Dont Ignore Trends

There is a tendency to ignore small problems. The gas gauge is low—I still have enough—it can wait. Forget about it.

Then we run out of gas, and it's a catastrophe.

Rocket scientists cannot afford to ignore small problems on a spacecraft in flight. Something must be done to understand the problem before it gets worse. A capacitor on the Voyager spacecraft became the most studied electronic component in history because it began to fluctuate (in capacitance), which changed the radio frequency the spacecraft was listening to. So the transmission signal from Earth had to be constantly adjusted so that Voyager would hear its commands. It was as if a radio station you were listening to kept drifting so that you would have to keep turning the knob on your receiver to hear it.

The capacitor on the Voyager was affected by variations in the onboard temperature. If Voyager ever stopped listening to the mission controllers on Earth, it would mean the loss of the spacecraft and the mission. So a great deal of effort went in to analyzing the trends of this faulty capacitor on Voyagers receiver.

In life we are constantly confronted with problems. We are very busy just following our usual schedules, and we don't have time to deal with new problems. When the great figure skater Scott Hamilton was diagnosed with testicular cancer, he was on tour with his Champions on Ice. His first reaction was, "I don't have time for this!" Fortunately, Scott took the time—and his life and career were saved.

We cannot afford to ignore the early warning signs of problems, whether they are a dripping faucet, a low tire, or a seemingly minor health complaint. Scott Hamilton's cancer started out with stiffness and stomach cramps, which he first thought he could work off.

It is not generally known that our deep-space probes need the constant attention of technicians on Earth. These mission controllers are affectionately referred to as "babysitters." Eventually, spacecraft will become fully automated adults, but today (in 2006) they are still babies in the crib. They simply are not smart enough to take care of themselves.

The babysitters continuously monitor the health of the spacecraft. They listen to the spacecraft every day and maintain a constant communication link. The early versions of our interplanetary probes were more like toasters than automated robots. When you toast bread, you push the slice down and set the dial anywhere from light to dark. But the toaster doesn't know what's happening to the bread. It simply times the heating element and pops the toast out. If the toast should burst into flames in the first five seconds, the toaster will continue to heat the element until the timer runs out (say in thirty seconds). This type of control is what rocket scientists call open-loop control, which means no control—just timing without knowing what is really happening.

Spacecraft even today do not have complete feedback control. That is, they don't know what they're doing. A feedback control on a toaster would mean that the toaster would be measuring the temperature of the toast so that once it got hot enough for long enough, it would turn off. If for some reason it burst into flames, it would immediately shut down the heating element, unlike the open-loop toasters. The thermostat control in your home is an example of such a feedback control system.

Spacecraft are still pretty dumb. When we command a spacecraft to take a picture of Saturn's rings (which the Cassini spacecraft is doing right now, at the time of this writing), it points its camera, blindly, to a predetermined direction and takes a picture. It does not have the capacity to look through the camera and check if Saturn is in the frame. But the pictures of Saturn's rings came out fine because the mission controllers had been monitoring the trends

Chapter 47 Don't Ignore Trends in the spacecraft for years and correcting for small errors along the way.

Paying attention to trends is an important concept, whether you're babysitting a spacecraft, watching your health, or just burning toast.

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