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Posted by: Steffen Mar 25 2006, 05:28 PM

Which device made the Huygens probe spin underneath its satellite?
I read that's the way how 360° images were made during descent...

Posted by: centsworth_II Mar 25 2006, 05:39 PM

I believe the probe had fins attached that were to spin it as it fell through the atmosphere of Titan - like the seed pods of a maple tree twirl as they drop, but much more slowly. As far as I know, it is still a mystery why the probe ended up spining in the opposite direction that it was designed to. It was unexpectedly windy (gusty?) during the descent. Now to hear from some more expert than I...

By the way, the Huygens probe spun beneath its parachute, not a "satellite".

Posted by: BruceMoomaw Mar 25 2006, 10:11 PM

Yeah, it had small vanes on the outer edges of its lower surface, which can be clearly seen in the drawings. (This, I believe, was also the setup they used to make the Pioneer 13 Large Probe rotate in Venus' atmosphere.)

As to why it spun in the OPPOSITE direction: that's still a mystery. (Pre-launch photos show that they did manage to avoid the supreme humiliation of having installed the vanes backwards.) My own suspicion is that the swivel joint on the parachute line jammed, and the parachute itself was what spun in the opposite direction, dragging the probe with it.

And actually, you know, it rotated beneath both its parachute AND Cassini, which had some implications for maintaining the radio link properly.

Posted by: Decepticon Mar 26 2006, 04:00 AM

^That works with me.


I never heard of the radio link issue!? The link between Cassini and Huygens would stop and start?

Posted by: BruceMoomaw Mar 26 2006, 05:44 AM

They had to do some careful checking of the antenna lobe patterns on Huygens during its design to make sure that the probe's rotation (a crucial part of the DISR experiment) didn't interfere with its radio link to Cassini. That part they got completely right, even given the extent to which Huygens was violently tossed around by unexpected air turbulence in Titan's stratosphere.

Posted by: Richard Trigaux Mar 26 2006, 08:45 AM

Any object under a parachute rotates naturally. They just relied on this to have 360° images.

I never heard of fins. Anyway even with fins it is not a mystery that air movements tossed the probe to make it rotate the other way.

Posted by: BruceMoomaw Mar 26 2006, 11:02 AM

See page 15 of Lebreton's article on Huygens ( http://www.rssd.esa.int/SB/HUYGENS/docs/SP1177/lebreton.pdf ): "It is required that Huygens spins during the whole descent to provide the azimuth coverage needed by several sensors. The realtime spin information requirements are imposed by DISR and are very stringent for the final part of the descent for imaging the surface, in order to adapt the time delay between consecutive frames during the mosaic image-taking cycle. The spin is induced by a set of 36 vanes mounted on the bottom part of the foredome. The spin rate is measured by a set a system-provided accelerometers covering O-15 rpm with an accuracy of 0.1 rpm."

The same page shows two nice diagrams of the external appearance of Huygens, with the vanes clearly visible. Titan's winds alone should not have been capable of making the Probe rotate in the reverse direction -- unless something very unusual like a jammed chute-line swivel joint occurred.

Posted by: BruceMoomaw Mar 26 2006, 11:52 AM

That same diagram revealed something else that I hadn't paid proper attention to: the heated inlet for the GCMS is squarely in the center of the probe's slightly convex bottom -- which, given that Huygens did land in fairly soft mud (albeit with pebbles in it) makes it highly likely that the inlet (heated to fully 80 deg C) DID come into direct contact with Titan's surface material. Indeed, Raulin and Owen's 2002 "Space Science Reviews" piece ( http://www.nasa-ksc.org/outgoing/SSR/raulin.pdf ) says: "The GC-MS has a heated inlet tube that extends several mm beyond the probe’s outer skin. A landing in a fluffy drift of aerosols would therefore provide access to an unusually concentrated sample of the organic compounds that the atmosphere of Titan has produced during many hundreds of millions of years. Even a successful touchdown on water ice could provide useful information."

