[X] My Assistant

[algorimancer]

Any showstoppers? I would envision something similar to the upcoming Mars Science Laboratory (RTG's are a given). Lot's colder on Titan... rough on lubricants, and parts would be brittle. Not sure whether the organics would pose a problem in the way of gumming up the works, but it doesn't seem likely at liquid methane temperatures. Smaller world, lower gravity, thick atmosphere... I'm inclined to think that a simple copy of the MSL, perhaps with some added insulation, would work just fine. The only alternative I've been hearing about is a balloon-borne probe, but that doesn't allow the same level of geologic prospecting.

[Steve G]

Any showstoppers?  I would envision something similar to the upcoming Mars Science Laboratory (RTG's are a given).  Lot's colder on Titan... rough on lubricants, and parts would be brittle.  Not sure whether the organics would pose a problem in the way of gumming up the works, but it doesn't seem likely at liquid methane temperatures.  Smaller world, lower gravity, thick atmosphere...  I'm inclined to think that a simple copy of the MSL, perhaps with some added insulation, would work just fine.  The only alternative I've been hearing about is a balloon-borne probe, but that doesn't allow the same level of geologic prospecting.

At the ludicrously low ambient temperatures, woudn't any heat form the probe's RTGs or other spacecraft parts just create havoc with the local environment?

[David]

Smaller world, lower gravity, thick atmosphere... 

And considerably longer turnaround times for commands from Earth.

[Guest_BruceMoomaw_*]

It's being seriously considered -- in fact, for a detailed design based largely on MER (but with big tires), see http://www.lpi.usra.edu/opag/jun_05_meetin...s/opagtitan.pdf . But the Outer Planet Assessment Group's Titan study subgroup is leaning strongly against it for two reasons. First, Titan's surface appears to be rugged and nasty enough (very steep-walled arroyos and cliffs, quagmires, etc.) that it would give even a MER with huge inflated tires a rough time. Second, we want multiple sampling over really long distances, because Cassini seems to be confirming that the major compositional differences in Titan's surface that we're interested in are spread out over long distances rather than short ones.

So the inclination is still strongly toward an inflatable airship that drops down periodically to within 100 meters or so of the surface, ejects tiny sampling harpoons, and then reels them back on cables into the gondola. The main debate now seems to be whether this should be a powered blimp (far more control, but also far more expensive), or a hot-air balloon that just gets blown along by Titan's slow near-surface winds. That's assuming, of course, that the next Titan mission is a sampling balloon at all -- the Titan study group also suggested that it might on balance be preferable to make the next Titan mission an orbiter combined with some kind of small fixed lander or non-landing balloon, before we move on to the next stage of exploration. (By the way, I AM giving away some secrets from my "Astronomy" article to tell you guys this.)

[ermar]

it might on balance be preferable to make the next Titan mission an orbiter combined with some kind of small fixed lander or non-landing balloon, before we move on to the next stage of exploration.

Wouldn't an orbiter in conjunction with any ground/atmospheric Titan mission be preferable regardless? In addition to observing Titan and other moons from a distance, it could serve as a relay for the surface mission, reducing the size of the probe's dish and meaning that it could be contacted during those looong 8-day nights...

[Guest_BruceMoomaw_*]

Obviously a Titan orbiter has massive utility as a com relay -- in fact, it was once thought impossible to fly any kind of Titan lander or balloon without it. But it also adds a hell of a lot to the cost of a mission, and so there is now great interest in the possibility of flying a sampling balloon mission without it.

The trouble is that -- for such a mission landed in the late 2010s -- you have to land near the north pole, or the vehicle will indeed be out of touch with Earth for periods of several days at a time. In the case of a powered blimp, during an extended mission you can later cruise southward out of the constant-contact zone, and have the blimp programmed to fly itself back later. But of course you can't do that with a passive balloon (and the Titan study group seems to be leaning toward recommending that at this point; the cost cut seems to be a lot bigger thn the expected science loss).

[ermar]

you have to land near the north pole, or the vehicle will indeed be out of touch with Earth for periods of several days at a time.

Of course, the atmosphere will be circulating in the meantime. I know that Titan's atmosphere is a hazy subject, but how would we expect to see an drifting polar balloon move near solstice - south, stuck in a stationary polar cell, or too slowly in any direction to matter much?

[tasp]

IIRC, one Voyager style RTG dissipates about 9000 watts of waste heat continuously.

Not sure you would want to deal with the consequences of this near the surface.

--However--

would 9000 watts (or a multiple thereof) be enough to buoyantify a hot air balloon with a useful payload of instrumnents in the Titanian gravity?

Kinda handy to have a near perpetually fueled hot air balloon for a lengthy traverse of the Titan aerodrome.

[Guest_BruceMoomaw_*]

That's exactly the plan. (Interestingly, a blimp requires a more sophisticated and efficient Stirling-type RTG that utilizes less plutonium and produces less waste heat that will interfere with the hydrogen-filled blimp's maneuverability -- whereas the passive hot-air balloon concept requires the less sophisticated and less efficient current RTG design to produce enough waste heat to inflate the balloon.) As for the heat produced by either RTG, studies have shown that -- even after the vehicle finally loses buoyancy and actually falls onto the suface rather than hovering 50 meters or more above it -- the Stirling RTG won't melt into the ice, while the lightweight cage around the hot-air balloon's RTG will keep it from melting into the ice either.

The pattern that a passive balloon might follow, however, does present a problem. The plan is to have a passive balloon hover 3 km or so up, as against only 1-2 km for the blimp -- thus allowing the balloon's controllers more advance view of the unpredictable upcoming surface features so that they have more time to decide whether or not to land the balloon at a particular spot. But Huygens detected winds below 10 km that completely reversed direction from the normal eastward winds of the superrotating atmosphere, presumably due to local terrain features -- so it may be impossible to predict just where a balloon at that low altitude would end up getting blown.

[algorimancer]

I'm afraid I don't have a lot of confidence in the practicality of balloons. Historically, even competently manned balloons & derigibles have had a nasty habit of crashing (look at the repeated failures involved in circumnavigating the earth in a balloon, for instance). Mix-in automated control in a novel enviroment hours away from intelligent reaction, and it seems to me that we're just setting ourselves up for an expensive disaster.

One nice thing that the MER's have established regarding rovers is that, if something goes awry you can just leave the rover parked for a few weeks or months while you determine a solution, then continue the mission. Hard to do that with a balloon.

I'm intrigued by the notion of roving an ice world for the first time. Comparison/contrast of geological processes under those conditions vs. those on rocky worlds ought to yield lot's of surprizes. I'd settle for Europa or Ganymede, but I think the broader interest will be Titan.

As to the waste heat issue, I would think that placing radiators on the top, shielding the ground with reflectors, ought to ameliorate the problem to a large extent.

[Guest_BruceMoomaw_*]

Titan balloons have a huge advantage over balloons to any other world in the Solar System -- including our own -- for the same reason that Titanian aircraft have one: Titan's unique combination of dense atmosphere and low gravity means that you need a much smaller balloon (or much smaller wings and propellers) to stay aloft, which in turn means that you can afford to make the balloon envelope out of thicker and tougher material than for a balloon on any other world.

As for the automated control problem: this is relieved in these proposed missions by the fact that the vehicle isn't supposed to come closer than 50-100 meters of the surface -- it will instead carry 5-10 tiny sampling harpoons (the design for these has been worked out in some detail, but they clearly require and will get more work) to drop down onto the surface and then reel back in on thin cables. This system should allow sampling to be done at heights of up to 200 meters above the surface, which provides the balloon a lot more latitude in avoiding dangerous terrain features. (The harpoon heads are little tripods which will hit the surface and instantly fire a small core tube downward into the surface, with the core tube then being released from the tripod and reeled back up to the gondola after less than a second on the surface.)

