Date: Tue, 29 Jun 1999 17:17:17 -0400
To: ngstaswg@hst.nasa.gov, kcook@llnl.gov
From: Peter Stockman <stockman@stsci.edu>
Subject: Questions for the ISIM Teams
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The ASWG has the opportunity to pose questions to the ISIM teams -- both
before and after the "Woods Hole" meeting. To get the ball rolling,
John Mather and I (mostly John) have put together an initial list. Please
review these and add any others that you wish. Send them to Knox Long at
STScI so that he can compile them and pass them on to the teams. Ideally,
most
of these will be addressed in their presentations or in the ISIM written
reports. Some -- like calibration issues -- may take years to address
quantitatively.

Your humble co-chair and secretary is now off to ESO for a long awaited
respite from the Balt-Wash area. See y'all in September.

Peter

--------

A list of questions to be addressed by ISIM Studies

*************************NIR Cameras**************************

1, What sets the image scales, and can they be changed in flight?

2. What filters, broad, narrow, or tunable, are provided?

3. Can one or one or more parts of the detector provide guidance
information to the Fast Steering Mirror (FSM) while the instrument is
running?

4. How many objects of each type can be seen in a reasonable time, and why
isit interesting to see this many?  How many different types can be studied?

5. Is a coronagraphic option available?

6.How can the camera be used to provide image quality information
(wavefront analysis), say by defocussing?



************************NIR Spectrographs*********************:


*****Multi-Object Spectrographs:

1. What's the scientifically acceptable stray light requirement, and why?

2. Each field has some rather bright stars, typically around m=16 according
to our guide star calculations, but we want to see m=33 or so, about 10^6.8
times fainter. Both micromirrors and microshutters have stray light from
other parts of the field.  Microshutters leak around the edges (maybe) and
micromirrors scatter by diffraction, and the radiation that gets by the
edges bounces around and comes back.  How well do the current concepts and
possible future concepts for shutters and mirrors do? What are the
theoretical predictions for the limits of these devices?

3.How easily are the spectral resolutions changed?

4. How about the reason for the spatial resolution choice, and can it be
changed?

5.What algorithm do we use to choose the right pixels? (targets)

6. How do we account for the time to scan across extended objects with
narrow slits?

7. How mature are the micromirror and microshutter technologies, and what
does it take to get them ready?

8. Do the microdevices have to be kept in vacuum or inert gas, hermetically
sealed forever, to keep them working?  If so, what do we use for windows?

9. How do you calibrate the slit transmission for all possible patterns of
neighboring open and closed shutters or mirrors?

10. What sets the angular scale of the micromirror or microshutters? Can it
be changed?

*****Dispersive Spectrographs (MOS and IFS)

1. What's the rationale for grating versus prism?

2. If grating, what's the loss for order sorting?

3. How can higher spectral resolution be achieved?  A different grating, or
a different instrument?

4. How many objects of each type can be seen in a reasonable time, and why
is it interesting to see this many?  How many different types can be
studied?

5. Is a coronagraphic option available?

*****Integral Field Spectrographs

1. What are the choices of spectral resolution? Can they be selected in flight?

2. What governs the choice of angular resolution? Can this be selected in
flight?

3. How much light is lost in the image slicers?

4. How do you approach calibrating all the ~1024^2 separate spectrographs?



*****Imaging Fourier Transform Spectrograph

1. What are the possibilities for hybrid instruments with dispersive
devices,tuned filters, and slits?

2. Is there an important difficulty with data rate, or is there a simple
form of on board data compression (or data rejection) that reduces this
greatly?

3. What choices of image scale are available, and why?  Can these be
changed in flight?

4. What broad or narrow band filters would be provided, where, and why?

5. What are the consequences of cosmic ray hits?

6. How can higher spectral resolution be achieved?

7. How many objects of each type can be seen in a reasonable time, and why
is it interesting to see this many?  How many different types can be
studied?

8. As the IFTS is also a camera, is there a way to use one or more parts of
the detector to provide guidance information to the Fast Steering Mirror
(FSM) while the instrument is running?

