Slashdot Mirror
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."
It was descending at an angle due strong winds. It's rate of descent could be something like 2ft of horizontal movement for every foot of vertical movement (numbers made up on the spot). It's sometimes called a Glide Ratio.
Everything that falls from space has a horizontal component to its descent.
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.
"Studies have shown that people who eat peanuts live longer than those who do not eat."
NASA? you do realize Huygens was a ESA+NASA effort...and in fact, most of the probe's development was european? NASA's Cassini was the carrier of the probe, but the probe is an European accomplishment first.
There are two kinds of people in the world: Those with good memory.
The second channel was not a redundant channel. Channel 1 was for the major data. Channel 2 was for half the total images uplinked to Cassini. Channel 2 was also dedicated to the Doppler data.
Someone failed to turn on the receiver on the Cassini device. The data was transmitted on channel 2, just never received by Cassini.
Over and out
They're quite old anyway, basically from the day after it landed. For example mentioned here.
Slashdot chose to post about the doomed mission instead, which made me believe it was indeed lost... but apparently it was like this all the time.
Beware: In C++, your friends can see your privates!
It wasn't NASA, it wasn't ESA and it wasn't easy...
The on-board equipment was intended to be accurate to 1 meter, rather than 1 kilometer. Much more accurate.
A whole lot more than 10; read the Planetary Society's account of just what it took to get the data back:
o -t racking_0207.html
http://www.planetary.org/news/2005/huygens_radi
Plus, they didn't know that this would work beforehand.
Dear Lord: One of your creatures may be hurt tonight. Please let it be the other creature.
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?
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.
e /oct04/1004titan.html
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/publicfeatur
Sorry if this is a repeat. Slashdot's search 503-ed on me.
IIRC about half of the picures taken were relayed via the A channel and what we have seen is all B channel stuff only....Any chance of reconstructing those images from the ground-based recordings of the A channel, or is the signal so weak that all that can ever be deduced is the carrier frequency, not any data?
There was a long discussion about this on a prior slashdot story. My speculation is that because they appeared to use digital compression algorithms, recovery of the images is probably mostly a lost cause. Compressed images tend to be very sensative to signal gaps.
Missions decades ago didn't use compression (other than palette reduction), and sometimes you can see spots of noise where there were gaps. A non-compressed image will just have spots where the individual pixel was lost, but compressed images can lose an entire segment if even one pixel is bad.
But, I have not confirmed that compression was used on Huygens.
Table-ized A.I.
Perhaps you should RTFA, or perhaps even this article?.
1: The DWE consisted of two modules. One on Huygens, and one on Cassini. Without the activation of the Huygens module, we would have had no data for earth-based telescopes to detect.
2: The DWE carrier signal did double duty as a channel for image transmission. Not only did the receiver screw-up result in loss of DWE data, but it also resulted in the loss of 350 images as well.
3: Reception by Earth-based radio telescopes was uncertain at the time the DWE was designed. In addition, at the time the DWE was developed, it was thought that Earth-based radio telescopes would only be able to detect one axis of motion. The second axis of motion would have to come from the Cassini data.
Just to clarify, the "command" to turn "on" the oscillator for Channel A was not sent due to human error.
:)
Lager version at spacescience.ca
So that equates to no data sent to Earth from Cassini for that Channel which contains the wind data and half of the photos.
Channel B does not have a similar oscillator so it did not suffer from the same problem.
So my question is, what data did they get, (or could get potentially)?
Sounds like the photos will be lost because all they seem to have accomplished with the global radar conglomerate was a measurement of Huygens's Doppler shifting carrier wave signal.
This is probably not as accurate as the direct measurements but will give us a replay of the descent to within 1km thanks to some correlation to VLBI measurements taken on Earth also.
There is a heated debate between project teams going on in the background as to exactly where the probe landed.
So this data should do well to help pinpoint the location.
Because, I made up a collage, Titan's Huygens Collage
I'm interested in seeing more images. Knowing wind speeds is good data, but personally I'd much rather have more photos for my collage.