Author Topic: Wired article on Pu-238 production for space missions  (Read 24800 times)

Online Blackstar

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This article just appeared yesterday. It is a bit problematic. I sent an email to the reporter, which I'll post as well.

http://www.wired.com/wiredscience/2013/09/plutonium-238-problem/all/

NASA’s Plutonium Problem Could End Deep-Space Exploration

By Dave Mosher
    09.19.13
   
In 1977, the Voyager 1 spacecraft left Earth on a five-year mission to explore Jupiter and Saturn. Thirty-six years later, the car-size probe is still exploring, still sending its findings home. It has now put more than 19 billion kilometers between itself and the sun. Last week NASA announced that Voyager 1 had become the first man-made object to reach interstellar space.

[SNIP]
« Last Edit: 09/21/2013 02:14 AM by Chris Bergin »

Online Blackstar

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Re: Wired article on Pu-238 production for space missions
« Reply #1 on: 09/20/2013 03:47 PM »
Here is a slightly condensed version of the message I wrote to the reporter:

Sir, I just read your Wired article on the Pu-238 situation. I think it presents some misconceptions about the current situation. As background, I was one of the study directors on the 2009 National Research Council report that you linked to in your article. Although I'm not part of the program, I am still very aware of NASA's planetary program.

Part of my complaint with the article is the tone. I think it is more dire than it should be. The head of NASA's planetary program has described the Pu-238 situation as one of the few "bright spots" in the overall planetary program. After years of trying, they are now gearing up for production. My understanding is that the equipment (the targets for the reactor and other laboratory equipment necessary for producing and testing the materials that get irradiated in the reactor) is essentially built and there is now agreement to fund production, ramping-up to producing about 1.5 kg per year. So now they really only have to worry about sustainment funding, not initial approval. It is the overall budget situation that constrains what NASA can do with planetary science, a fact that dwarfs the issue of availability of Pu-238.

You correctly note that some missions have essentially been deferred or put off the table due to a lack of Pu-238, but I don't know what you mean when you cite eight missions "delayed or canceled." There certainly were not that many missions requiring Pu-238. Most missions that NASA has delayed or canceled are due to budget cuts, not lack of Pu-238. The article is therefore misleading on this count. In addition, I would note that the Jupiter Europa Orbiter is no longer the baseline Europa mission. That is now the Europa Clipper (which would not orbit Europa), which JPL currently has under study and includes a solar power option. Also, the article should mention that NASA considered two ASRG-powered missions (Titan Mare Explorer and Comet Hopper) in its recent Discovery competition. They were not selected, but the fact that they were finalists was testament to NASA's interest in flight testing the ASRG on an operational mission and continuing Pu-238 missions.

Finally, I suspect that your statement that "two-thirds" of the Pu-238 identified in the 2005 DoE report was designated for "national security missions" is incorrect. As I read that table, it indicates that less than 25 kg was designated for that purpose, without explicitly stating what that amount was. Therefore the amount could be one kilo or 24.9 kilos. It states that in 2005 the minimum NASA requirement did NOT include the MSL/Curiosity rover. Of course, Curiosity was built and used 11 kg (some of which came from the 16.5 kg acquired from Russia), and there is also enough to power the Mars 2020 rover, meaning an additional 11 kg, plus enough to power two ASRGs.

Put another way, in 2005 the total available Pu-238 was: 39.51 kg PLUS 16.5 kg for a total of 56.01 kg.

NASA used 8 kg (New Horizons), 11 kg (MSL/Curiosity) and has 11 kg for the Mars 2020 rover, for a total of 30 kg. (Add in--I think--another 5 kg for the two ASRG-powered missions.) That implies that national security requirements were probably substantially less than the maximum 25 kg in the chart. (Put another way: NASA uses up all the Russian Pu-238 simply with MSL/Curiosity and the two ASRG mission reserves, so the 8 kg for NH and 11 kg for Mars 2020 have to be subtracted from the 39.51 kg that was available--approximately half.)