And Hasso Niemann's piece in the same issue ( http://www-personal.umich.edu/~atreya/Articles/P1997_The%20Gas%20Chromatograph.pdf ) says: "If the Probe settles into a deposit of aerosols, one needs to extrapolate the accumulated information from the descent measurements to interpret the data. This would offer an opportunity to determine the level of chemical complexity achieved by chemical synthesis in the atmosphere, as even rare aerosols may accumulate inmeasurable concentrations on the surface. Here the GCMS heated inlet will ensure that the more volatile components of such aerosols reach the instrument. Landing on exposed ice could still permit a measurement of H2O ice ‘bedrock’ and a search for condensed CO2, measurements of fundamental importance to an understanding of atmospheric evolution. A determination of D/H in H2O on the surface would be of great interest for comparison with atmospheric values in CH4 and other species. It is recognized, however, that this is the most challenging landing scenario, both for Probe survival and for a good interface between the gas inlet and the surface...

"The most probable landing position is expected to be upright, which is also optimum for the instrument. In case of a landing on a liquid surface, the heated inlet tube will be submerged in the liquid, which will rapidly evaporate in the inlet tube and the vapors will flow through the inlet lines."

OK. So the odds actually look pretty good that that very hot GCMS inlet tube did come into actual contact with Titan's surface, or at any rate came so close that it very dramatically heated the surface. What are the implications? Well, this makes it easier to explain how the GCMS detected benzene on the surface, despite the latter's very high boiling point (80 deg C, exactly the same temperature as the inlet). On the other hand, it makes it more interesting that Huygens apparently detected relatively modest amounts of other substances with tremendously lower boiling points which were expected to exist there in quite large amounts: methane, ethane, acetylene. (Even solid HCN -- which theory predicted to have accumulated there in fairly large amounts -- has a boiling point of only 26 deg C; but apparently they still haven't confirmed beyond doubt that Huygens detected it on the surface at all. And while Huygens did detect a fair amount of cyanogen there, its boiling point is only -20 deg C.)

So -- if I'm interpreting the raw graphs of the GCMS data at all correctly ( http://www.nature.com/nature/journal/v438/n7069/full/nature04122.html , Figure 1) -- the amounts of low-temperature volatiles on Titan's surface were much more modest than expected, but there was quite a bit of benzene there. Now, I'm not even remotely sure that I AM interpreting those GCMS graphs correctly -- if anyone out there knows more about the behavior of mass spectrometers than I do, I wish you'd take a look at them and report your own conclusions. Nevertheless, this is interesting -- especially since benzene is supposed to be one of the commonest polymers of acetylene, which was expected to exist in quite large amounts on the surface as frozen solid powder. Once again, I wonder if Titan's cryovolcanic activity isn't causing it to circulate the smog that lands at an incredibly slow rate on its surface down into Titan's interior, allowing those compounds to be exposed to the liquid water (or water/ammonia) down there and chemically modified before they are spat back up onto the surface. (In the "Nature" graphs, note all those intriguing little peaks over on the rightward part of the GCMS graphs implying the detection of some much heavier compounds on the surface.)

And, oh yeah, I can't resist annoying Alex further by reporting that while I was poking around in Google just now to find all this, I also stumbled across the fact that Prof. Erik Asphaug had reprinted my own lengthy description here of the ESA's post-landing Huygens press conference in toto to his grad students on his Solar System blog ( http://marsseminar.blogspot.com/ , Jan. 21 entry). So there: OTHER scientists appreciate me properly, Alex. Boy, will you be sorry some day you didn't treat me right. It almost makes up for that little three-orders-of-magnitude mistake I've just discovered that I made in calculating Enceladus' ice loss rate... (It also kind of makes up for the fact that during my own sojourn at UCSC three decades earlier, the only class I took remotely related to planetary science was an introductory geology course in which I got an extremely lousy grade.)

