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NASA Just Cancelled its Advanced Spacecraft Power Program

The Advanced Stirling Radioisotope Generator was to use less Plutonium for cheaper missions.

Posted by Casey Dreier

15-11-2013 16:06 CST

Topics: FY2014 NASA Budget, Space Policy, RTGs, future technology, Future Mission Concepts, Plutonium-238

In a stunning announcement today, NASA's Planetary Science Division Director Jim Green announced that work on the Advanced Stirling Radioisotope Generator would cease due to budget cuts:

With an adequate supply of Plutonium-238, and considering the current budget-constrained environment, NASA has decided to discontinue procurement of ASRG flight hardware. We have given direction to the Department of Energy, which manages the flight procurement, to end work on the flight units. The hardware procured under this activity will be transferred to the Glenn Research Center to continue development and testing of the Stirling technology.

Spacecraft that can't use solar power (e.g. when beyond Jupiter, landing on dusty surfaces like Mars, or bathed in long-duration shadows like lunar landers) depend on Plutonium-238 (Pu-238) to generate heat that is turned into electricity. NASA has used Radioisotope Thermoelectric Generators (RTGs) – basically large thermocouples – for decades to supply electricity, but those are inefficient. And since the 1990s NASA has been running low on plutonium-238.

The ASRG program was created to help extend the life of the remaining Pu-238 supply. It uses a stirling engine to generate electricity at four times the efficiency of a regular RTG. This means more missions to these harsh places using less Plutonium. While NASA has started to generate Pu-238 again, it won't be ready to use until 2019, and even then the Department of Energy will only produce about 1kg - 1.5kg per year. The New Horizons mission to Pluto used about 11kg, which would take anywhere from 7 - 11 years to generate under the current plan.

The cost of this program was contained within the Planetary Science Division's Technology budget, which has to pay for the entire cost of creating and maintaining the Department of Energy's Plutonium-238 infrastructure. Historically, this is unusual. But recent decisions by the White House and previous decisions by the Congressional energy committees have ensured that NASA is on the hook for the entire cost of creating and storing Plutonium-238. That new burden, combined with sequestration and the relentless desire to cut the planetary exploration by this White House, likely left NASA with little choice but to cancel this program. Creating Pu-238 is fundamentally more important than having an ASRG, even if that means fewer missions.

ASRGs had been under development by NASA for over a decade, and had been planned for use by 2016 in the next low-cost planetary exploration missions to be launched sometime later this decade. Because of the limited cost cap imposed on these missions, they're now essentially limited to the inner solar system. Missions with bigger budgets that could afford regular RTGs will be bottlenecked by the production rate of Plutonium to maybe once or twice per decade.

Goodbye, outer planets.

This is the latest consequence of the White House's war against planetary exploration in the United States. If you want to help change this dim future, please take 2 minutes to write the President and your Congressional representatives (use this form if you're outside the U.S.).

See other posts from November 2013


Or read more blog entries about: FY2014 NASA Budget, Space Policy, RTGs, future technology, Future Mission Concepts, Plutonium-238


Mark Brown: 11/15/2013 04:48 CST

This is disheartening to say the least. I was under the impression that funding was beginning to move in the right direction, but this seems detrimental. What can I do? (besides contact my Congress Rep). I don't want my son to grow up parched by the lack of adventures to the cosmos!

Casey Dreier: 11/15/2013 04:59 CST

Mark: funding is moving in the right direction, but slowwwwwly. In absence of Congress passing a budget, many internal priorities default to Administration preferences, of which Planetary Science is not one. Also, most of the money restored to Planetary recently has been to the mission lines themselves, not the Technology program, which funds the ASRGs. That limits how much they can do here.

Gerald R Everett: 11/15/2013 05:23 CST

This is sad but just the beginning of things to come. Every dime will be siphoned off to support the SLS/Orion boondoggle. This makes NASA an ever bigger target for the budget cutters who will eventually see NASA as an agency that has been gutted of any meaningful program and no longer having popular support.

Alfred McEwen: 11/15/2013 09:05 CST

This decision basically kills most of the low-cost PI-led missions to the outer Solar System recommended in the Decadal Survey. The MMRTG is much heavier, and getting mass to the outer SS is expensive, so you cannot just swap ASRGs for MMRTGs and stay in the same mission cost class.

Ted Stryk: 11/15/2013 09:14 CST

Sad to hear this. I just hope the savings are enough that they don't have to kill any of the ongoing missions.