Given the apparent extent to which Titan's surface composition varies over long distances, this system (including using the gondola's aerial cameras for detailed reconnaissance of the types of Titanian surface features in the area) is regarded as a workable substitute for the need we would have otherwise to launch several fixed landers to different places picked out by previous orbital reconnaissance more detailed than Cassini will probably be able to do. However, clearly this whole subject is still open to lots more debate, and will get it in the near future.

As for the heat from the RTG on a lander or wheeled rover affecting the surface, this can indeed be solved by putting a cone-shaped thermal shield around the RTG to divert the air which it heats straight upward, keeping it from hitting the surface.

[dvandorn]

As for the heat from the RTG on a lander or wheeled rover affecting the surface, this can indeed be solved by putting a cone-shaped thermal shield around the RTG to divert the air which it heats straight upward, keeping it from hitting the surface.

...turning your rover into the font of a trundling column of superheated air, rising rapidly up from any position the rover takes. Pulling cooler air in from the surrounding terrain, which is sucked up into the rising hot-air column.

Hmmm -- in fact, this could have some positive aspects. Your rover would act as a vacuum cleaner, sucking small fines and such toward itself wherever it went. You could also put turbines into the airflow and generate additional electricity that way.

And finally, since you're generating a truly anomalous (to the natural conditions) updraft, you might even create weather as you wander along.

Of course, you'd have to correct for these impacts in your observations...

-the other Doug

[ljk4-1]

And considerably longer turnaround times for commands from Earth.

By the time we get a rover on Titan, AI and robotics will be advanced enough that the rover will be able to handle most issues on its own and not need to wait for help from Earth.

How about a hovercraft?

[ermar]

How about a hovercraft?

I remember someone asking if anyone had read Stephen Baxter's Titan...

In summary, the protagonists try using a hovercraft, only to find that it's hopelessly unstable and throws them into the slush, repeatedly. "He went to the airlock. Once inside and de-suited he started to clean off the gumbo still sticking to his EMU. Fifty million bucks, he thought."

Aside from that... I don't see any reason why it shouldn't work, provided you can land it in a flat enough area. And if the surface really is the consistency of wet sand, it would seem to have an advantage over a rover in that it wouldn't be as likely to get stuck.

[Guest_BruceMoomaw_*]

A hovercraft, however, has one major problem that a rover doesn't: it's almost impossible for it to climb up or down even midly steep slopes -- and Huygens made it clear that these are a major feature of Titanian terrain.

Ralph Lorenz is an enthusiast for the idea of a Titan helicopter -- which, thanks to that combination of dense air and low gravity, would require fully 37 times less energy to hover than it would on earth -- but the control problems seem alarming to me, and in any case it lacks that really long range that one gets out of a balloon or blimp and which they badly want for Titan. The biggest goal of surface sampling, after all, is a region which has been exposed to liquid water -- or water-ammonia lava -- and it may take quite a lot of flying to find one.

[Bob Shaw]

Bruce:

A Titan helicopter need look very little like one designed for this planet, and could have a really stable flight regime. Look at the toy helicopters and other electric flying machines out there, and you can see a remarkable diversity - like four-engined ones, contra-rotating affairs and even a couple of honest-to-goodness saucers. Add in the experience from some of the smaller military UAVs and you really have the potential for a winner.

One thing that's certainly true about helicopters vs lighter-than-air is that the former would simply flit about, while the latter would be up and about for the longer term. Perhaps helicopters should be seen as an adjunct to a rover, or a lander - small, light and pretty much throwaway.

Bob Shaw

[tty]

Bruce:

A Titan helicopter need look very little like one designed for this planet, and could have a really stable flight regime. Look at the toy helicopters and other electric flying machines out there, and you can see a remarkable diversity - like four-engined ones, contra-rotating affairs and even a couple of honest-to-goodness saucers. Add in the experience from some of the smaller military UAVs and you really have the potential for a winner.

One thing that's certainly true about helicopters vs lighter-than-air is that the former would simply flit about, while the latter would be up and about for the longer term. Perhaps helicopters should be seen as an adjunct to a rover, or a lander - small, light and pretty much throwaway.

Bob Shaw

In my opinion this helicopter idea is utterly impractical. Helicopters are power-hungry, mechanically complex, highly stressed and dynamically unstable.

Yes, I know that a twin-rotor model like the CH-47 is stable, but at the cost of even greater mechanical complexity and the need to either synchronize the rotors, or have them far enough apart not to interfer with each other.

Just constructing a rotor head that will work at cryogenic temperatures would be an engineering nightmare. Metals will be brittle, standard lubricants useless, normal elastomers rock-hard etc. Building a rotor blade (which is highly stressed and has to move in a complicated way around all three axes during each rotation) wouldn't be easy either.

It is true that a helicopter for Titan would be very unlike an earth helicopter. It would also be impossible to test-fly on Earth. Temperatures and atmosphere composition it might just be possible (but very expensive) to simulate in a large refrigerated chamber, but never the gravity.

This also applies to the software. You could never test the flight control software (which must of course be completely autonomous) in a realistic way either. And remember, it must never re-boot and never safe itself. Also it had better be pretty good, so it doesn't get itself into a vortex ring situation, turns downwind at low altitude, overtorques or any other of the no-nos of helicopter flying.

Power: a RTG seems to be the only practical alternative. Unfortunately they're heavy and doesn't produce that much power. This is the best part of the balloon/blimp concept: the lift is produced by the waste heat, leaving all the electric power for propulsion and control/science/communications.

tty

[Bob Shaw]

FWIW, I believe that the proposed Titan helicopter concept would use a small RTG and storage using capacitors to give Ooomph! at takeoff. Think not so much of traditional helicopters here, so much as an electric boost-glide hopper, a bit like Zubrin's Mars Plane (which has actually flown), but using a rotary wing. We're NOT talking about sustained flight.

Bob Shaw

[tty]

FWIW, I believe that the proposed Titan helicopter concept would use a small RTG and storage using capacitors to give Ooomph! at takeoff. Think not so much of traditional helicopters here, so much as an electric boost-glide hopper, a bit like Zubrin's Mars Plane (which has actually flown), but using a rotary wing. We're NOT talking about sustained flight.

Bob Shaw

I'm still skeptical. Compared to winged aircraft helicopters have very bad gliding characteristics (steep glide, high rate of sink) and an unpowered (autorotative) landing is quite challenging.
You have very limited choice of landing site because of the steep approach and you must pull collective pitch at exactly the right moment or you're in big trouble.
The company where I work made a lot of money repairing the helicopters the army used to bend when training autorotative landings.

tty

[Bob Shaw]

I'm still skeptical. Compared to winged aircraft helicopters have very bad gliding characteristics (steep glide, high rate of sink) and an unpowered (autorotative) landing is quite challenging.
You have very limited choice of landing site because of the steep approach and you must pull collective pitch at exactly the right moment or you're in big trouble.
The company where I work made a lot of money repairing the helicopters the army used to bend when training autorotative landings.

tty

All the power-laws are in your *favour* on Titan! Less gravity, greater density... ...and no PIO (Pilot Induced Oscillation - the bane of autorotation!).

Bob Shaw

[ljk4-1]

Forget wheels: What about a Dante type crawler - you know, legs.

http://ranier.hq.nasa.gov/telerobotics_page/projects.html

[yaohua2000]

Power: a RTG seems to be the only practical alternative. Unfortunately they're heavy and doesn't produce that much power. This is the best part of the balloon/blimp concept: the lift is produced by the waste heat, leaving all the electric power for propulsion and control/science/communications.

Titan is full of methane, so why not bring some oxygen there as "oil" to make a normal chemistry engine?

