Radiation Shielding

[Phenix]

I would like to start the Radiation Shielding thread by relaying to some backgrounds I found intersting from this web site :

http://reat.space.qinetiq.com/Reat/wp1_tn/Reatwp1v1.1frames.html

Again, we do not want to "reinvent the wheel" as mother Nature has already provided the perfect Earth natural radiation shield.

I suggest that we should brainstorm in mimicking the Earth's protection layers at a small scale and applicable into a industrial manufacturing concept.

An example that comes to my mind : Manufacture a layered protection product with densified atomospheres volatiles (water) in between each layers.

The outmost layer would mimic the magnetosphere and Ionosphere by using retractable/deployable Ion shield pods issued from the Ion drive technology.

[Phenix]

Univ. of Washington, Rutherford Appleton Laboratory (RAL), the Universities of York and Strathclyde, and IST Lisbon are on the lead to provide mini-magnetosphere technologies :

http://www.ess.washington.edu/space/M2P2/

http://news.bbc.co.uk/2/hi/sci/tech/7706844.stm

http://www.sstd.rl.ac.uk/Research/Research.htm

[Phenix]

On Multi-layer textile-polymeric materials, here is a link to the web site :

http://www.fibtex.lodz.pl/article84.html

[jsteele235]

Recycling material already in space is certainly a good idea, considering the high cost of boosting material to orbital velocity. When it comes to the issue of shielding against radiation, I think this is too often overlooked. NASA certainly doesn't give a lot of publicity to the amount of cosmic ray exposure that astronauts experience. If you are going to provide radiation shielding, half measures can do more harm than good: It's better to have a primary cosmic ray pass through your body than be hit by a whole shower of secondary particles produced by collision with a too-thin shield. Having enough shielding to give you Earth sea level protection is more of a challenge than you might think. To estimate this, simply divide sea level atmospheric pressure (approx. 15 psi) by the density of the shielding material expressed in pounds per cubic inch. This will give a pretty good approximation of the number of inches of material required. (to convert from density in g/cc to lbs/in^3, multiply by 0.03613). This produces some surprising answers: 35 ft. of water, or 4.5 ft. of steel, or 3 ft. of lead!

Because structural metals and ceramics are abundant on the moon, I believe that a much higher priority for recycling of earth-launched materials should be given to carbon, nitrogen, and hydrogen. Assume that we were still going to be running the Shuttle system: It's not all that difficult to leave the external tank in orbit. What would be useful would be a small robotic crawler which would scrape the polyurethane foam insulation from the tank and place it in a mesh bag to be transported to support a moon base with the extracted C, H, and N. I would even suggest designing earth-launched non-reusable spacecraft to make use of such material as graphite reinforced ABS (acrylonitrile/butadiene/styrene) copolymer specifically for their recycling potential.

[moonus111]

The simplest and cheapest shield would probably be sintered regolith. This would make a ship very heavy though as it would take a large amount of mass, and add no value to the ship. It’s probably best suited for stationary structures like a L4-L5 space station, or a military ship that needs to “ram” other ships.

I like the idea of a water encased shield, or gas tanks being used. A thick layer of water and/or gas encasing the ship provides a shield and other benefits; aquaculture, heat-sink, and storage for water and air. The problem is that this shielding is just as heavy, so the tradeoff can be mitigated by using engineered shielding materials. When the need is for a lightweight ship using these materials would be expensive, but allow for speed. Typical aerospace montra… use expensive materials…

[Phenix]

The simplest and cheapest shield would probably be sintered regolith. This would make a ship very heavy though as it would take a large amount of mass, and add no value to the ship. It’s probably best suited for stationary structures like a L4-L5 space station, or a military ship that needs to “ram” other ships.