Enzo: 11/15/2013 10:36 CST

Spacecraft that can't use solar power (i.e. ...."landing on dusty surfaces like Mars"...) Come on! Opportunity has been using solar for nearly 10 years. Spirit did it for years too. You do not need plutonium on Mars, you need a mechanism to clean the panels which is a LOT easier to do than creating plutonium. Using plutonium for Mars was stupid and wasteful and, as I wrote before, the consequences of this squandering are finally emerging : no plutonium until 2019. Which means no outer planets mission well after 2030. Cutting ASRG just makes sure that there can't even be a small mission beyond Jupiter. The cherry on the cake really. And while billions are piled up on new Mars missions, let's cuts the crumbs from Cassini too, so that it can't even finish properly. These cuts fall always on the same side.

William McKinnon: 11/15/2013 11:16 CST

Jim Green is stuck with, as Casey says, a grim choice. He could opt to not restart Pu-238 production and keep ASRG alive with the $50M appropriated. But ASRGs w/o Pu seems silly. So, start Pu production and find $50M from elsewhere in planetary to keep ASRG alive, but where do you find $50M when your budget has been slashed and is slated to decrease further? Who takes the hit? I suggest PS members mention this specifically in their letters to Congress. There will be hearings, and this is a big technological investment that is about to be squandered. Congress has the power to pass an actual spending bill for NASA and restore planetary to a modicum of health.

Paul McCarthy: 11/16/2013 01:32 CST

Mmm - thoughtful comments. I certainly agree with Gerald re the giant SLS/Orion vortex; Alfred is provocative, and Enzo is very thought-provoking too. But it's not really "no plutonium until 2019" is it? There's a classified small amount in store right? Then new addition from 2019. And surely Pluto is the extreme case, so 11kg not needed again for ??? With the moving parts, there's the case that Stirling technology was always higher risk than RTG to fly on these huge-investment, enormous-life, Outer missions. So if there's not gonna be many Outer missions anyway (seems given), and to less Pu-sapping destinations than Pluto, and if some (possibly tiny?) "swing" amounts of Pu could be sponged from Russia or anyone, in exchange for suitable bribery (cash. kind, or shared mission prestige?), maybe there is, will be, or can be, just enough to eke out the limited Outer missions anyway - and with a very proven, reliable technology. So maybe this isn't the biggest thing to fight for? If NASA (disastrously of course) has to triage Planetary madly, how do the campaigning priorities here fall exactly?

Enzo: 11/16/2013 02:23 CST

@Paul McCarthy, The sensible thing to do to even things out a bit, would be to cancel MSL-2 and use its money ($1.5B) and plutonium for another mission (probably Europa or Titan, but others are possible). Then, IF more money becomes available, restore it. As things are we have a long series of very expensive Mars missions (Curiosity, MAVEN, Insight, MSL-2, tot $5B) and little else for a very long time. But that would be too logical, don't hold your breath. Ultimately the question is do we want a balanced exploration program or just a Mars program,

Scott Thomas: 11/16/2013 03:17 CST

This seems like a prudent step forward given the safety and security concerns surrounding fissile materials. I would strongly suggest that we focus on the development of fusion power and propulsion for interplanetary and interstellar exploration.

Pyrard: 11/16/2013 05:07 CST

@Paul McCarthy: The risk element is why I’m having a hard time getting upset over this. I don’t think it’s clear that NASA would launch an ASRG-powered Discovery or New Frontiers mission in the current environment (incredibly risk-averse due to tight funding, as witnessed by the TiME’s loss to InSight in the last Discovery competition), and the last Decadal Survey’s list of recommended New Frontiers missions were either in the inner solar system, in the “near” outer solar system where solar panels could be used (Jupiter system and Trojans), leaving only a Saturn probe. Given that solar-powered probes out to Uranus have been studied, if I were a bean counter I’d wonder about the necessity of the ASRG. @Scott Thomas I don’t believe Pu-238, which is used in NASA’s various generators, is fissile (Pu-239 and -241 are). It’s heat from radioactive decay that powers these generators, not fission (and Pu-238 is mostly an alpha particle emitter, making it relatively easy to handle).

Enzo: 11/16/2013 05:14 CST

@Pyrard, If NASA is so risk adverse, how do you explain entrusting the $2.5 B Curiosity mission to the never tried before and very complex sky crane ? TiME’s loss to InSight is much more easily explained by NASA strong bias for Mars. An obsession really :

Christopher Adams: 11/16/2013 08:12 CST

@Enzo, The Spirit and Opportunity rovers both use Pu-238 heaters to keep from freezing. They would not have been possible with a supply of Pu-238. *** As others have pointed out, Pu-238 is not fissile so it is not used for bombs or reactors. It has a relatively short half-life of 87.7 years which is why it gets so hot by natural decay (shorter half-life = more energy out per unit time). It is an alpha emitter which makes it easy to shield (a piece of writing paper is enough to block it) and store.

