Because the RTG will be hotter. It's that simple.

An RTG produces heat *energy*. If radioactivity produces enough heat to warm an object by 10 K, it will do so whether it is from 1K to 11K or 1000K to 1010K. (Well, barring phase shifts, which are avoidable in the Venus case.) And the temperature differential is what makes power.

Thank you Rakhir.

I assume it will be close to opposition during landing, is that correct? Does that not mean the night side of Venus? Not good for solar panels.

Is there a thermal gradient between day and night side, what temperature is the night side?

You can't do solar panels on the surface of Venus. Illumination is about 1% of that at the noon cloud-tops, and I don't know if any solar cells will work at all at the ambient surface temperature.

In thermodynamics, RTGs are thermal machines, just like a steam locomotive. They use a heat source (here a radioactive material) and a heat sink or cold source (usually space, it is why the Cassini RTGs are mounted outside the spaceship, painted in black with a radiator shape). The maximum possible efficiency of any thermal machine increases with the temperature difference between the two heat sources (This is the Carnot theorem) and you must in more account with many losses in heat or mechanical energy.

In a RTG the transformation of heat into electricity is done by thermocouples, which are semiconductor crystals with special properties and arrangement. Their efficiency closely matches the Carnot theorem, except for their electrical resistance and some loss of heat through them (from the hot source to the cold source). The maximum hot temperature and minimum cold temperature are determined by the working range of the semiconductors used, usually 300°C for the hot source and minus something for the cold source.

On Venus, the "cold" source is very hot (460°C) and thus the hot source must be much hotter. This is not a problem for the heat source itself, which is made of high fusion point materials (plutonium ceramics, graphite, irridium...) but the problem is to find a semiconductor able to function between, say, 450°C-1000°C.

A possible alternative is thermoionic electricity: in a vacuum between the two heat sources, the hottest projects thermal electrons, thus producing current. This was used into soviet military satellites, but with a miniaturized fission reactor in place of a plutonium source.

Thank you Bruce for your comments, which are always interesting.

AS a former envirnment activist I have some knowledge about solar cells, at least on Earth. (there are not yet environment activists on Venus):

Even by cloudy weather, solar cells can catch some solar energy, called diffuse radiation. On Venus, the direct solar radiation (not scattered by clouds) may be as low as 1% in visible light, but there may be more infrared radiation (that solar cells catch more easily) and a bunch more of diffuse radiation. So solar pannels are not ruled out so easily, they just need to be large. The only real problem is to get a material able to work at 460°C and resistant to chemicals in Venus air. This is not a simple problem I think. By the way, a solar cell working at 460°C and using the 6000°C solar radiation would not violate any thermodynamics principle.

A possible trick would be to have the lander race the sun, on Venus it may be possible at a low speed, and the lander would work all the time. But it would not be all the time into interesting places.

The worse problem may not come from sulphuric acid, which is not present at ground level. But there is steam, which at 460°C is a powerful oxydizer (it will burn a steel structure in some hours) and sulphur dioxyd, perhaps S and S03 and others, such as fluorine and iodine (which were seen from Earth, in the clouds, in an ultraviolet band). These bodies are even more powerful oxydizers at 460°C, and sulphur, iodine and fluorine may be able to react with bodies which do not react with oxygen. This is why I think a "venus test chamber" would be a mandatory test for any instrument and material on Venus.

Another reply soon, I have a rendez-vous now.

A windmill may make sense for the VGA because that probe is supposed to rise and fall REPEATEDLY over a months-long lifetime. As for solar cells on the surface of Venus, the official design I've seen for the VGA on JPL's website portrays them -- and actually, since Venus' cloud layer reflects back only about 80% of the sunlight hitting it, which is over twice as intense as that on Earth, quite a bit of sunlight reaches Venus' surface. (Of course, the VGA is supposed to spend most of its time floating around in the cloud layer, where the light level is higher than at the surface.)

Aha! Here's a nice detailed article by Geoffrey Landis on these subjects: http://mit.edu/aeroastro/www/people/landis/Venus_Power.pdf .

He thinks that solar cells are a possibility despite the fact that the light level on Venus' surface is only 2% of the sunlight hitting the clouds: "about the same as a rainy day on Earth". Also, we do already have solar cells that can endure Venus' surface temperature -- but so far they work only in the blue part of the spectrum, which is minimized on Venus' surface. However, this does allow you to see how they could be useful on the VGA, drawing most of their power during its time in the cloud layer to recharge its batteries for its occasional descents.

