[eagle] Re: CAN-Do noise abatement plan and questions

Steven Bible n7hpr at tapr.org
Thu Jun 14 19:08:51 PDT 2007


And is someone who happens to know a lot about radiation :-)

Did somebody ring?

- Steve N7HPR


On 6/14/07 2:15 PM, "Chuck Green" <greencl at mindspring.com> wrote:

> Hi Guys,
> 
> This is the first time I have seen something written about radiation
> where I came away believing that the author actually understood what he
> was talking about!
> 
> If you want the inside information regarding PICs and radiation, I'd
> suggest contacting Steve Bible.  But keep in mind that he is an employee
> of the company that makes PICs.
> 
> Chuck
> 
> Howard Long wrote:
>> Hi John
>> 
>>   
>>> OK. The PIC MCU that I'm considering should be safe. It's
>>> rated for 40 years data retention in an automotive
>>> temperature range. Most parts guarantee only 10 year data
>>> retention or say nothing on the data sheet.
>>>     
>> 
>> On ESEO, we have avoided PLLs because of the requirement to program them at
>> power on, although I have used them often before for programming PLLs on the
>> ground: those PIC10F SOT23 packages are really neat! ESEO has a default mode
>> of a traditional analog linear transponder. PICs have not faired
>> particularly well in radiation tests, and I'd suggest that it may be wise to
>> consider both SELs/SEBs as well as total dose.
>> 
>> You can shield against TID to a large extent by depending on tantalum as
>> previously described, as well as the spacecraft's aluminum structure and
>> enclosures, but this will not prevent SEEs from happening. After shielding,
>> SEEs that are predominently caused by high energy protons. You may well need
>> to consider other mitigation efforts against these high energy inner Van
>> Allen (proton) belt effects.
>> 
>> On designs with PICs, I have implemented over current protection using
>> INA200 devices that cut the power for about 30s as soon as a preset current
>> is passed. This is an attempt to reduce the chance of an SEB, when a FET
>> effectively turns into an SCR clamping VSS and VDD.
>> 
>> Care should be taken when setting the current trip - not only do you not
>> want to power down the device if it genuinely wants extra current, but
>> equally TID (total ionising dose) means that over time the FETs will take
>> gradually more current anyway.
>> 
>> Achim Volhardt DH2VA already did some radiation tests on a PIC12F device
>> programming an SPI DDS (AD9834) at CERN when the CANDo's were done also. I
>> attach his notes. As well as the CREME96 simultations that Achim describes,
>> there is also SPENVIS: unlike CREME96, SPENVIS can include both the electron
>> and the proton belts in its analyses. I cannot stress enough the effect that
>> the orbit has on the amount of ionizing radiation that a spacecraft is
>> subjected to! Indeed, the AO-10 IHU's early demise is due to its low
>> inclination HEO orbit, spending inordinate amounts of unplanned time within
>> the Van Allen belts. By increasing the inclination, significantly reducing
>> the time spent in the Van Allen belts during an elliptic HEO orbit, ionising
>> radiation can be reduced by orders of magnitude.
>> 
>> Although there is some science in this, it's a fairly subjective risk
>> analysis that guides the tradeoff between the complexity of mitigation
>> circuitry against the KISS principal. After all, if the planned propulsion
>> fails, you're left in a near equatorial orbit and a big dose of radiation!
>> 
>> 73, Howard G6LVB
>>   
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