I'm more struggling with the design of the vacuum chamber than all the other things (or at least as much, I guess). The model has a max distance of 15 m from the central axis to the edge, and if I'm not mistaken, they didn't run the big test at full vacuum, though I don't think they said what it was. The total force on the structure will scale with the square of the length, so at 45 m, it's 9x the force, while also having 3x the length in which there can be no internal supports--the max deflection in the middle is going to get saggy. Maybe they're going to put buttresses on the outside like a gothic cathedral? That could be feasible, right?
That's because you have some passing experience with vacuum and centrifuges. You can roll it around in your mouth. I, on the other hand, have some passing experience with materials science and this ...just breaks everything. Breaks it all to shit. The fundamental basis of this whole shitshow is A) a seatbelt capable of holding its own against at full thrust and B) a release mechanism capable of letting go of without setting off a supernova.
HOLLLLLLLLUPAMINNIT "So... that means... that the tether... at the tip... is going to need... to be able to support... one hundred THOUSAND metric tons. Or... one hundred MILLION kilograms. To put that in context, a FULLYloaded. FalconNine. Weighs about ZERO point five five... MILLION kilograms. So. This tether. Is going to need to support. The equivalent weight. Of one hundred and EIGHTY TWO falcon nines. Spinlaunch, payload to orbit: 200kg Falcon 9, payload to orbit: 22,800kg "One hundret. And EIGHTY TWO. FalconNines" payload to orbit: 4,150 METRIC TONS Now - energy is neither created nor destroyed, right? But first stage on a Falcon 9 is two minutes and change. This dumb thing takes like an hour to spin up. It seems to me that they're mostly using a lot of energy to create forces they'd really rather not deal with, and as a cherry on top they generate enough KE to push a Sputnik or two into LEO (with the help of a 20 metric ton rocket). How can you get to and "200kg payload" and not go "...where the fuck did all that energy go"
Also fukkit intermediate modulus carbon fiber is 800-1000 ksi. 1 psi is 6895 newtons per square meter. 1 ksi is 6,895,000 newtons per square meter. is 689 newtons per square cm. Is 155lb per square cm. Yield strength of mild steel is around 50 ksi, so a 1 square cm bar of mild steel is gonna yield at a little under 8,000 lbs. 1 square cm of aligned carbon fiber is gonna be able to pick up a fully-loaded M1A1 Abrams tank. You shouldn't tho. "One. Hundred MILLION kilograms" is 981 meganewtons. To support that, at yield, with carbon fiber is 0.2 square meters, or a round rod half a meter in diameter. Solid. No flaws. At yield. Where its elongation is 1.75% so your lawn dart is gonna be between 50 and 80cm closer to the inside of your can at the end of your process than at the beginning. I'm trained that carbon fiber actually kinda sucks more than you think from an engineering standpoint because you have to build it into a mat to do anything useful with it, and then you can't test it, but fuckin' hell the shit's tough in tension. It's just those places where it isn't in tension that you're in a world of hurt. Hmm. I got some carbon fiber printer filament. Maybe I should look into doing something with it.
The world of ice hockey the last 20 years has seen a dramatic shift from wood sticks to carbon fiber. Carbon fiber is superior in all but 2 ways. First, sticks used to cost $20-30. Now they cost $200-300. More importantly, whereas wood would splinter or crack, carbon fiber sticks are highly prone to catastrophic failure. They just explode sometimes. This happens because they get small nicks in them due to skates, pucks, ice, whatever. Then when you load the shit out of it, that tensile strength becomes tear strength and that’s a whole ‘nuther ball game. Obviously industrial applications will have different quality materials, but it’s still one more thing to fear.
When carbon fiber first hit the scene, Formula One built like every single part they could out of it. Then one of the Ferrari(?) cars bumped into someone else in like '91 and the thing shattered like a champagne flute, leaving the driver (and the motor, and the transmission, and the tires, and the fuel tank) bouncing around on the track like a craps hand. FIA decided that maybe the monocoque should be something that doesn't turn into kibble under force. I learned that the thing that keeps carbon fiber and aramid composites out of mainstream usage is the inability to non-destructively test it. At the time, airlines were busily swapping carbon fiber 777 components out for aluminum ones because while the aluminum parts were heavier, you could actually magnaflux them and see if they needed replacement, whereas the carbon fiber stuff flies X many hours and is grounded forever. This later became an issue for the Air Force in Iraq. I didn't buy a carbon fiber frame for my LA bike so hard. As I told my friends, I've only been hit by a car three times and carbon fiber frames can just f'n shatter on you. Which is not what you want to deal with when you need to run Schwalbe Marathons just to keep the flats under two a month.
