Satellitepayloads 170201001700

Technical Introduction to Geostationary Satellite Communication Systems
Original Prepared by
Telesat Canada
Slide Number 1Rev -, July 2001
Vol 2: Communication Satellites
12 Channel
Input
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Input
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Matrix Input
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12 Channel
Output
Multiplexer
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Multiplexer
C1 (LHC)
C2 (RHC)
C1 (RHC)
C2 (LHC)
7 Channel
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Matrix
Output
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7 Channel
Output
Multiplexer
Receiver
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24 for 18
9 for 7
Satellite Payloads
Section 3

Telesat Canada
2.3 Satellite Payloads
2.3.1 Introduction
2.3.2 Payload Types
2.3.3 Payload Units
2.3.4 Payload Testing
Satellite Payloads

Telesat Canada
2.3.1 Introduction
Satellite communication payloads form part of a wireless
telecommunication system, not unlike terrestrial (ground-based)
wireless telecommunication systems.
Satellite payloads function to receive, process and transmit radio
frequency (RF) waves in the same way as terrestrial microwave
relay towers.
One key difference lies in the fact that the payload hardware in a
Geosynchronous Earth Orbit (GEO) cannot be serviced, repaired
or replaced after launch, so reliability is paramount.
Sec 3: Satellite Payloads
Introduction

Telesat Canada
2.3.1 Introduction
In/Ch (H Pol)
R (V Pol)
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E/ME
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R (H Pol)
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3 Ch Input
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4 Ch Input
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3 Ch Input
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2 Channel
Output
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3 Channel
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R (H Pol)
Receiver
3050
MHz
Output
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Matrix
Input
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Receiver
2800
MHz
20 for 16
uplink beam
downlink beam
payload
Introduction
Figure 2.3.1a Introduction

Telesat Canada
2.3.1 Introduction
All conventional communication satellite payloads perform the
same basic functions:
• Receive signals from the Earth (uplink beam)
• Separate, amplify and recombine the signals
• Transmit the signals back to the Earth (downlink beam)
These basic functions resemble a “bent-pipe” in the sky, more
appropriately named a “repeater”.
Some advanced payload functions include digital signal
processing, also called “regenerative and non-regenerative on-
board processors”.
Introduction

Telesat Canada
2.3.1 Introduction
Unlike ground based wireless systems that are limited to
providing point-to-point, line-of-sight connectivity due to the
curvature of the Earth, satellite systems can provide
instantaneous wide-area network (WAN) connectivity of an entire
hemisphere.
This means that satellite communication systems are capable of
providing different types of connectivity to the end user.
The World Radiocommunication Conference (WRC) Service
Categories assigned for satellite communications are:
• Fixed Satellite Services (FSS) where signals transmit to and from
a limited number of fixed locations on the ground.
• Broadcast Satellite Services (BSS) or Direct Broadcast Service
(DBS) where signals transmit directly to every subscriber.
• Mobile Satellite Services (MSS) where signals transmit to and from
mobile terminals and/or fixed gateways.
Introduction

Telesat Canada
2.3.1 Introduction
Introduction
The use of FSS frequency bands has been expanding to include
some BSS applications.
Because of the very wide coverage areas and the variety of
communication services, interference from neighboring satellites
can degrade the quality of service.
For this reason, the RF frequencies and power levels for each
service type must be properly coordinated for operation from the
chosen orbital slot.
Some frequency co-ordination activities need to be revisited
frequently.

Telesat Canada
2.3.1 Introduction
The International Telecommunications Union (ITU) recommended
frequency assignments for satellite communications developed at
World Administrative Radio Conference’s WARC-85 are listed as
follows:
Sub Band Designation Frequency Range
L Band 1.5 - 1.6 GHz
S Band 2.5 - 2.6 GHz
C Band 3.4 - 4.2, 5.9 - 6.7 GHz
Ku Band 10.7 - 14.5, 17.3 - 17.8 GHz
Ka Band 18.3 - 22.2, 27.0 - 31.0 GHz
Introduction

Telesat Canada
2.3.1 Introduction
Many C- and Ku-Band payloads occupy a total bandwidth of 500
MHz. Each payload consists of a number of channels, also called
transponders. Operating bandwidth of each channel is typically:
• L - Band: 1.7 and 3.4 MHz
• C - Band: 36, 41 and 72 MHz
• Ku - Band: 24, 27, 36, 54, 72, 77 and 150 MHz
• Ka - Band: 250, 500 and 1000 MHz
Each channel can be used to carry 1 signal or many signals, each
with a reduced bandwidth.
Introduction

Telesat Canada
2.3.1 Introduction
Because of operating frequency and bandwidth limitations,
payloads typically employ frequency reuse schemes to maximize
the system capacity.
Spatial frequency reuse is accomplished by using multiple
uplink/downlink beams each dedicated to different coverage
areas.
Spatial frequency reuse is typically used for MSS and
intercontinental traffic and is very effective for providing dedicated
or switchable inter-beam connectivity.
Introduction

Telesat Canada
2.3.1 Introduction
Within each beam/coverage area, frequency reuse is
accomplished by using orthogonally polarized beams.
• Linear polarization schemes use vertical and horizontal
electric field (e-field) beams.
• Circular polarization schemes use left and right hand
circularly rotating e-field beams.
• The choice of polarization scheme affects the design and
cost of the ground terminals, ease of ground installation,
adjacent satellite interference and cross-polarization
interference.
Introduction

Telesat Canada
2.3.1 Introduction
Introduction
Figure 2.3.1b North American Up and Downlinks

Telesat Canada
2.3.1 Introduction
Figure 2.3.1c North American Up and Downlinks
Introduction