Posted by: BruceMoomaw Mar 26 2006, 01:44 PM

In this connection, one COSPAR abstract seems to say (although the phrasing is vague) that the DISR team MAY have come up with a model of Titanian surface composition that does match Huygens' puzzling near-IR spectra -- but, maddeningly, they don't say what it actually is:
http://www.cosis.net/abstracts/COSPAR2006/02830/COSPAR2006-A-02830.pdf

Posted by: PhilCo126 Mar 28 2006, 03:38 PM

Well, I'm still amazed how the Cassini-Huygens team managed to solve the issue with the frequency diffeence between the mothership and the probe ( Remember Cassini had to slow down in order to receive the Huygens data at a lower frequency ... O.K. there was another issue with chanels but they were happy to have the photos they received ! )
---O---
Saturn

Posted by: The Messenger Mar 28 2006, 03:56 PM

Nice essay, Bruce.

I tried to get a more expert opinion from a GCMS chemist, (Dr. Waffle), and his answer was basically your guess is as good as mine. The problem is that the GC separates the chemicals according to both their molecular size and functionality. It is easy to break down what-is-what if you know all the controlling parameters: column length, packing material, temperature at (sample, inlet port, transfer) pressure, exit times of known standards, – and on and on. So we are really at the mercy of the Huygens GCMS specialists to produce meaningful data.

We went the rounds a little on this on Jason’s blog, but I need to revisit the possibility that the heat shield separated later than expected: First, look at the Doppler – the delta V during the first 6 – 15 minutes was much, MUCH greater than expected, and whether this was due to shear winds or other unexpected forces is academic: The 8 meter parachute was sized to provide a sufficient ‘jerk’ that a small spring action would separate the heat shield. The high rate of acceleration was not predicted, and may have glued the heat shield in place - thus the unpredictable aerodynamics and backward rotation.

If you look at the axial accelerometers (Nature article, supplementary material), the acceleration went off- scale in one direction, and stayed there for several minutes. Again, regardless of the cause, could the force causing this acceleration have buttresses the heat shield against the probe up until the second parachute jerk? Perhaps it was jammed, or weakly glued by the glassy phenolics bleeding from the heat shield. Like a dog running blinded by a frizbee held in its face by the wind, Huygens may have been sniffing her own vapors during the early part of the descent.

This would explain the warmer-than-expected readings on the “exposed” thermocouple early in the descent, and the out-of-focus ‘round cratered disk’ seen in some of the earliest Huygens visual images – this would be the heat shield finally falling away shortly after the camera started clicking ~ 15 minutes into the descent.

This would put benzene and other phenolic derivatives from the heat shield decomposition in the general vicinity of the sample port. (There was supposed to be about a thirty second delay between when the heat shield seperated and the GCMS port was exposed.) However, this could only be the primary source of benzene if the benzene peak faded rapidly before the methane peak increased, which was after landing.

Posted by: djellison Mar 28 2006, 04:09 PM

Do you not think that if the descent profile were so very very far from nominal, they would have said so - if for no other reason than to say "look how different it was to what we expected, and it STILL worked great"

Anyway - the data is due into the PDS in a few months as I understand it - we can have fun then

Doug

Posted by: The Messenger Mar 28 2006, 05:05 PM

Thanks, I will look forward to that!

All oddball physics asside, benzene presents a curious issue: If it is in the atomosphere, it implies venting - a heating source well above the surface temperature of Titan. If it was only detected in the surface measurements, as Bruce explained, the heated inlet tube could have extracted it from the surface matrix. (In which case, it could even be a fairly major consituent of the surface.)

But in either of these scenarios, if we found benzene, we can write-off ammonia and more volatile organics, at least in the vicinty of where the Huygens probe landed. Otherwise, they should have shown up along with the benzene. Since Benzene is a known product during pyrolisis of heat shield materials, it would be good if this possible source of contamination can be completely eliminated.

