TIPS/JIM
April 17, 2008
Agenda:
INS Division News (Jerry Kriss)
Observing Moving Targets with JWST (Ed Nelan)
Operations Detector Lab: Status and Issues (Mike Regan)
Recent Improvements in CALNICA (Tomas Dahlen)
Next TIPS/JIM: May 22, 2008 (Note date change!)
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Instruments Division News
04/17/2008
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Welcome to our newest staff member:
o Parviz Ghavamian joined the COS+STIS team on March 31. Parviz is
located in the Bloomberg center at JHU.
Congratulations to Stefano Casertano, who was promoted to Observatory Scientist,
and to Roeland van der Marel, who was promoted to full Astronomer.
HST news:
o SM4 is now no earlier than Oct. 8, 2008, with slips of 1-2 more weeks
likely. Consequences of this 6-8 week delay:
We get some breathing room on SMOV preparations. The baseline
plan is to finish Phase IIs on schedule, but stretch out analysis
plans as needed.
Use the extra time this summer to get a head start on Instrument
Handbooks and ETC testing for Cycle 18.
Take vacation this summer!
SMOV will now overlap more with preparations for the Cycle 18
CP. We may slip the CP to mid May (from April), but keep the
proposal due date in July.
There will be a new request, at some time, for names for launch
tickets.
o WFC3 thermal vac 3 is nearly done. Science calibrations finished last
night! Thanks again to everyone who is helping with the round-the-clock
staffing and who helped make the test run so smoothly and successfully.
o The STUC met here last week, uneventfully. Recommendations included:
Agree with project that FGS repair should not be a core priority,
but on a par with STIS and ACS repair.
Agreed with recommendation of WFC3 team to not clean the
droplets off the UVIS detector.
JWST news:
o JWST successfully passed Mission PDR at the beginning of April, and the
Non-Advocate Review (NAR) of budget and schedule is this week.
o The review board raised several issues at PDR. A partial list includes: the
sunshade, I&T plans, and detector development and procurement.
The new Ombudsperson, Beth Spotts, started yesterday. She will be here once a
month, in Room S216C. I encourage you to please use Beth as a confidential resource
for any workplace (or personal) issues you might have. Confidentiality is strictly
protected in all cases (with limits on physical abuse or endangerment). Talk to Beth if
you have any questions.
The next INS lunch is next week, April 24, in the Boardroom from 12:00-1:30. If you
wish to help plan and host this event, please contact Danny Lennon, Norm Grogin, or
Dave Golimowski. Thanks!
o The WIT Team will host our lunch in May (location TBD).
o Volunteers to coordinate future events would be welcome!
TIPS/JIM
April 17, 2008
Agenda:
INS Division News (Jerry Kriss)
Observing Moving Targets with JWST (Ed Nelan)
Operations Detector Lab: Status and Issues (Mike Regan)
Recent Improvements in CALNICA (Tomas Dahlen)
Next TIPS/JIM: May 22, 2008 (Note date change!)
1
Observing Moving Targets with JWST
Ed Nelan
TIPS
April 17, 2008
Moving Targets and JWST
JWST requirements documents make numerous references to “moving
targets”, but are qualified with a “TBD”. For example:
MR-371 Strehl Ratio for Moving Targets
“ … NIRCam shall have a Strehl Ratio greater than (TBD) when tracking any
available target that exhibits an angular velocity v up to (TBD) mas/sec …’’
MR-372 Moving Target Tracking
“ … the Observatory shall track targets with velocity (TBD) mas/sec over a
total motion of (TBD) arcsec …”
NASA wanted “TBD”s associated with Moving Targets to be resolved
before Mission PDR (April 2008)
Moving Target Study Plan
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NASA HQ allocated $250K for a 3 month study in June 2007.
– Creation of the “Moving Target Working Group” (NASA, NGST, STScI)
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The objective of the study was to determine:
– A technical solution to implement MT observations
– Define departures from observations of fixed targets (requirements,
system architecture and development / verification plans)
– The cost to implement the capability
– Final Report was submitted in November 2007
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NASA considered cost and scientific benefit to determine if JWST
should be able to observe Solar System targets.
