Nice to see this area is still evolving, my PhD was in SiC-related tech, specifically how would you power a device embedded in a hostile environment so I was researching SiC-based photovoltaics, temperature response of piezoelectrics, high-temperature DC-DC converters and a very light touch effort on high-temperature storage.
As soon as you start heating electronics up to these sorts of temperatures the things we already take for granted become problematic. As highlighted already, solder joints become a huge pain, wire bonds pop off, even just building the test rigs to test these devices is usually a pretty interesting problem - I built a high-temperature photovoltaic characterization rig and a high-temperature vibration rig, which was involved enough but the true monster was the gas-sensor characterisation lab which had evolved over many years that could do gas, high pressure and temperature up to 700 degC (I think).
All good fun, if someone is looking at a PhD in electronics I would recommend this area if even vaguely interested as it's a good mix of practical and theory and when you can't even bank on your solder joints holding, let alone a dielectric surviving then it makes for some interesting problems away from the pure electronics.
I recall a story from a Russian aerospace engineer describing a Russian unmanned probe to Venus. They mounted a camera and arm to the probe to take pictures and to measure the chemical composition of the planet's surface. He said the camera cover popped off at the appropriate moment to land exactly where the arm hit the ground. They got a very good measurement of the camera cap's chemical composition. I'll see if I can dig up a link.
Found it... actually the arm was to measure the compress-ability of the Venusian soil
Actually, the camera was embedded deep inside the probe's pressure vessel. The aperture on the probe's surface was glazed with a quartz window, and the image projected through a long periscope arrangement to the sensor inside.
Reading through the paper I have to admit those are some really impressive numbers. A typical soldering station might run at 343C (650F) while Venus is 460C (860F) hotter than a reflow oven to be sure.
To clarify for anyone as dim as I - Venus is 460C (860F) and is hotter to be sure than a typical soldering station, which runs at around 340C (or 650F) - it's not the case that Venus is 460C hotter than a reflow oven.
The best part of that comparison is that solder might not even melt on Venus at that temperature. The atmospheric pressure on the surface is roughly 90 atm which is the pressure you'd experience if you were 1,000 meters underwater. Even modern nuclear attack submarines made out of titanium and high strength alloys can barely go past 800 meters without completely losing structural integrity so solder would probably be under way too much pressure to change phase from solid to liquid.
Interestingly, with a few hundred gates you can produce the circuitry needed to digitize data from a seismometer (one of the main reasons you'd want a long-duration lander on Venus), do some basic forward error correction, and transmit to a relay satellite. You'd have basically no memory, since memory is extremely expensive energy-wise and consumes a lot of gates, so you would just transmit the data as it is received. Just a few hundred gates is not unreasonable to make out of these relatively primitive high temperature circuits. A full computer with memory is not feasible, but neither is it required to accomplish the mission. Here is a paper describing a Venus mission operating entirely at high temperature using the kinds of digital circuits I described:
The thing that struck me was the Glenn Extreme Environments Rig (GEER), (https://geer.grc.nasa.gov/geer-overview/overview-of-geer/). That thing is a beast! Operating 24 days with 470 C and 1400 psia gas mixture (including acids) sounds like an amazing feat.
Electronics aren't the only problem for a Venus probe. You also need some way to power the thing. One interesting possibility is that lithium will combust in a carbon dioxide atmosphere, and it is also, conveniently, liquid at Venus surface temperature.
Idea: put a good insulator under the surface of the probe to keep as much of it as cool as possible (first making sure it cools off in space). Ship it with a thermoelectric generator. I'm not sure how much useful power you'd get from the spacy-cool - Venus hell temperature gradient, so maybe it's a stupid idea.
Heat dissipation is actually a gigantic problem in space: you can only radiate heat away (and try to reflectively shield against the sun) since you're in hard vacuum which is a fantastic insulator.
Basically, you need a sun-facing shield that is perfectly reflective, and diamond fins with a perfectly black surface coating, forever in its shadow.
An effective radiator is an equally effective absorber, so management of light and shadow is critical.
But it's still sort of moot when you consider atmospheric friction on the way down.
You're not going to get much power out of the gradient. Even if you cooled an object in space to near absolute zero, space probes must necessarily be low mass to get into orbit from Earth. The low mass of the whole object, and the low heat capacity of most space-grade building materials combines to make it a really awful cold sink. You would essentially need to harvest water and ammonia from somewhere outside of a gravity well, use your radiator to cool it off as much as possible, and then drop it in the heat well. That's an awful lot of trouble to go to for the amount of power you will then get out of it.
