How Safe Is Travel To Mars

[kane007]

Mars Daily - 2006/10/24<br /><br />As NASA lays plans for travel to the moon and Mars, the agency is exploring propulsion systems, crew modules, and habitat structures. It has looked at the psychology of being cooped up with fellow astronauts for a years-long Mars mission, and studied how to maintain bone structure and muscle strength in microgravity.<br /><br />But a new study should force renewed attention on one of the most intractable dangers of space travel: radiation. The review, published Sept. 29 in Mars, the International Journal of Mars Science and Exploration, identified major radiation hazards that must be solved before the safe completion of a human Mars mission.<br /><br /><i>Abbreviated to avoid copyright issues</i>

 

[spacester]

These radiation guys are getting annoying.<br /><br />All this dude has done is gathered together the same data the previous dude gathered. Then he uses his own silly assumptions to draw silly conclusions.<br /><br />The confidence interval approach is a good idea, I'll say that first.<br /><br />But he takes the level of shielding that we use in LEO, where we KNOW the radiation environment is more benign, and he sends his future astonauts off using that, and OMG they are not well enough protected! Go figure!<br /><br /><font color="yellow">. . . but I do know what answer is not: to go ahead with simple Mars mission plans, without radiation protection, on the vague grounds that because we don't know what it will be, we don't have to allow for it</font><br /><br />Oh, please! Who ever suggested such a thing? All the DRMs I can recall have protection designed in, and most have a storm shelter. <br /><br />If you want to make yourself useful in the field of space radiation, you might consider gathering new data and answering the important questions rather than hashing over the same old data one more time. <div class="Discussion_UserSignature"> </div>

 

[halman]

spacester,<br /><br />Yes, these radiation fanatics are tiresome, but perhaps what brings them out of the woodwork are proposals for Mars missions which seem to have little or no radiation sheilding. I still am not sure if I am understanding the Constellation proposal for Mars, because it seems to me to be based on the same 4 man capsule we supposedly will use to go to the Moon. The only concession to the length of the journey is an enlarged Service Module. At least, that is the impression that I am getting from the releases and artwork.<br /><br />There has been no mention that I have seen for a totally new NASA design for a Mars ship, which, if we go about it right, could also be used for survey missions to the Asteroid Belt. Probably because we just don't know enough yet to design with any certainty. Short of massive overdesign, we can't say what will work. Will regular bombardment by heavy particles mean the structure will become radioactive? Can we deflect high energy protons with magnetic fields, or will only mass provide shielding safely? Is the cosmic ray level constant, or does it fluctuate? So much of our research has been done within the Earth's magnetic field that we find our studies weighted heavily by those results.<br /><br />It seems to me that there are a lot of people who say that they are interested in space, but all that they really want is to go to Mars. Any other destination doesn't appeal to them. I see space as that vast emptiness that makes up the majority of the Cosmos, with planets sprinkled here and there. Learning to live and work in that environment is the first step to getting anywhere, and will have far more profound effects on our lives than sending a few people to another planet, I think. <div class="Discussion_UserSignature"> The secret to peace of mind is a short attention span. </div>

 

[scottb50]

I have been proposing just what is needed to provide adequate protection, as well as power, for a long time. If the living area is located in an inner core and the area between the core and the outer surface is filled with water there would be plenty of protection. If the water is used to power the mission, Solar power hydrolyizing the water and fuel cells providing power, as well as recycling crew use water and purifying it by hydrolysis would greatly reduce the total mass needed for a mission to begin with. <div class="Discussion_UserSignature"> </div>

 

[cuddlyrocket]

The CEV capsule's role in Mars missions will simply be to transport the astronuats into LEO (to dock with the rest of the craft) and to re-enter the atmosphere after the return to Earth.<br /><br />For the actual trip to and an Mars and back another vehicle will be used. The CEV will be docked to this and powered down until needed.

