Huygens Wind Experiment Salvaged

SeaDour writes "Earlier, it was reported that the data from a critical wind speed experiment onboard the Huygens probe to Titan was completely lost due to someone forgetting to turn on one of Cassini's communications channels. However, it now appears that ground-based radio telescopes from the National Radio Astronomy Observatory were able to record the transmission's many subtle doppler shifts and reconstruct that lost wind data. The winds altered the probe's horizontal rate of descent, thereby producing a change in the frequency of the signal received on Earth. Additionally, the resolution of the radio telescopes was good enough to track Huygen's position to within one kilometer, allowing for the creation of a three-dimensional model of Huygen's descent."

Comments

Re:Things like that just amaze me...

[another_henry]

The original experiment using Cassini's onboard receivers would have had an accuracy of better than 1 m/sec and presumably similar positioning accuracy. Still, the probe accomplished a lot and was several different kinds of awesome.

Re:R.E.S.P.E.C.T. !

[jmichaelg]

Figuring out that the wind data was embedded in the radio signal was an NRAO accomplishment.

It wasn't NASA, it wasn't ESA and it wasn't easy...

Re:Do I understand this?

[Rei]

A whole lot more than 10; read the Planetary Society's account of just what it took to get the data back:

http://www.planetary.org/news/2005/huygens_radio -t racking_0207.html

Plus, they didn't know that this would work beforehand.

Re:Horizontal rate of descent

[Mattcelt]

It's just you. ;-)

Seriously, if you think about it, this makes perfect sense. The Earth is a rotating sphere, right? So unless an object approaching ground level happens to maintain a perfectly geosynchronous orbit around the Earth as it falls inward, it will hit the atmosphere at an angle and not straight down. So almost inevitably, there will be a horizontal component (think the base of the triangle where the trajectory/vector is the hypotenuse) to go with the vertical component. How much and in which direction(s) the object is deflected from its ordinary horizontal state (the result of the pure angle of entry into the atmosphere) gives direct indication about the presence, speed, and direction of any wind which might exist at that place. (Vertical deflection from standard gravitational acceleration gives important information about the stratification and density of the atmosphere in the same manner.)

Does it make more sense now?

Larger story: All data nearly lost

[behindthewall]

This hasn't gotten as much coverage, but a design oversight nearly cost all Huygens data. Doppler shift was not accounted for in the signal decode process. The mission plan had to be rewritten to find an alternative flight path that reduced the Doppler shift to within the limited acceptable tolerances. Fortunately, Cassini's approach to Saturn was accurate enough that enough fuel existed to allow this while preserving the latter part of the existing flight plan.

Of course, in retrospect, maybe earth-based monitoring would have come to the rescue in this event, in an even bigger fashion.

"Titan Calling: How a Swedish engineer saved a once-in-a-lifetime mission to Saturn's mysterious moon"
http://www.spectrum.ieee.org/WEBONLY/publicfeature /oct04/1004titan.html

Sorry if this is a repeat. Slashdot's search 503-ed on me.