At any rate, Landis describes in detail an RTG power and cooling system. (He also proposes a solar-powered cloud-layer airplane.)

For batteries we have a ready-made solution: sulphur-sodium, which work at 300°C or more, have a good efficiency an high number of cycle. There was developments for car use, but the need to maintain them at high temperature made lithium-ion batteries prefered.

The idea of an aerobot cycling up and down is appealing, it would allow the probe to work at lower temp. The basic defect is that such a probe would work only a small part of the time, and wander without control with high altitude winds.

I think that, besides understanding formation and evolution of Venus, the search for past life (or at least past Earth like conditions) is the most interesting goal. If we find that Venus had granite or water, even a long time ago, that makes of it candidate n°1 for life in the solar system. Even finding a very ancient primitive fossil such as a stromatolith would be a breathtaking evidence, and the actual existence of life elsewhere than on Earth would have inhcredible philosphical/moral implications.


About the mountain ranges on Venus, I stated above that they could be continents like on Earth. But on Earth the surface and altitude of continents are the result of two opposite forces:
-plate tectonics which tends to gather and shrink the continents (small surface-high altitude)
-erosion by rain which tends to spread the continents and arase all what is above the ocean level (which makes flat continents, except where mountains are actually growing).

What happens on Venus could be a bit different, if a plate tectonics played alone and gathered small but high-altitude continents. If this is the case, it implies that there never was a large ocean. On the other hand, most theories of plate techtonics say it is driven by water on the surface, explaining why there is not on Venus. Anyway there could have be some running water on Venus before the today sulphuric acid cloud layer absorbs all the available water.

So, if the Venus mountains are really continents, they are certainly formed of granite and other light rocks, floating on a basaltic mantle (explaining why they keep their altitude despite softened rocks). This is the reason why searching for such rocks in continents is the N°1 geological objective (Some pancake volcanoes may be trachitic, a lava which is roughly molten granite).

To search for fossils at random is certainly hopeless. We need first a detailed geological map of all the mountains, in order to understand their formation and their detailed features.

For all these reason, I think that the geological exploration of Venus must begin with:

-A multi-frequencies high resolution several passes SAR radar mapping (low frequencies may have some penetration into rocks, allowing to better detect layering). This could be done with an orbiter, also using infrared cameras to probe the ground.

-A fleet of many small cheap aerobots, stabilized at an altitude just above the mountains. The main spaceship releases them in a timed sequence, on various trajectories, so that they enter the atmosphere and fly over mountain ranges, caried by high altitude winds. Their unique instrument would be a multispectral infrared imager, allowing to determine the composition of rocks in mountains and some other places of interest. They would be powered by batteries and cooled by a bottle of nitrogen, and last some hours or some days, so that we do not have to bother with new technologies. Some understanding of venusian winds are however required, and this is preciselly the main goal of Venus Express.

These aerobots may give an understanding of the geological structure of the venusian mountains, and give some hints of places to search for fossils, the later requiring to stay for long in the venusian inferno.

If they find that mountains are formed of basalt, we are all false.

About fossils themselves, we cannot expect to find organic materials, certainly decayed for long ago. Even limestone and shells cannot be expected, and sulphur chemistry is controversial. We shall certainly find no surface layer billions years old, even with the weak erosion on Venus. And continents may certainly have a heck of a geography, unpracticable on wheels and even on legs: most are formed of large folds, which reached and went beyong equilibrium slopes, forming cracks boulders and craggs everywhere. But, with a flying bot, this turns to be our chance: large sections of thick geological layers are available everywhere. This is why I suggested an aerobot musing vertically along cliffs, where it could examine closely the whole history of venusian sedimentary rocks (if there are some) in search of fossil traces: stromatholites, diatomites, vugs, worm paths and imprints in shales, etc.

The first instrument of this aerobot would be a radioactive datation system, and after a composition and crystallography lab. This would allow to understand the layer sequences. After, a large field microscopic imager with a shape detection software would allow to search for fossil traces, and send on Earth the most relevant among billions of images.

Eventually, if we find some unclear traces, the aerobot could end with the samples in a given rendez-vous place, holding the sample cannister ready for a further sample return mission. But, I think, if we do not find clear shapes, we shall no more find chemical traces, so that a sample return mission seems not very relevant for now.

