Changes in the Deep Space Network to Support the Mars Reconnaissance Orbiter

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Changes in the Deep Space Network to Support the
Mars Reconnaissance Orbiter Jeff Berner Al
Bhanji Susan Kurtik
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Agenda

• MRO Mission Overview
• DSN Overview
• DSN Challenges
• High Data Rates, Turbo Codes, Reliable File
  Delivery
• QPSK Mode
• Ka Band Link, Delta-DOR
• Results so far
• Conclusion

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MRO Mission Objectives

• Improve our understanding of Mars and its climate
  as part of the Follow the Water Strategy
• Provide data that supports eventual human
  exploration
• Help researchers select landing sites for future
  missions
• Provide relay operations support for landers
  (Phoenix, MSL)

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Science Data Return Comparison
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What is the DSN?

• The DSN is made up of several interconnected
  facilities
• Deep Space Communications Complexes (DSCC)
• Canberra, Australia
• Goldstone, California
• Madrid, Spain
• Network Operations Control Center (NOCC)
• Pasadena, California
• Ground Communications Facility (GCF)
• Pasadena
• DSCCs

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Components of the DSN
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DSCCs

• Each DSCC is made up of
• Antenna structural and mechanical systems
• 1 70-meter antenna
• Multiple 34-meter antennas
• 1 26-meter antenna
• 1 11-meter antenna (currently inactive)
• Front end area electronics
• Equipment hard-wired to a particular antenna
• Microwave components, Receiver, Exciter,
  Transmitters, etc.
• A Signal Processing Center (SPC)
• 24 X 7 operations
• Equipment switchable to any antenna or globally
  shared
• Data processing equipment for Telemetry,
  Tracking, Command, and Radio Science
• Central monitor and control for the DSCC
• Operator consoles
• Voice communications
• Video surveillance
• Communications equipment
• Supporting facilities

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Network Operations

• Network operations in the Pasadena area provides
  centralized control and coordination of DSN
  activities around the world
• Network Operations Control Center at JPL
• Real-time monitoring of DSN activities 24 X 7
• Coordination of activities between the DSCCs
• DSN Operations Maintenance contractors
  facility in Monrovia, CA
• Operations planning and scheduling
• Support product generation
• Engineering support functions
• Configuration management
• Documentation
• Logistics
• Remote Operations Center

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Challenges to the Deep Space Network

• Highest Deep Space Mission Telemetry Rates
• 1.6 Mbps turbo coded (MESSENGER at 104 kbps)
• 3 Mbps convolutional / Reed-Solomon coded
  (SPITZER at 2.2 Mbps)
• 6 Mbps Reed-Solomon only (IMAGE at 2.3 Mbps)
• High Volume with long passes at high rates (165
  Gbits per pass possible)
• QPSK (Quadrature Phase Shift Keying) carrier
  modulation
• Puts twice as much data in same spectral
  bandwidth
• CFDP (CCSDS File Delivery Protocol) for high rate
  telemetry
• Protocol to copy file from spacecraft to mission
  database (and vice versa)
• Ka-band Downlink Demonstration
• Parallel X-/Ka-Band downlinks
• Ka-Band Delta-DOR (Requires new Wide band VLBI
  Science Receiver (WVSR) to process 2F1/8F1 DOR
  tones)
• Simultaneous X- and Ka-Band Delta-DOR (possible
  WAN limitations)

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Block Diagram
Ranging Modulation
Transmitter
Exciter
Command Modulation
JPL Central Processing
Delta-DOR Processing
Data Routing
X-band
RF-To-IF Conversion And Distribution
Ka-band Signal
X/X/Ka Feed
Ka-band Signal
Ka-band Error
Receiver Ranging Processing
New equipment
Ka-band Error
Telemetry Processing
Symbols
Modified equipment
Antenna Pointing
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High Data Rates

• MRO has highest data rates ever tracked by DSN,
  requiring updates to the station downlink
  channels
• Turbo decoder software updates and additional
  hardware, using inherent parallelism of block
  codes
• Telemetry output formatter software updates and
  hardware upgrades
• QPSK demodulation based on feedback from the
  decoders to set carrier phase offset
• Additionally, capability to transfer the data
  from the complexes back to JPL needed to be
  upgraded
• Wide Area Network (WAN) bandwidth has been
  increased
• Data flow control system upgraded to support 6
  Mbps ingest
• Provides buffering to store the data when the
  transmission bandwidth is less than the incoming
  data rate

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Reliable Science Data Delivery

• CCSDS File Delivery Protocol (CFDP) is a
  relatively new standard for transferring files
  between spacecraft and ground
• Similar in concept to the internets FTP
• File on board is broken into data units, sent to
  ground and reassembled via CCSDS protocol to
  generate file products on the ground
• While CFDP is used by other missions, MROs high
  downlink data rates placed additional constraints
  on the implementation
• Limited WAN bandwidth means that all telemetry is
  not returned in real time to JPL
• Frame accounting in real-time at station for high
  rate science data
• Science data delivery within 24 hours, but
  engineers may need to know what data to
  retransmit before all data delivered to JPL
• Therefore, a Frame Accountability capability was
  designed to inform the project which data units
  were on the ground, awaiting delivering back to
  JPL, so that the project could let the spacecraft
  delete them from the recorder
• Downlink channels at the station generate
  real-time frame accountability information to be
  sent in near real-time to the project

