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AVIATR - Titan Airplane Mission Concept, Proposed unmanned aerial exploration of Titan
djellison
post Jun 23 2010, 06:27 PM
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algorimancer
post Jun 23 2010, 08:18 PM
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Doug, my intent wasn't to suggest 30mm/pixel routinely -- as I parenthesized, I suggested this might be associated with diving to lower altitude over targets of interest. I'm very aware that it is ludicrous to attempt this (or even 30 cm/pixel) for the entire surface of Titan. Essentially what I'm getting at is that I would like to see lander-like resolution for select spots of interest.
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Jason W Barnes
post Jun 28 2010, 03:51 AM
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QUOTE (algorimancer @ Jun 23 2010, 06:30 AM) *
the 30 cm/pixel maximum resolution of the surface is on par with what I would expect from an orbiter, not an aircraft. I'd be reasonably happy with 3 mm per pixel (presumably associated with occasional low passes over targets of interest),


Hi -- this is Jason Barnes. I'm proposing AVIATR as Principal Investigator. I appreciate the attention to AVIATR around here -- keep up the comments!

While 30cm/pixel is what HiRISE is getting at Mars, you're not ever going to get that from an orbiter at Titan. Here's why. Because Mars' atmosphere is so thin, and because its gravity is relatively high, you can orbit Mars at just 150 km altitude safely to take pictures. In contrast, Titan's atmosphere is super-thick and its gravity only 1/7 that of the Earth -- this means that if you're orbiting Titan, you need to be orbiting at 1500 km instead of 150 km. That's a degradation of a factor of 10 in spatial resolution. In addition, you're at 10AU from the Sun so you'd need to have a primary mirror 6 times the diameter of the equivalent for Mars, even with the lower resolution. Now take into account that HiRISE at Titan would see nothing but haze. You'll need to go out to 5 microns, where the atmosphere is nearly transparent, to do as well at Titan. But the Sun is much dimmer at 5-microns than it is in the visible. And this would mean super-cooled optics, and an infrared detection system.

The bottom line is that to do the equivalent of HiRISE at Titan would require something like a 10-meter JWST sent out to Saturn and burned into orbit around Titan. Not going to happen. Even TSSM was baselining 50-meters-per-pixel global imaging for the orbiter.

Taking high-resolution imagery for Titan's surface makes sense from an aerial platform. You can use all of that pesky air to your advantage, instead of fighting it with a giant orbiter. AVIATR would have 100 times better resolution than the TSSM orbiter. Resolution isn't everything, though, and we're going to great lengths in order to gather context imaging in order to be able to interpret our high-resolution postage stamps, too.

- Jason W. Barnes
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Jason W Barnes
post Jun 28 2010, 04:07 AM
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QUOTE (algorimancer @ Jun 23 2010, 06:30 AM) *
I'm really bothered by the very low (2 Gb) projected data return. This just doesn't sound like a lot of return for a billion dollar investment.


That should be 2 gigabytes (GB) and not 2 gigabits as written.

While AVIATR certainly is not going to be like MRO blasting back terabytes and terabytes of data, let me take this opportunity to suggest that data is not knowledge. Put another way, more bits does not always mean more science.

At Mars there's been 40 years of exploration. In order to make new scientific discoveries from a orbiter taking pictures, you need to do more and better than the missions that have gone before you. Because HiRISE is following on a very capable, very successful imager on MGS, it needed to do better in order be able to do things that MOC was unable to do. In the planetary exploration business, the general rule of thumb is that you need to do about 10 times better than the previous mission in order to be compelling enough to fly. HiRISE's pixel scale is 3 times better than MOC, its swath width at least 5 times wider, and it can send back more images due to the greater bandwidth available on MRO. Hence it was deemed a compelling investigation.

Cassini's RADAR has a best pixel scale of about 300 meters per pixel. Since pixel scale is not resolution, the actual resolution of the RADAR images is more like 750 - 1000 meters due to inherent speckle noise in the RADAR data. The best VIMS data are 250 meters per pixel, but those noodles are only 13 pixels across. AVIATR would do 1000 times better than these in terms of spatial resolution.

