospheric effects (below 10 GHz) – Faraday rotation of linear polarization – day to night variation

greatest during peaks of sun spot cycle

– Ionospheric scintillation – most pronounced near the geomagnetic equator (tropical regions) – frequency selective fading during evening and morning transitions of the F layers

• Tropospheric effects (low elevation angles) – Absorption

– Scintillation

– Ducting (Horizontal path)

– Rain – ITU-R Dissanayake, Allnut, Haidara (DAH) model

COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-32

Maximum Ionospheric Effects [US one-way paths at 30 elevation, NASA 1108(2) Table 2.2]

Effect 100 MHz

300 MHz

1 GHz 3 GHz 10 GHz

Faraday rotation

30 rotations

3.3 rotations

108° 12 1.1°

Excess time delay

25 s 2.8 s 0.25 s 28 ns 2.5 ns

Absorp (polar)

5 dB 1.1 dB .05 dB .006 dB .0005 dB

Absorp (mid Lat)

<1 dB .1 dB <.01 dB <.001 dB <.0001 dB

Disper .4 ps/Hz .015 ps/Hs

.0004 ps/Hz

.000015 ps/Hz

.0000004 ps/Hz

COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-33

Communication Payload Technology (Analog and Digital)

Analog repeater

– Bent pipe (no change in format; uplink and downlink noise combine)

– Supports any modulation and multiple access

– Limited routing capability

– Excellent dynamic range; impairments can aggregate

Digital processing repeater

– Channel routing or packet

switching

– Tailored to multiple access

(and modulation)

– Separates uplink from

downlink

– Excellent routing (and

switching) capability

– Limited dynamic range

COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-34

Analog (Bent-pipe) Repeater

• Standard design for FSS and BSS satellites

• Simple design, simple operation

• Very flexible

• Network optimization limited

Wideband

receiver

(500 MHz bandwidth)

F1 Pre A F1

F3 Pre A F3

F5 Pre A F5

F6 Pre A F6

F4 Pre A F4

F2 Pre A F2

LPF

5.925-6.425 GHz

3.7-4.2 GHz

COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-35

Frequency Plan for Bent Pipe Repeater

1 2 3 4 5 6 7 8

1 2 3 4 5 6 7 8

Uplink frequency range

Downlink frequency range

Fup(low) Fup(hi)

Fdwn(low) Fdwn(hi)

Channel spacing Transponder bandwidth Guardband

Not to scale: guardband typically 10% of channel spacing

Translation frequency

COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-36

The Spacecraft Antenna System

• Area coverage antenna – Most common approach for bent pipe repeaters

– Coverage area is similar to local broadcasting (but with less variation of received signal power)

• Coverage is defined by the antenna gain pattern

COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-37

Digital Signal Processing Repeater Design

• Need for flexible payload architecture – Channel routing

– On-demand reconfiguration

– Demod/remod performance

– Beam forming, multiple and flexible

• Constraints – Signal structure (multiplex, modulation and multiple access)

– Bandwidth

– Processor speed and complexity

– Power and weight

– Impairments

– Dynamic range

COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-38

Broadband Processing Payload

Rcv feed net- work

Tx feed net- work

Rcvr

Rcvr

Rcvr

Rcvr

Rcvr

Rcvr

HPA

HPA

HPA

HPA

HPA

HPA

Digital Processor:

A/D Demod

Routing and Switching

Multiplexing Modulation

Beam forming D/A

Rece

ive feeds

and a

pert

ure

Tra

nsm

it feeds

and a

pert

ure

Low-power transmission line High-power transmission line

Active redundancy not shown

Upconv or driver

Upconv or driver

Upconv or driver

Upconv or driver

Upconv or driver

Upconv or driver

COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-39

Inmarsat-4 Global Coverage

COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-40

Course Outline

• Comm Payloads and Service Requirements

• Systems Engineering to Meet Service Requirements

• Bent-pipe Repeater Design

• Spacecraft Antenna Design and Performance

• Comm Payload Performance Budgeting

• On-board Digital Processor Technology

• Multi-beam Antennas

• RF Interference and Spectrum Management

• Ground Segment Selection and Optimization

• Earth Station and User Terminal Tradeoffs

• Performance and Capacity Assessment

• Satellite System Verification Methodology

COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-41

The Microwave Link in Satellite Communications

• Frequencies above 1 GHz (but less than 60 GHz)

• Line-of-sight propagation

• Low received signal level due to large distance

P r P t

R0 2

P r R0 P t

Power

Flux

Density,

Watts/sq meter

P r A

= P t

4 p R0 2

COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-42

Path Geometry (GEO Link)

coscos29577.01107.42643 3

0 R

R0

h

km

Where

R0 = slant range (distance between satellite and earth station)

h = GEO altitude (35,788,293 meters)

= Earth station latitude

= Earth station relative longitude

COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-43

Gain and Effective Area of a Circular Aperture

p

p

p

4

4

2

2

2

GAA

DAG

E

D

COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-44

Antenna “Capture” Area

• Receive antenna “captures” power through its effective area

• Transmit antenna is a reciprocal device (yielding the same performance as in receive)

R P t AE

2

2

2

4

4

4

p

p

p

RGPP

GAA

AR

PP

rtr

rE

Et

r

COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-45

Polarization of the EM Wave

Linear polarization: (a) vertical

(b) horizontal

Circular polarization (c) Left hand

(d) Right hand

(d)

λ

COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-46

Vertically polarized horn

Horizontally polarized horn

a

b

Waveguide and Horn Polarization (Linear Polarization)

c =2a

b ~ a/2

COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-47

Co and CrossPolarization

Co-polarized

signal component

Cross-polarized

signal component

Relative polarization angle, degrees

Relative

received

signal

0 10 20 30 40 50 60 70 80 90

1.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0.0

COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-48

Linear CrossPolarization Isolation

Cross-Polarization Isolation

0

10

20

30

40

50

60

0 1 2 3 4 5 6 7 8 9 10 11

Feed offset angle, degrees

Iso

lati

on

, d

B

COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-49

Properties of Circular Polarization

• Special case of elliptical polarization

• Polarization sense established within the transmit feed system

• Little or no impact from the Ionosphere

• Isolation properties generally inferior to linear

Axial ratio = 20 log (a/b)

COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-50

Polarization Coupling

Polarization type Linear Circular

Linear -10log [Cos2] dB -3 dB

Circular (elliptical) -3 dB Graph

Ref: Johnson, Antenna

Engineering Handbook,

FIG 23-7, p 23-9

COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-51

Depolarization in Rain (Ku – Ka)

Cloud and Rain Cell Geometry

affect V and H polarizations differently

Circular Polarization is composed

of V and H polarizations

COPYRIGHT © 1999 - 2011 • BRUCE R. ELBERT PD-1-52

Link Degradation

http://descanso.jpl.nasa.gov/Propagation/1082/1082ch1.pdf