From: https://science.slashdot.org/story/16/05/11/0049228/atomic-oxygen-detected-in-martian-atmosphere
Venus is far better than Mars. Specifically, Venus's cloudtops - say, 54km altitude, 70 latitude (poleward might be even better, but you start facing more risk from the polar vortices, so we'll just compare 70). Earth by comparison will be equatorial, and Mars will be surface-average. Gravity (earth relative): Earth: 1.0; Mars: 0.38; Venus: 0.9 Air pressure (atm): Earth: 1.0; Mars: 0.006; Venus: 0.5 Temperature (avg, C): Earth: 26; Mars: -30; Venus: 31 Daily variation (C): Earth: 4-30; Mars: 90; Venus: 15 Day length: Earth: 24; Mars: 24.5; Venus: 48 Ability to relocate / explore new terrain: Earth: moderate; Mars: poor; Venus: high Overhead radiation shielding mass (meters H2O equivalent): Earth: 10,3; Mars: 0.36; Venus: 5.2 Magnetic field: Earth: 25-65uT, intrinsic; Mars: induced, 20-40nT MPR, 5-20nt magnetosheath; Venus: induced, 40-80 nT MPR, 10-40nT magnetosheath Health hazards: Earth: those humans evolved to; Mars: 1) Fine, abrasive electrostatic dust, 2) silicosis; 3) perchlorates; 4) hexavalent chromium; 5) other chemical hazards; Venus: 1) Corrosive acid mists; 2) hydrogen fluoride; 3) probably others of relevance Other local hazards: Earth: those humans evolved to; Mars: marsquakes, landslides, dust storms, probably others. Venus: poorly understood - lightning (although we don't know at what altitude), gusts/shear (probably Earthlike, but poorly quantified), icing (probably not, but maybe), possibly others. Needs more study, but Mars gets the lion's share of the planetary exploration budget and everything else competes for the scraps. Delta-V to habitable area from LEO (km/s, aerocapture assumed): Earth: 0; Mars: 4.7; Venus: 4.2 Delta-V from habitable area to LEO (km/s, aerocapture assumed): Earth: 9.8; Mars: 10.0; Venus: 15.5 Transit time (months): Earth: 0; Mars: 9; Venus: 5 Launch window frequency (months): Earth: 0; Mars: 25; Venus: 19 Landing difficulty: Earth: moderate (dense atmosphere, oceans to land in, compacting soil, readily available rescue); Mars: hard (reversed conditions of Earth): Venus: easy (no landing at all; your landing ellipse is "a large chunk of the planet") Solar energy (29% triple-junction W/m): Earth: 290; Mars: 45; sometimes almost none; Venus: 400 Capturable wind energy: Earth: moderate; Mars: effectively none; Venus: high Diversity / value of resources: Earth: moderate (that which we're used to); Mars: probably less than Earth, but not "poor"; Venus: the planet acts as a natural refinery, baking / dissolving minerals from rocks and redepositing them in other forms; surface appears to be highly enriched in "incompatible elements" (many of which are rare and valuable on Earth) and the planet is highly enriched in deuterium. Accessibility of resources: Earth: moderate (that which we're used to); Mars: like Earth, but hindered by mobility and the difficulty of removing overburden; Venus: mixed high/low; a large resource base is available to be drawn directly from the atmosphere and which can be distilled /decomposed by simple heating/cooling (for example, 85% H2SO4 -> H2O + O2 + SO2) - the list of known/likely elements in the clouds is very long, even involving significant iron in the form of iron chlorides). However, surface access requires heat-tolerant phase change balloons (the high atmospheric density makes "dredging" with the same fan used for maneuvering a reasonable approach) Venus is grossly underappreciated as a destination for human settlement, and for exploration in general. Normal Earth air is its own lifting gas. Rather than living in a cramped pressure vessel, colonists would be living in an expansive, bright space perfect for cultivation. Don't like one of your coworkers? Go hang your "room" from a catenary cable on the opposite side of the habitat from her, literally hundreds of meters away. Energy is almost unfairly abundant. No additional radiation shielding is required. It's faster and with more frequent launch windows to get from Venus to the asteroid belt than from Mars, and likewise faster and more frequent windows from Venus to Mars than from Earth. The "acid clouds" aspect is overplayed; it's only a few mg per cubic meter, while OSHA's limit for breathing sulfuric acid mists is 1mg/m^3 over an 8-hour work shift. The mists are stronger, and there's anhydrous acidic components as well (aka, it's certainly going to cause dermatitis with prolonged exposure), but it's not like sticking your hand in a vat of sulfuric acid. You actually could feel an alien wind on your skin, something you could never do on Mars. It's also worth mentioning that Martian regolith is expected to cause contact burns similar to lye, due to the perchlorates