A better comparison for AVIATR would be Huygens. Huygens returned mosaics from around its landing site of varying resolution. Obviously the picture from the surface had spatial resolution that we can't match from an airplane! But our image mosaics from sites of interest will resemble Huygens', but with better control, higher spatial resolution where desired, and better signal-to-noise since we're imaging in the infrared.

If you think that 2GB is too little for a mission, then would you fly a mission that would return a total of just 60 MB of data? That's all that we got from Huygens. AVIATR would return 30 times the total data that we got from from Huygens. The reason that 2GB is enough isn't because of the quantity of data -- its that we'll be returning images that can't be obtained any other way. AVIATR will have a huge science and exploration impact because we're looking where nobody's looked before.

It's not the number of bits that you have. Its how you use them wink.gif

- Jason W. Barnes
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Jason W Barnes
post Jun 28 2010, 04:23 AM
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QUOTE (djellison @ Jun 23 2010, 09:16 AM) *
If we're going to go back to Titan, I don't think AVIATR is the way to do it. The way to do it is with TSSM, so you can have the montgolfière + an orbiter for relay. You're still not going to get anywhere near your requirements. But you've going to get a lot more data, that's for sure.


I'd love to have a $4 Billion dollar Titan mission! But unfortunately, TSSM is dead. We're going to Europa instead.

The question now becomes: do we wait and hold our breath demanding a new $4 Billion Titan mission, or do we explore piecemeal instead of all at once? Even if Europa flies on time, and that's a big if, a future Titan flagship wouldn't get a new start until after EJSM launches. That's in 2020. So say we get a new start in 2020. And we take 10 years building before we launch, too. Then we launch in 2030. We have a 7-year, Cassini-like cruise, say. Now it's 2037, and we're finally back at Titan with a flagship, if everything goes perfectly. The flagship has a 4-year nominal mission, say. Without any extended mission, it would end in 2041.

Who among us will still be alive then, and not in a nursing home? I'm pretty young as far as these things go, and I'd be 64 then if everything went like that.

Instead I suggest that we take another approach. The Mars Exploration Program was implemented after Mars Observer blew up in 1993, and they realized that they could put together a more compelling scientific program by flying a small mission every 26 months rather than a giant mission every 20 years. This approach has been so successful that today more planetary dollars are spent at Mars than for any other target, by far. When you stop to think about it, this is pretty amazing. As recently as the mid-'90s it was not clear that Mars would become the focus of the American planetary program. The smaller, more frequent Mars missions keep the scientific community interested, have less programmatic risk, and allow follow-ups on previous discoveries in a human lifetime. They built an amazing program. Then they pissed it all away with MSL. But I digress.

We should be exploring Titan the same way as we used to explore Mars. One reason to do this is that we can. Numerous mission concept studies have shown that you can't get anything even into orbit around Europa for less than $1B. By the time that you get into orbit around Europa, the radiation will fry you in 6 months. This is why EJSM is going to cost $3B and only live for 6 months -- it's inherent in the physics of getting to Europa and doing science there.

In contrast Titan is easy to get to and explore. AVIATR is going to just fly straight into Titan's atmosphere without any engine burns at all. Just like Mars Pathfinder, or Mars Phoenix, or the MER rovers. Moreover Titan's atmosphere is so light and fluffy that we'll have very low heat loads and accelerations on entry -- 5 times easier than the easiest Mars entry. This is why it's possible to get to Titan on a Discovery budget.

If we launch a Discovery or New Frontiers class Titan mission every 5 years or so, we'll be in a great position to do amazing and sustainable science, on a budget that might actually get approved, and on a timescale over which we'll still be alive to care!