9. Is a coronagraphic option available?


***********************Mid-Infrared Instruments*************

1. Are there special thermal considerations that lead to different
instrument designs than those for the NIR?

2. What are the cooling requirements for the MIR detectors and how will
they be accomplished?

3. How cold must the final filters or gratings be to reduce the dark count
below that of the detectors or external backgrounds? What implications do
those temperatures have for the MIR cooling scheme?

4. What are the requirements for thermal radiation shielding within the ISIM?

5. Will nodding (30s-mins) be sufficient to achieve good background
subtraction? How will superflats and superdarks be achieved?

6. What will be the data downlink rates required for the MIR instruments?
Will on-board data analysis other than co-adding be required? How well do
high signal-to-noise, high dynamic range data compress?



*************************ALL INSTRUMENTS************************

1. How will they be calibrated in the development phase? After integration
on the ground? In flight? What standard objects can and must be seen?  Is
calibration an automated part of the operation?

2. How good must the detectors be?  efficiency, read noise, dark current,
cosmetic defects, electronic stability, self glow?

3. What stability is required?

4. How many essentially different modes of operation are there?  (i.e., how
many different experts and sets of software are required to run and
calibrate the instrument?)

5. What dithering patterns are required to cross calibrate the detector
gains and flat fields?  to fill in gaps?  Note that dithering is natural
for cameras and IFTS, not for some kinds of spectrographs.

6. What requirements and advantages and risks are there for remote
adjustment devices like focussing and alignment?

7. Are there single point failure risks?

8. Do the required detectors wear down with time, due to age, chemical
attack on the ground, or cosmic rays?

9. How might the choice of ISIM construction materials affect the design,
operations, and stability of the instruments?

H.S. (Peter) Stockman			NGST Study Scientist
stockman@stsci.edu			Space Telescope Science Institute
410-338-5007				3700 San Martin Drive
410-338-1592(fax)			Baltimore, MD 21218
--============_-1281431454==_ma============
Content-Type: text/enriched; charset="us-ascii"

The ASWG has the opportunity to pose questions to the ISIM teams --
both

before and after the "Woods Hole" meeting. To get the ball rolling,

John Mather and I (mostly John) have put together an initial list.
Please

review these and add any others that you wish. Send them to Knox Long
at STScI so that he can compile them and pass them on to the teams.
Ideally, most

of these will be addressed in their presentations or in the ISIM
written

reports. Some -- like calibration issues -- may take years to address
quantitatively. 


Your humble co-chair and secretary is now off to ESO for a long
awaited

respite from the Balt-Wash area. See y'all in September.


Peter


--------


<fontfamily><param>Times</param><bigger><bigger>A list of questions to
be addressed by ISIM Studies


</bigger></bigger></fontfamily>*************************NIR
Cameras**************************


1, What sets the image scales, and can they be changed in flight?


2. What filters, broad, narrow, or tunable, are provided?


3. Can one or one or more parts of the detector provide guidance
information to the Fast Steering Mirror (FSM) while the instrument is
running?


4. How many objects of each type can be seen in a reasonable time, and
why isit interesting to see this many?  How many different types can be
studied?


5. Is a coronagraphic option available?


6.How can the camera be used to provide image quality information
(wavefront analysis), say by defocussing? 




************************NIR Spectrographs*********************:



*****Multi-Object Spectrographs:


1. What's the scientifically acceptable stray light requirement, and
why?


2. Each field has some rather bright stars, typically around m=16
according to our guide star calculations, but we want to see m=33 or
so, about 10^6.8 times fainter. Both micromirrors and microshutters
have stray light from other parts of the field.  Microshutters leak
around the edges (maybe) and micromirrors scatter by diffraction, and
the radiation that gets by the edges bounces around and comes back. 
How well do the current concepts and possible future concepts for
shutters and mirrors do? What are the theoretical predictions for the
limits of these devices?


3.How easily are the spectral resolutions changed?


