Aerogel NERVA's last progress-report

Back in 2023 I noted a fission-fragment rocket engine - in passing, frankly. I had left to the linked article what this was, mainly because I (1) didn't know much and (2) didn't care to look it up. It had a few unsolved problems which made it not worth my while. Ryan Weed founded something called "Positron Dynamics" for this...

... and then fled the place, shifting to fusion propulsion at AeroFuse. Weed gave up on this too and is now fronting something called Eos Atomics. This is for fusion sparking, compact plasma heating. So the whole aerogel/fission scheme looks dead. Let's autopsy the corpse.

ToughSF links today that Weed was addressing some of these problems in that banner year 2024, in collab with Sandeep Puri et al.

Classical "atomic rockets" are nuclear-thermal, including NERVA. Heat a gas, offer a hole for escape, vroom at very-many m/s. That last is specific-impulse; I_sp opens up new delta-V routes. Among its (many) constraints, is the ability to force the temperatures into vrooming the gas and to control its plasma. The ideal plasma here was the proton, aka hydrogen. Other solutions exist out there to afterburn the hydrogen, like with some oxidiser or even to fuse it; we're not getting into that today.

Weed proposed to harness the energy of the fission-chain's fragments, bypassing other propellants. Much of the energy in fission actually doesn't go directly to heat; it goes to moving the fragments, like neutrons or (for uranium) iodine-135. Elsewhere alpha-decay should count as Nature's most common process. I think most fission-thermal solutions let the fragments bounce around to turn their bouncing into heat. Chernobyl enjoyers will recall, for 2-2.6% U-235 LEU, the fragment I-135. This becomes Xe-135 leading to Xenon Poisoning, gobbling neutrons meant for the reaction. As a heat-generator it's all very indirect so inefficient, and some capitalist reactionaries might consider it somewhat dangerous as well.

Aerogel comes in as a matrix to hold the fissile elements in a fine dust at some mutual distance. The notion is that the aerogel would not interfere with the runaway radioactive iodine (or whatever). These frags are ions, iodine in particular being quite reactive, so Weed added a honkin' magnet to run the ions toward the exit. That redirected iodine might not be the fraction of lightspeed that the sail's helium was, but it is still one hefty I_sp. As for the exhaust: this can decay into Xenon or whatever, far from the reactor. Thrust ain't great so it's for robots, as I noted at the time. This is similar to the T-FINER sail proposal.

Puri's crew chose fissile Americium, here -241 rather than -242m, I guess because this isotope could be handled in reasonable times in a lab. Opposite from NΘP they wanted to reduce attenuation into that Θ. For them a graphene matrix worked best: at 900 microns (μm) they wasted only 7.5%.

Aaaand that is where Weed left us. Radioactive critical-mass aerogel is expensive to manufacture, and difficult to justify launching into LEO. In the low-mass high-delta-V mission space generally, by 2024 several competitors were coming to press (if not to prod).

Over-dense planets

On topic of strange (in every sense) white dwarfs, Zim has something on J132800.85–145019.95, and the gaps in the cloud orbiting same. The star, being a WD, is basically Earth-sized. Its cloud(s) can be measured in fractions of the solar-volume: the inner planetesimal must be located between 0.14 R_⊙ and 0.34 R_⊙ and the outer one between 0.54 R_⊙ and 1.93 R_⊙ (pdf). The former 0.14 might be better expressed as 15.27 Earth radii, or 97.4 Mm.

Usually a ring-cloud with gaps implies some gravitational-exerting mass. They don't see the planets.

To that, a WD is not Earth-heavy. It's still a good fraction of the star it was in life, which was probably A or F. Paper estimates 0.47 ±0.09 solar. That point mass should be exerting a wider Roche than 2 R_⊙. Most planets in here should be sheared, to join the rings. The paper has some large estimates for density, which Zim is showcasing, although these only apply if the bodies lack internal strength (see below).

On the assumption that Young Modulus in fact exists, the outer planet could be rocky, they say minimum 3.5 g/cm³. Earth for contrast is 5.513; Psyche 16 isn't as dense, because it's considered to be fractured. So it could be a dwarf planet like those we have here (an expanding family, I hear).

Back to J1328–1450, the inner one is the problem. It would have to be 45-172 km in diameter. That is if it is pure iron and unfractured.

If internal strength is taken away, densities rise to beyond-possible levels... for normal matter. We do, however, have some papers venturing into abnormal matter. Abudushataer Kuerban et al. proposed such in 2019, in a paper taken more-or-less seriously since. The reasoning was that if quark stars exist, quark planets might also exist. GP Com[ae Berenices] b is mooted along with some others.

