UltraSafe keepin' on

Here's our update on how LEU-powered NTP is going. Demo 2027. Congratulations to UltraSafe for progress sufficient to earn this contract.

This might be a different contract than their NTP contract with NASA. UltraSafe here are talking the EmberCore. It's a rechargable radioactive battery.

Also contracted is Avalanche Energy. These guys are doing fusion, with the Orbitron. This looks more experimental thus far.

By then a Starship should be able to hoist all manner of stuff up there on the cheap. The promise is to cut the time it takes to get to "Mars", meaning Deimos; and - more so - to Ceres and beyond. I take it the engine is always-on except for the halfmark, when the ship does flip-n'-burn to decelerate.

Even half the time is too long for microgravity, and I don't think the ship is going a "torchship" 3.7 m/s². As to "why do this", it does improve upon the time taken. Kilograms of reactor and fuel are better than kilograms of extra supplies and, not least, external shielding. But I think the crew still need to take options like hibernation and centrifugal-spin.

Given regulations (and limitations on the chamber) the nuclear fuel will be low-enriched, so this doubles as a mechanic to deliver semi-spent fuel to the destination. Maybe on Deimos they can reprocess the fuel for more energy needs. Deimos will have solar energy but, not as much as Earth LEO gets. Every little helps.

Ethics for a sustainable globe

The global fascist is very, VERY concerned with the Globe. To that end his solutions always consider how to make the global poor, poorer. Because poverty can be sustained - sustained, that is, by the righteous men, men like Klaus Schwab.

Hence why the school you've sent your kids to are preaching against Population - that is, against your kids. It is part of the Schwab (and Polis) plan to ensure he doesn't give you grandkids. It wasn't your plan - but then you'd already given up control of them, didn't you?

If you want to practice effective altruism for a self-propagating people, the first law must be - not to curse Population. More energy availability has to be the startpoint. And no - not "renewables" (per se). If we're foreclosing political means - that is, indeed, the second ethic, because all the government can do is suppress one population involuntarily.

Ramjet thrust

As I fill in NASA's Ice Gun gaps, here is NASA's ramjet equation: thrust is ṁV_x-ṁV₀+(p_x-p₀)A_x.

It turns out that by now I know a lot of this, if A_x be exactly a Dragon's cross-section 4π m². ṁ₀=3040kg/s; ṁ_x=3648kg/s. Initial V₀=1000m/s. I was despairing of finding V_x... but now I find it here as I plug in temperatures 200K and 2000K out: 3160m/s.

The gross thrust minus ram drag make, then, for 11527680 - 3040000 newtons. So F = 8,487,680 + 4πδp but NASA assure me we can normally neglect δp.

Again that's the initial value. One of our checkpoints was V₀=4400 m/s. ṁ₀ is now 13376kg/s, ṁ_x=16051.2. For that V_x=13914m/s. 223336396.8-58854400: F = 164,481,996.8 N. The force, as you see, rises. Moreover on the assumption of pure hydrogen, much of the initial mass is an oxidiser (you DID notice that the mass going out was more than the mass going in...?). So, the mass that needs to be moved is at first decreasing at 608kg/s.

8487 kilonewtons at an acceleration 32 m/s² can move 265 tonnes, to start its 1000 km odyssey. At 96.8 m/s² this falls to 87 tonnes aiming at 100 km. I expect that to lessen G force on the cargo (which is why we are doing all this), NASA'll lighten up on the temperature of the jet. That is - the jet uses less oxidiser as it has less.

xHCI

I've run into some (Windows) laptop display issues over the years, now that we're working with laptops more than desktops. Some rooting around has turned up the Device Manager. In it, under USB, the "eXtensible Host Controller Interface".

The Wiki page is actually... good here. It tells me that a laptop made up to December 2013 even if it has muh USB 3 will be on xHCI 1.0. That means USB 3 point zero. Laptops made up to early spring 2019 are xHCI 1.1 which handles USB 3.1. My main work laptop is (now) 1.2 / 3.2.

Why does this matter? Bandwidth - but not only bandwidth. It happens that bandwidth also includes display. "DisplayPort" must have the "Alt Mode". This only exists for USB 3.2, and not for all of them. ("Thunderbolt" is an Apple protocol, tho' compatible with Alt Mode.)

That is... an annoyance. USB 3 stood to do away with connecting all those ports to wires; just one docking-station was supposed to handle it. Well - not display. Better hope your laptop has HDMI.

The good news here for older laptops, is that you can daisychain additional monitors to the one you've HDMI'd. Those have to be the newer monitors however; they would chain each other over... sigh... USB 3 with Alt (== DP 1.4), or plain DP wires minimum-version 1.2.

Another railgun down

h/t Glenn Reynolds, the Army had a railgun project too. Had.

The thing was, in theory, supposed to reach 1600 km. I'm not doing the maths on this but, the range isn't the model which even the military were really looking at. The grunts'd rather punch a hole into some hostile battleship maybe 160 km out, with more speed and accuracy. Hence why the Navy was researching the same thing.

The Army has other longrange weapons on deck, so this cancellation isn't (or shouldn't be) cause for complaint. More cause for... concern, is that the Navy had cancelled something that looks very like it. There may be technical issues around firing this thing in 1-bar atmosphere.

Casarabe

Over the last few days - h/t Turtle - all us "lost city of Z" types have been taking a W for a newly-discovered urban civilisation in Bolivia. This is Llanos de Mojos aka Beni; southeast of the lake Rogaguado.

The main site is Cotoca; Landívar is also noted. All these sites have been pinpointed by lidar, so not much excavated (yet). The dates are broad: AD 500-1400. This piques my curiosity inasmuch as it joins other sites as collapsed before the Pizarros Hermanos (the Supplement is adamant upon this). Rogaguado, as it happens, did not collapse with the rest.

I wonder if the fall of Tihuanaco at Titicaca had knock-on effects along the transAndes. Was there tuberculosis? Did the Cotoca survivors shift north to Rogaguado, for trade with the Inca?

More reason for supercritical-coolant reactors

If you use water for your coolant, you need to put the water back where you got it. France is learning that too much hot water in the river invites les inspecteurs. [h/t hbdchick]

Of course out here in the Mountain West, we REALLY don't have the extra water to play with.

Éire might consider nuclear-plants to help supply the Brezhoneg, but - as usual with wypipo - the Irish prefer to purchase virtue from someone else.

CO₂? Non? Ket?

Outside the bubble

Zimmerman relates from Berardelli this hadith, from February.

We (currently) inhabit an interstellar bubble, carved out by some supernova or other, which we moved into. This tenuous space-atmosphere is rendered even more tenuous by our own Sun's heat. Outside the heliosphere is "interstellar space" - although our Sun still owns a gravitational Hill Sphere, until and unless Scholz HD 7977. Hence, irradiated Eris. We know "interstellar space" because the Voyager probes now sail past Eris, although the first of said probes is acting weird now.

