Pluto Orbiter and Kuiper Belt Mission

[redliox]

Found this recently posted gem on Youtube:

Wasn't sure which thread this would be most relevant towards, but I will let moderators merge this with whichever thread they feel is the most appropriate.

[spacetraveler]

Just read an article on this. This mission has little chance of advancing imo, it needs to launch on an SLS block 2 and before 2032. Even then it still has a 20+ year travel time to Pluto.

And since we've already been to Pluto and are still analyzing the data from New Horizons, I think some of the other options in the next decadal survey would be more attractive, such as a mission to Enceladus, or a new mission to Neptune.

[Welsh Dragon]

Wont the need for FIVE RTGs mean this is dead on arrival anyway? Never mind that it needs an unplanned variant of of a rocket that isn't anywhere near certain of existing yet (SLS Block2 + Centaur). Disclaimer, I've only skimmed the video so far, so these questions may be addressed. It looks a wonderful fantasy mission though....

[yoram]

Wont the need for FIVE RTGs mean this is dead on arrival anyway? Never mind that it needs an unplanned variant of of a rocket that isn't anywhere near certain of existing yet (SLS Block2 + Centaur). Disclaimer, I've only skimmed the video so far, so these questions may be addressed. It looks a wonderful fantasy mission though....

At some point NASA and DOE have to fix the RTG issue, and once they do that it's quite conceivable that they are available in larger numbers and being cheaper. As far as I understand there is work underway on next generation RTGs.

[Zed_Noir]

After watching the whole video.

Agree that the requirement of 5 RTG means that this proposal is a non-starter. Never mind with the $2B+ SLS Block 2 paper rocket with kickstage that results in a non-extended mission cost of about $6B lasting over 25 years.

A Pluto system orbiter needs to get there faster and not wander off to visit other targets.

The PIs will have to consider non RTG power solutions that is more available and higher power generation levels for KBO missions. There will not likely to be enough Pu-238 available for everyone for the foreseeable future.

[vjkane]

Wont the need for FIVE RTGs mean this is dead on arrival anyway? Never mind that it needs an unplanned variant of of a rocket that isn't anywhere near certain of existing yet (SLS Block2 + Centaur). Disclaimer, I've only skimmed the video so far, so these questions may be addressed. It looks a wonderful fantasy mission though....

At some point NASA and DOE have to fix the RTG issue, and once they do that it's quite conceivable that they are available in larger numbers and being cheaper. As far as I understand there is work underway on next generation RTGs.

The work is underway, but I don't see any way that planned production rates could produce 5 RTGs.  The presentation doesn't discuss Pu 238 availability.

[Blackstar]

At some point NASA and DOE have to fix the RTG issue, and once they do that it's quite conceivable that they are available in larger numbers and being cheaper. As far as I understand there is work underway on next generation RTGs.

I don't know what you mean by "fix." Pu-238 production is happening (finally), and is ramping up to full-scale. So it's not broken. The relevant issue for this mission is if there will be sufficient Pu-238 to power 5 RTGs. I can almost guarantee that there is not enough unless production is increased beyond current planned levels.

[yoram]

At some point NASA and DOE have to fix the RTG issue, and once they do that it's quite conceivable that they are available in larger numbers and being cheaper. As far as I understand there is work underway on next generation RTGs.

I don't know what you mean by "fix." Pu-238 production is happening (finally), and is ramping up to full-scale. So it's not broken. The relevant issue for this mission is if there will be sufficient Pu-238 to power 5 RTGs. I can almost guarantee that there is not enough unless production is increased beyond current planned levels.

There is a next generation RTG program that is supposed to produce RTGs that need less Pu for a given power output. The talk was also referring to next generation RTGs

[Blackstar]

At some point NASA and DOE have to fix the RTG issue, and once they do that it's quite conceivable that they are available in larger numbers and being cheaper. As far as I understand there is work underway on next generation RTGs.

I don't know what you mean by "fix." Pu-238 production is happening (finally), and is ramping up to full-scale. So it's not broken. The relevant issue for this mission is if there will be sufficient Pu-238 to power 5 RTGs. I can almost guarantee that there is not enough unless production is increased beyond current planned levels.

There is a next generation RTG program that is supposed to produce RTGs that need less Pu for a given power output. The talk was also referring to next generation RTGs

Improvements can always be made, but there is nothing to be "fixed."

[ncb1397]

Under current planned production rates^[1], there will be enough for 5 MMRTGs by 2030ish if trident isn't selected (75% chance if all 4 proposals remaining have equal chance). It will deplete the stockpile though and will preclude another mission with a high MMRTG count in the same time frame (you could probably fit another 1 MMRTG unit in there between now and 2032 other than Dragonfly...especially for short time of flight missions that could use diluted plutonium).

