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Damburger
2009-Aug-07, 02:02 PM
The recent events on Venus, which might if they are volcanic in nature suggest a landing mission, got me thinking.

Only a handful of Soviet probes have landed on the surface of Venus, and didn't last long. With modern materials, engineering, and larger mass budgets, how long could we expect the next generation of Venus lander to last?

As a further question, would a Venus rover be viable at all? Or would any lander last for so little time that it would not be worth driving anywhere?

If you can last longer than an hour or so, I would suspect power is an issue also. Does enough sunlight get to the surface of Venus to make any kind of solar power viable?

Nicolas
2009-Aug-07, 02:42 PM
I'd think that given the violent nature of Venus, trying to make a lander work for a long time is a necessary demonstrator and learner before attempting to make a Venus rover.

kucharek
2009-Aug-07, 03:01 PM
Only a handful of Soviet probes have landed on the surface of Venus,...

Though not designed as a lander, one of the atmospheric probes of Pioneer Venus survived impact on the Venusian surface on December 9th 1978, continuing transmitting data for about an hour.

http://en.wikipedia.org/wiki/Pioneer_Venus_project#Pioneer_Venus_Multiprobe

Argos
2009-Aug-07, 03:11 PM
Hey, Kucharek. Nice to see you around. :)

Damburger
2009-Aug-07, 03:36 PM
I'd think that given the violent nature of Venus, trying to make a lander work for a long time is a necessary demonstrator and learner before attempting to make a Venus rover.

Fair point.

It seems to me the main problem is trying to keep the hot, high pressure, and corrosive Cytherean atmosphere out of your lander for as long as possible. Perhaps an alternative approach would be to give that up as a losing battle, and design each and every component from the start so that it can function in the atmosphere without protection.

Of course, its difficult to think what kind of technology could withstand those conditions without protection. It would probably have to be very basic in its function. Would it be possible to sacrifice complexity for durability to the extent that a lander would function long term?

Swift
2009-Aug-07, 03:41 PM
Only a handful of Soviet probes have landed on the surface of Venus, and didn't last long. With modern materials, engineering, and larger mass budgets, how long could we expect the next generation of Venus lander to last?
A very good question, and one I don't have a fast answer too. It would be interesting to know what exactly limited the Soviet landers; what exactly was the failure mode.

You have three main problems: temperature, pressure, and chemical corrosion. I don't know if one was the particular limit, or it was the general combination.

There have been some improvements in materials, but for dealing with these problems, I'm not sure there has been that radical a change in the last 20 years or so.



If you can last longer than an hour or so, I would suspect power is an issue also. Does enough sunlight get to the surface of Venus to make any kind of solar power viable?
I would guess that solar power would not be viable, and nuclear-thermal would be the way to go, but I don't have the data.

By the way, this (http://www.mentallandscape.com/V_Venus.htm) is an absolutely fantastic website about the Soviet work on Venus.

cjameshuff
2009-Aug-07, 04:13 PM
I see temperature as the major issue. Pressure can be handled easily enough, though it makes the structure heavier if low pressure portions must be maintained, and the corrosive environment only requires some care in material selection...it's a hostile environment, but not incredibly so.

Some level of functionality could be maintained indefinitely with equipment operating at ambient temperature and pressure. Passive resonant cavity devices could return seismic, pressure, temperature, and wind direction/speed telemetry by changing their radar returns: http://en.wikipedia.org/wiki/Thing_(listening_device)

I see these being metal and ceramic devices potted in a solid plastic material and scattered from high altitude, perhaps with a drogue ribbon to orient them for landing. The plastic would keep the device intact during a landing that perhaps could drive anchor spikes into the ground, and then would evaporate to free up moving parts...some components could be spring loaded, unfolding as the potting material evaporates. The deployed devices would then resonate to radar pings and continuous radio illumination from orbiting probes, and mechanically vary the characteristics of their radar echo to return telemetry.