[RNeuhaus]

Titan balloons have a huge advantage over balloons to any other world in the Solar System -- including our own -- for the same reason that Titanian aircraft have one: Titan's unique combination of dense atmosphere and low gravity means that you need a much smaller balloon (or much smaller wings and propellers) to stay aloft, which in turn means that you can afford to make the balloon envelope out of thicker and tougher material than for a balloon on any other world.

How accidented is Titan's surface? That is important factor about the ballon maneurability. On the other hand ballon needs control over the air direction, then how is the air flow pattern around Titan? The other problem is about the distance and time to send and receive commands from Earth to probe might be solved with an even more sophisticated artificial intelligence, doing more alike as a robot obeying any developed rules.

Rodolfo

[RNeuhaus]

Titan is full of methane, so why not bring some oxygen there as "oil" to make a normal chemistry engine?

Bring oxygen to Titan is prohibitive expensive due to its weight (liquid oxygen) and of short duration. I seems it as not a good idea.

Rodolfo

[Guest_BruceMoomaw_*]

Certainly all the proposed Titan rovers or flyers use RTGs to power their motors -- but some of the balloons use the RTG's waste heat to provide a balloon's hot air, and there's no reason that it couldn't be directly utilized to operate mechanical motors as well. After all, precisely that has been proposed for a long-lived vednus lander: having the motor for its internal refrigerator run directly by waste heat from its external RTG, rather than by electricity from that RTG.

As for the problems of using wind to move a passive Titan balloon: that really is a problem for the current design, which would hover only about 3 km off the ground -- an altitude low enough that local surface features seem to radically affect its direction, according to Huygens. 7 or 8 km altitude, by contrast, might get it back into the main westerly superrotation wind. But as for the long time between its taking images of an approaching landscape feature, and its reception of a command from Earth to lower itself to the surface at that point: the science definition team has already said that such a mission could still probably land accurately enough to get acceptable surface samples, since Cassini seems to be indicating that Titan's surface composition varies much more over long distances than over short ones.

[gpurcell]

I guess the way to think about some sort of floating Titan lander is as a succession of individual landers as opposed to a mobile roving platform that can provide a unified geological data set over a long distances. Seen in this way, 10 to 20 (maybe more) discrete landing zone portraits would seem to me to be able to establish a whole lot of ground truth, perhaps even more than a long term roving mission that focused on a much smaller area.

[tty]

Titan is full of methane, so why not bring some oxygen there as "oil" to make a normal chemistry engine?

CH4 + 2O2 => CO2 + 2H2O, so you need four pounds of oxygen to each pound of methane. Methinks a RTG would give better value for money.

tty

[EccentricAnomaly]

How about a slow lander or glider? With Titan's low gravity and thick atmo, you could do several circuits around the moon before landing... all of this for very little complexity in the vehicle design. Remember that Huygens had to use a third smaller chute to be able to land faster.

[EccentricAnomaly]

CH4 + 2O2 => CO2 + 2H2O, so you need four pounds of oxygen to each pound of methane. Methinks a RTG would give better value for money.

tty

What about fluorine?

[Guest_BruceMoomaw_*]

How about a slow lander or glider?  With Titan's low gravity and thick atmo, you could do several circuits around the moon before landing...  all of this for very little complexity in the vehicle design.  Remember that Huygens had to use a third smaller chute to be able to land faster.

I don't see anything you get out of this that you couldn't get much better from a balloon -- even a nonpowered one.

[Guest_BruceMoomaw_*]

What about fluorine?

Not much better, and much harder to store. Unfortunately, it appears that we have to stick with RTGs and Pu-238, much though I would prefer not to.

[EccentricAnomaly]

I don't see anything you get out of this that you couldn't get much better from a balloon -- even a nonpowered one.

No balloon has ever been successfully deployed on another planet. The inflation and the proper envelope material sound like a very complicated problem to solve... and therefore expensive. A slow lander could use a design very similar to Huygens, and it would be much cheaper as a result... and I think the science would be comparable to a balloon.

A balloon would cover a small area in more detail, but a slow lander or glider could cover almost the entire surface. I think it would be possible to design something that could take days or weeks to descend with altitudes of 500 km or so above the surface for most of the time, and maybe a day below 500 km on final descent.

Also a balloon would require better model of the low altitude winds then I think Cassini or Huygens will provide. I think it would be really hard to design such a system without accepting a risk level comparable to Beagle 2.

[The Messenger]

I vote for a very large parachute, with lots of scheduled drift time - who cares where - we don't know enough about the surface to know what is important and what is not. And we better be able to analyse the surface for something other than water and hydrocarbons. This substance 'not found on any other surface in the solar system' has to have a name.

[Gsnorgathon]

No balloon has ever been successfully deployed on another planet.
...

...Except for the two Vega balloons deployed on Venus in 1985 by the Soviet Union.

[edstrick]

The Vega mission balloons were 100% successful. They had a mission goal (I'd have to check to be sure) of 1 days and lasted some 2 days till batteries depleted. Science capability was somewhat rudimentary because of the small payload, power available and direct-to-earth transmission, but it was a considerable technical and scientific success. And the small payload was well thought out and designed.

[Bob Shaw]

I vote for a very large parachute, with lots of scheduled drift time - who cares where - we don't know enough about the surface to know what is important and what is not. And we better be able to analyse the surface for something other than water and hydrocarbons. This substance 'not found on any other surface in the solar system' has to have a name.

Er... ...Titanium? It's like Unobtanium. Oh, damn, someone's used that one. What about natiTium?

Bob Shaw

[ljk4-1]

I don't see anything you get out of this that you couldn't get much better from a balloon -- even a nonpowered one.

How about a rover that uses legs instead of wheels, like the Dante robots?

[Guest_BruceMoomaw_*]

Well, first, the balloon has already been test-inflated repeatedly in Titan-temperature air -- including the cigar-shaped blimp. That's no problem, especially given the fact that Titan's low gravity means that the craft is falling quite slowly while it releases and inflates the balloon. (The large electric motors they'd need for a blimp have also been tested at Titanian temperatures.)

Second, a glider can only land once -- whereas the desired goal for a Titan Organics Explorer is to make landings at several different places (around five). The big problem with a nonpowered ballloon is that, of course, you only have very rough control over where you land -- but to a great extent that's also true with a glider. The Titan Organics Explorer appraisal group carefully considered the possibilities of a Titan airplane as well as blimps and balloons, and ended up saying firmly that the airplane was seriously inferior.

[Guest_BruceMoomaw_*]

As for a rover with legs instead of wheels: first, they're complex and haven't really been proven yet in a real-world environment (consider how short a time it took for the "Dante" legged rover to foul up). Second, Titan's surface is so nasty -- riddled with very steep slopes and likely quagmires -- that a legged rover probably would find it as hard to get around on the surface as a rover with big inflatable tires, and maybe more so.

Finally, any short-range rover of any type has a scientific problem mentioned by the Organics Explorer appraisal group: the impression we're starting to get of Titan from Cassini is that long-distance compositional differences are much more important than short-distance ones.

[lyford]

This sounds like a job for Tumbleweed Rover!!!!!

Strong winds should allow it to travel all over, but calling back home seems to be a bit of a puzzler.

[Bob Shaw]

This sounds like a job for Tumbleweed Rover!!!!!

Strong winds should allow it to travel all over, but calling back home seems to be a bit of a puzzler.

Why did you resign?

Bob Shaw

[EccentricAnomaly]

I just realized the problem with a slow parachute... a parachute kills all velocity vertical _and_ horizontal. A balloon would be much better because it would have longer to drift on the wind.

Now, I'm leaning towards a plane powered by an RTG heat engine. The airspeed on Titan would be very slow, and the wings would be very small. An airplane would be almost as good as a helicopter or blimp, but much simpler to build. And there is less of a need to predict the atmosphere.