Thanks, I now have a new fear of carbon fiber. Just checked and thankfully my recently acquired bike is made out of aluminium. I’m also now morbidly curious what might happen to the i3 a few years down the line, as it has both a shit ton of carbon fiber and zero bolts.
Archetypal composite design in luxury vehicle is "make the non-structural stuff out of carbon fiber." It saves you weight, it gives you bragging rights, and it'll never be a problem. A carbon fiber component experiencing zero stress or strain is a new carbon fiber component for the sum total of its projected life. Aside from environmental damage, it will behave exactly the same in a crash twenty years from now as it will fresh off the assembly line. You start carrying math overhead when you put it somewhere structural. Bike frames... crack or they don't, and they ride spectacularly until they do. Generally the people who buy carbon fiber framed bikes don't do it by accident, and they know in the back of their head that mmmmaybe that thing is just not gonna come back from a crack-up. Formula One doesn't let you do carbon fiber structure without the safety aspects being non-carbon-fiber. It may fail? It may fail spectacularly but it won't do so in a way that threatens anyone's life. Motorsport learned that lesson early and often, you don't want to rely on components that will let you down because of something you thought was fine six weeks ago. Here's a thing to keep in mind about carbon fiber - it only absorbs energy so long as it's intact. It ceases to be a part of your crash protection portfolio the minute you exceed its yield strength. As a result, there's little incentive for anyone outside of high performance aerospace to use it in a life safety aspect. Aluminum? Steel? Once you push that stuff past yield it absorbs energy as it yields in a nice, calculable fashion. You can make a "crumple zone" out of metal but a "crumple zone" out of composite might as well be a pile of wine goblets. Push it past its yield and it's cracked eggshells. Which is a long way of saying there's very little in your life that relies on carbon fiber. As I said, even United Airlines got sick of (zero stress) carbon fiber body panels because while the plane is still flyable if a panel shreds at take-off, it's a bad look and with an aluminum hatch panel, you can check wear with a spray bottle and a UV lamp. With a carbon fiber panel you throw it away once it's over a certain number of hours, the end.
Re: your assessment of carbon fiber on luxury cars: I have a Polestar, and it had, for about a week after I bought it, a carbon fiber splitter. One rough bump and it was toast. And cost like 2 grand to get replaced…if I were to do the labor myself. Hence no splitter since week one, since I doubt the next one would last much longer.
What about nicks from the shrapnel of exploded counterbalances? Ohsmall nicks in them due to skates, pucks, ice, whatever
whatever
That's absolutely another major concern. I can't tell if they've designed their centrifuge to also provide structural support, such that I guess only an outer sleeve of the thing is able to rotate. Because, strangely, we're not afforded a view inside the latest build. And if I were there, in person, I'm not getting anywhere near that thing when it's running. So they're like "Hey we can pump down really quick, it's only a rough vacuum". Well, guess what the pressure differential is between 760 Torr and 1E-7 Torr vs. 760 Torr and 1E-3 Torr? Just about 760 Torr, for both. You've got 1 atmosphere trying to implode the thing (love the music). Yeah, the thing will have to live in a web of buttressed supports outside of it. Ideally, you want to cut a vacuum chamber from a single hunk of steel. There's not a forge in the world that has a 45 m radius capability, I just checked. ~15 m seems to be the current record. Not even close. So you'll unavoidably have welding joints in the chamber walls, and you'll have to pass through resonances with chamber vibration modes as the centrifuge spins up or down, with atmosphere pushing in from all sides. Cool, seems fine. Ideally, you'd want the walls to be thicc af, but... how do you weld something super thick together? Genuinely asking. Surely the steel you're fusing together only extends maybe 1/4" or 1/2" into the steel, right? Ladies and gents, I present to you - The Theranos of the space industry.
