Post on 15-Feb-2016
description
Dave Pitre
•Sierra Nevada Corporation( Space Exploration Systems, Louisville)• Dream Chaser Principle Systems Engineer for Comm & Instrumentation
•Space Shuttle Program• Shuttle Avionics Integration Lab Test Engineer (JSC, Houston)• Flight Design Engineer for Rendezvous/Prox Ops (JSC, Houston)• OV 105 Final Assembly Test Engineer (AF Plant 42 Palmdale, Ca)• Crew/Flt Controller Training (JSC, Houston)
• Comm/Instrumentation• Control/Propulsion• Training Lead• Simulation Supervisor
Spacecraft Communication
Spacecraft Communication
What does a spacecraft communication systems engineer do?
•Analyze Comm System Requirements
•Design Comm System Architecture
•Procure Comm System Hardware/Software
•Test Comm System Hardware/Software
•Integrate Comm System Hardware/Software
•Install/Test Comm System Hardware/Software
•Maintain Comm System Hardware/Software
•Train Comm System Hardware/Software
Commands
Voice
CommunicationNetworks
Satellite/Ground
MCC
Data/TelemetryRF
Systems
Video
Systems Level Overview
Challenges Unique to Space Communication
•Distance
• Speed
•Line of sight
•Ground Track
•Earth surface radiation limit
•Limited number of users
USA004460Basic
Ground Station Line of Sight
AOS Acquisition of Signal
LOS Loss of Signal
UPLINK
DOWNLINK
Horizo
n line
126
57
DFR
DGS
VTS
TCS
WLPMILA and
PDL
CTSNHS
HTS
GTS
Orbit Ground Precession
TDRS EAST and WEST COVERAGE
TDRSEASTTDRS
WEST
TDRS Z
AtlanticPacific
Indian Ocean
ZOE:
ZONE OF EXCLUSION
(LASTS 5-15 MINUTES)
USA004460Rev A
Practical Examples
TrackingDataRelaySatellite
MCC
Telemetry
Commands
GSTDN
GSFC
AFSCNARTS
WSC
Telemetry
Commands
Practical Examples
Payload
MCC
Downlink
Uplink
CommandsTelemetry
GSTDN
EVA
GSFC
AFSCNARTS
Voice
Data
Practical Examples
Payload
TrackingDataRelaySatellite
MCC
DownlinkDownlinkUplink
Uplink
Commands
Commands/Data/VoiceTelemetry
Telemetry/Data/Voice
GSTDN
EVA
GSFC
AFSCNARTS
WSC
Voice
Data
Practical Examples
Payload
TrackingDataRelaySatellite
MCC
DownlinkDownlinkUplink
Uplink
Commands
Commands/Data/VoiceTelemetry
Telemetry/Data/Voice
GSTDN
Space Station
EVA
GSFC
AFSCNARTS
WSC
Commands/Data/VoiceTelemetry/Data/Voice
Voice
Data
RF Overview Electromagnetic Waves
• Light, electromagnetic waves, radiation = electromagnetic energy.
• This energy can be described by frequency, wavelength, or energy.
• Radio usually described in terms of frequency (Hertz).
RF Overview Modulation and Waveforms
Modulation Data
Amplitude Modulation
Freq Modulation
RF Overview Time, Frequency, Phase Domain
Power is used to quantify a signal, instead of amplitude, and is expressed in Watts.
For low-frequency signals, the power is given by P = IE
RF Overview Signal Power
RF Overview Signal Power
Transmitter Power Output In radio transmission, transmitter power output (TPO) is the actual amount of power (in watts) of radio frequency (RF) energy that a transmitter produces at its output.
Effective Isotropic Radiated Power Power that comes off an antenna is measured as effective isotropic radiated power (EIRP). EIRP is the value that regulatory agencies, such as the FCC, use to determine and measure power limits in applications.
TransmitterTPO EIRP
cable
RF Overview Decibels
• The decibel is a unitless method of expressing the ratio of two quantities.