Telesat Canada
2.3.1 Introduction
Coverage refers to the uplink and downlink beam patterns
created on the Earth by the satellite receive and transmit
antennas.
Coverage can be tailored to any predefined shape using
conventional antenna reflector and feed technology.
Some examples of coverage beams include global, international,
national and spot beams.
Multiple coverage area systems can provide dedicated or
switchable inter-beam connectivity.
Introduction

Telesat Canada
2.3.1 Introduction
National Coverage Beam
Figure 2.3.1d National Coverage Beam

Telesat Canada
2.3.1 Introduction
International
Coverage
Beam
Figure 2.3.1e International Coverage Beam

Telesat Canada
2.3.1 Introduction
Spot Coverage Beams
Figure 2.3.1f Spot Coverage Beams

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Types of Traffic
Analog Signals (almost phased out in North America)
• Television
• Telephony (Asia)
Digital Signals
• Television (QPSK) compressed
• VSAT (QPSK)
• High data rate (8-QPSK)
• Satellite news gathering (QPSK)
• Date for multiple user systems (TDMA)
2.3.1 Introduction

Telesat Canada
Certain functions in the payload are required to be controlled from
the ground in order to optimize and maintain the service. Ground
control of this nature is called “commanding”.
Likewise, certain indicators of performance are required to be
monitored on a continual basis from the ground in order to
optimize and maintain the service. This is called telemetry.
Fundamental telemetry parameters include:
• Unit on/off status
• Unit temperatures
• Transponder channel gain setting status
• Power amplifier health status parameters (i.e. helix or gate
current, DC current and anode voltage)
• Antenna pointing position (if applicable)
Introduction
2.3.1 Introduction

Telesat Canada
2.3.2 Payload Types
FSS, BSS and Advanced Payloads
All types perform the same basic functions:
• Receive communication signals from the Earth (uplinks)
• Amplify the uplink signals and downconvert the frequency
• Separate the downconverted signals into channels
• Amplify the channelized signals
• Combine the amplified channels into a downlink signal
• Transmit the downlink signal to the Earth
Payload Types

Telesat Canada
To accomplish these functions, conventional payloads typically
comprise the following major units:
• Receive and Transmit Antennas
• Input Filters
• Receivers
• Input Multiplexers
• Redundancy Switch Networks
• Transponder Amplifiers
• Output Multiplexers
Payload Types
2.3.2 Payload Types

Telesat Canada
2.3.2.1 FSS Payloads
FSS C-Band Payloads
• Arabsat 2A @ 26º E, Arab
States
• Anik E1, 30:24 @ 11.5 W
Canada and CONUS
• Anik F1, 32:24 @ 40 W
North and South America
• Galaxy 10, 30:24 @ 40 W
North America
• GE 4, 2X 16:12 @ 20 W US
Part 2: Payload Types
FSS Payloads
Figure 2.3.2.1a
Picture Courtesy of
Telesat Canada
Vol 2: Communication Satellites, Sec 3: Satellite Payloads

Telesat Canada
12 Channel
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6 Channel
Output
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C1 (LHC)
C2 (RHC)
C1 (RHC)
C2 (LHC)
7 Channel
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Input
Switch
Matrix
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7 Channel
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Receiver
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24 for 18
9 for 7
FSS C-Band Functional Block Diagram
Figure 2.3.2.1b FSS C-Band Functional Block Diagram

Telesat Canada
FSS Ku-Band Payloads
• Arabsat 3A @ 26º E, Arab
States
• Anik E1, 18:16 @ 50 W
Canada and CONUS
• Anik F1, 58:48 @ 115 W NA
and SA
• Galaxy 10, 30:24 @ 108 W
NA
• GE 4, 2X 18:14 @ 110 W
US
FSS Payloads
Figure 2.3.2.1c
Picture Courtesy of
Telesat Canada

Telesat Canada
5 Channel
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Ku1 (H Pol)
Ku2 (V Pol)
Ku1 (V Pol)
Ku2 (H Pol)
7 Channel
Output
Multiplexer
Output
Switch
Matrix
18 for 12
FSS Ku-Band Functional Block Diagram
Figure 2.3.2.1d FSS Ku-Band Functional Block Diagram

Telesat Canada
Receive (Rx) and Transmit (Tx) Antennas:
The function of the Rx antenna assembly is to collect the signals
in the uplink beam and direct them into the payload.
Likewise, the Tx antenna functions to send the signals from the
payload down to the Earth in the downlink beam.
Each antenna assembly typically comprises a reflector and a feed
horn as a minimum, although other types of antennas are also
used.
FSS Payloads

Telesat Canada
In addition to a reflector and a feed horn:
• A dual polarization antenna assembly requires a device to
separate and combine the two orthogonally polarized beams
called an orthomode transducer (OMT) for linearly polarized
beams and a polarizer for circularly polarized beams, and
• A combined Rx/Tx antenna assembly requires a device to
separate the two frequency bands called a diplexer.
FSS Payloads

Telesat Canada
Input Filters:
Input filters function to remove any unwanted signals from the
uplink beam while permitting the wanted signals to pass into the
receiver.
The receiver and the performance of the payload are sensitive to
out-of-band signals so the input filters are typically comprised of:
• A bandpass filter to reject near band signals
• A lowpass filter to reject far out-of-band signals
FSS Payloads

Telesat Canada
Receivers
The functions of the receiver are:
• To amplify the uplink signal while suppressing the noise
• To downconvert the uplink signals to the downlink frequency band
(e.g. C Band from 6 to 4 GHz, Ku Band from 14 to 12 GHz)
Receivers typically provide approximately half of the total required
transponder gain.
Receiver’s noise figure dominates the payload noise figure or G/T
performance.
Receivers typically comprise:
• A low-noise amplifier (LNA) and a downconversion mixer with a
local oscillator
FSS Payloads

