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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?
djellison
QUOTE (Vultur @ Sep 13 2008, 02:22 AM) *
Why aren't there plans for a Titan version of MER?


Landing on Titan is indeed comparatively easy. However - if you put an MER on Titan it would die, very very quickly. You've got a significant atmosphere which is far colder than Mars to deal with, thus need a much better insulated vehicle and a LOT of power for heaters etc. You also need a different power source, an RTG almost certainly. You could use some elements of the MER - but not the design per se. At that point, you're building something that looks more like MSL than MER. But a Titan rover wouldn't end up looking like MSL either I'd expect.

There isn't the money to do it. I'd love to see rovers everywhere. However - we've done one preliminary survey of Titan - we need a better survey, full panoramic imagery of a possible rover landing site, before we can contemplate sending a Rover up there.

The long answer is that ballooning is arguably a better, faster, cheaper way of getting around Titan.

Feasible? Yes. Sensible? Maybe? Financially possible right now? No.
PhilCo126
Even if You could operate a rover on Titan, the visibility below the cloud deck is probably very poor.
Even for a camera in a pod underneath a ballon the visibility would be poor I guess...
ugordan
There is no definitive cloud deck on Titan, the haze is omnipresent. While having to look through hundreds of km of it does impede visual instruments severely, it's not actually a thick fog as Huygens demonstrated. You can still see comfortably through several kilometers of it with slowly reducing contrast. A low altitude baloon would have no problem picking up the ground nor would a rover have difficulty seeing quite far out.
angel1801
Another thing too. Mars takes just over 24 hours (or one earth day) to rotate and we can use the already present Mars orbiters to keep in constant contact with the rovers. But Titan takes 16 earth days for a full rotation. This means for 8 days of a Titan rotation, the rover is out of sight from Earth. So for full 16 day coverage, we would need a something orbiting Titan to make sure we get full coverage.

And another thing too. The one way light time to Titan is about 84 minutes, compared to Mars with 14 minutes.
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
QUOTE (Harkeppler @ Sep 13 2008, 05:14 PM) *
Supraconductivity would also be a surplus when designing electronics for titan.

How so?

QUOTE (Harkeppler @ Sep 13 2008, 05:14 PM) *
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.
centsworth_II
QUOTE (PhilCo126 @ Sep 13 2008, 06:45 AM) *
Even if You could operate a rover on Titan, the visibility below the cloud deck is probably very poor.

The Huygens images were pretty good in ambient light, and that was such a small camera.
centsworth_II
QUOTE (ugordan @ Sep 13 2008, 10:53 AM) *
Unless you bring your own light source as Huygens did.

Non of the Huygens panorama images used the artificial light source which was aimed down and turned on near the surface. I don't think any of the images taken with that light were in focus, so they are not part of the usual Huygens image gallery seen. I don't know if they provided any useful spectroscopic data. (That's all just my recollection.)
ugordan
QUOTE (centsworth_II @ Sep 13 2008, 07:25 PM) *
Non of the Huygens panorama images used the artificial light source which was aimed down

I never said as much. I meant you need a light source if you wanted to do spectroscopy, which was the primary purpose of Huygens' lamp. My point is bringing a classic color imager (with filters wheels and all) is somewhat useless. As much as I like color images, having a panchromatic panoramic camera might be just as sufficient for a followup mission.
Harkeppler
QUOTE
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 deginerīs 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.

ugordan
Fascinating. You have just proven my point from the very segment you quoted with flying colors. AND you managed to sneak in a few snitty comments about Rosetta NAC and Phoenix RAC, well done!

It shows you have a clear understanding of engineering challenges involved in these instruments as I alluded to. I think I'll leave it at that.
TheChemist
Designing missions in retrospective, using other people's money, and risking other people's careers is easy, but not very constructive.
In 3008, when Titan will be a popular tourist destination, our descendants will take all the photos they want. laugh.gif
ilbasso
I'm not 100% sure about it being a popular tourist destination...with the hydrocarbons in the atmosphere and the cold temperatures, I think Earthlings could get a similar experience visiting parts of New Jersey in January.
ElkGroveDan
QUOTE (djellison @ Sep 13 2008, 12:08 AM) *
The long answer is that ballooning is arguably a better, faster, cheaper way of getting around Titan.


