C

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Section 20 Command Data Handling (CDH)
. . . Philip Luers NASA/GSFC
. . . Steve Schumacher Swales Aerospace, Inc.
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ACDS Contents

• Block Diagram (for reference)
• Recent Activities
• Residual Risk
• Problem Reports
• Special Topics
• A/D converter anomaly
• MOC timekeeping
• Statement of Readiness

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ACDS Box Block Diagram
Power System Electronics (PSE)
1773 Fiber Optic Data Bus
ACE
CDH
Inertial Reference Unit (IRU)
Coarse Sun Sensors (4x)
GPS Receiver (GPS)
Three-Axis Magnetometer (TAM)
HOP Actuators (HOPS)
Autonomous Star Tracker (AST)
Light Flex Solar Array (LFSA)
Reaction Wheels (RWA, 3x)
WARP Science Data Recorder
Magnetic Torquer Bars (MTB, 3x)
S-band Transponder
Reaction Control System (RCS)
Spacecraft Heaters (Bays 1-6)
Pulsed Plasma Thruster (PPT)
Spacecraft Temperature Sensors
Solar Array Drive (SADA/ECU)
Solar Array (Hinge pots and Htr)
Solar Array (Dep HTR and pot)
Solar Array Drive Temperature
Umbilical and APTS Racks
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As Run Verification Matrix
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Projected Power On Time
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ACDS Recent Activities (1 of 2)

• Recent changes to the verification matrix since
  the initial red team review
• None
• Configuration changes since the initial red team
  review
• None
• Recent test results associated with T/V II
• Trending results showed no correlation of changes
  of voltage nor current with temperature of ACDS
• 4 temperatures, 4 voltages, 4 currents every 5
  minutes for a total of 135,924 points
• S/C timekeeping verification performed
• GPS ON verified to be identical in character to
  test results from 12/15/99
• GPS OFF verified to be identical in character
  to TV I results

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ACDS Recent Activities (2 of 2)

• Technical peer reviews since the initial Red Team
  Review
• None
• Operating time since last modification
• Total on time since beginning of environmental
  test
• 7/31/99 - 7/28/00 2553 hours on spacecraft
• On time since last modification (Interpoint power
  converter stiffener rework)
• 3/13/00 - 7/28/00 679 hours on spacecraft
• Open action items
• None

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ACDS Residual Risk

• Remaining work to be completed
• None
• Open action items that are still being worked
• None
• Open test anomalies
• None
• Could-not-duplicate test anomalies
• None
• Redbook candidates
• None

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ACDS Problem Reporting

• Flight Hardware Issue
• WOA 1095-20-5 185-1509 RCS Tank Pressure
  telemetry point varying by 3 PSI. Telemetry is
  toggling from 77F to 784 hex with no intermediate
  values
• See A/D converter special topic. Use as is.
• Misinterpretation of test results by ACDS Lead
• WOA 1099-20-23 Spacecraft time jumping
  erratically with GPS ON. Behavior with GPS OFF
  is nominal
• Magnitude of time jumps (with GPS ON) is 1-2 ms,
  mostly below 1 ms. Review of test data from
  12/15/99 showed that this is nominal behavior.
  ACDS Lead did not have access to prior test data
  when PR was opened. Requirement for spacecraft
  time to be no greater than 10 ms away from ground
  time is met with 80-90 margin.

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Special Topic A/D Conversion Anomaly
. . . Harry Culver EO-1 CDH Systems Lead
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Special Topic A/D Converter

• A/D conversion anomalies during MAP MAC box-level
  thermal vacuum led to investigation
• Stuck LSBs were found near A/D converter decision
  points (½-scale, ¼-scale), referred to as holes
  in data
• Readings of smoothly varying signals stick at
  point below decision point and then jump point
  above with no reading in between (for example 7F4
  straight to 804)
• All affected EO-1 subsystems in agreement at
  initial red team review that systems could be
  used as is
• Investigation of cause was undertaken by GSFC
  Code 561
• Performed extensive probing of MAP MAC
  housekeeping RSN ETU on extender card to identify
  character of signal
• Modified software to perform various instructions
  before start of conversion, and during
  conversion, noted high correlation between
  instructions and noise on analog signals

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Special Topic A/D Converter

• Determined cause and recommended solution
• ESN MCM (which includes microprocessor and analog
  in same package) has A/D converter analog signal
  input pin and instrumentation amp signal input
  pin interspersed with digital signals
• Source of noise is coupling of instruction
  address and data bus onto A/D input and
  instrumentation amp input pins
• MAP Flight Software engineer assisted in
  determining optimum instruction mix before start
  of conversion and during A/D conversion that made
  analog signals quietest and eliminated holes in
  A/D data. Tested on MAP HK RSN and others.
• Impact of flight software change to ACE, PSE, and
  HK RSNs was too great to implement at this point
  in program
• All subsystems in agreement that use as is is
  best policy
• Lowest 4 bits of A/D converter value are
  operationally unimportant

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Special Topic MOC Timing
. . . Harry Culver EO-1 CDH Systems Lead
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Special Topic MOC Timing

• Verified proper operation of S/C timekeeping
  12/99
• S/C verified with GPS ON, within 1 ms of ground
• S/C verified with GPS OFF, drift was measured and
  demonstrated compensation features of flight
  software
• Testing of the ground system was not complete at
  time of initial Red Team Review
• Ground station PTP generates ground time-tag of
  incoming marked frame.
• MOC software compares ground time-tag with
  telemetered S/C time of marked frame. Accounts
  for delays through flight system and ground
  system, and calculates difference to 1 ms
  resolution.
• PTP was unable to time-tag data to high enough
  accuracy to meet 10 ms requirement

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Special Topic MOC Timing

• Ground station PTP hardware and software were
  modified
• Fixed problems that arose due to telemetry
  sequence breaks
• Ground station personnel assembled procedure for
  correct usage of PTP
• Fixed drift problem with PTP
• Performed retest of PTP in full ground station
  configuration 7/18/00 during Thermal Vacuum II
• PTP version 1.49 software and drivers
• Same time reference configuration
• Operational MOC software
• No retest required

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Summary of Open Items from MarchRed Team Review

• Test and Verification flow -- no update necessary
  (page 19-13)
• Verification Matrix -- no update necessary (page
  19-14)
• PR 797-70-02 Bus Buster showed non-uniform
  distribution of retries when run with minimal
  spacecraft bus traffic (page 19-16)
• Further bus busting retest was performed
  following March Red Team Review with expected
  uniform distribution of retries
• PR 818-20-02 MOC issued commands when not enabled
  for commanding (page 19-16)
• MOC and IT have successfully handed over dozens
  of times without confusion and loss of commands.
  Issue resolved.
• Updated operating hours are included in this
  package on page 20-5 (page 19-19).
• Results of retest of Ground System time
  correlation verification (page 19-21 and 19-25).
• Retest detailed in special topic. Issue resolved.

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Statement of Readiness

• The EO-1 ACDS is ready for shipping to VAFB and
  subsequent launch