Merav Opher and Abraham Loeb consider, what would our heliosphere look like if/when we were NOT in a bubble. They calculate that, at worst, the heliosphere might not even reach 1 AU. In which case, Earth is fully exposed to cosmic radiation. On the plus side maybe our inheritors can make Bussard work again . . .

I counter that Earth's surface is never exposed as long as the magnet is working. I find difficult to believe that any record on Earth records interstellar events, excepting maybe an extreme Carrington, to be sought in geologic time and not in archaeology.

This is, however, a concern for our future, should our sats stop working.

The roots of Balkan failure

Bogdan G. Popescu and Mircea Popa, Romanian I think, have taken a shufty at the Ottoman legacy in the Balkans today. A correlation is derived between Ottoman-rule and modern dysfunction. Popescu and Popa blame the banning of the printing-press.

Such antiOttoman sentiments explain the EU's reluctance against Erdogan's sultanate today. I am, however, unsure whether the press-ban was a cause ... or a symptom, of an underlying problem. I did not enjoy Graham Fuller's book. But even "Islam!" might not be the underlying problem.

Duggan noted, because as an historical-fiction author he had to note, that the Macedonian system in the Balkans was not doing well for the Balkan people. Hence how the Normans, inheriting the Carolingian system, so easily enlisted the locals into their own rule. The Seljuqs, not even Christian and in fact adherent to the Christian Greeks' historical anti-ideology, also were able to acquire the locals' support against Byzantium.

The Comnenids, especially John, did see how narrow was their escape from the Seljuqs. Over Anatolia they attempted reform. But local interests persisted, who did not desire reform. When the Ottomans inherited the Byzantine Empire, they inherited the Byzantine lords - or at least the lordships.

Gas core NTP

ToughSF has pointed to a couple of gas-core NERVA ideas. One is from Terry Kammash in June 1993 (pdf); arguing for a denser core to lessen the Kelvin-Heimholtz instability. He chooses Americium-242 of the metastable isomer. Another article from Albert Kascak 2012 posts an upper constraint on specific-impulse. This, based on ye olde thermodynamics on the cavity-wall and nozzle. Uranium-235 is assumed but I suspect not required.

Where has Kammash found his Americium-242m: from Plutonium-241. This (he says) is a wasteproduct of pressurised-water reactors. I don't know if we still want those, or supercritical CO₂, but hey; the nuclear fuel will be the same. From a 1993 perspective that fuel is uranium. I don't know what isotope of uranium; it may be U-235, which worries me, since we don't have a lot of that and we're not making more. U-238 (breeding to Pu-239) is more promising. As bonus, at a higher atomic number, it should produce Pu-241 faster.

Problem here is that here we're proliferating nucleides, which we normally don't like. My suggestion is to build this breeder-reactor where the space programme resides; hook it up to all those coilguns and SpinLaunch slings, so the wider electric grid doesn't have to.

There's also the law. I don't know if Am-242m gets to weapons-grade as easily as U-235; UltraSafe has been diluting their uranium to "LEU" (such that it's not gas). The law limits I_SP more than do the thermodynamics, around Earth.

UPDATE 3/24/23: Gerrit Bruhaug discusses thermal reactors.

Mars' Colorado

Elon Musk likes to warn people that most people who go to Mars won't be coming back. Robert Zubrin for his part has warned that radiation be one risk for colonists - which he probably got from Total Recall. Tonight we'll nuance this.

Robotbeat compares Mars with, er, South Dakota-Minnesota. For our part in Colorado, especially in summer, we spend some of our time in cooler basements and the rest of our time in cooler mountains. Our basements have radon. Even with mitigation Robotbeat considers 10 mSv per summer ingested right into the lungs. And then there's sunburn. On Mars a basin (like Hellas) or that vast northern depression might be getting 100 mSv per year. I'm assuming this is an Earth year to be amortised over Mars' longer cycle and eccentricity.

This is not to ignore Martian radiation. On a Martian-globe scale, the radiation is a menace to terraforming. Various schemes exist to block it longterm. I have mine own notions, involving an orbital magnet. But none of that's any concern to Musk.

I was careful to say the basin would be getting those mSv's. The Martians down there won't. They will be burying their habs under rock (we'll get to muh lava-tubes), just to keep from, er, exploding in the light atmosphere. [UPDATE 5/27: - so let's don't panic.] When Martians do drive around the surface they'll be under space-suits at least. Mars' basins, further, do not have much uranium as compared to the basalt-heavy volcanoes. This takes their own radon out of the equation.

The lava-tubes, being from lava, will be more basaltic. These tubes will serve the copper-mines. Here I'd be more concerned with rads... mostly from, sigh, radon. Total Recall wins again.

Everything I just said applies also to Ganymede: 50-80 mSv/day, but surface in nonradioactive ice. (Callisto is fine.) Gany's colonies might not need that protective magnet after all. Longterm, I dunno.

The oxidiser's proportions

From these calculations: the ramjet is to burn 76 kg hydrogen and 608 kg oxygen per kilometer of (2m-radius) tunnel. Andrzej Nowicki's Ice Gun Page has this: If the ramjet flies in pure hydrogen, about 80% of [jet] mass is oxygen. If the ramjet flies in the mixture of hydrogen and oxygen, less than 60% of its mass is oxygen.

If in unmixed H₂, NASA's 100 "minimum" tonnes of ramjet has 20 tonnes of cargo-chassis Dry Mass and 80 tonnes of oxygen; or we can have 100 tonnes+400 O₂. NASA offered the 1000 km tunnel which takes 250 seconds, and the 100 km 10 G skullcrusher which takes 45.45 s. Note the former requires 608 total tonnes of oxygen; the latter, 60.8. So either the 1000 km is for an order of magnitude more cargo, or else it must include oxygen in the 2 bar hydrogen barrel.

Chemically the ambience can be 30.4 H₂ : 6.08 O₂ by mass. "Oxyhydrogen" at this 2 bar pressure might burn; but, as I look into flame-speeds, this burn runs 3 m/s, which our craft is already outrunning the moment it becomes a ramjet, at 1 km/s. So why are we still talking about lugging 50-something percent of oxygen and its tank up the barrel? It's not the barrel that we're risking, it's the cargo!

The real reason we don't dilute our H₂ is, I think, that it increases the mass of the (forward) gas to lower our Mach. Ramjets, it seems, like Mach Four and Stagnation Temperature gets bad at Eight. If the barrel have too much non-hydrogen its ramjet doesn't ever hit 8 km/s but runs more like a ramjet in 30 Ar+N₂ : 7.5 O₂; that is, like a ramjet over standard atmo.

