New Frontiers 4: Argo? Options

[vjkane]

"NASA has commissioned several concept studies for Discovery-class mission that make use of the new Advanced Stirling Radioisotope Generator (ASRG) power source, a more efficient RTG that makes use of plutonium for power. One of these concepts is the Io Volcanic Observer (IVO), a mission to study Io's volcanic activity." ... I didn't even think of this being a Discovery-class mission."

While this is being studied as a Discovery mission, I have doubts about whether or not this could be kept within a Discovery budget even with the free ASRG. Juno, which is about as simple of a Jovian orbiter as you can ask for (although a couple of the instruments are cutting edge), is ~$800m, which is ~$350m more than the Discovery price cap. I would love to see a Discovery Io observer but just have my doubts about the budget. Anyone out there more knowledgeable about this than I?

[Greg Hullender]

Juno, which is about as simple of a Jovian orbiter as you can ask for (although a couple of the instruments are cutting edge), is ~$800m, which is ~$350m more than the Discovery price cap.

Juno's an Atlas 551, not a 541, so it's a bit more expensive, but probably not $350m worth. ;-) From the Argos paper, an MRPG would cost them ~$35m, which is only 10% of the difference. Difficult to see where the rest would come from.

--Greg

[infocat13]

Juno's an Atlas 551, not a 541, so it's a bit more expensive, but probably not $350m worth. ;-) From the Argos paper, an MRPG would cost them ~$35m, which is only 10% of the difference. Difficult to see where the rest would come from.

--Greg

It seems to me that I saw the Argos PDF on the OPAG site however another paper speaks of the tight supply of the proper radionucliotides for enough RTG's to fly all of these missions let alone exsisting proposed missions.exciting discussion this one reminds me of new horizens 2!

http://www.lpi.usra.edu/opag/march_08_meet...s/dudzinski.pdf
we need more power scotty

http://www.lpi.usra.edu/opag/march_08_meet...ions/hammel.pdf
If you folks are reffering to another Argo paper and not this one I would love to see its URL please





You know that OPAG paper on RTG's issues leads me to ask a question.................Weapons grade plutonium and uranium can not be used in RTG's as those compounds are to "hot" and the radiation would interfere with spacecraft science instruments. The thought that occurred to me is could an RTG have a say 10 to 15 percent mix of the weapons grade material with the existing supply and/or could the weapons grade material pellets be in the interior of the RTG canister as to be shielded by the surrounding material. Reactor grade material is also not suitable for RTG’s but I would ask the same question here to for that material.
If this where possible could we stretch the supply of spacecraft suitable material enough to make an Argos mission possible?

and one last OPAG PDF for you Mongo!
http://www.lpi.usra.edu/opag/march_08_meet...ons/spilker.pdf
scroll down to page 19 these are the choises for an extended- extended cassini mission! They have chosen it appears a JUNO like polar orbit mission and saturn impact at end of mission but there where several other possible missions.One was a Saturn escape to another gas giant or to a centuar worldlit and not listed by the mission team would have been gas giant Trojans IE Cassini could have done some of the science of the Argos mission!

[Vultur]

I kind of hope New Frontiers #3 is a Venus lander - the last Venus landers were in 1985, and they didn't last long.

[Guest_Enceladus75_*]

Yes, I would love to see another landing on Venus (namely because I can't remember the original Russian ones at first hand...) and this time with a full panorama image taken of the lander's surroundings. Ideally if money was no limitation, there would be two or three landers, one on the volcanic plains, one on the tesserae and perhaps one close to a recently active volcano or in one of those coronae. NASA would do well to learn from the Russian Venera designs. They may not have been all that pretty, but they did their job.

But I am also very much in support of a new mission to Neptune using the existing NH platform. It was Voyager's flyby of Neptune that got me into space exploration and astronomy in the first place, back when I was an impressionable 14 year old.

Why has NASA allowed its supply of RTG ready plutonium to get so low? Surely they realised that if they were to continue to explore the outer solar system there would need to be a corresponding supply of RTG material?

Whilst I think it would be great if Cassini could explore another gas giant, I can't see this happening. Would it have the fuel to escape Saturn's gravity AND be captured by another planet? I also hope they don't crash Cassini into Saturn. Can't they leave it in a stable orbit so perhaps in the 22nd century or whenever humans eventually get out to Saturn they could collect and take it back home to a museum?

[jgoldader]

Why has NASA allowed its supply of RTG ready plutonium to get so low? Surely they realised that if they were to continue to explore the outer solar system there would need to be a corresponding supply of RTG material?