The old style thermoelectric generators (like used for Voyager 1 & 2) were able to operate at high enough temperature that they could dump heat at Venus ambient temperature and still generate power.
To be fair, lithium will react quite fast with our atmosphere as well, so we are pretty good at keeping atmosphere out of batteries. 460C temperatures on the other hand is a challenge.
Certainly not any time soon. A rover has a lot of complicated moving parts that will have to be exposed to work properly, and will almost certainly fail after a short time on the surface. All of the sensors will also have to be exposed, and the interface between the sensors and the enclosure will be vulnerable. A lander may work for some time, but a rover would be very difficult. Venus is a very, very harsh place.
So is the drilling end of an oil well, but there are sensors and motors for that.[1] "The heavy duty motor range is designed to withstand temperatures over 240°C at pressures up to 1,733 atmospheres. They can withstand vibrations to 25 Grms, impacts to 100 G." A 2005 study indicates how to get motors to run at up to 500°C, which is above what's needed for Venus.[2]
Power systems for a Venus lander have been studied by NASA.[2] Sodium-sulfur batteries, which need to be hot to work at all, were considered.
NASA has successfully tested electric motors at venusian ambient conditions[0]. Also, the atmosphere isn't corrosive at the surface. It's much too hot for sulfuric acid there.
The wind is apparently not too bad at the surface:
> Winds at the surface are slow, moving at a few kilometres per hour, but because of the high density of the atmosphere at the surface, they exert a significant amount of force against obstructions, and transport dust and small stones across the surface †
So maybe we could send some probes that would hover above the surface. Disposable instruments could be shielded behind covers, and only exposed once a sample was ready to be collected and analyzed, and then discarded or written off.
Since the atmosphere is dense, maybe a nuclear-powered hover-rover would be plausible, since it would be almost more like swimming than floating. Maybe an anchor could be dragged behind it to ensure that it doesn't get flung around too badly.
The issue with using a thermoelectric nuclear generator like the one on Curiosity is that there's nowhere to dump the heat. RTGs are all based on thermocouples to generate their power which requires a temperature delta between the RTG interior and exterior which is hard given the extreme temperatures of Venus. Maybe one based on thermovoltaic cells would work but those haven't been tried with RTGs yet.
Wind might be the best bet. Turn one of the dangers into a power source at least, designing one that would work for a long time in those conditions wouldn't be easy but maybe.
Forget RTGs; what about actual nuclear reactors? Obviously, this means a much larger probe. But even with Venus's high atmospheric temperature, a nuclear reactor's output is much higher, so theoretically it should be possible for it to work. Then, with a very large amount of power available, it should be possible to use active cooling for the electronics, at least until the nuclear fuel is depleted.
Can a nuclear reactor actually work if the steam never recondenses? Either way that's a long ways away, the smallest currently planned nuclear reactor is still the size of a shipping container. Building a probe around that would make and it's transfer stage the largest thing ever put in orbit by a long ways then there's the logistic of actually landing the thing.
IANANE (I am not a nuclear engineer), but I don't think you can use water here, for the reason you state. Water makes sense on Earth because the temperature and pressure range suits it, but on Venus I think you'd need to find some other fluid to transfer heat to the outside, perhaps liquid sodium? But nuclear reactors work the same way as any other heat engine: you have a source of heat and exploit a temperature differential by moving heat from the heat-source to the environment. So it should work just fine on Venus, but with some other working fluid.
You're right though: this would be rather large. However, it might be possible to make it smaller, by eliminating shielding. Your smallest planned reactor surely uses a bunch of shielding, because it's intended for use on Earth, around humans. For an automated probe on Venus, that's not a concern so you don't need shielding, except whatever's necessary for safe handling before launch. This is also a place where it'd be a lot better if we had a Moon base where we could build things like this; it's a lot easier to launch mass from the Moon than from the Earth. Landing the probe should be easy: Venus's atmosphere is extremely dense so a parachute (resistant to the sulfuric acid, at least for a short time) should be fine, though the high windspeeds could be a problem.
The cloud cover over Venus is 250 km thick. I don't think the wind speeds are uniform throughout the entire atmosphere, certainly in the upper reaches the sulfuric acid is less potent.
We do need more Venus exploration, but the reason Mars is getting all the attention is that we can actually settle Mars with our current tech, whereas Venus is probably only habitable with floating habitats that will need to be constantly supplied from Earth. There's a difference between exploration and colonization.
As an example, you can visit an Antarctic research station, but people actually live in Arizona.
The other thing to consider is: what the heck are you going to do there?