This makes me wonder if the 100 km option going to 4.4 km/s could, in fact, push their barrel gas-ratio. Mind, this particular ramjet is likely carrying the same oxygen anyway, plus something with hydrogen, to get into orbit; since 4.4 km/s ain't doing that on its own.

Copper on Mars

On 9 May we got a report from Confederation Helvèce on how to find porphyry on Earth. Massimo Chiaradia says the copper-heavy deposits are from "failed eruptions".

Porphyry is, then, of the volcanic specie of ore-deposit. They are deposited when a magma-chamber fills with mineral-rich water and then just... fizzles. 1-6 km beneath the surface.

It strikes me that Mars is a planet of dead volcanoes and will likely include failed eruptions, as well. We've been talking up the lava-tubes for some time on this blog. I should be very surprised if the tubular Martians cannot get at its copper.

Of course I am not saying that Earthers can get at its copper. I think hacking the metal out of asteroids will be more economical for us and for the Belt (and for Venus).

How not to run in exile

At risk of James Blish accusing me of jumping into the duck-pond, I got a Problematic on the exile-fleet trope. Namely: do they need to be going from system-to-system looking for Earthlike planets?

That first planet has some REALLY weird fauna on it, but never mind all that. Why are they even looking at the planet? The overcrowded colony ship doesn't need a whole planet. At present it needs water (mainly), agricultural resources (phosphor, nitrogen, organics), and living-space. That means asteroids fit for hollowing into O'Neills, for anyone who'd stay there. A shipyard, and more ships. If anyone is entirely unwelcome in this star-system, they can take one of those ships and THEN strike out for the next place.

Battlestar Galactica is a special case here - in 2003ish anyway - because they had a democracy (of sorts) alongside the fleet. More to the point they were fleeing a (lost) Butlerian Jihad - no stealth in space! So when Tundra Planet In Nebula showed up, they took it. Similar may be said for Homeworld where, in fact, the mothership DOES try to mine resources.

A few generations settling the planetoids as BELTALOWDA, and building more [seed]ships, seems the smarter play than settling someone else's planet. Excuse me if that seems oddly leftwing to my readers.

e Velorum

I stumbled across James Blish's ... And All the Stars a Stage at a used-book discount. 'Tis oft-excerpted at Atomic Rockets so I thought it might be good. Strange at Ecbatan has a full review to which I won't much refer, since I haven't finished the book. UPDATE 5/22 PM - this gun has been un-jumped. No, the book doesn't get better.

Best I can tell the book is a revision of a series which Blish wrote in the late 1950s; in 1960 he got what he had done, published, in two parts. Rich Horton tells me that Blish had lung cancer (and probably other ailments) in 1970 when this revision came out. The book is an interstellar Aeneid, precursor to Battlestar Galactica and to Kanata no Astra. Probably a direct inspiration to the latter.

Blish sets the stakes by setting his start NOT at Earth. Arthur C Clarke might be hack enough to do Songs From Distant Earth; our man Blish knows our own Sun isn't about to explode, and neither is any star near it. At least... he knew by 1970 and, possibly, by 1958. So his Sun is a white giant toward the end of his life, when it is burning titanium.

Blish leaves us guessing at first, sadly not well. I scented intertextual strain (but perhaps not where I should have been sniffing). The earth here has a single Moon which serves as Luna, and an innermost planet which isn't named but feels Mercurial. It all smelt like Asimov's Currents of Space before that one had to disavow his own story.

As revised, the story can rewrite the history of the industrial-revolution. A nova at the right place and the right time, which didn't happen at Earth, taught humanity about the Periodic Table and much other chemistry and physics, over the past "three hundred years". We are given to understand that a "year" in this yarn is like an Earth year. Because in the first revisions it was an Earth year.

Pity that Blish didn't know any physics. I mean, besides the obvious - that he's got hyperlight travel. Greedy bastard couldn't even conceive a warp bubble device, which keeps the crew young whilst the outside universe gets older. But we'll move on.

The habitable-zone of a white giant is large, as Blish knows, since he pegs in a couple other near-Earths. (They stand, I suspected and now know was supposed to be red-herring, at least for Mars in the original draught and a terraforming Venus also.) As to the star we're supposed to be thinking of the Crab Nebula; but to give Blish some rope, I picked one of the smaller "A" class biggies off of Wiki: HD 73634 aka e Velorum, 7.8 M_☉. Luminosity is 4140 L_☉; 7977 K. By this calculator the (dying) planet should run in 55 Earth AU semimajor.

I must point out, again, that "A" stars of this high mass do not last a thousand My as Blish assumes. HD 73634 is all of 40 My already. Stars in this range should expect 200 My. Blish knew, sort-of, this much already also. But he needed advanced life on his planet so could not allow this short of time for his civilisation.

Now let's bring Kepler in here. For "A" supergiants in our units GM/μ > 7.8 = 4π²a³/T². a = 55. So, 0.1975 = 55³/T². T=√842,080 = 917 of OUR years. (Compare our own Eris, 67.86 AU and 559 years.) Luckily for Blish he has his red-herring moon so his "year" can be lunar - although, he might be alternatively be using the variable-star cycles of his Sun, George Martin style. He does have a religion of "The Ghost" which might, like our own dear Church, know its way around a solar-cycle.

I think the story can only work if its humans are settlers here from a former Empire. Same can be said for Nightfall of course.

Horton directs us to Disclave #80 (1972) republished Vector June 1984, the piece about ducks. Blish, we learn, disavowed THIS book.

A small amount of oxygen

Andrzej Nowicki's Ice Gun Page doesn't tell us much about ramjet aerophysics. I must make do with this: Combustion of 1 ton of oxygen is sufficient to heat up 5 tons of hydrogen to 2000 K.

I'll bring in some other maths: 2 bar of gas in a 4π-meter tube: 3.04 tonnes of hydrogen per kilometer (or 3.04 kg/m). 3.04 tonnes per second, to rise as the speed rises; consuming 608 kg/km of oxygen, partly from the ramjet's tank and maybe from the ambience also. We'll talk about the ambience later.

At 32 (molecular) g/mol that consumes 19 kmol/km of oxygen gas into water - once added to 38 kmol of hydrogen gas. 76 kg/km of ambient hydrogen gas is consumed. 684 kg/km of 2000 K steam is expelled within the remainder 2964 kg/km of hydrogen.

This tube at 1800 δK against 200 K ice will do - something, to that ice. A pressure-cooker effect will be at play around 200 δK, I think. I don't really care, honestly; I just know our ice cave is at risk of distortion and needing remaking after our run. His nod to thermodynamics is to reinforce the back breech of the ice with steel, and the rest of it with - er - The New York Times. This just passes the distortion past the "Society" page.