As I understand it, that's not NASA's decision to make. NASA has to get its plutonium from the Department of Energy, which maintains the only facility(ies) for processing the proper isotope of plutonium. There is a presentation linked to a few posts above about RTGs for deep space missions that explains the problem. IIRC, DoE can't produce the fuel at a rapid rate anymore; I believe it has to do with the decommissioning years ago of the principal facilities involved.

Jeff

[mchan]

Weapons grade plutonium and uranium can not be used in RTG's as those compounds are to "hot" and the radiation would interfere with spacecraft science instruments. The thought that occurred to me is could an RTG have a say 10 to 15 percent mix of the weapons grade material with the existing supply and/or could the weapons grade material pellets be in the interior of the RTG canister as to be shielded by the surrounding material.

Pu-239 and U-235 (whether weapons-grade or not) has far less heat output per unit mass than Pu-238. Pu-238 has a relatively high heat output due to relatively short half-life (80-something years) vs Pu-239 or U-235 (24K or 700M years). In this sense, Pu-238 is "hotter" than Pu-239 or U-235. A piece of Pu-238 will probably be glowing hot depending on what it is alloyed with while you can hold a piece of Pu-239 in your hands without discomfort (it will still feel warm from alpha decay of other isotopes mixed in).

In the sense of penetrating radiation, the main decay mechanism of Pu-238 is spontaneous alpha decay which is stopped by several feet of air at standard atmospheric pressure. This vs the highly penetrating gamma rays from the fission reactions which are the main decay mechanism for Pu-239 or U-235, so Pu-238 may be thought of as less "hot" with less penetrating radiation. In order to get a high heat output from Pu-239 or U-235, you'd need a near-critical mass and some moderating material to produced a sustained chain reaction, i.e., a nuclear reactor. Then you'd have to worry about shielding against the gamma radiation and neutrons from the fission reactions.

In short, Pu-238 has an entirely different means of heat production and shielding requirements than Pu-239 or U-235. One does not mix with the other.

The "weapons-grade" part comes into play in reducing the overall mass of plutonium or uranium required to sustain a chain reaction, and allows for much more compact reactor designs. Reactors on naval ships and for space applications use "weapons-grade" material.

NASA has to get its plutonium from the Department of Energy, which maintains the only facility(ies) for processing the proper isotope of plutonium.

For a while, NASA also purchased Pu-238 from Russia, but even that source is dwindling. As pointed out, the facilities for Pu-238 production were shutdown. It is expensive to produce Pu-238.

[Mark6]

For a while, NASA also purchased Pu-238 from Russia, but even that source is dwindling. As pointed out, the facilities for Pu-238 production were shutdown. It is expensive to produce Pu-238.

Which makes me wonder about this passage in The Planetary Society Blog:

[Argo] can't happen in the next New Frontiers opportunity because the U.S. doesn't have enough plutonium available for the next New Frontiers to be nuclear-powered. So it has to be New Frontiers 4, which implies a launch date in 2019 or 2020, with the Neptune flyby happening around 2027.

Emily, what makes you think any more Pu-238 will be available in 2018? I do not know of ANY plans to restart its production.

[elakdawalla]

What makes me think that is that clearly Hansen and Hammel believe that the plutonium will be available. I assume it will be purchased from the Russians. Looking back at my notes from an OPAG meeting more than two years ago it seems that there was 15 kilos over and above what MSL will be using available for purchase (maybe more), and that the Russians could start production more easily than the US could, and that they're raising their prices because they realize how much NASA needs it. But it also seems that at least some of those 15 kilos has to be earmarked for the next flagship mission, I don't know how much. The same notes state that each MMRTG uses 2.9 kilos.

Actually, if I understand the situation correctly, as of the time I wrote those notes, MSL was being powered with two MMRTGs, but now they only have one, which is one of the main reasons they'll be limited to MER-like traverse rates -- can anyone confirm this?

One other thing to throw into the mix: NASA appears to be encouraging Discovery proposals employing the new Stirling RTG. I don't think though that a Discovery mission could be selected and flown in time to demonstrate the Stirling technology to make it available for NF4. Hmm. In that link, I quote Alan Stern as saying an MMRTG needs 18 kilos of plutonium, which is rather different from what I wrote above. Anybody who knows anything about this topic, please step in to clear up the numbers!

--Emily

[vjkane]

Both outer planet flagship proposals include the option for Stirling RTG's as an option to the more traditional MMRTG. There was no information in the presentations about which is preferred or how/when the decision would be made. If the Stirling RTGs are used, they would require only about 1/2 the plutonium, as I recall.

