To  : L.Culhane, G.Doschek
From: T.Watanabe
Cc  : H.Hara, M.Whyndham, T.Kosugi
Date: 14-Jan-1999

Dear Len and George,

	Takeo is finalizing the agenda of March meeting  consulting  with  NASA  and
	yourself. Basically the five days will be split into  the  plenary  and  the
	splinter sessions. Hiro and I were asked to finalize the EIS proper part  of
	the agenda with you all. I am writing this  message  for  appreciating  your
	comment. This will be also helpful for directing your  intensive  discussion
	in January at the UK-US kick-off meeting in NRL,  which  Hiro  is  going  to
	attend.

	First, we are going to have the Solar-B J-side s/c  design  meeting  at  the
	beginning of February. The s/c system contractors will be assigned  and  the
	basic system designs will come out  there.  I  am  afraid  that  the  system
	documents listed at the end of  Takeo's  draft  agenda  will  not  be  fully
	prepared by the time of your meeting,  but  Hiro  may  be  able  to  explain
	somewhat.   We will be able to provide those information on the  s/c  system
	with the basic requirements and conditions in the March meeting. This can be
	done on the first day in the plenary session.   Science required for  design
	of each instrument will be also discussed there. Then, the  following  three
	days will be dedicated to the splinter discussions  of  each  instrument.  I
	think full of two days may be all right for EIS  proper  discussion,  if  we
	prepare for it well. Finally, we will all gather again on Friday  to  report
	and confirm the conclusions and action items of the meeting.

	For discussion in the EIS splinter sessions, I have listed up the  following
	items in the sessions 3 and 4. They are  basically  based  on  the  previous
	meeting agenda we had last year between UK and US. You  may  certainly  have
	comments on those.    In the March meeting, we have to not only discuss  but
	reach consensus on the basic interface issues,  which  give  impact  on  the
	system design, and we need to settle these in rather  early  period  of  the
	Phase A.

	<EIS part of draft agenda of the March meeting>

	3. EIS design
	    - Subsystem requirements				[UK/US/J]
	          science targets/requirements
	                TRACE/CDS/SUMER results
	          wavelength ranges
	    - Opto-mechanical issues				[US],[UK],[J]
	          optical modelling
	                tolerances
	                scanning mechanism
	          grating
	          prefilter hood
	          filters/shutter
	          structural trade-offs
	    - CCD camera issues					[UK]
	          architecture
	          cooling/baking
	          development/testing schedules
	    - DPU electronics and software issues		[UK],[J]
	          architecture
	          observing modes/observation controls
	4. System and system interface
	    - DHU interface
	          commands, HKs...
	    - MDP interface					[UK],[J]
	          data transfer/exchanges
	          image compression
	          coordinated observation
	               flare occurrence
	               flare location

	I certainly believe the issue of EIS telescope configuration and  structural
	design will be the main topic to  be  discussed  in  the  US-UK  meeting  in
	January and have common understanding in the March meeting.  The  followings
	are my memo on those factors that should be considered in order to  fix  the
	configuration.

	Telescope throughput is, of course, closely related with the science we  are
	aiming for with this instrumennt. The peak  and  spectral  width  of  mirror
	reflectance are determined by multilayer coating and they both decrease with
	the increase of the number of reflections in the system - Less, the  number,
	is better. This also affects time cadence of our observations.

	Combination of two mirrors in the Cassegrain system has  merits  to  enlarge
	the plate scale at the focal plane  and  to  achieve  the  observation  with
	higher spatial resolutions with the same (or less)  telescope length.

	Selection the observing wavelengths having strong emission lines  formed  in
	a wide variety of temperature regimes is another scientific factor  we  have
	to consider in the  configuration  trade-off  study.   We  need  to  observe
	transition-region lines (T above 2-3 x 10^5 K), as well as lines formed into
	high coronal temperatures and flare temperatures.  Having a grating  working
	at least two different wavelengths (free spectral  ranges)  is  one  of  the
	important capabilities to cover a wide variety of emission lines.

	>From engineering point of view, I imagine the following factors may be taken
	into account: First is mechanical tolerance of the telescope  system.  Scale
	magnification in the Cassegrain system requires severer  tolerance  for  the
	primary-secondary distance than that of the single  mirror  system  for  the
	focal depth. This means that more resource is required for  thermal  control
	of the instrument, more power  for  heaters,  if  they  are  necessary,  for
	instance, or more cost for seeking new material of low expansion coeffs  and
	for contamination control etc...

	Scanning mechanism of the mirror is a must to have EUV-line heliograms,  not
	alone overlappograms.   Exchange of the slit or  slot  observations  of  the
	same portion on the solar disk can  be  also  done  by  moving  this  mirror
	system. The merit of the two reflection system is that this can be  made  by
	wobbling  the  secondary  smaller  mirror.     From  the  ACS   requirements
	presented in the preproposal briefing, every moving part is  recommended  to
	have counter wheels to compensate the s/c jitter generated by  those  moving
	parts in the spacecraft. In order to estimate the torque generated by mirror
	scanning, we also have to consider EIS observing modes and  find  the  worst
	case of scanning with the fastest speed of the mirror motion.

	I have explained so far  rather  qualitatively.  Hiro  has  presented  rough
	figures of our baseline design parameters in the previous meetings.  I  hope
	the more quantitative feasibility studies of these factors will be presented
	in the telescope configuration trade-off discussions in January, though many
	pieces of consideration are connected with each other.

	The other interface issue to be intensively discussed in the  March  meeting
	is the EIS-MDP interface. I believe  Hiro  and  Matt  have  already  started
	exchanging the concepts. In March we have to reach more  concrete  agreement
	for the interface. The MDP capability have  been  discussed  these  days  in
	fairy good pace, and you  will  be  able  to  get  more  concrete  idea  for
	designing the detalis of CCD camera DPU system. You will be  soon  asked  to
	fill in the subsystem questionaire, with which you  provide  the  structural
	thermal information and requirements; weight,  size,  etc.     and  electric
	power consumption, signal lines etc. of our instrument.

				Best wishes.
					Tetsuya WATANABE (NAOJ)
					WATANABE@uvlab.mtk.nao.ac.jp