The tunnel should have steam-vents every 10 km or so to the surface. There's no real value in recovering hydrogen but I'll suggest burning it, just to keep most of it to cover our barrel under ice.

The railgun equation

One megastructure idea which need not be polar is Erk Inger, "Mass Driver Design Traveling Earth to the Moon" (2019). That is, the railgun. If it "only" gets to 1 km/s this blog has been pondering this as an assist into the Ice Gun.

What we need is an equation as relates current to force. Unfortunately Inger's paper is chaotic. I do see a factor he names "inductance". Doesn't help that the diagram includes stuff in German (or Turkish) and includes variables like h which don't appear in the text. AT LEAST STEAL STUFF WE CAN UNDERSTAND

Further afield Ehresmann, Herdrich, and Laufer delivered "Low-Cost Prototype Development of a Lunar Massdriver" at a conference the prior October. Their equation (4) much resembles Inger's (3). Problem here? Ehresmann, Herdrich, and Laufer weren't building a coilgun! They're building something on horizontal rails. So they don't care.

It's also not the first space-enthusiast prototype. The O'Neillies at NSS have been at this since the late 1970s. I take it that the military has the best stuff and they just care about firing bullets.

For what it is worth, EHL's main equation is F=L' I²/2. They call L' "reluctance" and run with that. Best efficiency means raising L'I, that they get the most force for the least current(squared).

L' would (if EHL cared) equal μ₀/π ln[w/r - 1]. EHL point out that w cannot equal r or else they'll get singularity. I'll add w > r or else we're all getting Euler'd up (πi = ln[-1]). Also if w = 2r wouldn't L'I be, um, zero? Raising w to infinity might get the best results but then... is that one single "coil" extending the entire route? Then there's w between r and 2r which runs backward (negative F).

I'm thinking we need better papers. Barry's site seems good.

Ceres is not an asteroid

... well, okay; "asteroid" translating to "starlike" was always a crap name, for any of our rocks and snowballs which ain't Jupiter. But to the degree we define this term as "planetesimal between Mars and Jupiter", Ceres ain't that, neither.

To the extent the Asteroid Belt is made of planetesimals which Jupiter and the inner-planets prevented from coalescing; Ceres is an interloper. It is not even Jovian.

Lately I had been pondering the ice on Ganymede and Callisto. Theirs is a singular ice: water. When you go to Saturn, those moons also have ammonia - hydrocarbons, on Titan. Out 30 AU Triton and Pluto have nitrogen ice. Ceres is heavily ammoniac.

São Paulo propose that Ceres is a Saturnine body that has entered into a subJovian orbit.

Ashkenaz snapshot

h/t Razib, here is Shamam Waldman et al. doi 10.1101/2022.05.13.491805: "Genome-wide data from medieval German Jews show that the Ashkenazi founder event pre-dated the 14th century".

Currently all I can read is the abstract, but we seem to have - here - coverage of Jews in the Galician region as point to ancestors to those Jews. Thirty-three of them, in Erfurt blackdeath-era.

They were already bottlenecked so were already not mingling with Gentiles if they could help it; although they did hold a few introgressions from northern Europe as do not survive to our race today. To be kept in mind: these are Galicians, who like their gefilte sweet. I am a spicy Litwak, complete with M33 from the Burma highland.

They even share some (eight) of the mutations as afflict our present race. I do not know if the M33 mitochondrion is amongst them however. (I suspect not.)

The value of experience

This blog has worried about Mars Dementia, at least space-dementia, for some time now. On 6 May we heard that experienced flyers don't suffer as much. Lately Zimmerman is saying the Russians don't suffer as much either.

We have the same biology. As Sumner nagged us.

It seems to me the Russians (and Soviets) are about the most-experienced micrograviters in history on account of Mir staying up so much longer than it had to.

Tastepeler

This blog (and an earlier blog) has noted Göbekli Tepe a few times despite not knowing anything about the site for its own sake. One poast here concerned the zodiac; the other pondered Sweatman. h/t hbdchick; here's Sean Thomas. Allow me to emerge from the antipodian ice long enough to devote a poast to the tenth-millennium BC Tastepeler generally. Yes that's a "millennium".

Basically it's what Professor Daniel Jackson from Stargate should have been referencing, instead of muh pyramids. I wonder nowadays if we might even revisit that Sphinx . . .

Göbekli is 13 km from Adme / Edessa / Callirhoë. It is now a tourist suburb thereof. Göbekli is not the only tepe anymore; Thomas is noting also Karahan. (Tastepeler is the plural - "stonehills".) And Sayburc is coming. In fact, this may be what Thomas has contributed to the archaeology.

For this people the "T Shaped Pillars" came to be important. These are a subset of a general theme of the local sculpture. It's a man, covering his... manhood, with his hands. Sometimes six-fingered hands. (Base-12 numerics?)

Thomas does not note what the locals made of the "Younger Dryas" ice-age. Thomas says the culture founded Göbekli 10000 BC or before, and Karahan 11000 BC. The Göbeklites sabotaged their own site 8000 BC. YD started 10900 BC and lasted a millennium.

The Tastepeler did have locals. As of the mid 2000s AD (we only knew the place 1994!) only the temples were excavated; now, we know that people settled at least some of the sites. Again, I do not know if these people settled the sites first (with huts?), or set up their (archaeologist-visible) homes later - but, by the 8000s BC, they were growing (emmer) wheat and brewing "alcohol" probably nearbeer like the Mesoamericans.

Mach One in 2 bar hydrogen

A few days ago I asked what was Mach One - the speed of sound - in cold 2 bar hydrogen gas. I found an "ideal" equation √[γRT/M] where γ = heat capacity which for H2 is 1.41, R is the ideal gas constant, T is the temperature in Kelvin, and M is H₂'s molecular mass. I didn't trust we'd be ideal. Lately I figured - waaaait a minute, somebody's probably done this for us already. So: AH Hodge, "An Experimental Determination of Ultrasonic Velocity in Several Gases at Pressures Between One and One Hundred Atmospheres", The Journal of Chemical Physics 5.12 (1937), 9747. doi:10.1063/1.1749973.

At 273.15 K, Hodge sketches a linear graph going up 8.5 "m/sec" for every 10 bar of pressure added. 1199.5 m/s at 1 bar, 1207.2 at 10 bar, 1215.7 at 20 bar (it looks less linear around 100 bar but whatevs). So 2 bar should be 1200.35 m/s. At 1 bar √[γRT/M] collapses to 72.577√T; at 2 bar, 72.629√T.

Not much difference; 72.6√T will do for the extent of the gunbarrel. As for T, Antarctica especially under ice in darkness would track T = 200 K. Speed of sound will be 1026.7 m/s. Assuming it's not diluted with oxygen which would make it more like air.