 

[mithridates]

All the more reason to go to Venus (the clouds, not the surface) after the Moon instead of Mars. It's closer and the atmosphere provides shielding from radiation which Mars doesn't. Mars looks a lot friendlier than it actually is and it's only when studies like this come out that people start to remember that it's not as easily accomplished as some would like (including me, of course). <div class="Discussion_UserSignature"> <p>----- </p><p>http://mithridates.blogspot.com</p> </div>

 

[nyarlathotep]

We're most certainly not going to the surface. It has a massive gravity well, 670K+ temperatures, and a surface pressure of 9Mpa. We barely have submarines that can survive those conditions here, let alone after being exposed to launch, vacuum and reentry stresses.

 

[barrykirk]

We don't have any submarines that could survive those conditions. The temperature is the killer.

 

[mithridates]

Er...thanks. That's why I said "not the surface." <div class="Discussion_UserSignature"> <p>----- </p><p>http://mithridates.blogspot.com</p> </div>

 

[bdewoody]

New story on Space.com that proposes to use an asteroid or comet as a shield to go to other locations in the solar system. Either land on the object and mine it in transit or just use it as a shield. I suppose there several earth/mars crossing asteroids that could be used. <div class="Discussion_UserSignature"> <em><font size="2">Bob DeWoody</font></em> </div>

 

[alokmohan]

As NASA lays plans for travel to the moon and Mars, the agency is exploring propulsion systems, crew modules, and habitat structures. It has looked at the psychology of being cooped up with fellow astronauts for a years-long Mars mission, and studied how to maintain bone structure and muscle strength in microgravity. <br /><br />But a new study should force renewed attention on one of the most intractable dangers of space travel: radiation. The review, published Sept. 29 in Mars, the International Journal of Mars Science and Exploration, identified major radiation hazards that must be solved before the safe completion of a human Mars mission. Donald Rapp, an independent contractor in Pasadena, California, in study that was partly funded by NASA, pored over a number of previous NASA studies of radiation, in an effort to understand exposures to energetic protons from the sun, and the heavy ions in cosmic rays. These two forms of radiation will be the most hazardous to astronauts venturing beyond Earth. <br /><br />"What the article does is pulls together all the data I could find, from the various investigators who tried to assess what the impacts would be for a human mission to Mars," said Rapp. "When you do that, you find that it is extremely challenging. Some of the NASA design reference missions have not paid a lot of attention to radiation." <br /><br />Energetic protons are mainly produced during solar particle events, sporadic showers that usually coincide with maximum sunspot activity. More dangerous is galactic cosmic radiation (GCR), atomic nuclei produced during supernova explosions that travel at almost the speed of light. GCR arrives from all directions, and induces cancer as it hurtles through the body. On Earth, the planet's magnetic field and atmosphere combine to deter and block these particles. But shielding a spacecraft requires mass, and the mass of shielding that can practically be launched on a spaceship will only reduce GCR by 20% to 30%, says Frank C

 

[bdewoody]

I'm surprised that no one is commenting on the possibility of using an asteroid or comet as a radiation sheild on long duration interplanetary missions. The drawback I see is having to precisely launch in order to get in the vicinity of one or the other and whether it would require more fuel than a mission could carry. Plus how many such object exist that meet the requirements of being in the vicinity of the earth and mars in the same orbit? <div class="Discussion_UserSignature"> <em><font size="2">Bob DeWoody</font></em> </div>

 

[qso1]

You answered your own question. If you look at comet trajectories for example, how many match the precise velocity of a hohmann transfer orbit to mars? Non I'm aware of. How close does the mars craft have to be to the comet or asteroid to benefit from the shielding? <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>

 

[vulture2]

