SNAP Shield Group Meeting March 26, 2003 Dejongh, Diehl, Mokhov, Peterson, Rakhno, Striganov Next Meeting ------------ April 9th, 2003 Fermilab Cafeteria Report from Tom Peterson ------------------------ Tom is looking to see if he can identify the major components in the satellite that are relevant for shielding. He found: a) The optical bench is a large structure. Is it aluminum? b) Multi Layer Insulation (MLI) cover the whole thing. c) The cone shaped piece of the dewar. d) The cold plate. e) Mirrors? What are they made of? f) The radiator. There is little other material in that direction. What is it made of? Also, he has some questions related to thermal aspects of the dewar, etc. The dewar and coldplate are cold ~140 deg-K. The optical bench is warm ~280 deg-K. How is the thermal isolation between the cold plate and the optical bench accomplished? He noted the MLI has excellent transverse insulating properties but not very good lateral insulating properties. We'd like to get involved in these thermal issues, particularly with regard to the dewar region. Who do we talk to? Report from Nikolai Mokhov -------------------------- Nikolai reminded us of the overall shielding research plan. i) Build a simple geometry model ii) Define the radiation sources iii)Improve the simulation code as necessary. This means put heavy ions interactions into Mars. see if they have been done in Geant4. iv) Identify the radiation specs we have to meet. Q: What is the orientation of the spacecraft w.r.t. the sun? We suppose it is radiator-away, usually. Report from Igor Rakhno and Sergei Striganov -------------------------------------------- They have obtained documentation for the main radiation sources: the trapped radiation in the radiation belts, the galactic comics, solar proton events. The standard for NASA calculations of fluences in the radiation in the belts are called AP-8 for protons and AE-8 for electrons. These are available. There is perhaps a 2x uncertainty based on more recent measurements. A cross check is available NASA/CR-2002-211784 "Space Environment Effects: Trapped Proton Model", by S.L. Huston, Boeing, Huntington, CA. A further cross check is from the ISS mission AMS. It's published in Physics Reports 366 (2002) p 331, though this is at rather low orbit. The galactic radiation fluences are in the particle data book. These are isotropic. The AMS mission may provide a cross check for this as well. The model of solar ions, including solar flares, could be provided by Creme96. A URL is crsp3.nrl.navy.mil/creme96. It's an informative website. Creme stands for "cosmic ray effects on micro electronics". Mars Simulation Geometric Inputs (HTD) -------------------------------------- I studied the MARS documentation to see if there is a method common with Geant for importing geometric models. Such commonality would be convenient for our work, for we would only have to produce one satellite model. I've used GEANT in my work on the DZero upgrade detector simulation and I used MARS-12 and MARS-13 in my work on DZero upgrade shielding several years ago. I concentrated on the documentation updates for MARS-14, the current release. There are four major ways of defining volumes in MARS. The first is r-z-phi symmetric "zones" described by cards in the MARS input file MARS.INP. We could simulate the conical shielding part and cold plate using this method. However, because of the satellites overall asymmetric geometry, this method would not be particularly useful when extended past those two components. The second method is the "Extended Geometry Input" method. Six basic shapes are allowed: the box, cylinder, sphere, cone, etc. Their position and size are specified in a single line of data including the volume name. The angular orientation is provided in a subsequent line. This is similar, but not identical, to the GEANT geometry input format. It would not be difficult to adapt a MARS simulation geometry to the GEANT format or vice-versa. The third method is the "Reg1" method. One writes fortran code in the form of a great if-then relation that defines the material as a function of position. This is the most flexible method for simulating a complicated geometry. However, it would be difficult to translate a Reg1 MARS geometry into a GEANT format. It is less difficult to translate a GEANT format geometry into the Reg1 format as it is merely a matter of straightforward coding. The fourth method isn't in the documentation. It's a standard used in the nuclear industry, and at LANL, called MCNP. It's similar to the extended geometry method. It seems sensible to develop the GEANT and MARS simulations as closely as we can. That means using the extended geometry simulation in MARS. I showed the slides I would present at LBL. They are in this area as file diehl_03_26_2003.ppt.