[X] My Assistant

[Vultur]

I was just thinking -- Titan has a very dense atmosphere and lower gravity than Earth, so it seems like parachutes could be very useful, and the Martian airbag/skycrane tricks wouldn't be necessary. Why aren't there plans for a Titan version of MER?

[Harkeppler]

Some ideas for introducing a Titan Rover:

Interestingly, a rover could be made of metals relatively weak on Earth: tin and lead which gained enought structural stability under the cold conditions, when steel and aluminium get glasslike brittle. Supraconductivity would also be a surplus when designing electronics for titan. Insulating parts not to be very cold is not such a problem: double-walled compartments are commonly used in deep temperature technics ("Dewar bottles") for storing fluid gases like nitrogen and work also in an opposite direction: an dewar-like vehicle could be retain over-zero-temperatures for weeks. An excellent thermal insulation would cause another problem: to get rid of thermic energy produced by the systems.

Running RTGs on Titan will not create a havoc if distance to fluids is kept. Maybe heat radiating fins should be large and placed well above the ground.

With an well designed camera it would be possible to make color photos (a SSI-like camera would need 0.5 sec to take a well illuminated picture). The strange constructed Huygens-camera should not be considered as a non-plus-ultra.

The fluids on Titan are hydrocarbons; so there is not problem with short circuits when getting wet. With a correction lens (for refractive index) a camera arm could even look under "water". Nozzles spraying gasous helium or hydrogen could be used for cleaning and drying the optics.

Earthly biochemical compounds like amino acids, sugars and fats are completly inactiv at Titanian temperatures, and mostly unsoluble in liquid methane and ethane. There are only a few classes of active molecules at this deep temperature. A primary goal would be to get and concentrate them for analyzing purposes, maybe with a high performance liquid chromatograph and a mass spectrometer.

[ugordan]

Supraconductivity would also be a surplus when designing electronics for titan.

How so?

With an well designed camera it would be possible to make color photos (a SSI-like camera would need 0.5 sec to take a well illuminated picture). The strange constructed Huygens-camera should not be considered as a non-plus-ultra.

I wasn't "strange", it's what they were able to do with the mass budget they had and the available bandwidth. Over and over again people don't realize how difficult it was to actually land something on Titan that needed to piggyback on one of the heaviest planetary spacecraft ever launched. Not to mention when the Huygens probe design actually started.

In any case, sending color imagers to Titan is less useful because the haze filters out a good portion of the solar spectrum, making everything look orange-yellow and constraining useful compositional analysis from local illumination. Unless you bring your own light source as Huygens did.

[Harkeppler]

I wasn't "strange", it's what they were able to do with the mass budget they had and the available bandwidth. Over and over again people don't realize how difficult it was to actually land something on Titan that needed to piggyback on one of the heaviest planetary spacecraft ever launched. Not to mention when the Huygens probe design actually started.

It was more than strange: bad optic, misaligned rotation vains at the vessel, funny resolution, grotesque data compression producing weird artifacts... Optical investigation should be the prime objective instead of riddling years around what not was seen. A crucial problem seems to be in most planetary missions that the deliberatly long plannning, organizing and redefining phases are run over by the technical progress.

I do not see any useful effect of a crummy imager at all. And the Huygens imager is one, that can be proven with the test images gotten during parachuting experiments and even with the photos showing the parking lot under that university building - it is difficult to recognize even the lampposts there.

Besides this, the Huygens camera has nothing to do with the Cassini main craft at all, nothing with flight operations and nothing with landing procedures.
It is a "development" made by several people influenced by these experts of a special German Max Planck Institute which is "famous" for constructing funny but not really functional exotics like the Giotto-Camera. By the way: Their last "progress" could be seen in form of the Rosetta NAC, which shut down during the Steins-encounter. Fascinating, like the Phoenix RAC which is unable to make color photos over a range of three feet due to the limited range of LEDs...

Instead of constructing bunches of not properly intergrated instruments with deginer´s flaws it would be necessary to come to a more comprehensive standard.

Interestingly, years before Cassini launches, someone has decided that the camera would not make it to the ground, so surface imaging was not a topic at all. Without any reason it was determined, that Titan has to be covered by oceans or mud. The Huygens camera sent around 130 identical frames from the surface which are not giving increasing detail after adding due to the coarse compression artifacts. With a small turnable mirror and double resolution, four to ten more useful photos would have been possible showing a partially Titan panorama - with the same Cassini mass and the same bandwith.

"If there would be elephants on Titan, the Huygens imager would not have seen them", as it was stated by a french newspaper, which writer seems not to be payed for that destinct remark.

Furthermore, color imagery is an interesting perspective at all, especially in that strange chemical environment. Which the argument "atmospherical absorption" any color planetary camera could be thrown away, but I am glad that the soviet scientist had put some simple constructed ones onto the Venera lander 13 and 14 at all.

[djellison]

With a small turnable mirror and double resolution, four to ten more useful photos would have been possible showing a partially Titan panorama - with the same Cassini mass and the same bandwith.

Wrong. When Huygens was launched the expected duration of relay from the surface was FOUR...repeat FOUR minutes. A mirror would have been extra mass. Double resolution wasn't possible with CCD's sensitive enough to do the job when the camera was designed - and would have halved quartered the number of images that could have been sent given the bandwidth available.

Sorry - you just do not understand the complexities of the engineering involved to make such bold, swiping criticism of

Incidentally - the camera on Huygens was an American instrument. Nothing to do with the NAC on Rosetta (so how or why you decided to make that connection I do not know) - and the reason the RAC has LED's on PHX is because that is what it needs to do its job.

I would very strongly urge you to not make further comment - as to be blunt - you don't know what you're talking about.

[mcaplinger]

Double resolution wasn't possible with CCD's sensitive enough to do the job when the camera was designed...

FWIW, the MSSS proposal for Huygens had considerably higher resolution than DISR. It would have used a custom framing CCD for the descent imaging below the cloud deck. The fact that DISR used one CCD for everything and fiber-optic bundles to feed light from different optics was pretty constraining.

That said, the post did have a lot of misconceptions. We certainly made no specific provisions for landed ops in our proposal, since even surviving the landing wasn't (IIRC) in the baseline.

...you don't know what you're talking about.

Since when has that been a constraint on this forum?

[ugordan]

the MSSS proposal for Huygens had considerably higher resolution than DISR.

How would the number of images returned compare to the DISR proposal, given the same bandwidth? What compression would have been used - wavelets or DCT? Would some "devious" methods have been used - such as performing flatfielding onboard before compression to ensure data bits are allocated on actual image details?

Last, but perhaps a touchy question, why was the DISR proposal selected?

[mcaplinger]

How would the number of images returned compare to the DISR proposal, given the same bandwidth?...
Last, but perhaps a touchy question, why was the DISR proposal selected?

I don't recall what the total number of bits was supposed to be in the AO, nor do I know what DISR proposed and what their actual data return looked like relative to their proposal. I do know that the number of bits ultimately returned was supposed to be 2x what it actually was because of the Cassini commanding screwup.

I think we could have figured out a way to return some better imagery (onboard autonomy to pick good images from bad could be part of it), perhaps at the cost of multispectral coverage, but obviously this is just idle speculation.

I have no insight into why one proposal was selected over another. If I had to guess, I would suspect our proposal didn't seem very technically mature and perhaps somewhat risky, given that our only other hardware effort at the time (MOC1; this was 1990) had yet to fly.