Controlling the ACIS FP Temperature:

1
Controlling the ACIS FP Temperature Turning off
the DH Heater During Perigee Passages
ACIS Ops Team
2
New Proposed Test

• turn off the DH heater for an entire perigee
  passage
• monitor the Camera Body side A/B temperatures
  (1CBABT)
• If both side A and B read -72.2 C or colder,
  contingency response is to turn the DH heater
  back on

Success Criteria

• The Camera Body side A (1CBAT) -72.2 C and
  side B (1CBBT) -72.2 C for the duration of the
  test

Change to Standard Operations
If the test above is successful

• turn off the DH heater for all perigee passages

3
Summary of DH Cooling Tests

• proposed test is most similar to the first test
  and NOT like the other tests during the CDF-S
  observations in which the SIM is at the ACIS
  position
• first test resulted in a minimum temperature of
  -69.8 C for both 1CBAT and 1CBBT in 37 ks
• extrapolation of first test predicts
  temperatures of 1CBAT-71.6 C and 1CBBT-70.0 C
  after 56 ks
• 90 CL on asymptotic temperatures is 1CBAT-80.3
  C and 1CBBT-74.6 C
• primary survival heater should turn on at -71.1
  C and secondary survival heater should turn on at
  -73.6 C

4
How fast can the Camera Body get cold ?
First ACIS DH Cooling Test Perigee Passage
DePasquale (SAO), Vogrin predicts a steady state
temperature of -69 to -71 C at the HRC position
and pitch angle of 150
End
Begin
5
How fast can the Camera Body get cold ?
First ACIS DH Cooling Test Perigee Passage
Side B temperature, 1CBBT
End
Begin
6
How fast does the Camera Body warm ?
First ACIS DH Cooling Test Heating
DePasquale (SAO), commanded by SOP_61014_DAHTR_B_O
N DH heater draws a maximum of 60 W, survival
heaters draw 22 W If the survival heater turns
on, side A should respond faster than side B
7
Detector Housing Survival Heater Geometry
Trinh(NGST)

• HR7, HR8 22 W _at_ 29 V
• Prime survival -71.1 C
• Rdnt survival -73.6 C
• Better than 1.19 C accuracy (_at_ -70 C ) for
  1YA94 SSTS that controls survival heater
• Located on Z face of Detector Housing (side A,
  1CBAT)
• Closest telemetry thermistor is 1CBAT (FM07)

8
One Concern
The ACIS Camera Body and the Fid Lights get
colder than -72.2 C. Fid Lights
should not be allowed to drop below -76.0 C. How
could this happen ?

• primary survival heater fails to turn on
• thermostat for primary survival heater turns on
  at a temperature less than -71.1 C (how close are
  the temperatures read out by 1CBABT and the
  survival heaters ?)
• SCS 107 interrupts the load before the command
  to turn the DH heater back on is executed and one
  of the above is true

9
Implementation
-- DH heater will be commanded on and off in the
load (has been executed 6 times in the load) --
realtime COMs will be provided to monitor the
Camera Body temperature during the second half of
the perigee passage. FOT MP has identified COMs
on DOY 2007323 -- contingency CAP to execute
SOP_61014_DAHTR_B_ON will be ready to run
Time Elapsed Time Event 3230700 0.0 DH
side B heater is turned off 3231310 15000
s AOS, verify heater is off
3231410 18600 s LOS 3231545 31500
s AOS, verify temperatures
3231645 35100 s LOS 3232115
51300 s AOS, verify temperatures
3232240 56400 s side B heater turned on
3232310 58200 s LOS
10
Telemetry Verification
Camera Body temperature 1CBAT/1CBBT digitization
is 2.47 C

1CBABT
-71.1 C, primary survival heater set point
-73.8 C, secondary survival heater set point
-75.0 C, must not exceed

• side A (1CBAT) cools faster than side B (1CBBT)
• side B (1CBBT) warms faster than side A when the
  DH heater is used
• side A (1CBAT) should warm faster when the
  survival heater is used

11
Telemetry Verification
Five possible cases

• 1CBAT gt -72.2 C and 1CBBT gt -72.2 C -- allow
  test to proceed
• 1CBAT -72.2 C and 1CBBT gt -72.2 C -- allow
  test to proceed
• 1CBAT gt -72.2 C and 1CBBT -72.2 C -- allow
  test to proceed
• 1CBAT -72.2 C and 1CBBT -72.2 C --
  terminate test
• 1CBAT lt -72.2 C and 1CBBT lt -72.2 C --
  terminate test

12
Turn the DH Heater Off for FuturePerigee Passages

• Keeping the Camera Body colder will keep the FP
  temperature colder
• If the proposed test is successful, we want to
  turn off the DH heater for all perigee passages

Limit Changes
Mnemonic Current Yellow Low New Yellow
Low Current Red Low New Red Low 1CBABT -70.5
C -72.2 C -75.5 C -74.7 C Camera Body
Temp 1DAHBCU 0.80 A 0.0 A 0.20 A 0.0 A
DA Htr Current B 1DAHBVO 10.5 V 0.0 V 3.5
V 0.0 V DA Htr Voltage
B 1DAHHBVO 25.0 V 0.0 V N/A/ N/A
DA Htr Input Voltage B 1DAHTBEN Enb N/A

DA Htr B
Enb/Dis 1DAHTBON On N/A

DA Htr B On/Off