Why magnets

One idea to get to ramjet speeds might be to let gravity do the work.

First of all I get it: we wanted to accelerate at 32 m/s² or even 96.8. Let's say we have dug out a little railway before the main tunnel. The main problem for Antarctica: it's not a vacuum-tube. Terminal-velocity applies.

This is root[2mg / ρAC]. A Dragon is A=4π. g=9.81 m/s² down but we'll have this on an angle, so multiply that by cos or sin something. ρ=1.766 kg/m³ at 200K. C, the drag-coëff, is low for a ramjet say 0.1. So root[27.77 m cosφ / π]. (PS. Chromium doesn't do MathML.)

NASA's minimum mass was 100000 kg because why not. Let's just slide the thing down 45° so, "cos or sin something" is 1/√2. √625148 = 790 m/s.

We can tweak this or that: pile on more mass, tilt the ramp more downward, do something about the drag. The tweak which would help the most would be to lower ρ - to suck out more air beforehand. Um. Microwave the ice, let it re-freeze? Collapse and repeat for next time?

With the railgun it's simpler. The Mach number is a bit lower at Antarctic 200 K, but not so much lower; 1 km/s should be Mach 3, within Naval parameters (before they killed the project).

Next Question: whether it cost more to suck out the air (which up here isn't being replaced) or to run that railgun open to the surface. Keeping in mind a sight more tunneling is required, toward 1 km/s, if the acceleration thereto be 6.94 m/s² (on that 45°) versus 32 m/s².

Whence the hydrogen?

Now comes time to supply NASA's ice gun's barrel with 2 bar of hydrogen. Yes yes, we're probably diluting it. Hydrogen is the cost-centre here so we're pessimistically assuming the worst.

The first stretch of distance will be a rail to 1 km/s. For reasons we "will" get to on the "Saturday" post we're on a railgun. This means acceleration for the 1000 km plan: 32 m/s². However much power the rail needs I assume it can handle the journey to the hydrogen chamber without superconductors or vacuum or anything else this expensive. So we'll knock that off the total.

Follow the usual equations. First, we need the time on the rail: 32t = 1000 m/s, 31.25 seconds. Over that time 15.625 km would be crossed. The hydrogen tube would have the rest: 984.375 km.

If the brain-smushing 100 km option is used, 96.8 m/s² would take only 10.33 s on the rail for 5.165 km. So 95 km of hydrogen.

As to how NASA push out a real atmosphere to replace it with another one; I assume a moving membrane like in a syringe. It helps that the new atmosphere is twice the pressure. The membrane will need to be knocked out of the way either at the start ("the breech") or at the end ("the muzzle").

The cargo is supposed to be humanoid but, this must be balanced against the need to clear Earth atmo. Propose the payload is a SpaceX Dragon. That is radius 2 meters. So 2² x 95000 x π volume = 1,193,805 cubic meters. Given hydrogen density at 200 K 0.141 that - 2 bar - would be 288.9 tonnes. It'll be a bit less because NASA wanted to mix it with oxygen.

As for oxygen, the ramjet carries more of this in its own tank. NASA hoped for less than 60% wet mass; this depends on how far you want to push final velocity - somewhat (if too low, we're carrying our own propellant anyway). Even 80% worst-case compares VERY favourably against the usual Tsiolkovsky (that jerk) requirements.

The main cost as noted is hydrogen, which does not simply exist in our air. Normally 200something tonnes of H₂ (and O₂) would not be overly expensive but, this is Antarctica. NASA wanted the gas produced in-situ using regular wind-power, such as generated by katabasis at the Dry Valleys. NASA in the 1990s implied direct electrolysis for "Green" hydrogen (and oxygen). If an organic gas trap is found near one end or the other of the tube, they can likely be talked into "Turquoise" pyrolysis, whose energy-needs are less; oxygen would then just be condensed from the air by the usual ways.

BACKDATE 5/15

Ramjet in ice

Second installment, on ice gun physics. Looking here for how to get this thing from zero to 8 km/s.

In fact it does not go from zero. Here is the claim: At launch the ramjet is placed behind the breech of the gun. When the breech valve is opened, hydrogen flows through the ramjet at about 1 km/s; fast enough to generate thrust. At face value, something is blowing a 1 km/s gale through the pipe. Of mostly hydrogen. In mph: 2237.

And what's Mach-One in 200K 2bar H₂? NASA were mixing it with oxygen, such as to put it less in the km/s range and more in the hectometer/second range. There is already going to be a sonic-boom on this thing.

No, man. The windtunnel's not happenin'.

What's happenin' - possibly - is the ramjet running into the hydrogen at (supersonic) 1 km/s. Maybe there's a jetpack behind it. Maybe (my preference) it's accelerating into the gas by some other means. Partly by gravity perhaps; magnetic rail seems more-helpful. Since I think we aren't letting the ramjet touch the sides.

Another factor is the pressure of the gas. Best I can tell, they want pressure as to spark the ramjet process and to kick it from 1 km/s. Then, 4.4 km/s (if on the 100 km plan). Then maybe to 8 m/s and LIFTOFF. NASA thought they could pop the cork at the "muzzle" end to have the H₂ pressure at the last stretch be lower.

So: railgun to 1 km/s. Put up a brittle barrier (or a door with hinges) behind which is 2 bar of hydrogen - smash that barrier. Spark the ramjet. As it gets to 4.4 km/s, let the hydrogen attenuate (as it will naturally do, as the hydrogen leaves out the back).

I don't even know that 8 km/s is the limit in this scheme; but, if we only have 3.4 G and 1000 km to play with, that's probably about as good as we'll get on Earth.

Math check on the ice gun

Still on the ice gun, I'm considering the thrust and time-of-acceleration.

The chassis is a ramjet. Those travel between a minimum and a maximum velocity dependent upon airflow. NASA Ames promised final velocity - at the direction of the barrel - 8 km/s. The ice gun will be launching at an angle (New Guinea promises some mountains steep enough and uninhabited) to break atmo.

8 km/s even vertical won't beat escape velocity at 11.2 km/s. Per Erk Inger, "Mass Driver Design Traveling Earth to the Moon" (2019): it doesn't have to; 8 km/s can defeat atmospheric drag to enter a 185 km orbit. At least, energy-wise it can; once the craft is there, something must push this into LEO. NASA recommended carrying some sort of gyro, and using that in space.

As to thrust, NASA thought they could accelerate their jet over 1000 km. From zero to cover that with a steady acceleration this is GCSE Physics (or tenth-grade calculus), a t² / 2 = 1000. As to that acceleration this is 8/t. So 8 t / 2 = 1000; t=250 s. a is then 8000 m/s / 250 = 32 m/s² tangent. By Pythagoras the passengers will feel 33.5 m/s² which is 3.4 G. G-LOC doesn't hit 'til 5.4 G so, most of us can withstand it.

