The same thing is true of the UVIS, whose main purpose is obviously to identify the cloud UV absorber. In fact, Esposito proposed a "Venus Composition Probe" for the first Discovery AO (I don't know whether he repeated it) that would have been split into two modules: a vented one just for upper-atmospheric analyses carrying mass and UV spectrometers, and an armored module to survive until impact carrying atmospheric structure sensors and an IR spectrometer to proofile reactive trace gases.

As for Rehling's proposed composition-mapping high-altitude balloons: it might well be possible for them to get acceptable near-IR spectra of the local surface (at least through the limited spectral sunlight windows allowed by Venus' atmosphere and clouds); but it's more open to question as to whether they could get useful images. Tjhere have been quite a few studies of that, reaching differing conclusions:

http://www.sciencedirect.com/science?_ob=A...eb2b26976a8d59f (I ahve Moroz's complete 2002 article, but it's no longer available for free on the Web.)

http://www.lpi.usra.edu/meetings/LPSC98/pdf/1646.pdf

http://www.aas.org/publications/baas/v35n4/dps2003/376.htm

The 1998 one was done in connection with the "VEVA" Discovery proposal for droppable imaging probes ( http://trs-new.jpl.nasa.gov/dspace/bitstre...6/1/00-0365.pdf ), which actually reached quite optimistic conclusions: "Venus’ atmosphere has an opaque cloud deck above ~47-km altitude. Our simulations show that by imaging below the cloud deck in a window in the CO2 absorption at about 1 pm, interpretable images can be obtained even from 47 km altitude (images from this altitude will show primarily surface elevation differences due to the differing optical path lengths to the surface; lower areas will appear brighter). We also simulated the effects of near-isotropic lighting on aerial photographs and found that roughness-induced differences in apparent surface brightness (self-shadowing) provide good contrast between units even under these conditions."

With regard to long-life missions, the Russians developed quite a few techniques, some of which you see copied in the Pioneer Venus probes.

1. Phase-change materials to absorb heat. Venera-8 used Lithium Nitrate Trihydrate, a substance that has almost the latent heat of fusion of ice, but melts at 30 C instead of 0 C. In the Venera-9 to Vega landers, a small internal fan circulated the air through a "heat battery" of this material. Instruments that extended outside the insulated hull were also packed in a layer of LiNO3.3H2O, the cameras and x-ray soil spectrometer, and external instruments like the IR/Visible spectrometer.

2. Insulation. They did a lot of research on this, developing some special high-temperature organic polymer foams and ceramic foams for the landers. Their early long-life lander proposal was to be insulated with aerogel. Alternating sheets of fiber quartz and metal foil was also used in places.

3. High-temperature lubricants. Molybdenum Sulphide mixed with metal flakes was developed for things like the Venusian soil drill. The used MoS2 instead of graphite (used by NASA) in space and on their Lunokhod rovers, based on some automated fiction tests onboard the early Zond probes.

4. Connectors. Russians are fascinated by connector technology for some reason, and special ones were developed for the external electrical systems on Venera landers. Given that the Pioneer probes shorted out, perhaps this is not a problem to be underestimated.

5. Coatings. Polysiloxane was popular, as an enamel paint for some parts. An almost indestructable polymer, semiorganic on a Silicon-Oxygen-Silicon clain.

6. Hardened electronics. I'm amazed by the amount of external instrumentation on the later Veneras, Ksanfomality's seismograph for example. I'm not sure what the technology was, Silicon MOSFET or possibly even miniaturized vacuum tubes.

7. Power sources. The Venera landers were powered by batteries (Silver Zinc are extremely energy dense). But they did some research on radioisotope thermopiles, windmills and solar cells. The surface is too dim for solar cells as it turns out. Small windmills did operate some of the Venera experiments that requried mechanical action during descent. And the Venerokhod rovers were to be wind powered.

Of course, they also took advantage of heat. Many "timed" events were activated by links designed to melt at specific altitudes on Venus. This included things like parachute reefing and covers on instruments to keep cloud goop off.

Don:

Venerokhod?

Do tell!