Edited to add:

I missed the significance of this on first reading of Niemann et al:



The Vapor pressure of Benzene is pretty close to water (BP 80c), so if benzene was extracted from the surface, if ice water was also on the surface where Huygens landed, it should have been vaporized and detected by the GCMS as well.

The article clearly indicates Benzene was detected on the surface, but the article only contains the spectra averaged over the entire time the probe was on the surface. Did the benzene fraction curve behave like the methane concentration, or did it follow a different trend? Is the benzene curve consistent with a surface extraction? If it is, it is also reasonable to conclude there is no water ice directly beneath the GCMS inlet port!

Posted by: BruceMoomaw Mar 28 2006, 08:07 PM

"In principle, the water-ice value could have been measured directly by the GCMS after impact, if the end of the inlet tube had been in direct contact with surface ice. Evidently this was not the case, because the GCMS did not detect any H2O vaporized from the surface after probe impact."

You know, I totally missed that passage when I read Niemann. Gadfry. Now I'll have to rethink everything I said on the subject.

Posted by: The Messenger Mar 29 2006, 08:47 PM

I talked to Dr. Waffle again last night, about heat shield pyrolysis products – one of his specialties. Virtually all heat shields are fabricated with phenolic impregnated resins. Out-gassng of these resins starts at just above boiling, with the release of trapped water vapor and some light hydrocarbons. As the temperature increases, aliphatic phenols (tars) start to emerge, along with ‘a lot’ of gaseous hydrogen. As the temperature increases, the tars break down, releasing benzene and other, lighter derivatives, including acetylene and elemental carbon.

From the Nature articles, it is clear Huygens underwent unexpected accelerations and forces not yet fully characterized in the upper atmosphere. I have not seen any speculation that the heat shield did not properly detach (other than my own), but since benzene and acetylene are showing up where they are not expected, and there is quantitative disagreement between the Huygens’ isotope ratios in Titan’s atmosphere and ratio’s calculated from spectral analysis, I think the possibility of heat shield residue contamination of the GCMS port cannot be totally discounted.

Posted by: BruceMoomaw Mar 30 2006, 04:28 AM

Unconvincing. Take a look at those three mass spectral graphs from the "Nature" article, and it's clear that the concentration of benzene relative to nitrogen -- AND methane, AND argon-40 -- was much lower at 120-130 km altitude than at the surface, which is exactly the opposite of what you'd expect if the GCMS was sniffing whiffs of benzene given off by a still-attached heat shield. And the ratio of acetylene to those gases -- although it's harder to read that part of the graphs -- seems roughly the same at high altitudes as at low ones. Also note that one thing which DID precisely follow the expected pattern was Huygens' temperature/altitude profile of the atmosphere, which is hardly what one would expect if a heat shield was still attached that was hot enough to convey whiffs of its own vaporized ablatives to the Huygens instruments.

It seems to me, though, that -- given both our lack of expertise on this subject, and our lack of knowledge of the most recent conclusions of the Huygens researchers themslves -- at this point, when we speculate on what these graphs may say about Titan's surface composition, we're just spinning our wheels. It's time that I wrote directly to Niemann and/or Lorenz and asked them directly what THEIR current opinions are on the subject.

Posted by: The Messenger Mar 30 2006, 06:43 AM

I'm a little confused by the Temperature-at-altitude table; because in the early reports they were surprised by how how slowly one of the thermalcouples was cooling. On the other hand, in one of the presentations (Huygens one year later), the analysis seemed to indicate at least one thermalcouple did not heat up as much as expected during and after entry, so there are still a few question marks here.

I do agree, if the acetylene and benzene do not follow similar trends, the argument for contamination is very weak.

