Thin Film Isotope Nuclear Engine Rocket (TFINER)

[litton4]

Not seen any discussion on this concept of using the momentum of decay products to provide thrust.

https://www.nasa.gov/general/thin-film-isotope-nuclear-engine-rocket/

To me, it seems far fetched and can't provide the stated thrust over time, but what do I know?

[edzieba]

Sounds like a Fission Fragment Engine (or Robert Forward's Fission Sail) but using decay rather than neutron triggered fission. I can't recall the idea of using extra films to capture and reuse decay products being proposed before, though.

[InterestedEngineer]

"always be thrusting" would be the motto.
And a mission planning headache.

  Unless you make it refoldable, but then I don't see how such a mechanism can fit inside 30kg of payload.

The useful design metric at scale is ~8.5m² per kg of payload.

So if one wants a more realistic 10t payload (e.g. with a decent deep space antenna), that's 85,000m² of sail, or 300m on a side.  On the high end, but possibly deployable from a Starship.

Seems to me this should be combined with a solar wind sail, which gives it 400-1000km exit velocity and then 100km/sec of further deltaV.

[KelvinZero]

I was wondering... Could there be a version of this that starts with mostly just safe-to-launch fertile nuclear material?

Although I think their idea relies on alpha emitters, I guess any nuclear reactions tend to produce charge particles if only through ionisation of whatever they are embedded in.

I imagine something like long rolls of film stretched out by a slow rotation. They can be rolled in to soak up neutrons and then unrolled to produce some thrust and get rid of heat.

[sanman]

Sounds like a Fission Fragment Engine (or Robert Forward's Fission Sail) but using decay rather than neutron triggered fission. I can't recall the idea of using extra films to capture and reuse decay products being proposed before, though.

How is the absorber ("extra film" shown in blue) allowing trapped decay-product nuclei to produce extra thrust that is directional rather than omni-directional? Once those decay product nuclei are embedded in the absorber film, then isn't the ability to control direction of their further decay emissions then gone?

Isn't directional thrust only happening from the original film shown in orange?

[sanman]

I was wondering... Could there be a version of this that starts with mostly just safe-to-launch fertile nuclear material?

I thought the definition of fertile is that it can absorb a neutron to turn into fissile isotope. That's what Th-232 does.
When it comes to nuclear decay, there doesn't seem to be any way to control that. It's just a hard physical law.

I recall some experiment from ~2000 where a researcher trapped some heavy isotope inside a C60 buckyball, and then surrounded it with negatively-charged anions to see if it would somehow crowd the electronic orbital clouds into the interior of the buckyball, and possibly have an effect on the beta-decay of the trapped heavy atom. Apparently it didn't do anything.

Although I think their idea relies on alpha emitters, I guess any nuclear reactions tend to produce charge particles if only through ionisation of whatever they are embedded in.

I imagine something like long rolls of film stretched out by a slow rotation. They can be rolled in to soak up neutrons and then unrolled to produce some thrust and get rid of heat.

So would the film rolls be wrapped around some nuclear fuel rods acting as a neutron source?

[KelvinZero]

I was wondering... Could there be a version of this that starts with mostly just safe-to-launch fertile nuclear material?

I thought the definition of fertile is that it can absorb a neutron to turn into fissile isotope. That's what Th-232 does.
When it comes to nuclear decay, there doesn't seem to be any way to control that. It's just a hard physical law.

Fertile creates fissile, fissile could rapidly bathe the film in neutrons when rolled up to create the short lived isotopes.

It is not about triggering the short lived isotopes. We just rely on them usually happening to decay while the film is unrolled since it usually is.

I have heard some types of reactors are safe to launch because they don’t create all the dangerous isotopes until turned on.. but maybe by safe they just meant fissile with massively long half-lives. I may have confused myself there.

[InterestedEngineer]

Brief from NIAC Phase II

https://www.nasa.gov/directorates/stmd/niac/niac-studies/tfiner-thin-film-isotope-nuclear-engine-rocket/

The brief didn't discuss acceleration and mass flow rate, here's an LLM analysis that estimates the thrust is about 122uN, allowing net 100kg wet mass probe to achieve 150km/sec in 4 years (using a 225m² panel.  This roughly replicates the results in the above brief.

https://chatgpt.com/share/68363fc2-dff0-8013-bab9-042e01deadff


Pretty high deltaV, comparable to sailing the solar wind, but not sure what they are going to do with a mere 30-50kg of cargo.  It does have a thrust density over 100x that of the solar wind, so it'll be a much smaller sail area, though I can't imagine the cost of thin film deposition over such a huge area.

Has anyone ever done radioactive thin film deposition?  I would imagine it wreaks havoc on the equipment and is mildly dangerous.

[zubenelgenubi: Duplicate threads merged.]