Bob Shaw

Yep. They developed a couple working models. Was used wind-powered electric motors, and another powered the wheels by direct drive from the mill.

Is there really some wind on Venus ground? Not sure, it seems a very quiet environment. At least dunes were not detected. If most of the sun heat is absorbed into the clouds, it is expectable that all the convection will happen into these clouds, not on the ground.

External connectors shorted on Venus probes? Possible explanations into this exotic environment:

-droplets of sulphuric acid
-action of other gasses, like HF (which attacks nearby everything)
-oxydation/sulphurization of insulators

eventually a very thin layer of sulphide forming on the surface of an insulator can be enough to turn it conductive, especially on Venus temperature.

There is air movement of 1 or 2 meters per second on the surface, and keep in mind the gas is more than 100 times as dense as air at sea level. It's enough to blow the dust off the landing ring, which you can see in progessive panoramas.

You can also see some metal parts turning white over time, so clearly there is also some chemical action going on.

Personally, I'm not confident that they understand what happened to the Pioneer Venus probes. All four probes experienced serious malfunctions at about 12 km altitude. There's a special report about it, full of interesting speculations -- the parts maybe wet with sulphuric acid, maybe some of the materials eroded or ignited, maybe the probe passed through a zone of unexplained electrical activity. The Russians have reported a zone of strong turbulence at that level, but of course their probes were built like tractors.

What is your estimate as to how much is left of the successful landers on Venus?

Have the older ones essentially corroded away by now?

I believe they are probably still all sitting there, pretty much intact. The chemical betteries and lithium salts inside would boil, but at 100 atm of pressure outside, I don't think they would burst open. Must be a mess inside.

OK





Where can we see this?






What special at 12kms? It is far below the cloud top, so there must be something else.
Perhaps it is an altitude where the air is getting ionized (from some minority ion contributor) so there may be electric discharges or something, from the air or from te probe.
Or there is a dust layer. sulphide dust may play tricks with insulators.



What would remain of the probes today? Not intact I think. Everything organic must be burned, even beyond charring: carbon must burn. Everything metallic, save perhaps gold, must be oxydized and sulphurized in depth. Even ceramics are not insensitive to things like fluoridric acid. After, with years, all those oxyds and sulphides would disagregate and turn to a heap of dust.

That left us with a bit of a problem: there are already several earth hardware on Venus, and some of which position is unknown. If one day we find them back, there will be no way to tell if it is of earth origin of alien origin (an alien probe fallen on Venus could remain visible for 100 millions years or more). What I suggest for this is to use material with a known isotopic composition. Otherwise, if we find a remnant of an artificial part, there will be forever discutions about where it came from.

You can see some examples of wind and other changes over a period of an hour or so:

Click to view attachment

Hydrofluoric acid is only present in minute traces, and sulphuric acid only in the clouds. At the surface, it is not clear if the atmosphere is even oxydyzing. The atmosphere is primarily carbon dioxide and nitrogen, both relatively inert gases. I believe the Venera and pioneer probes will be laying around fairly intact for thousands of years.

Thanks for the images, Don.

Changes are not drastic, but they are visible.

Even if there is no oxygen at ground level, there is SO2, which is weakly oxydized sulphur. At 450°C it is not difficult that this molecule breaks in the contact of any metal, to oxydize it. Sulpur too is released, which is an oxydizer too. H2S too can release sulphur. Then it is easy to guess that materials like steel will quickly oxydize in depth. But it is not sure in how many time.



What I strongly suggest would be that any attempt to design something on Venus would be tested in a Venus simulation chamber, containing all the known or suspected gasses there, together with some wind or electric discharges.

Such a Venus test chamber would require special steels or ceramics coating. But it would assess which material can really withstand Venus conditions, and how many time.

Once the organics have charred to carbon the remains should be extremely stable. Elemental carbon is just about the most stable, heat- and corrosion-resistant substance around. If there is free oxygen/fluorine/chlorine in the atmosphere it might oxidize slowly, otherwise it could last almost for ever.

tty

Don:

Are there enough images of the dust being moved to make an animated .gif? Or just the two you posted?

