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New Horizons Arrives At Ksc
mike
post Sep 28 2005, 07:18 PM
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Chernobyl exploded rather spectacularly and yet people still build nuclear reactors.
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SigurRosFan
post Sep 28 2005, 07:29 PM
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QUOTE (helvick @ Sep 28 2005, 07:50 PM)
... degrade at around 0.79% per annum ...
*

0.79%? I thought the spacecrafts RTG generally loses 3 to 5 watts of power-generating capacity a year.

What is correct?


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helvick
post Sep 28 2005, 08:24 PM
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QUOTE (SigurRosFan @ Sep 28 2005, 08:29 PM)
0.79%? I thought the spacecrafts RTG generally loses 3 to 5 watts of power-generating capacity a year.

What is correct?
*


The loss is exponential not linear - it follows the half life of Pu-238 (more or less) which is around 87.7 years. So after 87.7 years you would have 50% of the power you have right now.
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deglr6328
post Sep 28 2005, 09:21 PM
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QUOTE (Sunspot @ Sep 28 2005, 10:33 AM)
I remember the fuss over the launch of Cassini and how envirnomental campaigners "emabarked on a campaign of misinformation" to get NASA's attention. ...... and even  Martin Sheen showed up lol
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Isn't Martin Sheen a chain smoker? rolleyes.gif rolleyes.gif hilarious.
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SigurRosFan
post Sep 28 2005, 10:41 PM
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Okay. I calculate 200.8 Watts for launch power.


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Guest_BruceMoomaw_*
post Sep 29 2005, 03:46 AM
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Yep, there is no doubt that environmentalism attracts zany fanatics. So, however, does space exploration. And NASA's previous straight-faced official estimates of accident probabilities (one in 100,000 of a Shuttle exploding during launch) are not the sort of thing calculated to bolster public confidence in the agency's competence -- or its honesty.

I myself strongly doubt that there's any danger whatsoever -- even in the event of a high-speed reentry. (The Pu pellets are encased in iridium shells, after all. And when the rocket carrying the Nimbus 3 weather satellite blew up in 1968, the Pu cores in its two RTGs not only didn't powderize, but fell into the sea off the coast of Vandenberg virtually intact, were recovered by a robot submersible months later, and were simply refurbished and flown again on Nimbus' successor the following year.) But there's always a first time; and I myself will breathe a little easier after this thing is successfully launched.
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Guest_Richard Trigaux_*
post Sep 29 2005, 10:03 AM
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[quote=BruceMoomaw,Sep 29 2005, 03:46 AM]
when the rocket carrying the Nimbus 3 weather satellite blew up in 1968, the Pu cores in its two RTGs not only didn't powderize, but fell into the sea off the coast of Vandenberg virtually intact, were recovered by a robot submersible months later, and were simply refurbished and flown again on Nimbus' successor the following year.)
*

[/quote]

Good info. Good test. Not the worse case, but the most probable.


[quote=Sunspot @ Sep 28 2005, 10:33 AM)
I remember the fuss over the launch of Cassini and how envirnomental campaigners "emabarked on a campaign of misinformation" to get NASA's attention. ...... and even Martin Sheen showed up lol[/quote]


I think you all should not laugh so easily about environmentalists: they have their concerns too, and if we had paid a little bit more attention to what they say, we would not have ozone depletion, nuclear wastes, climate change, etc. (only scientists gave earlier warnings). And it is not because we are interested in space exploration that we must just get egoistically blind to the related environment concerns. Please do not become zany scientists!

It happens that I am among the pioneers of the french environmentalist movement, in the 1970'. I still back up the idea, but I must admit that since there was much taking over by leftists shemanigancers and "zany" dogmatists, so I prefered to take some distance from the main stream. As everybody know environmentalists generaly reject all what is nuclear (electricity plants, and of course weapons), but they have no general agreement about "scientific nuclear" such as synchrotrons and space probes.