Telesat Canada
Input Multiplexers (IMUXes)
The function of IMUX is to separate the individual signals from the
250 - 500 MHz downconverted uplink beam into narrow band
channels (e.g. 27, 36 or 54 MHz).
The key device in the IMUX is the high order bandpass filter.
Typical IMUX designs configure the filters in a non-contiguous
(i.e. non frequency adjacent) arrangement using channel
dropping circulators.
Basically, there are two types of IMUXes (i.e. waveguide or
dielectric loaded).
FSS Payloads

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FSS Payloads
Figure 2.3.2.1e C-Band Dielectric Resonator IMUX
Supplied courtesy of COM
DEV Space (proprietary)

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FSS Payloads
Figure 2.3.2.1f Ku-Band Dielectric Resonator IMUX

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Redundancy Switch Networks
Electro-mechanical switches comprise an actuation mechanism to
switch the RF transmission paths from port to port.
Typically, high power switches have waveguide RF paths and low
power switches have coaxial RF paths.
There are various switch configurations used for both types
including:
• Waveguide C (2 position) and R (3 or 4 position)
• Coaxial C (2 position) and T (3 position)
FSS Payloads

Telesat Canada
Transponder Amplifiers
Transponder Amplifiers typically consist of two amplifier stages
and a common Electric Power Conditioner (EPC):
The first stage is the Driver Amplifier (DA)
• Typically, the DA is a high gain, low power, broadband, solid state
amplifier
• The DA provides the commandable gain control for the
transponder
• Some DA units also have an automatic level control circuit that
maintains the output signal level constant as the input signal level
varies over a large range
FSS Payloads

Telesat Canada
The second stage is the Power Amplifier (PA)
• Typically, the PA is a high gain, high power, broadband amplifier
• The PA provides the RF power required for the downlink EIRP
• Some PA units also have a linearizer that functions to optimize the
phase and amplitude
• Depending on the output power level and frequency band, PAs fall
into two different designs:
• Travelling Wave Tube Amplifier (TWTA)
• Solid State Power Amplifier (SSPA)
FSS Payloads

Telesat Canada
The power supply for both amplifier stages is provided by the
EPC.
• The EPC provides the required voltages for the PA (5 V for SSPAs
and up to 7 kV for TWTAs) from the bus.
• For TWTAs, the EPC typically has circuitry that protects the
amplifiers from the effects of microdischarge events that occur in-
orbit.
• If a large number of TWTAs are flown, it is common to have one
EPC provide power to a pair of DAs and TWTAs and this is called
a dual EPC configuration.
• For SSPA designs, it is common to house the DA and EPC with
the PA all in one housing.
FSS Payloads

Telesat Canada
TWTAs
Major components in the TWT are:
• The electron gun, containing a cathode and an anode
assembly, which produces a high density electron beam.
• The slow-wave or delay line circuit that supports a travelling
wave of electromagnetic energy that interacts with the
electron beam.
• The collector which collects the spent electron beam
emerging from the slow-wave field.
• Packaging hardware. This provides a means of attaching
the beam focusing structure and the cooling system for
power dissipated within TWT.
FSS Payloads

Telesat Canada
• The slow-wave circuit usually employs a step velocity taper
helix
• The collector employs a multi-stage (i.e. 3 or 4 stages)
design with thermal conduction to a cooler outside surface
• The EPC supplies power to TWT, provides protection
circuits and the command and telemetry data
• The key TWTA performance specifications are:
• RF Output Power: 10-250 Watts
• Saturated Gain: 50-60 dB and Efficiency : 55-65 %
• Weight: ~ 2.5 - 3.5 Kilograms
FSS Payloads

Telesat Canada
SSPAs
SSPAs have been available since late 1970’s and started in
commercial satellite services in early 1980’s.
The SSPA capability depends on the performance of the output
stage transistors and the efficiency of the combining techniques.
The types of transistor typically used are Gallium Arsenide
(GaAs) Field Effect Transistors (FETs) or High Electron Mobility
Transistors (HEMTs).
These devices can provide sufficient gain and power-added
efficiency for high power modules. However, GaAsFET transistor
output power is limited by the device’s gate-width, gate-length and
breakdown voltages.
FSS Payloads

Telesat Canada
Typically, SSPAs have the EPC and DA units integrated directly
into the same housing as the high power amplifier stages
Typical SSPA performance specifications are:
• RF output power: 5 - 40 Watts
• Saturated Gain: 55-65 dB and Efficiency: 20-40 %
• More linear than TWTAs
• Weight: ~ 1.5 - 2.5 Kilograms
FSS Payloads

Telesat Canada
The Output Multiplexer (OMUX)
The function of the OMUX is to combine the channelized,
amplified signals and direct the signals to transmit antenna input
port.
OMUXes typically comprise high power input isolators, lowpass or
harmonic reject filters, high power, low order bandpass filters, a
waveguide manifold and high power switches.
Some designs also employ a high power isolator and/or a high
power receive band reject filter at the OMUX output.
FSS Payloads

Telesat Canada
OMUXes can be designed to provide contiguous (i.e. frequency-
adjacent channels 1, 2, 3, 4, …) or non-contiguous (i.e. non-
frequency-adjacent channels 1, 3, 5, …) channel performance.
Typically, OMUX channel filters are fabricated with a temperature-
stable metal to minimize the filter’s sensitivity to temperature
changes.
Some designs incorporate a temperature compensation
mechanism to minimize the temperature effects and assist in the
dissipation of heat generated in the loss mechanisms of the
OMUX.
FSS Payloads

Telesat Canada
C-Band
OMUX
Figure 2.3.2.1i C-Band Dielectric Resonator OMUX

Telesat Canada
Ku-Band
OMUX
Figure 2.3.2.1j Ku-Band Temperature Compensated Dielectric Resonator OMUX

