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Water-cooled lander
JRehling
post Aug 26 2007, 03:47 PM
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QUOTE (tasp @ Aug 26 2007, 07:39 AM) *
{Going out on a limb here}
We would be looking for rapid (but tiny!) frequency variations caused by seismic vibrations in the return signal, and we could ignore the slow shifts caused by the (slow) Venusian rotation.


It would be quite easy to do this if the location we were scanning happened to be the place where a sizable quake were happening at that moment. Earthquakes of magnitude 7 to 8 can produce ground velocities (horizontally) of 50 cm/sec or so. Probably easy to detect.

I think trying to look at a seismic station at one location on Venus and detect (via doppler) the vibrations of a quake on the other side of the planet would probably be impossible. The ground velocity would be tiny indeed.

So an alternate approach would be to bet on picking the right location of a quake and to scan while one is happening. That seems like we'd have to get awfully lucky to get one detection, and wouldn't learn all that much from it.

I wonder if the solution isn't simply to take a "vacuum tube" approach to electronics that function on the surface of Venus (forget modern microchips) and plunk down a lander that survives 500C. Power source, seismometer, transmitter and nothing else.
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Greg Hullender
post Aug 26 2007, 06:20 PM
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Summary:

According to a 2002 NASA publication, it looks like Silicon Carbide-based semiconductors will eventually enable electronics that will work up to 600C, with enough Earth-based applications to spur their development.

Details:

Wondering whether we could do better than vacuum tubes, I poked around and found this NASA link depicting a diode operating at 600C.

http://www.grc.nasa.gov/WWW/SiC/SiC.html

On the same site, under publications/review papers, I found this 2002 IEEE paper on very high-temperature semiconductors:

"High-Temperature Electronics—A Role for Wide Bandgap Semiconductors?" PHILIP G. NEUDECK, SENIOR MEMBER, IEEE, ROBERT S. OKOJIE, MEMBER, IEEE, AND LIANG-YU CHEN, PROCEEDINGS OF THE IEEE, VOL. 90, NO. 6, JUNE 2002

http://www.grc.nasa.gov/WWW/SiC/SiC.html

It's not a hard read, but here are some highlights:

The two materials of most interest are SiC (Silicon Carbide aka Carborundum) and GaN (Gallium Nitride). SiC is the more developed of the two -- "mass produced single-crytstal wafers are commercially available." High imperfection rates in these crystals are one big obstacle at the moment. Another issue is the need to develop "high-temperature passive components, such as inductors, capicitors, and transformers" (although those don't sound nearly as challenging).

There's a very impressive list of prospective applications for these devices (Table I), ranging from Automotive (components in the cylinders), Turbine Engines, Industrial, Deep-Well drilling, and (yes) Spacecraft (Venus and Mercury Exploration). Based on that, even though "formidible developmental challenges remain," I'd expect there's a good chance that electronics suitable for use at Venusian surface temperature and pressure will end up getting developed.

Sort of that, existing SOI (Silicon on Insulator) work up to 300C (commerical devices rated to 225 exist), and GaAs (Gallium Arsenide) adds "perhaps an additional 100C". In fact, they cite three papers demonstrating short-term GaAs operation at 500C, but note that "long-term operation of these electronics appreciably beyond the capability of SOI remains undemonstrated." Still, that puts GaAs within the range claimed by the authors of the water-cooled-lander presentation.

On the whole, this looks very encouraging to me. That Venus rover we've been dreaming of may not be so ridiculous after all.

--Greg
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Greg Hullender
post Aug 26 2007, 07:12 PM
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ugordan: As I calculate it, the Sun-Venus L1 point is 1,002,000 km from the surface of Venus.

--Greg
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tty
post Aug 26 2007, 07:20 PM
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Completely mechanical seismometers were used for a long time and worked quite well. Most types were quite heavy, but at least one type (Galitzin's vertical seismograph) was quite small and handy. So what you need in the way of electronics is some type of electronic or electromechanical device to pick up the data and a simple transmitter to transmit it (perhaps to an orbiter) plus a power source. It doesn't sound impossible to build that to work at 700 K. It may be more difficult to build a lander that will guarantee a good coupling between seismometer and the ground (this problem in itself may well preclude elaborate insulation around the seismometer).
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Gsnorgathon
post Aug 26 2007, 09:21 PM
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Since the topic's already wandered somewhat from the OP, I'll just post this bit that I've been reminded of:


Mike Malin's Venus Geophysical Network Pathfinder: A Discovery Workshop Mission Proposal
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tasp
post Aug 27 2007, 02:25 AM
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I think we would want a retroreflector (and to use a microwave frequency absorbed by the surface materials) so we would be observing a point source on the surface. If we were monitoring an appreciable area the signals from the perimeter of the expanding shock would cause the beam reflections to interfere.

I think the drift of the spacecraft at the Venusian Lagrange spot would be held slow enough that we could distinguish the (relatively) faster surface jolts.