Offline vulture4

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Re: Wired article on Pu-238 production for space missions
« Reply #2 on: 09/20/2013 04:05 PM »
Good information. Nevertheless, in the long run wouldn't there be advantages to using a small reactor instead? Launch hazards are greatly reduced since uranium is virtually nontoxic compared to plutonium, power capabilities tend to be higher and fuel consumption rate can be varied to meet mission requirements.
« Last Edit: 09/20/2013 04:06 PM by vulture4 »

Online Blackstar

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Re: Wired article on Pu-238 production for space missions
« Reply #3 on: 09/20/2013 05:01 PM »
Good information. Nevertheless, in the long run wouldn't there be advantages to using a small reactor instead? Launch hazards are greatly reduced since uranium is virtually nontoxic compared to plutonium, power capabilities tend to be higher and fuel consumption rate can be varied to meet mission requirements.

For these missions they don't need the power of a reactor. And it would be expensive to develop it.

And it's hard to emphasize this enough, but one of the primary reasons for sticking with this technology for these kinds of missions is that we know so much about it. There is a tremendous amount of analysis and engineering history behind this work.

Online Robotbeat

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Re: Wired article on Pu-238 production for space missions
« Reply #4 on: 09/20/2013 05:09 PM »
And it works really well. For a long time. With low complexity (at least for RTG... ASRG is more complicated, but the heat source itself is simple as dirt, compared to a reactor). With very, very low radiation when operating. And feasible to make small devices with it. Nothing else really comes close to these things once you're out past the asteroid belt and/or Jupiter.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

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Re: Wired article on Pu-238 production for space missions
« Reply #5 on: 09/20/2013 05:18 PM »
During the decadal survey we commissioned a study on small fission power reactors. I'm attaching it here.

In all honesty, we did this because John Casani requested it and Casani is a legend (and nice guy). But I think there was little support for it among the planetary science community. At the very least they wanted the Pu-238 production line restarted so that they could consider missions that had been proposed in the recent past. Small fission reactors would be nice to have for more ambitious planetary missions, but there are no realistic missions that could use them that anybody could foresee in the next several decades.

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Re: Wired article on Pu-238 production for space missions
« Reply #6 on: 09/20/2013 07:56 PM »
Just received an interesting reply from the reporter. He disagreed with my statement that the tone of the article was too negative and provided some information indicating that the tone was in fact accurate. Don't think I can share all that here. We'll see what happens over the next few months with the budget battles.

Online Robotbeat

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Re: Wired article on Pu-238 production for space missions
« Reply #7 on: 09/20/2013 08:17 PM »
Just received an interesting reply from the reporter. He disagreed with my statement that the tone of the article was too negative and provided some information indicating that the tone was in fact accurate. Don't think I can share all that here. We'll see what happens over the next few months with the budget battles.
That sucks.

I really hope that Congress starts making the right decisions, here. It's shameful how messed up things are, how brinkmanship is destroying America's legacy.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

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Re: Wired article on Pu-238 production for space missions
« Reply #8 on: 09/20/2013 11:53 PM »
This may not be Congress being jerks. The problem may be with OMB. I don't know.

I know that it's popular on this board--as in the rest of the country--to blame Congress for everything that's wrong with American politics today. I'd just note that there are some good people in Congress (well, at least their staffs) trying to do things right. That's particularly true when it comes to the planetary science program where the allies are in Congress (not OMB).

I'd also add that there's another possibly very positive development re the Pu-238 in the making. That's contingent upon some other things happening, but it could be a good thing. It's not totally surprising to me, but I can't provide any other details now. Maybe in six months or so we'll know.

Offline EE Scott

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Re: Wired article on Pu-238 production for space missions
« Reply #9 on: 09/21/2013 03:43 AM »
This may not be Congress being jerks. The problem may be with OMB. I don't know.

I know that it's popular on this board--as in the rest of the country--to blame Congress for everything that's wrong with American politics today. I'd just note that there are some good people in Congress (well, at least their staffs) trying to do things right. That's particularly true when it comes to the planetary science program where the allies are in Congress (not OMB).

I'd also add that there's another possibly very positive development re the Pu-238 in the making. That's contingent upon some other things happening, but it could be a good thing. It's not totally surprising to me, but I can't provide any other details now. Maybe in six months or so we'll know.


Hey, a hint of positivity.  I'll take it! Us planetary science buffs are looking for good news wherever we can get it.  When it gets this grim, it's hard not to lash out at the shortsightedness of our representatives (President included).
« Last Edit: 09/21/2013 03:44 AM by EE Scott »
Scott

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Re: Wired article on Pu-238 production for space missions
« Reply #10 on: 09/21/2013 02:43 PM »
If it comes to pass, it will be a glass half full/empty situation, meaning that NASA may still not be better off because the budget isn't there.

