FYI For anyone starting their own space program (he mentions casually) there's a thing called ITAR registration, which is pretty much mandatory for anything space or rocket related
"International Traffic in Arms Regulations" is basically a set of rules in the U.S. saying you can't do business with anyone on the govt naughty list
But you have to register for this, which costs $2250 ($2750 renewal) every year, which is currently reduced to $500 because of COVID until 2021
Skipping = Jail+fine
Texas Instruments makes a nice D-type 16-bit flip flop with 3 states:
Put 4 of these together with a few capacitors and other helper components and you've got a 64 bit register appropriate for RISC-V CPU built from scratch
Also the 16374 has an operating temp range of -40C - 85C. Storage, -65C - 150C. Quite manageable with active controls
What you lose in space and power consumption, you gain with parts availability and development cost
It's not exactly radiation hardened, but a computer built with coarse electronics, even CMOS, is less susceptible in low Earth orbit
Besides RADHARD components tend to be much slower than contemporary consumer chips anyway. Might as well go bigger to make things easier and cheaper to build
Launch costs will tumble even more
Looking at the precautions for potting compound made me realize how incredibly toxic some of this stuff is. Especially the chemicals used in aerospace for high/low temperature tolerance
Some of this stuff will make your eyebrows fall out with one whiff
All of them need a respirator, long sleeves, and thick gloves to handle safety
The Curiosity rover has 2 radiation hardened computers (primary + backup) clocked at a maximum 200MHz. The CPU alone costs $200K, without the mainboard and other support hardware
Plan is to make my own radiation "tolerant" CPU with similar specs, but in RISC-V RV64, in my living room for the same price as a PizzaHut dinner for 2
Piece of cake
Found my starting point. The registers can be built with a bunch of these D-type 3 state flip flops:
According to my rough calculations, I need an O'Neil Cylinder built in Earth's Larange point 5, with a diameter no less than 1.14km and length no less than 7.61km, to support a renewable forest for firewood for a single a wood stove in a single orbit
Seasons like winter can be simulated with solar shading and moisture pumped through a central line of needle spray nozzles. The Coriolis effect on falling snow and rain would be remarkable
Maintaining this wouldn't require much processing power
TIL This is the "noise" captured by Voyager 1 in the interstellar medium. I can't be entirely sure there are no space whales
Wonder how practical it would be to build something approaching the Voyager probes' durability in my living room
A DIY space program needs lots of antennas
It's possible to build a fairly adequate parabolic dish (beam waveguide type so the base is stationary) with EMT electrical conduit. The dish just needs to support itself and EMT conduit is fairly easy to bend to the correct shape and is robust enough to survive outdoors even under heavy snow
There's a lot of "X has more processing power than the Apollo lander" and similar phrasing and that's usually not a good comparison
Spacecraft hardware is highly specialized and extremely capable in the narrow field in which they're used
From a biological perspective, it would be like comparing brain size and neuron count. Behavior is a lot more accurate indicator of intelligence and capability
I can't even guess how smart an octopus is, but we don't typically use their size to compare
And speaking of space hardware, being resilient is often more important than just capability and speed
In fact, most space-rated hardware is going to be slower than their consumer counterparts, but that's OK because the software is highly optimized to run on it
The trick to getting the DIY space program operational on that front is making sure the hardware is resilient and the programming optimized and actually fits the purpose more than increasing raw speed
There's a lot of reading involved when it comes to starting your own space program
Personal hygiene is important under the DIY space program. Of course, a spinning habitat would make things a lot simpler, but in the meantime, we'll probably go with the no-rinse shampoo too
I was looking at the engine detail of the Redstone rocket engine, the heart of the PGM-11 missile. It occurs to me that this particular geometry lends itself quite well to the expander cycle
This particular engine had a turbopump powered by decomposed high-test peroxide
In theory, H2O2 is a pretty neat way to power a turbopump (also used by Copenhagen Suborbitals is using it for their engines) and as a monopropellant for RCS thrusters, but it's kind of a pain to handle and store safely
Fiber optic cables don't seem to fare well without special shielding and different methods of construction in a high radiation environment. While they're resistant to transient EM spikes, they do tend to break down and attenuate more of the laser light over longer distances
This is a bit of a dilemma. Either go with copper lines for signaling and sensors and risk spikes and have them acting as antennas in a EM field, or go with fiber. Alternatively, I may have to make my own
Speaking of explosions...
