[jessriedel]

Hopefully everyone realized that this article is from 2004 and Huygens completed its descent onto Titan in January 2005. The problem discussed in the article was successfully fixed, saving the mission, but an unrelated problem (also with the telemetry) means a modest chunk of data was lost:

> Huygens was programmed to transmit telemetry and scientific data to the Cassini orbiter for relay to Earth using two redundant S-band radio systems, referred to as Channel A and B, or Chain A and B. Channel A was the sole path for an experiment to measure wind speeds by studying tiny frequency changes caused by Huygens's motion. In one other deliberate departure from full redundancy, pictures from the descent imager were split up, with each channel carrying 350 pictures.

>As it turned out, Cassini never listened to channel A because of an operational commanding error. The receiver on the orbiter was never commanded to turn on, according to officials with the European Space Agency. ESA announced that the program error was a mistake on their part, the missing command was part of a software program developed by ESA for the Huygens mission and that it was executed by Cassini as delivered.

>The loss of Channel A means only 350 pictures were received instead of the 700 planned. All Doppler radio measurements between Cassini and Huygens were lost as well. Doppler radio measurements of Huygens from Earth were made, though not as accurate as the expected measurements that Cassini would have made; when added to accelerometer sensors on Huygens and VLBI tracking of the position of the Huygens probe from Earth, reasonably accurate wind speed and direction measurements could still be derived.

http://en.wikipedia.org/wiki/Huygens_(spacecraft)#Channel_A_...

[antimagic]

Well, being pedantic for a moment, the problem never was fixed. The flightpath of Cassini was simply altered so that there was negligeable Doppler shift of the radio signal from Huygens, meaning that the inability to handle a Doppler shift.

Happily enough this was possible to do without using too much fuel, and indeed Cassini had more fuel available than planned, as the original launch and early course corrections had been so precise that fuel planned for course correction burns was available for other uses. One of the consequences of all of this is that Cassini is still operational today, more than 5 years passed the planned end of it's mission.

[keithpeter]

"Well, being pedantic for a moment, the problem never was fixed."

But a work round was found. And I have a really good example for teaching resolving vectors...