• The expression is in terms of the logarithm to base 10 of the ratio instead of
the raw ratio.
• This is done for convenience in expressing the ratio of numbers many
magnitudes apart with decibel numbers that are not as large.
PdBm=10log10(Pwatts/1mW)
RF Overview Decibels
The advantage of using decibels instead of Watts to express the power of a signal along an RF is that instead of dividing or multiplying powers to take care of amplifications and attenuations, we just add or subtract the gains and the losses expressed in decibels
TransmitterTPO EIRP
cable
RF Overview Analog v. Digital
RF Overview Analog v. Digital
RF Overview Analog v. Digital
Analog to Digital Conversion (A/D)
RF Overview Signal to Noise Ratio
Signal-to-noise ratio (often abbreviated SNR or S/N) is a measure that compares the level of a desired signal to the level of background noise. It is defined as the ratio of signal power to the noise power. A ratio higher than 1:1 indicates more signal than noise.
RF Overview Bit Error Rate
• For digital communications, there is a need for end-to-end performance
measurements.
• The measure of that performance is usually bit-error rate (BER), which quantifies
the reliability of the entire radio system from “bits in” to “bits out,” including the
electronics, antennas and signal path in between.
• On the surface, BER is a simple concept— its definition is simply:
BER = Errors/Total Number of Bits
RF Overview Latency
Latency is a measure of time delay experienced in a system, ccontributors to latency include:
•Propagation: This is simply the time it takes for information to travel
between one place and another at the speed of light.
•Transmission: The medium itself introduces some delay. The size of a
packet introduces delay in a round trip since a larger packet will take longer
to receive and return than a short one.
•Processing: Each node takes time to examine and possibly change the
header in a packet.
•Computer and storage delays: Within networks at each end of the
journey, a packet may be subject to storage and hard disk access delays at
intermediate devices.
RF Overview Coding Digital Data
• Digital information cannot be sent directly in the form of 0s and 1s, it must be
encoded in the form of a signal with two states.
• This transformation of binary information into a two-state signal is done in the
base band decoder.
RF Overview Coding Digital Data
• To optimize transmission, the signal must be encoded to facilitate its transmission
on the physical medium. There are various encoding systems for this purpose which
can be divided into two categories:
• Two-level encoding: the signal can only take on a strictly negative or strictly
positive value (-X or +X, where X represents a value of the physical quantity
being used to transport the signal)
• Three-level encoding: the signal can take on a strictly negative, null or strictly
positive value (-X, 0 or +X)
Hardware Transmitter
Voice
CommunicationNetworks
Satellite/Ground
MCC
Data/TelemetryRF
Transmitter
Video
Hardware Receiver
Commands
Voice
CommunicationNetworks
Satellite/Ground
MCC
DataRF
Receiver
Video
Hardware Transmitter/Receiver
Hardware Transmitter/Receiver
Hardware Transmitter
•Frequency(s) •Frequency stability •Frequency setting accuracy•Coherency •Input/Output impedance•RF power output •Input power•Current requirements •Temperature ranges•Cooling•Dimensions •Weight •Connector types•Form Factor•Space rated (rad hardened)•Modulation•Duty cycle
Hardware Receiver
•Frequency(s)•Bandwidth •Coherency •Input/Output impedance•Sensitivity•Signal to Noise Ratio•Input power•Current requirements •Temperature ranges•Cooling•Dimensions •Weight •Connector types•Form Factor•Space rated (rad hardened)•Demodulation•Duty cycle
Hardware Antenna
Hardware Antenna
Link Budgets
• The link budget allows the designer or analyst to alter the sizing of individual
communications components and view the resulting carrier-to-noise ratio.
• The C/N needs to be above a desired threshold decibel level in order for the
signal to be usable.
• The main alterables in the link budget equation are the size of the antenna on
the spacecraft, the frequency used and the power output of the transponder used.
• Link budgets are calculated at the worst conditions possible.