As for actual pictures of a 'late departure' of the heat shield, this could only be true if the raw images from the middle-to-the-end of page eleven; are the very first images showing detail taken; and not 'mud splotches' that occurred at the time of the landing.

http://esamultimedia.esa.int/docs/titanraw/file11a.html

Posted by: djellison Mar 30 2006, 09:25 AM

Are you refering to this one?
http://esamultimedia.esa.int/docs/titanraw/contrast/triplet.202a.jpg

Doug

Posted by: The Messenger Mar 31 2006, 05:54 AM

Yes - one of those images also shows up on page 9, there are three similar images on the left hand bottom of page 5. But the ones I think are least likely artifacts, are the round images that cross two different lenses at the first of page 4, and in the last frame of page three. These look like the shadows I would expect if the heat shield was falling away in a direction about midway between the ~45 deg and ~15 deg lenses. (The heat shield should have been long gone before the imaging sequence began.)

http://esamultimedia.esa.int/docs/titanraw/file4a.html

http://esamultimedia.esa.int/docs/titanraw/file3a.html

None of this is material, if the timing is such that these frames are known to be taken after the landing - they could be anything from frost, to a parachute to the 'mooning Titanian' mentioned on other websites

Posted by: BruceMoomaw Mar 31 2006, 07:46 AM

More to the point, if the heat shield had broken away just before landing, Huygens would no doubt have swung like crazy from its parachute during the release -- but its attitude data before landing indicated that, after it got below the gusts of the stratosphere, it retained great stability throughout landing.

Posted by: Big_Gazza Mar 31 2006, 11:00 AM

These sections of Huygens descent imaging triads (from the near-vertical camera) look like a droplet in the process of settling under gravity and draining away. Could it be either moisture (liquid methane) from the surface thrown up from the probes impact, or maybe condensation on the inside of the lens caused by cooling effect of low ambient temperature?

If the former, surely this proves that liquid does indeed lie just under the surface on the "dry lakebeds".

I'm sure these images have caused debate before, but I can't find mention anywhere.



P.S I've looked long and hard for anything that looks like an aquatic lifeform gasping for its life as its moisture drains away, but no luck i'm afraid!!

Posted by: edstrick Mar 31 2006, 11:49 AM

Big Gazza: "I'm sure these images have caused debate before, but I can't find mention anywhere. "

I'm pretty sure those images are highly out-of-focus data taken after landing.

The lower-left portion of the image is the out of focus surface. The upper right portion of the image expands from frame to frame and appears to show the structure of the fiber-optic bundle that routed the image from the focal plane of the downward looking lens to the CCD. It is entirely confined to the brightest part of each frame, and I think is the negative image of a flat-field calibration frame subtracted from the raw data. Where the raw data is within the dynamic range of the camera, the texture of the fiber-optic bundle in the raw data and in the calibration data cancel out. The brightest portions of the image appear to have been saturated in the raw data. There, the fiber-optic texture is not present and in the decalibrated image, the texture is put into what should be featureless saturated data.

Posted by: djellison Mar 31 2006, 12:02 PM

Just throwing this one into the mix...

Did the lamp start to fade before link-loss with Cassini, and thus could changes be as a result of that as well.

Doug

Posted by: edstrick Mar 31 2006, 12:27 PM

Assuming my hypothesis is correct. the image BRIGHTENED with time, perhaps something was evaporating off of the light.. who knows?.

The horizon-looking view shows some "odd" variations in image properties during the landed period, as does the intermediate angle view, as though there were variations in image-taking parameters such as camera gain and offset stages as well as possible light-brightness variations.

Until we have a complete set of images, time ordered, with full image engineering parameters and spacecraft attitude/sun-orientation parameters, it's really hard to tell what's going on.. especially in the high-altitude images.

