GOCE Workshop

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GOCE Workshop

• SATELLITE TO SATELLITE TRACKING INSTRUMENT
• DESIGN
• PERFORMANCE

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HERITAGE

• SSTI instrument is based on the LAGRANGE receiver
  architecture
• LAGRANGE receiver development started in 1998
  with Alcatel Alenia Space Italia S.p.A. internal
  funds
• The product is developed, manufactured and tested
  by the Navigation Department in Milan plant
• LAGRANGE X-prototype developed in 1999 with ASI
  contribution for demonstrative flight on SAC-C
  satellite
• LAGRANGE fully space compatible design completed
  end 2001
• LAGRANGE is onboard the following satellites
• RADARSAT-2 (2 FMs)
• COSMO SKYMED constellation 3 satellites (1 EQM
  6 FMs)
• OCEANSAT (1 EM 1 FM tailored for Radio
  Occultation application)
• Soyuz (1 FM)
• LAGRANGE was onboard Soyuz mission 10S in April
  2005 in the frame of ENEIDE mission

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DESIGN 1/3

• Receiver Type Integrated GPS receiver for
  spaceborne applications
• Channels 12 dual-frequency channels
• Frequency Band GPS L1 1575.42 MHz GPS L2
  1227.6 MHz
• Observables L1CA, L1P(Y) L2P(Y) Code L1CA
  L2P Carrier phase Instantaneous Doppler Time
  (Bias, Bias Rate)

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DESIGN 2/3

• Receiver Unit
• RF/IF Module
• Synch Module
• AGGA 2 Module
• Processor Module
• Power Supply Module
• Motherboard

• RYMSA
• GPS L1/L2 Antenna

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DESIGN 3/3
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MAIN FUNCTIONALITY

• Pseudorange measurements (Code Phase)
• C/A Code, for GPS L1
• P(Y) Code, for GPS L1 L2
• Integrated Doppler measurements (Carrier Phase)
• L1 and L2 Carrier Phase
• Signal and Noise measurements
• Signal to Noise Ratio C/No in dB/Hz units
  evaluated at the tracking loop input
• Real-Time Orbit Determination, determined using
  GPS C/A signal observations and navigation
  messages (PVT solution through SPS and Navigation
  Kalman Filter)
• Time measurements, determined from the GPS system

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ELECTRICAL INTERFACES

• POWER LINES
• N 1 Unregulated Primary Power Supply Interface
  (connected to Satellite Power Bus)
• TELECOMMANDS
• N 8 High Power ON/OFF Command (HPC) (Nom Red
  for Receiver ON, Nom Red for Receiver OFF, Nom
  Red for Watch Dog Enabling, Nom Red for Watch
  Dog disabling)
• TELEMETRY
• N 2 MIL-STD-1553B I/F (Nominal Redundant)
• N 1 Temperature Sensing Monitor I/F (TSMN)
  (Thermistor on the DC/DC Board)
• N 1 Analog Single Ended Monitor (ASMN) (5V
  Secondary Voltage Monitor)
• N 2 Relay Sensing Monitor (RSMN) (Unit ON/OFF
  and Watch-Dog EN/DIS Relays)
• SYNCHRONISATION
• N 2 External Synchronization Pulse Per Second
  (PPS) (Nominal and Redundant)
• RF INTERFACE
• N 1 RF Input (from Antenna)

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PHYSICAL BUDGETS

• Mechanical Dimensions
• 250 mm x 200 mm x 190 mm (LxHxW) including
  mounting feet
• 29.32 mm x 212.1 mm x 225.5 including Diplexer
  LNA Cables
• Mass
• Receiver Unit 5.35 Kg
• Antenna 490 g
• Cable to antenna 225 g
• Power Consumption
• 29.3 W (steady state)
• 32.1 W (OCXO warm-up)

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SSTI PERFORMANCE

• SSTI Characteristics
• Tight requirements in order to comply with system
  specifications
• Performance Requirements on three large areas
• Real-Time Navigation (PVT)
• Raw Measurements (errors, acquisition/tracking
  thresholds, biases)
• Robustness
• Temperature Sensors on-board placed on sensitive
  points of the RF board in order to allow
  calibration of Rx-specific biases (IFB)
• Precise Modeling/Testing of errors (Multipath,
  antenna CoP etc.)
• Peculiar measurement sampling procedure (sample
  after PPS in input), typical of timing receivers
• Freely drifting Rx time scale, Rx bias bound
  between 10 ms

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SSTI PERFORMANCE

• SSTI Performance Test Setup

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SSTI PERFORMANCE

• RT Navigation Testing
• Tested under Selective Availability ON and OFF
  (major source of RT navigation error)
• Output tested in different reference frames (ECI
  J2000, ECI TOD, ECEF)
• Orbital GOCE scenario, usually having a duration
  of 12 hours
• Period of time representative of GPS orbital
  period
• GOCE orbit modeled using a 70x70 gravity field
  model, GPS 8x8
• Drag-free simulation (DFAC compensation), no SRP
• Force model and reference frame basically limited
  by Spirent implementation.

