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posted by martyb on Monday April 24 2017, @04:18AM   Printer-friendly
from the power-to-the-lander dept.

On Wednesday, April 19th, in a seminar titled "An Air-Breathing Metal-Combustion Power Plant for Venus in situ Exploration", NASA engineer Michael Paul presented a novel idea where existing technology could be used to make longer-duration missions to Venus.

To recap the history of Venus exploration, very few probes have ever been able to explore its atmosphere or surface for long. Not surprising, considering that the atmospheric pressure on Venus is 92 times what it is here on Earth at sea level. Not to mention the fact that Venus is also the hottest planet in the solar system – with average surface temperatures of 737 K (462 °C; 863.6 °F).

Hence why those few probes that actually explored the atmosphere and surface in detail – like the Soviet-era Venera probes and landers and NASA's Pioneer Venus multiprobe – were only able to return data for a matter of hours. All other missions to Venus have either taken the form of orbiters or consisted of spacecraft conducting flybys while en route to other destinations.

[...] "What can you do with other power systems in places where the Sun just doesn't shine? Okay, so you want to get to the surface of Venus and last more than a couple of hours. And I think that in the last 10 or 15 years, all the missions that [were proposed] to the surface of Venus pretty much had a two-hour timeline. And those were all proposed, none of those missions were actually flown. And that's in line with the 2 hours that the Russian landers survived when they got there, to the surface of Venus."

The solution to this problem, as Paul sees it, is to employ a Stored-Chemical Energy and Power System (SCEPS), also known as a Sterling[sic] engine. This proven technology relies on stored chemical energy to generate electricity, and is typically used in underwater systems. But repurposed for Venus, it could provide a lander mission with a considerable amount of time (compared to previous Venus missions) with which to conduct surface studies.

For the power system Paul and his colleagues are envisioning, the Sterling[sic] engine would take solid-metal lithium (or possibly solid iodine), and then liquefy it with a pyrotechnic charge. This resulting liquid would then be fed into another chamber where it would combined with an oxidant. This would produce heat and combustion, which would then be used to boil water, spin turbines, and generate electricity.

Such a system is typically closed and produces no exhaust, which makes it very useful for underwater systems that cannot compromise their buoyancy. On Venus, such a system would allow for electrical production without short-lived batteries, an expensive nuclear fuel cell, and could function in a low solar-energy environment.

Stirling engines could extend the mission durations.


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  • (Score: 4, Informative) by VLM on Monday April 24 2017, @02:55PM (7 children)

    by VLM (445) Subscriber Badge on Monday April 24 2017, @02:55PM (#498871)

    Around 60 KM altitude the atmosphere is surprisingly cold but perfect pressure for a pure O2 habitat or you could go 50 KM and its sea level pressure but very warm.

    55 KM has a temperature like a comfy room while at earth 18Kft air pressure, so crew who aren't mountain climbers would appreciate some oxy supplementation and pressure tank time but with care it could be quite livable. I am unaware of any "halfway" space suits that could give just two PSI. In space if your suit pops you die rather quickly but on Venus at 55KM if your suit pops you're at 18K which is quite livable for some people for a little while.... it would be similar to being caught outside without a coat in the winter, depending on your personal health level and the weather today you'll be OK for anywhere from 5 minutes to a couple days but eventually for most people it would be required to fix your suit or enter a pressure chamber.

    So put your human filled research lab in a balloon at 55 KM and give them tethers to radiatiors at 45 KM (about 110 C) and 65 KM (about -30 C) and run a low temp diff Stirling engine off that... Or rely on nukes to keep your hot "air" balloon permanently hot and provide power, and run some heat pumps.

    I am too lazy to run the math but I think you can not buy COTS pipe material strong enough to hang out the window and suck up heat below to keep your hot air balloon warm... probably. You'll need nuclear heat.

    60KM puts you near the upper cloud deck AKA you'd see the stars. Also the sun would roast you quite well half the time. I could see there being "pressure" (ugh horrible pun) to descent to 50 KM on the sun side and run the heat pumps in "max cool" to keep out of the sun.

    Assuming infinite nuclear power for your heat pumps to cool, at least at reasonable temps, its interesting to consider scuba style limits to occasional deep voyages. So if 200 feet of water is about 6 bar and is no laughing matter WRT nitrogen and is about the limit, the balloon could dive to nearly 30 KM occasionally as long as the heat pumps can keep up with 200C outside temps for a couple hours as they decompress back up to 50KM. I know decompression into higher than sea level is an issue for scuba guys so going all the way back up to 55KM cruise altitude is going to be like a day or two's careful climb. Piloting a hot air balloon is likely to be very exciting because buoyancy drops as you descend because the air temp increases so you have to be careful about runaway descents.

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  • (Score: 2) by kaszz on Monday April 24 2017, @03:39PM (2 children)

    by kaszz (4211) on Monday April 24 2017, @03:39PM (#498888) Journal

    It should using your numbers be possible to put up a manned research station at least provided all exterior material is acid proof due to hydrogen sulphide and sulfur dioxide etc. The question is of course the purpose and if winds may rip the station apart. Another approach is the one I mentioned earlier in which a probe descends all the way. But returns using a balloon or rocket and docks with some station in the atmosphere. And if carbon nanotubes works out perhaps one could simply drop something to the surface and pull it up. 55 km is way less than needed for a space elevator on earth.

    Although liquid water isn't plentiful in the lower atmosphere of Venus, measurements by space probes
    suggest a reasonable concentration of several hundred parts per million (close to 0.1%). The pH value of 0 in the Venusian clouds

    (From: We Are Not Alone: Why We Have Already Found Extraterrestrial Life, by Dirk Schulze-Makuch, David Darling 2010, page 99)

    So it better be really acid proof.

