Printable Version of Topic

Posted by: SFJCody Jan 15 2005, 03:37 PM

Is a Discovery class Titan lander/aerobot remotely conceivable?

It would be nice to see Cassini's relay capability get a second workout...

Posted by: gpurcell Jan 15 2005, 05:50 PM

DISCOVERY class??? No way in Hell.

Posted by: tedstryk Jan 15 2005, 06:19 PM

Not unless it was piggyback on some larger mission.

Posted by: lyford Jan 15 2005, 07:24 PM

Unless you meant this Discovery class:


Sweet!

Posted by: SFJCody Jan 15 2005, 09:06 PM

Perhaps China or India will become convinced that a Titan mission is necessary for increasing national prestige.

Posted by: djellison Jan 15 2005, 09:18 PM

I certainly think a blimp or similar would be a wise idea - drifting during the long titanian day - and settling to the ground at night. In a world with a thick atmosphere and low gravity - Blimps work very VERY well

Problem is - it'd have to be RTG powered, so it'd have to be quite heavy - and thus very large - probably something like 1 - 1.5 tons to Titan - outside the scope of anything but the heaviest launch vehicles today - and even then, would require multiple flybys of multiple planets to get there.

Ideally you'd need a companion orbiter to relay - use electra technology relay in UHF - and get 100kbps from blimp to orbiter and orbiter to ground.

You could have a large heatshield of the blimp descent stage at the top/front of the spacecraft, and use it for Aerocapture at titan - saving a LOT on delta V

Doug

Posted by: tedstryk Jan 15 2005, 09:44 PM

India and China in 30 years maybe, but right now they are struggling with designing basic lunar orbiters. Russia, even if it stopped being so poor, probably couldn't, as it has had a very difficult time with anything farther away than Venus. True, the Vegas lasted a while, but they have never had a deep space probe last more than around three years or so, and that was only rarely achieved. And I don't think there technology has improved too much. The Japanese also have had problems with longterm missions and probably could not afford to go-it-alone on a Titan mission. This leaves NASA and ESA. Given the political weight the anti-nuclear freaks carry in France and Germany, it would surprise me if ESA launched a probe with an RTG. So this leaves NASA.....or perhaps another NASA/ESA colaboration.

Posted by: David Jan 15 2005, 09:46 PM

Do you mean a balloon (of whatever shape), not a blimp? I just ask because you use the word "drift", which is of course not what a blimp (a non-rigid dirigible airship) is supposed to do.

Because a blimp would have to contain gas at a higher pressure than that of Titan's atmosphere in order to keep its shape, it might be inferior to a rigid dirigible. On the other hand I suppose a heavier mix of gasses would provide greater lifting capability than on earth. But how do you generate and maintain the gas, given that there's always going to be some leakage?

What are the disadvantages of a light, fixed-wing remote-controlled drone aircraft? It seems unlikely that it would run into anything -- if we can discount the giant metal-eating Titanian bats.

Posted by: djellison Jan 15 2005, 09:55 PM

Well - I was thinking a balloon - not a powered blimp

Doug

Posted by: SFJCody Jan 15 2005, 10:11 PM

http://www.lpi.usra.edu/meetings/outerplanets2001/pdf/4003.pdf


http://www.lpl.arizona.edu/~rlorenz/jbis.pdf


http://www.lpl.arizona.edu/~rlorenz/IEEE.pdf


http://www.lpi.usra.edu/meetings/LPSC99/pdf/1088.pdf

Posted by: lyford Jan 15 2005, 10:25 PM

What about a fleet of these?


You would need an orbiter of course to relay the data to, but these little guys would be able float and roll over any thing, maybe even get "air" every now and then. They serve as their own landing system as well!

Long term power would be an issue, but perhaps there could be some generator that could convert the rolling motion from the wind into electricity.

Or not!

For the curious:

http://robotics.jpl.nasa.gov/~behar/southpoletw.htm
http://www.nsf.gov/od/lpa/newsroom/pr.cfm?ni=55

Posted by: BruceMoomaw Jan 16 2005, 02:36 AM

There has already been a great deal of design work put into a possible Cassini follow-up (especially considering how little we kenw about the surface!). And there seems to be a convergence on the idea that a "Flagship"-class mission -- that is, one costing about a billion dollars, like the originally planned chemically-propelled Europa Orbiter -- could be flown in the next decade, consisting of a small blimp (with some kind of surface sampling gear) accompanied by an orbiter for comm relay and mapping. One JPL engineer has even devised a scheme for an "Aerover" -- a combination rover-blimp, with four huge inflatable helium-filled tires (as have also frequently been proposed for later Mars rovers) which could periodically be augmented by an additional inflatable helium-filled bladder so that the rover could gain enough extra buoyancy to lift off the surface and take to the air again. A kind of Titanian flying monster truck.

