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Posted by: Mongo Aug 21 2008, 01:36 AM

There does not appear to be a thread about http://www.lpi.usra.edu/opag/march_08_meeting/presentations/hammel.pdf, so I am starting this one. If there is an existing thread that I am unaware of, then by all means merge them.

Argo is a proposed outer solar system multiple flyby mission, rather like an updated Voyager mission, but based on the New Horizons bus, and using a similar instrument suite. It would launch between 2017 and 2019, with either a Jupiter / Neptune / KBO or a Trojan / Saturn / Neptune / KBO trajectory. Even a combined Jupiter / Saturn / Neptune / KBO trajectory is possible.

Neptune would present a much different system than in 1989, as telescopic observations show a more dynamic Neptune atmosphere, due to the change in season, and much more of Triton and the other Neptune satellites would be visible (most of Triton's northern hemisphere was in darkness in 1989, but will be well lit in 2030).

The second big payoff would be the vastly greater access to KBOs (~4000 times the accessable volume of New Horizons), with several already-known large KBOs (400km diameter or larger) within reach. The objects reachable with Argo are expected to include:

18 cold classical KBOs (interesting because they apparently formed in situ beyond Neptune's orbit, rather than further inward)
40 KBOs with diameters between 200km and 400km
9 KBOs with diameters greater than 400km
several binary KBOs

plus the possible Jupiter Trojan early in the mission. The wide expected range of choices allows for the selected KBO to be of very high scientific interest (and naturally, follow-on KBO targets could be selected after the primary KBO target has been selected).

Typical flight times from launch to the Neptune flyby are about 10 years (Jupiter gravity assist) or 13 years (Jupiter Trojan flyby), with the large KBO flyby 2 or 3 years later.

Expected cost including launch vehicle (according to the linked pdf): under $800M with the following strawman instrument package:

High resolution visible camera: New Horizons (NH) or reduced Cassini heritage
Near-IR spectrometer: NH heritage
UV solar & stellar occ. spectrometer: reduced Cassini heritage
Far-IR linear radiometer: Diviner heritage
Magnetometer: replaces NH dust instrument
Charged particle spectrometer: NH heritage
Gimballed high-gain antenna: heritage radio science instrument

The big uncertainty at this point seems to be the availability of plutonium-powered RTGs by the time of launch.

Posted by: vjkane Aug 21 2008, 04:56 AM

This is my favorite mission option for the 2nd New Frontiers selection from now. In addition to all the reasons stated above for flying this mission, it would also carry modern instruments that would be much more capable than the mid-1970s technology carried by Voyager.

I wonder if there would be the mass margin to carry an atmospheric probe if it were supplied by another nation.

Posted by: tedstryk Aug 21 2008, 11:43 AM

Not only that, but It would catch different seasons on Triton and Neptune. I spoke with those involved with the project at the LPSC in March, and the mass margins would be pretty tight - a probe is unlikely. Still the science and the long range imaging capability is incredible.

Posted by: Greg Hullender Aug 21 2008, 03:43 PM

In one of the backup slides, they noted that they would save money by using an Atlas 541 instead of a 551. Using Wikipedia's numbers, that suggests they could increase payload 8.6% if someone (e.g. ESA) wanted to pick up the tab. Unfortunately, I can't find anything in the Argo slides that says what the payload to Neptune would be.

--Greg

Posted by: Mongo Aug 21 2008, 04:08 PM

New Horizons masses 478 kg. I assume that Argo would have a similar mass, since it appears to be based on the same bus, with many of the same instruments. 8.6% of 478 kg is 41 kg extra. Is this sufficient for an atmospheric probe plus its carrier, or would the extra mass be better used for more and/or better long-range instruments?

Posted by: ugordan Aug 21 2008, 04:20 PM

I think probe batteries alone would eat up a significant fraction of that margin so I'm not inclined to think you can cram an atmospheric probe into that much mass. Another instrument seems like a much better bet.