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STScI studied this issue in 2002: JWST-STScI-000398.
– But this only considered impact to S&OC.
Moving Targets, what they are:
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Moving Targets are Solar System bodies:
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Kuiper Belt Objects
planets
moons of planets
asteroids
comets
Compared to stars, they are nearby, and they move. Their
position on the sky is determined by
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JWST parallax (because they are close by)
Ephemeris (because they move)
stop!
HST Legacy of Solar System
Observations
HST Observations of Solar System Targets
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Between 2001 and 2007, 13% of all HST public out reach releases
involved Solar System observations.
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But only ~4% of the HST program was dedicated to Solar System
observations.
galaxy
89
star
61
nebula
58
Solar System
45
miscellaneous
44
exotic
35
cosmology
26
star cluster
22
survey
18
HST Observations of Solar System Targets
•
Between 2001 and 2007, 13% of all HST public out reach releases
involved Solar System observations.
•
But only ~4% of the HST program was dedicated to Solar System
observations.
galaxy
89
star
61
nebula
58
Solar System
45
miscellaneous
44
exotic
35
cosmology
26
star cluster
22
survey
18
JWST observations of Solar System objects
• MTWG identified several science
drivers for JWST observations of
Solar System objects.
• KBOs and comets are choice
targets.
• comets originating beyond the
orbit of Jupiter have a different ratio
of hydrogen to deuterium than
Earth’s oceans (2x).
• comets in the main asteroid belt
(there are 3 known) may be the
source of Earth’s oceans.
• MIRI spectroscopy can measure
their hydrogen/deuterium.
What’s involved in
Moving Target Observations?
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Proposal Preparation, Planning & Scheduling and Execution is
more complex for moving targets:
– Target ephemeris
– JWST parallax and ephemeris
– Tracking.
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Complicates:
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Proposal preparation, guide star selection system (S&OC)
AD scripts
FGS
ACS
Solar System target rates depends upon when
they are observed.
25 mas / sec
Mars
From J. Nella,JWST kickoff Meeting, 10/23/02
Solar System target rates depends upon when
they are observed.
25 mas / sec
Neptune
1 mas / sec
From J. Nella,JWST kickoff Meeting, 10/23/02
angular rates of selected objects when
observable by JWST from L2
Object
Min. Rate
(mas/sec)
Max Rate
(mas/sec)
Mars
Jupiter
Jupiter,Io
Saturn
Uranus
Neptune
Pluto *
KBO
2.5
0.070
0.004
0.040
0.020
0.004
0.160
0.002
28.6
4.5
10.2
2.9
1.4
1.0
1.0
0.5
Distance
Traveled in 10 Time to Travel 1’
hrs at Min Rate at Max Rate (hrs)
(asec)
90.0
2.5
0.14
1.4
0.7
0.14
5.7
0.07
* Includes motion about Pluto-Charon barycenter
0.6
3.7
1.6
5.7
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24
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Moving Target Study: Procedure
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NASA restricted moving target study to consider only:
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tracking rates up to 3 mas/sec
linear tracks
16 mas pointing performance over 700 second intervals
only one guide star is used for the visit, no handoffs
WG was also instructed to evaluate implications of rates up to 30 mas/sec.
MTWG developed an Operations Concept to observe moving targets.
– assumed maximum use of HST/MOSS ground system
– preserved JWST event driven operations.
– excluded solutions that require hardware changes to JWST.
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The Operations Concept was developed into a Use Case to facilitate
the identification new requirements.
Moving Target Study, guide star usability
• In event driven operations, the visit window should be large
compared to the visit duration.
• On board scripts are provided with a list of guide star
candidates with usability windows
• Scripts select the appropriate guide star when the visit is about
to execute.