A tip for a sample return mission would be to have the sample cannister raised up by a baloon, and sent in low orbit by a small rocket. The problem with a venusian sample return would be that, starting from the ground, we need a Earth-sized rocket, like a Soyouz, and working in a venusian environment, and all this after a several months travel, packing, unpacking, etc. Dreadful.

Bruce said: "...Aha! Here's a nice detailed article by Geoffrey Landis on these subjects..."

Much better to have data than my arm waving recollections. I'm somewhat surprised any conventional solar cell material can work at venus surface temps. I was expecting the temp to change semiconductor bandgaps and all too much.

Worse than that, simply the impurities and layer boundaries will migrate, destroying any semiconducting geometry. This is why we need special materials, on which there are very little searches. Think there are already not enough searches for materials working... on earth.

Bruce:

Regarding the racket from the nuclear refrigerator and it's effect on any surface seismometer, there's an fairly easy way to insulate one from 'tother - stick the noisy thumping stuff under a balloon, and simply feed power and data cables to the seismometer on the surface...

Bob Shaw

Emily:

The trouble with spin-off applications from Venusian surface technology is that there really aren't that many times we're going to find uses for deep-sea fireman's suits on Earth!

Bob Shaw

ESA's page on Venera-D
http://www.esa.int/SPECIALS/ESA_Permanent_...0LFW4QWD_0.html

And for those who can read russian , an interesting article about a long duration soviet Venus probe being developed during the 80s, but never launched.
http://www.novosti-kosmonavtiki.ru/content...rs/223/45.shtml

Good note. I am approaching to the reality. Your note has helped me to recall my physics' class and realized that the gas' law is not perfect. In spite of the fact that the greater pressure on the gas, the density of the gas will increase but it wont' be as dense as the water.

Now I understand clearly that the density is not related to the viscosity. The density is related to the weight by volume space and the viscosity is related to the material property.

Again thanks to JRheling

Rodolfo

Except that you probably have to cool the seismometer itself -- and of course that balloon is going to be tugging at its anchor on the surface, thereby producing a fair amount of noise that way...

Here's a thought...what about a probe that enters into one of those deep sea thermal vents? How much applicability would Venusian high temp/pressure technology have for Jovian exploration?

<funny>
Or maybe you could put electronics on an aeroshell...
</funny>

Ok. I just didn't have any idea at all of how hot an RTG gets. The only applications I've seen them used in are places that are potentially VERY cold, like say, space. So I just wasn't sure.

Just to throw a curve-ball into the discussion, I recall some comment from maybe 15 or more years ago, but the context entirely escapes me (who said it when and where).

The comment was that we already have an electronics technology that would work quite well at ambient venus surface temperatures: VACCUUM TUBES. You wouldn't even need filaments (so the commenter said) to heat the electron emitting cathode. Supposedly the tubes would be noisy due to the high temperature <electron-shot-noise or one of those statistically defined noise types), but it'd work.

Concievably, you could build really really DUMB seismic/ magnetometer <maybe> /meteorology stations and just let the suckers transmit raw data 100% of the time up to maybe 3 kinda data collection and relay orbiters about 1 1/2 venus radii out.

We have a real overkill problem with some spacecraft and missions. Mars Telecom orbiter was a good idea, but as bells and whistles were added, it blew the budget. I don't know what the cost of a barebones telecom orbiter would have been, and some very lightweight science could be added for almost no cost, but I think we ended up with the Mars Telecom Titanic. (glub glub)

There will be some big news shortly on that subject, which I'll be able to break in my "Astronomy" article if the MEPAG committee doesn't beat me to it.

I wish that Russia would send another Venera lander on the level of the old ones, as it could probably be done provided it was funded relatively quickly. There have been changes noted in the Venusian atmosphere since the late 1970s. It would shed light on possible activity.

In an issue of Omni magazine circa 1991, there was an article describing how the Russians had two complete, working Venera landers ready to go and for sale at a mere $2 million US. Apparently no one took them up on the offer.

Anyone know what became of those Veneras? If they are still in good shape, take them out of mothballs and aim them at Venus. I would rather look at full scale replicas in museums, knowing that the real probes were out there exploring strange new worlds.

That would be a cheap opportunity to do some excellent science. But it would have to be done soon, while there are still people alive who know how to operate Soviet spacecraft from that era.

