Example 1: The Viking 1 lander

In the 1970s, NASA sent a pair of probes to Mars, the Viking 1 and Viking 2 missions. Total cost of $1B (1970), equivalent to about $7B (2025). The Viking 1 probe operated on Mars's surface for six years, before its battery began to seriously degrade.

One might have thought a battery problem like that would spell the irrevocable end of the mission. The probe had already launched and was now on Mars, very far away and out of reach of any human technician's fixing fingers. Was it not inevitable, then, that if any kind of technical problem were to be discovered long after the space launch in August 1975, nothing could possibly be done?

But the foresightful engineers of the Viking 1 probe had devised a plan for just this class of eventuality, which they had foreseen in general, if not in exact specifics. They had built the Viking 1 probe to accept software updates by radio receiver, transmitted from Earth.

On November 11, 1982, Earth sent an update to the Viking 1 lander's software, intended to make sure the battery only discharged down to a minimum voltage level, rather than running for a fixed time after each charge.

The battery-software update accidentally overwrote the antenna-pointing software.

With the lander's antenna no longer pointed at the orbiter, no further software updates beyond that point could be received.

The error had destroyed the intended mechanism for recovering from errors.

All contact with the Viking 1 lander was permanently lost. Ground engineers tried some strategies for regaining contact, based on extrapolation of where the antenna could have ended up pointing, but none succeeded.

In this I observe a specific instance of a general idea: Murphy's Curse of Inaccessibility on space probes is a deep problem. A clever system designed in the hope of accepting later patches is a relatively shallower solution.

Putting wings on an airplane doesn't make it weightless and repeal the law of gravity. The weight of an airplane is an intrinsic property that goes on making it susceptible to falling out of the sky if the wings stop working. Your model of the airplane should include the ongoing weight and ongoing lift; not, argue that the curse of airplane-weight will be dispelled by wings.

The engineers' attempted strategy for mitigating the underlying oneshot quality of a space probe launch -- the engineers' intended mech...

Laurie Cheers

Laurie Cheers