Russia Plans "long-lived" Venus Probe Options

[Waspie_Dwarf]

Russia Plans "Long-Lived" Venus Probe

The press secretary of the Russian Federal Space Agency, Vyacheslav Davidenko, has said that Russia will design and launch a long-living probe to Venus by 2015. The probe is known as Venera-D.

Davidenko told a news briefing that within the federal Space budget for 2006-2015 was envisaged, “work to develop a principally new spacecraft, Venera D, intended for detailed studies of the atmosphere and surface of Venus”.

“It is expected that the craft with a long, more than one month period of active existence will land on the surface of the planet that is the nearest to the earth. Nobody has done such thing on Venus so far.”

Source: ITAR-TASS

[Guest_Richard Trigaux_*]

THE TECHNOLOGICAL CHALLENGE OF A LONG LIVED VENUSIAN LANDER

First of all, as many already pointed in this thread, a baloon is much better than an lander on Venus: with much higher pressure, the air is very dense and the same baloon can wear maybe 20 times more weight. The overal thing may look something between a submarine and a zeppelin, with a rigid skin and balast compartments. The easiest way to inflate it is with water steam, it is one of the lightest gaz (except helium or hydrogen) and it would be relatively easy to get in Venus air. Neon would work too, while being less corrosive.

Refrigeration or heat withstanding? I think refrigeration would be feasible for only a very small volume, or for a short time, thus offering little possibilities (or frustrating results like with Huygens). The reason is that the efficiency of refrigeration decreases very fast with the difference of tempereature. In a home regrigerator, the difference is 20-30K over 300K (10%) on Venus it would be 450K over 750K (60%) thus requiring much more energy. So I think that WE MUST THINK FROM HE BEGINNING TO 100% 450°C withstanding probe. This is the problem.

Corrosive air. Venus air is not only very hot, but it contains gasses which, at this temperature, react very vigorously to produce oxygen, sulphur and sulphuric acid, perhaps other acids. This is a problem, and every sensitive parts of a probe (electronic boxes, instruments, motors) will need tight seals.

Structural Materials They will have to withstand heat, but also corrosive air (acid, oxydizing, sulphurizing). Common materials like steel and aluminium alloys are ruled out at once, and even titanium (a steel sructure would burn in only several hours). We must from the very start think at precious metals, special alloys used in aeronautics turbines or nuclear plants, or even ceramics, composite ceramics, etc. Possible but need some development (including a "venusian test chamber").

semiconductors for computers, power control and radio emitters are perhaps the domain where a solution seems the less possible. But there are perhaps hundreds of couples of semiconductor materials, and many common materials become semiconductor at higher temperature, so it would be a really bad luck if we do not find one working at 460°C (perhaps diamond do this). This is a matter of research and development, which can go astray with bad solution for years, or we can be lucky to find a good material quickly. Few researches were done in this domain, as, on Earth, there is alway a mean to offset the electronic in a protected environment. But we do not need the highest performances in a venusian lander.
If really we find no semiconductors living at 460°C, we could go back to... vacuum tubes. Micro-sized, simplified technology with flat electrodes triodes, built with the technologies used for integrated circuits, may have electrical properties undiscernible from a N channel MOSFET transistor, which with we could make computers, power "transistors", etc. And, at 460°, it would need no heater... Here, the question is not to find some elusive material, but to test once if it works or not. The only serious problem I see with those triodes would be that, the anode being as hot as the cathode, it should be made from a much less electropositive metal than the cathode.
Another alternative would be static-electricity actuated micro-relays, which, at sub-micronic size, would be fast enough to build computers. And work with a very wide range of temperature... We could probe lava lakes with this electronics.


Electricity conducting materials pose a problem, as their quality much lowers with temperature. Of the three best metals, aluminium is ruled out, remain silver and copper. Silver is better on Earth, on Venus I do not know, but it may be used exclusivelly for wiring. This arises special problems with power transformers.