That's kinda the story for planetary science. There are a LOT of missions that they can do. Interesting, even relatively small missions with high science quality. But there's no funding.

Offline EE Scott

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Re: Wired article on Pu-238 production for space missions
« Reply #11 on: 09/23/2013 12:16 AM »
If it comes to pass, it will be a glass half full/empty situation, meaning that NASA may still not be better off because the budget isn't there.

That's kinda the story for planetary science. There are a LOT of missions that they can do. Interesting, even relatively small missions with high science quality. But there's no funding.

That is why I am interested in some kind of public-private partnership, where some foundation is somehow able to partner with NASA to get missions done. Even just modest missions; maybe purchase a launch from a smaller provider (less than EELV class) and sell it to NASA for $1.  However since there are currently no foundations who seem to have this type of function in their charter, I guess it's up to me to become hugely wealthy and start my own.  Until then I hope and wait for additional funding to flow back into planetary science.
« Last Edit: 09/23/2013 12:18 AM by EE Scott »
Scott

Offline vulture4

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Re: Wired article on Pu-238 production for space missions
« Reply #12 on: 09/23/2013 02:53 AM »
There are certainly foundations that fund scientific research, but for the most part those concerned with astronomical research focus on ground-based observation, since their funds are limited and ground-based observatoin is much more economical. A rare exception is a private attempt to raise funds for a spacecraft to search for near earth asteroids from a sunward orbit.

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Re: Wired article on Pu-238 production for space missions
« Reply #13 on: 09/23/2013 05:01 PM »
A rare exception is a private attempt to raise funds for a spacecraft to search for near earth asteroids from a sunward orbit.

As much as I would like to see B612 Foundation succeed, I think that they are going to not raise much funding and will shift to advocating government funding/private management of a spacecraft development. Indeed, I already see some signs of that shift in their tone.

Offline DarkenedOne

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Re: Wired article on Pu-238 production for space missions
« Reply #14 on: 09/25/2013 12:35 PM »
Good information. Nevertheless, in the long run wouldn't there be advantages to using a small reactor instead? Launch hazards are greatly reduced since uranium is virtually nontoxic compared to plutonium, power capabilities tend to be higher and fuel consumption rate can be varied to meet mission requirements.

Ultimately there are limits imposed on how small you can build a nuclear reactor that is imposed by the critical mass limit needed for the nuclear chain reaction.  Essentially RTG are ideal for missions that require less than 10 kw.

Offline DarkenedOne

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Re: Wired article on Pu-238 production for space missions
« Reply #15 on: 09/25/2013 01:16 PM »
First of all there are a number of important issues we are talking about here.

1.  Added Plutoium supply is insufficient to maintain current deep space exploration without new technology.  The Mars rover required about 4 kg.  The New Horizons missions required 11 kg.  Cassini required 32,7 kg.  A few calculations will tell you that we cannot sustain our current level of deep space exploration.  NASA hopes that new technology like the ASTG will allow for use to do more with less, but it is still a huge problem.

2.  Human exploration requires significant amounts of Pu-238 as well.  Radioisotope heater units were used in Apollo to provide heat for missions that lasted days.   While small nuclear reactors are probably what is going to be required for outposts, radio isotope heater units are ideal for smaller vehicles such as landers and rovers.  Ultimately if we are to have a real manned spaceflight program that does surface missions we will need significant amounts of this stuff.

3.  The DOD has been looking into using this stuff as well for a number of very useful applications.   We should not assume that nasa is going to get all of it by default.

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Re: Wired article on Pu-238 production for space missions
« Reply #16 on: 09/26/2013 04:34 PM »
I'm going to split these into separate replies because that's how I roll:

First of all there are a number of important issues we are talking about here.

1.  Added Plutoium supply is insufficient to maintain current deep space exploration without new technology.  The Mars rover required about 4 kg.  The New Horizons missions required 11 kg.  Cassini required 32,7 kg.  A few calculations will tell you that we cannot sustain our current level of deep space exploration.  NASA hopes that new technology like the ASTG will allow for use to do more with less, but it is still a huge problem.