- Jason W. Barnes
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jekbradbury
post Jun 28 2010, 02:59 PM
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It's certainly a shame the mass spectrometer can't be included (Mike's got me hooked on Titan chemistry) but this mission, if it can stand up to its objective of "flagship-class science with a Discovery-class cost", will revolutionize our understanding of one of the most interesting destinations in the solar system. I can't wait.
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algorimancer
post Jun 28 2010, 05:45 PM
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QUOTE (Jason W Barnes @ Jun 27 2010, 10:51 PM) *
While 30cm/pixel is what HiRISE is getting at Mars, you're not ever going to get that from an orbiter at Titan.
...
Taking high-resolution imagery for Titan's surface makes sense from an aerial platform.

My original post seems to have stirred a lot of discussion, and apparently it could have been more clearly written, as it seems to have spurred some misconceptions and overreactions. For the record, I am overall very impressed and even excited about the AVIATR proposal, but my perspective on its capabilities are shaded by experience with MER and MRO. I do realize that this is a small mission to a place orders of magnitude more remote than Mars. My fantasy mission would be something like AVIATR that lands periodically to provide both broad overview and local focus.

My critique of "30cm/pixel" was in the context of seeking a bit of that local focus which a landed vehicle would provide. Essentially I'm advocating that, for particularly interesting targets, that the aircraft fly closer to the ground such that millimeter-scale imagery can be acquired. This might be just a few times over the course of the mission, once the topography is better understood so as to avoid accidents, and would be the equivalent of sending multiple landed vehicles -- very cost-effective. Worst case, if engineering and environment provide a fundamental limit on how low the vehicle can fly and continue flying, this might be a single descent near the end of the mission. Beyond this, I'm really quite happy with 30cm/pixel -- this has worked beautifully with MRO -- but the benefit of an aircraft versus an orbiter is that an aircraft has the option to maneuver in altitude without much difficulty. Oh, I definitely agree that an aircraft is optimal for Titan, while an orbiter would border on a waste of time (possibly excepting an imaging radar mission).

The 2 GB limitation is less of an issue to me, but I feel that with a bit of creativity it is not out of the question that this might be expanded by a factor of 10. Potentially, if Cassini is still functioning, it might act as a local relay. Does AVIATR use a directional antenna? If not, might the dorsal surface be contoured to function as one, even perhaps only intermittently when the flight orientation is congruent with transmission to Earth, thus allowing higher rater transmission on those occasions? I realize that there would be a compromise between optimizing a surface for aerodynamics and as a directional antenna, but the low gravity and high density of Titan's atmosphere would seem to permit a fair amount of flexibility in this regard.

Overall, I would be ecstatic to see AVIATR fly as currently designed -- to me, Titan is in the top 3 of interesting places to visit in the solar system, and I've been itching to see another dedicated mission ever since those tantalizing images from Huygens.

Finally, I very much appreciate your taking the time and interest to discuss the mission here. I work in orthopedic research, and involvement with the public -- even educated semi-pro amateurs -- just doesn't happen in that world, so I don't have to deal with backseat drivers second guessing my research designs.
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Jason W Barnes
post Jun 29 2010, 10:15 PM
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QUOTE (jekbradbury @ Jun 28 2010, 07:59 AM) *
It's certainly a shame the mass spectrometer can't be included (Mike's got me hooked on Titan chemistry)


I guess that I don't consider it a shame not to have a mass spec! While the science from a mass spectrometer would be awesome, there's no need to have one on an airplane. In order to do better than Huygens you would need a high-quality, ultra-high-mass-resolution spectrometer. This would be heavy. Remember that we can only fly 10-14kg of instruments. Because the trace gas abundances should be the same all over Titan, there would seem to be no need for the mobility of an airplane. If trace gas measurements are your mission, then you should send an atmospheric probe or a lander, not an airplane (or a balloon for that matter).

