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Venus Exploration Plans, If you can't stand the heat...
JRehling
post Sep 4 2007, 04:13 PM
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After reading Emily's excellent review of last year's VEXAG meeting

http://www.planetary.org/news/2006/0502_Re...06_Meeting.html

I come away with a somewhat bleak outlook on future Venus surface exploration. In a nutshell, most of the science goals are dependent upon technology development to provide longer operating lifespans on the surface, and there is no programmatic system to nurture such development.

To complicate it a bit further, there are at least five strategies for overcoming Venus's heat, but feedforward of technology solutions depends quite a bit on the next three missions following similar strategies, and there's reason to believe that on a mission-by-mission basis, there is an incentive NOT to do this. NASA's bottom-up mission planning means that by doing what's right for each mission, the overall program will be in jeopardy.

Ways to explore Venus's surface:

1) Act fast. Accomplish your intended science mission in minutes to hours.
2) Rise above it all. Spend part or all of the mission at high altitudes to avoid the worst heat.
3) Just take it. Hardened electronics that can operate indefinitely at up to 500C.
4) Passive cooling. Bring some thermal ballast to the surface and live for as long as it lasts.
5) Nuclear refrigerator. Keep the spacecraft's essential parts at tolerable temperatures.

A mission need not choose just one of these -- you could combine two or more strategies -- but it would be absurd to expect all of these to apply to any one mission. The Rube Goldberg complexity would kill a mission that tried lots of these together. All five of them require technology development to different degrees (no pun intended). So the absolute worst case for a Venus program would be if the next three missions picked three different strategies, requiring ~triple the technology development.

Here are the putative next three Venus surface missions, with Venus Sample Return being the possible fourth.

VISE
Venus Geophysical Network (1 Earth year operation of a seismic/climate station network)
Venus Surface Explorer

The seismic network has the most stringent requirements, and would basically require either strategy (3) or (5) or some combination of them. If each mission follows just one or two of the strategies, then the only way to get synergy between these three missions is to start scratching some of (1), (2), and (4) off of the list.

There is also possible synergy with other-planet missions: giant planets could use (3) or (4)... Mars could use (1)... a Mercury lander/network could use (3).

The most synergy, then, for getting some scarce tech. development effort spread around would definitely involve the hardened electronics of (3). It also makes for the happiest ending, because if undertaken first, it takes the most problems off of the table. It also requires less onboard mass, which is much more important if VISE/VSE use aerial mobility, which would make (4) and (5) prohibitive.

It seems that (3) is the only strategy providing synergy to all of the possible Venus missions.

It's likely a less attractive option for VISE, however, which competes with other New Frontiers missions against a funding cap, and would be able to meet its needs most economically with (1), (2), or (4).

As long as mission planning is done one mission at a time, the Venus program is doomed to be a "problem" for decision makers. I would not be surprised if VISE slips from its designated slot in the NF program, putting the long hiatus of US exploration of Venus into at least another decade before the kind of programmatic overhaul that will make all of this possible.
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Greg Hullender
post Sep 4 2007, 05:23 PM
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Any feel for whether hardened electronics are apt to be developed anyway due to non-space applications?

--Greg
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JRehling
post Sep 4 2007, 11:33 PM
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QUOTE (Greg Hullender @ Sep 4 2007, 10:23 AM) *
Any feel for whether hardened electronics are apt to be developed anyway due to non-space applications?

--Greg


Here's a great one-sentence answer from a web search (I have no expertise on the matter):

<<Although the present market for high-temperature electronics is relatively small and has been dominated by the petroleum well-logging industry, the increasing demand for underthe-hood electronics from the automotive industry and the resurgence of the high-reliability military and aerospace market sector is expected to increase demand in the near future. >>

I suspect Venus is a lot hotter than car engines and logging saws, however.
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ElkGroveDan
post Sep 4 2007, 11:38 PM
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QUOTE (JRehling @ Sep 4 2007, 03:33 PM) *
Here's a great one-sentence answer from a web search (I have no expertise on the matter):

<<...has been dominated by the petroleum well-logging industry, the increasing demand for underthe-hood electronics ...
>>
I suspect Venus is a lot hotter than car engines and logging saws, however.


Well-logging has to do with documenting geologic cross-sections of petroleum wells, and some of those get pretty darn hot, though I'm not sure as hot as Venus.


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Greg Hullender
post Sep 5 2007, 04:31 AM
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It doesn't have to be as hot as Venus -- just hot enough to require "wide-band" semiconductors. Hotter than 300C would do, I think, since the next breakpoint is 600C or so.
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hendric
post Sep 5 2007, 05:01 AM
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There are plans to place Silicon Carbide based semiconductors inside of jet engines to watch the combustion using UV detection. So 500 C semiconductors aren't completely unlikely, and as a bonus, we might get UV detectors/spectrometers for free. They also tout SiC as a very rad-hardened semiconductor, but all the literature for this I've found is for neutron radiation, not the protons/electrons we'd get near Jupiter. But maybe they'll figure out a way around that, and Jason will finally get his Io orbiter mission!

