Cassini Saturn Orbiter vs. Tin Whiskers

Although I don’t often block-quote other sources, for this I’ll make an exception:

The Cassini Plasma Spectrometer (CAPS, off since June 2011) was powered back on on March 16 based on the unanimous agreement of the review board at the CAPS turn-on review held on March 8. All went as planned for both the instrument and the spacecraft during the turn-on. The high rail to chassis short internal to the instrument that was part of what prompted it to be turned off last June was not present, and no changes were seen in the bus voltages or currents when the turn-on occurred. On Tuesday, March 20, the high rail to chassis short in the CAPS instrument returned, generating the same condition that existed at the time the instrument was turned off. However, based on the tin whisker model developed by the NESC team, this condition is believed to be understood and is not expected to cause any problems for either the instrument or the spacecraft. The CAPS instrument has been left powered on and is sequenced to operate as originally planned for the 75 kilometer Enceladus flyby coming up on March 27.

Having seen a forest of tin whiskers myself, that’s a pretty scary diagnosis. One assumes NASA takes extensive precautions, based on their experience, but … 15 years in hard vacuum and free fall will do odd things to spacecraft.

Remember those Toyota unintended acceleration problems? Guess what caused some of them: yup. Read their report to find out what makes metal whiskers so hard to detect. Hint: combine a minimum threshold voltage with a very low current capacity.

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6 thoughts on “Cassini Saturn Orbiter vs. Tin Whiskers

  1. Interesting. I had heard of tin whiskers vaguely…. but learned a new thing or two from the NASA website and Toyota fault analysis. Will be spending a few more hours reading it. Very interesting stuff.

    Maybe it’s time we switch to tin-free solder as well… no lead, no tin…. no problem!

  2. “Remember those Toyota unintended acceleration problems?”

    What about A.D.H.D. ‘ s role in those problems?

    “Learning to Drive With A.D.H.D.”

    For a potentiometer? Just plain ridiculous.
    Further, this makes me question some pratices within Toyota. For example, I investigated a shutdown problem related to the servo throttle body. Instead of a pot, they are using magenetic non-contact postion sensors in the servo controlling the throttle blade. A large 550size DC brushed motor goes through a set of gears. The motor, gears and position sensor are in a sealed chamber except they put a port to the crankcase (like a PCV valve but no valve) to allow the space to breath with temperature to what they believed was clean and dry air. Also, the throttle body is smartly heated by coolant path to prevent throttle blade icing and sticking in the winter. What some engineer didn’t calculate was that a byproduct of combustion is water vapor and some very caustic compounds. The throttle body will cool much faster than the rest of the engine when shut off and pull a slight vacuum extracting that moisture from the crankcase and condense on the metal pinion of the DC motor in the servo causing the gears to corrode as well as the shafts and bushings. Over time, this extra friction slows the mechanism down due to friction and thus, the servo response can hit the threshold with fast throttle movements causing the computer to shut down the car. This is one area that the safety in the computer says I cannot control the car, shut it down. Later years, the throttle body is not connected to the crankcase vent.
    My concern though is why is a pot $400? If it was the resonable $12 (price of a GM throttle position sensor) then you would just replace the part after $10 years and keep driving the car safely or recall the part. It’s not that we don’t expect a pot to go bad, it that if it did go bad, we don’t expect it to be so expensive that most people wouldn’t replace it under maintenance costs, thus have a higher potential to be driving around unsafe!!!!

    1. For a potentiometer? Just plain ridiculous.

      Just took the van for a long-delayed recall about corrosion on the spare tire hanger cable. I checked it out when they sent us the first postcard, but they just won’t give up… so we took it in and drove a couple of new Toyotas around while the shop did the recall deed.

      The brake fluid is low, so they recommend a front end brake job: pads + rotors = $450. The timing belt should be replaced: $695. The oil pan needs resealing: $295.

      Well, the reason the brake fluid is low (but not below the “low” line) is that the pads are worn (but not below the “replace me” marks). The van has low mileage and high years; it’ll go to its grave wearing the OEM belt. And the oil pan is wet because every time I replace the filter, it blooshes oil all over the front of the block.


  4. Looks like your van is just old enough to have the non-interference engine – the 1MZ-FE without VVTi. So, if the timing belt goes, it just won’t run until replaced. The 2001 Sienna and some range of newer ones have an interference engine where a loss of the timing belt means Mr Valve meets Mr Piston and you buy a new engine…

    1. I suppose those negative-clearance pistons get you a bit more compression and fuel efficiency, but they turn a snapped belt (or chain or whatever) into a catastrophic failure. I guess it’s like lubricated-for-life CV joints: the lubrication lasts forever and then you buy a whole new drivetrain.

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