Pyrard: 11/16/2013 09:09 CST

@Enzo: Van Kane had a good piece here on risk and budgets here a while ago, mentioning InSight. In short, when budgets are small organizations tend to become more conservative in their decision-making: InSight had the lowest development risk, which was a big reason (not the only, but a big one) why it was chosen.

John Burch: 11/16/2013 10:47 CST

Not so sure this is a bad thing. Until a ASRG has been flight proven, which would have to be a 20 year+ demo mission, nobody is going to chance this technology and even then it might be deemed too risky. Solar is getting better with each passing year, JUNO would have been considered impossible not that long ago, so solar powered Europa and even Titan/Enceladus missions are quite possible in the near future. Given that some PU-238 is going to be produced then a mission beyond Saturn is still feasible.

Enzo: 11/16/2013 01:36 CST

@Christopher Adams, Spirit and Opportunity used 8 micro capsules each containing an amount of plutonium the size of a pencil eraser, outputting 1W of heat each: Curiosity uses 4.8 Kg. MSL-2 presumably just as much, for a combined total of ~10 Kg of plutonium, nearly enough for a Pluto mission. It's the amount that counts, not using a bit of plutonium to make a mission possible.

Dennys Angove: 11/16/2013 04:31 CST

Enzo: What effective mechanism(s) do you have in mind for cleaning solar panels?

kert: 11/16/2013 09:39 CST

This is pretty bad. The combined SLS/Orion budget is around 2 and a half billion dollars IIRC. Once they have their rocket ready, where are they going to go with it without things like substantial power sources and other technologies that are actually needed for deep space exploration ? Kill each and every enabling technology development program and you are left with what .. expensive rockets with 60ies technology with no place to go.

kert: 11/16/2013 09:47 CST

Also, why isn't this funded out of office of space technology ? Its certainly on their critical enabling technologies short list. The entire Pu-238 issue should be very much on their radar, no ? The thing is that ASRG or an evolved version of it would not be enabling for only outer planet planetary missions, it would also be enabling for all sorts of lunar and martian base plans, manned or unmanned, where everything will be power limited.

Paul McCarthy: 11/16/2013 09:53 CST

John Burch nicely sums up the different factors I was more hinting at. @Enzo, 4,8Kg seems an appropriate amount, given the mission potential and the Pu in store plus new production from 2019. But certainly it's desirable to ensure there's enough around for non-solar Outer missions - it's just that with the factors John Burch lists, plus stores, plus >2019 production, maybe that IS the case?

Enzo: 11/17/2013 04:49 CST

@Dennys Angove, Well, the first thing to notice that it is possible to clean (it happens naturally, so it doesn't get too entrenched). This is important because it means that it is possible to do. The simplest thing could be a brush on a robotic arm. I've seen same design with circular solar panels. Maybe a brush that rotates around the center like a windscreen wiper ? I guess there would have to be some slits on the panels so that the dust can fall through instead of accumulating in small mounds. Compressing small amounts of martian air and use it to blow it away, could be another possibility. I read that the dust is magnetic, so maybe there's a way to exploit this fact. Keep in mind that it doesn't need to be fast : even a little bit every day would help greatly. More importantly, it's not what I have in mind but what the same people that built the sky crane would be able to design. This looks like a much simpler problem than that.

Enzo: 11/17/2013 05:18 CST

@Paul McCarthy, "4,8Kg seems an appropriate amount....." Make it 10 kg with MSL-2. I read from Casey's comments/tone "Goodbye, outer planets", "it won't be ready to use until 2019" and "would take anywhere from 7 - 11 years" that the plutonium is essentially finished and/or is too small for a non ASRG mission. This has not happened out of the blue. I have been reading for years about the dwindling plutonium. And, because it had been going on for years, there was no guarantee that it would be fixed any time soon. It follows that an amount sufficient for a meaningful mission to the outer planets should have been quarantined and it wasn't. That effectively precluded such mission for years. Yes, solar cells improve, the Russians might sell some Pu etc. etc., but this is just speculation. As things stand, we are looking at a very very long period before the next mission to the outer planets can even start, even if it had the funds (which are not there anyway). And then it takes years to get there.

PeterS: 11/17/2013 11:47 CST

maybe the planetary Science team can organise a deal between DoE and Tepco in Japan ? according to the Washington Post at Japan holds nearly 10 tons in various storage facilities and nuclear reactors across the country. Plus more in other countries .... sure most of it is the wrong isotopes but they should be able to spare some

John Burch: 11/18/2013 08:17 CST

@PeterS Are you sure your talking about Pu-238 and not Pu-239? If there really was 10 tons of the stuff lying around I don't think we would be having this conversation.

