TIPS-JIM Meeting
17 February 2005, 10am, Auditorium
1.
Planning Activities for Deliberate
Entry Into 2 Gyro Mode
Bill Workman
2.
HST Guiding Errors in 3-Gyro
Ron Gilliland
3.
ASICs for JWST
Don Figer
Next TIPS Meeting will be held on 17 March 2005.
Planning and Scheduling 2-Gyro Analysis Activities
PLANNING AND SCHEDULING
2-Gyro Analysis Activities
February 17, 2005
Bill Workman
2
Planning and Scheduling 2-Gyro Analysis Activities
Purpose
!
Provide data on 2-Gyro execution rates to support decision making
for:
– Cycle 14 TAC - 2-gyro mode orbit allocation
– NASA decision on whether or not (and when) to deliberately enter 2-Gyro mode
!
Provide input to Phase I proposal selection process
– Summary of inherent planning difficulties in the Cycle 14 science program related
to target selection and observing constraints as reflected in:
• Potential observing conflicts
• Unallocated observing opportunities
– Recommendations/options for addressing potential problems
February 17, 2005
Bill Workman
3
Planning and Scheduling 2-Gyro Analysis Activities
2-Gyro execution rate analysis
!
Create complete operations test data set
– Select most of the Cycle 13 GO and DD data set
• ~ 3000 visits totaling ~ 4800 orbits
• Represents a typical 3-gyro beginning of cycle subscription level
– Process proposals and compute scheduling constraints using latest available 2-gyro
software
• TRANS, SPIKE
!
Build 2-Gyro constrained plan and weekly schedules
– Build 2-Gyro constrained Long Range Plan (LRP) using SPIKE
• Using the nominal Cycle 13 planning interval
– Allows direct comparison with 3-gyro plan
• Use 3-gyro execution rate (80 orbits/week) as upper resource limit
– Build 2-Gyro science calendars (SPSS) using 2-Gyro LRP plan window assignments
• verify individual visits can schedule where assigned by 2-Gyro SPIKE
• determine actual orbits/day execution limit
February 17, 2005
Bill Workman
4
Planning and Scheduling 2-Gyro Analysis Activities
2-Gyro execution rate analysis
!
Analysis will determine the range of probable 2-gyro execution rates
– Variables that can affect execution rate :
• % of visits with constraints (orient, timing)
• Target RA distribution of data set
– Limitations of evaluation data set:
• Cycle 13 observations are not ‘designed’ for 2-gyro
• ~40% of Cycle 13 data set is not compatible with 2-Gyro scheduling because of
timing and/or orient constraints
• Must plan and schedule these with PI specified constraints removed
• Essentially this allows us to evaluate a ‘best case’ scenario
– Creates assumption that either 40% of a 2-gyro observing cycle will be unconstrained or that the
constraints align with optimal observing windows.
• Can use the constrained portion of the data set that has scheduling suitability to help
evaluate a ‘worst case’ scenario
!
Details on 2-Gyro mode
– http://www.stsci.edu/hst/HST_overview/TwoGyroMode/
February 17, 2005
Bill Workman
5
Planning and Scheduling 2-Gyro Analysis Activities
Provide input to Phase I
proposal selection process
!
Process used in Cycle 13 Phase I process to identify potential conflicts
between Large and Treasury proposals
– Will be again for Cycle 14 Large and Treasury proposals and the full Cycle 14 TAC
selection
– Particularly necessary for 2-gyro mode since there will be an increase probability of HST
orbit resource conflicts
!
Process:
– Generate simulated Phase II observations (visits) and observing constraint data from
Phase I information
– Distribute requested orbit resources for each visit across its available observing windows
– Evaluate resulting resource plots looking for regions of potential over or under
subscription
– Correlate these areas with observing constraints and target RA’s
– Summarize results for use in proposal selection and Phase II implementation
!
Goal IS NOT to drive science program selection
!
Goal IS to provide early alert of infeasible HST science program cycle and
provide information which can help make it feasible.
February 17, 2005
Bill Workman
6
TIPS-JIM Meeting
17 February 2005, 10am, Auditorium
1.
Planning Activities for Deliberate
Entry Into 2 Gyro Mode
Bill Workman
2.
HST Guiding Errors in 3-Gyro
Ron Gilliland
3.
ASICs for JWST
Don Figer
Next TIPS Meeting will be held on 17 March 2005.
HST Guiding Errors in 3-Gyro
Ron Gilliland, ACS+WFPC2
Based on draft ISR TEL 2005-02.
Developed as background information to support interpretation of testing under 2-gyro.
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Reports results from GO programs aimed at high precision time-series photometry
for which very precise frame-to-frame registrations are part of the routine analysis.
Cases include programs from 1993 (WF/PC GO-4664 on 47 Tuc; 24 orbits), 1999
(WFPC2 and STIS on 47 Tuc; 120 orbits), and 2004 (ACS/WFC GO-9750 on the
Galactic Bulge; 105 orbits).
Analysis technique involves formation of an over-sampled mean image, combining
all of the frames in a given filter, and carrying the result as an analytic function for
each pixel representing how the intensity changes as a function of x,y motions -- the
basis for developing difference image analysis.
