On Tue, May 07, 2019 at 11:37:46AM -0400, William H. Fite wrote: > And it drives SpaceX nuts. Likely the other privates, as well. SpaceX > recovers a faulty part or system, analyzes the problem, resolves it, tests > the revision, and is ready to go. "No no," says NASA. "First we must have a > workgroup to define the problem. Then we must have a workgroup to identify > possible solutions with a subgroup to analyze the resource requirements for > each. Then there is a workgroup to analyze the findings of the previous > workgroups and offer recommendations to senior leadership. Leadership > checks to assure that the distribution of suppliers and contactors to > implement the solution provides sufficient lagniappe to key congressional > districts. The chosen solution is then referred to a feasibility workgroup. > Its findings are sent to a materiel acquisitions workgroup that ultimately > lets bids for the required engineering, parts, and labor. An oversight > workgroup is empanelled to coordinate the fix, overseen by a quality > assurance workgroup. A validation and certification workgroup takes a final > look, 113 concurring agency approvals are solicited, and the fix is > declared ready to go back to space." > > > > On Monday, May 6, 2019, jimlux <[email protected]> wrote: > > > On 5/6/19 7:04 PM, William H. Fite wrote: > > > >> Mother of God, really? > >> > >> I had a friend, now of blessed memory, who was lead communications > >> engineer > >> for Grumman on the lunar lander. He used to boggle our minds with stories > >> of the truly absurd lengths that NASA made them go to have hardware "space > >> certified." > >> > >> > > > > This is changing.. > > > > Recognize that for NASA, they're usually building just one (or maybe 2 > > flight units plus a spare, if you're on a big budget Class A mission with > > redundant strings). So they don't think in terms of MIL-HDBK-217 kinds of > > reliability calculations of statistics.. It's more a matter of "what could > > go wrong, and how can we prevent that". > > > > So you wind up with a lot of requirements and tests that may not be > > statistically justifiable. They tend to require large design margins (since > > you're building just one, the unit test campaign is both verifying the > > design AND doing acceptance testing). > > > > For instance, some years ago voltage/frequency stress testing was popular > > - run it at a variety of frequencies and voltages, well beyond the design > > range, and show that you've got margin. > > > > There's also a "if it doesn't meet the datasheet specs under all test > > conditions, it is deemed to have failed" philosophy. A classic problem is > > optocouplers. You might choose a part that has a current transfer ratio of > > 100, and your design needs a CTR of 1. But the data sheet says > > 90<CTR<110. So after radiating it with some dose, the CTR has degraded to > > 85. The part still works just fine (you need a CTR of 1) but the parts > > engineer says "nope, that part has failed at the dose, you can't use it". > > > > A lot of space qualification is paperwork to prove you have "traceability > > to sand" for the parts. Lot numbers, production dates, etc. So when the > > GIDEP (http://www.gidep.org/) comes out for a 2N2222A (yes I've gotten > > one), you can go and see if YOUR particular NPN transistor is covered. > > > > And then there's testing at many levels (not all of which is valuable)... > > > > Incoming inspection of resistors. Back in the 60s, someone must have > > gotten a "out of spec" resistor in a box of 5% resistors - so the procedure > > was put in place: Measure each resistor (after assigning a serial number, > > and verifying the color stripes, including the stripe width and > > colorimetric properties) with a calibrated ohmmeter(with calibration data > > recorded), record each measurement, and attach that the to the build book. > > > > So, today, you get a reel of 1000 resistors all 100 ohms. Someone in > > incoming inspection in a clean room at an ESD safe (to 50V) workstation, > > pulls each resistor off the tape, takes a picture of it, verifies the > > physical size on a coordinate measuring machine, measures the resistance, > > logs that information, and carefully places the resistor into an assigned > > cell in a waffle pack. Then, later, someone takes the resistors out of > > the waffle pack, puts them back into a tape, after measuring the resistance > > and dimensions, so that it can be loaded into the automated assembly > > machine. > > > > This is what makes space qualified equipment expensive. > > > > > > > > _______________________________________________ > > time-nuts mailing list -- [email protected] > > To unsubscribe, go to http://lists.febo.com/mailman/ > > listinfo/time-nuts_lists.febo.com > > and follow the instructions there. > > > > > -- > Homo sum humani a me nihil alienum puto. > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there.
-- Dave Emery N1PRE/AE, [email protected] DIE Consulting, Weston, Mass 02493 "An empty zombie mind with a forlorn barely readable weatherbeaten 'For Rent' sign still vainly flapping outside on the weed encrusted pole - in celebration of what could have been, but wasn't and is not to be now either." _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