If the goal is to probe atmospheric changes, I'm sure there's a cheaper way. The Veneras were the size of tanks, and if all we need is a GCMS and a transmitter, and don't even need to worry about surviving the heat (the readings could be done at altitude), designing a simple mini probe from scratch on the smallest possible booster would surely beat the cost of putting a free Venera on a big booster.

I think VISE will be the next surface probe to Venus, and not within ten years. Prepare to wait. :|

Right, but I was meaning that looking for atmospheric changes would be a good justification for a mission that would do a lot more science, such as giving us basic data on another area of the surface.

Bad decision. If we compare two missions such as the MERS and Huygens, there is a tremendous difference, mainly because of the data rate. With huygens we had only some poor quality low bit images, when with the MERS we have a constant flood of high quality images. This is because we have three satellites in orbit around Mars which offer large band communication channels at nearby every time.

So sending a bare communication satellite around Mars, Venus, or any other Planet (I suggested a 50 years lifetime radio relay around Saturn for exploring Titan with large band communication) this is perhaps the very first thing to do.

The problem is that such a satellite would made no discoveries, it would bring no glory to the sender. So it must be associated with science equipment or more complex mission.

To send large band long lived radio relay around the different planets would be a good topic for international missions, kind of basic space UN. The relay would be used by everybody afterward.

Well, I don't know about the space-based U.N. ... the purpose of telcom satellites is to make communications more efficient, not less. Seriously, the comparison between the MERs and Huygens really isn't fair - Huygens had so little time to return its data, and so much to image. The MERs have had years.

Space-based U.N. ... good joke... and a very serious allusion. My stance is that countries must co-operate in space exploration, not do this childish competition. In a way it is what happens, due to the terrible constrains of designing and operating a space mission. But I find appaling that some countries which posses irreplacable technologies refuse to grant the use of them to others, for bad political pretexts.


Yes comparing MERs to Huygens is not completelly fair, but it is understandable. A really fair comparizon would be between Galileo and Cassini, which provided comparable science outputs. But alas Galileo was impaired with her dead large gain antenna, and she produced only scarce images awaited for months, when Cassini yelds a constant flow of tremendous images.

My idea was, like yours, that a telecom satellite around Mars, Venus, etc, is an indispensible condition for sending aerobots and landers, as the later cannot send large flows of data directly to Earth.

I should even say SEVERAL telecom satellites, which would also operate a kind of GPS, which is also indispensible to efficiently locate landers and flyers, especially on cloud-shrouded planets.

VENERA D - future Russian mission (5 to 30 days on planet surface)

O. Korablev, L. Zasova, M. Gerasimov, A. Rodin, A. Basilevsky, V. Linkin

Abstract:

http://www.aero.jussieu.fr/VEP/abstracts/K...ev_abstract.doc

Presentation (940 Kb):

http://www.aero.jussieu.fr/VEP/presentatio...resentation.pdf

NASA and ESA have deep "not invented here" issues. They would spend a fortune instead of buying a Russian lander. Look at how the Venus/SAGE mission has evolved. It started out as a Venera lander on a Fregat, cheap proven technology, and now its been almost completely redesigned by NASA.

Is Russia still a major partner in SAGE? The list of experiments look like their stuff (rock drill, panoramic camera, x-ray spectroscopy).

I guess its not all bad. If they think that can make progress, do it better. But I sure hope they are talking to the Russians. The Pioneer Venus landers didn't do so well in the lower atmosphere.

"Is Russia still a partner in SAGE?" No. Two years before this public report came out, Esposito accidentally put the list of SAGE experimenters on the Web (though not the experiments they were associated with), and I stumbled across it. Not a Russian among them.

The main reason for not using a Venera for "SAGE", however, is very simple: they weigh far, far too bloody much for our cheaper boosters -- and the law currently forbids launching any US craft on a Russian booster, lest it interfere with our own launcher industry.

As for the still-mysterious incident that screwed up the Pioneer 13 probes at 14.5 km above the surface: the general feeling is that it was insulation actually catching on fire in a reaction with some of the trace gases in Venus' air at that temperature. And while we still don't know exactly what it was, taking a whole set of corrective measures against various possible causes should nail it (as the swarm of protective changes made in Ranger 7 eliminated the cause of the Ranger 6 failure, although that exact cause wasn't nailed down until later).