Telesat Canada
2.3.2.2 BSS Payloads
• NIMIQ, 44:32 @ 120 W or
22:16 Combined @ 230 W
NA
• Echostar 4, same as NIMIQ
• USDBS 3, 32 Channels @
120 W US
• Koreasat 3, 9:6 @ 120 W
BSS Payloads
Figure 2.3.2.2a NIMIQ, A Broadcast Satellite
Picture Courtesy of
Telesat Canada

Telesat Canada
8Channel
ImuxOdd(1-29)
8Channel
OMUXOdd(3-31)
11for8
OutputSWNetwork
11for8
OutputSWNetwork
8Channel
ImuxOdd(3-31)
11for8
InputSWNetwork
8Channel
ImuxEven(4-32)
11for8
InputSWNetwork
8Channel
ImuxEven(2-30)
11for8
InputSWNetwork
11for8
InputSWNetwork
108”
Deployed
Xmit
KEY
RHCP: Right Hand Circular
Polarization
LHCP: Left Hand Circular
Polarization
IFA: Input Filter Assembly
DALC: Driver w/ ALC
LNA: Low Noise Amplifier
s: Phase Shifter
TWTA: Traveling Wave Tube
Amplifier
SW: Switch
108”
Deployed,
Xmit
•
•
s
s
IFA
17/12
GHz
LNA/
Rcvrs
LO=
5100
MHz
4 for 2
DALC
DALC
DALC
DALC
SW
SW
#1
#11
Input
Boost
Network
Input
Boost
Network
120 Watt TWTAs
Output
Boost
Network
Output
Boost
Network
120 Watt TWTAs
sDALC
DALC
SW
#11
Input
Boost
Network
Output
Boost
Network
120 Watt TWTAs
•
•
•
•
•
•
•
•
DALC
DALC
SW
#1
Input
Boost
Network
Output
Boost
Network
120 Watt TWTAs
s
HY
HY
44”
Fixed, Receive
RHCP
LHCP
POL
POL
RHCP
LHCP
CH #
1,5...
CH #
2,6...
CH #
4,8...
CH #
3,7...
LHCP
RHCP
POL
8Channel
OMUXOdd(1-29)8Channel
OMUXEven(4-32)
8Channel
OMUXEven(2-30)
IFA
11for8
OutputSWNetwork
11for8
OutputSWNetwork
•
•
•
•
•
•
•
•
•
•
•
•
Figure 2.3.2.2b BSS Ku-Band Functional Block Diagram

Telesat Canada
Basically, BSS payloads are the same as FSS except that they
either employ higher power PAs or output power combining
circuits that function to “boost” the output power by pairing PAs.
This is done to provide a higher EIRP which translates to a higher
PFD at the Earth, so smaller (i.e. 45 cm) dishes can be used by
each subscriber.
Typically, BSS payloads comprise FSS powered TWTAs with
additional power combining hardware (the boost assemblies) that
effectively doubles the EIRP for up to half of the channels.
BSS Payloads

Telesat Canada
The power combining hardware typically comprises:
• Input boost assemblies (IBAs) that split the DA output in
order to equally drive a pair of TWTAs
• Phase adjusters that can be used to phase match the split
DA signals such that the TWTA output signals have a
known phase relationship
• Output boost assemblies (OBAs) that phase combine the
TWTA output signals to, effectively, double the EIRP
• Due to practical limitations, the power usually only increase
by 2.7 dB or a factor of 1.86
BSS Payloads

Telesat Canada
2.3.2.3 FG vs. ALC Mode
Fixed Gain (FG) and Automatic Level Control (ALC) Modes refer
to the two different gain control methods for the DA.
In the FG mode, the DA is commanded to a specific gain setting,
regardless of the uplink PFD.
In this state, the DA drives the PA proportionally to the the input
signal received by the DA.
The FG mode is effective for multi-carrier operation from multiple
uplink sites.
But, uplink PFD fluctuation and any gain frequency variation in the
receive common input section causes the operating point of the
PA to change, even if the PFD is ideally set for saturation of the
PA (i.e. SFD).
FG vs. ALC Mode

Telesat Canada
In the ALC—also referred to as Automatic Gain Control (AGC)—
mode, the DA is commanded to a specific output power level
setting, regardless of the uplink PFD.
In this state, the DA samples its own output power and
automatically changes the gain in order to achieve the
commanded output power level.
Thus, the power amplifier is driven with at a constant operating
point because any PFD fluctuation and gain frequency variation is
removed by automatically controlling the gain.
The ALC mode is very effective for single carrier, steady state
operation at PA saturation.
FG vs. ALC Mode

Telesat Canada
Certain frequency bands (Ku and Ka) are typically very
susceptible to atmospheric attenuation fluctuations (e.g. rain fade)
while others (L, S and C) are less susceptible.
Thus, ALC mode is a typical requirement for Ku- and Ka-Band
payloads, especially if steady state operation at saturation is a
required application.
Sufficient commandable and dynamic range of operation is
required in FG and ALC mode to account for the uplink dynamic
range settability, thermal noise contributions and PA aging
effects.
FG vs. ALC Mode

Telesat Canada
2.3.2.4 Advanced Payloads
Advanced payloads have been designed for 3rd generation of
MSS and for multimedia FSS.
The lack of spectrum at L-Band, coupled with the desire to
provide service directly to small, hand-held user terminals,
requires the use of multiple beams (i.e. up to and sometimes over
100 beams) and digital processors to interconnect them.
The large throughput requirement for multimedia and small user
terminals also requires multiple beams and digital processing.
Advanced Payloads

Telesat Canada
Main Design Features
• Complex multiple beam antenna system with analog or digital
beam forming.
• Large number of receivers and amplifiers in comparison to
conventional payloads.
• Additional level of downconversion to baseband and
upconversion to Ku- or Ka-Band.
• Use of regenerative or non-regenerative on-board processor to
interconnect the user’s terminals to gateways and gateways to
user terminals (some systems also provide user-to-user
connection).
Advanced Payloads