Posted by: The Messenger Mar 31 2006, 08:52 PM

Bruce, that is my point. The attitude data show a baby nursing for the last hour-and-a-half of the descent, but the images clearly show Huygens reeling like a drunken sailor - Notice how the viewing angle of the circular feature (Pages 24-27) rotates ~50 degrees in azimuth, and moves from lens to lens, and this is clearly near the end of the descent. You can't tip the platform that much, and show nothing, naughta, on the accelerometers!

http://esamultimedia.esa.int/docs/titanraw/file24a.html
http://esamultimedia.esa.int/docs/titanraw/file25a.html
http://esamultimedia.esa.int/docs/titanraw/file26a.html

Larry Soderblom commented about this in an early Planetary Society article, but I can't pin it down. (The problem with Emily's prolific writing is my failure to build a useful index, seperating the science from the contests.)

This article does talk about Huygens change in direction near the surface:

http://www.nature.com/nature/journal/v438/n7069/full/nature04126.html;jsessionid=4B6AD1131C8A8E7D22AA41F084DD3D47

I have yet to see an accelerometer that does not show a change in direction as a change in accleration...except near the surface of Titan!

Posted by: djellison Mar 31 2006, 08:58 PM

We don't know which order those images go on. Ed's right - we need to have them in the right order to try and make a call on that.

Doug

Posted by: BruceMoomaw Apr 1 2006, 09:28 AM

It was instantly clear from looking at the photos as originally published on the ESA's Huygens image website that the loss of Channel A, and therefore of half of the returned images, had totally scrambled the order in which the images were printed, instead of their forming the nicely arranged triads originally planned. Therefore the fact that the apparent viewfield keeps suddenly jumping around for each of the three different cameras means exactly nothing -- indeed, you'll note that for each of the 3 cameras, a lot of the printed images are actually duplicated from one triad to the next.

As for the failure of the accelerometers to dramatically show that final change in descent direction, one would hardly expect them to -- the article makes it plain that it stretched over the last 15 minutes of descent and involved wind speeds of only 0.3 to 1 meter per second; that is, extremely gentle accelerations.

Posted by: The Messenger Apr 1 2006, 09:42 PM

We thought this might be the parachute, being blown or wrapped about the imaging system after the landing, but this is a better explanation.

From the articles they have written, the ESA seems to have a good handle on the imaging sequence. I wish they would clarify this for us. Even so, there are two features - the "arrow" and the 'round kiva' that provide unambiguous evidence that the asimuth of the platform was changing significantly. The probe had to be bouncing or swinging, either of which should have been recorfed by the accelerometers.

Let me put things in prospective a little. While I was pouring over the Huygens data, my wife, who is a detail artist, was assembling mosiacs from the images, ala Rene Pascal. She kept saying, "Look at this, these are images of the heat shield."

I kept nodding my head but not really paying attention, because I knew they could not be: The heat shield was long-gone before the images were recorded. But she didn't know that, and eventually I had to agree with her analysis, especially after I saw the Doppler indicating there was much more acceleration during the first twenty minutes of the descent than expected.

There was a light spring that was supposed to push the heat shield away as the parachute tugged at the other other end of the probe. The Doppler data indicates that the probe continued to accelerate after the parachute deployed, which would have kept an effective load on the bottom of the probe, holding the heat shield in place. The heat shield falling away as the images were taken, explains a lot of otherwise very weird images.

Posted by: BruceMoomaw Apr 2 2006, 05:25 AM

Whoa, horsey. What could have rammed the probe downwards fast enough for acceleration to hold the heat shield in place? The only possibility would be an EXTREMELY powerful downdraft -- and in that case, its radar altimeter would have showed it dropping very dramatically in altitude for a substantial period after parachute deployment, which it doesn't. Thus any such downdraft must have lasted, at most a few seconds, in which case it's totally irrelevant to Huygens' lower-atmospheric measurements and photos. Where did you hear about this "Doppler data"?