Doug is a big fan of balloons these days wink.gif
djellison
QUOTE (Harkeppler @ Sep 14 2008, 10:51 AM) *
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
QUOTE (djellison @ Sep 14 2008, 09:55 AM) *
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.
QUOTE
...you don't know what you're talking about.

Since when has that been a constraint on this forum? rolleyes.gif
ugordan
QUOTE (mcaplinger @ Sep 14 2008, 07:29 PM) *
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
QUOTE (ugordan @ Sep 14 2008, 10:37 AM) *
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.
JRehling
One seemingly zero-cost way to improve the DISR return would have been to have some subset of the post-landing imagery be uncompressed. I would qualify that "zero" with the reminder that any added *anything* you put into software carries some cost and risk. (As the failure to receive the other channel demonstrates.) But no one would doubt that having *any* full-resolution images from the surface would trump having dozens that are identical at sub-optimal resolution.

However, suggesting that a mirror with moving parts be added is another matter. I couldn't say how the pros and cons and risk balance, but it sure would involve risk of significant data loss if the moving parts failed.

Also, I doubt if the science return of a panorama would be equal to the "aesthetics" return. The cameras were after all quite close to the surface. Maybe there was a monolith in the opposite direction, but there's no reason to believe that there would have been anything unlike what was seen as it was. Not much chance of seeing into the middle distance.
lyford
QUOTE (ElkGroveDan @ Sep 14 2008, 07:46 AM) *
Doug is a big fan of balloons these days wink.gif

Balloon - Rover - It can be both!!!!!
Admittedly, I have a soft spot for this maybe Mars mission - but might be well repurposed for Titan if the uplink to Earth could be solved. That is if it won't stick in the goo....
David
QUOTE (lyford @ Sep 15 2008, 04:01 AM) *
That is if it won't stick in the goo....


One way to keep it from sticking in the goo would be to keep it out of the goo altogether -- I'm sure there's plenty of non-gooey terrain.

Of course, my preference is for a liquid-craft -- maybe a sailboat on one of the north polar lakes, or -- and this would be really cool if it could be done -- a riverboat, gliding down one of Titan's many channels (if you can find one that's continuously wet, that is).

Maybe one could combine both: a balloon tethered to a liquidcraft, acting as a sail and pulling the craft along behind it, while also carrying higher-altitude instruments.

The obvious objection is that the craft is likely to snag on something, leaving your balloon stationary and your craft useless... but one can dream!
lyford
QUOTE (David @ Sep 15 2008, 07:00 PM) *
... but one can dream!

I know - Titan for all it's oddity, feels more like a real* world of sci fi and fantasy. Immediately recognizable and yet very alien at the same time. The prospect of sailing, floating, roving Titan seems so fantastic but so easily pictured, with a great pale ringed Saturn filling the sky. It's hard to let engineering interfere with that imaginary vision!


* By this I mean no disrespect to the other fine planets, satellites, dwarves and bodies of our fair neighborhood. But as one raised on green dancing girls, wonderful, desiccated Mars is no longer a haven of sci fi fantasy daydreams and has entered the realm of the actual and hopelessly scientific. **

**By this I mean no disrespect to the fine science done by the Saturn Titan team. Plenty of real science there, I know. smile.gif

Greg Hullender
QUOTE (JRehling @ Sep 14 2008, 08:53 PM) *
But no one would doubt that having *any* full-resolution images from the surface would trump having dozens that are identical at sub-optimal resolution.

This might be another place where the EO-1 software would be applicable.

http://eo1.gsfc.nasa.gov/new/extended/sensorWeb/ase.html

You'd try to take perhaps 100x as many pictures as you could transmit, and let the software choose the 1% most interesting ones to send back.

--Greg
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