Titan Review article |
Titan Review article |
Dec 14 2007, 05:02 PM
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#1
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Member Group: Members Posts: 613 Joined: 23-February 07 From: Occasionally in Columbia, MD Member No.: 1764 |
This just out. Not earth-shattering, but colorful - maybe handy as an up-to-date
Titan intro http://www.jhuapl.edu/techdigest/td2702/lorenz.pdf |
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Dec 16 2007, 08:12 PM
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#2
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Member Group: Members Posts: 100 Joined: 30-November 05 From: Antibes, France Member No.: 594 |
I bought in 2004 "Lifting Titan's Veil".It's of course the reference for Titan and I will reread it very soon to compare with what we know now ( presented in Titan revealed).
I'm fascinated by the radar images of the lakes in your Titan review.Unfortunately, the radar images don't give any indication on the appearance of the liquid.Does it appear dark, orange, blue... from a human eye? Some dark and uniform patches located on the "white snow" of Iapetus made me think they were pools of hydrocarbons, similar to what we might find on Titan. Do you think that the idea is relevant? |
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Dec 17 2007, 01:37 PM
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#3
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Member Group: Members Posts: 613 Joined: 23-February 07 From: Occasionally in Columbia, MD Member No.: 1764 |
I'm fascinated by the radar images of the lakes in your Titan review.Unfortunately, the radar images don't give any indication on the appearance of the liquid.Does it appear dark, orange, blue... from a human eye? Some dark and uniform patches located on the "white snow" of Iapetus made me think they were pools of hydrocarbons, similar to what we might find on Titan. Do you think that the idea is relevant? Lakes - get asked this a lot. Dunno. Probably like one of those 'Random_City at night' postcards - black. Since the lakes are at the poles, its often nighttime. Sun and saturnshine is always low on the horizon, never high in the sky, and only red light filters down to the ground. If you brought your own white light with you, depends. Pure methane would look blueish - like Neptune - because of the methane absorptions in red. But if there is a lot of reddish tholin suspended in it, maybe brownish (wine-dark sea?). So mostly black White snow - even stuff like benzene (for example) at liquid nitrogen temperatures is white. I think maybe anthracene is yellow (maybe Juramike can explain how things get dark/colored?). Soot of course is black. I don't think we can rule out any of these of Titan (or Iapetus, for that matter..) |
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Dec 17 2007, 04:53 PM
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#4
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Member Group: Members Posts: 715 Joined: 22-April 05 Member No.: 351 |
Pure methane would look blueish - like Neptune - because of the methane absorptions in red. But if there is a lot of reddish tholin suspended in it, maybe brownish (wine-dark sea?). Ralph - In all the discussions of Titan missions, has anyone discussed putting a "lander" in the one of the lakes to study their composition? All - At the AGU conference, there was a poster proposing that the "land" area around the lakes might be a lot like the karst regions of Earth where the liquid has eroded the surface into dramatic shapes. It would be beautiful to see, but I can't imagine an engineering team ever agreeing that such an area would be safe to land in. ("What part of cliffs and unsafe don't you understand?...) -------------------- |
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Dec 17 2007, 06:46 PM
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#5
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Member Group: Members Posts: 723 Joined: 13-June 04 Member No.: 82 |
In all the discussions of Titan missions, has anyone discussed putting a "lander" in the one of the lakes to study their composition? I would love a "Pioneer Venus" style mission with at least five Huygens-style landers plus an orbiter, with each lander directly sampling one of the major terrain units: 1) the bright terrain as seen at Xanadu 2) the dark brown equatorial dune fields 3) the dark blue channel deposits 4) the very bright, possibly volcanism-related deposits as seen north of Hotei Arcus 5) the north-polar liquid hydrocarbon "oceans" (or Ontario Lacus, depending on approach geometry) If there were room in the budget for a balloon in addition to this, it would be great, but I have a feeling that even these five landers would be a budget-buster. Bill |
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Dec 18 2007, 12:22 AM
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#6
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Member Group: Members Posts: 613 Joined: 23-February 07 From: Occasionally in Columbia, MD Member No.: 1764 |
(we identified the same 5 terrain types as possible targets, btw)
Problem with this concept are (1) that this would mean having 5 sets of expensive chemical analysis payloads (2) that in a battery-limited lifetime of a few hours (remember you need to stay warm as well as functioning) it is difficult to be sure that you will acquire the surface sample you want (3) Huygens-style landing might not be viable on cryovolcanic terrain, or Xanadu (4) short-duration landers do not get long-term science like meteorology, seismology, magnetometry, changing illumination, rotation state determination I would love a "Pioneer Venus" style mission with at least five Huygens-style landers plus an orbiter, with each lander directly sampling one of the major terrain units:
