Yay, Cassini (as of this writing) finished its 96 minute burn and entered orbit around Saturn (it’s still got to pass through the ring plane, in under an hour). This is pretty cool.
Here’s an excellent article on the events in the Saturn Orbital Injection sequence; particularly interesting (to me, anyway) is the fault handling mechanism for the critical 96 minute burn. Normally, spacecraft fall into a ‘safe mode’ when something unexpected happens, and there’s a longish protocol (during which the craft is largely quiescent, to prevent further damage) for re-establishing communication with controllers on Earth. Spacecraft have been recovered weeks after they’ve nearly died. But during periods like the SOI, specific things have to happen or the mission is toast. For instance, if the craft’s computers crash midway through the burn, it should figure that out and complete the burn. There’s a seven hour window to get into orbit.
In his book The Evening Star, Henry S.F. Cooper wrote about the problems encountered by the Venus probe Magellan, which entered safe mode many times until the problem was diagnosed (a race condition in the craft’s software, plus bits of floating insulation that fooled star sensors).
Of course, there are alarmist wackos who can’t do math or threat analysis. It’s amazing that we’re all still alive with all that super massively dangerous plutonium floating around in space. “Why doesn’t it all fall down, are you sure it can’t.” Jeez.