[The Messenger]

I just realized the problem with a slow parachute...  a parachute kills all velocity vertical _and_ horizontal.  A balloon would be much better because it would have longer to drift on the wind. 

I like the tumbleweed approach, but there do not appear to be strong winds. How about an airbag balloon with spider accessories? Not a blimp, but a collection of hydrogen filled airbag-like cushons configured in a spherical shape with the landing probe in the middle, and an array of instruments dangling from tethers that analyses and broadcasts. When the probe is ready to land, the instrument clusters are reeled back in. Once on the ground, the probe can inertially drive the balloon coccoon across a verity of terrains, navigating with radar that can see through the bag fabric. Surface analysis is accomplished with drop down analytical tools.

[ljk4-1]

How about a robot probe that moves along the ground like a snake or catepillar?

Why reinvent the wheel that Nature has already developed for the last few million years?

I would call it The Undulator - though they call it Hydra:

http://europa.eu.int/comm/research/headlin...5_12_26_en.html

http://www.robots.org/images/2001_Robot_Ga...e%20planets.htm

http://www.space.com/businesstechnology/te...s_010911-1.html

http://astrobiology.arc.nasa.gov/news/expandnews.cfm?id=367

Paper - Biomimicry as Applied to Space Robotics:

http://cswww.essex.ac.uk/technical-reports...cott_Ellery.pdf

[tty]

I just realized the problem with a slow parachute...  a parachute kills all velocity vertical _and_ horizontal.  A balloon would be much better because it would have longer to drift on the wind.

Now, I'm leaning towards a plane powered by an RTG heat engine. The airspeed on Titan would be very slow, and the wings would be very small. An airplane would be almost as good as a helicopter or blimp, but much simpler to build. And there is less of a need to predict the atmosphere.

Nix - a parachute will, after a short while, drift with the wind just like a balloon. If You could invent a parachute that doesn't You would rich, since landing with a parachute in a high wind is difficult and can be dangerous.

Also I can't understand where you got the idea that an airplane has less need to predict the atmosphere than a blimp - if anything it is the other way around. Also an aircraft has the same problem as a helicopter - it can never be realistically test flown on Earth.

In my opinion the only realistic first-generation air vehicle for Titan is a free balloon or possibly a blimp. A blimp can always revert to a free-flying mode if there are control problems or the computer has to safe itself. At such times a crude altitude hold function could be maintained by a simple pressure sensor directly linked to the RTG heater. Try that with an aircraft!

Incidentally a spherical balloon while the optimal form for a free-floater is not good if you want to moor it when "landing" it since a moored spherical balloon is violently unstable. In such situations a "kite baloon" that works as a weather foil is preferable.


tty

[Guest_BruceMoomaw_*]

The Titan Organics Explorer design team is now trending toward two alternatives (I think I've mentioned this before):

(1) The more expensive one is a hydrogen-filled blimp with a complex celestial navigation system (apprently usable even on Titan if you use near-IR cameras to observe the Sun and Saturn itself), with two big motors that can be swivelled to drive it temporarily downward vertically for sampling.

(2) The less expensive is a big (and round) wind-driven balloon filled with hot air from the RTG, which would ordinarily hover at higher altitude (about 3 km, versus 1-2 km for the blimp) so that its ground controllers could see in advance if it was being blown toward a region worthy of sampling, after which they'd lower it in classic hot-air balloon fashion by opening a vent. Obviously far less control over landing spots; but the team concluded that it may be acceptable anyway, given Cassini's growing conclusion that Titan's surface composition varies more over long distances than over short ones. (The balloon would also have those navigation cameras, simply to tell the ground precisely where it was at any given time.)

Both these things would descend to within about 100 meters of the surface for 5-10 times over their lifetimes (that number has been downscaled from the previous 20 times), and drop a tiny tripod down to the surface on a line. The tripod would then instantly fire a core tube into the surface, which would then be detached from the tripod and reeled back up into the gondola on the cable. Thus ground contact is required for only a second or two, and there's considerable slack in the cable during the contact.

The point of this mission is that they want to make multiple sampling landings, primarily to look for local spots where liquid water/ammonia lava has been mixed with the deposited organic smog prticles to produce interesting prebiotic compounds that actually contain oxygen. Which mission will be chosen would depend both on cost and on the need for precision landings (the blimp would actually spend about a week quartering each of its 20-km wide landing regions in detail before deciding precisely which spot to land on in it). But if you want to make repeated landings, an airplane or glider is simply out of the question.

Alternatively, if you just want to do aerial reconnaissance (which is another real possibility for the first Titan mission, perhaps accompanied by a stationary lander at one good spot picked out by Cassini), an airplane would be usable, but wouldn't be any more scientifically productive than a balloon with a long lifetime. The trouble -- as with Europa missions -- is that the time gap between Titan missions is so long that you don't want to make any mistakes in designing each mission for maximum scientific output.

[The Messenger]

Thanks Bruce,

Any word on instrumentation? Are they planning on including a Mossbauer?

[Guest_BruceMoomaw_*]

Well, the payload is strictly strawman at this point -- and it's also pretty barebones:

(1) Cameras and air temperature and pressure sensors (naturally).

(2) The main GCMS package to analyze the core samples taken, along with atmospheric samples (also naturally). They definitely want an ability to look for chirality.

(3) A microscope to inspect the retrieved cores of surface ice before they thaw (looking for physical structure, not microbes).

(4) A Raman spectrometer to analyze inorganic materials in the ice cores. This intrigued me; it turns out that they're looking for rocks from Titan's interior that might be ejected onto the surface along with the ammonia-water lava flows that they're looking for.

One can easily envision other things that could be added to this: other types of weather sensors; a near-IR spectrometer for remote surface composition mapping (even given the limited spectral winds through which near-IR sunlight hits Titan's surface); a subsurface radar sounder; a magnetometer to look for induced magnetic fields and thus a subsurface ocean.

[mchan]

Why did you resign?

Bob Shaw

That would be telling.

(since no one else replied)

[Bob Shaw]

That would be telling.

(since no one else replied)

Before anyone objects, this topic is entirely, er, on-topic, being on the subject of a Rover which travels across a beach-like landscape, and has some form of AI!

Be seeing you!

Bob Shaw

[ljk4-1]

Before anyone objects, this topic is entirely, er, on-topic, being on the subject of a Rover which travels across a beach-like landscape, and has some form of AI!

Be seeing you!

Bob Shaw

Using the beachball rover may not be the best approach for finding life on Titan.

The poor things have probably been monitoring Earth television for years, with The Prisoner being their favorite program. Then here comes along a Rover approaching them - they'll all run away or burrow under the methane slush and then we'll never find them.

The blimp may not work any better, as they also have seen Black Sunday.

I am not a number, I am a free Titanian!

[lyford]

DOH - I am sorry Bob - I was too slow. It was even called Rover, ferchrissakes. Well played.
Though apparently I am mistaken, I thought there were measurable winds at the surface of Titan that would aid our little wanderer on its large scale feature hunt.

[The Messenger]

Well, the payload is strictly strawman at this point -- and it's also pretty barebones:

(1)  Cameras and air temperature and pressure sensors (naturally).

(2)  The main GCMS package to analyze the core samples taken, along with atmospheric samples (also naturally).  They definitely want an ability to look for chirality.

(3)  A microscope to inspect the retrieved cores of surface ice before they thaw (looking for physical structure, not microbes).

(4)  A Raman spectrometer to analyze inorganic materials in the ice cores.  This intrigued me; it turns out that they're looking for rocks from Titan's interior that might be ejected onto the surface along with the ammonia-water lava flows that they're looking for.