- Jason
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Juramike
post Jun 30 2010, 04:54 PM
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AVIATR image posted in Planetaria blog:

http://web.me.com/planetaria/planetaria/bl..._for_Titan.html


--------------------
Some higher resolution images available at my photostream: http://www.flickr.com/photos/31678681@N07/
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Drkskywxlt
post Jun 30 2010, 05:35 PM
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Jason (or anybody in the know) --

What is the expected mission duration? Are you able to target any location on Titan? If so, do you have a particular target in mind? Is a soft landing (with a short surface operation) a possibility as the mission ends?
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Jason W Barnes
post Jul 1 2010, 08:27 PM
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QUOTE (Drkskywxlt @ Jun 30 2010, 10:35 AM) *
Jason (or anybody in the know) --

What is the expected mission duration? Are you able to target any location on Titan? If so, do you have a particular target in mind? Is a soft landing (with a short surface operation) a possibility as the mission ends?


Our nominal mission (right now anyway) is 1-year. Since we're flying the whole year, and we can't stop, we can and will go anywhere and everywhere on Titan: dunes, mountains, channels, Xanadu, lakes, you name it.

The problem with a surface mission is thermal. We rely on the cold air that we're flying through to keep the ASRGs cooled. Once we land we lose that cooling. We do have an end-of-mission plan whereby we land, but we're not designing to be able to survive and/or do science from the surface. Note that Huygens wasn't designed to survive landing, either, though, and it did fine! Titan's atmosphere is thick enough that the speed that we're flying at is very similar to the speed of Huygens when it landed.

- Jason
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Jason W Barnes
post Jul 9 2010, 08:30 AM
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Another point of comparison for missions' data return: Mars Pathfinder returned 2.6 gigabits, or 325 megabytes of data total, near as I can tell. It was also communicating direct-to-Earth.

- Jason
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rlorenz
post Jul 11 2010, 02:45 PM
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QUOTE (Jason W Barnes @ Jun 27 2010, 11:07 PM) *
Cassini's RADAR has a best pixel scale of about 300 meters per pixel. Since pixel scale is not resolution, the actual resolution of the RADAR images is more like 750 - 1000 meters due to inherent speckle noise in the RADAR data. The best VIMS data are 250 meters per pixel, but those noodles are only 13 pixels across. AVIATR would do 1000 times better than these in terms of spatial resolution.


Hoi! mad.gif Misrepresentations like that will get you kicked from the team, pal.

The archive pixel scale (oversampled) is 175m/pixel. The formal range and azimuth resolutions vary throughout
a flyby, but are typically 300m (sometimes less) at closest approach - these resolution histories per flyby, and all
the other radar-voodoo parameters such as prf, bandwidth etc. are documented in the
sequence design memos (in the 'extras' directory on the PDS archive). Resolution (and thermal noise) are
separate consideration from speckle noise, which is a function of the number of looks.

Whether you consider the 'useful' resolution to be the same as the real resolution depends
on the application; some tasks require higher signal-to-noise than others. This is also true for VIMS data, which
does not always have the signal-to-noise to do what you'd like to do (and will be for AVIATR).
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Jason W Barnes
post Jul 12 2010, 01:29 AM
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QUOTE (rlorenz @ Jul 11 2010, 07:45 AM) *
Hoi! mad.gif Misrepresentations like that will get you kicked from the team, pal.

The archive pixel scale (oversampled) is 175m/pixel.


I'm not impressed. That's like me saying that the VIMS data are 0.5 km/pixel because I've interpolated them that way. What's the actual Nyquist-sampled pixel scale? I don't think that I'm the one misrepresenting wink.gif

- Jason
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rlorenz
post Jul 12 2010, 12:20 PM
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QUOTE (Jason W Barnes @ Jul 11 2010, 09:29 PM) *
I'm not impressed. That's like me saying that the VIMS data are 0.5 km/pixel because I've interpolated them that way. What's the actual Nyquist-sampled pixel scale? I don't think that I'm the one misrepresenting wink.gif

- Jason


No, that's why I said oversampled. (Since the resolution elements, defined by doppler bandwidth etc.
are not square, the archive product is oversampled so as not to lose information when the data are
projected onto a square grid.)
Like the post said, the real resolution can be 300-350m (and there are many good SAR tutorials on-line
to explain how we get that.)
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