Interesting. So SAGE seems to be an all-American version of the Venera-Discovery proposal. The thing about Venera-Discovery that I liked was the neutron-activation experiment.

Are you sure it is still illegal to launch US crafts from Russian rockets? I thought Protons were being used to put up US satellites. There's also the Sea Launch project. Galazy-14 was launched by Soyuz-Fregat last year. I think there was a law, and it was dropped after US companies became heavily invested in Russian space facilities.

It is the case that Europe just made it illegal for them to use foreign launchers. The exceptions seems to be when they need Soyuz/Fregat. I believe Ariane is only capable of excuting pitch control from equatorial launch point -- a cheap way to loft geosynchronous satellites, which skims the cream off the top of that market.





Definately, that was a great post!

The seismographs on Venera-13 and 14 were external, as was an electronics unit associated with it. I think RNIIKP has gotten very good at that game. I haven't been able to get any details about its electronics technology from my friends at IKI. That may be a sensitive subject.

The Russians have supposedly developed both radio-isotope thermopile and windmill generators for the surface of Venus. They did some tests with solar cells on several of the Venera landers, geared toward a study of using solar cells for balloon-born probes, which are up at a much higher light level. I would guess that light levels are too dim at the surface.

One thing Esposito's SAGE does not carry is any kind of gamma-ray spectrometer, with or without a neutron source. It seems to rely on the combined XRD/XRF (which I believe is a duplicate of the one on MSL, although I'll have dig up and recheck the list of experimenters for that) for all its element measurements.

This brings up a point I've been interested in for some time -- which is that tests have already shown that the LIBS which MSL will also carry for instantaneous and long-range element analyses which should be as good as those from its APX spectrometer (the two instruments will double-check each other) should also work fine on Venus ( http://www.lpi.usra.edu/meetings/lpsc2004/pdf/1338.pdf ). If so, then any Venus lander can use LIBS for a whole multitude of very fast and very accurate element analyses on the surface for meters (maybe even tens of meters) around its landing site -- without the need for any drill, airlock, or port through its pressure hull, except for a fiber-optic lead! LIBS, in short, may be a Godsend for future Venus exploration.

The question is whether we can devise an acceptable instrument with the same characteristics for mineralogy. X-ray diffractometry, which requires that the lander ingest a sample, is universally accepted as by far the best way to analyze minerals -- but work is already under way to combine LIBS with a Raman spectrometer (using the same laser beam) for long-range and instantaneous mineralogy on Mars. (There's been a lot of successful lab work on this, but it couldn't be gotten ready in time for MSL.) No one seems to know yet whether Raman -- which depends on analysis of an extremely tiny component of the reflected laser pulse -- could work at long range in the light-blurring atmosphere of Venus; but even if it can't, one can conceive of a Venus lander using a simple movable instrument arm, with a fiber-optic lead at its end, to touch places on local rocks and soil and do Raman analysis (and microscopic imaging) of them that way.

There are, however, things that Raman cannot do, such as -- if I remember correctly -- analyzing iron minerals. How much of this, however, could be done by near-IR reflectance spectrometry instead --especially with an artificial light source on the lander to provide those wavelengths that Venus' atmosphere filters out of the natural sunlight there? (Add a shadowing shroud to that movable instrument arm, and such an instrument could also do separate thermal-emission IR spectrometry of local patches of the surface without reflected sunlight getting mixed up with the short-wavelength thermal IR from that very hot surface.) A surface lander which used these instruments instead of having to drill up and ingest any samples -- and which didn't carry the atmospheric-composition instruments on SAGE (which could be carried on a single separate entry probe) could be lightweight and cheap enough that several of them could be dropped onto different places on Venus by a single lander, and quickly analyze dozens of different samples in the lander's vicinity.

As for the nature of the current US laws on the use of foreign boosters: you know more than I do.

US commercial spacecraft can use foreign LV's. But US Gov't spacecraft are prohibited, except in barter agreements.

Good description of the original Russian/American "SAGE" can be obtained indirectly at http://adsabs.harvard.edu/abs/1993LPI....24.1381S .

Now for the instruments on the proposed American SAGE. As I mentioned, back yonder in 2003 I stumbled across a list of the experimenters for Larry Esposito's "SAGE" which he had inadvertenly put on the public Web where no-gooders like me could see it. After I sent him a message asking for further information, he reacted with shock and horror and hastily yanked it off the Web -- but not before I'd made a copy, heh heh. And now that JPL's public technical report on SAGE is finally available ( http://trs-new.jpl.nasa.gov/dspace/bitstre...4/1/03-2520.pdf ) we can match some of them up nicely.