[I'm leaving aside, for this poast's sake, what "zero" means for ramjets.]

Pity 1000 km ain't gonna happen. Their 100 km alternative settled for 4.4 km/s. 4.4 t / 2 = 100 means 45.45 s, 96.8 m/s² so 97.3 m/s² which is, yes, approaching 10 G. Also this is a literal toss-up: it will need assistance to orbit-speed.

In theory the maths check out. It's just that 200 km is pushing the limit of what we can do with Antarctic ice, 4.4 km/s pushes the limit of a useful earth-to-orbit trajectory, and 5.4 G pushes the limit of human endurance.

BACKDATE 5/14

Thwaitamageddon

The diploma-mill o'er the ridge warned last January about thath Thwaiteth Thweath. Looking around the 'web, Thwaites seems to get warned about every January. Around the antipole, "January" corresponds to "July". As Antarctica approaches the long night we hear rather less about the Rapidly Melting Glaciers.

I got interested because I was pondering natural caverns under ice, how stable they might be. A few years ago a topography of Antarctica's land was pinged; the fabled Ross Ice Shelf, thereby, got ruled not a problem. Attention then shifted to Thwaites.

Thwaites has come up as host to an under-Manhattan like in Futurama. Or maybe it's double the size. Or two-thirds. Either way, Manhattan's sixty square kilometers of land plus thirty of water(?) is the standard.

This cavern, then, seems not stable.

Timing is everything

Two articles are now out concerning time-synchronisation from cosmic events. Last week Illinois proposed using pulsars and today Tokyo wants cosmic rays.

A cosmic event is an instantaneous event visible over many sites, which do not require a human to ping them. They are best for deep space, underwater, wherever else are blindspots.

Only the pulsar-method will work in deep space. Cosmic rays work in (thick) atmospheres when they scatter into mu-leptons and the like; mind, if underwater, one might not be seeing pulsars, for their part.

Constraints on the ice gun

It occurs to me that, for the Ice Gun, I could use this little trick I know called "maths". Namely: how long can the barrel go?

Earth is an ellipsoid whose radius at the poles is 6356 km. The initial proposal for the gunbarrel there was 1000 km; straight at first but pointing diagonal-upward at the end. The first half is the straight half, so about the middle would be the deepest point.

These people could not literally mean that it's straight, much less concave against the Earth. Its least distance from the core is Pythagorean: square root of (6356² - 250000). That's 6336 km: in depth from the top a nice even twenty kilometers. Nowhere in Antarctica is the ice-sheet 20 km thick. It's a continent, so we are probably not hitting asthenosphere; but we are deeper into bedrock than the Mponeng. By a factor of five.

I concede: a straight line has some advantage in starting acceleration, inasmuch as it's using the Earth's pull to help out. We want something more like root [6356² - 6355²] especially if we are worried about the sheet melting to less than a kilometer. 112.74 km straight to the middle of the barrel and deepest under ice, which (for simplicity) we double for the total: 225 km.

The authors of that page perhaps should have started with that. Better: they should have ended with that; nobody wants 10 G, given that classical G-LOC starts 5.4 G.

For the 1000 km option I must assume that by "straight" they mean in the Mercator sense. This barrel will be skating the circumference, fighting gravity all the way. Anyway it's never going to happen, so whatever.

The end of crypto

Cryptography entails making a message secret; blockchain entails making it (perhaps paradoxically) so public it cannot easily be deleted. Crypto-currency is one result of the marriage between the two.

Currently crypto-currency is enjoying much favour on account it might even be superior to government-backed scrip, on account it cannot (easily) inflate. You own a prime number, best I can tell. It's difficult to print more of these. Like it's difficult to print more physical gold. It is also difficult to hack (although the people running the exchanges sometimes figure out ways).

Suppose someone owns a quantum computer tho'? Roger Grimes published a warning a year and a half back, Cryptography Apocalypse. He explains quantum-mechanics, best he can (almost as best ANYONE can); then lines up what, in theory, a quantum computer can do; why these computers are difficult to build (error is a thing, they need supercooling, etc); and how long it might take for them to catch up with standard crypto algorithms.

It's a Y2k-level crisis which needs preparation-for, he concludes. Y2k was a nothingburger but that was only because we (I was there) did prepare for it. Quantum computing will crash all crypto-currencies as are not, themselves, quantum.

On that day I can see national governments basically being the only form of cash-exchange, as being the only entities with the clout to own a quantum computer. By "national" I mean they'll pretty much be the only governments to maintain their sovereignty, any other declared-independent nation being no nation at all.

So, if you own some poocoin you bought from an ad on 4chan, you might want to do some homework on how well it will stand up to what's coming.

The fall of the Imperium Rattorum

Last week the university of Eboracum explained the Rattus rattus conquest of Europe. And then its reconquest.

Rattus rattus isn't quite the feature he used to be, but that is less because our sanitation and ratcatching has improved so much as that Rattus norvegicus has displaced him.

We learn there were two heydeys of the former rodent. First was the Roman expansion along with, we may assume, the secondary-states such as held along the limes in Germany (especially). Then this population crashed, later enjoying a Renovatio. Unlike the Carolingians, never really a resurgence of the Roman people as such; this new generation of squeaker (still R-R) actually did travel from a founding Mediterranean population. Trade had recovered in the Middle Ages; as had population, and population-density.

A vindication of Heather and Ward-Perkins, to the extent we still wanted one.

Surgery is bad for you

Anyone considering surgery, especially elective surgery as might require anaesthesia, should probably read this.

Anaesthesia is an unnatural whack to the brain from inside. Not only that but surgery itself means getting stabbed, usually where it hurts. If you are in your 20s all this is likely bearable. The bad news hits in elder age; they are saying that it might be a trigger for autoimmune troubles in the nervous-system. Younger people call this "multiple sclerosis" but the article suggests this might result in Parkinson's and worse for the elderly.

Also reckoned in this article are the very young. Given that vaccines are, by definition, triggers to the immune system, one should be very cautious as to which vaccines are delivered, to whom, and when. Although to be considered is that the disease itself, if caught without a vaccine, will trigger its own immune response.

Overall it appears that, where possible, the patient should be sedated without full knockdown.

Will Barrie's PhD

If Will Barrie's work holds up, which it should, we should start calling him "Doctor" sometime oh, maybe 8:01 AM Monday morning. The full preprint is arxiv'ed and Razib has highlights.

Here are 317 new ancient genomes from the Mesolithic/Neolithic, allowing us to study the major transition from hunter-gathering to farming in Europe. Remember Mal'ta Boy and how he showed direct ancestry which, formerly, was only surmised through cross-reference between ancient Siberians, Indo-Europeans, and Native Americans? There are many, many Mal'tas in this collection.

