SNAP Shield Group Meeting September 3, 2003
        DeJongh, Diehl, Limon, Marriner, Nicol, Page, Peterson, Stefanik

 Next Meeting
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 Wednesday September 17, 2003 IB1 2nd floor West 10:00 to 12:00 Noonish. 
 This includes the instrumentation meeting with LBL starting at 11:00.
 
 Agenda
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 Verbal Reports -  Tom Page and HTD
 Presentation and Discussion of FY'04 Engineering Work Plan - HTD & All
 
 Verbal Reports
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 Tom Page has been assisting Igor Rakhno in obtaining details of the 
 mechanical design for the MARS model. Igor got the composition of
 the carbon-fiber composite material used in the deck, optical bench, 
 etc ... from Bobby Besuner. Page notes the spreadsheet and solid model
 are in reasonable agreement for the optical bench (92 vs 97 kg) and
 "Coffin" (23.75 vs 23.38 kg).  The primary mirror is 209 kg, the 
 tertiary mirror is 14.3 kg, ang the "fold-flat" mirror is 8.0 kg.
 All of this was in email conversation. Igor has noted that the 
 previous estimate for material overestimated the shielding capability
 by about an "order of magnitude".

 Tom Diehl talked with Allan Tylka at the Naval Research Lab about 
 the CREME96 limitations, particularly solutions to the limited orbital
 apogee. A 100,000 km limit causes us to overestimate the orbit-averaged
 particle flux from trapped radiation by approximately 72/42.  We should
 multiply the TRP output from CREME96 by that factor.  
   Tylka retracted his email remark on the number of orbits that go into 
 the trapped-radiation calculation. It's not 7 days worth.  Apparently 
 instead it's 100 orbits. That's almost good enough, though it doesn't take 
 into account a years worth of precession.  
   Tylka agreed if we were at or near the electronics specification in 
 our rad-damage calculations he would make available the code or a 
 modified version. 

 Presentation and Discussion of FY'04 Engineering Work Plan - HTD & All 
 ----------------------------------------------------------------------
 The FNAL Directorate now encourages us to make a written work plan.
 This will lead to an MOU with Fermilab. We have been working on the 
 shielding plan and spent most of this meeting working over details
 for FY'04.  At the same time, we need to work with SNAP management 
 so that we have one and the same plan for the shield work. 

 The draft plan is file fy04req.txt in this directory. The skinny is that
 we want to be responsible for all aspects of the cosmic ray shield.
 This includes: 
         i. Physics design of the cosmic ray shield involves understanding 
            the components of the ionizing radiation in the SNAP orbit,
            simulating its effects on the detector and electronics using
            GEANT and MARS, and optimizing the shield design for reduction 
            in both flux and spacecraft weight.
        ii. Engineering design takes the requirements of the physics 
            design and optimizes the shielding for mechanical and 
            thermal stability, integration into the spacecraft,
            detector instrumentation, cost, etc. 
 
 In this meeting we concentrated in improving detail of item ii, the 
 engineering. The original estimate is that we need to have 4 FTE
 engineers working by the end of FY'04 on the following. 
 0.  1/4 to 1/2 FTE in support of the physics effort,
 1.  1/2 to 1 FTE of finite element structural modeling,
 2.  1/2 to 1 FTE doing thermal analyses and thermal integration,
 3.  1/2 FTE planning design verification test venue, apparatus and
     instrumentation,
 4.  1 FTE helping with all of the above, bringing in information 
     from the LBL models, communicating with Lafever et. al., and working 
     with a draftsman who is assembling the CAD model here, doing 
     design concepts, and coordinating the efforts.   
 
 Comments iterated in the meeting were as follows.
 0. About right.
 1. The upper number of 1 FTE for mechanical modeling is a better 
    estimate than the lower, especially given that this calculation 
    has static and dynamic (vibrational) aspects. 
     Engineers experienced in dynamic mechanical calculations 
    at Fermilab use ANSYS, typically.  We have seen some SNAP calculations 
    using another program (MSE NATRAN?).  It's not a big problem to get that 
    software. 
 2. We believe we have a lot of work to do.  The cold plate is at 140 deg-K.
    The mirror is at room temperature. The shield is thermally decoupled 
    from the cold plate, yet it absorbs light reflected from the focal
    plane and shields the focal plane detectors from external sources.
    We need to understand the shields thermal characteristics and environs. 
    Again, the estimate should be 1 rather than 1/2 FTE by FY'04 end.
 3. A small test stand could provide us verification of calculations
    for thermal model of the shield, including couplings and so forth.
    Also, if we are going towards composite models of the shield itself,
    we will need to know how they will behave in space.
 4. It's clear that this is going to require a lot of direct communication
    with the LBL and SSL people. This means we have to begin to attend 
    their mechanical meetings at least by phone/audio/video connection.
    And travel money. 

 Included in the shield design is how it handles the light reflected from the 
 focal plane.  We may dedicate some of our physicist effort to this. And 
 that is my only excuse for why it isn't written in the engineering 
 work plan. But it should be part of our responsibility.

 We should also include into our plan that this results in a zeroth-order 
 design of the actual shield by the end of FY'04 and timed so as to be
 useful for SNAP's "ZDR". 

 In the Instrumentation Meeting we gave Chris and Natalie a heads-up that
 we were getting this onto paper.  They expect us to integrate our plan 
 into SNAP plan and to hear from us quickly.
 
 
                                                 Cheers,
                                                 Tom