Chandra X-Ray Observatory CXC ACIS Ops team September 27, Controlling the ACIS FP Temperature: Results from the First Two Tests ACIS Ops Team

Chandra X-Ray Observatory CXC ACIS Ops team September 27, ACIS FP Temperature DePasquale (SAO) First ACIS DH Cooling Test: Perigee Passage Begin End

Chandra X-Ray Observatory CXC ACIS Ops team September 27, DePasquale (SAO), Vogrin predicts a steady state temperature of -69 to -71 C at the HRC position and pitch angle of ~150 First ACIS DH Cooling Test: Perigee Passage End Begin

Chandra X-Ray Observatory CXC ACIS Ops team September 27, DePasquale (SAO), commanded by SOP_61014_DA HTR_B_ON First ACIS DH Cooling Test: Heating

Chandra X-Ray Observatory CXC ACIS Ops team September 27, DePasquale (SAO) Second ACIS DH Cooling Test: OBSID 9593 CDF-S Begin End

Chandra X-Ray Observatory CXC ACIS Ops team September 27, DePasquale (SAO), Vogrin predicts a steady-state temperature of -68 to -70 C at the ACIS position and a pitch angle of ~120 Second ACIS DH Cooling Test: OBSID 9593 CDF-S Begin End

Chandra X-Ray Observatory CXC ACIS Ops team September 27, DePasquale (SAO), commanded in the load Second ACIS DH Cooling Test: Heating

Chandra X-Ray Observatory CXC ACIS Ops team September 27, What Have We Learned ? 1)The side B heater can be turned off and turned back on 2)The commands/script in SOP_61014_DAHTR_B_ON worked as expected 3)The commands in the load worked as expected 4)The time constant for cooling is shorter than expected (25-30 ks), this means that it is possible that the camera body temperatures (1CB[AB]T) could reach the point at which the survival heaters will turn on (primary C, redundant C) if the camera body is allowed to cool long enough and the spacecraft orientation permits 5)Asymptotic temperatures determined from the fits are consistent with Vogrin’s predictions 6)The DH heater will draw W when turned on for a short amount of time. 7)It takes the DH about 1 hr to get back to the nominal operating temperature of 1CBAT/1CBBT C/-59.9 C

Chandra X-Ray Observatory CXC ACIS Ops team September 27, New Proposed Tests 1)Conduct one test per week in upcoming CDF-S observations, there are CDF-S observations in the OCT1507, OCT2207, OCT2907, NOV0507, and NOV1207 weeks -- pitch angles vary between 130 and model predicts that 1CB[AB]T should not drop below -68/-66 C -- exposures vary from 28 ks to 160 ks (subject to change of course), we would select observations around 80 ks -- commanding in the load, with monitoring by ACIS Ops and CC/OC Possible Future Tests 1)Turn off the side B DH heater for perigee passages -- the HRC position is a colder orientation for the camera body, temperature might drop to the point at which the survival heaters would come on -- the CTI measurements would benefit from a colder camera body since the FP temperature would be colder -- we need to be comfortable with relying on the survival heaters to turn on at C and then off again at C -- we would like to come back to an FDB meeting in the future after we have thought about this more

Chandra X-Ray Observatory CXC ACIS Ops team September 27, ACIS Detector Housing Survival Heater Geometry HR7, HR8: V Prime survival °C Rdnt survival °C Better than 1.19 °C accuracy -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) Heater description Pr or Red Htr Bus Enable Cmd Disable Cmd Heater Flight Telemetry Mnemonic Heater Power at 29 volts (watts) Heater Resistance (ohms) Heater Close Set Point Temp (°C) Heater Open Set Point Temp (°C) Primary Heater Monitor Thermistor Mnemonic Backup Heater Monitor Thermistor Mnemonic ACIS Det. Hsg. Survival PR2NA CBAT1CBBT ACIS Det. Hsg. Survival RD7NA CBAT1CBBT Trinh(NGST)