(MOD NOTE: Started a new topic for this discussion to continue. Please remember the 'no sci-fi engineering' provision of rule 1.9. Have fun!)


Also, since I'm thinking about surface operations on Venus, the state-of-the-art in high temperature electronics has advanced quite far in the past decade.
Its now possible to buy off the shelf chips from vendors designed to operate at the 250-300 C range.

Meanwhile basic functionality has been tested at and beyond the temperatures needed for long-term surface operations on Venus:
http://www.grc.nasa.gov/WWW/SiC/
http://www.gizmag.com/extreme-silicon-carb...ctronics/16410/
http://www.grc.nasa.gov/WWW/SiC/publicatio...Contact2010.pdf

Another decade or so and a long-term Venus lander could be possible with (practically) off the shelf electronics!

Having electronics operate at a higher temperature works 2 ways to make for a longer operating time on the surface.

Firstly, it takes longer to heat them up more, and also, the rate of heat flow into the probe decreases as the temperature difference between inside and outside decreases.

Additionally, having a wider temperature operating range might allow the use of different/better phase change heat absorbents.

We could be seeing quite a jump in operating time that's possible.

Of course, if you can operate at 500C, you don't need to have phase/change...

Resistors, Capacitors, inductors, all those sorts of things can work at 500C, though not the usual components. A resistor is fundamentally a simple device, as are capacitors and inductors... They can technically be constructed entirely with just some conductor and some insulator material.

Now that we have silicon carbide ICs of tens of gates operating at 500C, lots of stuff is possible. A turing-complete computer (provided you have some sort of memory, could be coil or capacitor based) can be made with just a couple hundred gates, though you have to be satisfied with very low performance (maybe just a 4-bit or 8-bit computer, but it's Turing Complete so can simulate higher). Whether it's worth it...

http://spectrum.ieee.org/semiconductors/de...ng-temperatures

has some interesting details. Problem now isn't the semiconductor per se, but everything around it such as interconnect between the transistors (metal layers) and packaging etc.

In addition to high-temp industrial applications, I wonder whether technologies like this could eventually avoid the need for ridiculous active cooling of server farms. I think the ideal would be servers that reliably operate around 100C, so that you could simply cogenerate (if that is the right term) by circulating water and creating steam. Right now 40C is the typical limit.

Silly question: How are they doing surface-mount boards? My first guess is silver solder, which is what is used on aircraft engine thermocouples, but curious to see if a better technology has arisen.

I wonder about sources of power. Is there any high temperature solar panel? Also, there is not much light on the venus surface. I remember Venera description of "same as noon in a winter day in Moscow", which is probably not a whole lot. RTG is worse. To generate any electricity using a thermocouple, one needs a temperature gradient, which would be extremely hard to maintain on venus.

Tungsten solder, Nick. I have a patent pending.

I'm officially your distant relative now, Dan, and I got a few bills...

Seriously, this is not a trivial problem. A Venus lander of any sort either requires a VERY well-controlled temperature environment for its electronics (which IIRC was the Venera strategy) or not only electronic components that can survive extreme temp swings during the cruise phase but also the same for all required electrical connections.

The latter are obviously quite vulnerable to materiel expansion/contraction cycles, which ultimately loosen connections over time and introduce either spurious or high-resistance interface points which can do all sorts of nasty things to signal flow. (For example, MIL-STD-1553 data buses really don't like impedance changes; tends to turn perfectly good data words into gibberish.)

How I see this playing out is a loosening of environmental control constraints over time for the silicon itself but capability bounded by a hard constraint on connection methods unless suitable (and workable, as Dan pointed out) connection/wiring alloys of some sort can be developed that are extraordinarily resistant to thermal cycling. That's a rather daunting challenge in metallurgy.

The cruise environment is fairly benign and once you get to Venus it's just hot all the time, there isn't a lot of diurnal variation. Exactly what the interconnect is made of is another question. That said, the SiC components are at a very early level of development so I'd say we are quite a ways away from having real and capable systems that would work at Venus ambient conditions.

RTG-powered refrigeration systems are feasible:
http://web.archive.org/web/20010106124800/...p/vgnp.txt.html

but for the foreseeable future I think short-lived landers are all we are likely to see, unfortunately.