PSPACE

Comp-Sci has an old tradeoff between the time one needs to run an algo, and the space required to hold relevant data for it. Database engineers, and here the term "engineer" may indeed apply, are always pondering how best to index their tables. Last year Ryan Williams researched (famous) polynomial P and PSPACE, and failing at that (like we all do) instead succeeded at time[f(n)] and memoryuse[f(n)] whether P or not. It got to the arxiv February 2025; our man did a seminar last October, and now some autodubber did a youtube so I guess it's serious.

Like experimental physicists don't really grok HEP theory, I'm not pretending I understand more than the basics of what Ryan Williams has done here. All I understand is that he might be able to cut down on RAM usage for any given algo as hasn't already been so "optimised". With the understanding that we're not saving on time.

RAM matters. Prices keep rising, which is trickling into game boxes and further giving the impression of inflation, for the average man[-child]. The engineers buying RAM are doing it for data centers, themselves becoming a political problem for their needs in energy, thermodynamic release thereof (by water, mayhap), and land-area. "Reckless data centers!" has united slopulists from Brandon Herrera to Mary Peltola, neither of whom this blog is endorsing. And the antigrowth crowd including various lawyers and other scum might be keeping compute from launching to NEO space as well.

Data centers solve more the ROM problem than RAM. Those Taylor-series algos require storing (small) arrays, as does the geode rising rather larger. If the numbers can't change, they can be offshored to some shared server. Deterministic random-number results also count as ROM-storable, although in graduation from dev to unit-testing we should be using natural noise (quantum noise seems most-scalable; here's a paper).

RAM would be used where the random-number seed expands dimensionally, to the limitless possibilities of the human imagination. We don't distribute this memory.

I'm considering here how (deterministic) random numbers can give rise to a generated maze for some game. Or to cellular-automated caverns. Fractal landscapes.

I found with some of these algos (including the geode as solution to quintics, since the geode was not in 2025 stored in any offsite server) that storing an array that is too large will, itself, cost time. This is because of the Swap File pattern in just-about any machine with an internal hard drive. If you don't tell the computer otherwise, it will use the drive as an extender to RAM. That is unpleasant for the drive and it wastes your time.

This puts us back to the good ol' days of the TRS-80 when you saved your code on tape and all RAM was hard-limited to, what, 32KB (K for kibi-, these days). Modern bithackers experience those days with stackalloc, after limiting that memory themselves to maybe just one kibi.

The Catholic state

A few days ago Paul Thompson poasted at Anxious Bench a tantrum: on the topic of race, hierarchy-construction, and Christianity. I find difficult to describe this article in any other sense. Little argument was made; we do get some definitions, but only at the end at which point it simply isn't earned. Meanwhile a Christian, Eric Aaron Castro, has offered the classic Habsburg view of hierachy-construction. This one, also a bit screedy, does offer its own definitions up front.

"This is the time of the blog that we juxtapose", as Small Dead Animals used to say. I don't believe that the two articles were aware of each other.

To link the two, race has existed since the old folk of Neander Valley. Families are good; extended families inevitable. But. The Catholic argues by Divine writ - preceding Paul - that race ceases to exist in heaven, which is glimpsed at the Altar of Christ. Likewise the Catholic argues from Queen Isabella's decision against Columbus that race does not exist in her court, either. The Admiral of her fleet enjoys the same rank as the cacique of an Haitian village, and likewise the meanest sailor and the dirtiest villager under each.

"Nationalism" from this perspective is an abomination. Nahuatl (say) can be the voice of sermons and hymns; but the celebrant priest speaks (more-usually, sings) Latin to God, be he a Tlaxcaltec or a Castilian. We can argue over whether we should be using New Testament Greek or Jesus' dialect of Aramaic, or Imperial Persian, rather than Latin. Doesn't matter. It's not like the Basques are any of the above either. Latin is nothing more or less than some link to a shared transnational culture. Gotta choose something.

We are not here to argue for or against the Catholic conception of a transnational and dyothelete Church and State in harmony. This blog has handled that ad, as they say, nauseam. We are here to argue for whether, from a Western Christian perspective, Thompson offers a rational counter. I don't think he is.

Thompson is speaking the cant of a rather different Jew than that of the son of Mary when he speaks of "oppression". He slips into critical-race cant when devolving to "discrimination", "racializing", "European colonialism and imperialism", "inequities". Thompson should know what Castro knows about what Empire meant; but Thompson elects not to cite those sources. It is all resentment, for Thompson. Likely affected, for his Anxious Bench base.

Thompson may want a dictatorship of the racialized proletariat. Christians must oppose this... and oppose the Patheos website.