and other oxidizing compounds. Work outside in Venus would be in a facemask and loose-fitting full body suit, rather than a restrictive pressure suit like on Mars. There are, as per above, a couple fields where Mars is better than Venus - but not many. One is returns from Venus; the disadvantage to Earthlike gravity is that it takes earthlike delta-V to get to orbit. That said, the combination of somewhat lower gravity, somewhat lower pressure, and a number of other factors too long to get into here make it somewhat easier to reach orbit, quite possibly enough as to make an SSTO a reasonable approach. If not, an 1 1/2 stage rocket using a locally-produced drop tank would probably be the best option. The other issue is lesser - day length. Venus's superrotating atmosphere presents a varied day length, from "constant sunrise/sunset" at the poles up to "nearly a week" at the equator. At 70 degrees, as stated, it's about 2 Earth days. If the polar vortices prove not to pose a threat to aircraft, then the habitat could be moved further poleward to a 1 Earth day cycle (also a more favorable pressure/temperature combination). However, concerning the main concern (flowering of long or short-day plants), in addition to the obvious solution (covers and lighting triggers when you want to force flowering), or the even more obvious solution (don't grow these plants, or only grow varieties selected to be less affected), it's worth noting that such plants often flower better on bidiuranal and triurnal cycles than they do on 1,5x, 2,5x, etc day lengths - it's not a simple issue of scaling the day length. In general, however, a colony on our sister planet Venus - unlike a cramped pressure vessel on Mars - would be a floating paradise. A heaven drifting over hell.
> I would assume Martian dust isn't quite as problematic as Lunar dust is, since the former gets moved around more and hence has fewer sharp edges. > > 3) perchlorates; 4) hexavalent chromium; > > You're not supposed to stick Martian soil in your mouth. Martian and lunar dust have both similarities and differences. Martian dust particles are finer, athough it doesn't make them less hazardous. Despite attempts to minimize it, some exposure to the dusts will be inevitable; it's fine, ubiquitous and sticks to everything. It's well recognized as a significant hazard in mission design. One hazard of martian dust over lunar dust is that it appears to contain significant more chromium, and it's often hexavalent (a highly toxic form rarely found in nature on Earth). A number of other compounds such as arsenic appear to be of relevant risk as well. > Yes ... but fail at landing, and you'll plummet into a 450 degree C hellhole. A rough landing on Mars might kill you, a rough landing on Venus kills you before you hit the surface. Expecting to survive a crash landing on Mars is far beyond positive thinking. The landing processes on both planets start out roughly the same. But the processes on Venus end before the hardest parts of a Martian landing end. Once you're down to under 100m/s or so on Venus, you're ready to start with deployment**. Once you're down to ~100m/s on Mars, you still have the part that's most likely to kill you remaining. ** - Although any type of reentry system works, a ballute reentry seems particularly well-suited for Venus, as it give you an initial inflation of warm, light gases. Ballute reentry has been proposed on a number of Venus proposed Venus probes, but so few Venus probes ever get funded due to Mars' domination in the budgeting process. > And Mars has quite a bit of water. More than Venus, probaly. Not probably - it does. But it's not in the atmosphere. It's frozen in permafrost, mixed with sand and gravel and contaminated with a good number of toxic substances. And Martian backhoes aren't exactly dime-a-dozen / low-maintenance objects. Venus's water for a colony comes from the mists. There are two potential sources: 1) direct absorption, and 2) condensation. 1) The habitat requires propulsion no matter what. This is because in addition to the strong zonal winds that comprise the superrotation, there are weaker meridional winds that would cause a craft to drift from its desired location. While the zonal winds are too strong to overcome (nor would you want to), the meridional winds are nothing particularly challenging for an airship. An aircraft under propulsive load will have a constant stream of air moving past it - fastest directly in the propeller wash. Hence, the best way to get lots of mist along lots of surface area is to handle steering with a flexible windsock-style thrust vectoring system comprised of permeable tubing for direct absorption, and/or hydrophilic collection/drainage surfaces (see #2). Hence, the collection system is little added mass over the base propulsion system. In the case of absorption, the absorption fluid would be weak H2SO4. The ideal situation involves large volumes of air moving at (relatively) low speeds. This means a large propeller. Hence, the ideal design for launch on a mid-sized rocket involves a propeller with two 6m folding blades stowed vertically in the center of the packed habitat during launch and cruise, rather than multiple smaller propellers stacked horizontally. A large prop is also more efficient. 