Posted by: Greg Hullender Aug 21 2008, 04:29 PM

The Galileo atmospheric probe weighed 339 kg, of which 152 was for the heat shield. The Huygens probe weighed 319 kg. Pioneer Venus had four atmospheric probes: a big one, weighing 315 kg, and three small ones weighing 90 kg each.

That last stat sounds promising.

A better question, though, would be whether this would interfere too much with the other work Argos is supposed to do. All these other probes were monitored by orbiters, so it didn't matter if they blew one orbit's observations tracking probes. But every minute of a flyby mission is precious -- or so it seems to me, anyway. Even if it could carry a probe, could it afford to collect the data from it?

--Greg

Posted by: Ken90000 Aug 21 2008, 04:32 PM

Actually, the Pioneer Venus sent their data directly to Earth. The orbiter had not yet arrived. Of course, I am not advocating the same is possible from Neptune.

Posted by: vjkane Aug 21 2008, 04:48 PM

I remember reading that with modern instruments and materials that atmospheric probes can be much lighter today. The probes listed above were all mid-70s technology.

It sounds like Argo would have steerable antenna, so it could in theory handle the relay while still gathering data. Actually, I wonder why it has the steerable antenna since that adds mass and risk. New Horizons has a fixed antenna.

Some alternatives to a traditional atmospheric probe would be (1) a small carrier that takes a Juno-like microwave radiometer to Neptune (such an instrument has been proposed to be carried by possible Saturn entry probes (and discarded prior to entry)) although I have a vague memory that the depth of the water vapor level on Neptune would be so deep that the instrument couldn't measure that far; (2) a carrier that traverse the upper Triton atmosphere for composition measurements; (3) a really good remote sensing radiometer to study the Neptune atmosphere

Posted by: mchan Aug 21 2008, 06:32 PM

A steerable antenna would add complexity and cost.

I also find this the most exciting of all the next NF mission proposals. From a self-centered view, it will be the only chance in my lifetime for a revisit to Triton / Neptune.

The key appears to be getting the budget and the RTGs. The Outer Planets Flagship will be underway, and possibly MSR. Constellation will be at high sustained activity on the manned side. All will demand money and Pu-238 (though I am not aware the Constellation will require Pu-238).

Posted by: Greg Hullender Aug 21 2008, 07:07 PM

Wow! Forgive me, but I found that so hard to believe, I looked it up, and you are correct:

http://www.honeysucklecreek.net/dss44/pioneer_venus.html

Even though Venus was just past inferior conjunction, it was still at least 41 million km away, so that's pretty impressive.



If Argos' antenna were 6.4m, then, one might expect it to be able to collect data from the probe from 4.1 million km away, which ought to be enough in advance of the flyby to present no problems.



One then wonders just how long such a probe might survive on Neptune. Could it even float above its crush depth and still be able to transmit anything?

--Greg

Posted by: vjkane Aug 21 2008, 08:03 PM

A balloon, if I remember correctly, would work in the atmosphere, and a parachute could allow the probe to transmit for a considerable time, especially since (from memory) the water vapor level is down around 400 bars. In fact, one of the problems with a Neptune probe is that it takes so long to reach the warmer atmosphere that there are (1) severe pressure issues (2) transmission issues (lots of methane to absorb radio waves and (3) relay problems because the relay craft has to stay in line of sight for hours.

One person once told me that a Juno-like microwave radiometer would not work at Uranus and Neptune because of the depth of the atmosphere before you sample all the regions (e.g., water vapor) desired. However, it was an off the cuff remark and I don't know the source. It seems credible.

Posted by: Mongo Aug 22 2008, 01:34 AM

It is interesting that from what I read here at Unmanned Spaceflight, NASA is leaning toward a Jupiter orbiter for the third New Frontiers mission, with the candidates from the existing list being Io Observer and Ganymede Observer (I would prefer Io, myself). That would (if Argo is also chosen) result in the first four New Frontiers starts being 'outer solar system' missions (where the outer solar system begins at Jupiter's orbit) and the 11 Discovery starts being 'inner solar system' missions.