Descent Imager and Spectral Radiometer -- Uwe Keller, Max Planck Institute (a member of the Titan DISR team)

X-Ray Fluorescence and Diffraction -- David Blake, ARC (PI for the "CheMin" instrument on MSL)

Gas Chromatograph/Mass Spectrometer -- Paul Mahaffy, GSFC (PI for the "SAM" instrument on MSL)

UV Imaging Spectrograph -- Bill McClintock, LASP (U. of Colorado)

The others are harder to match firmly. One is "Colaprete", which has to be Anthony Colaprete of ARC -- an atmospheric specialist, which seems to link him with the Atmospheric Structure Experiment. Another is "Boynton", which seems to be John Boynton of LASP -- one of the two people mentioned on the Web as associated with the Camera Hand Lens Microscope (which has already been tested). Finally, we have "Crisp", which is probably either David Crisp or Joy Crisp of JPL (married, I presume). David seems to go in more for meteorology instruments, though, while Joy seems to be a geologist, which links her closer to the PanCam.

Anyway, as I say, not a Russian in the lot, and indeed there seems to be virtually no intersection between the experimenters (and instruments) on the first SAGE and the second, all-American SAGE.

Maybe it was a politcial mistake for Brown University to include the Russians. So they lost the mission to a rival team. But in any case, they would be wise to take a peek at how the Russians built Venus landers.

Bruce:

Some grabs from the .pdf you pointed us at showing the SAGE spacecraft layout - note also the substantial drill assembly.

Bob Shaw

It's a clever mission plan. The Venera spacecrafts were 6 tons, and required a Proton rocket to launch. This proposal is basically the Vega lander stuck on a Fregat. It can be launched by a Soyuz, and the pieces are probably all sitting in a warehouse at NPO Lavochkin.

But it's Not Invented Here. :-)

Those are probably the very landers mentioned in Omni magazine in 1991
that Russia tried to sell for just $2 million.

Actually, the first and second "SAGEs" never even had the chance to become rival concepts. The first one was an idea for a possible Discovery mission mentioned back in the early 1990s, a couple of years before the first AO for any Discovery mission even went out. It never even became an actual proposal.

Esposito's "SAGE", on the other hand, was a proposal for the first AO for the new New Frontiers program, which was released a decade later. The only thing they have in common is their name.

Really, though, if ever I saw an opportunity for a possible US/Russian collaboration that might actually work, this is it. The Russians just might be able to build a copy of their old Venera spacecraft without screwing it up. (Mars 96 -- based on the Phobos design, which they had never been able to get to work -- was so complex and built on such a shoestring that, even had its launch succeeded, insiders thought the chances that the spacecraft itself would work were virtually nil. They were building the thing by GASLIGHT, for God's sake, because the Russian space agency couldn't pay its electric bills!) Have the Russians build and launch 1 or 2 Venera landers equipped with good American (or European) instruments and you might really have something -- and at this point Russia might actually be able to afford to build them properly.

I have a bit more information coming on Esposito's SAGE later today.

And here it is. One of the primary investigators on SAGE was Bruce fegley of Washington university (located, oddly, in St. Louis); and in 2003 he put a Powerpoint rpesentation on the Web regarding the desirable goals for such a Venus lander (keeping in mind that his own Venusian specialty is chemical interactions between the surface and atmosphere). That presentation no longer seems to be there -- but, once again, I recorded it at the time. It was nicely detailed, but here are what seem to me to be his most important spefications:

(1) The key atmspheric measurements include temperature and pressure profiles from the surface to the clouds. (Oddly, he says that not only did the Pioneer probes fail to get data below 12 km, but so, for some reason, did Vega 1 -- and since the 1970s Veneras were of questionable accuracy, Vega 2 sems to have provided us with our only good low-altitude T and P profile so far.) They also include composition, using a GCMS -- in order of priority:
Overall abundance of H2O, CO, SO2, N2 and the noble gases
Vertical profiles of the first three
COS, H2S, HCl and HF
Isotopic ratios for H, C, N, O, S and the noble gases
H2, H2SO4
CO2 abundance below the clouds

(2) The top priority surface analysis site should be a big representative region for average Venusian chemistry and mineralogy. Second priority is an anomalous region -- either a tessera ("some propose these are metamorphic"), or one of the high-altitude high radar-reflectivity regions. Both primary rocks and phases that have reacted with the atmosphere are needed -- preferably a depth profile using a drill core, and including if possible an examination of the atmospheric gases at different depths in it (here his own biases show).

