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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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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


--------------------
“The trouble ain't that there is too many fools, but that the lightning ain't distributed right.” -Mark Twain
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