New Frontiers 1 : New Horizons --> Jupiter flyby / dwarf planet (Pluto) flyby / small KBO flyby -- launched 2006
New Frontiers 2 : Juno --> Jupiter polar orbiter (focus on Jovian gravity & magnetic fields) -- launch 2011
New Frontiers 3 : Io Observer --> Jupiter orbiter (focus on Io) -- launch 2013
New Frontiers 4 : Argo --> Jupiter Trojan flyby / Saturn flyby / Neptune flyby / dwarf planet flyby -- launch 2017-19

To fly all of these NASA would have to use the Advanced Stirling Radioisotope Generator (ASRG), which it seems they would like to do (at least for Discovery-class missions).

It makes sense that the slightly larger budget per mission New Frontiers program be focused on the more expensive to explore outer solar system, although I would not be upset if New Frontiers 3 ends up being the Venus In Situ Explorer, which is another favourite of mine.

Posted by: vjkane Aug 22 2008, 03:40 AM

The next New Frontiers (#3) will be solar powered because the the tight plutonium supply. I think that makes a Jovian system mission unlikely, although it is probably technically feasible for the Ganymede observer and possibly an Io observer, although the interaction of radiation and solar cells is a big risk.

My guess is that the next New Frontiers (3) will be a comet or a Venus mission and New Frontiers 4 will be an outer planet mission with Argo in competition with a mission to whichever system (Jovian or Saturnian) does get the choice for the Flagship mission.

It's possible that Stirling plutonium Discovery mission could go to the Jovian system, but Juno barely fits in the New Frontiers cost cap. I have doubts that any Discovery mission could, even with a free power source.

Posted by: Mongo Aug 22 2008, 05:05 AM

According to this report entitled http://www.lpi.usra.edu/opag/march_08_meeting/presentations/dudzinski.pdf, New Frontiers 3 would be non-nuclear-powered; however Io Volcanic Observer would be a nuclear-powered Discovery-class mission. From http://gishbar.blogspot.com/search/label/Io%20Volcanic%20Observer:

"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."

And http://gishbar.blogspot.com/2008/04/io-volcanic-observer.html:

"NASA has decided to make two ASRGs available for the next Discovery-class mission, to be launched in 2013-2014. All previous Discovery-class missions have used solar panels for power. The cost of the RTGs will not be counted against the Discovery mission cost cap. [...] I had thought this was a study for a New Frontier-class mission. I didn't even think of this being a Discovery-class mission."

Posted by: vjkane Aug 22 2008, 02:42 PM

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?

Posted by: Greg Hullender Aug 22 2008, 03:55 PM

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

Posted by: infocat13 Nov 2 2008, 08:54 PM

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_meeting/presentations/dudzinski.pdf
we need more power scotty

http://www.lpi.usra.edu/opag/march_08_meeting/presentations/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_meeting/presentations/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!

Posted by: Vultur Nov 3 2008, 12:11 AM

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

Posted by: Enceladus75 Nov 6 2008, 01:08 AM

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?

Posted by: jgoldader Nov 6 2008, 01:52 AM

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

Posted by: mchan Nov 6 2008, 05:00 AM

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.



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.

Posted by: Mark6 Nov 12 2008, 10:10 PM

Which makes me wonder about this passage in http://www.planetary.org/blog/article/00001729:

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.

Posted by: elakdawalla Nov 12 2008, 11:14 PM

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 http://www.planetary.org/blog/article/00000570/ 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: http://www.planetary.org/blog/article/00001285/. 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

Posted by: vjkane Nov 13 2008, 12:17 AM

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.

Posted by: Mark6 Nov 13 2008, 03:46 AM

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.