But since the Solar System Decadal Survey recommends only one non-Mars Flagship-class Solar System mission per decade -- and Europa almost certainly has dibsies on the first one -- I imagine we won't see a follow-up Titan mission until the 2020s. And when we do get one -- espcially since one of its most important goals would be to study any areas which have recently had short-lived outbreaks of liquid water, to see what stimulative effect that has had on the local organic chemistry -- the more high-resolution mapping of Titan's surface we can do from space before dispatching another lander, the better. This is another argument for having Cassini focus intensely on Titan during at least part of its extended mission.

Posted by: tedstryk Jan 16 2005, 02:56 AM

And indeed it should, after a few more icy satellite flybys, except of course if there is some great discovery at Enceladus that changes its priorities. Also, it will be interesting to see what happens once we know more about Titan's chemisty from Huygens and Cassini, and have better mapping. In a way, I am hoping JIMO hangs on another year or two....with some major discoveries, without a flyable Europa mission on the drawing board, Titan may leapfrog Europa in priority should major discoveries be made. Remember, when the decadal survey was done, for all we knew Titan could be a cratered, dead world with an atmosphere. Frankly, I think Io is the most interesting of the Jovian moons and I would put Ganymede and Europa in a tie. Europa's privledged status us due to the astrobiology folks who think they are going to find ET under the ice. Interesting moon, but not more than the other Galileans, except maybe dead old Callisto.

Posted by: SFJCody Jan 16 2005, 03:21 AM

That would be a great pity. A JGA to Saturn is possible for a spacecraft launched in the mid/late 2010s, but not for one launched in the 2020s. A similar opportunity does not reoccur until the 2030s.

The last time such a window was missed was in the late 50s/early 60s.

Posted by: BruceMoomaw Jan 16 2005, 04:15 AM

First, the number of "shitheads" who think there's a serious chance of life under Europa's ice is very large indeed; see the National Research Council's reports specifically on that subject. (Indeed, the possibility of complex prebiotic compounds on Titan -- espeially in areas where cryovolcanism or big meteor impacts may have generated reservoirs of near-surface liquid water in its ice -- is by far the most important argument for exploring it.)

And a good case can be made that the discovery of Europan life might turn out to be far more scientifically important than the discovery of Martian life, since it's coming to be accepted that even if we do find evidence of present or fossil life on Mars, there's an excellent chance that we will never be able to determine whether it appeared there originally or whether it's just the descendants of Earth germs catapulted to Mars via meteorite. Or, perhaps, the opposite is true -- but in either case, we would still be unable to prove that life isn't after all the result of some incredibly unlikely chance event that just happened to occur on one world in this Solar System and then got transplanted to another. (Ths is a very real scientific possibility.) Meteorite exchanges between Europa and the inner worlds, however, are extremely rare. While they're not quite nonexistent, if we discover Europan life the odds will be extremely high that it did evolve separately, and so -- since life appeared independently on two worlds in one solar system -- we will be able to conclude with a high degree of certainty that it IS a common phenomenon in the Universe. (Moreover, if life ever did evolve on Europa, the odds that it's still around are much higher than on Mars, since there's no evidence that Europa's environment has gotten more hostile over time. )

As for the lack of a JGA opportunity to Saturn in the 2020s: this is nowhere near being a really serious stumbling block. A mission could use one or two Earth gravity assists -- plus, perhaps a solar-electric propulsion stage that would greatly acelerate the spacecraft in the inner System before being ejected during the trip out through the Asteroid Belt -- to reach Saturn in a very reasonable time without a boost from Jupiter. Moreover, the plans for a follow-up Titan mission usually call for it not to carry a big load of fuel to brake into orbit around Saturn (let alone Titan), but insted to just fly directly past Titan at low altitude and aerocapture itself directly from solar orbit into orbit around Titan, thus tremendously cutting down on the mass of fuel needed. (A pity we can't do that with Europa!) And such a spacecraft therefore wouldn't have to approach Saturn as slowly as Cassini did in order to slow itself into Saturn orbit -- it could race there as fast as the Voyagers did. (To do this, however, we do need very accurate data both on Titan's ephermeris and its atmospheric density profile, along with any changes over long periods of time in the latter -- still another reason for Cassini to observe Titan in detail during an extended mission.)

