How a Swedish engineer saved a once-in-a-lifetime mission to Titan (2004)

He didn't have a hunch, he just knew that the standard comprehensive test was skipped, which is why the standard test procedure only detected a problem, and he had to end early and go off book in order to reveal the doppler problem.

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_...

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.

Take this with a grain of salt because it's been a while since I've done telecom/telemetry stuff, but even with a Manchester-encoded signal, one of the first steps in the demodulation process is clock recovery from the signal. This usually involves some sort of PLL (phase-locked loop), which has parameters to control it's freq tracking range. However there are trade offs for widening the range, in terms of time-to-lock and increased probability of locking onto noise etc. so for the original application of the system in earth satellites, they probably used a tight range to improve performance.

Very much agree. Taken to the extreme, complete suppression of tribalism would not only be extremely difficult but also extremely harmful to society, as even the love between children and parents will be destroyed in favor of egalitarian love. Our biological nature causes children to prefer their parents more than any other parents, and in doing so, prefer their siblings (their parent's other children), more than any other children, and prefer their parents' siblings and parents more than any other elderly persons and adults. It is this nature, as it radiates outwards, that causes one to feel greater love to those who are similar than those who are different.

I don't want to live in a world where children are taught to betray their parents in favor of their state, where children are taught to report on their parents for their crimes, where brothers treat each other as strangers, where husband betrays wife and vice versa, at the same time. I've already read about it in 1984.

The harm in suppressing this aspect of humanity comes from having to involve the state. It takes the state to educate children to report on their parents crimes. It takes the state to force children to attend schools to study the same subjects. It takes the state to extract wealth from parents to distribute it to other children. It takes the state to enact taxes on children to distribute their income amongst other parents. Taken to the extreme - you'll get a very big, very powerful state, because it must involve itself in everyone's personal relationships, to ensure equality amongst all. And with a big state, you get corruption, you get misallocations of capital, you get a concentration of power, all of which would lead to a state that would monitor its citizens every communication, to protect its power in actuality, and to maintain equality and protect its citizens in name. And, as you reduce every person's natural relationships, people will form relationships with others, leading to divisions not amongst genetic or even geographic lines, but amongst other arbitrary lines such as class and wealth, government and private. As a group of people gain control of state, the actions of the state will begin to benefit some, but not others, arbitrarily, so that in actuality equality (in wealth, status, whatever) will always only be an illusion, and inequality will always manifest itself in other ways, so that all those resources supporting a very big state to maintain equality, are mostly wasted, except in so far as it provides an illusion of equality, which it can maintain for only so long.

Oh, wait.