If one is willing to constrain the landing site by altitude the engineering challenge can probably be lessened as well. Maxwell Montes is almost 100 C cooler that the mean; any lander would last a bit longer there and at the other high points.

It's a real problem but I'm confident that existent materials technology can solve it -- especially the problem of conductive connections. I would imagine a mechanically secure solution such as clamping or spiral threading which is secondarily secured by a high temperature polymer. (If I were building it in my garage I'd be using RTV silicon or two part-epoxy which are reliable to 600F. I'm sure the JPL toolbox has even better stuff in it).

The electronic components are another story but frankly I'm pretty certain there are already temperature rated ICs and such in use in military and industrial applications which offer a starting point for this kind of high-temperature electronic circuit design -- probably servos, relays and optical applications as well.

Venus ambient is around 450C or almost 900F. There are no ICs I'm aware of that get anywhere close. Most mil-spec parts go to 150C or maybe 200C in a few cases (junction temps, not ambient.)

One small thing in favor of high temperature electronics for Venus is that, while very high, the temperature is relatively stable. You don't need components that works at both 20 C and 450 C. They only need to work at 450+/-50 C, which is probably somewhat easier task. The lander can have a separate set of electronics for the cruise and native high temperature ones after landing.

That would enormously simplify testing, though.

For our Venus proposals we spent a fair amount of time worrying about how we could even simulate the environment in any practical way. How do you put a scope probe on something that has to be at 450C to work?

Agree. I didn't think of it from this aspect. But in the end of day, you cannot rely solely on testing at 20. You need to test in a similar environment as Venus. Also, what about the atmosphere? I guess CO2 at 90 bars and 450 C is rather corrosive.

I've found a microcontroller that's supposed to work at 250C:
http://www.ic72.com/pdf_file/i/141332.pdf
Doesn't look to be widely available, but it's still the very best I've found for a microcontroller (it's hard to even find transistors in this range...).
http://www.ims.fraunhofer.de/news/detailan...electronic.html

That's getting close. Some people think the highest altitude parts of Venus are around 350-380C (100 degrees cooler than the average surface). This would allow long-duration stays in the lower parts of Venus's atmosphere (tethered balloon?) or perhaps make simple cooling techniques feasible (high-temperature solar panels hooked directly up to Peltier cooling devices... though the long and hot night would be a problem...).

Which reminds me, are there any electronics that could /survive/ at 400C, even if they can't operate at that temperature? The instruments could be operated only during the daylight when there is power to run the cooling equipment. Of course, operation by an RTG (even a small one) would be preferable, but that increases the minimum cost significantly. Which reminds me, are there any betavoltaic devices (far cheaper, less restriction on usage I think) which can operate at 400C? Too bad they only output on the order of 1E-6 Watts. We need at least one Watt before we can talk about cooling electronics (more like tens of watts, for a very small device).

What is the insolation (Watts per meter squared, not just direct but also diffuse) at noon on the surface of Venus?

All the ideas are very strange, but NASA Glenn Research Center is already working on it.

http://www.lpi.usra.edu/meetings/ipm2012/pdf/1133.pdf
Development of a High Temperature Venus Seismometer and Extreme Environment Testing Chamber

A lander mission without camera is not a mission.
One point is: Is it possible to have a CCD or MOSFET camera at 4500-500°C?

Yes it is. Not all spacecraft can, should or must carry cameras. Would it be nice to take a more modern imaging suite to the surface of Venus? Obviously.

There is still huge quantities of science to be done without one, however.

The Solder question is very interesting. Looking into the state of the art for down-hole operations, it seems the solders used are at the very edge of being useful in their current applications (150-200 C) - for COTS it seems the mix of 5% tin, 93.5% lead, and 1.5% silver is useful up to ~250 C.

Beyond that point it seems that we're off into specialty solders for research projects - I see references to Aluminum being used (692 C melting point), though I imagine that's hard to work with (and how long will it last?). I do see a recent announcement of a cheaper solder of gold-silver-germanium which may fill the gap (ceiling of 350 C) - which if it does take off commercially would get COTS printed circuit boards right on the edge of being useful for a Venus mission with minimal cooling.