Posted by: vjkane Nov 13 2008, 06:34 AM

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.

Posted by: mchan Nov 13 2008, 07:13 AM

The link http://www.lpi.usra.edu/opag/march_08_meeting/presentations/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-plutonium-shortage-fin.html has some info on remaining Pu-238 inventory.

Posted by: infocat13 Nov 13 2008, 08:10 AM

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



http://www.unmannedspaceflight.com/index.php?showtopic=5595&pid=130689&st=0&#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.

Posted by: Mark6 Nov 13 2008, 04:58 PM

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.

Posted by: dvandorn Nov 14 2008, 07:29 AM

I know where you can find a few pounds of Pu-238. It's in a graphite cask that ought to be no more than a little singed around the edges.

Oh, and it's located under some 7 miles of ocean, near (perhaps in) one of the deepest ocean trenches in the southwest Pacific. And it's been lying on the ocean floor for a little more than 38 and a half years. So, I guess maybe it might be a little more depleted than we'd want, eh?



-the other Doug

Posted by: infocat13 Nov 14 2008, 08:24 AM

The other Doug..................
I could have sworn there is another "broken arrow" from the early 1960's that fell from an bomber into a marsh off of Georgia or the Carolinas and still has not been found, someone posted above that weapons grade plutoniem is the "wrong kind" for RTG's. I had suggested in a post above blending the weapons grade stuff with the RTG plutonium to strech the supply to make possible the argo mission....................................

and there are a few sunken soviet and american subs out there that Howerd Hughes falled to retrieve complete with fueled reacters

Posted by: dvandorn Nov 14 2008, 08:55 AM

Oh, this isn't a bomb, it's not weapons-grade Pu. It's RTG-grade. It wasn't launched in an RTG, though -- it would have been transferred into an RTG at its destination. It just never got to its destination.



-the other Doug

Posted by: mchan Nov 14 2008, 11:33 AM

There _were_ classified uses outside UMSF. Whether the cost is justified may be debatable, but not on this forum.

http://www.nytimes.com/2005/06/27/politics/27nuke.html?pagewanted=print

Posted by: stevesliva Nov 14 2008, 06:38 PM

Thought you meant Mars 96 for a bit.

And yeah, I wouldn't be too surprised if the listening devices on ocean floor cables were Pu238 powered at some point.

Posted by: Ken90000 Nov 14 2008, 07:17 PM

Apollo 13's ALSEP?

Posted by: imipak Nov 14 2008, 10:17 PM

ISTR reading about RTG powered cable taps*, but "would have been transferred into an RTG had it reached it's destination" suggests that's not it. Aargh! Must know the truth!! I stumbled overhttp://www.nytimes.com/2005/06/27/politics/27nuke.html?_r=1&oref=slogin, though; presumably nothing came of it (?)

*I must have been thinking of http://www.unmannedspaceflight.com/index.php?showtopic=4992&view=findpost&p=110085 about http://en.wikipedia.org/wiki/Operation_Ivy_Bells, which turned up a couple of searches later and links to the same NYT article. Om...

Posted by: dvandorn Nov 14 2008, 10:41 PM

Give Ken the Kewpie doll, we have a winner!

-the other Doug

Posted by: infocat13 Nov 15 2008, 04:53 AM

mars 96 came down over ocean/land coast over Peru and the "stuff" we want so bad was never found so maybe we should look again. and did mars 96 use our must have compound?

yep the "lifeboat space craft" was carrying a power source for a planetary experiment.

Posted by: dvandorn Nov 15 2008, 06:09 AM

Actually, while I was mostly kidding about any attempt to find and salvage the Apollo 13 RTG fuel cask, it occurs to me that the only really huge factor against such an undertaking is the rather large portion of ocean floor you'd have to comb trying to find a cask that's less than a meter long and less than 30cm in diameter. There wasn't much tracking of the LM for the last 15 minutes or so before it hit the atmosphere, and the random break-up of a tumbling LM could have imparted a wide variety of different vectors to the cask as it separated from the vehicle.

