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New Frontiers 3 - updates
vjkane
post Feb 27 2008, 05:54 AM
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NASA posted this update on its website today. No nuclear power for the next mission and list of acceptable candidate missions likely to come this spring:

"The National Aeronautics and Space Administration (NASA) Science Mission Directorate (SMD) plans to release an Announcement of Opportunity (AO) for the third New Frontiers (NF-3) mission no earlier than June 2008. Downselection would occur in 2009. This NF-3 AO will solicit only missions that do not require nuclear sources for power generation or propulsion.

Once the National Research Council's (NRC's) New Opportunities for Solar System Exploration (NOSSE) committee reports to NASA on mid decade NF science mission priorities in March 2008, NASA plans to release more details about allowed targets for the upcoming NF-3 AO."

http://www.spaceref.com/news/viewsr.html?pid=27162


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nprev
post Feb 27 2008, 07:50 PM
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Kind of puzzled about the prohibition on RTGs; is this just to stay within the cost cap? It sure as hell rules out any outer-system proposals.


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vjkane
post Feb 27 2008, 08:56 PM
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QUOTE (nprev @ Feb 27 2008, 08:50 PM) *
Kind of puzzled about the prohibition on RTGs; is this just to stay within the cost cap? It sure as hell rules out any outer-system proposals.

My understanding from other websites is that it is primarily to stretch out the availability of the existing plutonium supply. If I remember correctly, MSL and the next Flagship missions use up the bulk of the remaining supply. After that, NASA wants to switch to Stirling-based power supplies, but probably isn't willing to commit a New Frontiers class mission to be the first flight demonstration.

Cost may also be a consideration, although I have not heard that mentioned.

All missions currently in the queue -- lunar sample return, comet sample return, Venus lander, Saturn probe (and I think I'm missing one) -- can be done with solar power.


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Mariner9
post Feb 27 2008, 10:29 PM
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Yeah, for the first time in my life I'm bummed that the US does not have an active nuclear weapons production program. At least then we would have supplies of plutonium around.

From what I remember reading, Alan Stern is dividing up the plutonium (that NASA gets) between the MSL, the expected ballpark requirement for the Flagship mission, and then one Sterling RTG powered Discovery class mission.

I'm not really sure why it is limited to Discovery and not allowed on New Fronteirs. One reason may be flight duration. New Fronteirs mission budgets are big enough that outer planet missions are practical (and indeed, the first 2 missions in the program are to the outer planets). An outer planets mission is likely to be operating much longer than an inner planets probe. Unlike a tradition RTG (which has no moving parts) the Stirling generators are comparatively new and I don't think anyone has tried running one continuously for 10 years.

A real shame, because I still want the New Fronteirs class Io Observer that volcanopele keeps wishing for.
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nprev
post Feb 27 2008, 10:35 PM
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Thanks, VJ; makes sense. They might also be trying to drive innovation by imposing such a fundamental constraint, but I'm still not wild about it.

Increasingly, the outer Solar System is where most of the really intriguing things in planetary exploration seem to be, and it would be nice to see a process/administrative framework dedicated to encouraging its exploration. Solar-powered Saturn probes are just barely within the realm of the possible, but for Uranus & beyond...fuggetaboutit.


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vjkane
post Feb 28 2008, 12:27 AM
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QUOTE (Mariner9 @ Feb 27 2008, 11:29 PM) *
is limited to Discovery and not allowed on New Fronteirs. One reason may be flight duration. New Fronteirs mission budgets are big enough that outer planet missions are practical (and indeed, the first 2 missions in the program are to the outer planets). An outer planets mission is likely to be operating much longer than an inner planets probe. Unlike a tradition RTG (which has no moving parts) the Stirling generators are comparatively new and I don't think anyone has tried running one continuously for 10 years.

I talked with a guy in NASA advanced technologies about this. Stern wants to limit the risk both of $s and time (i.e., no ten year missions that might fail before data collection). There are a number of interesting missions that could be done with two pairs of Sterling engines and electric propulsion, but only one pair is allowed in the Discovery mission. So I am really going to be curious to see what is proposed. My guess is that a lunar polar crater rover or a Mars network station will win out. A repeated Io flyby mission would be nice, but I don't think you can do that on a Discovery budget even with a free Sterling engine.


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nprev
post Feb 28 2008, 12:46 AM
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QUOTE (vjkane @ Feb 27 2008, 04:27 PM) *
Stern wants to limit the risk both of $s and time (i.e., no ten year missions that might fail before data collection).


That's sort of a surprising statement given the demonstrated longevity of recent missions. The state of the art seems to lend a lot of credence to the idea of spacecraft surviving at least ten years, particularly for orbiters or fly-bys that don't have to cope with the ancillary factors introduced by planetary environments. Is this focus on short-term projects perhaps driven by a need to conserve costs incurred by maintaining ground support teams?


