Quote from: Go4TLI on 11/19/2012 04:22 pmYes, you have an opinion on everthing and seem to act like an expert on just about everything as well. As I said, carry on. To quote Jim: Pot, meet kettle.
Yes, you have an opinion on everthing and seem to act like an expert on just about everything as well. As I said, carry on.
Don't mistake experience for anything else but what it is. If you and others don't like it, don't read it or don't comment on it. Hell, it's not like I don't have other things to do anyway if true experience is not welcome here.
Quote from: Go4TLI on 11/19/2012 09:37 pm Don't mistake experience for anything else but what it is. If you and others don't like it, don't read it or don't comment on it. Hell, it's not like I don't have other things to do anyway if true experience is not welcome here. Your posts are always welcome as far as I'm concerned. I agree with you. Using redundancy can be a good way to increase reliability, but it's often used as a way to slack off on standards. I've seen a lot of equipment and more than one life lost because of redundancy induced complacency. (A phrase I just invented for this post) Saying that one computer failing isn't a big deal because there are two more is a great way to insure a LOM. It's no more acceptable than ignoring the loss on an engine because you still had 8 working ones. Knowing SpaceX they'll get into the radiation hardened electronics business now. Probably mine their own silicon.
They didn't loose a computer it rebooted just fine. NASA just didn't want them to resysnc it while it was at the ISS due to the complication of explaining it to all the partners. According to what's been reported elsewhere SpaceX just plans to make the resyncing an automatic operation.
Knowing SpaceX they'll get into the radiation hardened electronics business now. Probably mine their own silicon.
Quote from: JBF on 11/20/2012 01:34 pmThey didn't loose a computer it rebooted just fine. NASA just didn't want them to resysnc it while it was at the ISS due to the complication of explaining it to all the partners. According to what's been reported elsewhere SpaceX just plans to make the resyncing an automatic operation.These issues that crop up because their electronics are unreliable or under the constant threat of being disrupted by rad hits will make it much more difficult and just inputs additional risk into the mission for little reason as far as I can tell.
The whole idea of making rad-hardened extreme-expense parts is part of the era of too-big-to-fail philosophy. Using enough computation and redundancy you can automatically correct and adjust for failure in hardware.
Latch-ups are always a possibility (although small in LEO for memory).
... I've seen a lot of equipment and more than one life lost because of redundancy induced complacency. (A phrase I just invented for this post)...
With added redundancy, you have the additional benefit of more "near misses," which gives you more opportunities to improve the system. Without redundancy, you either succeed or you fail hard, much fewer near misses.
Quote from: Robotbeat on 11/20/2012 02:35 pmWith added redundancy, you have the additional benefit of more "near misses," which gives you more opportunities to improve the system. Without redundancy, you either succeed or you fail hard, much fewer near misses.As far as I can tell not a single person has suggested there should be no redundancy. Redundancy is obvious thing to have.The discussion is wheter or not unlimted redundancy should be the anwer-all for unreliability. I suggest there is a middle ground where reliability is high but redundancy is there because things happen.
Nobody disagrees with you on the idea there should be a middle ground. Or at least, nobody should.
There is no way in hell SpaceX will actually start manufacturing its own integrated circuits. They said they don't even manufacture their own printed circuit boards in house when I asked them about it at the career fair here a few months ago.
Quote from: Go4TLI on 11/20/2012 02:40 pmQuote from: Robotbeat on 11/20/2012 02:35 pmWith added redundancy, you have the additional benefit of more "near misses," which gives you more opportunities to improve the system. Without redundancy, you either succeed or you fail hard, much fewer near misses.As far as I can tell not a single person has suggested there should be no redundancy. Redundancy is obvious thing to have.The discussion is wheter or not unlimted redundancy should be the anwer-all for unreliability. I suggest there is a middle ground where reliability is high but redundancy is there because things happen. Nobody disagrees with you on the idea there should be a middle ground. Or at least, nobody should.
Quote from: Robotbeat on 11/20/2012 02:42 pmNobody disagrees with you on the idea there should be a middle ground. Or at least, nobody should."You can go a LONG ways just adding redundancy and still end up with a much /more/ reliable system even with FEWER reliable components. This is more true with computer systems than it is for other engineered systems."That's a quote from you. I read that as suggesting reliability is unimportant as long as there is sufficient redundancy to compensate.
The problem is how deep that redundancy has to be is likely a variable that is a function of the issue at hand the operations being performed at the time.
Another point is that while throwing redundancy at the problem can indeed solve almost any reliability issue, the cost of such a decision may be an order of magnitude increase in complexity and software development costs.
A properly designed system should be plug-n-play being able to drop any number of computational "modules" into the loop as you want. As long as they didn't hardcode the 3 modules of 2 computing units architecture, it may already be capable of dropping additional modules into the loop.