The number of accidents in rocketry is too damn high!
Some of that is the inherent danger of the fuel + oxidizer and the complicated plumbing involved. I have neither the intelligence or patience to grasp all of that mess so if I build a rocket, it will probably use the expander cycle
The plumbing is *far* less complex with fewer moving parts. Which means fewer places for things to go wrong and fewer areas of concern to monitor (less work for the computer)
I know the new hotness is Methane right now, but I'd go with Dimethyl Ether as the fuel instead. It's very cheap and can be made from biofuel (possibly on Mars via a different process as well)
As the oxidizer, I'd use Nitrous Oxide. Laughing gas, basically. It's also very cheap and made by the millions of tons. Best of all, it can be decomposed into a very hot gas at 577 C
Dimethyl Ether auto ignites at only 350 C so there's the startup process solved. No need for pyros, sparks, etc...
No nonsense that can fail explosively. Just a tiny electric pump to get the N2O going over the catalyst, which is more than hot enough to ignite the mixture
Also, the expander cycle limits the maximum size of an engine, which means you have to build more smaller ones anyway. While that's extra work, you get spares if one or two shutdown mid-flight
And expanders don't have complicated turbopumps which need high temp/high speed moving parts and seals so they're cheaper to build
Going with Dimethyl Ether and Nitrous Oxide as fuel and oxidizer also because they can be kept liquid at similar temps
-141 C To −24 C for Dimethyl Ether and −90.86 C to −88.48 C for Nitrous Oxide. Which means, they can share a bulkhead in the tanks
This significantly cuts complexity and reduces weight
Also, both have enough expansion at warmer temperatures that I can use "Autogenous pressurization". Same as SpaceX's Starship (though mine will probably be made of glue and aluminum foil)
Apparently a turbocharger from a V8 isn't actually designed to funnel liquid propellant at -89 C at turbopump tolerance. Or survive reentry down from orbital speeds (because reusable rockets or GTFO)
My plan to use a rice cooker to make homemade high-temp composites is probably gonna have issues too
I hope lockdowns lift a bit so I can go trash diving. I'm sure someone's thrown out an orbital grade turbopump somewhere
@jens I like to bathe my laptop keyboards with at least two cups of steaming hot coffee over their lifetime 😇
I try to avoid that. But my left hand seems to rub/burn the surface it rests on. With one of those aluminium PowerBooks, that's eaten pits into the metal, it's almost scary.
@brennen Mine is technically a kitchenette because it's a small apartment. I also have a roommate and it would be unfair to cannibalize his space to build a turbopump
@p I do indeed! In fact, I used his tutorial on making benzene for some ideas. Also the one on fuming nitric acid (before I went with a different propellant for safety reasons)
There are a few places available in Huntsville AL to build and test your rockets. Matter of fact there is a old rocket stand just outside the city in the middle of a field.
Bunch of stuff left over from the Apollo missions there.
You could even steal one of the original V2 bombs to reverse engineer, its just sitting on the side of a intersection.
@jens That's a very brave person
LOX is the most terrifying substance I've ever experienced. And I once spilled hydrogen peroxide on my boots and they caught fire
Well, him and the others in the group are also working at the German space agency. The whole point of this hobby project was to lower the cost of a rocket to tens of thousands, and they weren't entirely unsuccessful. I just tried to find their website, but it seems to have shut down.
@cypnk you've probably read it, but "Ignition!" by John Clark was a suitably nerdy and hilarious read for me last year.
@loppear My favorite was the description of what high test peroxide does to things (and people). Also, indirectly, the reason I'm avoiding it even though a lot of other amateur rocketry folks do use it
@Tay0 Yup. Any kind of stress, even on "outdoor armored" cables is a problem. Another reason we would dig trenches for ours even if it's a huge pain (and in New York, you can't move a stick without a permit of some kind)
We run a cable called OPGW as static or ground lines on our transmission lines. It's a stranded, weather proof ground line with fiber in its core. I hear it's tough stuff. The stuff they run on regular distribution electric poles needs some kind of treatment like this.
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