Posted by: djellison Apr 2 2006, 11:20 AM

You don't know the order of the images - so you don't know what the evidence is. You're so desperate to find an out-of-the-ordinary situation where ever possible that you're jumping to conclusions.I don't see a single image that is clearly the heatshield - not a single one. At best there is a "it might be"

How about, before jumping to such extraordinary conclusions that are so off-nominal that they WOULD have said something about it, we wait for the PDS release of the imaging, accelerometer and other data this summer? Then we can look at the best possible quality of images, in the right order, combined with accelerometer data and have a sensible, valid debate about this? Until then, it's nothing more than idle speculation. There is nothing that is unambiguous yet.

Doug

Posted by: Bob Shaw Apr 2 2006, 12:00 PM

Doug:

There *is* unambiguous evidence that the released images are strangely disordered, though!

As ever, ESA's outreach is without peer. I hope.

Bob Shaw

Posted by: ugordan Apr 2 2006, 01:45 PM

You do realize that the raws were the responsibility of the DISR instrument team. Which was U.S. built, IIRC. Any information or lack of it is the responsibility of the instrument team and not ESA as such. There were mentions that the scrambled order of images arose because only half of the expected images were returned, but apparently no one ever bothered to fix the issue on the raw site.

This ESA bashing business is getting really, really old already. Whining about ESA's PR here certainly won't do anything about it.

Posted by: Bob Shaw Apr 2 2006, 02:25 PM

Gordan:

Whining? Anything but. More of a screaming noise, really, with a few grating moans thrown in when I it all gets too much. Or, rather, too little!

As for the order of the images, etc, look elsewhere on this site for discussions regarding MER camera pointing, Cassini images, etc - the uncalibrated images contain sufficient information to allow all sorts of games to be played, and the data to do that is produced on the fly, day in and day out. ESA can't even ensure that a one-off package of a few hundred small images is archived in a meaningful way!

Still, the ESA approach does have a good side, as it demonstrates just how well the US does it!


Bob Shaw

Posted by: ugordan Apr 2 2006, 02:49 PM

That's because the planners knew at the time what their cameras would be pointing at! Cassini is 3-axis stabilized and the precise (more or less) pointing can be assumed from the predicted spice kernels themselves. I'm sure the same goes for MER cameras. Huygens had no reference attitude or pointing knowledge so you can't expect the same amount of data. If you want more complete data sets, I really suggest waiting for the official PDS release, they're bound to contain much more engineering and metadata. Again, it's not ESA who is responsible for preparing images for archiving, it's the instrument's team. Which, ironically is located in U.S. of which you have so high an opinion obviously.

As for the lack of info in the original raw image release on ESA's site -- that could be attributed to the desire to release them as soon as possible to the general public.

You'd think that alone merits gratitude, but some folks are never satisfied, I guess.

Posted by: Bob Shaw Apr 2 2006, 02:55 PM

Ah, right, Ted. That'd be the same guys that run the MEX outreach, and who so generously distribute the SMART-1 data? Maybe it's because the spacecraft are so far away that the quantity of images seems so, well, small...

A cup of tea, Mrs Doyle?

Bob Shaw

Posted by: djellison Apr 2 2006, 03:26 PM

We're not after the sun - we just want to know the order the images were taken in. That's all.


Doug

Posted by: BruceMoomaw Apr 2 2006, 07:45 PM

While it's certainly permissible that we don't know the horizontal azimuth in which the photos were taken -- given that the probe's Sun sensor went completely on the fritz, first due to the wild rocking during descent and later due to the fact that the sensor got colder than expected -- we DO need a set of DISR images (raw or otherwise) which properly displays the sequence in which those photos that were actually returned from the three different cameras were taken.

That is: in those cases in which we didn't get back 1 or 2 of the three images from a single three-camera triad (which is most of them), we need simple blank spaces in those frames for that particular triad, rather than duplicates of photos taken by that same camera from the previous triad, which is confusing as all hell. ESA (or the DISR team) CAN be blamed for that. (It would also be nice if we got a report on the altitude at which each returned image was taken -- and we do have that data, thanks to both the radar altimeter and the air pressure sensor.)

