May 20, 2015
Low Mars Gravity, Radiation Shielding Suits
Kill 2 birds with one stone on Mars: use lead-laced protective clothing to reduce radiation exposure and also reduce bone loss from low gravity.
Since gravity on Mars is only about 38% of its force on Earth a 180 person on Earth will weight only 68.4 pounds on Mars. That's a problem for the eventual return to Earth. But suppose an astronaut visiting Mars wore a lead jacket, pants, and hat. The weight on their body would probably make their bones weaken more slowly. Also, the radiation would reduce radiation exposure.
Suppose a person who weighs 180 pound wears an amount of lead that would weigh 294 pounds on Earth. The total combined weight would be 474 pounds on Earth. But on Mars the additional lead would raise their weight to only 180 pounds. So a person on Mars could wear a large amount of lead shielding.
Someone taking a hike on the surface of Mars could easily carry a backpack that weights hundreds of pounds on Earth. A longer duration hiking trip on Mars would be possible because of the amount of weight hikers could carry. If the hikers had a cart to put their equipment on and pushed the cart a pair of hikers could probably easily push materials that would weigh 700+ pounds on Earth.
From the comments: Plastic is a better choice than lead to shield against cosmic rays. Plastic is more effective per pound than aluminum.
DURHAM, N.H. –- Space scientists from the University of New Hampshire (UNH) and the Southwest Research Institute (SwRI) report that data gathered by NASA’s Lunar Reconnaissance Orbiter (LRO) show lighter materials like plastics provide effective shielding against the radiation hazards faced by astronauts during extended space travel. The finding could help reduce health risks to humans on future missions into deep space.
Water would also work well because any material with a large amount of hydrogen is expected to work well. This suggests that the ability to extract frozen water from the ground on Mars would help astronauts not just for drinking, cleaning, and plant growing but also for shielding.
Randall Parker, 2015 May 20 02:38 PM
This article says that exercise is not very successful in preventing bone loss in low gravity environments:
Since Gemini, exercise has been tried as a way of preventing bone loss, but it has not been shown to be successful. This may be in part due to lack of adequately designed studies (no controlled study had been done as of 2005, either in space or using bedrest as an attempt to simulate conditions which lead to bone loss). It is not known whether a different exercise regimen (perhaps including larger loads than past ones) would be effective.
However, at a Mars colony it is possible to build affordable giant centrifugal rotary apartment complexes on the planet for the astronauts to reside either on surface or underground, so that the people who go to Mars will only experience low gravity when they are outdoors. And since most of the time they would be indoors and they would be outside only for a few hours per day, this would resolve the problem.
Cosmic rays are probably the worst problem on Mars, and lead is not necessarily the best shielding material for this. High density plastics test better. Lead is good for gamma ray protection, but other materials which are lighter are now being used even here on earth for personal shielding...such as tungsten.
It is also conceivable that superconducting magnets and creating an active magnet field to shield from cosmic rays will need to be developed. But in the end, I doubt Mars astronauts will be covering themselves with lead.
Dantes: " but other materials which are lighter are now being used even here on earth for personal shielding...such as tungsten."
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The density of tungsten is 19.25, is much higher than the density of lead (11.34).
In fact even greater than uranium's density (19.1) is less than that of tungsten.
"Someone taking a hike on the surface of Mars could easily carry a backpack that weights hundreds of pounds on Earth."
"hundreds of pounds" is at least 200. A 200-lb backpack would weigh 76 pounds, which is a lot of weight to carry on a hike for any distance. Has Mr. Parker ever tried it?
And that is only the vertical load. The mass of the backpack would be the same: greater than the body mass of most people. That much mass attached at my shoulders would make me extremely top-heavy. Walking under those conditions might be possible, but certainly not easy.
Not all the weight would have to come in at the shoulders. A lot of the weight could come in on the hips.
76 pounds would be added onto a body that is weighing only 38% of what it weighs on Earth.
"I think on Mars people are going to need to spend very little time outside."
At least until we started Terraforming:
Computer calculations performed by myself, Owen B. Toon and James F. Kasting suggest that if Mars's atmosphere contained just a few parts per million of the super-greenhouse gases, the average temperature at the planet's surface would rise from -60 to -40 degrees Celsius (-76 to -40 degrees Fahrenheit). This warming could be enough to trigger the release of carbon dioxide from the polar caps and soil into the atmosphere. Carbon dioxide would then augment the greenhouse effect even further, driving the release of more carbon dioxide and water vapor into the atmosphere. Such positive feedback would be sufficient to create a thick, warm atmosphere--the carbon dioxide Mars. - Dr. Christopher McKay
McKay suggests that the entire PFC process will take a mere 100 years before average global temperatures reach an Earthly level. This number is such good news that scientists who were once skeptical of the concept of terraforming now look forward to the day when they can take part in it. And that day may be closer than anyone might imagine
Carbon dioxide sublimation
There is presently enough carbon dioxide (CO2) as ice in the Martian south pole and absorbed by regolith (soil) on Mars that, if sublimated to gas by a climate warming of only a few degrees, would increase the atmospheric pressure to 30 kilopascals (0.30 atm), comparable to the altitude of the peak of Mount Everest, where the atmospheric pressure is 33.7 kilopascals (0.333 atm). Although this would not be breathable by humans, it is above the Armstrong limit and would eliminate the present need for pressure suits.