Also, figured I'd throw in some references to some off the shelf ICs that I found while looking into this - I see references from TI for a PCB rated at up to 250 C (and down to -55 C). Honeywell claims they have an IC that is rated for 5 years operation at 225, and that their max temp is close to 300 C.

Amazing how far they've come in the past decade.

EDIT - and it may be moving a lot farther. Just found this Department of Energy grant to United Silicon Carbide to demonstrate an electronic sensor package for downhole operations that runs at 500C (!). Based off the linked abstract, they were able to demonstrate a working package...

Flash Memory would be vital-- avoids mechanical storage:
http://www.ti.com/ww/en/hirel/high_temp_fl...-htflash-bti-en

It'd be useful to have a camera even for just a few minutes (during descent and on the surface) for situational awareness. It just needs to take a few pictures then can burn up. It would help tremendously to know exactly where on the surface of Venus your lander landed and what sort of soil or rock you landed on. Not needed for the long-term, though, like temperature, pressure, wind speed, and seismograph measurements would. A disposable camera is a good 80/20 solution for a lander (it's difficult to keep a camera cool, since heat can travel more easily through windows, for instance).

I suppose an old tube-style camera may be workable at high temps.

Interesting about the DOE electronic sensor package at 500C...

And when you're talking about 350+C, the term is usually "brazing" not soldering. But yeah, the non-active portions of the circuit become basically just as difficult at these temps...

Don't know specifically about vacuum tube cameras (iconosocope I believe is the archaic term, LOL) in high heat, but vacuum tubes in general have a problem with high temperatures, surprisingly enough.

Despite the vacuum tube cathodes being strongly heated during operation (and that's why we used to wait for things to warm up before they would work), the anodes (which tubes need too) cannot be too hot. Going back 40 years in my schooling, I think the problem is secondary emission at high temp on the anode. The tube won't work right (or at all) if the anode is as hot as the cathode, and performance decreases as the temperature difference between anode and cathode decreases.

Solid state electronics as noted above are the best bet. Amazing the advances they have made in this regard.

A camera at these temperatures, even neglecting the electronics, is a fussy thing. having it stay in focus when that hot since the housing will likely expand and move everything. Lens coatings, seals, chemical attack from the corrosive atmosphere, etc. this is a tough challenge all the way around.

You'd also not want too much IR sensitivity in the image pickup or it would be swamped with it!!

Why is everyone talking about cameras on Venus like it's never been done?
Click to view attachment
http://photoshopnews.com/2006/09/12/old-so...resh-surprises/

I'm guessing folks are thinking of design for long-term survival. A camera that lasts a few hours is a bit easier than one that might last long enough to see sunrise on the morning following the landing. (And wouldn't that be something?)

No roving. Probably very little change in local weather. Changes in shadow patterns on the ground over the course of weeks, but how likely is it you would see anything else different in the landscape in the short term? We really don't know for sure.

I'd say two highly detailed 360 pans in color, offset for 3D (raising or lowering the camera a bit), each pan transmitted twice, and maybe if you get the seismometer emplaced quickly enough, a quick parting shot of that. You're good to go and the camera can fry.

I think it is unreasonable to expect a full fledge high-temperature computer with tons of flash memory; at least early on. The more likely system would be something akin to the late 1960s or early 70s technology (say Voyager style). One solution is to have most of the telecommunication systems and memory and command handling in a separate orbiter (which of course uses regular electronics), which then commands the lander in realtime and records the data without need for much memory in the lander. The orbiter could be in a low polar orbit and can probably communicates with the lander 10 minutes every 90 minutes or so.

For instance, the longer the camera lasts, the longer the focal length you can have on the camera (assuming a scan platform or a moving mirror of some kind).

The idea being, you have more time for more pictures, so a longer focal length gets you higher resolutions further from the probe. You'd want the time available (indefinite would be GREAT!) and the data rate available for the camera system to be utilized in sending as many pixels as possible of the area the probe lands in. Probably too much to hope for that the probe could analyze the pictures and aim for 'interesting' rocks or hills/mountains in the distance. So the probe should attempt to mosaic the entire area. (maybe a simple filter might be possible, even analog techniques might be useful. For instance, a photo of sharp angular details will have more high frequencies in an analog readout of the camera than will a photo of an area with rounded/soft forms. Presumably the sharp angles pictures would be more interesting)

Also should factor in transmission efficiency of the atmosphere, a hazy or dusty area (assuming areas on Venus vary in these details) would limit how much detail could be recorded at a distance.