Bob Shaw

Do you have any pictures of the Venerokhod's?

Kodiak:

I found one - it seems they used Czarist-era technology, but kept quiet about it for reasons of Political Correctness! It appears that the lower part (the bit with eight legs) was known as a 'Turtle'.

Bob Shaw

Of course, Comrade Turtle had the honour of setting many a long and glorious Soviet space record!

Bob Shaw

And why didn't they have the Venerokhods launched if they were cheaper?

Economic problems forced big cutbacks in the Russian scientific space program. The failures of Phobos-1 and 2 and Mars-96 cost those teams credibility. Space stations seem to have had much higher priority than planetary probe missions. They also make good money from commercial launches, they're good at it, and they pretty much stick to that now.

Also, after the death of Keldysh, there was no longer a powerful acdemic champion of interplanetary exploration. The head of IKI, R.Z. Sagdeev, was much more interested in theoretical cosmic astrophysics than in interplanetary probes.

Click to view attachment

Don:

Ludicrously close to my joke version!

Ah, if only...

Bob Shaw

Thanks for the Pics

The turtle looks as if it came straight from a mini-putt course

Thank you for the image DonPMitchell.

And even though it looks like a crazy idea, it IS one working solution for a rover on Venus.
With solar cells not that efficient, a nuclear powersource that would risk overheating and melt.
(Unless you design something entirely new with a moderating liquid like lead which would be difficult at best.)

So yes the two windmills might look ludicrous, but with the round time for signals to Earth the Venerokhod would have to crawl rather than run.

And with the dense atmosphere the Venerokhod could have been provided with a larger generator than one might imagine since the rotors would have been pulled with a force more resembling that of running water than just a wind here on Earth.

I wonder if it would work for a Titan rover as well?

The image I posted is the direct-drive version, which used a transmission system to send torque from the mill to the wheels. Probably simpler and more efficient than trying to generate electricity and run motors. It was designed with an expected lifetime of one year on the Venusian surface, performing soil mechanics and temperature/pressure readings.

Click to view attachment

VNII TransMASH is an intersting and (by Russian standards) one of the more excellent design bureaus. They build turbine-powered army tanks and industrial robots, and were the designers of the Lunokhod rovers. They also built the little mini rover on Mars-3 and various penetrometer devices on Venera and Phobos missions. TransMASH robots helped clean up the Chernobyl accident.

Interestingly enough, they were involved with NASA in the design of our Mars rovers, and built parts of the ill-fated Beagle lander on Mars Express. They've done a lot of experiments with low-gravity and micro-gravity traction, and materials and lubricants for hostile environments. They have a whole lab in a "vomit-comit" aircraft, to run experiments at Lunar or Martian gravity levels.

Click to view attachment

It might be one idea to consider as a powersource, especially since any nuclear power source would have so much waste heat that it could cause problems both on the surface and also in the atmosphere around the rover, and in worst case turn it into the first Titanian submarine - providing the hypothetical ocean are there.

Even so im not certain that a rover is the best vehicle for exploring Titan, with a surface which might be a colloid over wide areas a rover might end up being one record breaking expensive machine for making whipped cream while getting nowhere.

Titan's atmosphere is so dense, I would look at some sort of low-altitude balloon probe for mobile exploration.

OPAG's Titan subgroup has alredy put in a lot of thought on the wheeled versus aerial rover controversy. Rovers have already been designed for Titan and other worlds years ago with inflatable tires so gigantic than they can cheerfully roll across the surface of water: http://www.space.com/scienceastronomy/sola...tan_001020.html . But the steep-walled gullies discovered by Huygens, which are probably very common on Titan, might still present a serious problem for them.

However, the main reason why OPAG prefers an aerial Titan vehicle is simply that the really interesting differences in Titanian surface composition seem to be spread across very long distances rather than short ones. This was mentioned at the November COMPLEX meeting, and is also mentioned at http://www.lpi.usra.edu/opag/oct_05_meetin...an_work_grp.pdf (pg. 5).