Moving Target Tracking and Offset Maneuvers
GS position after
Target Tracking is Disabled
current GS position
Combined Offset Maneuver
(GS Acq, Target Acq, Dither) and
(Moving Target Correction)
GS position moves while
Target Tracking is Enabled
GS position when Target Tracking is Enabled
Offset Maneuver 1
(GS Acq, Target Acq, Dither)
FGS Track Box after Offset Maneuvers
GS position for Target Tracking
after Offset 2 at Ts + Toff1
GS position for Target Tracking
after Offset 1 at Ts
Offset Maneuver 2 (Moving Target Correction)
compensates for the time it takes to execute the slew and re-acquire the guide star
Continuous tracking w/offsets (TA & dithers) *
11 - Science Exposure (Tracking ON)
Moving Target Tracking
(Tracking ON)
Combined Offset to Target
10 - Cmd Dither Offset
Moving Target Correction
(Tracking ENABLED)
9 - End Science Exposure
Commanded Offset
to Target
8 - Science Exposure (Tracking ON)
Moving Target Tracking
(Tracking ON)
Combined Offset to Target
7 - Cmd Target Acq Offset
Moving Target Correction
(Tracking ENABLED)
Moving Target Tracking
(Tracking ON)
Commanded Offset
to Target
1 - Acquire GS
2 - Specify GS ephem
3 - Enable GS tracking
4 - Cmd Offset to Target
6 - End Exposure
Combined Offset
to Target
5 - Target Acq Exposure (Tracking ON)
Moving Target Tracking (Tracking ON)
Commanded Offset
to Target
* from John Isaacs
Moving Target Correction (Tracking ENABLED)
New Requirements
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Observation planning and scheduling changes
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Very similar to moving target tracking on HST (affects APT, GSSS, etc).
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Affects ground-to-AD interface
Only six new or modified onboard commands
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AD sends GS ephemeris (Ps, dPs, Ts) to ACS
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ACS sends back computed GS position P(T) to AD
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AD sends estimate of command overhead time to ACS
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AD requests FGS to set 8x8 Track box (instead of 8x8 Fine Guide box)
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AD requests ACS to begin tracking moving GS ephemeris
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AD requests ACS to stop tracking moving GS ephemeris
ACS must add capability to evaluate moving GS ephemeris
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Some subtlety in keeping separate from dithers and offsets
FGS must accept new command to set 8x8 Track box
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Very similar to setting 8x8 Fine Guide box
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No other new requirements on FGS
Moving Target Capability Approved
A decision from today's science management council was to proceed with
including the moving target capability in JWST. Additional funds will be
provided to the program to cover these costs. The Planetary Science division
recognized this capability's value and has agreed to pay for it. We are
definitely going to do this.
I would like to thank George Sonneborn and the crew at STScI who worked on
this study. It was an easy sell because of all the excellent groundwork they
did.
Tuesday, Feb 07, 2008
Eric Smith, JWST Program Scientist
TIPS/JIM
April 17, 2008
Agenda:
INS Division News (Jerry Kriss)
Observing Moving Targets with JWST (Ed Nelan)
Operations Detector Lab: Status and Issues (Mike Regan)
Recent Improvements in CALNICA (Tomas Dahlen)
Next TIPS/JIM: May 22, 2008 (Note date change!)
1
ODL: Status and Issues
Mike Regan, Eddie Bergeron,
Kevin Lindsay, & Doug Long
Outline
• Using warm reference
pixels to test for EMI
• How to drop bits to
improve data compression
• Current Issues and
Testing
Raw reference pixels look significantly
different on a warm detector
• RMS is 5 times higher
• Standard deviation of the RMS is 20 times higher.
COLD
WARM
Our selectable noise source, the fans in
the readout electronics.
Filtering out the 1/f noise leads to an RMS
that is only 10% higher when warm.
Webb generates a lot of data and has
only one 8 hour contact a day.
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The assumption has always
been that we could do
lossless 2:1 compression in
hardware.
Using simulations with CRs
and bad pixels -> 1.7:1
What if we drop low order
bits?
– 1 bit = 1.9:1
– 2 bits = 2.1:1
– 3 bits = 2.5 :1
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What is the noise effect?
You can drop up to three bits and have no
effect on the noise.