PeterS: 11/18/2013 07:13 CST

"sure most of it is the wrong isotopes but they should be able to spare some" a quick look in wikipedia suggests that separating the 1% or 2% pu-238 from plutonium fuel is not practical which is why DoE go through the current process using neptunium and americanium

Paul McCarthy: 11/19/2013 04:38 CST

Monday: "Boeing [NYSE: BA] subsidiary Spectrolab recently set a new world record by producing a solar cell that converted 38.8 percent of solar energy into electricity, more than any other ground-based solar cell not using concentrated sunlight. The U.S. Department of Energy's National Renewable Energy Laboratory in Golden, Colo., verified the new record, which beats Spectrolab's own previous world record by 1 percent. Spectrolab manufactured the high-efficiency multi-junction solar cell, which was developed from new Boeing semiconductor bonding technology. This solar cell technology could be used to power high-power spacecraft and unmanned aerial vehicles." A relevant trend?

Enzo: 11/19/2013 05:48 CST

@Paul McCarthy, Solar flux is ~1.3 KW per square meter at 1 AU. With 38.% efficiency, you get ~500 W/m^2. Unfortunately, it goes down with the square of the distance from the sun. At ~5 AU (Jupiter), it's 25x less, you get 20W/m^2. Saturn, ~10AU, 100x less, ~5W/m^2. Uranus, ~20Au, 400x less, 1.25W/m^2. So, a slow and difficult increase in efficiency is quickly eaten out by the distance. Also,it would be interesting to know how well solar cell resist to high radiation environment close to, say, Europa. For example, ESA JUICE mission is a Ganymede orbiter powered by solar cells. I believe that ESA would have chosen the much more interesting Europa if it wasn't for the high radiation. JUICE will only make two flybys of Europa because ESA's radiation hardened technology is not as good as NASA. I have no information on this, but solar panels are so exposed (compared to a computer partially shielded by a box inside) that I wonder how much they would be degraded in high radiation. That could be a weak point of an otherwise radiation hardened mission to Europa. Juno uses solar panels too, but it avoids most of the high radiation thanks to its particular orbit.

RickK: 11/20/2013 11:22 CST

I’ve been pondering whether ASRG development should move out of PSD to another NASA organization. I’m going through the document “NASA Strategic Space Technology Investment Plan” (SSTIP). Power Generation is not a core, but “adjacent technology investment”. And in that list (page 40), radioisotope power generation is not one of the NRC-associated top priorities. The problem will be, even if ASRG responsibility comes out of PSD to some other part of NASA, the associated priority, starting with the NRC, is not ranked very high. By contrast, solar power generation (photovoltaic and thermal), and fission power generation have higher priority. So if future RTG or ASRG work were assigned to a different NASA organization, even if the NASA budget is increased, this work is likely to get dropped. It simply appears to not be important enough… to anyone except outer planets researchers. Something in the SSTIP doesn’t feel right.

Enzo: 11/20/2013 05:08 CST

@RickK, " It simply appears to not be important enough… to anyone except outer planets researchers. Something in the SSTIP doesn’t feel right." It's not just one act in isolation, it's a clear sequence that points to a complete withdrawal from the outer planets : 1) Assign the largest part of funding to Mars missions (Curiosity, MAVEN, Insight, MSL2 = $5 B) to make sure the budget is all allocated. This is very effective in lean times. 2) Use almost all the plutonium for Mars missions where is not strictly necessary. 3) Then cancel ASRG to make absolutely sure that the little plutonium left is not used on outer planet missions. 4) Make RTG and ASRG “adjacent technology investment” for good measure. 5) Cancel Cassini ? You know, those pesky $50M/yr could pay for a good part of another Mars lander of some sort. All these actions point inescapably to a strong narrowing of the focus of the space exploration program and a big loss for science in general. Why the outer planets ? My guess is because going there is expensive, they have no connection with human space flight and they get in the way of more Mars missions.

Dennys Angove: 11/23/2013 03:21 CST

Enzo: I think the energy requirements for electro-mechanical and/or electro-magneto solutions to cleaning a solar panel surface may be under appreciated in a hostile environment.

Enzo: 11/25/2013 02:12 CST

@Dennys Angove, Well, Opportunity has a mass of 180 kg and it can be driven for 100 m or more for a day with the power available. Thus I expect that moving a much smaller mass for only a few cm/day on the panels should not be an issue. In any case, Opportunity has worked for nearly 10 years without intentional cleaning and ESA ExoMars will use solar panels. So, it is clearly possible, especially if the nuclear alternative precludes other outer planets missions. That should have been taken into account and it wasn't. At the very least, approve one rover, not too, leave a bit for something else. It's not just the funding, it's how they are allocated.

Dennys Angove: 11/29/2013 04:16 CST

Enzo: So, it would appear that we agree with the cleaning solar panel prospect. However, I think it is logical to have redundant systems where possible and the nuclear option seems to me to be a proven option.

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