There have been a lot of studies about more balloon missions to Venus. The French proposed a couple concepts in the 1970s, a large complex balloon probe or many small simple ones. Of course the Soviets actually flew a couple balloons (often incorrectly attributed to the French, but it was not their balloon).

There was a joint discussion of imaging the surface with a balloon at a lower altitude. Moroz pointed out that you have to get quite close to the surface to see anything, except at long wavelengths.

The "clear" atmosphere on Venus is not really clear. I remember Grinspoon on a BBC program described how you would see the surface as soon as you got below the cloud layer, but I think that's way off. Look at how opaque the atmosphere of Titan is, and it is quite a bit less dense than Venus. Rayleigh scattering is the problem, not just haze.

Just an idea off the top of my head, but I wonder if you could build a sort of tumble weed probe for the Venus surface, that would just be pushed around by the wind. You couldn't control where it went, but it would sure be a lot simpler than some sort of radio-controlled rover.

Don:

A stainless-steel bellows, able to expand (and thus take off as the density of the whole structure is reduced) and then drift to a new landing site, that's the way. You could even design it to be wholly automatic, with no clever mechanisms employed, just some phase-change chemicals and thermocouples...

Not a rover in one sense, so much as a series of landers...

I still like the windmills, though!

Bob Shaw

(1) Grinspoon isn't the only one who's lots more optimistic than Moroz about imaging Venus' surface optically from high altitudes. See my May 15, 2:14 AM entry on this thread. (Also note how sharp shadow edges and the horizon seem to be in the Venera 13 and 14 shots.)

(2) That stainless-steel bellows balloon is already being talked about. Viktor Kerzhanovich described it in http://www.lpi.usra.edu/meetings/lpsc2005/pdf/1223.pdf , and at the first VEXAG meeting in December somebody during the final summary talks orally described it as far preferable to a wheeled rover -- especially since, given Venus' high atmospheric density, a craft using it would really be more like a submersible, precisely adjusting its buoyancy to cruise along just a few meters above the surface and periodically touching down for sampling. (We are, once again, assuming a rover capable of surviving Venusian surface temperatures for long periods without cool-off periods.)

One side note: Kerzhanovich says that polybenzoxasole apparently isn't working out as well for Venus surface balloons as hoped. "Prior technology development efforts had concentrated on a single balloon that could operate across the entire 0-60 km altitude range, tolerating both the sulfuric acid aerosols and the extreme temperatures of -10 to +460 deg C. However, this problem was unsolved because no combination of sufficiently lightweight balloon material and manufacturing (seaming) technology was ever found to tolerate the high temperatures at the surface." However, when I E-mailed him to check this, he qualified that previous statement somewhat. I'll need to dig up his E-mail for more details.

(3) Since Don Mitchell has come late to the party: shortly before his arrival we had quite a long exchange here of recent information about Titan exploration techniques -- notably the "Titan Organics Explorer" airship designed in two altenative models by a JPL team (propeller-driven hydrogen blimp vs. wind-blown hot-air balloon): http://www.lpi.usra.edu/opag/oct_05_meeting/jpl_titan.pdf . There was a presentation on this at last December's COMPLEX meeting, which I attended -- in which a scientific appraisal group concluded that the wind-blown version, while obviously far less controllable in its selected touchdown sites for surface sampling, was nevertheless probably scientifically acceptable for this mission, as well as obviously being a lot cheaper.

The sample-return plans are fascinating. That's why I talk about getting out of ISS, because I'd like to see them take on some meaty challenges like that.



Rayleigh scattering is straightforward math, which Moroz did. Rather than be optimistic or pessimistic, I calculated the effect in a special purpose ray tracer.

The Venera surface images don't tell you much. The horizon is only 50 or 100 meters away, and aerial perspective is already evident. Especially in the color images, where you can see the greenishness of the in-scattering of distant areas.

Click to view attachment Click to view attachment

Here's an example of calculating first-order rayleigh scattering (a more accurate multi-scattering calculation would look more opaque). Unlike the image I posted a few days ago, I've turned the Venusian atmospheric scattering up to 100 percent. You can see a couple kilometers, but you cannot see the surface from the cloud level.

