Spacecraft Communication. 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) - PowerPoint PPT Presentation
Dave Pitre Sierra Nevada Corporation( Space Exploration Systems, Louisville) • Dream Chaser Principle Systems Engineer for Comm & Instrumentatio 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
Transcript
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?
• 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.
• 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
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