For insulators plastics are widely used, as they have two magical properties: when we bend an electrical wire, plastic does not break, and it does not change thickness as a soft material would do. On Venus kapton and even Teflon are out. Remains things such as fiber glass guipures impregnated with some soft mixt. (In ancient times silk guipures were used as insulator in power transformers and turbomachines, while paper ribbons were the rule in telephone cables).

Magnetic materials used in power transformers and motors arise a special cconcern, as at 460° most magnetic materials have degraded quality, if they do not have reached their Curie point (where magnetic properties disappear completelly). Things are still worsened if we consider that all these machines work at at temperature which can be 100°C more than their environment, and this is worsened by degraded electrical and magnetic properties. May be some special alloys or rare earths may still have some interesting efficiency, I do not know. Anyway transformers windings and motor windings would need special techniques, working at higher frequency, or at resonnance (which would require a very precise winding of thin ribbons), and cooling from inside (at least a circulation of fluid to bring it back at ambient temperature).
The alternatives to electromachines are piezoelectric crystals or pneumatic actuators. Piezo crystals can work at high temperature, and a design with a U-shaped crystal oscillating around a shaft may replace an electrical motor.

Lubricants also are a problem. When we think at a lubricant, it is nearby alway to oil, understand an hydrocarbon. No hope for anything such on Venus, the only stable hydrocarbon is methane, and it is not really oily... But basically a lubricant is a liquid which 1) sticks on the parts to lubricate 2) has relatively low fluidity 3)is stable enough (not an emulsion, not solidificate or evaporate) so that it forms a layer between the parts, preventing them from the devastative metal-to-metal contact. Many fluids can do, liquid metals or minerals, eventually mixtures to ensure the right properties. Solid lubricants like graphite or molybdene sulphide can also do, but I do not believe very much o such solution for a long lived mechanism. Once the solid lubricant is gone, it is gone, while a liquid lubricant is alway pumped back to the right place.

Etancheity must be achieved thoroughly, not only from dust, but also from corrosive gasses. Tightness around rotating shafts or parts is usually achieved with elastic materials, but nothing such may exist at 460°. Tight tolerance and wetting the joint with a liquid metal would do the trick, together with a chemical control of the inner atmosphere of the probe.



Energy is perhaps the biggest problem. There is little solar energy on Venus, and no wind, rivers etc. (perhaps some thermics could be used for navigation). A RTG would not be at ease: the thermocouple semiconductors are limited to 300°C. Only thermoionic generators could work.
It exist on Earth generators made of a source of heat (fire) and infrared-sensitive photovoltaic cells. Could some photovoltaic cells be able to harness the abundant infrared emitted by venusian rocks, while being themselves at the same temperature? Why not, you will say. Except that this would violate the second principe of thermodynamics: a one source thermal engine... I wait for explanations of this... or for experiment.



Where to go??? Once visited the basic lava flows of Venus, we shall have many overal explanations of the hystory, structure and compsition of Venus. But after?
My idea is as follows: Venus may have experienced a stage with an Earth-like climate, with water, ocean and plate techtonics. Until the greenhouse effect increases itself and trips out to reach the today conditions. If this is true, the mountain ranges of Venus would be in fact continents (which would maintain their alitude by isostasis, floating on the unerlying basalt mantle, this explaining why they do not collapse witht he high temperature softening the rocks). Maybe the oceans and continents of Venus evolved for two billion years (infered from the increase of Earth continents).
But if so, LIFE HAD GOOD CONDITIONS AND PLENTY OF TIME TO APPEAR ON VENUS. Of course it hopelessly disappeared since, witht the increase of temperature. This increase also destroyed limestone rocks and any trace of coal or oil near the surface. So only very few would remain today.
So the idea is of an aerobot exploring the mountains (cooler places) for years, hovering along the many cliffs and examinating them closely mith a microscopic imager in search of... fossils. Microscopic fossils, but fossils anyway. Large animals? civilization? I don't hope so much, but who knows. At least with what we know of Mars now, we have more chances on Venus.

Sorry for the long post, but it was worth writing it I think.