Posted by: BruceMoomaw Jan 16 2005, 04:22 AM

One additional note: one of the Galileo mission's major discoveries -- thanks to its gravitational-field profiles of the moon's inner density -- is that "dead old Callisto" is actually every bit as geologically interesting as the other Galilean moons, and maybe even more so. The very fact that its internal rock is only partially differentiated into a core separate from its ice mantle has become a major puzzle/clue in understanding how the Galilean moons (and the moons of the other giant planets) formed -- since standard theories had predicted that the heat from the impacts of the inrushing small "satellitesimals" that crashed together to form Callisto should, by themselves, have generated enough heat to allow its rock to completely separate from its temporarily melted ice and settle in its core, as with Ganymede. The distribution of material in the debris disk orbiting early Jupiter must be radically different from what had been thought.

Posted by: David Jan 16 2005, 04:30 AM

Well, I certainly don't want to say anything against a mission to Europa, or anywhere else in our still mostly-uncharted Solar System. I might question whether the discovery of life really is or ought to be the only reason for exploring space, but this is probably not the time or place. But I suppose I can say that on a scale of planetographical interest (my reason for being here), where 10=Earth and 1=any random heavily cratered inactive icy moon, Titan has just leapfrogged up to a 9.5 (with Io a 9 and Mars maybe an 8).

And yes, I agree that Cassini should be extracting every last bit of data out of Titan that it can. May Cassini's mission be a long one.

Posted by: Mongo Jan 16 2005, 04:49 AM

This is becoming OT for this thread, but I thought that I would register my opinion that, assuming Earth-type life existed on both Earth and Mars, is is FAR more likely that it would have originated on Mars, and then was transported via meteorite to Earth, than the reverse. I think this for two reasons:

1) The mass of (possibly living microbe-carrying) rock transported from Mars to Earth would be several orders of magnitude greater than that from Earth to Mars, mainly due to the smaller gravity well of Mars compared to Earth. It's a double effect--rocks are much more likely to be blasted free of Mars's gravitational infuence (while avoiding being heated to lethal temperatures) than is the case from Earth's considerably larger gravitational influence, and then the meteoroids are more likely to be captured by the larger Earth than by the smaller Mars.

2) Mars apparently would have been inhabitable by some form of life considerably earlier than was the case on Earth--and of course would have soon become more-or-less uninhabitable, at least on its surface, while Earth remained inhabitable ever since.

So it seems to me that the most likely path that 'terrestrial' life took would be the following:

1) Mars becomes stably inhabitable (i.e. no more giant sterilizing impacts).

2) Life emerges on Mars. Large impacts scatter meteoroids containing live Martian bacteria or spores through the inner Solar System, but no other place is inhabitable. Life may have repeatedly established itself on Earth, only to be destroyed by giant impacts each time.

3) Earth becomes stably inhabitable.

4) Almost immediately after 3) happens, Martian life establishes itself on Earth. This fits the geologic record, which shows that life seems to already be established almost instantly (in geologic terms) after conditions on Earth's surface allow this.

5) The surface of Mars gradually becomes uninhabitable. Life may still, however, exist underground, producing the anamolous methane/ammonia readings.

6) A rock is blasted from Mars fairly recently (about 15 million years ago) and lands in Antarctica. It appears to contain evidence of life.

Bill

Posted by: ustrax Jan 12 2007, 05:12 PM

http://www.esa.int/esaCP/SEM7QJRMTWE_index_0.html

Not THAT cold...

2 years since the landing...How time flies!

Posted by: nprev Jan 12 2007, 05:23 PM

Hmm...the argon-40 ratio seems to indicate current internal activity. That's kind of an unexpected finding for a body of Titan's gross composition, isn't it? Given that, maybe Enceladus really DOES have an unusual abundance of radionuclides after all...

Posted by: ustrax Jan 12 2007, 05:53 PM

That's a good one, but what made me scratch the head was the wind no-velocity...Creepy stilness!
I'll be doing http://spaceurope.blogspot.com/2007/01/further-ahead-dr-jean-pierre-lebreton.html to the mission manager during this weekend.
Do you want me to add yours?

Posted by: nprev Jan 12 2007, 06:14 PM

If you think it's appropriate, then by all means please do. Thanks!

Posted by: JRehling Jan 12 2007, 07:15 PM

I'm not sure the Argon 40 indicates current activity: It only indicates that there was a lot of post-primordial outgassing.