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QPSK Modulation

• QPSK puts twice as much data in the same spectral
  bandwidth
• Data on both the Inphase and Quadrature
  components of the signal
• Industry standard, but never previously used in
  Deep Space
• QPSK carrier demodulation capability has been in
  the DSN for ten years, but there has never been a
  mission using it
• To correctly decode the telemetry, feedback from
  the decoders was required to correctly set the
  carrier phase offset
• Recent consolidation between receiver and
  telemetry was used
• Since this is only done on high rate data,
  feedback process causes no noticeable delay in
  acquisition

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MRO Ka-band Demonstration

• MRO is the first major user of Ka-band (32 GHz)
  downlink for telemetry
• Ka-band is a demonstration for MRO
• Ka-band capability is in process of being added
  to the Beam Waveguide (BWG) antennas
• At least one antenna in each complex now has
  Ka-band operational
• MRO Ka Band experiments will include
• Demonstrating higher data return with Ka-band
• X-/Ka-band performance comparisons (transmitting
  same data on both bands simultaneously)
• Collecting Ka-band weather statistics

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MRO Ka Band Challenges

• Microwave implementation needed to minimize
  system noise temperature (required for power
  constrained deep space communications) and not
  reduce performance of X-Band at the same time
• Narrower beamwidth of Ka-Band reception required
  new antenna pointing techniques (DSNs closed
  loop CONSCAN pointing will not work)
• Narrow beamwidth means antenna pointing is much
  more susceptible to wind effects
• Delta-DOR measurements using Ka-band downlink
  will also be demonstrated
• This requires a new radio source map for Ka-band
  sources
• Since both Delta-DOR and radio source mapping are
  open loop processes, this requires more accurate
  antenna blind pointing capabilities
• Due to the large variation in performance due to
  the weather, Ka-band operations needs to take
  weather predictions into account and adjust
  downlink data rates accordingly

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Ka Band RF Implementation

• Minimal system noise temperature challenge
• Integrated feed to provide X-Band up and down,
  Ka-Band down (X/X/Ka feed)
• Ensures low noise reception for both downlink
  bands and high power capability for uplink
• Housed all Low Noise Amplifiers (LNAs) in one
  cryogenically cooled dewar and compensate for the
  fact that the X-band horns phase center is not
  coincident with the Ka-band horns phase center.
• Enhanced closed loop pointing challenge due to
  narrow beamwidth
• System needed to provide fast pointing updates,
  on order of a second or less (versus minutes with
  CONSCAN) to avoid simple degradation by winds
• System creates a difference signal in the X/X/Ka
  feed, which is detected open loop by the
  receiver, sending measured error signal 20 times
  a second to the antenna pointing controller
• Monopulse system still requires more accurate
  open loop, or blind, pointing capabilities

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Antenna Blind Pointing Enhancements

• Antenna blind pointing performance at Ka-band
  improved (requirement is 4 mdeg) for Delta-DOR,
  Quasar Cataloging, and Monopulse support by
• Developing Track Level Compensation (TLC) models,
  to remove the fixed biases due to the antenna
  azimuth track imperfections
• Updating the antenna pointing model from a first
  order model to a fourth order model
• Implementing an antenna calibration program
• Initially concentrated on models that cover the
  MRO trajectory
• Manual measurement effort
• Automated calibration equipment for complexes to
  use is being developed

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Cruise Phase Test Results

• During the cruise to Mars, testing and check out
  of some of the changes took place. Some of the
  preliminary results are as follows
• Ka-band
• Successfully used for both telemetry and
  Delta-DOR
• Pointing model work still being done, but 4 mdeg
  blind pointing was seen on some passes
• Monopulse demonstrated
• Problem with unexpected frequency dependence in
  the calibration process caused some work arounds
  that will need to be fixed
• Ka-band Delta-DOR
• Measurements done, with both Goldstone-Canberra
  and Goldstone-Madrid baselines
• Results as expected
• High rate telemetry
• 6 Mbps successfully demonstrated
• QPSK used
• WAN and Data flow control system upgrades were
  not in place, so equipment operation and
  scheduling work arounds were needed

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Cruise Phase Test Results (Cont.)

• Two performance issues regarding the strong MRO
  signal were found during the cruise phase
  testing
• Filtering of the symbols by the transponder for
  the high telemetry rates caused Inter-Symbol
  Interference (ISI), which degraded the Symbol SNR
  (SSNR) estimator
• Also degraded the System Noise Temperature (SNT)
  measurement, due to the fact that it uses the
  SSNR estimate to remove the data power from the
  measurement
• Extremely strong downlink ranging signal (on the
  order of 60 dB-Hz) caused degradation of SSNR
  estimator
• Depended on the symbol rate relative to the
  ranging frequency (1 MHz)
• Normal ranging signal strength is 10 dB-Hz or less

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Conclusion

• To support MRO, changes have been made in the DSN
  to
• Increase the data rate
• Reduce downlink data spectrum used
• Implement low noise X/X/Ka-Band feed
• Improve Ka-band antenna pointing
• Implement Delta-DOR at Ka-band
• Provide high data rate support for CFDP
• These changes are either in place or will be in
  place to support the missions need dates