Power

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Section 18 Power
Allan Billings EO-1 Power Lead, Swales
Aerospace, Inc. Vickie Moran GSFC EO-1 Power
Lead Ralph Sullivan Power Consultant to Swales
Aerospace, Inc.
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Power System PSR Outline

• Power Mission Element Response
• Redbook Candidate
• Power System Readiness
• Special Topic

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As Run Verification Matrix
4
Projected Power On Time
5
Power Mission Element Response

• Changes in Verification Matrix---None
• Configuration Changes---
• New Version of PSE Software (Version 8.1)
  installed on 6/23/00.
• Purpose To ensure a defined, safe, load
  condition upon PSE restart.
• PSE to Load Shed on a Cold Restart.
• Switchable Loads to be shed
• ALI, LAC, X-Band XMTR, PPT, WARP, Hyperion
  Electronics Cryogenics
• Switchable Loads to be activated
• S-Band XMTR, ACE LVPC, CDH LVPC, Hyperion
  Survival HTR, SADE, RWA X, Y Z Control.
• Describe Recent Test Results Associated With T/V
  II
• Power System performed as expected
• All deviations from expected values were
  explained in PRs
• Thermal Vacuum II Test Results -- (Following
  Charts)
• Includes data trends test margins

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Test Results Calibration/Characterization

• A trending procedure was run in the background
  throughout TB/TV capturing the critical Power
  System telemetry points every 15 sec.
• The bus voltage, battery voltage, battery
  current, battery temperature, solar array module
  current, chassis current, output module 1
  current, and output module 2 current were
  sampled every 15 sec and compared to the
  GSE/Umbilical telemetry.
• All PSE telemetry was in agreement with
  GSE/Umbilical telemetry to within acceptable
  limits and the error did not change with
  temperature or pressure.
• A special calibration/verification of the half
  battery voltage differential against the battery
  GSE was added to the testing since the last
  thermal vacuum. As a result, a correction was
  made to the ground system conversion polynomial
  to increase accuracy.
• Additional telemetry was added to the trending
  procedure since the first thermal vacuum--PSE RSN
  15V, -15V, 5V, and battery PRT
  temperature--just to provide a more complete data
  book on the power system.
• Previous thermal vacuum verified that these
  telemetry were within red and yellow limits.
• The PSE was fully characterized in all modes of
  operation full charge/current limited charge,
  V/T clamped charge, and trickle charge.

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Significant Test Results For T/V II Test

• Key Telemetry Same As Thermal Vacuum 1
• Parameter Actual Range Requirement
• Battery Voltage 26.5V lt VBATT lt
  32.8V 22VltVBATT lt35VBus Voltage 26.4V lt
  VBUSS lt 33.1V 22VltVBUSS lt35VBus Power
  (Hot--DCE) Pavg275W, Pmax375W 300W average
  Battery Current--(Hot--DCE) ImaxCHG13A,
  ImaxDISchg-13A 18A chg i max Bus Power
  (Cold--DCE) Pavg300W, Pmax350WBattery
  Current(Cold--DCE) ImaxCHG12A,
  ImaxDISchg-12A 18A chg I maxBus Power Maximum
  Peak Peak 520W

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Significant Test Results For T/V II Test

• Parameter Actual Range Requirement
• Battery Temp Max (Launch) 21.5 deg C Tlt25C
• Battery Temp 6.5 deg CltTlt20 deg C 0ltTlt28C
• Solar Array Module Temp -4CltTlt53C -10CltTlt60C
• VT Setting Desired Did Not Change
• Determined that VT4 resulted in 100 SOC only at
  very end of charge cycle (day).
• V/T 5 resulted in 100 SOC well before end of day
  and will be nominal setting for mission.
• XTE and TRMM (both using the same battery)
  launched in V/T 5 with no anomalies to date.
• A higher V/T level at launch is preferred to
  enable maximum charging of the battery during the
  stressful sun acquisition phase of the mission.
• The V/T level can be lowered upon sun acquisition
  or at any time if desired.