I don't know that it's revolutionary inasmuch as the genetics / ancestry folks have been talking about these groups all through the 2010s or before; but it certainly constrains the outliers.

HOTOL

Thumblegudget talks HOTOL [h/t ToughSf]. This was a British proposal to get around the Smithsonian Problem.

The issue here is that although Superheavy and Starship exist (sort-of), they didn't exist in the 1980s. Multiple-stage rockets were expensive on account the early stages weren't retrieved. Proposals back then noted that Earth actually does allow for retrieval of the first stages if these stages are air(=oxygen)-breathing. Which we don't get over any other planet in this system.

But then they'd be: jet, ramjet, scramjet, orbit. Assemble everything from a comprehensive museum of aeronatics! Hence the Lightcraft, among others. Not only is this a recipe for error at any point in the process, but after each engine is done we don't need the engine. So you're bringing a lot of extra mass up there. Retrieve each piece now, or retrieve it all after the mission is over...

This isn't my field so all I've done here is summarise Thumblegudget, whose youtube I recommend.

Thumblegudget explains some core principles. He starts with the heat-engine on the classic thermodynamic cycle: suck, squeeze, bang, blow. After "blow", the classic solution reheats the high-pressure gas in the main-combustion chamber / "afterburner". There's an Expander Cycle which is more efficient, but those aren't good for thrust so tend to the second-stage (like the Starship).

HOTOL - says Thumblegudget - is a modification of the Expander Cycle, which can do high-thrust down below and high-efficiency up above. Only one engine needed. Overall efficiency suffers - but it's all much more efficient than carrying a second engine you only want half the time.

This was made possible by compressed liquid hydrogen at 15 K; the hydrogen that isn't burned (yet) can be used as a coolant in the earlier parts of the cycle. When the Brits asked, what about the water-vapour (with a U) in our air that will freeze up inside the machine; this project was, er, cancelled. Later researchers who carried on this design introduced antifreezes.

Regolith as catalyst

Last night I was reading a brief for lunar colonisation, although I didn't feel up for poasting on it. Today Yingfang Yao et al. have posted "Extraterrestrial photosynthesis by Chang’E-5 lunar soil", doi 10.1016/j.joule.2022.04.011; there's a writeup at ScienceDaily. They think they can use the regolith, which is titanium-oxide and iron-oxide dust, as a catalyst. It is not a very good catalyst but they further speculate it might be made better, by melting it. This would serve to scrub carbon off CO₂.

The energy for all this chemistry would be provided by solar-conversion. If it works better than nuclear on Mars it'll work that much better at 1 AU with no atmo.

PROVISO 8/22/23: The above assumes we're short on hydrogen so can't make acetates (which also produces oxygen). Hydrogen is admittedly scarce on Luna and on S-type asteroids; instead, their cargo can be shipped from Earth or, better, from hydrated NEAs.

Ensoulment

Okay, OKAY I'll bite. Roe v. Wade might no longer be with us. This would entail a victory for the Christian Church up to the 19th century (in the West). Then, the Catholic communion must revive that debate about ensoulment. It's not as early as you'd think!

In the European West - looking mainly at France - the early-modern consensus has been that ensoulment happens after the first trimester of pregnancy. The Vatican moved in the 19th century to its present position, based on a reading of the Hebrew Prophets, that G-d conceives life and its potential at the moment the DNA combines. Protestant Europe balked at this; so did laïciste France.

Roe v. Wade doesn't deal with the soul at all, instead focusing on spurious "privacy" so legitimising abortion up to near-infanticide. [PS. Winchell Chung's Twitter supports Charles Stross who - from afar - supports RvW; keep this in mind when considering to donate to the Atomic Rockets patreon. Or when considering to purchase Stross books, which I personally don't, because they're not good books. At least HalfSigma is honest about his eugenics.] But we're not here to debate RvW. RvW itself was outright nonsense and not worth the hassle.

On the basis of science the Vatican here was ahead of its time; which - this post concedes - hasn't always been the case. Here the science in question is information-theory: DNA is the person. Also memory, and the sum of accidents occurring upon the human body over time; but, ultimately, DNA is foremost.

Planetary menopause

On the hunt for Goldilocks (assuming nonvenerean), one more factor must be the planet's age, mass, and composition. This isn't so much the problem for the whiter suns, which burn out faster than the planet will; but it starts to hit home with the G class's planets. Like ours.

The issue is that without plate-tectonics, carbon stops entering the atmosphere and the planet gets cold. I'd worry about the dynamo keeping the rads out but that's just me [TOUGHSF 5/8: convection is 80% outer-core but still core]. Anyway they just care about the mantle, not [any part of] the core.

They bemoan that they cannot tell the composition of a planet's mantle. We actually... can, but only for the dead stars which we can spot chewing up those planets. Mostly hot white A class in life.

The study claims that Earth-mass planets should run out of radioactives in 2 billion years; the heavier Earthlikes more like 5-6. I must point out here that our planet is... fine. This may be because we have the core of a larger planet, having ejected our silicates up to our Moon.

The more-numerous K stars supposedly "goldilocks" include some fairly elderly systems, on that main-sequence for longer. Luckily there are more of them.

Sewage to fertiliser

I don't really want politics on this blog (especially this week) but I do want to address the Psaki comments about our fertiliser issue. Psaki points out we make fertiliser right here in the Denver area, so why not just treat this like we treat cow manure: ship it to some remote location, ferment it awhile, kill the germs and move it elsewhere.

Last February, Frank Carini saw all this coming and explained, why not. The sewage from cities isn't just Wholesome Farms (TM, Sysco) manure. It comes with whatever molecules come off the pipes, along with engine exhaust and various other schmutz from the cities. Also, humans take medications which cows don't: antidepressants, birth-control... fentanyl. Heavy metals make their presence known as well, somewhere.

This blog isn't here to complain but to propose solutions so: I see an analogy with coal waste. (Ironically, for Psaki.) How about treating all this nasty with similar treatments? It used to be that those treatments were worse than leaving the nasty alone but, that may no longer be the case.

Hibernation recap

Last week Roberto F. Nespolo, Carlos Mejias, and Francisco Bozinovic submitted doi 10.1098/rspb.2022.0456 on the logistics of hibernation. Last weekend this got applied to space travel.

Hibernation is a proven strategy to get through lean months by bears, groundhogs, and maybe Neanders and Triassic survivors. Much depends upon what "hibernation" means - we will get to this.

If we're going cheap-seats such that we're even considering the hibernation option then we're using the cheapest travel possible. The baseline is Hohmann-transfer, to deliver all the freight and all the wrapping, which then stays at the (solar) orbit until the next "window" opens for return (to 1 AU). Certain cycler-orbits be cheaper for the investors and insurers back home, who want their metal back not trusting the passengers to return it. Such orbits get to the destination faster, at cost of carrying a detachable shuttle with its own tank of delta-V (fuel). Either way we are talking many weeks of transit, even to Venus (SVL2?) and Mars (Deimos?); well within the hibernation-range.

