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35meter Deep Space Antenna

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LAN interfaces to FEC, ACU, WSDS (weather server), radiometer, and TMS ... After the scan is complete, radiometer results are read ... – PowerPoint PPT presentation

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Title: 35meter Deep Space Antenna


1
  • 35-meter Deep Space Antenna
  • Pointing Calibration System

2
Authors
  • Ron Osterried
  • SED Systems, a division of Calian Ltd.,
    Saskatoon, Saskatchewan, S7N 3R1, Canada
  • Peter Droll
  • European Space Operations Centre of ESA (ESOC),
    Darmstadt, 64293, Germany
  • Bob Plemel
  • SED Systems, a division of Calian Ltd.,
    Saskatoon, Saskatchewan, S7N 3R1, Canada

3
Background
  • In 2005 SED Systems installed and commissioned
    the X/Ka-band 35-meter antenna system at
    Cebreros, Spain including a pointing calibration
    system (PCS)
  • The pointing error (PE)requirement is 5.5 mdeg
    or 1.2 dB under worst conditions
  • The PCS is fully automated and under remote
    control.
  • The PCS measures and provides corrections for
    systematic pointing error.

4
Systematic Pointing Error Sources
  • Sources of pointing error
  • Refraction (actively corrected)
  • Gravity (SPEM)
  • Misalignment (SPEM)
  • Beam squint (SPEM)
  • Thermal deformation (active thermal correction)
  • Wind (stiff antenna structure and drive)

5
Systematic Pointing Error Model
6
PCS System Design Main Elements
  • The main elements of the PCS are
  • Pointing Calibration Computer (PCC) Server
  • PCS Workstation (PWS)
  • Radiometer/Noise Diodes
  • Temperature Measurement System (TMS)
  • The main interfaces of the PCS are
  • Antenna Control Unit (ACU)
  • Front End Controller (FEC)
  • WSDS (Weather Station Data Server)
  • Noise injection RF Couplers before LNAs
  • Downconverter IF outputs to radiometer

7
PCS System Design Block Diagram
8
PCS System Design PCC and PWS
  • Pointing Calibration Computer Server (PCC)
  • Runs the PCS application software to control the
    pointing calibration process
  • IRIG-B time interface
  • LAN interfaces to FEC, ACU, WSDS (weather
    server), radiometer, and TMS
  • Pointing Calibration Workstation (PWS)
  • Provides the local user with a graphical
    interface for the PCS
  • A remote access capability is provided to allow
    the same functions from a remote workstation
  • MC, initiate measurements, view historical
    results, interactive SPEM coefficient calculation

9
PCS System Design Radiometer
  • Radiometer
  • Used to measure system noise temperature
  • Standalone chassis / LAN interface
  • Separate inputs for each downlink frequency band
    and polarization
  • 100 MHz bandwidth at X band, 200 MHz at Ka band
  • IRIG-B time interface
  • Scheduled measurements to 1 msec timing accuracy
  • Noise adding and total power modes
  • Custom designed circuit boards populated and wave
    soldered in plant at SED
  • Menu driven, intuitive local front panel control

10
PCS System Design Radiometer Boards
Radiometer MC Processor Board
Radiometer RF and Measurement Board
11
Temperature Measurement System
  • Antenna Physical Temperature Measurement System
    (TMS)
  • 252 temperature sensors located on the main
    reflector back-structure, K-strut, ballast
    cantilevers and the subreflector quadrapod struts
  • Temperature data is used by the PCS to calculate
    thepointing error due to thermal distortion of
    the mechanical structure
  • Sensitivity of pointing change for a unit
    temperature change for each sensor node is from
    finite element analysis
  • Update rate 30 seconds

12
PCS TMS Window
13
Installed PCS Antenna Rack
14
PCS Operating Modes
  • PCS Operating Modes
  • Calibration Mode and Schedule
  • PE Measurement (within a calibration)
  • SPEM Calculation and Transfer to ACU
  • Compensation
  • Operator Direct PE and Noise Temp Measurements

15
Calibration Mode
  • Calibration Mode
  • PCS enters calibration mode if PCS has control
    and a calibration is requested locally or
    remotely
  • Typical calibration for one frequency band, one
    polarization, will take approximately 8 hours
  • Approximately 230 PE measurements are taken
  • Main elements of the calibration process
  • Scheduler
  • Individual PE measurements
  • SPEM coefficient calculation using results
  • Coefficient Transfer to ACU