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vjkane
post Feb 28 2008, 03:07 AM
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QUOTE (nprev @ Feb 28 2008, 01:46 AM) *
That's sort of a surprising statement given the demonstrated longevity of recent missions.

My understanding is the concern that the Sterling engine would have to perform for the full 10-15 year period, not with any other part of the spacecraft. I think this makes sense. Who would want to bet $500M on a new piece of technology with moving parts lasting 10-15 years if the entire scientific payback could only come at the end of that period? I could easily see a mission that would have earlier payback, and then a mission of opportunity that bet a small amount of money on that the engines would last that long. I think the Sterling engines would last 10-15 years, but if I were the manager with the budget authority and responsibility to the taxpayers, I would pick a demonstration mission that paid back within a much shorter time period.

I would not be at all surprised to see NASA keep whatever craft is launch alive for as long as possible just to monitor the long term performance and possible failure of the Stirling Engine. Sounds like a great candidate for a Mars Network station, although I don't know that a lander could fit in the Discovery budget.


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nprev
post Feb 28 2008, 03:41 AM
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Okay, gotcha now; I wasn't thinking in terms of the Stirling engine alone.

Frankly, they probably should do an LEO/MEO technology demo flight before committing to using it on planetary missions; lots of Earth science objectives still exist, and you can still have an array in place as a backup in case the thing dies prematurely.


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dvandorn
post Feb 28 2008, 03:56 AM
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QUOTE (Mariner9 @ Feb 27 2008, 04:29 PM) *
Yeah, for the first time in my life I'm bummed that the US does not have an active nuclear weapons production program. At least then we would have supplies of plutonium around.

The U.S. alone has more than twenty thousand thermonuclear devices, at varying states of age and maintenance, lying around in storehouses around the world. Most of them contain a fair supply of weapons-grade plutonium. We're probably talking *tons* of weapons-grade plutonium in existence today.

How many weapons would you have to cannibalize to construct enough RTGs for, say, a dozen outer-planet missions? One? Ten? Twenty?

Is it at least *possible* that we need those outer planet missions more than we need those very few weapons (out of a large stockpile)?

It just seems to me that saying there's a shortage of plutonium is not correct. We just have to be willing to lose a few bombs out of an enormous stockpile in order to replenish the supply available for RTGs.

-the other Doug


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nprev
post Feb 28 2008, 04:09 AM
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Don't forget half-life burn-out, oDoug, to say nothing of engineering considerations. I strongly suspect that dismantling weapons to harvest Pu might well be more expensive, labor-intensive, and produce less of a yield then producing it directly from reactors for the express purpose of using it for UMSF. (Also don't forget that there's a very narrow bottleneck for any such process: the Pantex plant in Amarillo, TX.) My thinking here is that NASA needs to submit a requirement to DOE to cover missions that will launch over the next 10-15 years, and continue doing so.


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mchan
post Feb 28 2008, 04:32 AM
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QUOTE (Mariner9 @ Feb 27 2008, 02:29 PM) *
Yeah, for the first time in my life I'm bummed that the US does not have an active nuclear weapons production program. At least then we would have supplies of plutonium around.

Nuclear weapons production is not directly related to the production of Pu-238 used in RTGs / SRGs. The same reactors may be used to produce Pu-238 and Pu-239 (for weapons), but the feedstock and breeding profiles are different. A reactor being used to produce Pu-238 can't be used to produce Pu-239 at the same time.

Side note: there is an excess of Pu-239 around from retiring and dismantling a large part of the huge stockpiles from the Cold War. Can't use it for RTGs / SRGs, though.
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nprev
post Feb 28 2008, 04:39 AM
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Ah! Very enlightning, MC; thank you! smile.gif

Guess the question then becomes what is the demand for Pu-238? Damned if I can think of any besides UMSF...so, it's even more critical that NASA asserts its needs.


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centsworth_II
post Feb 28 2008, 04:56 AM
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Wikipedia mentions one other use (now obsolete):
"...as of 2003 there were somewhere between 50 and 100 plutonium-powered
pacemakers still implanted and functioning in living patients."
ohmy.gif
http://en.wikipedia.org/wiki/Plutonium
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vjkane
post Feb 28 2008, 04:59 AM
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QUOTE (nprev @ Feb 28 2008, 05:39 AM) *
Guess the question then becomes what is the demand for Pu-238? Damned if I can think of any besides UMSF...so, it's even more critical that NASA asserts its needs.

I've read that there is a game of budgetary chicken going on. DOE wants NASA to foot the entire start up bill for restarting the production of the correct type of plutonium.


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