And radiogenic heat is not the only explanation. Titan has an elliptical orbit and its primary is 95 times the mass of the Earth.

As for the lack of surface wind, Titan receives only 1% the solar input the Earth does, it rotates 16 times more slowly, and much of the solar heating takes place at altitude.

So there's some explanation for all of these things. Not necessarily the right explanations...

Posted by: edstrick Jan 13 2007, 12:57 PM

Argon 40 is a radioactive decay product of Potassium 40, a common isotope of a common element with a very long half life.

Argon 36 is primordial, not a decay product. An atmosphere could have primordial argon, which would be an approximately solar mix (whatevern the number is) of 36 and 40, together with outgassed decay product argon 40.

Over time, you HAVE to start out with 100% primordial argon, and then add outgassed argon 40 to whatever is there. While you're adding outgassed decay product, you can also outgass trapped primordial argon with it's original ratio, AND have the atmosphere lose whatever argon is there on a continuing (potentially/probably) varying rate.

Note that from the density of Titan, you can make a good estimate of the ice/rock fraction by mass, and assuming reasonably "solar" composition of the rock, calculate the amount of Potassium 40 in the moon. Given that, and the amount <or lack of amount> of Argon 36 in the atmosphere, you can model away to your heart's content the evolution of argon in the atmosphere as the moon outgasses and as atmosphere is stripped away.

Posted by: nprev Jan 13 2007, 06:31 PM

Thanks for the great explanation (as usual! ), Ed. I just found it a bit puzzling that the argon-40 ratio was cited in this fashion in the press release. It almost seemed as if they were implying that the ratio was unexpectedly high, which in turn might indicate that Titan has more potassium-40 then expected with implications for the entire Saturnian satellite system.

I know that argon isotope measurements are often problematic; IIRC, some of the early Soviet Mars data was really jaw-dropping. Hopefully Ustrax will get some more detailed answers as part of his Q&A.

Posted by: edstrick Jan 14 2007, 10:53 AM

Regarding Argon and soviet mars probes, as I recall it...

Mars 3 was warming up instrumentation during descent for taking a panorama immediately after landing. Warming up may have been literally true: vaccuum tubes in some circuitry.

Mars 6 was prepping a mass spectrometer during descent for atmosphere composition analysis immediately upon landing. One of the very limited telemetry parameters transmitted during descent was a voltage or current on the mass spec's "ion pump" or something like that, that functions to maintain the vaccum in the analysis chamber. The pump current (i think) was abnormally high and way above expected levels. Since the vehicle was never heard from again after retrofire (followed within a fraction of a second of first impact, like the MER rovers), all they had was this anomalous engineering data to interpret. It could be reproduced by having a very significant amount of Argon in the atmosphere, which would be hard for the ion pump to trap or remove, compared with C02 or N2, and they suggested the atmosphere could be 30% or some largish fraction Argon, in addition to the CO2.

This was of major interest to the Viking GCMS team as their instrument was potentially damagable by ion pump overloading in a high argon atmosphere. As it turned out, both argon and nitrogen are in the few percent range. 1.5 % and 2.5% or so for one and/or the other. <can't remember which is which>

Posted by: edstrick Jan 14 2007, 11:20 AM

As I recall from press release stuff last year, Huygens saw little or no Argon36 and no Krypton and Xenon, despite a special concentrator for inert gasses that was to remove nitrogen and other reactive gasses from a sample for analysis during descent.

This means that Titan has *no* remnant of a primordial atmosphere of gasses trapped form the circum-saturn nebula.

This means that Titan either has *no* remnant of a primary outgassed atmosphere (formed immediately after accretion) that contained Argon, Krypton and Xenon that was physically trapped in the rocks and ices that form Titan, or that those gasses were never released from the interior <not likely, see below>.

This means that essentially 100% of the Argon 40 seen in Titan's atmosphere was outgassed progressively over it's history as a decay product of Potassium 40, and essentially zero % of the Argon 40 is primordial.

Thus, since the decay rate of K40 is known, and the total amount of K40 in Titan is approximately known (solar abundance in the rock component of Titan), we know that Titan has outgassed it's accumulated Ar40 with at least enough efficiency to put the observed amount in the atmosphere. This is ***NOT*** a trivial observation. The only things we don't know is (1) when the outgassing happened: efficiently and early, or more inefficently and later (when there was more Argon 40 produced) and (2) whether Titan has lost large amounts of Ar40 from it's atmosphere to space and has thus outgassed more than the observed amount.