16
Scheduler
  • The operator begins by specifying
  • Start time and duration of a calibration
  • Constraints, if any (min/max elevation, min flux)
  • The scheduler automatically selects calibration
    sources defined in the PCS database
  • Sources have an angular extent of less than 1
    mdeg
  • Flux density gt 1.5 Jy in both X- and Ka-band

17
Scheduler (contd)
  • The scheduler automatically builds a measurement
    schedule
  • Maximizes the number of PE measurements to be
    made in the calibration period by minimizing
    antenna motion
  • Provides near-uniform distribution over the
    hemisphere
  • Gives preference to radio stars crossing through
    infrequently covered areas of the sky
  • Gives preference to higher flux density sources
  • Avoids sun and moon

18
PCS Scheduler Output Window
Scheduler Output for 8 hour Calibration (227 PE
Measurements)
19
PE Measurement Method
  • PE Measurement Method
  • PCS calculates the track of the star using
    TpointTM slalib Software
  • Uses a grid of Az and El offsets around the
    nominal position of the star
  • X-band beamwidth 64 mdeg
  • Ka-band beamwidth 17 mdeg
  • PCS commands the antenna to follow a trajectory
    through the grid points
  • PCC schedules N x N radiometer measurements of
    system noise temperature centered at each grid
    point

20
PE Measurement Method (contd)
  • After the scan is complete, radiometer results
    are read
  • Typical time for one PE measurement is 1 minute
    including calculations
  • A mathematical model is fit to the measured Tsys
    data to determine the location of the RF beam
    relative to the commanded position
  • PE measurement data is stored in the database
    including raw pointing error which is the
    measured pointing error plus all current
    systematic corrections
  • PE measurement results can be viewed live or
    historically

21
PE Measurement PCS Result Window
22
SPEM Calculation
  • SPEM Calculation
  • Can use between 30 to 10,000 PE measurements
  • Mathematical model (SPEM) is fit to the PE
    measurements
  • Model for DSA2 contains 10 independent
    coefficients (14 total with redundancies)
  • Interactive calculation tool with exclusion to
    user specified statistical threshold (e.g. 3
    sigma)
  • Operator defined database filters. Filters are
    logged with all calculation results.
  • Residual pointing error graphical views provided
    by PWS gui

23
SPEM Calculation Raw Pointing Error
24
SPEM Calculation Residual Error
25
Transfer and Compensation Mode
  • SPEM Transfer
  • After SPEM Calculation, the PCC transfers SPEM
    coefficients to the ACU
  • ACU is in maintenance mode during transfer
  • Compensation Mode
  • Normal operating mode of the PCS
  • PCS calculate thermal correction values from the
    current TMS data and transfers the values to the
    ACU
  • ACU applies corrections to all commanded antenna
    positions
  • SPEM, Refraction, Measured Tilt, thermal from PCS

26
Other PCS Capabilities
  • Direct Mode Noise Temperature Measurements
  • Measure Tsys at any azimuth/elevation
  • Useful for monitoring system performance over
    time especially for changes due to the cryogenic
    LNAs
  • Measure elevation dependence of the noise due to
    atmospheric thermal emission
  • Direct Mode PE Measurement
  • Verify pointing by selecting any visible radio
    star
  • Can be used to repetitively measure PE on a
    single radio star
  • Can be used for G/T measurements using offline
    formulae
  • Available under remote control

27
Direct Mode PE
28
Beam Squint
Measured Difference between LHCP/RHCP SPEM (1-2
mdeg)
Predicted Difference between LHCP/RHCP (1.8-1.9
mdeg)
29
Moon Scan
30
Conclusion
  • PCS accurately determines systematic pointing
    error
  • Ideal for high usage TTC systems full
    automation allows effective use of small blocks
    of antenna time
  • PCS provides flexible tools for monitoring and
    antenna performance

31
References
  • Droll, P., Cozzani, A., Sieber, R., Schäfer, M.,
    A Thermal Distortion Model for the ESA DSA in
    Perth for Compensating Thermally Induced Pointing
    Errors, Second ESA Workshop on Tracking,
    Telemetry and Command Systems for Space
    Applications 2001, ESA/ESTEC.
  • SLALIB, Positional Astronomy, Software Package,
    Tpoint Software, Abingdon UK, 2003.
  • Vertex Antennentechnik, Technical Note Systematic
    Pointing Error Model, VA Document No.
    TN1003057-31440, Release 1.5, Internal Document

32
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