GPS

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Section 29 Global Positioning System
. . . Dave Quinn EO-1 GPS Receiver Lead Engineer
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GPS Subsystem

• Off the shelf GPS receiver (Tensor),
  preamp/splitter and antennas from Space Systems /
  Loral.
• Power Conditioning Unit designed and built
  in-house.
• Provides orbital navigation and time information
  for CDH and ACS/EFF applications.

Hemispherical Antennas
Telemetry / Data IO
Power Conditioning Unit (PCU)
Receiver Processor Unit (RPU)
Preamp / Splitter Assembly (P/SA)
Power Input
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As Run Verification Matrix
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Projected Power On Time
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GPS -- Performance Summary

• Position Requirement 450m - 3s, in-track and
  cross track
• 1 Hz SPS Solution Capability m 95.35 m, s
  62 m
• 1 Hz Filter Solution Capability m 43.28 m, s
  33 m
• Velocity Requirement 1.0 m/s - 3s, in-track and
  cross track
• 1 Hz SPS Solution Capability m 0.74 m/s, s
  0.44 m/s
• 1 Hz Filter Solution Capability m 0.13 m/s,
  s 0.14 m/s

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GPS -- Summary

• Operating hours (as of 28-JUL-00)
• 976 failure-free hours for GPS Tensor, RPU, and
  Pre-Amp
• Configuration change, GPS Power Control Unit
  DC/DC Converter doubler
• No other configuration changes, zero
  non-conformances, no action items, no RFAs, no
  PRs
• No outstanding waivers
• No Redbook candidates

GPS is READY
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Special Topic Follow-Up GPS Signal Drop Outs
. . . Dave Quinn EO-1 GPS Receiver Lead Engineer
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Loss of GPS Signal During TV/TB

• During Thermal Balance/Thermal Vacuum test in OCT
  1999, significant GPS dropouts occurred during
  both hot and cold soaks
• Telemetry indicated that 1/4 of time GPS not
  providing timing information to CDH.
• Cause Isolated
• Cable Losses and insufficient signal strength
  between GPS rooftop antenna and antennas
  resulted in inability to lock onto 4 SVs even
  though they were available.
• RF Engineers brought in to correct GSE problem
• High loss RG-142 cable eliminated from GSE set-up
  wherever possible.
• Low Noise amplifier included in special
  weather-resistant rooftop antenna enclosure.
• Low noise cable runs shortened as much as
  possible.
• Significant improvement in signal levels noted
  with NO data dropouts
• Each of the four GPS antennas validated during
  T/V II test at Ambient, hot and cold plateaus.