¹https://rps.nasa.gov/about-rps/about-plutonium-238/

Anyways, remove some instruments or whatever to downscale the whole thing to 3-4 RTGs and it starts looking a lot more feasible.

[Robotbeat]

At some point NASA and DOE have to fix the RTG issue, and once they do that it's quite conceivable that they are available in larger numbers and being cheaper. As far as I understand there is work underway on next generation RTGs.

I don't know what you mean by "fix." Pu-238 production is happening (finally), and is ramping up to full-scale. So it's not broken. The relevant issue for this mission is if there will be sufficient Pu-238 to power 5 RTGs. I can almost guarantee that there is not enough unless production is increased beyond current planned levels.

There is a next generation RTG program that is supposed to produce RTGs that need less Pu for a given power output. The talk was also referring to next generation RTGs

The next gen RTGs, (actually not “T”, not thermoelectric) are ASRGs (Advanced Stirling Radioisotope Generators), but that program was (shortsightedly) canceled a few years back. So it’s not an option.

However, the Stirling Generators from that project are being used for Kilopower. Kilopower doesn’t require any Pu-238 and scales up to higher power levels easier... but is probably even further away than ASRGs. On the other hand, I think Kilopower is being funded. So if they can somehow get buy-in from Kilopower, maybe they have a chance?

[ncb1397]

At some point NASA and DOE have to fix the RTG issue, and once they do that it's quite conceivable that they are available in larger numbers and being cheaper. As far as I understand there is work underway on next generation RTGs.

I don't know what you mean by "fix." Pu-238 production is happening (finally), and is ramping up to full-scale. So it's not broken. The relevant issue for this mission is if there will be sufficient Pu-238 to power 5 RTGs. I can almost guarantee that there is not enough unless production is increased beyond current planned levels.

There is a next generation RTG program that is supposed to produce RTGs that need less Pu for a given power output. The talk was also referring to next generation RTGs

The next gen RTGs, (actually not “T”, not thermoelectric) are ASRGs (Advanced Stirling Radioisotope Generators), but that program was (shortsightedly) canceled a few years back. So it’s not an option.

However, the Stirling Generators from that project are being used for Kilopower. Kilopower doesn’t require any Pu-238 and scales up to higher power levels easier... but is probably even further away than ASRGs. On the other hand, I think Kilopower is being funded. So if they can somehow get buy-in from Kilopower, maybe they have a chance?

My understanding is that ASRG was cancelled because the stirling generators weren't reliable. And given that the plutonium supply issue was known to be solvable, the money was directed there rather than reducing the plutonium required. It will be interesting to see how kilopower deals with this (reliability might be less of a thing for manned missions that are shorter duration and repairs/replacements can be done). Anyways, ASRG and kilopower aren't the only next generation technology that could be used here. There was a next generation RTG study ^[1], but it is export controlled and not available to the public.

^[1]https://rps.nasa.gov/resources/73/next-generation-rtg-study-final-report/

[Robotbeat]

No. The Stirling Generators themselves were plenty reliable; they operated for years. there’s just a lot of risk averseness about the fact that ASRGs have moving parts and these missions can last decades.

Additionally, the claim you made isn’t in the link you provided. In fact, the pdf of that report isn’t in that link either. Can you provide an actual quote? Because from what I remember, the cancellation wasn't due to failure of the ASRG technology at all (after all, Kilopower is based on it) but because of the increase in Pu238 production and a shift in priorities.

[ncb1397]

There is more to it. After the cancellation of flight unit development, the flight hardware was dedicated to laboratory testing.

The Advanced Stirling Radioisotope Generator (ASRG) Engineering Unit 2 (EU2) is the highest
fidelity electrically heated Stirling radioisotope generator built to date. NASA Glenn Research Center
completed the assembly of the ASRG EU2 in September 2014 using hardware from the now cancelled
ASRG flight development project. The ASRG EU2 integrated the first pair of Sunpower’s Advanced
Stirling Convertors (ASC−E3 #1 and #2) in an aluminum generator housing with Lockheed Martin’s
(LM’s) Engineering Development Unit (EDU) 4 controller. After just 179 hr of EU2 generator operation,
the first power fluctuation occurred on ASC−E3 #1. The first power fluctuation occurred 175 hr later on
ASC−E3 #2. Over time, the power fluctuations became more frequent on both convertors and larger in
magnitude. Eventually the EU2 was shut down in January 2015. An anomaly investigation was chartered
to determine root cause of the power fluctuations and other anomalous observations. A team with
members from Glenn, Sunpower, and LM conducted a thorough investigation of the EU2 anomalies.
Findings from the EU2 disassembly identified proximate causes of the anomalous observations.
Discussion of the team’s assessment of the primary possible failure theories, root cause, and conclusions
is provided. Recommendations are made for future Stirling generator development to address the findings
from the anomaly investigation. Additional findings from the investigation are also discussed.

