I haven't seen this before either. And it's a great compliment to the DISR descent movie referenced above - especially how it ties in the last few images taken during descent and post landing image to the landing video.

A decade later, and the surface science continues (an apparent fog bank is identified!):
http://www.planetary.org/blogs/guest-blogs...e-of-titan.html

Bouncing on Titan: Motion of the Huygens Probe in the Seconds After Landing

https://arxiv.org/abs/1702.00667

Please know that this is an older paper. I decided to put it on arXiv to make the work available for free. I consider it a poor man's open access.

Thanks for posting this. I hadn't heard of the notion that the lander may have tilted during the surface lifetime. It seems like, if so, the imaging should show a very clear signal to this effect even if the tilt was very subtle.

I've been looking at this recently (2015) narrated and improved video of the Huygens descent and landing. They pay good attention to detail with rendering of atmospheric colors, and haze/visibility. The view from the surface shows how the sun would look, a small pale red disk in the middle of a fairly uniformly lit sky.

https://www.youtube.com/watch?v=9L471ct7YDo

Inferring from this (and some published papers), it seems Saturn would be a little challenging to see from the surface with the naked eye. Perhaps a ghostly reddish image at night superimposed on the uniform scattered light background, if Saturn isn't too close to the horizon. Titan aerosol tau values are about 6.5, 8, and 11 in red, green, and blue wavelengths. Rayleigh scattering has some effect as well, more than on Earth.

I think I talked about this a bit in 'Lifting Titan's Veil'.... maybe with red-tinted sunglasses, and better yet, perhaps polarizing ones, you might see well enough to pick out a limb (remember Saturn will show phases, but only from the subsaturn hemisphere of Titan!)
I recall reading somewhere that the optical sensitivity of women typically extends to longer wavelengths than men (meaning the red/infrared distinction may be dependent on the individual!)

At 940nm - the near-infrared methane window most often used by Cassini's camera to observe Titan's surface, and the wavelength used by TV remotes, and accessibly by 'Nightshot' video cameras etc. the optical depth is only one or two. Since you probably don't want your eyeballs to freeze anyway, it would be easy to implement some near-IR goggles or a visor to go with the oxygen mask you'd need to enjoy the view

Glad this is talked about in your book. I was taking "naked eye" rather literally, though I agree red glasses would help a bit. I'm unsure how polarized the skylight would be with the multiple scattering going on. For daytime sightings I would pin some hope on when Saturn is near the sun (<6 degrees or so) and forward scattering in Saturn's atmosphere brightens the high phase angle crescent (with surface brightness >10 times the low phase value). It should also be located near the zenith. An artistic example I can find online that gets the general idea is here. The disk of Saturn subtends about 6 degrees.

Agreed. I'm also unsure about whether a Saturn crescent with high surface brightness (seen in the daytime sky) would be easier or not to see than a dimmer (per steradian) full-phase Saturn in Titan's night sky...

I've been waiting/hoping someone will set up a decent spherical-geometry Monte-Carlo scattering code to really understand the astronomy-on-Titan possibilities (which bear on navigation, btw)

I think the nighttime scenario would usually be quite a bit easier. The possible exception is if Saturn is within a couple of degrees of the sun and there isn't too much of a solar aureole. The sun's glare itself could be then be an issue - holding out your thumb would be in order.

It would indeed be nice to use the Monte Carlo method - I'm in the very early stages of assembling some code. I'm also seeing if my more approximate scattering model developed for Earth can be applied to Titan.

15 years after the event, what do we actually know about the root causes of the loss of Channel A. As far as I know, the results of the investigation announced at that time were never openly released.

Incredibly, this still seems to be one of the most detailed accounts of the incident available in the public domain, many questions remain unanswered:

http://emits.sso.esa.int/emits-doc/ESTEC/A...l-Functions.pdf

It's not a big mystery, it was just human error, no doubt exacerbated by the complex cross-organizational, international nature of the mission and the fact that the commanding was somewhat arcane and error-prone.

Still no explanation why a (seemingly simple) mistake was not discovered until it was to late. In general, I would say the human operator must be allowed to make mistakes. An intriguing detail given in the above document is the non-latching character of the "USO powered on" command which may played a critical factor in forming the error, however the brief document does not elaborate much on it. A description of the whole command-test pipeline and maybe workplace conditions would be interesting. But probably this has to wait until the 50th anniversary.

Don't hold your breath. "Success has a thousand parents but failure is an orphan." And they already documented the useful lessons learned.

A recently published ESA article on the cause of the Huygens landing rotation: Huygens landing spin mystery solved
Fernando

Yes, but Bobik is right, there should have been a more complete and open description of the circumstances and procedures to avoid similar occurrences in future (and IIRC David Southwood, ESA D-SCI at the time said in front of the cameras that the investigation would be published, but it never was). There are a couple of SpaceOPS papers by some of the relevant individuals 2005-2006, but these remarkably fail to mention the commanding error at all. One does note some useful background, setting the context for the missing command, but doesnt discuss the failure as such :

"The Probe Relay critical sequence only required 38 commands to set the proper spacecraft configuration and
enforce the required tracking attitude. However, in order to provide the necessary critical sequence infrastructure
and provide enforcement of the spacecraft state in response to a fault, 107 more commands were added. The
distinction of the Probe Relay critical sequence is its integration of changes to various fault protection algorithms to
achieve full autonomy and complete its objectives even in a fault scenario. The critical sequence was designed with
a “mark and rollback” logic that supported these objectives. This capability allowed the critical sequence to interact
with fault protection and adapt to the different hardware configurations and states deemed necessary by fault
protection."

(Allestad et al., Systems Overview of the Cassini-Huygens Probe Relay Critical Sequence, AIAA 2005-6388)


The guy whose job it was to assemble the PSA commands once told me it was 'headslap' moment, as soon as the telemetry started coming in, he knew what had gone wrong. And on the documentary 'Destination Titan', you can hear Robin Dutta-Roy of the Doppler Wind Experiment asking on the voicenet 'what time was the RUSO to be powered on', so the DWE team (hurt most by the failure) knew pretty quickly too.

As you note above, though, there were lots of interfaces and steps here. When there are singular events like this, it is not always possible to test things in the configuration they are going to be in. So it's easy for such things to be missed, which is why such failures should be documented for the benefit of all. At this point, there's no need for ESA to be bashful, no careers are at stake at this point, Huygens was a success and will always be considered such, warts and all.

Ralph