Dude. 5:33. Whizzy spinny arm. Watch the sun. They shot that shit timelapse They aren't even in the regime of approximation here. They straight up welded up a beer can, got a motor spinning, and then broke the shit out of it. Probably when they let their load go in an insufficiently synchronized fashion and smashed the bearing first one direction and then the other. Does it really matter? They pretty much need it to be vacuum from launch to the Karman Line or else they're fucked. There's no aspect of their design that indicates they've even done wind tunnel tests. They haven't so much as watched a redneck sandcasting aluminum with a propane torch. "Mach 6" is a phrase for them, not a fluid regime. The thing that blows my mind about that video is the only stuff that we didn't call out a year ago is stuff that is actually worse.
Thanks, I gave up after a while of scrubbing through the vid. Blink and ya miss it, eh? So, no support along the chamber axis of symmetry, yet. LOL Hey, here's another entire thing we haven't ragged on yet: The orbit!! You get one orbit per facility. But you can steer a first stage rocket quite a few degrees by gimbaling the engine to one side. And now I'm in stitches trying to imagine attempting to steer a spunlaunch with little thrusters in the lower atmosphere. I'm sure they'll target geosynchronous orbit, since that'd be the most in-demand. But, like you said, who cares? It doesn't matter. It really doesn't. Yeah I was cruising that first thread from 900-odd days ago and feeling like a smug bastard. It's good that this place is pseudonymous because these are the types of companies that'll go after you for "slander", I'm sure.5:33
The thing that blows my mind about that video is the only stuff that we didn't call out a year ago is stuff that is actually worse.
Oh god. You're right. You're putting it in that spot, that spot right there, that's the spot you're putting it in. Theoretically second-stage is a full-on rocket (so, like I said last time, why bother with the fuckin' tilt-a-whirl) so you can do rockety stuff with that stage, but this is a bunch of people who flew their one and only drone into the ground in 2015. That said, I don't think it will get to geosync, dude. They're claiming 200 kg "to orbit" but you know that's LEO. That means they're prolly like 70kg to GTO. What the fuck do you do with that? Their entire embarrassing website makes much of cubesats but really - what the fuck do you do with cubesats other than make your community college proud?Hey, here's another entire thing we haven't ragged on yet: The orbit!! You get one orbit per facility.
btw everyone, GTO is geosynchronous transfer orbit, but if you don't know LEO, delete your account. For sure, the second stage could (very theoretically, after 182 Falcon 9's) perform some corrections, but the changes would have to be comparatively minor. Maybe the best way I can explain the mechanics simply is to point out that the most efficient orbital inclination corrections are performed near apogee, after orbit has already been achieved, and the spunlunch first stage does not even make it to LEO orbit with YOUR 182 FALCON 9 MOM!!! onboard. Presuming you couldn't steer the "first stage" spunL equivalent. (you can't; your mom) Unless they build a luncher near the equator? Best of luck with the 10k g's compliant gimbal system or any other scheme whatsoever to park longitudinally in GEO without roving +/- 30 degrees of latitude every orbit or two or so. Now, imagine the military contracting SpinRanch to put something in low latitude LEO. That's all, that's this paragraph, I hope you enjoyed it. Thank you. Time for minor NASA sacrilege. There is a case to be made against the current paradigm, I will confess. Many things could benefit from serious miniaturization. But many things are very difficult to miniaturize further. Many things should just be shot up into space with way less testing, b/c diminishing returns. Sadly, institutional reputation prevents a bit of progress, for now, cubesats and microsats aside (if only relatively). Everything's all over the board, but the idea that any scientific, military, comms, seriously ANYfucking type of payload can be both miniaturized and 10k g's hardened, and the SpinLaugh scheme would make up for for the hit$ you'd be taking is so fucking hilarious that this is legitimately embarrassing for the current culture of American capitalism's distrust of expertise. There was even a small part of me that was like "wow, this almost kinda diminishes from the respectable successes of the SpaceX business model", but I just cut off both my baby toes, and I'm feeling a lot better. #subsideezNUTSwhat the fuck do you do with cubesats other than make your community college proud?