1) the bright terrain as seen at Xanadu 2) the dark brown equatorial dune fields 3) the dark blue channel deposits 4) the very bright, possibly volcanism-related deposits as seen north of Hotei Arcus 5) the north-polar liquid hydrocarbon "oceans" (or Ontario Lacus, depending on approach geometry) If there were room in the budget for a balloon in addition to this, it would be great, but I have a feeling that even these five landers would be a budget-buster. Bill |
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Dec 18 2007, 12:58 AM
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#7
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Member Group: Members Posts: 723 Joined: 13-June 04 Member No.: 82 |
(we identified the same 5 terrain types as possible targets, btw) Problem with this concept are (1) that this would mean having 5 sets of expensive chemical analysis payloads (2) that in a battery-limited lifetime of a few hours (remember you need to stay warm as well as functioning) it is difficult to be sure that you will acquire the surface sample you want (3) Huygens-style landing might not be viable on cryovolcanic terrain, or Xanadu (4) short-duration landers do not get long-term science like meteorology, seismology, magnetometry, changing illumination, rotation state determination It sounds like the biggest problem would be the short lifetime of a battery-powered lander, combined with the limited power available and the lack of choice about where the lander touches the surface. Not to mention that the probe would be duplicated four or five times, and the same mass budget could presumably send a much more capable single payload. The other option would be some form of dirigible balloon, with ducted fan(?) for some degree of directional control, that mainly stays in the troposphere with occasional descents to the surface for samples. It would have to be powered by RTGs or perhaps a nuclear reactor, which should also allow enough power for a direct link to Earth, eliminating one link in the communication chain (although the bit rate may be higher if an orbiter can relay its transmissions). The orbiter would have to be the highest priority in my opinion, as it would provide at a reasonable cost considerably better radar and optical coverage than Cassini, as well as a possible telecom capability if there is budgetary room for a surface probe. Most of the (very valid) objections to the Huygens-style landers suggest that any surface/atmospheric probe must be nuclear-powered, as well as having airborn capability -- and indeed would spend almost all its Titan time well above the surface. This is discussed in far more detail in the OPAG reports. The combination of orbiter and dirigible balloon would be very expensive, though. This is one time that a collaboration with ESA and perhaps other space agencies would be helpful (if ITAR allows it). The additional administrative workload would be difficult, but I think that the increased mission capability would be worth it. Of course I am not the one who would have to shoulder the extra workload. Bill |
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Dec 18 2007, 05:05 PM
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#8
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Member Group: Members Posts: 715 Joined: 22-April 05 Member No.: 351 |
The other option would be some form of dirigible balloon, with ducted fan(?) for some degree of directional control, that mainly stays in the troposphere with occasional descents to the surface for samples. It would have to be powered by RTGs or perhaps a nuclear reactor, which should also allow enough power for a direct link to Earth, eliminating one link in the communication chain (although the bit rate may be higher if an orbiter can relay its transmissions). Leaving aside the question of power source, designing a system that can touch down repeatedly with a high probability of survival is really hard. Winds could easily blow you around at low altitudes. When you start your descent, you will be over point x, but as you descend the winds may take you to very dangerous point y, and you are too far away for real time control from Earth. I'm not an engineer, but it might be easier to have a balloon that drops small landers (although once they have to carry heavy instruments like a mass spectrometer, they may not be so small...) at interesting points. In a side conversation with Ralph L, he pointed out that there are many, many mission options. The hard part is to nail down the science goals and establish the budget. Once that is done, the engineers can apply their creativity. So send your checks to NASA and letters to Congress. -------------------- |
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Dec 18 2007, 10:09 PM
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#9
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Member Group: Members Posts: 688 Joined: 20-April 05 From: Sweden Member No.: 273 |
Leaving aside the question of power source, designing a system that can touch down repeatedly with a high probability of survival is really hard. Winds could easily blow you around at low altitudes. When you start your descent, you will be over point x, but as you descend the winds may take you to very dangerous point y, and you are too far away for real time control from Earth. I couldn't agree more. Landing a dirigible in any sort of wind is quite tricky even with a live crew, real time control and a landing team on the ground. Lowering an instrument package on a cable might be barely feasible in flat terrain. If the wind is reasonably steady and not too strong an autopilot could probably hold the dirigible more or less still. However if the probe got stuck the only option would be to cut the wire. |
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