We can also simultaneously illuminate the retroreflectors with 2 different microwave frequencies and correct for atmospheric scintillations.

As Venus rotates, the reflectors directly below will affect the return signal via verticle oscillations, retroreflectors illumed near the Venusian limb will reveal motions parallel to the surface.

If the technique would work from the 60 degree leading and trailing Venusian Lagrange positions also, we might be able to simultaneously study specific retroreflectors from 2 sats, and be able to characterize ground motions more precisely.
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Greg Hullender
post Sep 13 2007, 12:42 AM
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For some reason, NASA issued a press release yesterday saying they've built an integrated circuit that runs at 600C.

http://www.nasa.gov/home/hqnews/2007/sep/H...licon_Chip.html

From the article, "This chip exceeded 1,700 hours of continuous operation at 500 degrees Celsius - a breakthrough that represents a 100-fold increase in what has previously been achieved. The new silicon carbide differential amplifier integrated circuit chip may provide benefits to anything requiring long-lasting electronic circuits in very hot environments."

Can't find a relevant paper about it yet though.

--Greg
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JRehling
post Sep 14 2007, 06:20 PM
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QUOTE (Greg Hullender @ Sep 12 2007, 05:42 PM) *
For some reason, NASA issued a press release yesterday saying they've built an integrated circuit that runs at 600C.

http://www.nasa.gov/home/hqnews/2007/sep/H...licon_Chip.html

From the article, "This chip exceeded 1,700 hours of continuous operation at 500 degrees Celsius - a breakthrough that represents a 100-fold increase in what has previously been achieved. The new silicon carbide differential amplifier integrated circuit chip may provide benefits to anything requiring long-lasting electronic circuits in very hot environments."

Can't find a relevant paper about it yet though.

--Greg


That's great news. I wonder how much of the workload that chip can handle, or if it's of toylike simplicity and is more of a proof of concept. And if it adheres to any other standards so that programming it doesn't require a boatload of software technology development.

I think this could go one of two routes: Either the new chip technology ends up producing a crude but servicable brain for Venus missions, which end up resembling 1970s computers, or they put still more effort in to interface the CPU and memory chips into prevailing standards, so that the programming work is similar to what it would be for using off the shelf technology on a typical space mission.

But this is a huge step. The steps that remain are something we know can be done.

Three Venus landers with camera and seismometers -- the Venusian Viking, after so many decades -- let's see it happen!
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nnyspace
post Nov 7 2007, 05:58 PM
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Could a liquid/solid that has a lower density change (volume change) between solid/liquid phase be found, So then it could simple be place in the space between the electronics and would not need its own containment vessel?
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djellison
post Nov 7 2007, 07:05 PM
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The problem is that the latent heat of evaporation of water is so huge -I don't know of anything else that can match it.

Doug
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dvandorn
post Nov 7 2007, 07:12 PM
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Apollo's Lunar Rover used bee's wax to cool its Lunar Communications Relay Unit (LCRU), the self-contained comm system that allowed good comm (and TV) from wherever the Rover was parked. It cooled at the phase change between solid and liquid, and was pretty effective up to about 150 degrees C. (It *may* also have used the phase change from liquid to vapor for cooling, I just don't recall right now. But I know it used bee's wax.)

-the other Doug


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“The trouble ain't that there is too many fools, but that the lightning ain't distributed right.” -Mark Twain
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AndyG
post Nov 7 2007, 08:31 PM
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So we have wood used in Apollo hatches (is that right, or am I misremembering details?) and cork in some ablative coverings...it seems strange in such a high tech frontier of plastics and alloys that any natural products could find a role in such harsh environments.

Andy
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nnyspace
post Nov 7 2007, 10:01 PM
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QUOTE (djellison @ Nov 7 2007, 07:05 PM) *
The problem is that the latent heat of evaporation of water is so huge -I don't know of anything else that can match it.

Doug


Well yes water does have a very high heat of fusion and specific heat capacity. But others come close for example it would take water 34.8 hr to go from -20 to 60C with 500 watts of input heat, for formic acid it would take 24.5hr, and if formic acid has a much small density difference between it phases (can't find density of solid phase formic acid) you could get a weights savings by using formic acid without the need for another containment layer/vessel.

--nny
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JRehling
post Nov 8 2007, 05:21 AM
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QUOTE (AndyG @ Nov 7 2007, 12:31 PM) *
So we have wood used in Apollo hatches (is that right, or am I misremembering details?) and cork in some ablative coverings...it seems strange in such a high tech frontier of plastics and alloys that any natural products could find a role in such harsh environments.

Andy


Now, yes, but Apollo got its start 40+ years ago, before Benjamin Braddock was told that the future was plastics.

I've seen a Mercury training capsule up close (and at length), and was quasi-surprised to see leather used inside. But, hey, it works, so why not?
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tedstryk
post Nov 8 2007, 11:32 AM
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Also, natural materials had been used for a long time. Plastics were relatively new.


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