4. How about the reason for the spatial resolution choice, and can it
be changed?


5.What algorithm do we use to choose the right pixels? (targets)


6. How do we account for the time to scan across extended objects with
narrow slits?


7. How mature are the micromirror and microshutter technologies, and
what does it take to get them ready?


8. Do the microdevices have to be kept in vacuum or inert gas,
hermetically sealed forever, to keep them working?  If so, what do we
use for windows? 


9. How do you calibrate the slit transmission for all possible patterns
of neighboring open and closed shutters or mirrors?


10. What sets the angular scale of the micromirror or microshutters?
Can it be changed?


*****Dispersive Spectrographs (MOS and IFS)


1. What's the rationale for grating versus prism?


2. If grating, what's the loss for order sorting?


3. How can higher spectral resolution be achieved?  A different
grating, or a different instrument?


4. How many objects of each type can be seen in a reasonable time, and
why is it interesting to see this many?  How many different types can
be studied?


5. Is a coronagraphic option available?


*****Integral Field Spectrographs


1. What are the choices of spectral resolution? Can they be selected in
flight?


2. What governs the choice of angular resolution? Can this be selected
in flight?


3. How much light is lost in the image slicers?


4. How do you approach calibrating all the ~1024^2 separate
spectrographs?




*****Imaging Fourier Transform Spectrograph


1. What are the possibilities for hybrid instruments with dispersive
devices,tuned filters, and slits?


2. Is there an important difficulty with data rate, or is there a
simple form of on board data compression (or data rejection) that
reduces this greatly?


3. What choices of image scale are available, and why?  Can these be
changed in flight?


4. What broad or narrow band filters would be provided, where, and
why?


5. What are the consequences of cosmic ray hits?


6. How can higher spectral resolution be achieved?


7. How many objects of each type can be seen in a reasonable time, and
why is it interesting to see this many?  How many different types can
be studied?


8. As the IFTS is also a camera, is there a way to use one or more
parts of the detector to provide guidance information to the Fast
Steering Mirror (FSM) while the instrument is running?


9. Is a coronagraphic option available?



***********************Mid-Infrared Instruments*************


1. Are there special thermal considerations that lead to different
instrument designs than those for the NIR?


2. What are the cooling requirements for the MIR detectors and how will
they be accomplished?


3. How cold must the final filters or gratings be to reduce the dark
count below that of the detectors or external backgrounds? What
implications do those temperatures have for the MIR cooling scheme?


4. What are the requirements for thermal radiation shielding within the
ISIM?


5. Will nodding (30s-mins) be sufficient to achieve good background
subtraction? How will superflats and superdarks be achieved?


6. What will be the data downlink rates required for the MIR
instruments? Will on-board data analysis other than co-adding be
required? How well do high signal-to-noise, high dynamic range data
compress?




*************************ALL INSTRUMENTS************************


1. How will they be calibrated in the development phase? After
integration on the ground? In flight? What standard objects can and
must be seen?  Is calibration an automated part of the operation?


2. How good must the detectors be?  efficiency, read noise, dark
current, cosmetic defects, electronic stability, self glow?


3. What stability is required?


4. How many essentially different modes of operation are there?  (i.e.,
how many different experts and sets of software are required to run
and

calibrate the instrument?)


5. What dithering patterns are required to cross calibrate the detector
gains and flat fields?  to fill in gaps?  Note that dithering is
natural for cameras and IFTS, not for some kinds of spectrographs.


6. What requirements and advantages and risks are there for remote
adjustment devices like focussing and alignment?


7. Are there single point failure risks?


8. Do the required detectors wear down with time, due to age, chemical
attack on the ground, or cosmic rays?


9. How might the choice of ISIM construction materials affect the
design, operations, and stability of the instruments?

H.S. (Peter) Stockman			NGST Study Scientist

stockman@stsci.edu			Space Telescope Science Institute

410-338-5007				3700 San Martin Drive

410-338-1592(fax)			Baltimore, MD 21218