There was a significant amount of debris found at various locations throughout convertor. The
composition was analyzed and determined to be from the permanent magnets, the titanium
magnet can, and the alternator laminations.
• Rubs were found on the magnets; significant damage to in-end magnets and magnet can on one
side.
• There were dark marks on magnet can beams determined to be from a Sharpie marker put on by
Sunpower during production.
• Microscopic inspection of the magnet can beams revealed deformed tooling marks on magnet can
beams at the locations of the Sharpie marks. It was later determined that the deformed tooling
marks appeared during production at Sunpower, and with deformation at some locations
occurring later. The location of the tooling mark deformation is in line with the location of the
retaining ring on cylinder assembly.
• There was an axial crack in magnet can in line with in-end magnet damage.
• There were out-end magnet damage and cracks in magnet can about 120° from in-end magnet
damage. Rubs were found on the magnet can.
• There was a noticeable rub on piston, on side towards the location of the in-end magnet damage.
• There was a noticeable rub on the displacer, in line with location of magnet damage.
• Not surprisingly, with the extensive damage observed to the magnet can, there were significant
changes to magnet can dimensions

There was a significant amount of debris found at various locations throughout convertor of
consistent nature as with ASC−E3 #1.
NASA/TM—2018-219400 11
• There were rubs on magnets and damage to in-end magnets on one side and out-end magnets on
opposite side of the magnet can.
• There was a circumferential crack on the out end of the magnet can and a crack in a magnet can
beam.
• Rubs were found on the inside diameter and outside diameter of the magnet can.
• There was a noticeable rub on the piston, located in line with location of magnet damage.
• There were significant changes to magnet can dimensions.
• Microscopic inspection of magnet can beams showed no evidence of tooling mark deformation.
Photos show slight markings on three beams corresponding with the cylinder assembly.

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20180002070.pdf

[Nomadd]

No. The Stirling Generators themselves were plenty reliable; they operated for years. there’s just a lot of risk averseness about the fact that ASRGs have moving parts and these missions can last decades.

Additionally, the claim you made isn’t in the link you provided. In fact, the pdf of that report isn’t in that link either. Can you provide an actual quote? Because from what I remember, the cancellation wasn't due to failure of the ASRG technology at all (after all, Kilopower is based on it) but because of the increase in Pu238 production and a shift in priorities.

There are RTGs out there still going more than 40 years after launch. During the Kilopower presentation at the Mars society convention in Pasadena a while back, they said the one bit of maintenance they expected was replacing the Stirlings. They thought ten years would be asking a lot for anything on the drawing boards.

[Blackstar]

There is more to it. After the cancellation of flight unit development, the flight hardware was dedicated to laboratory testing.

There's more to it that never got publicly reported. Simply put, the cost of making the ASRG flight ready was going to be way higher than the people developing it had been telling people--even NASA people--for a long time.* So there was a publicly stated reason for the cancellation, but that was probably only the tip of the iceberg.

I don't know any specifics, but there were a number of hints with that project that in retrospect implied that it was a lot more of an engineer's sandbox to play around in than a technology development program intended to develop flight hardware. For one thing, they were constantly changing the design rather than settling on a final design--even a sub-optimal one--and doing a full lifetime test on it.

You have to ask why, if ASRGs were so promising, that NASA killed the program completely.







*Keep in mind that NASA is not a point entity. NASA is a bunch of centers and different organizations, and they don't all talk to each other very well or tell the truth to each other. So the ASRG people may not have been honestly reporting the status of their program to Headquarters. That happens.

[vjkane]

Under current planned production rates^[1], there will be enough for 5 MMRTGs by 2030ish if trident isn't selected (75% chance if all 4 proposals remaining have equal chance). It will deplete the stockpile though and will preclude another mission with a high MMRTG count in the same time frame (you could probably fit another 1 MMRTG unit in there between now and 2032 other than Dragonfly...especially for short time of flight missions that could use diluted plutonium).

¹https://rps.nasa.gov/about-rps/about-plutonium-238/

Anyways, remove some instruments or whatever to downscale the whole thing to 3-4 RTGs and it starts looking a lot more feasible.

ncb1397, based on the projected plutonium supply chart attached, which is on the website you linked, I see the equivalent of two standard* RTGs available around 2030.  One could be fueled by not using the fuel for Trident (the only Discovery proposal that would use RTGs) and the chart says one additional one would be available around 2030.  So that seems like two to me.  Am I missing something?