Telesat Canada
• Regenerative processors are used in a technique that
reconstructs the original digital signal before transmission back
to Earth.
• As with regeneration in terrestrial links, noise and distortion
imparted on the uplink will not be present in the downlink.
• Non-regenerative processors do not reconstruct the original
digital signals (i.e. uplink noise and distortion will be present in
the downlink). Thus non-regenerative payloads are said to
have “bent-pipe” architecture.
Advanced Payloads

Telesat Canada
RCVR
A/D Demux Demod/Decod
A/D Demux
A/D Demux
A/D Demux
Concen-
trator
Digital
Packet
Switch
RCVR
A/D Demux Demod/Decod
A/D Demux
A/D Demux
A/D Demux
Concen-
trator
RCVR A/D Demod/Decod
DOWNLINKUPLINK
Beam 1
Beam 40
MF-TDMA
MF-TDMA
Gateway 1
Gateway 40
Beam 1
Beam 40
Gateway 1
Gateway 40
TDMA 120 MHz
120 MHz
30 MHz
30 MHz
HPAUpconvertMod/Cod
TDM
120 MHz
Vertical Polarization
Horizontal Polarization
Horizontal Polarization
Vertical Polarization
TDMA
HPAUpconvertMod/Cod
TDM
120 MHz
HPAUpconvertMod/Cod
TDM
120 MHz
HPAUpconvertMod/Cod
TDM
120 MHz
RCVR A/D Demod/Decod
Demod/Decod
Demod/Decod
Demod/Decod
Demod/Decod
Demod/Decod
Demod/Decod
Figure 2.3.2.4a Regenerative Digital Processing

Telesat Canada
140 Inputs
Beams 154 Transponders
LNA
1 to 17
Divider
Channelizer
Switch
Combine
Matrix
140 Inputs
Beams154 Transponders
Filter
TWTAs
/
Combi
UpconvD/ADistri/Mux
Beam-
Forming
Network
SSPA
and
Filters
LNA
Beam-
Forming
Network
Switch
Combine
Matrix
LNA
LNA A/D Demux/ConcRcvr
A/D Demux/ConcRcvr
A/D Demux/ConcRcvr
A/D Demux/ConcRcvr
A/D Demux/ConcRcvr
A/D Demux/ConcRcvr
UpconvD/ADistri/Mux
UpconvD/ADistri/Mux
UpconvD/ADistri/Mux
UpconvD/ADistri/Mux
UpconvD/ADistri/Mux
17 Transponders 17 Transponders
Figure 2.3.2.4b Non-Regenerative Digital Processing

Telesat Canada
MSSs were first able to use an advanced payload because of
their relatively low data rates (i.e. 2.4 to 64 kbps).
Application Specific Integrated Circuit (ASIC) power consumption
and size reduction during the past few years has made higher
rate, multimedia payloads possible.
• The required speed of the ASIC is directly impacted by the
bandwidth that requires processing (i.e. the larger the
bandwidth, the more ASICs are required).
Advanced Payloads

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The power consumption and mass of digital processors are
directly proportional to the overall throughput of the payload.
Main differences between MSS and Multimedia:
• Data rate of Multimedia is much higher (i.e. 2.4 Mbps)
• Traffic is asymmetric in multimedia, with higher traffic from
gateway to user
• Multimedia will require data rate conversion on-board, in addition
to format conversion, so it requires regenerative processors to
demodulate, process, and remodulate for transmission
• For MSS, the uplink signal is identical to the downlink with no need
for a format conversion or data rate conversion, so it utilizes non-
regenerative processors
Advanced Payloads

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Overall Assessment
• Advanced payload capability is much greater than that of
conventional payloads
• Advanced payloads are more complex, larger, heavier and
require higher power
• Advanced payloads represent deployment of new technology,
thus presenting high risk
• Advanced payloads are more expensive than conventional
payloads
Advanced Payloads

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2.3.3 Payload Units
Payloads consist of three different types of “units” or “devices”
that introduce different levels of risk for in-orbit operation:
Passive RF units:
• Do not require the application of DC power to operate
• Cause the RF signal passing through to lose power
• This loss of RF power produces heat. This is called RF
heating
• Do not typically exhibit wear-out or life-limiting features, so
redundant units are not typically provided
Payload Units

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2.3.3 Payload Units
Active RF units
• Require the application of DC power to operate
• Cause the RF signal to either lose or gain power
• RF losses generate RF heating as does the consumption of
DC power
• Typically exhibit wear-out or life-limiting features, so
redundant units are usually provided
On-Board Processors
• Can be analog active intermediate frequency (IF), RF
processors, or digital processors
Payload Units

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2.3.3.1 Passive Low Power Units
These units typically have the lowest operating power levels in the
payload, and the most benign environmental effect on the
spacecraft.
Because of this, these units typically present the lowest risk for in-
orbit operation.
These units include:
• Input filter assemblies (IFAs), hybrid couplers, circulators and
isolators, input multiplexer (IMUX) assemblies, attenuators and
phase adjusters, switches and input switch networks (ISNs), low-
level beam-forming networks (BFNs), interconnecting waveguide
and coaxial cable
Passive Low Power Units
Part 3: Payload Units

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2.3.3.2 Active Low Power Units
These units typically have moderate operating power levels.
They typically comprise components such as transistors,
capacitors, Monolithic Microwave Integrated Circuits (MMICs) and
hybrids that present a risk of failure in-orbit.
These units provide most of the required signal amplification in
the satellite and perform all of the frequency down conversion and
analog signal processing functions, so they typically present low
to medium risk for in-orbit operation.
Active Low Power Units
• low noise amplifiers (LNAs), down converters, driver amplifiers (DAs)
with commandable gain controls, limiters (LIMs) and linearizers
(LINs), ferrite and solid state switches and switch matrices, analog
on-board processors including Surface Acoustic Wave (SAW), IF and
RF signal processors