    • (Score: 2) by VLM on Monday April 24 2017, @04:47PM

      by VLM (445) Subscriber Badge on Monday April 24 2017, @04:47PM (#498941)

      Speaking of

      carbon nanotubes

      ,

      So it better be really acid proof.

      Its "easy" to find acid proof carbon fiber. The fundamental problem is graphite laughs at acid and (some) plastic laughs at acid and separately their physical stats aren't very good but combined their physical stats are pretty impressive and retain their relative acid-proof nature.

      You don't have to worry about a fire as there's not much O2 in Venus atmosphere and the inside of the ... balloonship will probably have a layer of water for thermal buffering.

      Its interesting to think about the part of the lander most likely to survive the longest without corroding as an archeological relic is a carbon heatshield for reentry.

      If you insist on plain old metal, some of the nickel-steel "Hastelloy(tm)" alloys pretty much laugh at chlorine and acid corrosion. I'm sure theres something aerospace thats somehow even more expensive than Hastelloy.

      Yes home depot steel from China won't last long on Venus, or Earth.

    • (Score: 0) by Anonymous Coward on Monday April 24 2017, @06:12PM

      by Anonymous Coward on Monday April 24 2017, @06:12PM (#498970)

      if winds may rip the station apart.

      I don't think that's likely -- you're floating with the wind, so you'd need a drastic change in wind speed over the diameter of your vehicle; something like a tornado might do it for smallish balloons, while larger ones could also be susceptible to more ordinary forms of wind shear. But at least on Earth, tornadoes are a low-altitude phenomenon, and most wind shear is directly related to terrain, and we're talking altitudes far, far above that. The exception is clear-air turbulence at the edges of jet streams, but AIUI Venus either (depending how you look at it) doesn't have proper jet streams (if they exist, are barely faster than the adjacent prevailing winds), or has one big jet stream covering the whole equatorial region to ±50-60°, so we probably don't need to worry about that either.

      Obviously we should send some unmanned balloon-probes first, to be sure of the weather at any altitudes we might want to fly in, but I'd really be surprised if wind shear turns out to be a big deal.

  • (Score: 2) by Grishnakh on Monday April 24 2017, @03:45PM (1 child)

    by Grishnakh (2831) on Monday April 24 2017, @03:45PM (#498893)

    One problem I see with this whole airship-city idea: doesn't Venus have storms?

    • (Score: 2) by VLM on Monday April 24 2017, @04:20PM

      by VLM (445) Subscriber Badge on Monday April 24 2017, @04:20PM (#498915)

      That's a problem with a tower anchored to the ground, which would admittedly be pretty cool.

      Floating in the air it won't matter as long as there's not too much windshear or turbulence.

      Think of flying a small plane, if there's 60 MPH tail winds that'll be tearing up trees and damaging roofs down on the ground but to the plane in the air all it means is the groundspeed is a little higher.

      If the balloon ever landed everyone would die so I'd envision some kind of get away capsule where you'd end up at the orbital station if the balloon starts sinking uncontrollably.

      Also from what little I've read the lower dense atmosphere is nearly static and the high winds don't pick up until pressures are a bit lower than earth normal.

      A long time ago I wanted to make what boiled down to a tower defense type of video game in Venus atmosphere using all this Venus atmosphere weirdness. It sank (which I guess is an on topic pun). Venus's atmosphere is cool (well, above 60 KM or so LOL) yet its not FUN. It was intellectually interesting for awhile.

  • (Score: 1, Informative) by Anonymous Coward on Monday April 24 2017, @04:28PM (1 child)

    by Anonymous Coward on Monday April 24 2017, @04:28PM (#498922)

    Around 60 KM altitude the atmosphere is surprisingly cold

    What is surprising about it? I see at 60 km (3rd column) the temperature is ~244K (6th column) and pressure ~194 mbar (8th column)[1]. Temperature in the Earth atmosphere at ~200 mbar is ~ 210 K.[2] Venus is ~ 1/0.7233 ~ 1.383 AU times closer to the sun.

    Further, Steffan-Boltzmann law says that temperature should be proportional to the 1/4th power of incident radiation (at thermal equilibrium).[4] Since the radiation from the sun drops off by the inverse square of the distance, the Venus temperature should be ((1/0.7233)^2)^0.25 = (1/0.7233)^0.5 ~ 1.176x that of earth, ceterus peribus. So I would expect the temperature at 60 km up in the Venus atmosphere to be around 210*1.176 = 247 K. As we saw, orbit 3212 of the magellan probe reported a temperature of ~244K at this altitude.

    [1] http://pds-atmospheres.nmsu.edu/PDS/data/mg_2401/data/mgn_rtpd.dat [nmsu.edu]
    [2] http://acmg.seas.harvard.edu/people/faculty/djj/book/bookchap2-8.gif [harvard.edu]
    [3] https://en.wikipedia.org/wiki/Venus [wikipedia.org]
    [4] https://en.wikipedia.org/wiki/Stefan%E2%80%93Boltzmann_law [wikipedia.org]

    • (Score: 2) by VLM on Monday April 24 2017, @04:58PM

      by VLM (445) Subscriber Badge on Monday April 24 2017, @04:58PM (#498944)

      There's a lot of indoctrination in the USA about the trivia fact (which is true) that the surface of Venus is hotter than the surface of Mercury due to the greenhouse gas effect. If normies know anything about Venus, they know its hot. So a layer of high altitude atmosphere at a low but survivable pressure that's kinda cold by earth standards is a bit of cognitive dissonance to "all I know is its the hottest surface temp in the solar system". It probably varies by country and education system.

      Its an interesting trivial pursuit problem of another sort to wander thru the solar system and find locations where the temp and pressure are simultaneously human survivable. There's aren't many places off the earth other than that 55 KM level of atmosphere in Venus.