[time-nuts] Rubidium Cells for Sale ?!

[David I. Emery]

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 <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.
> >
> >
> >
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> >
> 
> 
> -- 
> Homo sum humani a me nihil alienum puto.
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-- 
  Dave Emery N1PRE/AE, die at dieconsulting.com  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."