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NASA does things this way but SpaceX explicitly does not. Rather than using 1 space hardened part, SpaceX usually uses 3 non-space hardened parts (processor, me
by pilom 9y ago
NASA does things this way but SpaceX explicitly does not. Rather than using 1 space hardened part, SpaceX usually uses 3 non-space hardened parts (processor, memory, bus, etc) that all do exactly the same calculations simultaneously and then compare every single answer and ignore it when one out of 3 parts disagree. This allows them to be both cheaper and much less power hungry because they operate at least 2 process nodes smaller than NASA hardware. I've seen data that says that while each individual processor will experience space related errors quite often, the whole 3 part voting system is at least as accurate as the way NASA does it.
- ygra 9y agoThere's also a difference between a space probe, built once and having a mission that spans years or decades, and a rocket that gets built more often and operates only in Earth orbit (especially the first stage has to worry far less about radiation flipping bits). This isn't solely a difference between NASA and SpaceX, but also a difference in mission requirements.
- kjs3 9y agoThat's not how it works. Cassini's primary computer also has redundant processors in a voting configuration (rad-hard MIL-STD-1750A's), a configuration common in high-reliability systems, which SpaceX borrowed. SpaceX is cheaper, possibly lower power, but not necessarily just as reliable.
- branchan 9y agoIt's not a SpaceX-only scheme, nor is it novel technology. It's got a long history in fighter jets, as well as modern passenger planes for example (Boeing 777). Triple Mode Redundancy: https://en.wikipedia.org/wiki/Triple_modular_redundancy https://en.wikipedia.org/wiki/Triple_modular_redundancy Also, the longest life span SpaceX has ever really needed is maybe the Dragon, which is a month-long mission. Cassini has been in space for 20 years. Very different design requirements.
- lodi 9y agoNASA must be well aware of the triple redundancy logic you're describing since they themselves used it on the Saturn V in the 60's. https://en.wikipedia.org/wiki/Saturn_Launch_Vehicle_Digital_Computer https://en.wikipedia.org/wiki/Saturn_Launch_Vehicle_Digital_...