The Venusian atmosphere is hot, but it's also very dense, so RTGs may still be viable. You won't be able to get the hot side much hotter than the "cold" side, but you won't have much trouble keeping the "cold" side very close to ambient. An RTG power source and actively cooled circuitry in a vacuum flask could allow more complex devices to operate for years.

samkent
2009-Aug-07, 04:23 PM
My impressions have been that it isn’t the power factor. You can design the experiments to run around the given batteries, for long periods of time.
Nor is it the corrosion factor. There have been many materials available for many decades that would be impervious to the corrosion.
The pressure is a concern since there has to connectors to the external mother craft as well as antennas, sensors etc.

But the overriding problem is the temperature. At over 860F, electronics just can’t handle it. There is no way to create an A/C unit that will operate over 800F differential. The best you can do is super insulate the electronics from the outside. But that will only get you an hour or two at best.

Damburger
2009-Aug-07, 04:34 PM
But the overriding problem is the temperature. At over 860F, electronics just can’t handle it. There is no way to create an A/C unit that will operate over 800F differential. The best you can do is super insulate the electronics from the outside. But that will only get you an hour or two at best.

Hence my idea of going as primitive as possible.

Another thing I have thought of with the heat; would RTGs operate at all at that temperature? If the atmosphere is as hot as the radioisotope, how can you generate power?


I see these being metal and ceramic devices potted in a solid plastic material and scattered from high altitude, perhaps with a drogue ribbon to orient them for landing. The plastic would keep the device intact during a landing that perhaps could drive anchor spikes into the ground, and then would evaporate to free up moving parts...some components could be spring loaded, unfolding as the potting material evaporates. The deployed devices would then resonate to radar pings and continuous radio illumination from orbiting probes, and mechanically vary the characteristics of their radar echo to return telemetry.

Thats pretty clever :)

samkent
2009-Aug-07, 05:06 PM
We could go back to analog electronics. Vacuum tubes operated at high temps. Your science would be limited by the amount of tubes you could cram into the lander. But this method would only exacerbate the power problem.

Damburger
2009-Aug-07, 05:16 PM
Vacuum tubes? Surely that is trading one problem (operating temperatures) for another (holding back the immense pressure)

Ilya
2009-Aug-07, 05:32 PM
Vacuum tubes? Surely that is trading one problem (operating temperatures) for another (holding back the immense pressure)

Not at all. The tubes would be inside sealed hull under normal Earth pressure. Which was the case with all electronics in all previous landers.

Somehow people seem to forget than 90 atmospheres of pressure is a solved problem -- deep sea subs handle it all the time. Heck, people in articulated hard suits had been that deep! Temperature is the real problem on Venus.

Larry Jacks
2009-Aug-07, 06:32 PM
A very good question, and one I don't have a fast answer too. It would be interesting to know what exactly limited the Soviet landers; what exactly was the failure mode.

You have three main problems: temperature, pressure, and chemical corrosion. I don't know if one was the particular limit, or it was the general combination.

From memory, the Soviet landers lasted about 45 minutes or so. Those landers were heavily insulated and employed cold-soaking before hitting the atmosphere. Basically, they got the landers as cold as possible while still in space. Even with relatively simple electronics (and they could've been vacuum tubes for all I know) and excellent insulation, they lasted less than an hour. Venus presents really severe engineering challenges.

I remember reading in Omni magazine back about one of the landers back around 1982. The article noted that the lander proved Murhpy's Law works on Venus. One of the experiments was a mechanical scoop to measure the density of the soil. When the lander touched down, it ejected a lens cap. Sure enough, the cap landed exactly where the scoop needed to work. The scoop dragged the lens cap across the surface, ruining the experiment.

Off hand, I don't know of any modern electronics that could last very long on Venus. It's certainly too hot for silicon-based semiconductors and probably for other types of semiconductors like gallium-arsenide. You'd need to design every electronic component to handle the heat (resistors, capacitors, circuit boards, batteries, etc) to last more than an hour. It's quite possible no existing electronics technology would be up to the challenge (after all, how many applications on Earth would require handing such temperatures). If that's the case, developing a long-lived Venus lander would be a very expensive process. It's possible the technology would be useful for other applications on Earth such as deep Earth probes.

cjameshuff
2009-Aug-07, 08:11 PM
But the overriding problem is the temperature. At over 860F, electronics just canít handle it. There is no way to create an A/C unit that will operate over 800F differential. The best you can do is super insulate the electronics from the outside. But that will only get you an hour or two at best.