This is great news! A Raman can evaluate atomic spectra through very fine optical fibers. There is a (slight) possibility I will be able to work on the GCMS package - that is, if they decide they must address the possibility of analyzing tar residues.

[ngunn]

Has anyone suggested a balloon (or a number of balloons) with surface-dragging ballast tail? Small buoyancy changes only would be required to alternate beween 3 modes of operation: 1/ free floating for reconnaissance from altitude, 2/ small part of ballast tail grounded keeping balloon a constant few metres above any undulating surface but able to drift with the wind - photography of the drag trail would yield data on surface consistency over large distances, and 3/ more of tail grounded, sufficient to anchor balloon temporarily at one spot for static surface experiments. No sohisticated navigation or flight control system required.

[EccentricAnomaly]

Nix - a parachute will, after a short while, drift with the wind just like a balloon. If You could invent a parachute that doesn't You would rich, since landing with a parachute in a high wind is difficult and can be dangerous.

Originally I thought a parachute would give you greater range than a balloon, but it's actually the other way around since the balloon stays aloft longer and has longer to drift. I should have said that you have almost zero horizontal velocity wrt the atmosphere.

Also I can't understand where you got the idea that an airplane has less need to predict the atmosphere than a blimp - if anything it is the other way around. Also an aircraft has the same problem as a helicopter - it can never be realistically test flown on Earth.

You can design an aircraft that is inherently stable which will let it survive in worse weather. Also an airplane has greater control authority which means it can tolerate higher winds than a balloon, blimp, or helicopter.

Also it is a much simpler thing to build than a balloon (no inflation, maybe even no deployable parts). And it could be test flown on earth, using what is called the Buckingham Pi Theorem [http://en.wikipedia.org/wiki/Buckingham_Pi_theorem] which lets you build a wind tunnel to approximate Titanian flight just by matching the non-dimensional parameters. You can even account for the lower gravity this way.

[The Messenger]

Also it is a much simpler thing to build than a balloon (no inflation, maybe even no deployable parts).  And it could be test flown on earth, using what is called the  Buckingham Pi Theorem [http://en.wikipedia.org/wiki/Buckingham_Pi_theorem]  which lets you build a wind tunnel to approximate Titanian flight just by matching the non-dimensional parameters.  You can even account for the lower gravity this way.

...Kind of, Sort of. We are still scratching our heads over the the over-performance of the Viking Parachutes; and under-performance of the Pathfinder parachutes; relative to wind tunnel testing of the designs. It will be interesting to see if the modeling [both atmospheric, and structural] has improved to where the Spirit and Pathfinder results are closer to expectations.

[ljk4-1]

...Kind of, Sort of. We are still scratching our heads over the the over-performance of the Viking Parachutes; and under-performance of the Pathfinder parachutes; relative to wind tunnel testing of the designs. It will be interesting to see if the modeling [both atmospheric, and structural] has improved to where the Spirit and Pathfinder results are closer to expectations.

If this helps any:

Viking '75 project: Scale model test results of the Viking parachute system at Mach numbers from 0.1 through 2.6

http://ntrs.nasa.gov/archive/nasa/casi.ntr..._1977071083.pdf

VIKING '75 PROJECT: PRE-TEST REPORT FOR FLEXIBLE DECELERATOR WIND TUNNEL TESTS AT AEDC PWT 16S

http://ntrs.nasa.gov/archive/nasa/casi.ntr..._1977071081.pdf

[Guest_BruceMoomaw_*]

This is great news! A Raman can evaluate atomic spectra through very fine optical fibers. There is a (slight) possibility I will be able to work on the GCMS package - that is, if they decide they must address the possibility of analyzing tar residues.

Actually, they intend to use the GCMS to analyze tar residues -- by roasting the hell out of the sample at very high temperatures, since their test runs have shown that a lot of the more complex organics are very refractory and sometimes won't pyrolize until you give them a squirt of oxygen as well to actually burn them. (Which, you'll recall, was what Pillinger's "Beagle 2" GCMS would have done.) They've also found that some of the organics are so sticky that they'll have to use a fresh GC column for every sample, which is another reason why they've cut the total number of surface samples down to only 5 to 10. Indeed, they also chose the Raman for inorganic analyses because it doesn't have to actually touch the possibly sticky sample.

Since these are instrument design strategies, they're likely to be maintained even if the actual Titan mission chosen is nothing like the Organics Explorer -- which is a very good chance. (The design of the Organics Explorer, including its instrument selection, is a strawman exercise to confirm that the idea is workable. Beyond cameras and a GCMS, the actual instrument selection on the next Titan mission is a very wide-open question.)

[RNeuhaus]

You can design an aircraft that is inherently stable which will let it survive in worse weather.  Also an airplane has greater control authority which means it can tolerate higher winds than a balloon, blimp, or helicopter.

If my memory does not fail, the upper skies of Titan has strong storms. Any plane are able to be under a good control during its fly thru any storms. Besides, a plane flying at a distance of 1,500 millions kilometers from Earth, the plane will only fly only for few seconds and hence it will need a very sophisticated Artificial Intelligence to pilot as a good soldier robot obeying any Earth's sent instructions commands. Besides, any plane need to know with advance of any places to land if the emergency arises. We have no good idea what planes is feasible for airplane landing. I won't be thinking an airplane as a feasible for a little known word such as Titan. There is only three good alternatives: Orbiter, Ballon or Blimp or Rover. The Orbiter is a MUST as a communications and spoting support for any motorized on the surface.

Rodolfo

[Guest_BruceMoomaw_*]

Actually, the thinking on a Titan orbiter as a mandatory accompaniment for any suface craft has come under major fire lately -- the redesigns of the Titan Organics Explorer are noteworthy for NOT including one, on the grounds that it would massively increase the mission's cost, and that our technology now allows an aerial vehicle or rover to communicate at acceptably high speed directly with Earth, and to use near-IR cameras observing Saturn and the Sun through the haze layer for navigation accurate to within less than a dozen kilometers. This does raise the problem, however, that such a vehicle can only communicate with Earth when it is on the side of Titan facing the Earth -- which is why the current scenario for the Organics Explorer calls for it to land near the north pole at a time when this will allow it to maintain continuous radio contact with Earth.

I should emphasize that the possible design of the next Titan mission is still extremely flexible -- it may well end up consisting of an orbiter instead of any surface vehicle (or accompanied by only a small nonlanding balloon or stationary lander). But the question is still open.

[ngunn]

Actually, the thinking on a Titan orbiter as a mandatory accompaniment for any suface craft has come under major fire lately -- the redesigns of the Titan Organics Explorer are noteworthy for NOT including one, on the grounds that it would massively increase the mission's cost, and that our technology now allows an aerial vehicle or rover to communicate at acceptably high speed directly with Earth, and to use near-IR cameras observing Saturn and the Sun through the haze layer for navigation accurate to within less than a dozen kilometers.  This does raise the problem, however, that such a vehicle can only communicate with Earth when it is on the side of Titan facing the Earth -- which is why the current scenario for the Organics Explorer calls for it to land near the north pole at a time when this will allow it to maintain continuous radio contact with Earth. 

I should emphasize that the possible design of the next Titan mission is still extremely flexible -- it may well end up consisting of an orbiter instead of any surface vehicle (or accompanied by only a small nonlanding balloon or stationary lander).  But the question is still open.

I would have thought that at least one orbiter with a very long projected lifespan would be a major priority for a future mission. We already know or suspect that significant events on and around Titan may take many years or decades to unfold. The seasons, the presumed infrequency of precipitation events, even the chemistry - everything happens with glacial slowness. How can we hope to gain insight into such an environment with just a short-lived (and accident prone) atmospheric probe, or a lander that, like Huygens, samples only one time and location? I would make a robust orbiter priority one and if possible supply it with a number of 'disposable' balloon probes of fairly simple design to be deployed over a period of years at times and places of particular interest. This aspect of the mission could then be kept under continuous review from Earth as our understanding grows.

