Hey, I'm glad you responded, and that I misinterpreted where you were coming from and your intentions, but I guess that happens when limited to text (not that a misunderstanding-free medium exists). But as you've probably gathered by now, most of my response came from reading "I don't see any reason why someone shouldn't make this. [and I doubt a good one exists]" instead of "I don't see any reason why someone shouldn't make this. [and I would like to hear some]"

> Fast, Cheap, and Out of Control

The first thing that popped into my head when I saw this title was NASA's "Faster, Better, Cheaper" initiative. I will admit that I do not know much about it, but what I do know is that there were some failures (as you would expect) and the public did not react well. The failures did not come from not having space-grade parts, IIRC, but for various other reasons. The most infamous was the Mars Climate Orbiter, known for failing due to an imperial-metric conversion error [1], that is still brought up in almost every space-exploration piece that gets sufficient attention. Anecdotally, the lessons learned by those I've talked to are (1) choose 2 and (2) the public will not tolerate failure on large NASA projects, even if those projects cost a fraction of what it takes to host an Olympics, or to buy Instagram, or fight a war for a day.[2] But I have just now hopefully started a discussion with my coworkers about this paper[3] on our message board.

So anyways, about the paper. It looks like your idea is only mentioned briefly in the one section, and not fleshed out. The idea was somewhat more fleshed out in the talk I went to. What I meant by my line of questioning was that I haven't seen an implementation of these concepts outside academia, even though the idea has been around for some time, and the industry isn't entirely driven by irrational beings, so there must be some technical reasons why the ideas haven't been fully adopted.

>> * Having an identical copy is not redundancy

> Is it because the failure points remain the same?

Essentially, yes. His argument that most failures were systematic, and not due to unequal 'wear' of various kinds. Software especially, since on space missions it is implemented to be as deterministic as possible. That means that even if the primary processor fails gracefully due to bad internal logic, and a hot backup immediately takes its place, the backup will behave in exactly the same way given those inputs, which are likely to stay the roughly the same across the switch. Another example is a mission where the high gain antenna succumbed to a systematic failure, and they completed the mission on its low gain antenna. If there had been 2 identical antennas, they would not have been able to.

Designing and testing components to last a long time under the conditions you expect and test for is relatively easy. It's when the designs and tests don't match reality is when the problems happen. If you write something and make a copy, it will retain all of the typose of the original, and it's the same with Code/CAD/etc (and you might be more likely to introduce bugs than fix them). Ground-based systems can get away with this because of how easy it is to replace/repair broken units in a redundant setup.

[1] Even though it was due to a much larger issue related to how the project was carried out, and just happened to manifest in that error. It could have easily been a kilometer/meter mixup instead. And having a backup string of landing hardware/software wouldn't have helped in this case, unless the backup units had a different design/implementation.

[2] And yet, JPL still chose to use the skycrane. Very couragous.

[3] http://www.dau.mil/pubscats/ATL%20Docs/Mar-Apr10/ward_mar-ap...