Now this gets better very quickly with longer wavelength. Rayleigh scattering is proportional to the fourth power of the reciprocol wavelength. So the answer is to just design a long-wave IR camera. Note that the nice images of Titan's surface are all infrared. A possible problem with Venus is that as you go into the infrared, the thermal radiation from the surface might wipe out features. Blackbody radiation varies with reflectivity (how black the body is, literally), but it may be a very bad way to see any features of relief. We will see first-hand if the ESA ever shows us some VIRTIS images!

Was it a "smart" rover, could it be controled, or was it dumb(preprogramed?) like the Prop-M on Mars-3?(go forward, hit something, backup, turn, go forward.....like todays robotic vaccum cleaners)

Speaking of Venus rovers, does anyone else remember the Soviet Venus rover
that battled Steve Austin in The Six Million Dollar Man?

http://cgi.ebay.com/KENNER-SIX-MILLION-DOL...1QQcmdZViewItem

Someone actually built one (includes episode synopsis and how a Soviet
Venus Rover actually got back to Earth to menace humanity:

http://www.teamdelta.com/venus/venus-a.htm

"Exterminate! Exterrrrrminate!"

I do. (My nephew, who was 8, was watching the episode.) I also remember it was a much better actor than Lee Majors.

Indeed Venus surface is nearly red hot, so we may expect that it is bright in very near infrared. That would still allow us to get IR spectrum (not reflexive, but emissive). Perhaps from the blackbody curve of a given spot we could derive its altitude, and thus obtain an altitude map, but still inaccurate.

This makes that a Venus flyer would need a mapping radar altimetre in more of a camera. And the Rayleight opacity makes that the flyer needs to be relatively close to the ground, and thus heat-resistant.

I agree that a low-altitude aerostat would be more interesting that a rover. I think it would be very valuble to just get an idea of the diversity of terrain on Venus. The four Venera surface images show at least three completely different terrains (flat lava field, rolling hills with rocks and soil, and a steep hillside covered with boulders). There are lots of technical problems with a Mars or Venus balloon mission, but then again, landing on the surface has not been trivial either.

For surface missions, a network of seismometers would be intersting, because it would answer questions about the deep structure of the planet. The Russians have already done most of the research on that, and such landers could be small and simple if they do not include cameras and other complex experiments.

Obviously, what we need is a giant instrumented yo-yo anchored high up in the atmosphere, that would roll down, take readings/images, and roll back up again.

Hehe. But maybe an aerostat would be designed to dive down for short times and then rise up to cool off.

Such a network could do its work in a short time, without need to be heat-resistant, provided that a seism is triggered during this time. But the only way to trigger a seism on Venus is to land an explosive (an impactor would lose its speed into the atmosphere). The problem is that a high charge is required, ten tons or more, perhaps 100 tons.

Otherwise, it is prettily difficult to guess how many times Venus has natural quakes, and how powerfull. To wait for one would require heat-resistant landers.


With my opinion the key of studying Venus is a true heat-resistant probe, able to sustain the full brunt of the surface temperature. THis was discussed earlier in this thread.




It would have so much advantages, the main being that it could see or analyze much more places than a rover.

Also it is so easy to fly on Venus that a rover don't make sense. A very small aerodynamical baloon can sustent an heavy vehicule, and this baloon can be filled with a variety of gasses, some available on the place: water vapour, methane, nitrogen, all this fly very well in Venus C02, and the leak rate is much slower than with hydrogen or helium. (Important, as this leak rate will be much higher at 450°C than on Earth.) Even the envelope is not a problem, a sheet of metal could do the job. The only problem is that common metals will be quickly oxydized by the Venus air, even if it contains only little oxydizing gas (oxygen, S02...)