Meantime it looks like I'll have to write to Tomasko, too, to enquire whether there really IS any evidence whatsoever that the heat shield was imaged falling away. I will, however, be very, very surprised if the answer is "yes". I will also be surprised if he gives the slightest credence to the idea that it may have gotten hung up on the probe for any significant time. (I believe I mentioned some time back that he's already told me that those curious optically distorted circular regions on a lot of the images -- which I at first thought might be drops of liquid methane on the camera window -- are actually the result of slight temperature distortions in different parts of the fiber-optic cables leading from the lenses to the CCD, and that they were expected in advance. I suspect that "Messenger's" peculiar circular black spots on a few of the frames are the same thing.) Once again: without actual further testimony from the scientists as to what they believe, all these speculations of ours are just spinning our wheels.

Posted by: The Messenger Apr 3 2006, 05:32 AM

Agreed - Unless Bruce can coax definitive information from the PIs before then.

I don't mind posting ideas that can be refuted with evidence, and it just might happen that the PI's will say, 'you know, we never even though of that possibility', and they will then go through the evidence and determine what can and cannot be ruled out. Here are some of the data I think must be definitive:

1) Time-Stamped ground radar data - there should be two channels - these were offset about six minutes on the times that the data was transmitted, (just in case part of the transmission was garbled), and both sets of radar data were transmitted on both A & B Channels.

2) VLA trianglulation data (constrains Huygens motion in lateral planes, limiting two more degrees of freedom.)

3) Time stamps on the Raw images files (It is possible this does not exist, but the best ESA estimates would be helpful.)

4) Time Stamped sonar data - I haven't seen any plots of this, to date - but they would help clarify Huygens movement near the ground.


Let's look at what we have in July

Posted by: djellison Apr 3 2006, 06:34 AM

Point 1 is mute - channel A was lost. (and it was a few seconds, not six minutes - and it was the SAME data being sent, just X seconds apart, so your point isn't valid anyway)


Doug

Posted by: BruceMoomaw Apr 3 2006, 01:24 PM

We got all the radar data (which started at 45 km altitude) even without Channel A. Except for the extremely data-intensive images (without which Huygens' bit rate could have been cut by a factor of 10), all the data was entirely duplicated on both channels, except for a few of the very high-speed surface VNIR spectra obtained just before landing.

We also have good already-published sonar data on Huygens' descent rate during its last 90 meters -- and it shows a nice, steady descent, except for one brief jump of about 2 meters that is thought to be due to its drifting horizontally over a very small bluff.

Really, if any extraordinary jumping around such as you posit had occurred, it would have been mentioned by at leaat one experimenter -- and almost certainly more than one. I've just been going again over the published results from the ASI, DISR, SSP and DWE experimenters -- and not one mentions any such extraordinary phenomena as you mention occurring at ANY altitude. Figure 5 of Lebreton's "Nature" article -- http://www.iwf.oeaw.ac.at/files/lebreton_et_al_2005a.pdf -- shows a graph of Huygens' altitude and descent rate over time as calculated by all onboard instruments, and there are no signs of it ever dropping fast enough to keep the heat shield pinned onto it for more than a few seconds, even given its violent jerking around due to wind turbulence under the big main chute between 145 and 115 km altitude. After that it cut the big chute loose and descended under the smaller stabilizer chute, with the result that its jerking from the turbulence immediately and drastically dropped, and disappeared completely under 60 km altitude -- after which it descended very smoothly all the way to the surface. Fulchignoni's HASI article -- including the data from the accelerometers -- is at http://www.iwf.oeaw.ac.at/files/fulchignoni_et_al_2005a.pdf and makes no mention of any such peculiarities.

Your obsessive pursuit ot this idea is starting to remind me of Captain Ahab, and we all know what happened to HIM.