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NUCLEARSPACE MESSAGE BOARD (ACTIVE) -> NUCLEAR POWER AND PROPULSION IN SPACE -> Power Glitch with Curiosity's Power Supply
Post Info TOPIC: Power Glitch with Curiosity's Power Supply
GoogleNaut


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Power Glitch with Curiosity's Power Supply
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Here's an interesting story, although details are lacking:

http://www.space.com/businesstechnology/mars-science-lab-rover-power-100331.html

It seems that there is a 'power glitch' in the plutonium power source--the implications of this glitch appear to include more stringent power controls because "...batteries will be slower to charge in winter..."

This implies that the Pu-238 Radioisotope power source isn't producing as much power as was originally thought.

How can this be? The only way I can think that this could happen is if the initial Pu-238 were 'heavily' salted with a faster decaying isotope such as Pu-241. Pu-241 has about a 12 years half life, so if a significant portion of the Pu-238 were actually Pu-241 (say 5%-10%) this would significantly throw off thermal power to isotope mass calculations. I wonder if spectral analysis of the alpha/gamma radiation was ever performed? Surely a physical sample of the fuel isotope was analyzed for isotopic purity? Maybe too much focus on rover and not enough on the power source?

Who knows?


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NUKE ROCKY44


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                                           B-
237Np + 1n  -----> 238Np---------->238Pu
  93         0               93    2.117d     94

I was under the impression neptunium target bombardment was the new stock source of USA Pu238 since this Pu238 was no longer Russian stuff that is currently employed on some RTG powered deep probes.

I could ask around but I can't guarantee what happened in this case if in fact the claim is correct or deliberate designed damper.

-- Edited by NUKE ROCKY44 on Thursday 1st of April 2010 07:29:12 PM

-- Edited by NUKE ROCKY44 on Thursday 1st of April 2010 08:14:37 PM

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Bruce Behrhorst
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I thought that this was the last of the Russian purchased Pu-238...but then the Pu-241 would have decayed a while ago, woudn't have? Hmmm...

Not really sure what's going on.


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NUKE ROCKY44


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So, apparently the news report was correct.

As you know this is SNAP-19 (odd SNAP) 30+ year technology. Stuff that's not surprising to veterans. But some people on the project were 'surprised'. They thought by running MMRTG thermoelectric elements at a lower temperature than SNAP-19 thermoelectric elements they could reduce degradation. They forgot to include the effects in changing the geometry of the thermoelectric legs and the 'hot' shoe [see image] and the possibility that for these elements at lower temperature might not gain them that much (arresting degradation). If the elements has been tested earlier back in 2005-2006 on the MMRTG project they would of seen the effects and designed workarounds for the issue.

Not happy campers...Top it off with their MMRTG sitting in storage locker since hardware production for the MSL/rover didn't come out sequentially like they hoped for two years waiting to mission does not help Pu238 degradation matters.

Personally...I sort of understand NASA is not the stable agency it once was maybe the DOE is a little better during a funked economy and all the talk of structure and budget changes. I think this is a good unit maybe it's not the excellent unit but it will work fine but for a shorter mission overall lift time output. I'm sure the next ones will be better since so much of future robotica will depend on these units for power. 

Maybe they should leave MMRTG team and govt labs alone on the management side [plan] with what worked successfully on Galileo and Ulysses RTG's I realize this is a new adaptation and some kinks need to be sorted out next time I'm sure this Curiosity rover once delivered on Mars site will work out fine.


 MMRTG




-- Edited by NUKE ROCKY44 on Wednesday 7th of April 2010 06:14:53 PM

-- Edited by NUKE ROCKY44 on Wednesday 7th of April 2010 06:15:50 PM

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Bruce Behrhorst
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Interesting--thanks for the info. Yet another problem involved with 'stale' engineering--you've got to fly this stuff after its made. Also, current engineers don't necessarily have the 'history' that the older crowed had....

Interesting...


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