Drop 5 bits
Drop 4 bits
The noise effect is larger for reference
pixels.
Drop 5 bits
Drop 4 bits
Drop 3 bits
We have many issues we are investigating that
will not be dealt with in instrument testing.
TIPS/JIM
April 17, 2008
Agenda:
INS Division News (Jerry Kriss)
Observing Moving Targets with JWST (Ed Nelan)
Operations Detector Lab: Status and Issues (Mike Regan)
Recent Improvements in CALNICA (Tomas Dahlen)
Next TIPS/JIM: May 22, 2008 (Note date change!)
1
Recent improvements to CALNICA
“a few highlights”
Based on work by:
Eddie Bergeron, Mike Regan, Vicki Laidler,
Robert Jedrzejewski, Helene McLaughlin & the
rest of the NICMOS team
TIPS, April 17, 2008 - Tomas Dahlen
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CALNICA overview
CALNICA performs instrumental calibration of NICMOS data:
- zero-read subtraction
- dark current subtraction
- correction for non-linearity
- flat-fielding
- cosmic ray identification and rejection
- calculation of count rates
- population of photometric keywords
CALNICA is used by pipeline/OTFR to produce final calibrated images
CALNICA is available in STSDAS so that users can customize calibration
Major improvements
• Optimum weighting when calculating count rates from up-the-ramp sampling.
• New way of handling cosmic rays.
Additional updates includes
• Detecting and flagging curvature in detector response
• Spike rejection
• Saturation in zeroth read
•…
TIPS, April 17, 2008 - Tomas Dahlen
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Highlight #1: optimal weighting
CALNICA uses up-the-ramp sampling with non-destructive read-outs during the exposure.
The count-rate is given by the slope of a straight line fitted to the data using a least square fit.
High count rate case
Low count rate case
Which is the best way to weight the reads in the up-the-ramp sampling?
TIPS, April 17, 2008 - Tomas Dahlen
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Highlight #1: optimal weighting
Fixen et al. (2000) show that for pure read noise, equal weighting of each sample gives
best result, while for pure Poisson noise, only using the first and last read is the best.
For any normal situation, the case will lie in between these.
Optimum weighting
from Fixen et al. 2000.
Weighting applied by
CALNICA in previous
version.
 The variance in the flux estimate decreases by up to 15%
 “Meaningful” errors - representing read noise
TIPS, April 17, 2008 - Tomas Dahlen
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Highlight #2: proper CR rejection
Previous CALNICA version subtracted the CR-jump from post CR affected reads
Introduces √ 2 x read noise bias in all post CR reads
Black dots: counts
as read by Calnica.
Red curve: old way of calculating the slope
CR jump between
“stars”.
Black curves: new CALNICA calculates
separate slopes that are weighted together.
A maximum of three separate slopes are used.
Red dots: counts
corrected for CR
jump in old Calnica
Preliminary results:
Median increase in S/N for a set
57 different flat-fields is ~ 9%.
TIPS, April 17, 2008 - Tomas Dahlen
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Highlight #3: “curvature” detection
In some special cases, NICMOS shows a variable
response that can have either positive or negative
curvature.
Occurs at “sharp” sources (points sources, CRs).
Appears to be due to insufficient settling time in A/D
conversion while clocking.
Old CALNICA did not detect these.
New CALNICA detects positive curvature via CR
detection (initially led to crash).
If there are >2 CRs in one read, then CALNICA
interprets this as curvature and not CRs. New DQ flag
is set DQ=16384 (curvature in detector response).
The slope is calculated ignoring the curvature.
 Combined effect of positive and negative curvature seems to average out.
TIPS, April 17, 2008 - Tomas Dahlen
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Summary
Two main features in the improved CALNICA:
• Optimum weighting when calculating count rates from up-the-ramp sampling.
• New way of handling cosmic rays.
A number of minor additional updates (will be presented in an ISR).
Final testing is ongoing.
To be included in OPUS 2008.2 and in next STSDAS release (~after Summer).
TIPS, April 17, 2008 - Tomas Dahlen
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