Radiation exposure during a single 18-month trip to Mars would be somewhere around 100 Rem from solar wind, solar flares, and cosmic rays, assuming only a typical spaecraft hull with some additional shieding for a sleeping area and solar flare shelter. This is over 20 times the nominal annual occupational exposure limit on earth, but considering the other risks of spaceflight many people would probably consider the risk perfectly acceptable.<br /><br />However to live for years in space, or to travel repeatedly between the planets, better shielding is needed. Otherwise prologed radiation exposure will cause an unacceptable incidence of cancer, most commonly leukemia. The brain is not very susceptible to cancer because nerve cells do not multiply, but heavy nucleii such as iron can kill individual neurons, which (because they do not regenerate), can eventually lead to neurocognitive deficits. <br /><br />Enough mass shielding (i.e. 30 cm of aluminum) will stop even most cosmic rays, but if we can ever develop spacecraft with the energy to carry massive amounts of shielding, we could just as easily reduce the travel time instead. Moreover, mass shielding cuts us off from direct contact with space. <br /><br />One alternative is magnetic (or possibly electrostatic) shielding. Virtually all hazardous radiation in space consists of charged particles; superconducting magnets could (in theory) generate a field that would deflect them. If we are thinking beyond a single dash to Mars, to a time when people can live for years in space, something of this sort is needed if we are not to wall ourselves off from the space we have come to explore.<br /><br />

 

[oscar1]

Couldn't we just produce a shield made out of a very dense metal, like Osmium for instance?

 

[vulture2]

On earth the weight of the shielding doesn't usually matter, so it's common to use a dense material such as lead. But shielding effectiveness is generally proportional to the total mass, and putting another kilogram in space costs about the same regardless of what it is made of, so there is no real advantage to using a denser material except that it takes up less space.<br /><br />To some degree shielding with a lower atomic weight is actually more effective than a similar weight of shielding constructed of a high atomi weight material like lead. Consequently polyethylene blocks are sometimes used on the Space Station to shield sleeping areas.

 

[oscar1]

So the issue is rather one of cost, and not of technical nature?

 

[nexium]

Scott is correct that water is effective for radiation protection, but electrolosizing water to get large amounts of hydrogen and oxygen is practical only if we have a nuclear reactor of several megawatts, but light weight, or square kilometers of solar panel.<br />By the kilogram, kerosene or other liquid rocket fuel is almost as effective as water for radiation shielding, even considering slightly larger tanks. As I see, it we shield perhaps 1% of the living space with water, 2% with fuel, 3 % with misc equipment and supplies and the rest with (not very effective) magnetic and/or electrostatic shielding. We might find an asteroid which can provide effective shielding with only minor compromise of the mission, but it will be one time, as orbits repeat, approximately, but not with respect to the constantly changing position of Earth and Mars. Using an asteroid shield effectively likely requires slowing the rotation of the asteroid to about one turn per year. The launch window for the Mars mission is only minutes wide instead of days long, if we don't use an asteroid, or so it seems to me. Neil

 

[alokmohan]

Question is how to get van allen belt in mars?Mars is non magnetic.

 

[oscar1]

I am sure we can make a plan where the first visitors/explorers are concerned. When eventually we set up shop there, we can build sub-terrain habitats and grow veg there too (in Holland tomatoes are grown in winter using overhead lighting in greenhouses already).

 

[spacester]