*The next generation of RTGs will be scalable - they can be bigger or smaller depending on the mission.  A 'standard' RTG, though, is roughly twice the power and twice the plutonium of an MMRTG.  That's why Trident would need two MMRTGs while New Horizons needed just one (under fueled) RTG.

[vjkane]

Pluto is a cool destination (literally, too), as is Neptune, Uranus, Enceladus lander, Europa lander, Venus (not cool, literally).  All are candidates for the Decadal Survey to pick for the Flagship mission to follow Perseverance, Europa Clipper (~2024 launch), and Mars sample return (2026 or 2028 launch). 

Pluto and Neptune launches need to occur around 2030-2032, take a long time to reach their targets (up to 20 years for Pluto, 11 years for Neptune, but could be much longer without SLS), and require either 5 or 4 RTGs based on the concepts being put forward.  Both Pluto and Neptune missions really want SLS, so a very expensive launch.  Figure that both of these are ~$3Bish without the SLS launch.

Both JPL and APL are putting forward New Frontiers-class Uranus orbiters (RTG requirements not specified) and flight times to Uranus are shorter.

My prediction is that the key challenge for the next Decadal is what can be afforded after a string of three Flagship missions.  I think the key decision will be between an ocean world flagship mission and an ice giants flagship mission (with full recognition that many other targets are available for Flagship missions, but IMO these are the most compelling).  It's not clear to me that very expensive missions to the outer edge of the solar system will be the choice.

[ncb1397]

Under current planned production rates^[1], there will be enough for 5 MMRTGs by 2030ish if trident isn't selected (75% chance if all 4 proposals remaining have equal chance). It will deplete the stockpile though and will preclude another mission with a high MMRTG count in the same time frame (you could probably fit another 1 MMRTG unit in there between now and 2032 other than Dragonfly...especially for short time of flight missions that could use diluted plutonium).

¹https://rps.nasa.gov/about-rps/about-plutonium-238/

Anyways, remove some instruments or whatever to downscale the whole thing to 3-4 RTGs and it starts looking a lot more feasible.

ncb1397, based on the projected plutonium supply chart attached, which is on the website you linked, I see the equivalent of two standard* RTGs available around 2030.  One could be fueled by not using the fuel for Trident (the only Discovery proposal that would use RTGs) and the chart says one additional one would be available around 2030.  So that seems like two to me.  Am I missing something?

*The next generation of RTGs will be scalable - they can be bigger or smaller depending on the mission.  A 'standard' RTG, though, is roughly twice the power and twice the plutonium of an MMRTG.  That's why Trident would need two MMRTGs while New Horizons needed just one (under fueled) RTG.

Nope, you are correct. Serves me right for not paying attention. Thought they were MMRTGs, but it looks more like 16 GPHS unit RTG(see attached image). The listed power output in the presentation roughly matches as well. So, you would need 10 MMRTG worth of GPHS units (80 units).

I did find this though...

In February 2017 Ontario Power Generation and its venture arm, Canadian Nuclear Partners, announced plans to produce Pu-238 for space exploration at the Darlington nuclear power plant and signed a contract for this with NASA. OPG is seeking regulatory approval to begin Pu-238 production at Darlington by 2020, using a similar process to that at its Pickering units to produce cobalt-60. The process was developed by Technical Solutions Management (TSM), which will also mange the project. In this, Np-237 targets will be made by DOE’s Pacific Northwest National Laboratory (PNNL) and shipped to Chalk River Laboratories in Ontario where they will be assembled into reactor bundles. These will be irradiated at Darlington then returned to Chalk River for processing. Production target is 5 kg Pu-238 per year by about 2022.

https://www.world-nuclear.org/information-library/nuclear-fuel-cycle/fuel-recycling/plutonium.aspx

With output of 5 kg per year, you should be able to fuel this mission by the end of the decade. The question is what happened to this project?

[Zed_Noir]

<snip>
Pluto and Neptune launches need to occur around 2030-2032, take a long time to reach their targets (up to 20 years for Pluto, 11 years for Neptune, but could be much longer without SLS), and require either 5 or 4 RTGs based on the concepts being put forward.  Both Pluto and Neptune missions really want SLS, so a very expensive launch.  Figure that both of these are ~$3Bish without the SLS launch.
<snip>

My bold. There are other cheaper launch solution other than the paper SLS Block 2 that should be available by the late 2020s. However most of those require some sort of orbital refueling.

As I see it the only way that a near future mission could operate beyond Saturn is by using Kilopower reactors. Since it appears that there will not be enough RTGs available by the proposed launch date.