[Twark_Main]

/stmd/niac/niac-studies/tfiner-thin-film-isotope-nuclear-engine-rocket/

The brief didn't discuss acceleration and mass flow rate, here's an LLM analysis that estimates the thrust is about 122uN, allowing net 100kg wet mass probe to achieve 150km/sec in 4 years (using a 225m² panel.  This roughly replicates the results in the above brief.

https://chatgpt.com/share/68363fc2-dff0-8013-bab9-042e01deadff

Extremely painful reading.  Like someone posting a 1 hour screen recording of themselves Googling for a school paper.

"LLMs will always give you the right answer, after giving every possible wrong answer."


Please in the future if you want a mammalian fact-check, just post the LAST, (supposedly) correct answer, not the dozens of mistaken starts / human corrections / sickly sweet apologies it took to get there.  As for me. I'm going to start reading these from end-to-beginning. Or not at all. 

I do detect a couple flaws with ChatGPT's final answer, but that'll be $1 per token.  After all, I already know you're willing to pay for it...



Any opposition to merging this in with the existing TFINER thread?

[Twark_Main]

Sounds like a Fission Fragment Engine (or Robert Forward's Fission Sail) but using decay rather than neutron triggered fission. I can't recall the idea of using extra films to capture and reuse decay products being proposed before, though.

How is the absorber ("extra film" shown in blue) allowing trapped decay-product nuclei to produce extra thrust that is directional rather than omni-directional? Once those decay product nuclei are embedded in the absorber film, then isn't the ability to control direction of their further decay emissions then gone?

Isn't directional thrust only happening from the original film shown in orange?

The absorber traps the alpha particles, not the heavy decay nuclei. They don't go anywhere.

[InterestedEngineer]

Sounds like a Fission Fragment Engine (or Robert Forward's Fission Sail) but using decay rather than neutron triggered fission. I can't recall the idea of using extra films to capture and reuse decay products being proposed before, though.

How is the absorber ("extra film" shown in blue) allowing trapped decay-product nuclei to produce extra thrust that is directional rather than omni-directional? Once those decay product nuclei are embedded in the absorber film, then isn't the ability to control direction of their further decay emissions then gone?

Isn't directional thrust only happening from the original film shown in orange?

The absorber traps the alpha particles, not the heavy decay nuclei. They don't go anywhere.

the alpha particles get absorbed and turned into heat.

Half of the spherical flux of alpha particles gets absorbed, and thus no thrust is produced for that hemisphere.

The other half flies off into space, and thus net thrust is produced in one direction.  The total thrust in the desired direction is 1/4 the total alpha emission rate (1/2 for the absorbing  hemisphere, another 1/2 for the emitted hemisphere since it's not all in one direction)

It's assymetrical!   It's a perpetual motion machine!

Only it's not, it's just radioactive decay.  Harvesting of potential energy contained in the nucleus of the atom.  But it does remind us to not be so suspicious of asymmetric thrust setups, as long as we know where the energy is coming from.

One could in theory design a magnetic nozzle to channel the alpha particles all out the back and get say 80% of the thrust instead of 25%, but the mass of the nozzle would likely exceed the benefit of doing so.

In this case it's better to put thermocouples on the hot side and harvest some electric energy - a few hundred watts in this case - so that we can power the electronics of our tiny 30kg probe.

[InterestedEngineer]

/stmd/niac/niac-studies/tfiner-thin-film-isotope-nuclear-engine-rocket/

The brief didn't discuss acceleration and mass flow rate, here's an LLM analysis that estimates the thrust is about 122uN, allowing net 100kg wet mass probe to achieve 150km/sec in 4 years (using a 225m² panel.  This roughly replicates the results in the above brief.

https://chatgpt.com/share/68363fc2-dff0-8013-bab9-042e01deadff

Extremely painful reading.  Like someone posting a 1 hour screen recording of themselves Googling for a school paper.

"LLMs will always give you the right answer, after giving every possible wrong answer."


Please in the future if you want a mammalian fact-check, just post the LAST, (supposedly) correct answer, not the dozens of mistaken starts / human corrections / sickly sweet apologies it took to get there.  As for me. I'm going to start reading these from end-to-beginning. Or not at all. 

I do detect a couple flaws with ChatGPT's final answer, but that'll be $1 per token.  After all, I already know you're willing to pay for it...



Any opposition to merging this in with the existing TFINER thread?

we seem to oscillate between "show your work" and "don't show your work" around here a lot.

[edzieba]

/stmd/niac/niac-studies/tfiner-thin-film-isotope-nuclear-engine-rocket/

The brief didn't discuss acceleration and mass flow rate, here's an LLM analysis that estimates the thrust is about 122uN, allowing net 100kg wet mass probe to achieve 150km/sec in 4 years (using a 225m² panel.  This roughly replicates the results in the above brief.

https://chatgpt.com/share/68363fc2-dff0-8013-bab9-042e01deadff

Extremely painful reading.  Like someone posting a 1 hour screen recording of themselves Googling for a school paper.