We have not considered the effects of long microgravity. Some good news, at least short-term: tech to counteract that. Nespolo, Mejias, Bozinovic assume either that this tech is perfect or else the artifical ms^-2 is good-enough, like we're spinning two Starships around an axis.

NMB here say that humans "hibernate" more like bears than like dormice. That is: there's no point in chilling ourselves before the trip and thawing out at the end. We're better off simply going into torpor, maybe just sleeping and occasionally playing a video game. (h/t to, guess what, 4chan.) CLOTS 4/13/23: I'd forgotten the Thrombosis but, here's the bear-protein.

The NMB study assumed present-tech and affects how we travel inner-system. We do have to start somewhere and the study has value for that much. I agree that Event Horizon's backstory - wherein a big bulky ship that doesn't spin somehow gets human cargo to Neptune - can't happen. Not in this century.

I do think, though, that future tech might offer future hibernation options. This might not take many centuries.

The newly-discovered supervolcano

This morning everyone who follows accounts unapproved by Homeland Security's truth-patrol woke up to news of a supervolcano on the Antarctic circle. That is: if they (like me) hadn't been following those blogs over the weekend.

This is an analysis of an earthquake-swarm back in 2020 at the Orca Seamount. This is in the Bransfield Strait close to King George Island of the South Shetlands. I do not know if the Orca has been studied for any other supervolcanic activity as has Toba, Crater Lake, or Yellowstone. Still, as they say - first time for everything.

As to why the Right has got itself involved, they're downplaying the Global Warming... as I do. Although honestly I don't care to play this game anymore. I'm more concerned with how bad it might get if this monster wakes up.

I suspect: not all that bad. The Antarctic Circle is sequestered from the rest of the planet by strong winds around a vortex. Some dust might escape north to shield, oh, Chubut Province in Argentina or maybe even Tasmania. Not really our problem up here tho'.

Perhaps if the snow-line is a bit further north, this would cause more precipitation around Antarctica and increase its ice-sheets. Sea levels set to ... lower, worldwide. Until a few years later when the Ross icebergs calve, and (suddenly?) raise them again. Although the new snow on Antarctica proper will likely stay there.

Good news for that ice gun, I guess.

The new Brittany

Cornwall and Wales are proposing their second joint colonisation effort: low-Earth space. The proposal is to build factories up there. In microgravity and no oxygen contamination, much work can be done cheaper than down here.

The reason nobody thought of doing this before is that, er, first you have to get all this material up there, and then gently glide the finished product down to where you want it. This was not possible before the Falcon 9 era.

Of course doing dangerous chemistry in space by robots is also a lot "greener" than doing it down here next to winds and rivers. I submit this consideration to all our Walter Pecks whilst they're bogging the Starship. Or at least for American voters to consider.

Some people care about the "carbon footprint". Chemical launches burn carbon. This might be cancelled by the carbon footprint of forcing vacuum-conditions upon factory production on Earth. I'd not even be surprised if the orbital factories can just ship the product to the continent which submitted the request, cutting down on all that cargo-freight.

Navigating Alpha Centauri

Alpha Centauri consists of a binary of two stars, orbited by the red dwarf Proxima. A few days ago Centauri Dreams considered the sail methods of getting (milli-)probes from one sort of star to the next. Per Greg Matloff, the "Solar Sail" - which uses photons - is for hot stars, G+ like our Sun or, for that matter, the main Kentaurân. Proxima doesn't deliver enough light - unless you're in one of its flares, and good luck predicting those. But such M stars do deliver atomic hydrogen, especially from in close. A magnetic sail will work for these.

Where I think this will really shine (as it were) is where the stars are up close to one another. Say Proxima's planet has colonists on its orbital-ring. With modest delta-V the colonists unfurl their sail and zoom off to wherever else around Centauri they need to be. Might "only" take one of Earth's years. When comes time to decelerate they fold up (or jettison) the magnetic sail and use the solar sail.

I doubt the Centauri system has any starfaring life. But systems like Centauri are common. Consider a G star binaried with a red dwarf out, oh, 10000 AU. I can easily see its inhabitants conceiving a multiyear project to "New-Horizons" that dwarf. Currently we don't do this at Earth because our closest system is, exactly, Centauri whither our best "starshot" would take over a generation. But if it just took a decade? No-brainer, for them; we just did it for Pluto.

The ice gun

Courtesy ToughSF on this 31st day of April is presented here, the Ice Gun, claimed by Andrew Nowicki. In all its 1997 university \public_html glory. Boy I wish I still had my sbcglobal directory... but anyway.

This is what they call a Megastructure and how. 1000 km through an ice sheet, to lift cargo into LEO without the Vernean 100 m/s² from SpinLaunch and others like that. More like those bridges and loops.

On Earth, our only permanent icesheet of this size is the Antarctic one. Also it is worried that Antarctica won't always have its sheet, although there I call shenanigans; even if you believe CO₂ is a problem - I don't - it seems mainly a problem for the northern hemisphere. The extra water raised there will fall on the south and make Antarctic (and southern Andean) ice thicker. Someone who cares, who isn't me, might see this as a factor in how come our seas haven't risen already.

More serious is that the ice cannot be bored just anywhere; only where it is stagnant i.e. not subject to glacial movement. Given the possible tunnels the poles impose some hefty constraints on when is good to fire cargo into the ecliptic, rather than orthogonal to the Solar System into nothing. And then there's the whole summer/winter thing to consider. Why not just blast Orion? Maybe the nuclear fuel is problematic to mine and/or import.

Also, stress in the ice contributing to gradual collapse of the tunnel. Also also Stagnation Temperature.

If Vernean G is accepted, the gun can be shorter, like "only" 100 km. [UPDATE 5/8: 225 km concave seems the sweet-spot.] Of course then you're competing with SpinLaunch leaving absolutely no point in this structure much less in Antarctica. Treat this as proof-of-concept.

I'd consider the ice-gun mainly for the icy asteroids and for Callisto. In lower gravity the glaciers should run slower and be less subject to collapse; although, still at risk from the heat of any exiting spacecraft.

This gun would be wonderful for Ganymede as an underground structure; that's where the first colony will be. For this Medici moon I'd build for escape-velocity / v_∞ as to make the trajectory intersect Callisto; I do not expect Ganymede to host a human-rated orbital station, nor for regular shipments inbound to Europa etc. Another complication (lengthening the barrel) is that long-term Ganymedeans will be, er, twinks. Not as resistant to the hard G as is a good Venerean.