Colorimetry will be a little different. We already know from the color filters used in the Soviet era that there is essentially no blue or violet light at the surface. Color analysis will be confined to red thru ~green. Also, viewing the surface in IR will be hindered at wavelengths corresponding to the ambient temperature, an IR camera won't record much detail in that band, nor at longer wavelengths. I don't know about polarized IR, maybe somebody knows if that has any practicality in this tough environment?

How difficult would it be to park a satellite in a geostationary orbit for full-time communication with a lander? Would it require too much fuel to achieve such an orbit?

The rotation period for Venus is sooo long . . .

How long is it ???

It's Hill Sphere isn't big enough for a geostationary (Venusostati, whatever) satellite!!

However, there are alternatives.

For folks with Sirius satellite radio (to cite a terrestrial example of something you might have), the satellites are in highly elliptical polar orbits, with their high points over the northern hemisphere. This means those satellites spend very little time over the south pole, but quite a bit over the north pole (but at a great altitude)

So if you had a probe on the surface, and it was anticipated to last long enough for this to matter, you might want to put it poleward and have an orbiter in a path similar to the Sirius radio satellite.

{BTW, Sirius did not invent that technique, the Soviets used it extensively for many years prior}

Why? Once you have ICs working at your target temp, making them small/highly integrated is something we've figured out how to do really, really, well in the past 40 years since Voyager was state-of-the-art. Sure, you may be able to demonstrate a discrete component system at 600C while ICs only work at 250C. The thing is, though, once you have the basic IC components working at your target temp, I think it's entirely reasonable to assume you'll have a very competent microcontroller with decent volatile storage. Nonvolatile storage might have a different temp spec, but all that means is the power has to be on.

Given those 40 years since Voyager, I'm not sure that with the skills we've gained in highly integrated circuits that we're ever going to have any high-temp technology that's "IC" without it being good enough to make a pretty complex integrated microcontroller. Either you have a lander with relatively unprogrammable instruments transmitting all data in real time-- and perhaps that would be really cool if it was long-lived-- or you have enough integration to do C&DH on the lander. It's really hard to imagine an in-between.

Making an IC is the difficult part. It is not clear if you have a high temperature semiconductor, it can be turned into an IC easily. I'm no expert by any mean, but my understanding is that the reason silicon ICs exist and work great is the favorable crystalline structure of Si and the existence of insulator bases that integrate well with Si (such as SiO2 and, in case of radiation hardened electronics, Al2O3=sapphire). I'm not sure if silicon carbide shares these favorable features. I guess that the earliest systems will be mainly based on discrete elements and few low density ICs.

They've already started making Silicon Carbide IC's - so the barrier has been breached. My understanding is that the problem is making them durable for long term use.
This article is about 4 years old, so the state of the art has advanced since then, but I found it to be a good overview.

That sort of gets at my point-- I tend to think if you have the technology to get reliable "low density ICs" at your spec high temp, you'll very soon have enough VLSI to get a damn decent microcontroller. If it involves wafers--SiC, sapphire, whatever-- and lithography, they sort of hit the ground running these days. Technologies mature with VLSI as a given. I tend to agree that if other technologies aren't mature, the board those ICs go on might be a trip back to times when things were handmade rather than on PCBs, but again, just my opinion, is that if you have anything proven in manufacture that you can call an IC, lithography is probably going to allow you to have a microcontroller with an instruction cache and data cache. Technologies exit the lab with that level of integration. [It's my opinion that] When there is a facility that starts making qualified SiC IC's, it will have the ability to enable microcontrollers from the get-go, so it's fun but not necessary to imagine system architectures that don't need LSI.

The big problem, I am told, is memory. We can probably make devices with hundreds or perhaps a couple thousand transistors (enough for a microcontroller, the Intel 4004 had 2300 transistors), but we pretty much can only do SRAM right now, which limits us to maybe 100-200 bits (not even bytes) in the near term (next few years). And even that is difficult. I don't get the idea that it's just a few steps to a big VLSI.