The eclipse of Lu

In our 709 BC, the core of what is now called "China" was under the Zhou regime... sort of. Many duchies were autonomous and dynastic, rather like what Pourshariati says of Sasanian Iran. We've all heard of Song, where the old Shang survived. Another such was Lu. It seems Lu, at least, had shifted from the old Shang practice of oracle-bones and were doing astrology instead. On 17 July (Julian), their observatory at Khoɡ-Bu' saw an eclipse. By modern pinyin it's Qūfù.

To make a correction here, this is hardly the first eclipse in astrologic history. The Mesopotamia observed one in 763 BC, heralding (or underlining) the failed Tiglath-Pileser III in Assyria, albeit invisible to Chinese. We'll get to that. For another interjection of personal frustration, ScienceDaily saw fit to tell us only now, almost a year after the paper. Weak!

We know Lu's eclipse from two later records: the "Spring and Autumn" annals, in a time when the Zhou were pretty-much being ignored; and Jīng Fáng's still-later (78-37 BC) account. I think the latter ended up in "Book of Han". For Jing, all these events were (literal) ancient history, like the various Jewish Antiquities books were for the Romans. The former is taken more seriously given that Confucius himself will be born in Lu, and seems to have had a hand in preserving their annal. But the Hans' Shu adds detail of two ears around the lunar-disc. A Japanese-led quintet, including a Meng Jin presumed Chinese, believes the latter was corona.

Although everyone has accepted the date (-708\07\17) and the place (old Lu... somewhere) of this eclipse, discrepancies persisted about the exact time and place of the Qufu observatory. It seems we've pinned down that capital, correcting other estimates that it was eight kilometers away (later dukes may have moved house). On the assumption the ducal astrologers were close to the palace, the paper must adjust ΔT to run its totality over the new site. This further adjusts ΔT for the later eclipses over Lu until ~548 BC.

For the sun himself, all this validates a maximum around 709 BC, perhaps on par with 18 October 1848. This particular eclipse, of course, was invisible to the astrologers of Babylon; but as I've noted, they had others. Coronae might not have been observable for what eclipses they had 808-717 BC which is tagged the "Neo-Assyrian Minimum". Which mostly it was... for said Assyrians, between Shamshi-Adad V and Pulu that second "Tiglath-Pileser III".

Gravettian migrations in the Upper Palaeolithic

Gelabert et al. have a new paper, on the evolution-or-replacement of the Aurignacian culture in Iberia by Gravettian. They've used sedimentary DNA, which also gets laid down in layers, easing our ability to set dates. The dates for the new remains, themselves late in Gravettian-even-Magdalenian ages, point to an event in the millennium 31500-30500 BC.

Among the finds is a female, or at least her maternal line, with mito-DNA U8a. This is presently rare outside northern Iberia, which is Basque-country today. U8a is elsewhere known in famous Bacho Kiro also deemed Aurignacian. Otherwise there is continuity.

This suggests the local Aurignacians, called here the "Fournol cluster" exemplified by "Goyet Q116-1" in Belgium, responded to an incursion of the central Europeans. The latter are the "Věstonice" descended from Bacho Kiro, but not itself well-documented. Together they made, or brought, the Gravettian in/to Aurignacian Iberia.

The Věstonice by including their women was indeed a migration. I don't know if we can call it a forced invasion; populations may have been small enough, the newcomers culturally-compatible enough, and resources plentiful-enough that a merger was possible. The paper believes Věstonice itself had been a merger of Bacho Kiro and some western population. So a back-migration and assimilation seems a better bet than if the incomers had not brought their women; or if the locals had simply vanished.

The Isturitz seems also to have the widest breeding-pool, inferred to 265. Their kids should have been reasonably healthy.

Which brings us to the south Italian sample, a sad one. This is miscarried "Ostuni1b", so called because he is, or would have been, the son of Ostuni1 previously-published: mitochondrion M (like me; no longer common in Euroland). These two samples allow for narrower dates in the middle 25kBC millennium; and gets us about half Ostun1b's father, who had yDNA in the C family (also no longer common here). This is, further, flagged as about the second-least inbred Gravettian: population size inferred to 160 [breeders].

Ousiometrics

Human language - left on its own - has a positive bias, sometimes called the "Pollyanna principle". A fair example is the indo-european *arktos, which we Germanics call a "bruin". Last May, Vermont has clarified that this bias is safety.

Nobody should be surprised that animal thought should gear toward survival, balancing "can I eat this" against "will it eat me" (per Mimic). That our communication should be aimed specifically toward warning, suggests the Prairie Dog.