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eppur_se_muova

(42,482 posts)
2. Previous ion engines have favored very heavy atoms as propellant -- mercury or xenon. More atomic mass --
Sat May 16, 2026, 01:42 AM
Saturday

more efficiency. This engine uses lithium, the third lightest atom known, so the operating principles must benefit from light atoms in this technology. Smaller atoms are faster-moving at the same temperature compared to heavier atoms, and faster-moving ions would create larger currents and larger magnetic fields. Would be nice to see the math breakdown on this.

If that's correct, use of Li-6 enriched fuel could give a significant performance boost over natural isotopic abundance lithium. DOE currently separates lithium isotopes on a huge scale to use Li-6 in hydrogen bombs. Surely we could spare some that to power a space probe, thereby increasing its acceleration and chances of mission success.

(The IUPAC reports the gradual slow increase in the atomic weight of commercial lithium as the lighter isotope, Li-6, is withdrawn from circulation.)

Nuclear weapons manufacture and other nuclear physics applications are a major source of artificial lithium fractionation, with the light isotope 6Li being retained by industry and military stockpiles to such an extent that it has caused slight but measurable change in the 6Li to 7Li ratios in natural sources, such as rivers. This has led to unusual uncertainty in the standardized atomic weight of lithium, since this quantity depends on the natural abundance ratios of these naturally occurring stable lithium isotopes, as they are available in commercial lithium mineral sources.[29]

https://en.wikipedia.org/wiki/Lithium

Recommendations

2 members have recommended this reply (displayed in chronological order):

Another fucking waste of money. 3Hotdogs Saturday #1
Previous ion engines have favored very heavy atoms as propellant -- mercury or xenon. More atomic mass -- eppur_se_muova Saturday #2
The NERVA engine used hydrogen, so (you know) lithium is heavier than that, but certainly lighter than mercury OKIsItJustMe Saturday #4
Hydrogen is being used there as ejectable mass, nothing more. It's handled by mechanical pumps and pressure. eppur_se_muova Saturday #5
Check out the NASA paper I added to the bottom of the reply OKIsItJustMe Saturday #6
Thanks for the paper. I knew about the older nuclear interest. eppur_se_muova Saturday #7
NERVA was not the same as Orion OKIsItJustMe Saturday #8
Yes, I know that, thank you. In fact you're just repeating things I've already said in my replies. nt eppur_se_muova Saturday #10
We both realize that (I was even repeating myself) OKIsItJustMe Saturday #12
Ah, OK ... writing for a larger audience ... eppur_se_muova Saturday #14
I've been watching "For All Mankind" on Apple TV OKIsItJustMe Saturday #15
Isn't lithium in somewhat short supply? erronis Saturday #3
Meanwhile, at a grossly overspent under intellectual trump supported SpaceX 3825-87867 Saturday #9
NASA is facing serious cuts OKIsItJustMe Saturday #11
More from the paper cited by OKIsItJustMe .... eppur_se_muova Saturday #13
"It must have been a real pleasure to work out the mathematics of MPD for the first time..." OKIsItJustMe Saturday #16
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