Orbiter Communications.   Communications Windows   Microwave Band   Signal...

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Transcript of Orbiter Communications.   Communications Windows   Microwave Band   Signal...

  • Slide 1
  • Orbiter Communications
  • Slide 2
  • Communications Windows Microwave Band Signal Characteristics Orbiter Communications Systems Orbiter S-band Communications Orbiter Ku-band Communications Orbiter UHF Communications Orbiter Audio Communications Orbiter Operational Instrumentation (Telemetry) Orbiter Payload Communications Orbiter Communications Antennas NASAs Communications Networks
  • Slide 3
  • Communications Windows
  • Slide 4
  • Communications - Space Space communications is limited to the microwave band because of atmospheric attenuation and scattering at most other frequencies Three windows through the Earths atmosphere are found at: Visible band not always available because of clouds & rain Infrared band too narrow and poor background signature (hot spots looking upward from the ground and downward from space) Microwave useful from approximately 1-10 GHz
  • Slide 5
  • Communications - Space Communications through more dense atmospheres (Venus, Titan) have only microwave windows The microwave band has become a standard for space communications 1-10 GHz typical through the Earths atmosphere Much higher frequencies used for space-to-space communications (10-50 GHz) since there is no interfering atmosphere
  • Slide 6
  • Communications - Space Most of the Earths atmospheric attenuation of microwave signals comes from the oxygen and water molecules Scattering of electromagnetic radiation is most common from water droplets Lowest noise band available for Earth- space communications is roughly 1-10 GHz
  • Slide 7
  • Microwave Band
  • Slide 8
  • Communications Microwave Band Microwave frequencies are defined as 300 MHz300 GHz 1 MHz = 1 Mega Hertz = 1 Million Hertz = 10 6 Hz 1 GHz = 1 Giga Hertz = 1 Billion Hertz = 10 9 Hz Common designations for the microwave bands used for spacecraft communications are: UHF 300 MHz to 3 GHz L-band 1-2 GHz S-band 2-4 GHz * C-band 4-8 GHz X-band 8-12.5 GHz K, Ka, Ku-band 12.5-40 GHz * Most commonly used space-terrestrial communications band
  • Slide 9
  • Communications Microwave Band Higher frequency X-band and Ku bands are used in space since there is no atmospheric interference The higher frequencies also have the advantage of higher data transmission rates which means higher bandwidth Higher bandwidth offers greater signal density Higher signal density allows more instruments and/or data on increasingly complex spacecraft Newer technology also allows higher signal density with lower mass and lower power consumption
  • Slide 10
  • Signal Characteristics
  • Slide 11
  • Communications Signals Signal characteristics The three fundamental characteristics of the communications signal are 1. Center (or carrier) frequency Frequency of transmission and reception 2. Signal bandwidth Signal data capacity 3. Modulation and encoding Used to format the data to make it compatible between the transmitter and receiver
  • Slide 12
  • Communications Signals Center frequency Orbiter communications covers three different microwave frequency bands UHF S-band Ku-band Each of the Orbiter's numerous communications systems includes two center frequencies, one to transmit signals and a separate frequency to receive signals simultaneously Known as duplex communications
  • Slide 13
  • Communications Signals Center frequency Each of the communications system operate on two frequencies called duplex links Uplink transmission from the ground station that is received at the spacecraft Downlink transmission from the spacecraft received at the ground station The exception to the duplex link is the Orbiter's S-band command data link The simpler format called half-duplex allows transmission and reception, but not simultaneously
  • Slide 14
  • Communications Signals Signal bandwidth Higher frequencies have inherently higher bandwidths unless the design incorporates a smaller bandwidth for lower noise content. The highest bandwidth in the Orbiter communications links is the highest frequency High-bandwidth Ku band is used for the TDRSS satellite link Lowest frequency link on the Orbiter which is the UHF communications links that carry voice communications and also has the smallest bandwidth
  • Slide 15
  • Communications Signals Data and signal modulation Data and data signals are modulated in two stages The first stage is data modulation Data are first encoded for easy digital conversion, transfer and identification These modulation types include Pulse code modulation (PCM) the most common spacecraft data modulation scheme Phase modulation (PM) Phase shift key modulation (PSK) Pulse amplitude modulation (PAM)
  • Slide 16
  • Communications Signals The Orbiter communications system's data modulation is Pulse Code Modulation (PCM) Analog signals are converted into digital signals by sampling circuits that function at specific levels (8 bit, 24 bit, 32 bit, 64 bit, etc.)