And for people like me who feel environmentalist AND scientific, I have no ready made reply about such a question than "should we use RTGs?". The only thing I would state is that we should urge smart fusion research (not the cumbersome tokamaks) which does not arise such heartbreaking environment issues. Imagine a ion engine powered by a 1Mw lithium hydride cell: it will be the key for real freedom of move in the whole solar system and beyond. And I am in the process of writing a novel in where all rely on fusion interstellar spaceships and terraforming machines (with real physics).
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djellison
post Sep 29 2005, 10:08 AM
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QUOTE (Richard Trigaux @ Sep 29 2005, 10:03 AM)
I think you all should not laugh so easily about environmentalists: they have their concerns too...


But in this case - totally unfounded concerns - and they embark on a mission to spread missinformation. I dont laugh at those who object to the launch of RTG's into Space - they make me angry.

Doug
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Guest_Richard Trigaux_*
post Sep 29 2005, 10:16 AM
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QUOTE (helvick @ Sep 28 2005, 08:24 PM)
The loss is exponential not linear - it follows the half life of Pu-238 (more or less) which is around 87.7 years. So after 87.7 years you would have 50% of the power you have right now.
*



Add to this the degradation of the thermocouple junctions by the neutron flux. Semiconductors are used to build thermocouples to convert the heat into electricity, and these semiconductors crystals must be perfect and very pure, and thus they are very sensitive to impurities and crystal defects. The neutrons emanating from the RTG heat sources are not very numerous, but they can transmute some of the semiconductor atoms, forming impurities. Or most probably the atom recoil and secondary beta/alpha emissions will disrupt the crystal lattice. I am sure of what I say, having worked in the domain. But I cannot give figures about the degradation rate. It is slow enough to allow Cassini (and Pioneer and Voyager) to work, but Cassini will be very probably out of power before being out of nuclear fuel.

Add to this that the thermodynamic efficiency of the convertion of heat into electricity may decrease with the temperature of the heat sources.
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tty
post Sep 29 2005, 11:39 AM
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QUOTE (mike @ Sep 28 2005, 09:18 PM)
Chernobyl exploded rather spectacularly and yet people still build nuclear reactors.
*


It was actually a steam explosion but OK. However I think that reactors (and RTG's too) built and operated now conform with the main safety lessons from Chernobyl:

Don't build reactors of materials that will burn (graphite)

Don't build reactors where power goes up when the coolant goes down

Don't monkey around with reactors unless you know what You're doing

Don't build reactor enclosures from wood and tarpaper

tty
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djellison
post Sep 29 2005, 02:04 PM
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A little bird tells me, NH is...

72 pellets, 190+ Watts in 2015

Doug
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SigurRosFan
post Sep 29 2005, 02:20 PM
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What is the birds name?


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djellison
post Sep 29 2005, 03:38 PM
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It was from Alan via email to me - I think he just clicked reply to a private-message email smile.gif



From Alan:
"You know we're getting closer to launch when this happens: You too can spend, spend, spend on cool NH gear at:

http://www.pcxhost.com/store/st7/tp8/produ...8B53D04D5CC0A8A
"

Doug
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Guest_Richard Trigaux_*
post Sep 29 2005, 04:11 PM
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QUOTE (djellison @ Sep 29 2005, 10:08 AM)
But in this case - totally unfounded concerns - and they embark on a mission to spread missinformation.  I dont laugh at those who object to the launch of RTG's into Space - they make me angry.
Doug
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I understand your anger, Doug. But usually it is polluters and authors of catastrophes who spread misinformation, to justify their shemes or to escape punishment.
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Guest_Richard Trigaux_*
post Sep 29 2005, 04:15 PM
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QUOTE (djellison @ Sep 29 2005, 03:38 PM)


Hey but this is not a science site, it is a shop. Do they sell T-shirts to fund the new Horizon project? rolleyes.gif
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