<font color="yellow">But shielding effectiveness is generally proportional to the total mass . . . </font><br /><br />My understanding is that this is very much wrong. We are not talking about dental x-rays here, we are talking about CME (Coronal Mass Ejection) events and CBR (Cosmic Background Radiation), which are themselves two very different animals.<br /><br />My understanding is that the effectiveness is generally proportional to the density of Hydrogen atoms in the material. It's weird & I would dearly like to have a deeper understanding, but apparently an inch thickness of water is a better shield than an inch of lead!<br /><br />Lead is of course much denser than water so on a per-pound basis it is not even a close comparison.<br /><br />The shielding question is actually surprisingly straightforward - the two most effective radiation blocking materials in the space environment, on a per-pound basis, are water and polyethylene!<br /><br />I know that flies in the face of common perception, but that's the deal: this is not a problem in search of an exotic material science solution. All we need to do is incorporate plastic water tanks in our spaceship design. <br /><br />IIRC, water is slightly better than PE at blocking solar particles while the reverse is true when blocking CBR. I might have that reversed, but the point is that between the two materials, we can get the job done.<br /><br />There are unanswered questions on exactly how each performs outside the VanAllen belts, and this is what I was referring to in my original post here: let's quit hashing over the same old data and let's get a test article out there to nail down the parameters, so that spaceship designers have the parameters they need to get the job done.<br /><br />FWIW, I did some calcs way back when and IIRC I came up with 2 inches of PE and 8 inches of water to cut the exposure down to nearly Earth surface levels. <div class="Discussion_UserSignature"> </div>

 

[drwayne]

Shielding effectiveness is a function of what you are trying to shield against.<br /><br />In general, if you are trying to shield against particle radiation (such as Alpha or Beta), you would prefer to have particles of similar mass to the particles in question. This enables a more effective transfer of energy to the matrix than heavier masses, which tend to scatter, rather than absorb the energy.<br /><br />On the other hand, in the case of radiation such as x-rays etc, then you want as much stuff, as densly packed as possible - the classic lead solution.<br /><br />One other thing you need to be aware of if that you can get a transformation of EM to particle radiation via Compton scattering - leading to electrons flying around. In hardening of electronics, these electrons are a major concern.<br /><br />Wayne <div class="Discussion_UserSignature"> <p>"1) Give no quarter; 2) Take no prisoners; 3) Sink everything."  Admiral Jackie Fisher</p> </div>

 

[vulture2]

Virtually all the hazardous radiation present in space is particulate. Electromagnetic radiation in space is biologically insignificant except for solar UV, which is easily blocked. There are secondary x-rays produced by collisions of particles (particularly cosmic rays) with the spacecraft, of course.<br /><br />Modest amounts of shielding with water or polyethylene can block most solar particles, both solar wind and CME, which are mostly hydrogen and helium nucleii. However for galactic cosmic rays (GCR) the most biologically hazardous fraction are the heavy nucleii with high linear energy transfer (HZE), more specifically the fully ionized nucleii of iron, the ash of fusion and the heaviest nucleus found in substantial amounts in GCR. Even shielding adequate for solar particles will not substantially reduce the radiation from GCR. Only about 20% of the incident radiation is GCR, but for longer missions (i.e. several years) this alone will reach unsafe levels without shielding of about 80gm/cm2 which would weigh tons.<br /><br />Unlike mass shielding, which is less effective against the HZE particles found in GCR, the effect of a magnetic field depends on the charge/mass ratio, which (except for hydrogen) is roughly constant. <br />

 

[spacester]

Nice posts, gentlemen! <br /><br /><font color="yellow">. . . the most biologically hazardous fraction are the heavy nucleii with high linear energy transfer (HZE), more specifically the fully ionized nucleii of iron, the ash of fusion and the heaviest nucleus found in substantial amounts in GCR . . . </font><br /><br />Nice description, now I have a chance of remembering it this time. Clearly, I'm rusty on this subject. <img src="/images/icons/frown.gif" /> 'The ash of fusion', that's cool prose.<br /><br />I can see now that I did not read your previous post as carefully as I should have. Ooops, <img src="/images/icons/blush.gif" /> <br /><br />80 gm/cm^2, huh? That would be mass of water per surface area? <div class="Discussion_UserSignature"> </div>

 

[gunsandrockets]

"...but for longer missions (i.e. a few years) this alone will reach unsafe levels without shielding of about 80gm/cm2 which would weigh tons."<br /><br />Shielding of 3 feet of water? Yep, plenty massive. One obvious solution is to bury the crew compartment inside a propellant tank. That would provide tons of shielding.