The overriding problem is the temperature, but you're being overly pessimistic about the difficulties in refrigerating the electronics...you don't need to operate electronics at room temperature, for starters.

Currently, commercial semiconductor devices exist that are rated for operation at 300 C, leaving just 160 C of differential for the refrigeration, assuming no function at higher temperatures...higher temperature devices probably exist, I didn't spend much time looking. Peltier coolers exist that can handle half of that in one stage, albeit with a cold side near room temperature. Thermoelectric junctions that operate at higher temperatures, with higher temperature deltas, are being used currently in RTGs. Other cooling technologies can also handle that differential, or large components of it...perhaps something like thermoacoustic cooling of the radiator itself. Thermionic cooling technology might be particularly applicable.

The dense atmosphere is a plus, here. Your radiator temperature will essentially be ambient temperature...you'll have a hard time getting it any hotter than that. Aerogel and vacuum bottles can insulate very effectively, leaving only a small leakage to pump out. Might not even use those 300 C parts...it may well be that most of the heat to pump out is produced by the electronics rather than leakage from the surroundings. Cooler components often produce less heat, so the optimum may well be cooler electronics and a larger temperature differential.

Mean surface temperature of Venus is only 735 K, which is actually not that much above typical "cold" junction temperatures, and well below the hot junction temperatures of GPHS RTGs...remember that radiating to vacuum at low temperatures requires very large radiators, so they operate at 1270 K on the hot side, 566 K on the cold side. So, RTGs still work, and won't require big radiators.

High temperature semiconductor devices. Mostly rated for -55 to +255 C, with derated operation up to 300 C. Amplifiers, logic, power regulation and switching...
http://www.cissoid.com/high-temperature-electronics/ht-standard-products/high-temperature-standard-products.html

Some information on RTGs:
http://books.google.com/books?id=CIEnt1r6TgkC&pg=PA293&lpg=PA293
http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/38757/1/06-0429.pdf

Drbuzz0
2009-Aug-07, 08:55 PM
Only a handful of Soviet probes have landed on the surface of Venus, and didn't last long. With modern materials, engineering, and larger mass budgets, how long could we expect the next generation of Venus lander to last?


The "larger mass budget" would be one thing, but also the budget for the project in general would be an issue. I'd say that a probe landing on venus would last about as long as it is designed to last, which would be dependent on how much money you want to spend on it.

We have materials that you could clad a lander in that would withstand the conditions, but the heat would eventually get to the interior and the circuits. You could have a very effective active cooling system. Of course this would require a lot of energy. I'm not sure about solar power, as the panels are rather fragil. A small nuclear reactor could provide a lot of power. You'd need it to operated at very high temperatures due to the high ambient temperature.


But it's not like we couldn't make a probe to last a long time. The question is would the data it returned be worth the enormous price tag versus the data from a much cheaper probe designed for a short lifetime?

kucharek
2009-Aug-07, 09:01 PM
Before doing a long-time lander, a long-time probe floating in the atmosphere may be a better first step. Perhaps we could later design some kind of steerable ballon, putting down a probe on the surface for a short time before retuning to a height where it is possible to cool it down in preparation for the next surface mission.

Glom
2009-Aug-07, 09:43 PM
Fair point.

It seems to me the main problem is trying to keep the hot, high pressure, and corrosive Cytherean atmosphere out of your lander for as long as possible.

"Cytherean"? Where does that word come from?

JonClarke
2009-Aug-07, 10:31 PM
"Cytherean"? Where does that word come from?

It is the correct formal adjective, I understand. "Venusian" is wrong "Venerian" while technically correct, conjours up salacious images.

Jon

Romanus
2009-Aug-07, 10:33 PM
Only a handful of Soviet probes have landed on the surface of Venus, and didn't last long. With modern materials, engineering, and larger mass budgets, how long could we expect the next generation of Venus lander to last?