I wonder if a "two-brain" strategy might make sense for a Venus lander. One that has sensitive parts and stays alive for hours, then dies as expected, and one that has tough, robust, vacuum-tube-style electronics that transmits low-bandwidth data for months. In particular, if that could break down into imaging and gas chromatography that is done during descent and just after landing -- perhaps a laser-induced spectrometer -- and then long-term seismological monitoring.

It's encouraging to think that improvements in electronics might make this mission cheaper one day, if not now. The last and only time a US mission transmitted data from the surface of Venus was 1978. That's astonishing.

Indeed, I had thought of such an approach. It makes certain things a lot easier, for instance the camera and as you said some kind of spectrometer. You'd also want probably a pressure probe, temperature probe, and anemometer (wind speed), too, to determine if seismic events are really just caused by the wind.

As an example, I don't necessarily think that once a technology is reliable, there's any hurdle between 4004 and 8085 these days. Took them 5 years in the 70s, but the lithography was all new. Today, there's no point in technology development where anyone would cut and run with a 4004 thinking they next step to the 8085 wouldn't be quickly surmountable. Sure, a Pentium (22 years) might be a leap. I don't think it serves much purpose to imagine it will take as many years to move up the Moore's law curve as it did in the 70s, when microns were considered really small geometries. There's not going to be a long period comparable to the 70s when we could make microcontrollers, but only laughably piddling ones. Plus, the thing is that even if it did take the whole 5 years it did in the 70s, that doesn't seem that long when you're talking about unmannedspaceflight! I think it's conceivable they could solve board reliability and instrument reliability before they solve IC reliability, and someone will send a system with discrete components. I just don't think it's that plausible we'll send one with a 4004-level IC when the wait for 8085 or 8086 will not be long at all.

I'm wondering if something like a corner reflector might be made of some high temperature (and chemical) resistant material, that could have it's dielectric properties, or reflection angle, (or something) that varies in a predictable way with temperature and or pressure.

The reflector could be dropped and then illuminated with a radio signal from an orbiter, and the return echo would be phase modulated, or whatever the device can be made to do to alter the signal, and then you would have a point on the surface that could me monitored for one or a very few parameters, for as long as the orbiter lasted.

A reflector on an anemometer would frequency modulate the reflection (if done properly) in proportion to the wind velocity. Two such reflectors on a bimetallic arm on a pivot would introduce a bias to the wind signal that would be temperature related.

Might be a way to get some very basic long term data from a few interesting sites. Just need to have a very simple, and robust device in the right location.

I think you're missing something, here... With high-temp electronics, we don't have access to Moore's Law. There are just one or maybe two places that really are even trying to do complex integrated circuits. There's very, very little financial incentive for improvement, it's essentially ALL gov't funded. The state of the art can improve, but it is a direct function of money spent, not purely time. This is markedly different from the situation with the early IC CPUs like the 4004, where you have a huge market for improvements. Nowadays, tens of billions of dollars are spent on fabs and improving the technology for making conventional integrated circuits. Definitely not the case for silicon-carbide circuits, nor is it likely to ever be so. The market is tiny, you can't simply wait for it!

That said, an 8-bit architecture may make more sense than a 4-bit even at the extreme limit of minimal transistor count.

Yeah, but you have access to anything that trickles down from the silicon ecosystem. It's unlikely that you're going to end up with an IC made on a 50mm wafer with 10um geometries. Something like SiC wafers with W wiring... that will still get proven in a 150mm or 200mm research fab at submicron geometries. They aren't reinventing everything from the 1970 level.

The funding is otherwise a huge issue. But I think automotive applications will help. And for whatever reason, it seems LED makers are interested in SiC.

Power draw is a huge issue, because you can't do CMOS. Memory draws a ton of power, so even if you can build a big chip, you would need a very large power source. Which is a pretty big problem on the surface of Venus, where very little light gets through, your cold end for a heat engine is already nearly as high as the hot end for MMRTG.

Doesn't seem to me that high temperature memory is that far behind IC's. As someone mentioned before, TI is selling an off-the-shelf flash memory unit that is rated up to 210 C currently. I've seen some research documents that refer up to 300 C memory units in lab tests being run now, so the OTS max temperature should keep pushing up over the next few years.
EDIT: and I now see this note by Raytheon that they are working on a SiC based CMOS rated at 450C.
So why can't we do CMOS on Venus?