Cassini-Huygens was a bold and imaginative mission which has begun to reveal to us the second most interesting place in the Solar System. Millions of people the world over have been engaged by the excitement of discovery. The follow-up must not be a damp squib from NASA's bargain basement.

[dvandorn]

...How can we hope to gain insight into such an environment with just a short-lived (and accident prone) atmospheric probe, or a lander that, like Huygens, samples only one time and location?

Man.... I can recall, very very clearly, when there was not a single photographic image in existence from the surface of *any* planet other than good old Terra Firma. A lone, highly contrasted, poor resolution and difficult-to-interpret Luna 9 image from the surface of the Moon was an absolute revelation.

As blurry and compression-artifact-filled as they are, the Huygens images of Titan's surface (limited though they are in location and clarity) are magnitudes greater in their revelation than even those first Luna 9 images.

But in this post-MER world we live in, methinks we've gotten just a little spoiled. Let's not under-appreciate what even those short lived, accident-prone atmospheric probes and one-location landers can teach us -- especially when *any* probe costs billions of dollars to deliver to its worksite.

-the other Doug

[EccentricAnomaly]

If my memory does not fail, the upper skies of Titan has strong storms. Any plane are able to be under a good control during its fly thru any storms. Besides, a plane flying at a distance of 1,500 millions kilometers from Earth, the plane will only fly only for few seconds and hence it will need a very sophisticated Artificial Intelligence to pilot as a good soldier robot obeying any Earth's sent instructions commands. Besides, any plane need to know with advance of any places to land if the emergency arises.  We have no good idea what planes is feasible for airplane landing.  I won't be thinking an airplane as a feasible for a little known word such as Titan. There is only three good alternatives: Orbiter, Ballon or Blimp or Rover. The Orbiter is a MUST as a communications and spoting support  for any motorized on the surface.

Rodolfo

There isn't any evidence of storms on Titan yet... but its reasonable to guess that there might be storms. But just like on Earth, it should be possible to fly over the weather. And just like panes on Earth can fly for hours on auto-pilot, so could a plane on Titan (i.e. just stay on straight and level flight). And of you power the plane with an RTG heat engine, it should never need to land and it could just fly around until the RTG runs out.

An airplane couldn't get samples like a blimp... but it could get better science than an orbiter, and it would be cheaper than a blimp. And it would probably last longer than a blimp and it would need much simpler autonav software.

[tty]

There isn't any evidence of storms on Titan yet...  but its reasonable to guess that there might be storms.  But just like on Earth, it should be possible to fly over the weather.  And just like panes on Earth can fly for hours on auto-pilot, so could a plane on Titan (i.e.  just stay on straight and level flight).  And of you power the plane with an RTG heat engine, it should never need to land and it could just fly around until the RTG runs out. 

An airplane couldn't get samples like a blimp... but it could get better science than an orbiter, and it would be cheaper than a blimp.  And it would probably last longer than a blimp and it would need much simpler autonav software.

You have a highly optimistic view of airplane reliability and durability. They aren't nearly that good yet, even here on Earth after a century of development work. An airplane must have many moving parts in constant use, at least in the propulsion and flight control systems. These wear out and break. And this would be the first aircraft ever built for Titanian conditions! Remember that most of the materials we have practical experience of will not work well at Titanian temperatures, certainly not lubricants, elastomers, bonding agents, textiles or plastics, and even many metals and alloys will be too brittle for use.
As one who has had a great deal of experience of aircraft maintenance and reliability I think we would be very lucky to get a hundred flight hours out of our first Titanian airplane.

Incidentally, why should autonav software be simpler for an airplane than a blimp?

tty

[Guest_BruceMoomaw_*]

The whole point about the roving multiple-landing balloon concept is that it's supposed to make studies of a very widespread part of Titan that are, on balance, scientifically better -- or at least more urgent -- than those we could make from an orbiter. (Ralph Lorenz wrote on this years ago. One thing he pointed out that is that, thanks to the phenomenal scale height of Titan's atmosphere, it will be very hard to get an orbiter close enough to the surface to do any meaningful subsurface radar sounding -- which is starting to look like a crucial element in any attempt to understand the place.)

But this is admittedly still up in the air, so to speak. At the October OPAG meeting, the committee's Titan Study Group -- led by Lorenz -- suggested that an orbiter with an unambitious surface package might on balance be preferable as the next Titan mission ( http://www.lpi.usra.edu/opag/oct_05_meetin...an_work_grp.pdf pg. 7). The one thing that can probably be stated with confidence is that the next Titan mission will include either an orbiter or a multiple-landing long-range balloon vehicle. (Assuming, of course, that we ever fly another Titan mission at all, given the inability to get Europa Orbiter funded at all this year and the apparent greater importance of having astronauts wave pointlessly from the surface of the Moon again.)

[RNeuhaus]

The whole point about the roving multiple-landing balloon concept is that it's supposed to make studies of a very widespread part of Titan that are, on balance, scientifically better -- or at least more urgent -- than those we could make from an orbiter.  (Ralph Lorenz wrote on this years ago.  One thing he pointed out that is that, thanks to the phenomenal scale height of Titan's atmosphere, it will be very hard to get an orbiter close enough to the surface to do any meaningful subsurface radar sounding -- which is starting to look like a crucial element in any attempt to understand the place.)

That is true. The frontier which won't make any trouble to any orbiter from Titan's atmosphere would be greater than 1,000 km above ot the surface. Not sure about this.

As an example, a spacecraft can orbit as low with little propulsion adjustments if it is around above than 250 km of Earth, above than 50 km of Moon and above 200 km of Mars. Maybe, the spacecraft mass will play the influence about the right height.

Rodolfo

[Bob Shaw]

Perhaps the way to deal with the Titan atmosphere issue is to have a powered SAR-bearing spacecraft, with a serious nuclear electrical source and a big ion engine, and a (slightly) aerodynamic shape. Such a vehicle could descend to an altitude where it would quickly spiral in and burn up, except that it's engine is keeping it in a forced orbital path. Obvious issues with redundancy, biological and radiological contamination etc exist, but it's a technique which is already in use (albeit with chemical propulsion) for certain spy satellites. Oh, and you'd need a Prometheus re-start...

Bob Shaw

[ngunn]

Man.... I can recall, very very clearly, when there was not a single photographic image in existence from the surface of *any* planet other than good old Terra Firma.  A lone, highly contrasted, poor resolution and difficult-to-interpret Luna 9 image from the surface of the Moon was an absolute revelation.

As blurry and compression-artifact-filled as they are, the Huygens images of Titan's surface (limited though they are in location and clarity) are magnitudes greater in their revelation than even those first Luna 9 images.

But in this post-MER world we live in, methinks we've gotten just a little spoiled.  Let's not under-appreciate what even those short lived, accident-prone atmospheric probes and one-location landers can teach us -- especially when *any* probe costs billions of dollars to deliver to its worksite.

-the other Doug

Yes, and only a matter of decades before Luna 9 there were no photographs of Antarctica. Come to think of it the tree at the bottom of my garden can remember when none of the people round about knew that America existed . . .
I don't think it's so much a case of being spoiled, more a matter of seizing our opportunities. This being the 21st century, and Titan being the fascinating place that it is, I think it is reasonable to talk of keeping it under continual surveillance from orbit from the next mission onward.