2) Direct collection on the envelope. While the original Vega data was interpreted as there being no condensation/rain on the balloons, some more recent work has challenged that view, suggesting that it indicates progressively increasing mass loadings as moisture collects, then peaking as runoff rates matched collection rates. This is intere
> So you set yourself up somewhere high up. How exactly do you propose to come by non-gaseous resources? Let's compare individual resources, shall we? Water: Mars: frozen in permafrost, mixed in with sand and gravel, containing perchlorates, hexavalent chromium, and other toxic chemicals. Have to build and deploy a Martian equivalent of a bobcat and scrape it out (note that mining equipment is famous for high maintenance needs). If chunks are too big they need to be run through a rock crusher. They then need to be loaded into a bin and pressure sealed, then heated, with the steam driven off creating the necessary pressure for water to be able to exist at a liquid state and flow off through filters (which will need periodic cleaning); the sand and gravel has to be emptied. The contaminated saltwater now has to either be distilled or run through reverse osmosis, the latter being unfortunately rather contaminant sensitive. It's enough of a headache that most near-future proposals just call for bringing the water (or just hydrogen to make it) from Earth. Venus: Acidists naturally condense or absorbed (see an above post on the subject) and run straight into a boiler. There they're heated. Free water is driven off and H2SO4 decomposes, emitting more water. The steam is isolated and condensed. The latter is much easier. Oxygen. Mars: There are two main proposals for oxygen production. One is electrolysis. Electrolysis systems as used on ISS have however proven to be rather finnicky, and you're dependent on the water mining above to replace any water loss in the system (which will happen over time). The other proposal is to be tested on Mars 2020: MOXIE. Martian air is drawn in and compressed, troublesome impurities removed, CO2 frozen out then reboiled at pressure, then run through a SOFC which uses a lot of electricity to turn CO2 into O2 and CO. Venus: SO3 decomposes at elevated temperatures (much faster in the presence of a catalyst) into O2 and SO2. So the only added step here over water production is the catalyst. Separation from SO2, O2, and other elsser chemicals can be done in a specialized stage or in distillation. Again, winner: Venus. Let's look at starting to form an industry. So, let's look at the top 10 industrial chemicals on Earth H2SO4: This is the number one produced chemical on Earth. Do we even need to go into how much easier it would be to get on Venus? N2: Venus's atmosphere is denser than Mars's and N2 is about in the same percentage concentration, so the advantage is again to Venus. C2H4: The process is roughly the same on both Venus and Mars O2: Already covered. Chlorine (Cl2): On Venus, this is conducted by the Deacon process (4 HCl + O2 = 2 H2O + 2 Cl2). You get free HCl from distillation and you have cheap O2. On Mars, this would be done by the much more energy-intensive electrolysis of brine. Furthermore, you'd need to either isolate out brines containing specifically chlorides first. Ethylene Dichloride (C2H2Cl2): Used for PVC, which honestly isn't a great material for either Mars or Venus. The routes are basically the same on both Mars and Venus. Phosphoric Acid (H3PO4): On Venus, this comes for free during distillation. On Mars... honestly, we don't really know. We've found phosphate minerals (chlorapatite and merrillite) but no concentrations of them. Ammonia (NH3): Haber process, same on both planets. Sodium Hydroxide (NaOH): Ah, finally something Mars can win at! Various hydroxides will be produced as a byproduct of chlorine production. As far as is known, both sodium (and similar-use potassium) can't be gotten from the atmosphere (although they're abundant in any surface rocks that may be mined for other purposes - Venus's surface-mining throughput potential being lower than that of Mars'). That said, Venus lends itself perfectly to cation recycling [nih.gov]. Any waste (plant, human, industrial