I'm now confused by the numbers. The DoE document that was linked in the article says that New Horizons required 8 kg and Curiosity required 11 kg.

http://www.wired.com/images_blogs/wiredscience/2013/09/final72005faqs.pdf

But this NASA document says that the MMRTG used on Curiosity required 4.8 kg:

http://mars.nasa.gov/msl//files/mep/MMRTG_Jan2008.pdf

As for "sustain our current level of space exploration," well, we aren't. Planetary has been cut back. And there was (still is) a vicious cycle with Pu-238: Step 1 "We don't have enough Pu-238 to fly many missions, so don't propose missions that require Pu-238." Step 2 "You have not proposed many missions that require Pu-238, so obviously you don't need much of it, so we will not restart production."

Apparently that cyclic argument was still working in Congress and (sorta) OMB and the only thing that broke us out of it was that NASA was able to successfully (we hope) argue that the existing Pu-238 supply is becoming too weak to be used, and its energy density must be increased in order to make it useable.

As for new technology? We have it. The ASRGs. NASA has built two flight qualified models that are now in storage and the agency would like to fly one of them on a Discovery mission. Except that the Discovery budget is being cut, so there are not many opportunities to fly. Another Catch 22.



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Re: Wired article on Pu-238 production for space missions
« Reply #17 on: 09/26/2013 04:47 PM »
2.  Human exploration requires significant amounts of Pu-238 as well.  Radioisotope heater units were used in Apollo to provide heat for missions that lasted days.   While small nuclear reactors are probably what is going to be required for outposts, radio isotope heater units are ideal for smaller vehicles such as landers and rovers.  Ultimately if we are to have a real manned spaceflight program that does surface missions we will need significant amounts of this stuff.

We looked at this when we did our radioisotope power sources (RPS) study in 2009. The Constellation program's requirement was significantly more than the science requirement. It was something like twice as much. That was for a baseline lunar outpost, primarily to act as backup power for the main site. For example, if you had solar or a reactor as your main power source, you'd want something that was totally reliable as backup power. An MMRTG was great for this. In fact several of them would be really nice. I believe that one person I talked to even said that the radiated heat from them would be useful--you could place it near your habitat and it could radiate heat to the habitat (and the radiation risk is pretty much nonexistent). I've got the charts somewhere showing nominal human spaceflight requirements for the Pu-238.

But...

When we were doing the study, we would look at the human spaceflight requirements for the Pu-238 and it looked great. It looked like the human spaceflight program would pay for most of the costs and the science program would just skim some extra Pu-238 off the top and use it for their own missions. But we were not born yesterday. We knew that was an illusion. Some of us knew that Constellation was going to get canceled, or at least severely scaled back very soon.

And within agencies different departments will play games of budgetary chicken. The obvious question was who needed more Pu-238 first, the human spaceflight program or the science program? Well, if you assumed that both were funded for all their requirements (which was a dumb assumption), science would need it sooner than the human spaceflight program, but eventually Constellation would require a lot more. So the human spaceflight program said that they had no plans to fund Pu-238 production restart, because they weren't going to need more until the 2020s or so. That shifted the funding requirement to science. Of course, the science program (planetary) knew this, and they also knew that the human spaceflight requirement would probably disappear. So we all took the base assumption that science was going to have to shoulder the burden for Pu-238 production.

Online Blackstar

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Re: Wired article on Pu-238 production for space missions
« Reply #18 on: 09/26/2013 04:52 PM »
3.  The DOD has been looking into using this stuff as well for a number of very useful applications.   We should not assume that nasa is going to get all of it by default.

That was never the assumption. If you read the article, and this thread, you'll see that "national security requirements" have always been factored into this. There is a total amount of Pu-238 that currently exists, and a certain amount is allocated to NASA, and the remainder is allocated to "national security."

There was a baseline assumption that the NASA Pu-238 belonged to NASA and could not be taken over for national security missions. I believe (and I'm too lazy to check) that around 2001/2 there was suddenly an announcement by the Secretary of Defense that DoD could take some of the NASA Pu-238 if they needed it. There was never a clear explanation why this was, and my suspicion is that it was simply because the Secretary of Defense was a jerk and wanted to build his empire. I believe that policy decision was later reversed.

But stay tuned. As I mentioned earlier, there may be more news on this subject in the next few months.
« Last Edit: 09/26/2013 04:52 PM by Blackstar »

Offline baldusi

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Re: Wired article on Pu-238 production for space missions
« Reply #19 on: 09/28/2013 03:43 AM »
Good news, bad news, some other types?

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