[EccentricAnomaly]

You have a highly optimistic view of airplane reliability and durability. They aren't nearly that good yet, even here on Earth after a century of development work. An airplane must have many moving parts in constant use, at least in the propulsion and flight control systems. These wear out and break. And this would be the first aircraft ever built for Titanian conditions! Remember that most of the materials we have practical experience of will not work well at Titanian temperatures, certainly not lubricants, elastomers, bonding agents, textiles or plastics, and even many metals and alloys will be too brittle for use. 
As one who has had a great deal of experience of aircraft maintenance and reliability I think we would be very lucky to get a hundred flight hours out of our first Titanian airplane.

Well, there's Helios: http://www.skytowerglobal.com/news-archive/715flight.html Which will ultimately lead to solar powered aircraft that loiter for a long time as a satellite replacement... but designing for titan is much more benign. The atmosphere is thick, and the gravity is low.
So an underwater glider is maybe a better comparison: http://www.space.com/businesstechnology/te...r_020410-1.html

And submarines cruise the oceans for a very long time between maintenance.

A titan airplane would look like a submarine with toothpick wings and would move very slowly because it wouldn't need much airspeed to produce lift. It could either have a propeller (which would move slowly) or it could maybe even have some sort of low speed heat engine jet with no moving parts.

Incidentally, why should autonav software be simpler for an airplane than a blimp?

tty

because an airplane has better control authority than a blimp and can respond to larger disturbances (i.e. stronger winds). Blimp autonav will need much more information about its environment and an ability to plan around bad weather. An airplane could be designed to fly through any weather... just keep it above the local relief.

Now I think a blimp would be more fun.. and I'd rather see a blimp. but I think an airplane would be much cheaper to the same level of risk.

...a side note... and maybe an incendiary one... does anyone know if people with formal engineering training are involved in the formulation of new missions (at JPL)? It seems like a lot of these mission concepts start with people with more of a science background than an aerospace engineering background.... or at least a mission design background.

[Tom Tamlyn]

...a side note... and maybe an incendiary one...  does anyone know if people with formal engineering training are involved in the formulation of new missions (at JPL)?  It seems like a lot of these mission concepts start with people with more of a science background than an aerospace engineering background.... or at least a mission design background.

Look at the CV of Ralph Lorenz, enthusiast for a Titan helicopter and a leader of current JPL and NASA Titan mission planning. Although he's a research scientist in the department of planetary science at the University of Arizona, you'll see that his bachelor's degree was in aerospace systems engineering, and that he spent a year on the Huygens engineering staff before going back to university for a PhD in space science.

You'll also see that he's devoted much of his career to the engineering and operational aspects of Titan exploration missions.

Tom Tamlyn (RL fan)

This post has been edited by Tom Tamlyn: Feb 10 2006, 04:15 PM

[EccentricAnomaly]

Look at the CV of Ralph Lorenz, enthusiast for a Titan helicopter and a leader of current JPL and NASA Titan mission planning.  Although he's a research scientist in the department of planetary science at the University of Arizona, you'll see that his bachelor's degree was in aerospace systems engineering, and that he spent a year on the Huygens engineering staff before going back to university for a PhD in space science.

You'll also see that he's devoted much of his career to the engineering and operational aspects of Titan exploration missions.

Tom Tamlyn (RL fan)

I'm an RL fan too An I don't mean to criticize him or anyone else... just the system by which these missions are born at JPL. (As far as I can tell, ESA doesn't appear to have this problem.) JPL has huge numbers of mission designers that are highly trained and current on the latest techniques (heck many of them invented the latest techniques)... yet the mission designers aren't brought in until after a mission is formulated. So you get things that don't fully leverage what can be done with the trajectory.

Ideally there should be retreats where scientists, systems engineers, and mission designers get together and brainstorm about what can be done... and then take these ideas to the science committees that decide what should be done.

...and... investments in new technology should be focused on enabling new types of missions not just what is currently thought to be sexy by the technologists.

[tty]

Well, there's Helios: http://www.skytowerglobal.com/news-archive/715flight.html  Which will ultimately lead to solar powered aircraft that loiter for a long time as a satellite replacement...  but designing for titan is much more benign.  The atmosphere is thick, and the gravity is low.
So an underwater glider is maybe a better comparison: http://www.space.com/businesstechnology/te...r_020410-1.html

And submarines cruise the oceans for a very long time between maintenance. 

A titan airplane would look like a submarine with toothpick wings and would move very slowly because it wouldn't need much airspeed to produce lift.  It could either have a propeller (which would move slowly) or it could maybe even have some sort of low speed heat engine jet with no moving parts.
because an airplane has better control authority than a blimp and can respond to larger disturbances (i.e. stronger winds).  Blimp autonav will need much more information about its environment and an ability to plan around bad weather.  An airplane could be designed to fly through any weather... just keep it above the local relief.

Now I think a blimp would be more fun.. and I'd rather see a blimp.  but I think an airplane would be much cheaper to the same level of risk.

Submarines have highly qualified crews aboard, with tools, spare parts and LRU's (Line Replaceable Units).

The only heat engine without any moving parts I know of is a ramjet, which by definition does not work at low speed. And besides there is no oxidant available on Titan.

It is true that an aircraft is more maneuvrable than a blimp, but on the other hand maneuvring is also much more time-critical. Also a blimp can go into a free-floating mode in case of problems, which an aircraft can't.

I don't know much about Titanian weather, but we definitely have not yet managed to design any aircraft here on Earth that can safely fly through any weather.

As an aside, does anybody know if there might be "icing" problems on Titan? Is there any substance in the atmosphere that might freeze onto the structure of an airplane or balloon? I don't think ice itself is likely to be a problem at such a low temperature, but what about CO2, various hydrocarbons etc. Icing can be quite a problem with earthly aircraft, so it's definitely something to think about.

tty

[ljk4-1]

I had to post this link to a science fiction novel cover from July of 1955:

http://www.noosfere.com/showcase/IMAGES/winston_24.jpg

I wonder if that rover would work? And what about jet or rocket propulsion?
Of course the air in this scenario seems pretty clear.

[Guest_BruceMoomaw_*]

It looks from Huygens' photos as though the biggest problem for both stationary Titan landers and wheeled rovers are those steep-walled liquid-carved arroyos that seem common on its surface.

[Guest_Richard Trigaux_*]

This is why a flyer was proposed. We don't know the actual conditions on Titan surface. The black areas seem smooth plains, but the clear areas (the most interesting) could have cliffs, boulders, etc even if they don't have real mountains.

To fly on Titan could be easier than on Earth, thanks to high air density and low gravity. But it is not at all easy. This is why the previous discutions (if I remember well) emphasized on some kind of hybrid between an hot air baloon, a gas baloon, and an aircraft. I personally proposed a gas inflated rogalo wing, which could be inflated thick and behave like a baloon, or deflated thin to behave like an aircraft. Such a device could hover on a given place, land precisely, or undertake long travels and stay useable for years and explore all Titan's spots of interest. Others pointed that the only possible energy source on Titan would be a RTG, which provides about 2000W of heat for 200W of electricity. Such a powerful heat source could easily inflate a classical hot air baloon, which could land easily or travel on large distances. But without an engine it would fly at random.

[Guest_BruceMoomaw_*]

This particular note really belongs over in the Venus thread; but the presentations from the second VEXAG meeting have just arrived ( http://www.lpi.usra.edu/vexag/May2006/presentations.html ). In the one on the latest update of the Solar System Roadmap ( http://www.lpi.usra.edu/vexag/May2006/VEXAG_52006_ELLEN.pdf ), Ellen Stofan's group recommends that for the projected Flagship-class Venus Surface Explorer, an "air mobility platform with long traversing" is now "preferred over a surface rover" for Venus as well, logically enough. (Not only does it allow much longer traversing, but in the case of Venus it would also allow the vehicle to land, hastily take a look around and grab some samples for later digestion, and then take off again for the cooler upper atmosphere, thereby reducing its heat burden.)

