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

John B. Stephensen kd6ozh at comcast.net
Tue Jun 19 09:41:41 PDT 2007


Howard:

The discussions last year were about placing Eagle in a low inclination HEO 
orbit. Your comments imply that the ionizing radiation dose will increase by 
a factor of 100. This would be 500 krad over 10 years. Is this literally 
true?

73,

John
KD6OZH

----- Original Message ----- 
From: "Howard Long" <eagle at howardlong.com>
To: "'John B. Stephensen'" <kd6ozh at comcast.net>; "'Chuck Green'" 
<greencl at mindspring.com>
Cc: <eagle at amsat.org>
Sent: Thursday, June 14, 2007 20:58 UTC
Subject: RE: [eagle] Re: CAN-Do noise abatement plan and questions


> 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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