[time-nuts] Rubidium Cells for Sale ?!

[William H. Fite]

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 <jimlux at earthlink.net> 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 -- time-nuts at lists.febo.com
> 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.