Download Increased Thermal Background for the post-NCS NICMOS

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
 Accounting for DQE increase, the
average thermal background was
predicted to be approximatly 20%
higher than in Cycle 7
So, Where’s 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
T-1-1 Temperature Sensor vs. Time
Telescope Warm
Season
9/10/2002
Commanded Setpoint change
-
5/30/2003
Thermal Stability of the NICMOS
Enclosure 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)
Representation of Cold Mask
Misalignment
See Robberto, Proc. SPIE v4013, p.386 and Krist, NICMOSISR-00-011 for more details on the cold mask alignment
Rough Optical Path Diagram for the
NICMOS Fore-Optics
Thermal stability of the HST
optics 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
Thermal Environment of the HST Aft
Shroud around NICMOS 2001-2002
Thermal Environment of the HST Aft
Shroud around NICMOS 2001-2002
Aft Temperature Comparison of HST and
NICMOS
naftbtmp
NIC3,
F222m
HST AFT
TASINAFB
TAFTBULK
C7 & C11 NICMOS Aft Temps
NICMOS Temperature Variations
Avg. C7
Temp
Avg. C11
Temp
Delta T
Key
Descrip.
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
The NIC fore-optics swing in temperature in the same
manner as the aft end, but with a smaller amplitude
Direct plot of thermal background vs fore-optics
temperature
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
Simple blackbody comparison of HST and NICMOS
optical surfaces using NIC2 Optical Parameters
Comparing to the NICMOS Thermal
Background Code Estimates
Conclusions
The 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