XPAA

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Section 23 X-Band Phased Array Antenna
. . . Kenneth Perko EO-1 XPAA Lead, Microwave
Systems Branch
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X-Band Phased Array Antenna (XPAA)

• Validates electronically scanned antenna
  technology for future missions.
• No moving parts, redundant SSPAs, simplified IT.
• Designed and built by Boeing for NMP
  Communications IPDT under fixed price contract
  with GSFC.
• Boeing assumed cost risk for deliverable item.

• Provides 105 Mbps QPSK primary science downlink.

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XPAA Performance Summary

• Frequency - 8225 MHz
• Bandwidth - 400 MHz
• Scan Coverage - 60 deg half-angle cone
• Radiating Elements - 64
• RF Input - 14 dBm
• EIRP - greater than 22 dBW at all commanded
  angles
• Polarization - LHCP
• Command Interface / Controller - 1773 / RSN
• Input DC Power - lt58 watts over 0 to 40 C
• Mass - 5.5 kg

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EO1 X-Band Subsystem Diagram
Pointing Commands from Spacecraft via 1773
interface
XPAA
2 dB Attenuator
ESN Control Interface / Processor
Phase Settings
Science Data
Exciter/ Modulator
x 64
WARP
Coax Cables X-band Signal Modulated with Data
X-band Signal Radiated to Ground
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XPAA Acquisition / Review Process

• Contract Negotiations -- Continuous QA
  involvement to ensure satisfactory quality
  controls given the tight, fixed budget.
• Technology Verifications -- Independent
  evaluation of RF modules, their packaging, and
  array communications performance by GRC on Boeing
  EM hardware. EM was environmentally tested by
  Boeing at their cost prior to PKR.
• Formal Contract Reviews -- Program Kickoff Review
  (PKR), Interim Design Review (IDR), Antenna
  Acceptance Review (AAR). Weekly telcons.
• Post Delivery Test -- Approach developed with
  expertise from Swales and NSI, Inc.

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XPAA Principal Team Members

• Name Role Relevant Experience
• Ken Perko (567) XPAA Lead NMP Comm. IPDT
• Fernando Pellerano (567) Requirements Ka-Phased
  Array Procurement
• Don McMeen (Boeing) Program Mgt. Mil. Array
  Developments
• Ray Huggins (Boeing) Array Design GRC/Mil. Array
  Developments
• Richard Kunath (GRC) Array Testing ACTS Array
  Developments
• Kurt Shalkhauser (GRC) RF Module Packaging ACTS
  Array Developments
• Tom Dod (Swales) Near Field Tests GSFC Antenna
  Group
• Alan Newell (NSI, Inc) NF EIRP Developed NF
  Tech. At NIST Measurements

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XPAA -- Scope of Box-Level Testing

• Contract Acceptance Testing
• Random vibration, shock, thermal vacuum, EMI/EMC,
  1773, and RF functional tests using hat coupler,
  near-field scanner and anechoic chamber.
  Environmental levels determined by Swales
  document "Verification Plan and Specification for
  NMP Earth Orbiter 1 (EO-1)".
• Bench Testing
• RF and 1773 functional tests using a hat coupler
  to absorb and sample the RF output. Results
  compared with contractor supplied acceptance
  data.
• Near-Field Scanning
• Verifies antenna beam characteristics and
  pointing performance, does not require an
  anechoic chamber. Results compared with
  contractor supplied acceptance data.

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XPAA Qualification Test Flow (1998)
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XPAA Test Flow (2)
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XPAA Trended Parameters
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NF Scanner in Position in Front of the XPAA
During Near Field Test 3
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Processed NF3 Data for XPAA (Theta0, Phi0)
Aperture Amplitude Far Field Cut Aperture
Phase Far Field Contour
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XPAA Hardware Changes Since Delivery

• Change
• Replaced 1773 interface connector (1 of 4).
• Reason
• During pre-integration inspection and test this
  connector was found to have a cracked internal
  ceramic sleeve.
• Action
• RSN card was removed and connector was replaced
  at GSFC FOIL.
• Result of the Modification
• After repair and workmanship vibration,
  end-to-end 1773 and RF performance was verified
  with GSE and Near-Field Scanner at Swales.

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XPAA Software Changes Since Delivery

• Change
• Updated RSN operating system.
• Reason
• EO-1 requires all RSNs use the same operating
  system version.
• Change
• Box-level fault detection constants updated.
  (Addressed PRs on next slide.)
• Reason
• Prevent false alarms.
• Change
• Telemetry A/D time constants changed (all RSNs)
  after NF3.
• Reason
• EO-1 requires all RSNs use the same operating
  system version.

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XPAA Critical PRs
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XPAA Action Item Status

• No open items.
• XPAA on-time since integration as recorded by
  EO-1 -- gt350 hours, Data Collection Events
  (downlinks) gt300.

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XPAA Statement of Readiness

• The XPAA is ready to fly.
• There are no known Redbook issues.
• No special tests for the XPAA (such as pointing)
  are planned beyond normal IT activities.
• There is one issue of low residual risk
• Software change after last NF test, to an A-to-D
  wait-state constant, required for all RSNs.
• This affects analog measurements (telemetry) on
  the RSN.
• Does not affect the XPAA beam-pointing code at
  all.
• Telemetry will be re-evaluated during IT.
• Software is repairable in-flight using a patch to
  RAM.