  • Slide 17
  • Communications Signals Data and signal modulation The second modulation stage is signal modulation Data that are communicated between spacecraft and ground stations are handled at a much lower frequency than the 2-3 GHz frequency used to transmit and receive the signals Therefore, the data must be mixed with the carrier (center) frequency that is in the 2-3 GHz frequency range The two types of Orbiter RF signal modulation are FM frequency modulation) and PM (phase modulation)
  • Slide 18
  • Communications Signals Following the two modulation stages in the transmitter and two demodulation stages in the receiver, the signal output from the receiver will be approximately the same as the signal input into the transmitter The difference in the two signals is a function of the quality of the transmitter and receiver, and the influence of external and internal noise Reproduced signal quality is determined by the communications system design
  • Slide 19
  • Orbiter Communications Systems
  • Slide 20
  • Orbiter Communications UHF Voice Duplex and simplex S-band Data, voice Duplex Ku-band Video, data Duplex
  • Slide 21
  • Orbiter Communications Data Types Telemetry Downlink data of the Orbiter's operating conditions and configurations, systems, payloads and crew biotelemetry measurements Command Uplink data directed to the Orbiter systems to perform functional or configuration changes Rendezvous and tracking Onboard radar and communications system for tracking and performing rendezvous with orbiting satellites/spacecraft Video Video imaging is used onboard, or relayed to ground from the crew cabin or on EVA activities, or from the payload bay, or from the remote manipulator arm Voice communications Intracommunications between the flight crew members, and between the flight crew and ground Documentation Printed data from the Orbiter's thermal impulse printer system
  • Slide 22
  • Orbiter Communications Data Types The Orbiter communications system frequency bands include: 1. S-band PM (Phase Modulation) FM (Frequency Modulation) Payload 2. Ku-band TDRSS data & video communications Rendezvous radar 3. UHF voice Ground EVA Note: Voice communications are also available through the military TACAN unit Other frequencies are used for the Orbiter's navigation subsystems and include C-band for the radar altimeter, L-band for the GPS and TACAN units, and Ku-band for the MSBLS landing system
  • Slide 23
  • Orbiter S-band Communications
  • Slide 24
  • Orbiter Communications S-band S-band communications are the most versatile of the Orbiter's communications bands Payload data, telemetry, commands, voice, and some video are handled with the multiple S-band units The versatile functions of the S-band communications include two modulation types Phase modulation (PM) Frequency modulation (FM)
  • Slide 25
  • Orbiter Communications S-band The Orbiter's S-band communications are used for Inter-Orbiter communications TDRS satellite uplink and downlink Payload communications Telemetry to/from ground Video and audio to/from ground DoD payloads (discontinued)
  • Slide 26
  • Orbiter Communications S-band PM The Orbiter's S-band Phase Modulation unit is the primary communications system which provides a duplex link between the Orbiter and ground, either through the STDN stations or through the TDRSS relay satellite S-band PM is the most versatile of the Shuttle's communications modes, providing communication channels for four primary functions
  • Slide 27
  • Orbiter Communications S-band PM Command channel - used to send commands from ground control to the Orbiter Voice channel - used for one-way and two-way voice communications between ground and Orbiter. Also used for the thermal impulse printer system Telemetry channel - carries real-time Orbiter and payload operational telemetry data to ground Turnaround tone ranging channel - used to aid in tracking the orbiter A precise RF carrier is transmitted to the Orbiter for timing and Doppler measurements
  • Slide 28
  • Orbiter Communications S-band PM S-band PM uplink The Orbiter's S-band duplex forward (up) link operates through the STDN or TDRS Carrier frequency is at either 2.106.4 MHz (primary) or 2.041.9 MHz (secondar