Some links:
http://www.grc.nasa.gov/WWW/SiC/SiC.html
http://www.grc.nasa.gov/WWW/SiC/reviewpapers.html

It's one of those "5-10 years" technologies that might be here in 3-5, or 20-never (like fusion!).


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pgrindrod
post Sep 5 2007, 09:03 AM
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there's a mission proposal (european venus explorer - eve) in with esa at the moment, which is for a balloon to stay around 40-60 km altitude, where it's pretty clement. so i guess this is your textbook option 2 - keep well away from the nasty conditions near the surface.

my own (probably biased) impression from conferences and meetings is that there are lots of interesting and important scientific questions about venus, and people would love to have a crack at them, but until it gets less risky, it's very hard to sell a venus surface mission. electronics that can cope with the heat would go some way to making that job easier.

pete
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JRehling
post Sep 5 2007, 04:35 PM
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QUOTE (pgrindrod @ Sep 5 2007, 02:03 AM) *
there's a mission proposal (european venus explorer - eve) in with esa at the moment, which is for a balloon to stay around 40-60 km altitude, where it's pretty clement. so i guess this is your textbook option 2 - keep well away from the nasty conditions near the surface.


That's a great mission profile for Venus, and I hope we see it come to pass. But it's never going to do some of the surface science that's also needed. You can only do so much from 40 km up. Especially in a place where IR sensing is polluted by thermal IR and there's a big, thick atmosphere absorbing so much of the IR spectrum. IR spectroscopy from orbit has had limited success at Mars (with TES, anyway -- the higher resolution of THEMIS may prove to work better) and the Galileans, and they don't present half the problems that Venus does. Even Titan is more favorable, probably, from OVER the haze than Venus from just below the clouds.

If hardened electronics were around, they could even benefit a balloon mission, allowing lower altitudes, or giving the payload a last hurrah as a surface station at mission's end.

Development of this stuff would pay off more the earlier it's in hand because it could go into more missions at Venus and elsewhere.

I'm afraid that Venus exploration below the cloud decks will turn into an endless no-go until this step is taken. The last time data was returned from a spacecraft on the surface was 1985. It's going to be a 30-year drought in the best-case scenario.
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Greg Hullender
post Sep 6 2007, 02:11 AM
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Someone at lunch pointed out today that if we had the hardened electronics maybe we wouldn't have to air-condition the big data centers. Apparently the big cost of running a data c enter is the power, of which 70% or more is for air-conditioning.

Of course, neighbors might complain if a data center got up to 500C. Might be tough doing maintenance too. :-)

--Greg

Disclaimer: I work for Microsoft, but I'm obviously not speaking for them here.
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JRehling
post Sep 6 2007, 05:22 PM
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QUOTE (Greg Hullender @ Sep 5 2007, 07:11 PM) *
Someone at lunch pointed out today that if we had the hardened electronics maybe we wouldn't have to air-condition the big data centers. Apparently the big cost of running a data c enter is the power, of which 70% or more is for air-conditioning.


Interesting market analysis.

There must be an optimal breakeven point. With hardened electronics, you'd be shifting the burden on the lower processing power.

A lot of data centers nowadays, though, run on off-the-shelf CPUs, which are very cheap. Consumers buy the same CPUs and don't have the fancy AC because they're not as concerned with failures, and don't pack thousands of CPUs into the same room. For your typical Internet company, there'd be significant pain to using hardened electronics that have less development market behind them, and might require special support, software, etc.

But a big company that needs to mass-produce the same sort of data center (Google is a great example) might find that this makes sense for them. Google definitely got started using (pioneering, even) the lots-of-cheap-CPU data center, but they and other big data companies might see the wisdom in using tougher CPUs.

The question is if their breakeven point would involve electronics that are helpful at Venus. I'd think that 200C would be far on the fat side of any requirement on Earth. The question is if electronics that suit the earthly case end up overly hardened for free (the spec. is only for 150C, but it happens to be good at 500C). Of course, even electronics good for 200C would be a big help in combination with any of the other survival strategies. A nuclear refrigerator that only had to keep things under 200C instead of under 50C would definitely be easier to fly.
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dvandorn
post Sep 7 2007, 06:18 AM
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Has anyone ever given any serious consideration to David Brin's "energetic arm-waving" concept of a refrigerating laser?

After all, the whole idea is to dump heat outside of the probe, right? To do so, you need to generate it out into heat pulses that are *hotter* than the ambient outside temperature, since you can't dump heat into an environment that's hotter than the dump.

So -- use the heat that leaks through your outer skin to power a laser that's a *lot* hotter than 500C, and then dump the energy by blasting the laser out and away from the probe.

What are the engineering challenges in such a system? And does it violate any basic laws of thermodynamics?

-the other Doug


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