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SSTI PERFORMANCE

• RT Navigation Scheme

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SSTI PERFORMANCE

• Real Time Navigation Requirements
• RT Navigation Results (S/A on)

Results with S/A off (current GPS status) - much
better NKF Position J2000.0 (3D - 3s) 30.35
m NKF Velocity J2000.0 (3D - 3s) 0.12 m/s
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SSTI PERFORMANCE

• Navigation Results (example)

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SSTI PERFORMANCE

• Visibility to GPS (example)

Direction Of Arrival Density Plot
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SSTI PERFORMANCE

• Acquisition-Tracking thresholds Measurements
  accuracy

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SSTI PERFORMANCE
SSTI Sensitivity to Ionospheric Scintillation

• A dedicated test campaign has been carried out to
  check robustness against ionospheric
  scintillation activity
• Ad-hoc test set-up (Test Equipment, SSTI firmware
  modifications)
• GISM (Global Ionospheric Scintillation Model)
  simulator by IEEA has been used to generate the
  scintillation time series in terms of amplitude
  and phase errors
• Amplitude fades injected at RF level using a
  programmable RF attenuator
• Phase errors injected at DSP level in the SSTI
  (pre-correlators carrier rotation)
• Orbital scenario in the RF simulator,
  scintillation error applied repeatedly during a
  pass.
• S4 values from 0 (no effect) up to 0.8. GISM
  version has S4 sigma_phi linked
• Analyses in terms of loss of lock on carrier
  phase in post-processing

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SSTI PERFORMANCE

• Ionospheric Scintillation Test Setup

Test Setup
Phase error injection
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SSTI PERFORMANCE

• Scintillation Time Series

• Example of amplitude and phase errors applied

Characterization in terms of loss of lock
sensitivity to S4 parameter
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SSTI PERFORMANCE

• Example of Results

S4 0.76 Not OK!
S4 0.6 OK!

• SUMMARY

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SSTI precursor ENEIDE
SSTI-Like experience on ENEIDE experiment (May
2005) different target application (combined
GPS/EGNOS/WAAS tracking from space) but same
technological base of SSTI

• LAGRANGE receiver installed inside the Soyuz
  Orbital Module
• GNSS antenna installed outside the Soyuz vehicle
• Laptop installed inside the Orbital Module and
  connected with LAGRANGE Receiver via MIL-BUS1553
  data cable
• The Crew MMI provides commanding and monitoring
  functions
• All the data acquired by LAGRANGE Receiver
  handled by the Laptop Software and stored on the
  PCMCIA Hard-Drive

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SSTI precursor ENEIDE
ENEIDE experiment antenna
LAGRANGE receiver
T. Col. Vittori ENEIDE Experiment Conductor
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SSTI precursor ENEIDE

• All the analyses conducted on the flight data
  allow to say that the ENEIDE experiment was
  carried out successfully.
• ENEIDE proved to be a benchmark for the
  validation of the AAS-I receivers of LAGRANGE
  class, like GOCE SSTI. The different
  environmental conditions in which the receiver
  operated (Sun-pointing attitude, orbital
  attitude, peculiar antenna pointing constraints
  etc.) made the experiment an important laboratory
  for different applications like attitude
  analysis, atmospheric sounding, space weather,
  real-time navigation and control.
• Reference
• A. Zin, S. Landenna, A. Conti, L. Marradi, M. S.
  Di Raimondo, ENEIDE an Experiment of a
  Space-borne, L1/L2 Integrated GPS/WAAS/EGNOS
  Receiver, European Navigation Conference 2006,
  (ENC 2006), May 08-10 2006, Manchester, UK.

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GOCE SSTI FACTS

• State-of-art GPS space receiver technology
• Advanced performance
• Twelve LAGRANGE flight models built (two SSTI
  FMs)
• Fully qualified for space applications for
  several satellites
• Flight proven

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• Thanks for your attention !