The iterative solution involves field dependent fits of a registration model -- usually
taken to be x,y zero point offsets, plate-scale in x and y, and a rotation.
Formal errors in these programs for frame-to-frame registrations, where 1000’s of
stars at high signal-to-noise are used, would be under 0.001 pixels.
Results will be summarized in a series of plots showing x,y offsets in time -- the
guiding error after removal of known dithers, and in some cases plate scales and
rotation.
Times of SAA passages, and full guide star acquisitions will be shown, as well as
the commanded dithers in order to easily see if there are correlations in guiding with
any of these.
This presentation will document empirical results, but will not in general attempt to
explain what is seen.
Observations with the original WF/PC
from September 1993.
No dithering was used for these CVZ
observations.
Top two panels show relative shifts
frame-to-frame for the 99 exposures of
1000s in a 40 hour block. Units of
milli-arcsec.
Lower two panels show plate-scale
Changes in parts per 10,000.
Horizontal bars show times having
SAA passages.
A drift of ~50 mas occurred on a
timescale of ~12 hours.
This is the first of five figures
providing results from the 120
consecutive orbits with GO-8267
from July 1999.
This page shows the relative
positions in x, each panel covers
a 3-day period.
Vertical tic marks show GSACQs, horizontal bars are
periods with SAA passages.
Series of zzzz show the
commanded dither values.
The remaining symbols ‘+’ and
‘*’ show relative positions for the
F555W and F814W exposures
respectively.
The next 4 slides will show the
same for y-position, roll, and xscale, y-scale.
Note drifts within orbits at ~10
mas and offset between first two
orbits of ~15 mas.
Same, but showing errors in
the y-position over the 8.3
days of these 47 Tuc
observations.
Note the large change orbitto-orbit at the start.
Shows frame-to-frame
differences of orientation.
A change of 0.1 arcmin from
center to corner of a WFPC2
image corresponds to 0.016
pixels, although real these
changes are not important.
Same, but showing variation
of plate scale change in X.
0.5x10-4 corresponds to center
to edge stretch of 0.02 pixels.
For these near-CVZ
observations the plate scale
changes far exceed that from
differential velocity aberration.
Same, but y-plate scale.
This and the next 4 slides show
x, y, rotation, and x and y platescales for the same observations
with STIS in parallel.
Note a pronounced one-day
variation perhaps following from
thermal changes within STIS as
the MAMA detector electronics
were cycled.
Same, for y-position.
Same, showing rotation.
Same, for x-plate scale.
Peak-to-peak these changes
yield edge-to-edge stretch of
0.3 pixels.
Same, for y-plate scale.
ACS/WFC observations for
105 consecutive orbits in
February 2004.
Again, series of 5 slides
detailing x, y, rotation, and
the x and y plate scales.
Units of milli-arcsec.
Note largest changes occur
in the first couple of orbits.
Any changes associated with
GS ACQs, or dithers, are
smaller than inherent drifts.
Same, for y-position.
Same for roll.
Same, for x-plate scale.
Unlike WFPC2 and STIS the
changes are at a level that is
consistent with differential
velocity aberration (not
confirmed in detail).
Same for y-plate scale.
Conclusions
• Although this report noted deviations from perfection, it is worth emphasizing that
the guiding stability of HST is excellent and a prime contributor to successes in
many science areas.
• Drifts within the first orbit of 10-15 mas seem to be common.
• Offsets between first and second orbits of 15-25 mas occur routinely.
• On a timescale of 5-10 orbits a full range drift of 25-50 mas occurs.
• For WFPC2 and STIS plate scale changes are observed at levels far in excess of
velocity aberration, apparently not so for ACS.
• Compared to normally occurring drifts:
– errors from full GS ACQs on the same guide stars are small
– errors associated with POS TARGs on scale of pixels are small
• Normal drifts are too large to allow accurate sub-pixel placement at the level of
<0.1 pixel, especially true in the first few orbits at a new pointing.
– solving for frame-to-frame offsets is a must for precise work
• Guiding errors in 3-gyro can be substantial, and this needs to be taken into
account for contrasting new results from 2-gyro.
TIPS-JIM Meeting
17 February 2005, 10am, Auditorium
1.
Planning Activities for Deliberate
Entry Into 2 Gyro Mode
Bill Workman
2.
HST Guiding Errors in 3-Gyro
Ron Gilliland
3.
ASICs for JWST
Don Figer
Next TIPS Meeting will be held on 17 March 2005.
Conclusions
•The ASIC performs all required analog functions for driving/
reading H2RG arrays.
•The ASIC meets JWST noise requirements and is not as noisy
as the array.
•Rockwell will deliver 16 flight ASICs to the JWST NIR
instruments
•Rockwell are making minor modifications to the design, and
new parts will be ready in June.
•Rockwell will deliver one part to the IDTL in June.
TIPS-JIM Meeting
17 February 2005, 10am, Auditorium
1.
Planning Activities for Deliberate
Entry Into 2 Gyro Mode
Bill Workman
2.
HST Guiding Errors in 3-Gyro
Ron Gilliland
3.
ASICs for JWST
Don Figer
Next TIPS Meeting will be held on 17 March 2005.