increased thermal background for the post-ncs nicmos
DESCRIPTION
Increased Thermal Background for the post-NCS NICMOS. TIPS – June 19, 2003 Megan Sosey NICMOS. Cycle 11 Calibration Plan. Parallel observations in NIC3:F222m, NIC2: F222m & F237M were crafted to re-measure the thermal background for cycles 11 and beyond -See proposals 9269 and 9702 - PowerPoint PPT PresentationTRANSCRIPT
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Increased Thermal Background for the post-NCS NICMOS
TIPS – June 19, 2003Megan Sosey
NICMOS
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CycleCycle 11 Calibration Plan 11 Calibration Plan Parallel observations in NIC3:F222m,
NIC2: F222m & F237M were crafted to re-measure the thermal background for cycles 11 and beyond
-See proposals 9269 and 9702
Accounting for DQE increase, the average thermal background was predicted to be approximatly 20% higher than in Cycle 7
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So, So, Where’sWhere’s the extra signal? the extra signal? NO correlation was found between the
variation in the thermal background and – telescope pointing – sun angle – prime instrument – time since SAA passage – or spacecraft orientation
The T-1-1 temperature sensor shows the detectors are stable under operation of the NCS and do not change by more than 0.1K on long time scales
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Telescope Warm Season
Commanded Set-point change
T-1-1 Temperature Sensor vs. Time
9/10/2002 - 5/30/2003
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Thermal Stability of the NICMOS Thermal Stability of the NICMOS Enclosure and Telescope AssemblyEnclosure and Telescope Assembly
NICMOS elements which affect the TB:re-imaging mirror (RM), FOM, PAM, filters, FDA(imaging mirrors), cold mask, bend mirrors, baffles, pupil
HST optics which affect the TB: primary mirror, secondary mirror, spiders,pads – these play significant roles in the TB because of their high temperatures (~290K)
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Representation of Cold Mask Representation of Cold Mask MisalignmentMisalignment
See Robberto, Proc. SPIE v4013, p.386 and Krist, NICMOS-ISR-00-011 for more details on the cold mask alignment
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Rough Optical Path Diagram for the Rough Optical Path Diagram for the NICMOS Fore-OpticsNICMOS Fore-Optics
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Thermal stability of the HST Thermal stability of the HST optics and aft shroudoptics and aft shroud
The primary and secondary have remained thermally stable, introducing no extra thermal emission - however, the aft shroud has increased approximately 10K since Cycle 7
There are multiple thermistor sensors (thermally sensitive resistors) in the aft shroud which are used to monitor temperature
-TAFTBULK is a weighted average of the internal sensors located on the aft bulkhead
-TASINAFB is an effective sink measurement from all the internal sensors, including some of the ones from the TAFTBULK average
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Thermal Environment of the HST Aft Thermal Environment of the HST Aft Shroud around NICMOS 2001-2002Shroud around NICMOS 2001-2002
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Thermal Environment of the HST Aft Thermal Environment of the HST Aft Shroud around NICMOS 2001-2002Shroud around NICMOS 2001-2002
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Aft Temperature Comparison of HST and Aft Temperature Comparison of HST and NICMOSNICMOS
naftbtmp
NIC3,
F222m
HST AFT
TASINAFB
TAFTBULK
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C7 & C11 NICMOS Aft TempsC7 & C11 NICMOS Aft Temps
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Key Descrip.
Avg. C7 Temp
Avg. C11 Temp Delta T
nfob2tmp Fore-optical brkt.
-5.82 C -0.48 C +5.34 C
ndosftmp Dewar Fore -7.27 C -1.21 C +6.06 C
ntrs3tmp Truss Aft 1.22 C 7.52 C +6.3 C
ndosatmp Dewar Aft -1.60 C 5.30 C +7.24 C
naftbtmp Aft NIC Encl. 8.5 C 17.5 C +9.0 C
taftbulk HST Aft Shroud
-17 C -7 C +10.0 C
NICMOSNICMOS Temperature Variations Temperature Variations
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The NIC fore-optics swing in temperature in the same manner as the aft end, but with a smaller amplitude
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Direct plot of thermal background vs fore-optics Direct plot of thermal background vs fore-optics temperaturetemperature
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Does this explain the increase?Does this explain the increase?
The previous plot indicates that a 2K variation in temperature, translates to a 1.5DN change in the thermal background
An increase of 5K between Cycle 7 and Cycle 11 yields an additional 3DN of thermal background signal! - this makes up the difference between the predicted and observed thermal background
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Simple blackbody comparison of HST and NICMOS Simple blackbody comparison of HST and NICMOS optical surfaces using NIC2 Optical Parameters optical surfaces using NIC2 Optical Parameters
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Comparing to the NICMOS Thermal Comparing to the NICMOS Thermal Background Code EstimatesBackground Code Estimates
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ConclusionsConclusionsThe overall temperature environment of NICMOS
and the operating temperature of the detectors has changed since cycle7 resulting in:
• Increase of ~17K in detector temperature• General temp. increase in the aft HST• Increased temperatures in the aft NICMOS• Increased thermal background in long
wavelength, or extra wide, camera 2 and camera 3 filters
• Thermal background exposures are still affective in removing the excess signal