A nuclear charge in the kiloton range weighs only a few hundred pounds, and that is for a ruggedized charge meant to be shot from a gun.
Incidentally such charges are usually U235-based gun-type weapons since it is difficult to make an implosion-type Pu239 bomb narrow enough to fit into an artillery shell. U235 of course means that the possible contamination from a launch accident would be minimal.

tty

It might be a fantasy. I think that the aerobot will have more troubles to try to have a good navigation control than a rover. As I have learned that on the surface, there is very low wind speed, at about 1/2 meters per second but it pushes very hard toward one direction and if the aerobot want to stop there, so, it will need good enough propulsion (helix) to maintain in a fixed point during the scientific mission. Now, the other problem, when aerobot want to cool down, at upper atmosphere has stronger winds and probably some thunderstorms or lightings which is still not well known. The Gallileo fly-by mission has ascuted some strange lightings from Venusian's atmosphere.

I think that before to nominate that the aerobot is the most factible than a rover for a scientific mission, first we need to know much better about Venusian atmosphere. Hope VEX will give some understanding lights in spite of the fact of a big loss from unoperative PFS.

Rodolfo

Yes, this is a problem. But the solution could be, simply, to land. the aerobot can land to observe the ground, otherwise it slowly shifts above it, and can go at higher altitude to have faster winds. Anyway an aerobot won't go very fast, unless it has plenty of power. The reason is that Venus air is very dense, it is like into water. So a baloon-sustended aerobot will be slow.

A solution would be to have the aerobot using a kite (with some gas in to keep it high). This would give some differential wind speed and allow some manoeuver. Or a guiderope, which would maintain it at a constant altitude.

Anyway a lander will have to sustain the full temperature of the ground, otherwise it will be limited to some hours, at best some days. An aerobot will not be able to yoyo fast enough to cool, so we have the same requirement. There could be a high altitude baloon letting descend an instrument case with a rope, but there is now the danger of storm, perhaps tornadoes, hail, lighning, etc.

What I see the best would be an aerobot made of a baloon, but a baloon operating like a submarine ballast: pumping in and out the sustentation gas will allow the aerobot to land efficiently (without being drag by wind) and lift-off when required. But this aerobot would also operate a kite (with some gas too in it) with a wind mill. Wind mills will certainly operate like thunder on Venus, even with slow winds at ground level. If the kite is high enough, it could get better winds. This would give the probe plenty of power without the need for a RTG. At a pinch, a baloon alone could operate a wind mill. When flying, it obtains no power, but when landed, it has plenty.

Lightning seems unlikely to be a problem for cloud-level balloons -- Cassini's much more sensitive measurements during its second Venus flyby showed no trace of radio-burst evidence confirming Galileo's extremely ambiguous earlier results. As for winds: JPL has already done a great deal of study on the complex problem of a balloon trying to use Venus' strong upper-level cloud winds for actual navigation across the planet (which will require using suah an aerobot's altitude control to ascend or descend to different atmospheric layers where the winds are flowing in different directions.)

As for the need for controlled variable buoyancy in such an aerobot: the solution that was devised over a decade ago is considerably more ingenious -- and less wasteful of gas -- than Richard's idea. Describing it here would take a bit too long: see:
http://trs-new.jpl.nasa.gov/dspace/bitstre...7/1/99-0750.pdf
http://trs-new.jpl.nasa.gov/dspace/bitstre...7/1/95-0437.pdf
http://trs-new.jpl.nasa.gov/dspace/bitstre...0/1/95-0375.pdf
http://trs-new.jpl.nasa.gov/dspace/bitstre...9/1/99-1802.pdf
http://trs-new.jpl.nasa.gov/dspace/bitstre...3/1/96-1466.pdf

On the navigation question, see:
http://trs-new.jpl.nasa.gov/dspace/bitstre...3/1/97-0880.pdf
http://trs-new.jpl.nasa.gov/dspace/bitstre...5/1/96-1155.pdf

And for a detailed discussion of the possible design of such a mission, see
http://www.planetary.brown.edu/pdfs/2056.pdf

My idea was to have a baloon working like a submarine ballast. A submatine ballast compresses air into a reservoir to lower buoyancy, and releases it in the ballast to increase buoyancy. This requires energy, but basically don't waste gas. Anyway it may be possible to have a compact instrument able of extracting some lighter gaz from the Venus athmosphere (steam, neon...)