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2.3.3.3 Passive High Power Units
These units typically have the most stringent operating power
levels and environmental conditions in the spacecraft.
This is because the higher the RF power, the higher the RF
heating, and the higher the operating temperature.
Also, RF heating can increase dramatically as the signal
frequency drifts away from band-centre toward the band-edge
(this is known as a “band-edge carrier”).
Furthermore, units that pass multiple channels will exhibit a
proportional increase in the RF heating (i.e. if one channel causes
10 W of RF heating, then 8 channels would cause an average of
80 W of RF heating).
Passive High Power Units

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In units that pass multiple channels, the signals can superimpose
upon each other in a manner in which their total RF power briefly
reaches peak levels that are much higher than the average.
In these cases, the increase is proportional to the square of the
number of channels (i.e. from the earlier example of 8 channels,
the increase is 82
= 64 times).
This peak power level is not typically sustained long enough to
increase the RF heating, but it can lead to a vacuum breakdown
phenomenon known as multipaction that can cause a temporary
interference to the signal or even permanent damage to the unit.

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Passive high power units are subjected to several potentially
damaging operating conditions that must be precluded by:
• Proper design
• Proper fabrication by special materials and processes
• Proper testing
• Proper in-orbit operation
Since the industry trend toward higher downlink EIRP directly
translates into higher RF power in these devices, the technology
is continuously being driven to its limit.

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Because of these stringent operating and environment conditions,
and the industry trend towards higher RF power, these units
present low to medium risk for in-orbit operation.
• output receive reject filters, harmonic filters, power dividers and
combiners, circulators with remote loads or isolators, output
multiplexer (OMUX) assemblies, output switch networks (OSNs),
high-level beam-forming networks (BFNs), coaxial connectors,
receive/transmit diplexers, antenna feed horns, orthomode
transducers (OMTs), polarizers and interconnecting waveguide

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2.3.3.4 Active High Power Units
These units have the most stringent operating power levels and
environmental conditions in the spacecraft. They require a large
amount of DC power to operate.
These units and their EPCs are susceptible to performance
degradation and/or wear-out over the life of the satellite.
These units are susceptible to RF and DC power consumption
heating effects and peak power effects.
Active High Power Units
Moreover, the performance and reliability of these units
significantly depends on the RF power operating points that are
used.
With higher amplifier RF powers being used, operation above the
well defined and safe operating point can introduce life-limiting
damage to these units.

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Because of these stringent operating requirements and their
susceptibility to damage and wear-out, these units present
medium to high risk for in-orbit operation.
These units are the power amplifiers, which can be:
• Travelling wave tube amplifier assemblies, or
• Solid state power amplifiers

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TWTA risk issues:
• In-orbit experience (has the chosen model seen orbit, and if
so, how did it perform?)
• Heritage and design changes from heritage units (is the
chosen model based on an earlier model, and if so, how
has the new model been changed?)
• Qualification and life-testing (was is thoroughly tested?)
• In-orbit anomalies and corrective actions taken (if it
experienced problems in orbit, were these correctable?)
• Overdrive and ESD susceptibility (how “delicate” is the
chosen model with respect to typical forms of misuse and
damage?)
• Output power, and telemetry (helix current, DC current,
anode voltage) anomalies (is this unit capable of reporting
on itself reliably?)

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SSPA risk issues:
• In-orbit experience
• Heritage and design changes from heritage units
• Qualification and life-testing
• In-orbit anomalies and corrective actions taken
• Power stage design (GaAs FET vs. BJT)—strengths and
weaknesses in each design
• Overdrive, multi-carrier traffic and ESD susceptibility
• Burn-in and screening is paramount

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2.3.3.5 Overview of Digital Processors
Two Types of Digital Processors:
• Regenerative: Where the original information is recovered
on-board the spacecraft by demultiplexing and
demodulating the signal
• Non-regenerative: The signal is not demodulated on-board,
only demultiplexed for switching circuit by circuit
Non-regenerative processors are ideal when uplink and downlink
data rates are identical and the same format is used.
Overview of Digital Processors

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Main Functions
• Interconnect large number of inputs to a number of outputs
according to ground commands or according to information
located within the signal (regenerative)
• Performs data rate conversion
• Performs format conversion
• Power level measurement for uplink power control at Ka-Band
• Synchronization of TDMA networks

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Circuit
Switch
Overheads
Processor
Command
& Signaling
Processor
PCR
Insertion
A/D DecodeDemod
DVB-S Demodulator - 33 MHz
IF
to
Baseband
A/D Demux DecodeDemod
IF
to
Baseband
IF
to
Baseband
IF
to
Baseband
IF
to
Baseband
1
2
3
18
DVB-S
Modulator
Forward
Data
Handler
D/A
Baseband
to
Ka-Band
DVB-S
Modulator
Forward
Data
Handler
D/A
Baseband
to
Ka-Band
DVB-S
Modulator
Forward
Data
Handler
D/A
Baseband
to
Ka-Band
DVB-S
Modulator
Forward
Data
Handler
D/A
Baseband
to
Ka-Band
Figure 2.3.3.5 Regenerative On-Board Digital Processor

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Main Components
• Analog-to-Digital (A/D) Converters
• Application Specific Integrated Circuit (ASIC)
• Random Access Memories (RAM)
• On-Board Processor (OBP) Controller, Command Controller
• Internal or external power supply unit

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Evolution
First commercial non-regenerative processor deployed was
Skyplex on-board Hotbird-4 and 5. No switching was involved,
only a multiplexing function.
The Asian Cellular Satellite (ACeS) was the first non-regenerative
processor with only digital components with the exception of A/D
converters, called hybrids.
Power consumption of ACeS ASICs is approximately 0.5 micro
watt per MHz per gate. Federal System is offering ASIC with 0.02
micro watt and Honeywell is offering 0.06, a reduction by 10 to 20
times in 4 years.