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Power Mission Element Response

• Additional Peer Reviews
• None
• PSE Failure Free Time (to 7/28/00)
• 433 hours since last FSW load (6/23/00).
• 2553 hours since start of Environmental Test
  (Since installation on the S/C - 7/31/99).
• PSE Total Operating Time (to 7/28/00) 3527 hours
  since last hardware change
• No failures of PSE on S/C since 2nd integration
  into S/C.
• Open Action Items
• FSW004----Determine Low Voltage Limit for FDC by
  Launch - 15 days. Requires flight battery data
  which will be available before that time.
• All RFAs, PARs, PRs Closed
• Residual Risk--- One Redbook Candidate
• PR 837-20-1 - See following charts

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Redbook Item

• PR- 837-20- 1 The PSE LVPC Load Current Sum
  telemetry point (PLVPCLDI2) tripped its Red-Hi
  (9A) limit on Day 357, 1999.
• The event occurred after T/V I at ambient
  conditions.
• An FF value 19.275A (corresponding to the
  maximum value of the A/D converter in the RSN)
  was recorded for 1 sample only.
• This is the only recorded occurrence of this
  anomaly in 3527 hours (3.174 109 A/D
  operations _at_ 4ms rate).
• The RH limit tripped for 4 seconds (1 cycle).
• There was no other indication of an
  over-current.
• Other load-current samples in the 4-second packet
  (PLVPCLDI1, 3 and 4) were all nominal.
• The LVPC 8-Ampere over-current limit did not
  trip.
• No over-current recorded on the (active) the
  Umbilical monitor.

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Redbook Item

• Request for Action (RFA 33.04), including fault
  tree analysis completed
• Following possible sources of the event were
  investigated
• RSN Software --- no explanation found.
• Hardware --- There is an unlikely possibility
  that a narrow (lt25us) pulse could generate an FF
  in the A/D converter and provide no other
  indication.
• FEDS --- Source of the problem was not found at
  the time of the RFA
• Recent Investigation
• Currently, there is an investigation into the
  possibility that occasional, corrupted data
  packets might have been received by the ground
  system.

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Power System Readiness

• Statement of Readiness
• The Power System is Ready for Launch.
• All required test procedures complete and
  released.
• Solar Array successfully passed final
  inspection.
• Battery handling plan (SAI Proc. 242) complete
  and released.
• PSE thoroughly tested and ready for launch.

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Special Topic PSE Oscillation
Allan Billings EO-1 Power Lead, Swales
Aerospace, Inc. Vickie Moran GSFC EO-1 Power
Lead Ralph Sullivan Power Consultant to Swales
Aerospace, Inc.
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Issue

• During S/C simulation testing PWM solar array
  current was reduced from 4A to 2A to simulate a
  possible (but unlikely) S/A anomaly.
• Description of Issue
• As designed, a reduction of the PWM current to 2A
  caused the shunts to switch on and off, resulting
  in a low frequency oscillation in the battery
  charging current.
• This is an expected result.
• This condition is not likely to occur in orbit.
• However, there was some concern that the low
  frequency oscillation may have over-heated two
  damping resistors inside the PWM circuit.

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Test Analysis Performed

• EO-1 software loaded into MAP PSE ETU. Tests
  revealed that PWM cycle rate was 41Hz. Voltage
  waveforms across damping resistors indicated
  acceptable power dissipation
• R185 .69W, rated at 3W (1.5W De-rated per
  PPL-20)
• R186 .89W, rated at 7W (4.2W De-rated per
  PPL-20)
• Thermal analysis assuming 2W (in vacuum)
  indicated a temperature rise of the resistors
  less than 15 degrees.
• Assuming worst case board temperature of 53
  degrees (based on T/V I data), the worst case
  resistor temperature is less than an acceptable
  68C versus a maximum rated temperature in excess
  of 125 degC.

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Impact on EO-1 Mission

• There is no impact on the EO-1 mission.
• An impact is possible only if the the PWM solar
  array current is reduced to the current of the
  switched shunts (2A BOL) or less
• If this event occurs, the battery charging
  current will add approximately 2A p-p of low
  frequency oscillation to the power bus. The PSE
  can operate indefinitely this way without damage.

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Conclusions

• This condition is not likely to occur in orbit.
• If oscillations do occur, the PSE will not be
  damaged. The power system will function and
  complete the mission with increased noise on the
  power bus.
• There is negligible residual risk.