Posted by: JRehling Jan 14 2007, 05:18 PM

It's nitrogen then argon.

They're in the same order on Venus, as well as Earth, as well as Titan. Argon's the bridesmaid.

CO2, SO2, H2O, and CH4 may come and go, but N2 and Ar show up everywhere.

Posted by: MarsIsImportant Jan 15 2007, 02:47 AM

Just a clarification...The actual numbers for Mars are:

95.32% carbon dioxide
2.7% nitrogen
1.6% argon
0.13% oxygen
0.07% carbon monoxide
0.03% water vapor
trace of neon, krypton, xenon, ozone, methane

Surface pressure 1-9 millibars, depending on altitude;
average 7 mb

Viking measured the % amount of carbon dioxide, nitrogen, argon, oxygen, carbon monoxide, and water vapor. The trace gases were found later.

*****
IMHO
The argon 40 number is significant for Titan.

Posted by: edstrick Jan 15 2007, 11:48 AM

"Viking measured the % amount of carbon dioxide, nitrogen, argon, oxygen, carbon monoxide, and water vapor. The trace gases were found later".

Without digging into inaccessible reports, I believe that Viking did measure the Krypton and Xenon isotopes with the GCMS. It was a difficult measurement and the results were a bit noisy and had poorly quantified systematic errors, but they got it. Nothing else has landed a precision Mass-Spec on Mars <and survived> since Viking.

You look on the reports of gasses evolved from SNC Mars Rock Meteorites from 15 or so years ago and they plot the rock-trapped gasses (from shock-glassified feldspar mineral grains) vs Viking measurements and it's almost a perfect straight line over many orders-of-magnitude abundance on a Log-Log graph. It was the damn-near-absolute-proof that SNC meteorites were Martian the people were asking for. Nobody had ANY PLAUSIBLE EXPLANATION for that measurement except "they came from Mars".

Posted by: nprev Jan 15 2007, 12:49 PM

...it sure isn't! What the heck is going on there? Argon-40's much heavier than nitrogen or carbon, so if there's no primordial argon left that probably means that there are NO primordial atmospheric constituents left at all.

The ESA release makes much more sense now. Sustaining that massive atmosphere must require some extraordinarily active processes (whatever they may be).

Posted by: JRehling Jan 15 2007, 09:43 PM

Nice thought, but Cassini wouldn't be around for that. Its lifetime is going to be terminated when it runs out of the propellant needed to point, and it would have to be mothballed soon to wake up years from now for a very small amount of relay-ing. I think Cassini is going to be a whiff of titanium vapor in Saturn's core before the next human artifact crosses the orbit of Phoebe.

Discovery? No way. Unless the lander were to be an inert sphere of metal.

Posted by: nprev Jan 15 2007, 10:29 PM

That's a glum but probably quite accurate assessment, JR.

Probably OT here, but has the success of Huygens whetted ESA's appetite for a future Titan surface mission? The buzz can easily start from either side of the Atlantic...

Posted by: Rob Pinnegar Jan 16 2007, 02:24 PM

Regarding the idea of a Huygens follow-up:

I suppose that, if we really wanted to go all-out, we could go for double mission: a rover with a detachable balloon tethered to it. This would reduce the odds of complete mission failure:

(1) If the balloon malfunctions during the initial landing, ditch it and send out the rover.

(2) If the rover doesn't survive the landing, cut the balloon loose so that it can independently explore Titan.

(3) Otherwise, leave the balloon tethered to the rover to act as a high-tech "crow's nest" to help the science team choose targets.

Since the rover has moving parts, it will likely break down first. Once that happens:

(3a) If the rover's wheels lose power while its science instruments are still functioning, put the rover in neutral and let the balloon act as a sail to drag it along the surface.

(3b) If the rover stops working completely while the balloon is still functioning, cut the balloon loose, and let it go on its merry way.

Actually, now that I think of it, this would really be a triple mission: the tether itself might also be useful for scientific purposes. Some thermistors could be woven into it to get vertical temperature profiles and, after the balloon was cut loose, the tether could be left hanging to give some idea of wind shear effects. Maybe also with some piezoelectric crystals to measure wind pressure?

There are two major caveats to this plan (besides the fact that it is wildly speculative and, in all likelihood, completely unfeasible from both economic and engineering standpoints):

(1) The rover had better be a lot heavier than the balloon. Otherwise the rover might get tipped over if the wind picks up. This might make option (3a) above impossible.

(2) There had better not be any lightning on Titan.