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Design Requirements
• ASICs are vulnerable to Single Event Upset (SEU) so they
must be radiation-hardened
• ESD protection is required
• Clock distribution and timing disruption could lead to serious
problems
• Processor needs to meet performance specification in addition
to functional requirements

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Digital Processor Units
Performance specifications, such as implementation losses, can
be measured during integration.
Functional requirements require a much more elaborate test set-
up:
• Terminals
• Command Link
• Gateways
• Extensive test equipment such as signal/ATM cell generators

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2.3.4 Payload Testing
Beyond design integrity, proper material and process selection
and well controlled fabrication techniques, the integration and
testing (I&T) of payload equipment provides the last opportunity
for payload risk mitigation prior to launch.
I&T typically comprises very detailed and procedural operations at
3 distinctive levels throughout spacecraft construction:
• Unit level I&T
• Payload subsystem level I&T (i.e. prior to bus mate)
• Spacecraft level Testing (i.e. post bus mate)
Payload Testing

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2.3.4.1 Unit Level I&T
Payload units must be tested extensively in order to mitigate in-
orbit insurance risk.
For brand new unit designs with no flight heritage, typically
several models are fabricated and subjected to various levels of
environmental and operational tests prior to fabricating the units
that will actually be flown.
These tests inlude:
• Engineering Breadboard Models (EBB or EM)
• Engineering Qualification Models (EQM)
• Life Test Models (LTM)
Unit Level I&T
Part 4: Payload Testing

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Environmental and operational testing performed at these levels
typically exposes the units to levels beyond the expected
exposure levels in-orbit.
With the exception of LTMs that may continue to be tested even
after launch, successful completion of these tests is typically
required prior to fabricating the units that will be launched.
Unit Level I&T
The units to be launched are called Flight Models (FMs) and are
typically tested to environmental and operational levels that are
less severe than EQMs and LTMs, yet marginally more severe
than the predicted in-orbit requirements.
Sometimes, the first FM in a batch of units is tested to
environmental levels that are intermediate to FMs and EQMs.
These units are called Protoflight Models (PFMs).

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Environmental Testing includes:
• Vibration, shock and acoustic tests
• Thermal and thermal vacuum tests
• Electromagnetic compatibility (EMC) tests
Operational testing includes:
• Unit burn-in, RF power overdrive, under/over voltage, average and
peak RF power tests
• Performance testing is conducted at hot, cold and ambient
temperatures
Unit Level I&T

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2.3.4.2 Payload Subsystem I&T
Payload Subsystem I&T typically comprises:
• Payload sections I&T
• Payload Subsystem I&T
The Payload can be divided functionally into four subsections
during integration:
(1) The Common Input Section comprises:
• receivers, input test coupler, input isolator, input filter
assembly, RF switches, output hybrid, interconnecting
waveguide and coaxial cables and select-in-test (SIT)
attenuators
Payload Subsystem I&T

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Common Input Section I&T comprises:
• Gain alignment for the primary and redundant receiver
paths by choosing the correct SIT attenuator values
• RF path switching functional check
• Receiver DC current drain measurements once the unit
is turned on
(2) The Second Section comprises:
• IMUXes, input redundancy switch networks, interconnecting
coaxial cables and SIT attenuators

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The Second Section I&T comprises:
• Equalizing the channel path losses by choosing the
correct SIT attenuator values
• RF path switching functional check
• Input Group Delay and Frequency Response
measurements
(3) The Transponder Amplifier Section comprises:
• DAs, TWTAs or SSPAs, interconnecting waveguide and
coaxial cable, SIT attenuators and for BSS payloads, IBAs,
OBAs and phase adjusters

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The Transponder Amplifier Section I&T comprises:
• Gain alignment for the primary and redundant
transponder amplifier paths by choosing the correct SIT
attenuator values
• Phase adjuster alignment for TWTA pairing (BSS only)
• DA and PA DC current drain measurements after the
units are turned on
• Command and telemetry functional checks
• Gain transfer measurements

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(4) The High Power Output Section comprises:
• OMUXes, harmonic/lowpass filters, output redundancy
switch networks, output test coupler, high power output
isolators and receive rejection filters and interconnecting
waveguide
The High Power Output Section I&T comprises:
• A functional check of the RF switches

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Once all 4 sections are integrated and tested, the Payload
Subsystem is then subjected to its first end-to-end testing
Payload Subsystem End-to-End I&T typically comprises:
• Command and telemetry function
• RF Leakage and Susceptibility (“Sniff and Spray”)
• DC power drain
• Receiver frequency translation
• Gain Transfer
• Input power to saturate
• Saturated output power

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• Overall Inband and Out-of-band Frequency response
• Overall Group delay response
• Linearity
• Gain Control
• Inband and Out-of-band Spurious
• TWTA Helix current/SSPA Gate current telemetry
• TWTA Anode voltage telemetry
• RF continuity verification for all possible RF paths in the payload

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Anik E
I&T
Figure 2.3.4.2 Anik E I&T
Picture Courtesy of
Telesat Canada

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2.3.4.3 Spacecraft Level Testing
After the Payload Subsystem is mated with the Bus Subsystem,
the next phase is referred to as Spacecraft-Level Testing and it
comprises several distinct test phases:
• Initial Spacecraft Test
• Spacecraft Vibration Test
• Spacecraft Thermal Vacuum Test
• Final Spacecraft Test
• Antenna Range and EMC Test
Spacecraft Level Testing

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Anik F Just Prior to
Spacecraft Level
Testing
PhotoCourtesyofTelesatCanadaPhotoCourtesyofTelesatCanada
Figure 2.3.4.3 Anik F Prior to Spacecraft Level Testing