I'm not so sure we have that much of an advantage over the earlier generation of space probes; Venus seems to be a place that demands one build big. The large probe alone on Pioneer Venus was more than one and a half times more massive than the MERs (and surviving to the surface was purely a bonus, which it didn't, though the smaller probes were under MER weight), and the Veneras over four times more. Long story short: we're probably going to be launching T-34s to Venus for some time, which means more weight and higher cost. Our electronics may be more sophisticated, but they also tend to be more fragile.

As for how long: probably no way to tell without testing various models to destruction. Perhaps the real question is that of how long it would take to finish the requisite tests to complete a nominal mission, before termination? If I had to guess, I'd be surprised if we could do better than an Earth-day, but hey, that would be something.

Solar power: In terms of light, no problem at all. Now, getting panels to work under those conditions. An RTG might work, if it used a truly incredible, hot isotope that could generate a heat differential greater than the atmosphere's (think of some polonium or curium oxides...). But, that kind of heat and radiation of course presents its own problems.

RE Dr. Buzz0:
But it's not like we couldn't make a probe to last a long time. The question is would the data it returned be worth the enormous price tag versus the data from a much cheaper probe designed for a short lifetime?

Excellent point.

cjameshuff
2009-Aug-07, 11:15 PM
Our electronics may be more sophisticated, but they also tend to be more fragile.

Not in terms of operating in extreme environments. Improvements in process control and in materials allow us to achieve reliable operation in temperature ranges that would have been absurd a couple decades ago. I pointed out a few posts back a company that's making logic, analog, and power control electronics that operate at temperatures up to 300 C.



Solar power: In terms of light, no problem at all. Now, getting panels to work under those conditions. An RTG might work, if it used a truly incredible, hot isotope that could generate a heat differential greater than the atmosphere's (think of some polonium or curium oxides...). But, that kind of heat and radiation of course presents its own problems.

Again, the surface of Venus is only a bit higher than the cold junction temperature of RTGs in use in space probes now, and the atmosphere is an excellent heat sink. There's a loss in efficiency due to the smaller temperature difference from hot side to cold side, but you don't need a super high temperature RTG, or even any real changes in RTG technology.

Solar power...about 2% of sunlight reaches the surface. Venus gets about twice as much sunlight per unit area as Earth, so a solar panel would generate about 4% of the power it would in Earth orbit. There's also the problems of wind and possible dust to deal with. Huge solar arrays on for power on the ground are probably not the way to go.

JustAFriend
2009-Aug-08, 12:03 AM
It is the correct formal adjective, I understand. "Venusian" is wrong "Venerian" while technically correct, conjours up salacious images.

Jon

As long as you dont call it a Venerial Probe, I think you're OK....

:lol:

01101001
2009-Aug-08, 02:30 AM
It is the correct formal adjective, I understand. "Venusian" is wrong "Venerian" while technically correct, conjours up salacious images.

Jon

Wikipedia (lister of all things): List of adjectival forms of place names :: Planets (http://en.wikipedia.org/wiki/List_of_adjectival_forms_of_place_names#Planets)


Name: Adjective / Demonym

Earth, Terra, Tellus, World: Terran, Terrestrial, Tellurian / Earthling, Terran, Terrestrial, Tellurian
Jupiter: Jovian, Jovial / Jovian
Mars: Martian, Martial, Arean* / Martian
Mercury: Mercurian, Mercurial, Cyllenian / Mercurian
Neptune: Neptunian / Neptunian
Saturn: Saturnian, Saturnine / Saturnian
Uranus: Uranian / Uranian
Venus: Venerian, Venusian, Cytherean* / Venusian

*: Rare

Tuckerfan
2009-Aug-08, 04:21 AM
Solar power...about 2% of sunlight reaches the surface. Venus gets about twice as much sunlight per unit area as Earth, so a solar panel would generate about 4% of the power it would in Earth orbit. There's also the problems of wind and possible dust to deal with. Huge solar arrays on for power on the ground are probably not the way to go.