The top-priority measurements are element and mineralogical composition together (elements by themselves are not worthwhile). The best mineralogical instrument is an X-ray diffractometer; element analyses should include elements from C through Na, which X-ray and gamma-ray spectrometry can't detect. Then, in order of priority, come:
Color imaging of the surface and the drill core
Fe oxidation state (he recommends Mossbauer for this)
Visible/IR reflection spectra
Oxygen fugacity in the surface (using a ceramic O2 sensor)

SAGE's payload, as indicated by the JPL description, doesn't include all Fegley's desired measurements, but it would include most of them.

Oh yes those are really interesting, and might be really wortwhile to investigate. Whatever it is that covers high peaks of Venus, it certainly cant be anything we're used to. Especially interesting if it turns out those areas are covered by semiconducting metal salts as some have proposed as one explanation for the data.

Why does he think Venera-9 - 14 had questionable readings? Their platinum-wire thermometers are not as good as our platinum-wire thermometers?

Damned if I know, except that his slide says that there was "low accuracy P and T data from the old Veneras". Nor does he say why he has more faith in the results from Vega 2 (or, for that matter, why there apparently were no good measurements from Vega 1), but he wonders whether the Vega 2 data was "representative". I should add that he wants really accurate data: "Measure T and P with ~0.01% accuracy. At the surface, this is +0.1 K and +0.01 bar."

Accurate measurements of stability and convective power of an atmosphere that is marginally stable or unstable against convection, like the sub-cloud Venus atmosphere, require extremely high precision. Unfortunately, the Net Flux radiometers on the Pioneer Venus small probes had a design defect that put poorly calibratable biasses and errors in the science results. Venera 7 and 8 temp data were very crude. Later Venera data were better, but maybe not as accurate as the Pioneer data.

If there are measurable abundancies of such gasses as HF, H2S, HCl and the like, at a temperature of 450°C, it is expectable that the surface rock are completelly rotten, see metamorphized, as are rocks around earth fumaroles. As sulphates or carbonate could not from at such temperatures, we may find a lot of other salts, sulphides and sulphites, chlorures and fluorures. Many of them could be semi-conducting.

It looks like the accuracy of the Venera-9 to 13 and the Pioneer atmosphere probes were about the same, on the order of 2 to 5 degrees C. The Vega-2 probe had an accuracy of about 0.5 degrees.

The standard atmosphere is still based on a combination of Pioneer and Venera-10 data, fit to a thermodynamic model. Keep in mind that when you fit hundreds of measurements to a model, you get much better statistical accuracy than the error of the individual measurements.

Hopefully, the Venus DISR would return more data than the Titan DISR. The bottleneck seems to be less restrictive, since there is no relay necessary. I think the Huygens DISR did a fine job, even with half the data, of returning a full overhead panorama at reasonable resolution (although it was hell in terms of processing on the ground). But that one x-axis-narrow surface view aside, DISR returned nothing whatsoever from below a certain ceiling.

I think the imaging goals would be:

1) To locate the landing site in context (registering descent images with Magellan data).
2) To provide high-resolution (cm-order resolution) imaging of the immediate landing site.
3) To produce resolved multispectral imaging at a variety of altitudes.
3a) ...for its own scientific value.
3b) ...to benchmark the usefulness of such imaging to evaluate the worthwhileness of including such imaging in future high-mobility (aerobot) missions.

Per 3b, the benchmarking could potentially be performed with a much smaller mission before SAGE. If multispectral imaging has any use in making mineralogical discrimination on Venus, a dream mission would be one or more aerobots that spun around the planet returning imaging noodles that crossed many different types of surface unit, "coloring" in representative terrains that are mapped comprehensively by radar, giving us a pretty good inference of the mineralogy of the whole planet. If an aerobot could return this data while flying a Vega-like trek across Venus (~9000 km), one or two well-chosen entry locations could sample all the major terrain types.

GCMS could also be flown on a smaller mission; unless Venus is being washed in new volcanic eruptions on a colossal scale, this only needs to be flown once, ever.