> (my agenda, for transparency: I want to send SOC's in space on tiny RISC-V satellites, and the lowest layers of those should be 100% error-free because there's no going physically there to reboot a working shell, remote is all we have.)

Speaking from a bit of experience at Satellogic as well as folklore, trying to make the lowest levels 100% error-free isn't a good strategy. A better strategy is to make the lowest levels capable of recovering from the errors that will occur most frequently. Radiation is going to flip bits; processors are going to fail and sometimes hang; batteries are going to go low; temperatures are going to exceed specifications. If your system is built on the assumption that the lowest layers are going to be 100% error-free, you won't give sufficient attention to handling those errors when your assumption inevitably turns out to be wrong.

One suggestion: include a remotely-triggerable reset sequence in a hardware state machine. A 4-bit state machine driven by 4-bit symbols will work reliably if your channel error rate is small compared to one error per 16 symbols, and it has a false positive trigger rate of 5.4 × 10⁻²⁰. (This is of course vulnerable to malicious DoS attacks if a malicious party learns the 64-bit reset code, but in practice those have historically been an enormously smaller concern than satellites failing randomly in ways that a reset switch can correct.)

It's worth thinking through the fault tree of that reset mechanism. It needs to use omnidirectional antennas, for example, because otherwise it's dependent on attitude control. It needs to be on all the time, not just when you're passing over ground stations, because otherwise it depends on the clock and whatever kind of navigational system you have. It needs to be unencrypted, because otherwise it depends on your encryption protocol, which typically also involves clocks. It unavoidably depends on some kind of power source, but you can connect it directly to the solar panels and/or batteries, rather than through a switch. You probably want to use logic that can tolerate a fair bit of uncontrolled variation of the power supply voltage, not, say, TTL. But then you need like 4 flip-flops and a couple dozen gates. It can fail, but it's simple enough that you can make it highly reliable, unlike a RISC-V.

So, don't think in terms of making the bottom level 100% reliable. You won't get there. Think in terms of how to prevent inevitable unreliability from snowballing, how to make the satellite resilient against inevitable damage and malfunctions, as well as reducing that bottom-level unreliability to an absolute minimum.

As for blockchains, I think they're a very pragmatic solution to serious problems that are otherwise unsolvable: how can I send money to a friend in Venezuela? How can refugees carry their money safely without it being confiscated by pirates, corrupt police, or immigration authorities? How can people pay for illegal drugs without meeting in person with the vendors? How can we fund Wikileaks so they have the resources to transport Ed Snowden to safety? How can we fund Sci-Hub so that knowledge is available to everyone and not lost? Even international remittances to family members work enormously better with Bitcoin than with Western Union or SWIFT, particularly between countries with some degree of unfriendly relations.

It's a similar approach to that with satellites: we know there are bad actors in the financial system, and we want to engage in transactions with them, without giving them the opportunity to sell our credit card numbers to the Russian Mafia or take all our money. We want to prevent the small amounts of inevitable unreliability from snowballing and destroying the entire civilization. Also, we want to minimize the number of attempted ripoffs, so that our defenses against them can be less costly. It turns out that thieves, unlike cosmic rays, respond to incentives, so by making thefts more difficult to pull off, we can also decrease the number of attempted thefts.

Obviously I don't trust Facebook to design the world financial system, though. They elected Trump.