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

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 Communication Networks Satellite/Ground Communication Networks Satellite/Ground MCC Data/Telemetry RF Systems RF 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

USA Basic Ground Station Line of Sight AOS Acquisition of Signal LOS Loss of Signal UPLINK DOWNLINK Horizon line

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DFR DGS VTS TCS WLP MILA and PDL CTS NHS HTS GTS Orbit Ground Precession

TDRS EAST and WEST COVERAGE TDRS EAST TDRS WEST TDRS Z Atlantic Pacific Indian Ocean ZOE: ZONE OF EXCLUSION (LASTS 5-15 MINUTES) 67 USA Rev A

Practical Examples Tracking Data Relay Satellite MCC Telemetry Commands GSTDN GSFC AFSCN ARTS WSC Telemetry Commands

Practical Examples Payload MCC Downlink Uplink Commands Telemetry GSTDN EVA GSFC AFSCN ARTS Voice Data

Practical Examples Payload Tracking Data Relay Satellite MCC Downlink Uplink Commands Commands/Data/Voice Telemetry Telemetry/Data/Voice GSTDN EVA GSFC AFSCN ARTS WSC Voice Data

Practical Examples Payload Tracking Data Relay Satellite MCC Downlink Uplink Commands Commands/Data/Voice Telemetry Telemetry/Data/Voice GSTDN Space Station EVA GSFC AFSCN ARTS WSC Commands/Data/Voice Telemetry/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

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. Transmitter TPO 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 Transmitter TPO EIRP cable

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 Communication Networks Satellite/Ground Communication Networks Satellite/Ground MCC Data/Telemetry RF Transmitter RF Transmitter Video

Hardware Receiver Commands Voice Communication Networks Satellite/Ground Communication Networks Satellite/Ground MCC Data RF Receiver RF Receiver Video

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

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.