From the accountings I have seen, NASA seems to be confident of having enough plutonium for MSL, an outer planet flagship mission powered with MMRTG, and a Discovery mission using Stirling RTGs. Assuming no new supplies of plutonium, Argo could either use the plutonium currently reserved for a Discovery mission or any plutonium not used by the flagship mission if it uses Stirling RTGs. Actually, if the flagship mission uses the Stirling RTGs, there should be enough plutonium left over for a couple of smaller Stirling RTG-based missions.

[Mark6]

From the accountings I have seen, NASA seems to be confident of having enough plutonium for MSL, an outer planet flagship mission powered with MMRTG, and a Discovery mission using Stirling RTGs. Assuming no new supplies of plutonium, Argo could either use the plutonium currently reserved for a Discovery mission or any plutonium not used by the flagship mission if it uses Stirling RTGs. Actually, if the flagship mission uses the Stirling RTGs, there should be enough plutonium left over for a couple of smaller Stirling RTG-based missions.

I hope you are right, but my understanding has been that the total amount of Pu-238 in US and Russia together is just sufficient for MSL, next Flagship, and one Stirling RTG presumably for a Discovery mission. That's how I interpreted the line in Emily's blog: "[Argo] can't happen in the next New Frontiers opportunity because the U.S. doesn't have enough plutonium available for the next New Frontiers to be nuclear-powered." -- as in, the world's current supply is already allocated but more would be produced in time for a 2019 launch. Which presumes that SOMEBODY will restart production of Pu-238.

[vjkane]

I hope you are right, but my understanding has been that the total amount of Pu-238 in US and Russia together is just sufficient for MSL, next Flagship, and one Stirling RTG presumably for a Discovery mission.

It has not been decided whether or not to allow the plutonium to be used for a Discovery mission. I hope not. The New Frontiers class missions which could be done with the Stirling RTG (including several that are being scoped as part of the Discovery program, but which seem to me from very brief descriptions to be too ambitious for the Discovery program -- remember that Grail, which is a very simple (but scientifically very valuable) mission is $375M (although with two spacecraft)). Also, if the outer planets flagship mission can be done with Stirling RTGs, they will use only about half the plutonium currently budgeted (for MMRTGs). That would free up enough plutonium for 1 or 2 New Frontiers class missions. The tradeoff, of course, is the risk of using a new technology on a $3B mission.

I'm hoping for a very frugal and careful use of the remaining plutonium to allow MSL, an outer planets flagship, and 2 New Frontiers class missions.

[mchan]

What makes me think that is that clearly Hansen and Hammel believe that the plutonium will be available. I assume it will be purchased from the Russians. Looking back at my notes from an OPAG meeting more than two years ago it seems that there was 15 kilos over and above what MSL will be using available for purchase (maybe more), and that the Russians could start production more easily than the US could, and that they're raising their prices because they realize how much NASA needs it. But it also seems that at least some of those 15 kilos has to be earmarked for the next flagship mission, I don't know how much. The same notes state that each MMRTG uses 2.9 kilos.

One other thing to throw into the mix: NASA appears to be encouraging Discovery proposals employing the new Stirling RTG. I don't think though that a Discovery mission could be selected and flown in time to demonstrate the Stirling technology to make it available for NF4. Hmm. In that link, I quote Alan Stern as saying an MMRTG needs 18 kilos of plutonium, which is rather different from what I wrote above. Anybody who knows anything about this topic, please step in to clear up the numbers!

The link http://www.lpi.usra.edu/opag/march_08_meet...s/dudzinski.pdf provided by infocat13 above states MMRTG uses 3.52 Kg Pu-238 (slide 3 upper left).

This link http://www.space.com/news/080306-nasa-plut...ortage-fin.html has some info on remaining Pu-238 inventory.

[infocat13]

Mango and Emily and our other posters.........................



http://www.unmannedspaceflight.com/index.p...mp;#entry130689


the thread above has alot of exciting PDF files on the November OPAG meeting files posted three days ago! hey you (and me!) government workers honored the dead of wars past and have not been posting here on UMSF lately. on the conference thread there is a PDF file on the proposed saturn mission with.................well read it maybe there is the secret of the extra radioisatopes needed to run the Argo mission.

[Mark6]

Yet it is still the case of squeezing as much as possible out of very limited supply remaining in the entire world... unless someone invests in making more of it And unfortunately Pu-238 does not seem to have any uses outside UMSF -- none that justify the cost, anyway. I've heard that NASA and Department of Energy are each trying to saddle the other with the cost of production -- just how expensive would that production be, anyway?

I guess I am just in a black mood lately.