"LLMs will always give you the right answer, after giving every possible wrong answer."


Please in the future if you want a mammalian fact-check, just post the LAST, (supposedly) correct answer, not the dozens of mistaken starts / human corrections / sickly sweet apologies it took to get there.  As for me. I'm going to start reading these from end-to-beginning. Or not at all. 

I do detect a couple flaws with ChatGPT's final answer, but that'll be $1 per token.  After all, I already know you're willing to pay for it...



Any opposition to merging this in with the existing TFINER thread?

we seem to oscillate between "show your work" and "don't show your work" around here a lot.

Show your own work.
Getting a statistical-sentence-completer to make up some plausible-sounding-but-generally-wrong 'work' for you and posting that is just wasting everyone else's time along with your own.

[edzieba]

But it does remind us to not be so suspicious of asymmetric thrust setups, as long as we know where the energy is coming from.

Every rocket engine (or atmospheric turbojet, or turbofan, or turboprop, or EDF, or etc, for that matter) is an 'asymmetric thrust' setup. 'Symmetric thrust' is only a thing when you're trying to vent gasses overboard whilst minimising trajectory perturbations - and even then it's never exactly symmetric in practice.

[sdsds]

Is this proposed for something like a Kuiper Belt mission? Where else can a spacecraft go with acceleration measured in μm/s²?

[InterestedEngineer]

Is this proposed for something like a Kuiper Belt mission? Where else can a spacecraft go with acceleration measured in μm/s²?

TFA is full of mission ideas

[Twark_Main]

Extremely painful reading.  Like someone posting a 1 hour screen recording of themselves Googling for a school paper.

"LLMs will always give you the right answer, after giving every possible wrong answer."


Please in the future if you want a mammalian fact-check, just post the LAST, (supposedly) correct answer, not the dozens of mistaken starts / human corrections / sickly sweet apologies it took to get there.  As for me. I'm going to start reading these from end-to-beginning. Or not at all. 

we seem to oscillate between "show your work" and "don't show your work" around here a lot.

We seem to oscillate between "fact-check this please" and "no I don't want to hear it." 

"Show your work" is great, but if possible show the relevant work. It's not helpful to emit a firehose of irrelevant false starts, just like it wouldn't be relevant to review a livestream of your whole life since birth. More data isn't always better. It's a matter of signal-to-noise ratio.

I'm actually more optimistic than edzieba and think LLMs can be useful (if used properly and with sufficient skepticism and cross-checking), but please show restraint with your newfound power and don't use it to inexpensively bury fellow mammalian brains in a big pile of irrelevant text.

As I said, I'm happy to meet you halfway and be more AI literate about reading these in an efficient way when people don't edit out the irrelevant parts. But simply copy-and-paste the relevant bits and you're more likely to get help from people other than just me.


Or I could have chosen the Dark Path and had an LLM summarize your transcript, and then neither of us would really know whether it's right or not...     See attached.


P.S.  One useful tip for LLMs is don't tell it the answer you're expecting. You seemed to think the LLM getting the same answer as the NIAC brief was a level of validation, but you told it what you wanted first so it's perfectly expected that the LLM would regurgitate it back whether or not the math is actually correct. If the LLM independently arrived at the same answer that would be some evidence of accuracy, but AI is perfectly happy to fudge its way to the answer you told it.

[tea monster]

I took the liberty of doing a quick model and render.

[InterestedEngineer]

Extremely painful reading.  Like someone posting a 1 hour screen recording of themselves Googling for a school paper.

"LLMs will always give you the right answer, after giving every possible wrong answer."


Please in the future if you want a mammalian fact-check, just post the LAST, (supposedly) correct answer, not the dozens of mistaken starts / human corrections / sickly sweet apologies it took to get there.  As for me. I'm going to start reading these from end-to-beginning. Or not at all. 

we seem to oscillate between "show your work" and "don't show your work" around here a lot.

We seem to oscillate between "fact-check this please" and "no I don't want to hear it." 

"Show your work" is great, but if possible show the relevant work. It's not helpful to emit a firehose of irrelevant false starts, just like it wouldn't be relevant to review a livestream of your whole life since birth. More data isn't always better. It's a matter of signal-to-noise ratio.

I'm actually more optimistic than edzieba and think LLMs can be useful (if used properly and with sufficient skepticism and cross-checking), but please show restraint with your newfound power and don't use it to inexpensively bury fellow mammalian brains in a big pile of irrelevant text.

As I said, I'm happy to meet you halfway and be more AI literate about reading these in an efficient way when people don't edit out the irrelevant parts. But simply copy-and-paste the relevant bits and you're more likely to get help from people other than just me.