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2.3.4.3.1 Initial Spacecraft Test
The purpose of the Initial Spacecraft Test, also called the Initial
Performance Test (IPT), is to establish a performance reference
prior to Spacecraft environmental tests (vibration and thermal
vacuum).
Typically, the test requirements resemble the Payload Subsystem
End-to-End testing, and IPT is performed by:
• Terminating the payload output ports with either high power
loads or by high power RF absorber boxes
• Calibrating the uplink and downlink test interface before
performance testing

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2.3.4.3.2 Spacecraft Vibration Test
The purpose of Spacecraft Vibration Testing is to verify the
integrity of the Spacecraft mechanical structure after integration
by subjecting it to a simulated launch environment
Typically:
• The antenna assemblies and solar panels are installed prior
to the test
• The command and telemetry functional test is conducted
before and after the vibration
• Payload performance testing is not done during this phase

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2.3.4.3.3 Spacecraft Thermal Vacuum Test
The purpose of Spacecraft thermal vacuum test (SCTV) is to
gather performance test data in a simulated space environment,
to thermally exercise the recently integrated payload and to
perform tests that mitigate the risk associated with the quality
workmanship.
The SCTV phase typically consists of:
Performance Tests:
• Ambient environment testing (also called open door testing)
similar to IPT
• Vacuum hot and cold plateau performance testing similar to
IPT

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Workmanship Tests:
• Thermal vacuum cycling
• Thermal balance to ensure that the payload units operate at
their predicted temperatures
• Transponder small-signal gain monitoring through
temperature transitions (i.e. hot to cold and cold to hot)
• Hot, high power soak monitoring in which several
transponders are operated at the designed operating point
simultaneously until thermal stability is achieved

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Unit failure identified,
unit was replaced and
retest confirmed
nominal operation
Unit failure identified,
unit was replaced and
retest confirmed
nominal operation
Figure 2.3.4.3.3a Small Signal Gain Monitoring Test

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Latent workmanship problem found (sudden
drop in the RF power). Contamination was
found inside one of the RF connectors. The unit
was replaced and retest confirmed stable hot
operation.
Latent workmanship problem found (sudden
drop in the RF power). Contamination was
found inside one of the RF connectors. The unit
was replaced and retest confirmed stable hot
operation.
Figure 2.3.4.3.3b Hot, High Power Soak Test Data

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2.3.4.3.4 Final Spacecraft Test
The purpose of the Final Spacecraft test is to demonstrate that
payload performance did not degraded after exposure to
environmental tests and to establish a reference for Antenna
Range and Launch-site Spacecraft tests.
• Test requirements are typically identical to IPT
• Testing is typically conducted through the input and output test
coupler ports because the Antenna assembly is typically integrated
prior to testing

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Figure 2.3.4.3.4. NIMIQ: Just Prior to Final Spacecraft Test
Picture Courtesy of
Telesat Canada
2.3.4.3.4 Final Spacecraft Test

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2.3.4.3.5 Antenna Range Test
Antenna Range test is typically performed in a near-field range or
a compact antenna test range (CATR) facility with the Spacecraft
in full flight configuration (i.e. all thermal blankets and sun shields
installed).
Tests typically comprise:
• Receive antenna airlink pattern measurements
• Transmit antenna airlink pattern measurements
• EMC and Passive intermodulation measurements

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Figure 2.3.4.3.5 MSAT Just Prior to
Antenna Range Test
Picture Courtesy of
Telesat Canada
2.3.4.3.5 Antenna Range Test

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The purpose of Launch-site Spacecraft testing is to verify the
integrity of the payload after spacecraft delivery to the launch-site.
Typical tests include:
• Command and telemetry functional check
• Sometimes, a transponder noise mound test is conducted
for each channel
• Results are then compared with data that was measured at
Final Spacecraft testing
Launch-Site Spacecraft Test
2.3.4.4 Launch-Site Spacecraft Test

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The purpose of performance trending is:
• To track the performance of key payload parameters across all
Spacecraft test phases in order to identify any anomalies prior to
launch
• To provide a baseline for predictions of performance during in-orbit
testing
The following charts show examples of:
• Saturated gain vs. test phase
• SFD vs test phase and vs. frequency (3D plot)
• Receiver conversion frequency vs. test phase
Performance Trending
2.3.4.5 Performance Trending

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Unit failure identified, unit was
replaced
Unit failure identified, unit was
replaced
Transponder realigned for in-family gain
Transponder realigned for in-family gain
Figure 2.3.4.5a Performance Trending Test (Transponder Gain at Saturation)

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Pronounced sensitivity at cold identified and
correlated to unit level data
Pronounced sensitivity at cold identified and
correlated to unit level data
Figure 2.3.4.5b Performance Trending Test (Sensitivity at cold)

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Receiver vacuum sensitivity highlighted, unit was
retuned for vacuum operation
Receiver vacuum sensitivity highlighted, unit was
retuned for vacuum operation
Figure 2.3.4.5c Performance Trending Test (Vacuum Sensitivity)

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The purpose of In-orbit testing (IOT) is to demonstrate that the
Spacecraft performance has not degraded after launch and drift
orbit environmental exposure.
The payload IOT typically commences after the fully deployed
Spacecraft has arrived at its IOT orbital slot.
The major payload tests typically include:
• Antenna patterns
• Gain transfer, EIRP and SFD
• Gain-to-noise temperature ratio, G/T
• In-band frequency response
• Transponder gain control
• Frequency conversion
Test results are then compared to the trend of test results taken
during ground testing and to the in-orbit predicted performance.
In-Orbit Testing
2.3.4.6 In-Orbit Testing

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The purpose of in-orbit monitoring is to continue the performance
trending of the key payload parameters that indicate the “health”
of the payload
Typically, this is done by monitoring the following telemetry
parameters:
TWTA helix and DC current or SSPA gate current
TWTA anode voltage
In-Orbit Monitoring
2.3.4.6 In-Orbit Testing

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