Wonder how much Cosmic Ray flux would be stopped by .333atmosphere?. And Of course .333atmosphere under Mars gravity is the equivalent of .333/.38= .87 atmosphere under Earth's gravity.
Unfortunately terraforming itself won't solve the problem of health problems caused by long-term low gravity, which is very important. Artificial centrifugal gravity can only be available when the residents of Mars are confined into large rotating buildings or vehicles. This would be tantamount to staying indoors for most of the time. And besides, although terraforming will happen, it will take time to build the atmosphere, probably centuries after the astronauts have already colonized Mars.
"Unfortunately terraforming itself won't solve the problem of health problems caused by long-term low gravity, which is very important. Artificial centrifugal gravity can only be available when the residents of Mars are confined into large rotating buildings or vehicles. This would be tantamount to staying indoors for most of the time. And besides, although terraforming will happen, it will take time to build the atmosphere, probably centuries after the astronauts have already colonized Mars."
What health problems will occur with permanent colonists who live/grow up under 0.38 Earth gravity? It is by no means clear that the lower gravity of Mars would cause health problems. The biggest issue with a Mars trip is the many months travel time (with current tech) to Mars and back where astronauts would be subjected to zero-gravity for long periods of time. A permanent Mars colonist would be under .38 gravity 24/7; remains to be seen if that would be a health issue. As for your 2nd point from my link above: "McKay suggests that the entire PFC process will take a mere 100 years before average global temperatures reach an Earthly level." They are talking about a much shorter time frame roughly 100yrs (not centuries) to get to normal earth temperature thick atmosphere earth similar pressures, liquid water on the surface. They were also talking about manufacturing the super greenhouse gases on earth and shipping them to Mars. I would have the colonist manufacture the NF3 on Mars using indigenous raw materials present. It would still be unbreathable, you would need to wear an oxygen mask, but you could wear normal clothes. You would be making Mars far more habitable in a relatively short period of time.
I agree, we don't know what health problems intermediate gravity would cause. We're basically familiar with the health effects of two levels of gravity: 1G, and 0G.
It's one of my great frustrations that we've never built the rotating habitat in orbit that would have told us what intermediate levels of acceleration did.
It hadn't occurred to me before that there is an atmospheric pressure level that could be established on Mars at which you could walk around outside without a complete pressure suit but still require oxygen. Yes, that lowers the bar for making the surface a lot more livable. But at what atmospheric density does the harm from cosmic rays go down to a safe level?
I think Mars colonists are going to have to live underground for decades at least. I'd like to see the development of robots that can build up a large underground enclave for colonists.
What might be possible after a few decades: Create a large building on the surface that has thick glass and plastic covering. But the covering might need a water layer to help stop the cosmic rays.
I wonder whether Mars colonists or even Mars visitors are going to have to spend part of their time in some large rotating underground apparatus to give their bones a needed work-out.
We don't know, Randall, but finding out wouldn't be as expensive as sending people to Mars, and IS kind of necessary for mission planning. Hence my complaint. All these people talking about a Mars mission, without that one basic piece of information, which we know how to obtain: How much acceleration is necessary to maintain human health long term?
If Mars gravity is enough, cool. If it isn't, a Mars colony just got MUCH more expensive. We need this information not just for Mars, but for all our deep space manned mission planning.
It's just ridiculous that we still don't know.
"It hadn't occurred to me before that there is an atmospheric pressure level that could be established on Mars at which you could walk around outside without a complete pressure suit but still require oxygen. Yes, that lowers the bar for making the surface a lot more livable. But at what atmospheric density does the harm from cosmic rays go down to a safe level?"
Well let's see...Mars has a very long wide Canyon. After the CO2 has outgassed (and along with it the water which would be liquid under these conditions) the base of the canyon might be an ideal place for a large Colony (or colonies). Water would tend to pool in the low lands (base of the Canyon) forming nice river(s)/lake(s). The high Canyon walls would greatly attenuate the Cosmic Ray flux (as well as the occasional solar flares). Settlements might tend to form then in the relative protection at the bottom of the Canyon, (where also the atmospheric pressure would be highest) there might even be caves at the base that could be expanded upon. It might also be possible to run super conducting cables at the top of the Canyon to deflect radiation (at least from charged particles) away from the settlements at the bottom of the canyon.
People worried about Martian cosmic rays need to go re-read Tim's excellent comment above.
Solar X-rays won't make it past the upper wispy fringes of air. Solar protons, not much further. Cosmic rays will hit something high up, so what reaches ground level will certainly be mostly muons as they are here. If people are healthy taking 400 mSv/yr on the beach at Guarapari, they'll be fine on a Mars with 300 mb of atmosphere.
Stuff is going to weigh a lot less on mars, but it will have the same mass, so a suit that weighs 57 kilograms on mars will still have 150 kilograms of mass and will require the same amount of energy to start and stop as 150 kilograms on earth. Once you get a rhythm going it might not be too bad, but a rhythm might be difficult to get on broken ground or when working outside. The Apollo astronauts wore 91 kilogram suits and they were pretty cumbersome. Obviously we'd want to avoid a situation where an astronaut could get "turtled" and unable to rise from a face up prone position. Fortunately, robots should eliminate most of the need for humans to walk around. For one thing, it is far more payload efficient to use elecric motors to move stuff around than food fueled human muscles.
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