ESA ESOC 35meter Deep Space Antenna FrontEnd Systems

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• ESA / ESOC35-meter Deep Space Antenna Front-End
  Systems

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Authors

• Dennis R. Akins
• SED Systems, a division of Calian Ltd.,
  Saskatoon, Saskatchewan, S7N 3R1, Canada
• Rolf Martin
• ESOC / ESA, Darmstadt, 64293, Germany

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Overview

• In July of 1998, SED Systems of Saskatoon, Canada
  was awarded a contract by ESOC to supply the DSA1
  TTC antenna system
• 35 m diameter
• Initial operation in S-band and X-band downlink
  and uplink
• Upgradeable to Ka-band reception
• Installed at New Norcia, Western Australia
• Operational since November 2002
• Currently Supports the European Mars Express and
  Rosetta Missions

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DSA1 35 m S/X Deep Space Antenna
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DSA2

• SED is currently supplying a second 35 m
  front-end antenna system for ESOC
• Based on the DSA1 design
• Initial configuration X-band downlink and
  uplink, and Ka-band downlink
• Upgradeable to Ka-band transmit
• Will be installed at Cebreros, Spain
• Scheduled for acceptance in July 2005
• To be used for the European Venus Express
  spacecraft to be launched in November 2005
• Remotely controlled from ESOC Mission Centre at
  Darmstadt, Germany

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System Design

• Mission Requirements
• RF Design
• Optical Design
• Antenna Building
• Antenna Mechanical Structure
• Servo System

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RF Requirements
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Mechanical and Servo Requirements
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RF Design DSA2
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Major RF Equipment

• Passive RF components
• Feeds
• Beam waveguide mirrors
• Frequency selective dichroic plates
• Cryogenic LNAs - redundant
• Downconverters - redundant
• Upconverters - redundant
• HPAs
• DSA1
• 20 kW S-band and X-band KPAs
• 2 kW backup S-band and X-band KPAs
• DSA2
• Primary 20 kW X-band KPA
• Backup 2 kW X-band KPA and 500 W X-band SSPA

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Major RF Equipment

• Ranging calibration system for medium and long
  loop back testing
• Test Subsystem (uplink power/frequency
  monitoring, noise temperature measurement)
• Monitor and control equipment and software

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Optical Design
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Beam Waveguide (BWG) Optical Design

• Consists of reflective mirrors
• Dichroic plates (frequency selective surfaces)
• DSA1 M6 S/X and future M4a SX/Ka
• DSA2 M6 X/Ka and future M7a KaRx/KaTx
• Permit the use of separate feeds optimized for
  each band
• Feeds
• Optimized independent of one another
• X-band feeds are water cooled to operate with 20
  kW uplinks
• Are stationary, mounted in the antenna base near
  LNAs, HPAs and other RF equipment

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Antenna Building

• Ten-sided reinforced concrete structure
• 14 m diameter, 5.4 m high ceiling
• Conical roof supports the azimuth bearing
• Provides an environmentally controlled room for
  feeds and RF equipment
• Foundation is a reinforced concrete ring beam on
  reinforced concrete piles
• The outer walls are clad with insulating panels
  to keep deflections due to differential thermal
  expansion to less than 1 mdeg

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Antenna Building

• Ancillary systems are tightly integrated with the
  building
• Redundant air conditioners
• Non-deionized chilled water system for waveguide,
  feeds, helium compressors, and air-conditioners
• Deionized chilled water system for 20 kW HPAs
• Electrical power distribution (short break,
  no-break)
• Maser room
• Shroud to provide safety and RFI isolation from
  high power feeds in AER

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Mechanical Subsystem

• The azimuth housing is mounted on the antenna
  building by means of a roller bearing and a fixed
  steel base ring
• Azimuth housing
• Three story steel structure
• Two fixed bearings are mounted to the azimuth
  housing and define the elevation axis
• Supports the elevation portion on which the main
  reflector is mounted
• Elevation drive
• Four gear boxes and drive motors
• Gearboxes drive toothed gear segments on the two
  ballast cantilevers

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Mechanical Subsystem
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Main Reflector

• The main reflector is 35 meters in diameter
• DSA1 and DSA2 use identical surface shapes
• Over 300 high-accuracy panels made out of
  aluminum
• Panels attach to the reflector back-structure via
  adjustable studs
• The main reflector supporting structure
• A rigid truss constructed from steel pipes
• Supports the quadrapod for the subreflector
• Reflector and supporting structure are
  counterbalanced about the elevation axis by
  ballast cantilevers
• Precision alignment of the reflector surface uses
  a photogrammetry technique

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Subreflector

• 4.2 m diameter shaped hyperboloid
• Cast and welded aluminum
• Subreflector positioner
• Adjusts subreflector position to compensate for
  gravity displacement and tilt of the subreflector
  as the elevation angle changes
• Improves antenna efficiency
• S-band the effect is negligible
• X-band up to 0.7 dB loss if positioner is not
  used
• Ka-band up to 5 dB loss, if positioner is not
  used

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Servo Design

• The servo system consists of
• Antenna Control Unit (ACU). Interfaces to the
  Front End Controller (FEC) for receiving remotely
  generated program track data
• Safety interlock system
• Servo drive amplifiers
• Az and El axis drive motors and encoders
• Tiltmeters, used compensate for deflection of the
  azimuth part and tower due to wind pressure,
  thermal gradients, and/or foundation settling
• Pointing Calibration System (PCS) for DSA2

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Servo Design

• The ACU implements compensation models, in
  conjunction with the PCS to reduce systematic
  pointing errors
• Tower tilt
• Az and el encoder offset errors
• Gravity deformation of the main and subreflector
• Azimuth and elevation axis misalignment
• Collimation error between the RF beam and the
  optical axis
• Beam waveguide mirror and feed misalignment
• Polarization and frequency dependent beam squint
• Azimuth encoder gearing and toothing errors
• Thermal gradient deformation of main and
  subreflector
• Atmospheric refraction

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Servo Design

• The PCS is designed and manufactured by SED
• Measures systematic pointing errors
• Uses a sensitive radiometer to measure system
  noise temperature
• Tracks radio stars to determine the pointing
  error
• Determines the systematic pointing error model
  (SPEM) for the antenna
• Uses many individual pointing error measurements
• Curvefit technique is used to determine the SPEM
  (pointing error as function of Az and El)
• Compensates for thermal gradient
  deformation/displacement of main and subreflector
• 250 temperature sensors are distributed over the
  main reflector back-structure and subreflector
  support struts
• PCS reads these every 60 seconds
• Calculates the correction for the servo system to
  apply

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Conclusion

• The implementation of ESAs 35 m Deep Space
  Network is well advanced
• DSA1 is in service at New Norcia for European
  Mars Express and Rosetta missions
• DSA2 is scheduled completion at Cebreros, Spain
  in mid 2005
• Planned Ka/Rx Upgrade for DSA1
• Planned Ka/Tx Upgrade for DSA2
• DSA3 is in planning stages
• Lessons learned are being applied to achieve
  higher performance of successive antennas

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