IIRC, heat is really bad for solar cells. It degrades their efficiency and shortens their life span by a significant degree.

Damburger
2009-Aug-08, 11:52 AM
So from what I understand has been said so far:

* Pressure isn't a long term problem. You can hold back 90 atmospheres for a long time because deep sea vessels do it all the time

* Corrosion isn't a major issue either, so its temperature that kills you

* Solar panels are useless, but RTGs would work OK

* Electronics are still a few hundred Kelvin short of where they need to be to work at Cytherean (yes, I know its rare and old fashioned, but its so much nicer than the alternatives) surface temperatures.

It seems there wouldn't have to be too many technological leaps to get to the point where the lifetime of a lander is measured in Earth days rather than minutes, at the very least. Furthermore, making such technological leaps might provide some nice spin-off technologies.

cjameshuff
2009-Aug-08, 04:08 PM
* Pressure isn't a long term problem. You can hold back 90 atmospheres for a long time because deep sea vessels do it all the time

Correct. It requires a somewhat heavy shell around the vacuum bottle containing the electronics, that is all.



* Corrosion isn't a major issue either, so its temperature that kills you

* Solar panels are useless, but RTGs would work OK

Right. It's not a nice environment, but we commonly deal with far worse here on Earth in various industrial processes. High temperature solar panels probably can be made, but there's little sunlight to feed them, so they're pretty worthless unless you only need miniscule amounts of power. (An aside...I think typical silicon photovoltaics actually perform better at higher temperatures. High temperatures do decrease the lifetime of any semiconducting device, though, and they probably peak at something rather far below the surface temperature of Venus.)



* Electronics are still a few hundred Kelvin short of where they need to be to work at Cytherean (yes, I know its rare and old fashioned, but its so much nicer than the alternatives) surface temperatures.

Just 160 K, and that's for commercially available parts found after a few minutes of searching. And the electronics do not have to operate at the temperature of the Venusian (yes, I know Cytherian is etymologically "cleaner", but Venusian sounds better and is more likely to be understood) surface.



It seems there wouldn't have to be too many technological leaps to get to the point where the lifetime of a lander is measured in Earth days rather than minutes, at the very least. Furthermore, making such technological leaps might provide some nice spin-off technologies.

I'm confident we could achieve mission durations of months to years without any technological leaps, though such developments would of course improve the instrumentation we could include, or extreme expense beyond that of any RTG powered mission. And the passive instruments I described earlier could operate indefinitely and would be very inexpensive.

The idea of moving between high altitude regions and the surface has possibilities as well. Compress and freeze CO2 at high altitude, perhaps compressing some of the left over nitrogen for lift gas (requires a very large balloon). Vent the CO2 on the surface for cooling, rising back to high altitudes to complete the cycle. A lot more complexity and possibilities for failure, and would likely have a much shorter lifetime, but could touch or closely approach the ground at several different locations, and would sidestep the expense and political issues of an RTG.

Rhaedas
2009-Aug-08, 06:05 PM
Why not have the idea of short term probes, but a lot of small ones, dropped by a blimp stationed in the less extreme upper atmosphere? Controlling where it goes might be a problem, but as long as it had power and could maintain altitude, it could have a lifetime far beyond anything limited to one spot on the surface.

KaiYeves
2009-Aug-08, 08:27 PM
"Venusian" is wrong "Venerian" while technically correct, conjours up salacious images.
Salacious (http://starwars.wikia.com/wiki/Salacious_B._Crumb)?

JonClarke
2009-Aug-08, 11:45 PM
Salacious (http://starwars.wikia.com/wiki/Salacious_B._Crumb)?

http://www.thefreedictionary.com/salacious

;)

KaiYeves
2009-Aug-08, 11:53 PM
Aren't I allowed to make Star Wars jokes once in a while?

JonClarke
2009-Aug-09, 03:12 AM
Aren't I allowed to make Star Wars jokes once in a while?

They will be the Darth of me!

ravens_cry
2009-Aug-09, 05:21 AM
They will be the Darth of me!
Don't Force it.
I like Venusian, 'correct' or not.