This might be of interest - a report by Honeywell on the challenges (and solutions) for building 250 C rated ICs, that goes into memory solutions as well.
--
IC related Bonus - found this paper describing the results of actual testing at 500C with a custom IC built by NASA. Think I missed this on my last review of papers on high temperature ICs.

The tech that works up to 250C is not usable to the ~500C needed for Venus (it /can't/ work, the tech simply stops producing gain at that point). The Raytheon CMOS SiC stuff is interesting, but a lot of this stuff has been "talked about" for a good couple decades without significant progress towards something actually usable. Goes on the list, though!
Ah, yes, Philip Neudeck... One of the people I've talked to on trying to see what will and won't work. This field is so small that a lot of the references are by the same people. Some people are really optimistic about getting a usable large-scale IC in a short time, others are quite pessimistic. The consensus currently is that memory is a really hard problem. You need Megabytes of memory, not just the 100 bits that might be doable in the next 5 years.

(And Mike K, also one of the authors of that paper, is probably the most interesting person I've ever met at NASA. He's on my list of most favorite people ever.)

And the question isn't about physical impossibility or not, but on state of the technology... If you want a mission that actually /happens/ and isn't a paper study, we can't be happy with a TRL of "well, physically it's possible." The people who decide whose mission to build will reject that every time.

...That said, prove me wrong!

I think you're being pessimistic. The state of the art for commercial tech is moving to a 500C package. Automotive want it, and drillers need it - with immediate potential sales in the 10K-100K annual range, and potentially in the Millions if it becomes standard in engines, there's enough sales carrot to push research. NASA can wait, and in 5-10 years use COTS equipment as the basis of a Venusian lander.

The question of pushing existing tech into the 500C range is interesting - found this abstract that claims they were able to get existing Silicon-on-Insulator EEPROM cells working at up to 450C in a lab, well beyond the ~200C they are rated for now. That bodes well for getting memory working at venusian ranges in the near-future, rather the nebulous "5-10 years from now" that never arrives.

As for existing tech - there definitely isn't anything outside of a lab that will work over long durations, but short duration missions are possible now with existing tech from what I can see. For example, here is an existing pressure/temperature sensor package that is rated at 4-5 hours at 400C. While the sensors in this particular unit may be of limited interest*, my point is that they can get modern electronics to last long enough to return useful data from the upper elevations of the highlands for a few hours - now.

EDIT * - thinking about it, measuring temp/pressure/motion at a lot of locations would probably be useful. Wonder how expensive it would be to equip borehole sensor packages with a transmitter and a parachute, and dump a bunch across the highlands of Venus? Gotta be cheaper than doing it from scratch...

I've thought of the same thing... The issue is partially that if you /actually/ press the borehole guys about operation at 460C, they dither a bit. They aren't nearly so optimistic as their websites claim.

I hope you're right about me being pessimistic

Its a good thing that Ishtar Terra has temperatures that drop as...low... as ~380 (Maxwell Mons - +11km above surface), and averages "only" 420 or so at its average height of ~+5km.
Gotta start somewhere on Venus, and Maxwell Mons and the other high peaks around Ishtar Terra might be a good place to start with existing tech.

EDIT: Another project for ~450 C operation, through the DoE:
http://www4.eere.energy.gov/geothermal/projects?filter[field_project_technology][0]=%2214%22
This presentation in particular (from last year - final results in the forthcoming 2013 report) indicates they were able to get data back from a 450C environment (vacuum flasked electronics).

A quote from the NASA paper: "While silicon electronics experience clearly demonstrates that complementary MOSFET (CMOS) technology is desired for implementing integrated circuits, development of the necessary high electrical quality gate-insulators that would enable long-term 500 °C operation of SiC MOSFETs will likely prove elusive for many years to come [21]."

^ Yeah, JFETs don't need that gate insulator. They also only had n-type, so of CMOS, they have MS. Nothing people haven't worked around in the past to make large devices. But, unfortunately, at the 10um geometries I poo-pooed earlier and with really low reliability, which isn't something that's easy to work around. Infinite money and access too commercial dev fabs, though... sigh.