Shielding and Programmables
With the drive to use more advanced, commercial off the shelf (COTS) technology,
coupled with the increase of composites, total ionizing dose is becoming more of a concern
and a frequent topic of discussion. The implementation of radiation shields is generally
quite straightforward but requires mission-specific analysis. For instance, one cannot
have a '50 krad (Si)' radiation shield. Parameters that affect the performance of the
shield include the shield material, shield thickness, shield geometry relative to the die
size and location, amount of material surrounding the device (i.e., box walls), and the
type of particle and its energy. For instance, electrons are generally easier to stop than
protons. Also, there are practical limits to the amount of shielding that can be added
since the shields can get quite massive and thick. There is a point where the benefits of
additional shielding decrease to the point where the increases in mass are not worth the
marginal benefit.
NASA, through the SBIR and DDF programs are studying and testing different shielding techniques and their integration into space flight hardware. Below are curves recently obtained using 46 MeV protons. Note that for this energy proton, two shields actually increased damage to the integrated circuit with the protons exiting the shielding material at a decreased energy; the third shield, which was dense and thick, stopped all of the protons and fully protected the part. Additional tests, evaluations, and analyses of various techniques will continue.
Click Here for a better quality, larger image (.pdf 14 kbytes)
A more detailed report on our shielding study has been scanned in and posted in .pdf format (1326 kbytes) so it is a bit large. We'll try to reduce the file size in the near future. This report is based on our DDF (Director's Discretionary Fund) work in partnership with the Jet Propulsion Laboratory (G. Swift and Dina El Deeb). Shielding.pdf
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Last Revised: January 09, 2002
Digital Engineering Institute
Web Grunt: Richard Katz