Or I could have chosen the Dark Path and had an LLM summarize your transcript, and then neither of us would really know whether it's right or not...     See attached.


P.S.  One useful tip for LLMs is don't tell it the answer you're expecting. You seemed to think the LLM getting the same answer as the NIAC brief was a level of validation, but you told it what you wanted first so it's perfectly expected that the LLM would regurgitate it back whether or not the math is actually correct. If the LLM independently arrived at the same answer that would be some evidence of accuracy, but AI is perfectly happy to fudge its way to the answer you told it.

In general I agree but alas the sharing mechanisms don't allow for editing right now, and sharing via screenshot makes looking for text difficult, and this forum doesn't have good support for Latex equations.

Any ideas how to solve all of these problems?


NOTE:  This is a very fruitful discussion but it doesn't belong here, so I forked it to the forum meta forum, please post responses there

https://forum.nasaspaceflight.com/index.php?topic=62978.0#new

[InterestedEngineer]

Here's an edited down version of TFINER giving possible mass flow and force numbers for the TFINER proposal

https://chatgpt.com/share/683a17fd-b63c-8013-b1c9-0e3305af7728

[Twark_Main]

In general I agree but alas the sharing mechanisms don't allow for editing right now, and sharing via screenshot makes looking for text difficult, and this forum doesn't have good support for Latex equations.

Any ideas how to solve all of these problems?

Ahh, I understand now.  Yeah here I was naively thinking they had implemented some sort of sane and disability accessible text fallback when you copy the math equations. 

Thanks.

Here's an edited down version of TFINER giving possible mass flow and force numbers for the TFINER proposal

https://chatgpt.com/share/683a17fd-b63c-8013-b1c9-0e3305af7728

I really appreciate you making the effort. Thanks again.

As far as fact-checking, I would double-check:

   * Is it just assuming the same decay energy (48 MeV) for all alpha particles?  Are there substantial differences in energy between the original decay and the subsequent daughter isotope decay energies?

   * Naturally there's going to be some self-absorption in the reverse direction in the 10 micron Thorium film. I'm guessing they chose 10 microns because any thicker and this becomes too much of an issue. It would be interesting to see if you can get ChatGPT to run a First Principle (vs fudge-based) estimate of those losses, including the spherical trig.

   * Similarly with the forward absorber, I expect they chose 50 microns not because it absorbs all forward alpha particles, but because any thicker and you lose more to the extra mass than you gain from the extra absorption.  I wonder if it can construct a simple model to estimate the "break even" point, and what the resulting efficiency might be.

  * The other possibility is that they chose 50 microns because of gauge issues, and the material simply isn't available in thinner sizes.

   * Maybe it can give suggestions into what material might be chosen for the absorber. I'm assuming it's just a bog standard kapton film, but it would be interesting to see if ChatGPT can come up with any other possible materials that might have been chosen.

[InterestedEngineer]

   * Similarly with the forward absorber, I expect they chose 50 microns not because it absorbs all forward alpha particles, but because any thicker and you lose more to the extra mass than you gain from the extra absorption.  I wonder if it can construct a simple model to estimate the "break even" point, and what the resulting efficiency might be.

you can calculate the absorption thickness needed from https://physics.nist.gov/PhysRefData/Star/Text/ASTAR.html which gives the range in g/cm² units.

then to get thickness:

Thickness (μm) = 10,000 × (Range in g/cm²) ÷ (Material density in g/cm³)

which for Mylar:

Thickness = 10,000 × 0.00475 ÷ 1.39 ≈ 34.2 μm

for the entire 225m² of the panels:

Mass (kg) = Area (m²) × Thickness (m) × Density (kg/m³)

Mass = 225 × (34.2e-6) × 1390 ≈ 10.7 kg


source:  ChatGPT - I got it to put equations in plaintext format so a little easier to post here directly.

[InterestedEngineer]

   * Naturally there's going to be some self-absorption in the reverse direction in the 10 micron Thorium film. I'm guessing they chose 10 microns because any thicker and this becomes too much of an issue. It would be interesting to see if you can get ChatGPT to run a First Principle (vs fudge-based) estimate of those losses, including the spherical trig.

Thickness (μm) = 10,000 × (Range in g/cm²) ÷ (Material density in g/cm³)

Range for Thorium is about 0.01843g/cm²  at 5.5MeV - a guess, they don't have TH-228 on the list. but all the high density metals are in the same ballpark.

Density is 11.7g/cm³

so that makes 15.75μm.   Since it's a radioactive decay chain we'd have to do this for each decay product, which is too tedious for now, but suffice it to say there's some but not much self-absorption in the reverse direction.  The average is 5μm which is 1/3 the absorption length.

Not to mention a geometry problem, as particles that go at 45 degrees go through 1.4x the material.

still, seems to be in the ballpark of "that'll work".