The one other piece of real news from that particular presentation is that apparently Enceladus has now officially been added to the list of Solar System candidates that may be worthy of a Flagship mission (unless they're talking about a combined Titan/Enceladus mission).

[elakdawalla]

....The one other piece of real news from that particular presentation is that apparently Enceladus has now officially been added to the list of Solar System candidates that may be worthy of a Flagship mission (unless they're talking about a combined Titan/Enceladus mission).

My impression from Ellen's VEXAG presentation was that they were in fact talking about a combined mission.

--Emily

[djellison]

I wonder what sort of mission design you could do there.

A smaller spacecraft to visit Enc rides piggyback on the Titan orbiter which would I presume have a v.large HGA for radar and downlink. It could then act as a relay for the smaller craft.

Doug

[Guest_Richard Trigaux_*]

A smaller spacecraft to visit enceladus piggybacking on a larger ship to Titan?

Two remarks

-The small ship to Enceladus could be a stardust-like sampler harvesting enceladus dust and sending it back to Earth. This poses some constrains on the entry trajectory of the main probe into the Saturn system: to lauch the enceladus sample return in an hyperbolic trajectory to Enceladus and earth, and only after to brake to get in orbit into Saturn. Feasible I think.



-Once empty of fuel, the main ship could stay in orbit around Saturn, or even around Titan if this is possible. Even without fuel it still has RTG power and it could be used as a radio relay, GPS emitter, etc, for further missions, not to speak of course of a permanent observatory: a SAR swath every two hours!!

Eventually this could be a good end for Cassini too, but I don't know if it would have enough fuel to get satellized around Titan, or even in a safe orbit around Saturn.

[Guest_BruceMoomaw_*]

I can't help feeling, though, that this is one pair of targets that really don't get covered very well by a single large spacecraft -- at any rate, I can't think of any way to do so that isn't better done by two separate spacecraft. Time to exercise our ingenuity, I suppose.

Actually, one POSSIBLE way: a single Saturn orbiter drops off a lander (or, in Titan's case, a balloon) at one moon, and then puts itself into a Saturn orbit timed to be resonant with that moon's period of revolution -- so that it makes repeated flybys of the moon to serve as a com relay for the surface spacecraft. Then it modifies its orbit, drops off a lander at the other moon, and modifies its orbit to do the same thing in that case. (The main problem here might be that a Titan balloon will do a considerable amount of wandering over the surface, forcing the main craft to keep modifying its Titan flyby path on rather short notice to stay in touch with the balloon during its flyby passes. I mentioned earlier that Ralph Lorenz says that, as an initial relatively low-cost Titan mission, he'd rather have a nonlanding balloon for a detailed surface survey than he'd like a stationary lander.)

[Guest_Richard Trigaux_*]

Bruce, this is again the idea of a satellite which would serve only as a radio relay. Perhaps such a non-glorious mission will have to be launched, to save money for true science missions, in place of repeatedly lauch the same radio-large antenna-RTG gear. Such a satellite would also serve as a GPS emitter, very useful to precisely locate a lander or flyer.

[Guest_BruceMoomaw_*]

Well, NASA has decided that, for the next few decades, a pure comsat isn't even worthwhile at Mars unless it also does a lot of science studies. This argument is even stronger for the outer planets, since the time between science missions to any of them is so long that the chances are greatly diminished of a pure comsat lasting long enough to do relay duty for two different science missions.

A Saturn orbiter of the type I'm talking about, in addition to doing com relay duty for spacecraft at either or both moons, would presumably also itself do more detailed scientific studies of Titan -- and maybe of Enceladus and other parts of the Saturn system -- than Cassini has. (At a minimum, it would surely map more of Titan's surface, using radar and near-IR. Even if Cassini devotes all of the 15 or so additional Titan flybys it may be able to make during its extended mission to radar mapping, that will still mean that only about 40% of Titan's surface will have been radar-mapped -- which, on a world as varied as Titan has turned out to be, is an important deficit. And Cassini's coverage of Titan's surface in the optimum 2-micron window which only VIMS can use will also still be seriously limited by the end of the mission. I also wonder what it could do at both moons using a radar sounder.)

[Guest_Richard Trigaux_*]

Well, Bruce, I understand the argument.

... I also wonder what it could do at both moons using a radar sounder.)

What do you mean with a radar Sounder? something able to penetrate the ice? I don't know if this is possible, but if so, it would be wonderful. Even looking only some kilometres into Enceladus would perhaps make us able to see the the rising "hot" ice, and water flows if there are.

[Guest_BruceMoomaw_*]

A subsurface radar sounder (like the one proposed for Europa Orbiter) has also been talked about for a long time as an important instrument for understanding Titan, for reasons that should be obvious. At this point, I really don't think we will be able to understand that place without it.

As Ralph Lorenz points out, though, it will be difficult to do subsurface radar sounding at good resolution from an orbiter, simply because any Titan orbiter must stay at a very high altitude above Titan (1500-2000 km) just to keep that moon's vastly extended upper atmosphere from dragging it to its doom in a matter of a few days -- and if you use a radar wavelength long enough to penetrate into the surface of Titan, it will be very hard to distinguish those echoes which return late from very deep directly underneath the craft, and those echoes which return late from shallower depths at places off to one side of the orbiter's orbital path. At such high altitudes for the Titan orbiter, it will be hard to make the horizontal "footprint" of the sounder's downward beam narrow enough to minimize this problem. Therefore, Lorenz uses a subsurface radar sounder as one of his big selling points for a Titan balloon or powered aircraft.

[Guest_Richard Trigaux_*]

Yes Bruce, I understand that radar sounding Titan in the way you describe above would be very difficult, especially without any extra-large antenna. This is my domain, so I can just confirm. Some improvements may come though:
-scanning Titan surface could allow to apply a deconvolution to the information gathered, so this could better the discrimination of side features.
-they could design some extra-large antenna, in a stripline technology with emitting slots, made of a supple material which could be rolled and stored into the spacecraft. But usually such revolutionarry solutions are not retained (or if they are, they often don't work). Perhaps such antennas should be tested first into Earth TV satellites.

On the other hand, radar sounding Enceladus should be easy, as the distance of a meaningful pass is very short. But no radar on a small piggy-back small probe! So I imagine the following scenario:

-The craft enters Saturn system into an hyperbolic trajectory grazing at Enceladus.
-It observes Enceladus springs, radar probe them, image them, and scoop dusts with an aerogel
-it releases the aerogel capsule, still into its hyperbolic trajectory back to Earth
-It brakes like Cassini did and began a more conventional mission aimed at Titan.

perhaps this is not the right order of events, but it may look like that. For instance the aerogel capsule could be released before the Enceladus encounter, with the main ship at a safer distance. But in this case radar sounding is not so good.

[ljk4-1]

Has someone considered a Titan airship that would drop ministations
across the moon and then deposit some explosive charges a short
distance away to record the effects?

The ministations could also serve as weather stations for as long
as they can survive. Hopefully by the time such a mission arrives
at Titan, batteries will last much longer than Huygens did.

Or maybe they could get energy from the moon itself? Perhaps by
converting some of the local chemistry to fuel?

[Guest_Richard Trigaux_*]

Or maybe they could get energy from the moon itself? Perhaps by
converting some of the local chemistry to fuel?

Windmills!!

Green energy!

Nobody expected winds on Titan surface, due to the scarcity of solar energy. But there seems to be noticeable winds generated by tides on the atmosphere.

Are such winds really strong enough to run a wind mill? I don't know. And anyway it will have some drawbacks too. But if it works, it may be a very convenient source of energy for a local station, which could then last one or two years, at least as long as the buffer batteries hold. It's enough to catch titan quakes, if there are, or Titan meteorology.