The other factor that makes it less useful to try and recover such a resource would be the fact that it was produced a good 40 years ago, now, and has been sitting in its current location, in its current form (a rod about 35 to 40cm long and about 5cm in diameter) for the aforementioned 38.5 years. While I imagine it could be further refined to separate out the remaining Pu-238 from the decay products, that process would look a lot like the original production process, wouldn't it? A production process that's shut down for now.

However, if that Pu-238 was in a known location, and if it would be useful for future RTGs, we have the technology to retrieve it. And I bet that the retrieval costs would be less than (or at worst comparable to) the cost of producing the same amount from scratch. And, of course, if you don't have the means of producing more, then the comparison becomes a divide-by-zero error...

Seriously, I know that the ALSEP RTGs had all run down far enough by the time an attempt was made to re-start them in the '90s that none of the five stations responded (assumedly because the power levels had dropped to the point that the transmitter/receivers had shut themselves down). Just how useful would a 40-year-old Pu-238 rod be for future RTGs?

-the other Doug

Posted by: mchan Nov 15 2008, 07:47 AM

With a radioactive half-life of 87.7 years, you'd have about 73% left after 40 years.llion

Using the production cost of $1.5 billion for 330 pounds (quoted in the link) yields a cost of ~$4.5 million / pound or ~$10 million / Kg. The SNAP-27 RTG in ALSEP contained about 3.8 Kg. 73% of 3.8 Kg is about 2.8 Kg or ~$28 million worth. My SWAG is that the cost of the search and recovery operations will exceed that amount. That is for an amount that will fuel one and only one ASRG.

Posted by: sci44 Nov 20 2008, 09:14 PM

I wonder how far you can go by just reducing the size/output of the (AS)RTG and putting bigger/better modern batteries in place. For a one day flyby period you could run everything off one decent charge, plus ongoing RTG output - then charge up again for the last look back - with modern memory capacity you can store everything for comms much later. I would guess the limit would be when there is not enough heat from the RTG (direct, or indirect through heaters) to keep the instruments/electronics alive during cruise.
Going back to ARGO, is there any possible mission profile that also allows Uranus as well as Neptune? Or is Eris available as a KBO target?

Posted by: vjkane Nov 21 2008, 12:52 AM

The Stirling RTG's use about a quarter (as I recall, please correct if necessary) the plutonium of an MMRTG for the same power output. The plan is to fly two Stirling RTG's per mission. These are mechanical devices (moving piston) so you want a spare.

Uranus is not possible. Don't know if Eris would be in the targetting window for Argo, but Eris is ~3X the distance of Pluto from the sun. That's a long time to ask a spacecraft to survive.

Posted by: mchan Nov 21 2008, 07:24 AM

The slides in the March OPAG presentation showed MMRTG with 3.52 Kg and ASRG with 0.88 Kg of Pu-238, so one-fourth the amount is correct. However, the MMRTG electrical output is shown as 123 W vs 140-160 W for ASRG, so ASRG has slightly higher electrical output for the one-fourth amount of Pu-238.

Posted by: sci44 Dec 1 2008, 10:33 PM

Eris seems to be in the right sort of area, and its no further than Voyager is now - heck, if its possible they should go for it. Just call it the "post Neptune interstellar mission" - to probe the heliopause/bow shock - if it gets to Eris, thats a bonus. After all, it is the tenth planet..

As for Uranus, are you sure there is no mission profile? Pioneer 11 did a very sharp turn at Jupiter to get to Saturn. Is the later Jupiter-Uranus-Neptune profile possible? Oh, and then Eris..

Posted by: infocat13 Dec 9 2008, 01:26 AM

http://www.lpi.usra.edu/opag/nov2008Meeting/presentations/argo.pdf


November OPAG ARGO pdf is now up