On Mars, you can do a lot of things. You can mine, you can build underground habitats, you can try to grow stuff in the soil, you can explore the place and learn about the geology, etc. And you can do these things a lot faster and easier in some ways than with remote-control rovers.
On Venus, what are you going to do there? Sit around in your giant dirigible city and enjoy the scenery? You can't send people to the surface, and you can't even send probes there for very long. You can't mine (the equipment won't last long enough to make any progress), you can't do too much geology (again, the probes won't last long), you certainly can't dig and build underground habitats, and you sure as hell can't grow anything on the surface. You're limited to whatever you can do in your floating habitat. And I fail to see how you're really going to get that much more done on-site in a floating habitat than just using using automated probes sent from Earth.
According to everything I've read, floating habitats are perfectly feasible on Venus, but getting them there would be a huge and expensive challenge, and what's the point when you can't go to the surface? Yeah, it'd be kinda cool to hang out there in a giant dirigible for a little while, and supposedly you could even go outside with just a breathing mask on for a little while, and it is nice that the gravity is almost the same as Earth's, but that's a huge investment for not much return. The Moon, Mars, and even Mercury and Ceres all make more sense for sending humans for long-term missions.
The is intense. I've often thought about the Russian Venus lander. In the same vein I occasionally think about what could survive deep within the Earth. Of course I then immediately get tripped up wondering if any useful satellite could be made to work within the Sun, and that's where I realize I should just think about something else.
In The Killing Star by Charles Pellegrino and George Zebrowski, one group of survivors orbits a ship around the Sun, just below the chromosphere. There's also a story about "distilling antihydrogen" near the Sun, in Vernor Vinge's Marooned in Realtime.
David Brin's Uplift series had mechanised lifeforms "floating" on the sun to collect matter, and IIRC Sundiver has life forms floating in the chromosphere.
A closely related subject is radiation. If you want to explore Jupiter, Saturn, or Fukushima you have some new challenges.
In the latter case, they're talking only a few hours of lifetime for ROV's going into the 500+ Sv/hr environment. I bet the military has a bunch of research on rad-hard equipment they're not keen to share.
Some sources claim that in the 1980s USSR already developed instruments that were capable of operating at surface environment of Venus as part of their Venera program. From [1]:
While never deployed, a seismometer and thermopile battery were developed and tested, capable of operating indefinitely on the surface of Venus.
Venus has very little water, so a starting point would be to launch large solar-powered balloons that just float around and collect water by cracking the sulfuric acid in the clouds. Living systems also require a lot of trace minerals that would have to be harvested from the surface. I think it could all be done, but probably not for a price that anyone is willing to pay.
At 50km where the temperature and pressure are nearly Earthlike you've got about 25 ppm of water. Which is rather dry but not so much that it would be unprecedented on Earth. The concentration of sulfuric acid is around half that so it makes more sense to extract the water directly like so:
"While Venus’s surface is awful, its upper atmosphere is surprisingly Earthlike. 55 kilometers up, a human could survive with an oxygen mask and a protective wetsuit; the air is room temperature and the pressure is similar to that on Earth mountains. You need the wetsuit, though, to protect you from the sulfuric acid."
Maybe if your plants can deal with the acid you might be able to do it. (I am not a biologist, chemist or anything relevant to answer this question, this is just my best guess).
Has anyone ever bumped into similar articles about electronics longevity? Sayyy.. Could we build a simple Voyager like probe that can last 1000 years? 10000?
Given the challenges involved in making a 10,000 year clock, a 10,000 year space probe seems currently infeasible: http://longnow.org/clock/
Putting it in space opens up some advantages, though that comes with its own whackload of disadvantages, too. Perhaps you could stick something in permanent shade on the moon to avoid 10,000 years of thermal stress, for instance, but you've got a decent chance of something hitting you hard enough to break something over that time span, too.
It just blows my mind that Soviet Venera landers were sending digital (!) images back from the surface of Venus in early 80s. This would be a heck of an achievement even today some 35 years later.
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As soon as you start heating electronics up to these sorts of temperatures the things we already take for granted become problematic. As highlighted already, solder joints become a huge pain, wire bonds pop off, even just building the test rigs to test these devices is usually a pretty interesting problem - I built a high-temperature photovoltaic characterization rig and a high-temperature vibration rig, which was involved enough but the true monster was the gas-sensor characterisation lab which had evolved over many years that could do gas, high pressure and temperature up to 700 degC (I think).
All good fun, if someone is looking at a PhD in electronics I would recommend this area if even vaguely interested as it's a good mix of practical and theory and when you can't even bank on your solder joints holding, let alone a dielectric surviving then it makes for some interesting problems away from the pure electronics.