The solution proposed here is a baloon which alternates short excurtions to the ground with longer stays at high "cool" altitude. The gaz is liquefied at high "cool" altitude, and it evaporates with the heat near the ground. So the atmosphere itself is the energy source which "compress" or release the gaz into the ballast. This solution is certainly smarter to work, it eliminates the need to sustain the ground temp for electronics, but it is much less flexible for a detailed ground operation. With my opinion it will be retained for a first attempt, but further missions should not elude the need for a high temperature ship, able to remain near the ground for a long time, and no more elude the energy source, RTG or better a wind mill.

The mission profile studied here is enough to get some samples of the ground, and have for instance isotopic annalysis or datation. But we want to search for ancient sedimentary layers (in mountains), which could even contain fossils, we shall need an aerobot able to change altitude at will and remain for years near the ground.

There can be no doubt about that at all. The variable-buoyancy aerobot was designed from the start on the assumption that we will not yet have a lander capable of operating for long periods at Venus' surface. If we develop the latter, there will be no need to have it lift high above the surface -- except when we want to rise to a high altitude in order to let the faster winds up there send the craft swiftly to another part of the planet.

One footnote: while some versions of this aerobot use solar cells capable of enduring Venusian surface temperatures to power the craft, other models use a windmill which would be powered by the aerobot's own constant vertical motions up and down through the air. Given the fairly fast descent/ascent speed (and the dense air at lower altitudes), such a windmill could generate quite a lot of power.

Probably, the windmill would be the best solution. It is simpler and it would have greater probability to work nicely. However, the windmill will only work if the aerobot is fixed on the land. Otherwise, it would drive crazy. Maybe, with Richard's suggestion is that before using the windmill, aerobot must use some kind of anchor and rope to grasp the Venusian's surface.

Rodolfo

The Russians found that light on the surface is too dim for solar cells to be practical. There were three experimental solar cell panels on Venera-11 to Vega. They did develop an RTG for Venus, based on silicon and germanium, and that seems like the best bet. Solar Cells are OK if the balloon flies at a high altitude.

I haven't read Moskalenko's papers yet on Balloon navigation. He was the (largely uncredited) brains behind the Vega balloon system, but I am told he designed a more complex system with controllable altitude.

Given an RTG power supply, another possability for a long-term surface mission is to simply refrigerate a small well-insulated compartment, for any components that cannot operate at ambient temperatures.

I think that a wind mill would be even better than a RTG, technically (besides that Greenpeace would not oppose it, and other political problem, like fitting an american , or worse russian RTG to an european mission.).

The wind mill won't look like traditionnal Earth models, it would rather look like some bulbous turbines used into running water. A large bulb containing a sustentating gas (of constant up buoyancy), blades, a rope attached to the rover, and a wing attached to the bulb to give it an appropriate horizontal position despites the oblique pull of the rope. If the rope is long enough, the wind mill could catch better winds than on the ground. For this the rope could be carbon nanotubes, which will at least achieve this role before being used into the space elevator.

The only problem with the windmill is that it works only if the aerobot is fixed to the ground. The only reliable solution to fix it to the ground is to remove all buoyancy, with a ballast-like compartment. We could try to grastp at the ground, but it can be too flat, or loose (sand).

Another solution to create a negative buoyancy without adding mass would be to compress the air until it becomes liquid. But is this is thermodynamically possible at 450°C?

The solution of a very long cable would allow to use the difference between ground wind and altitude wind, whenever the aerobot is fixed or moving.



This was discussed sooner into this thread. I think it is no, because, thermodynamics dixit, such a refrigerator, working with a very large range of temperature, would be very inefficient, consuming much power. At a pinch, a RTG producing large amounts of waste heat, could be used for certain cycles which consume heat rather than mechanical energy ("fuel fridges" used in regions without electricity).

I did a little presentation of possible solutions for electronics working on Venus, sooner in this thread. There was some interesting comments about searches already done.

Venera-D is a Russian mission, not European, so I think their RTGs will fit. I also don't think they care much what Greenpeace thinks. In general, it is not important what they think. That has never stopped NASA or Russia from sending an RTG into space.

Who is thinking seriously now about doing a balloon probe to Mars? ESA and NASA separately?