I like the idea of a water encased shield, or gas tanks being used. A thick layer of water and/or gas encasing the ship provides a shield and other benefits; aquaculture, heat-sink, and storage for water and air. The problem is that this shielding is just as heavy, so the tradeoff can be mitigated by using engineered shielding materials. When the need is for a lightweight ship using these materials would be expensive, but allow for speed. Typical aerospace montra… use expensive materials…

Moon, ok, I am not thinking of mil stuff at all. Yes, those heavy shields are for infrastructures and we will need them as soon as man will settle in space for long term jobs. Yes, this product can be build from asteroids minerals and volatiles. Again, losing one life caused by radiation is not an option at all.

[jsteele235]

That was a very interesting article referenced in the OP: very good info on radiation effects on electronics. One part that I found particularly interesting was; "In large space structures, secondary neutrons become very significant and can provide a third of the dose equivalent for certain missions." This seems to argue for materials, which 1) can slow neutrons to thermal velocities and 2) have a high thermal neutron capture cross-section. Carbon, as used in the Manhattan Project reactor, is applicable to the first of these. For the second of these gadolinium is the best-known material. It's a rare-earth element, which suggests that lunar KREEP minerals could be a source. I'm not talking about large amounts for this purpose, but about fractions of a percent of gadolinium metal or oxide added to an alloy or ceramic, respectively. Cadmium (used in nuclear reactor control rods) is another possibility.

There's just no getting around the fact that if you want to provide anywhere near the radiation protection of Earth's atmosphere, you are going to have to provide extremely thick and massive shielding. Lower atomic weight elements are going to be somewhat more effective, but the mass penalty is still going to be huge. Water is probably one of the most effective solutions for providing a given amount of protection per unit mass. For an orbital space station or habitat, I like the idea of an 'ocean on the outside'. This could be several meters deep, and covered with a transparent shell of glass or alumina (synthetic sapphire). This would allow sunlight in and allow you to grow algae to recycle CO2.

It seems clear to me that we are going to have to accept a lesser level of radiation protection than the Earth sea-level environment. If anyone has references on how various types and levels of radiation effect long-term cancer risks, please let me know. I would also like to hear from forum members about their opinions on what risk levels are acceptable: How many excess cancer deaths (compared to earth environment) per 100,000 people exposed is an acceptable level of risk? btw, I realize that this has to be balanced against the benefits of a particular mission. Please let me know your thoughts.

[Sam Fraser]

Some good links there, Phenix and great follow-up from moonus111 and jsteele235. Part of the solution lies within the human body itself:

Another line of research is the development of drugs that mimic and/or enhance the body's natural capacity to repair damage caused by radiation. Some of the drugs that are being considered are retinoids, which are vitamins with antioxidant properties, and molecules that retard cell division, giving the body time to fix damage before harmful mutations can be duplicated.

http://en.wikipedia.org/wiki/Health_threat_from_cosmic_rays#Drugs

Also this:

Medication that can protect humans against nuclear radiation has been developed by Jewish-American scientists in cooperation with a researcher and investors from Israel.....The medication works by suppressing the "suicide mechanism" of cells hit by radiation, while enabling them to recover from the radiation-induced damages that prompted them to activate the suicide mechanism in the first place.

http://www.ynetnews.com/articles/0,7340,L-3748014,00.html

Although the goal is "protection against a nuclear attack by Iran or against 'dirty bomb' attacks by terror groups", does this ability to suppress a cell's self-destruct apply to journeys beyond LEO as we envision? From what I understand, radiation from a nuclear explosion or radiological source isn't quite the same as cosmic rays and solar radiation our intrepid explorers would face.

[Sam Fraser]

Also these promising developments:

Researchers from Boston University School of Medicine (BUSM) and collaborators have discovered and analyzed several new compounds, collectively called the ''EUK-400 series,'' which could someday be used to prevent radiation-induced injuries to kidneys, lungs, skin, intestinal tract and brains of radiological terrorism victims.

http://www.eurekalert.org/pub_releases/2009-07/bumc-noa071009.php

The Department of Defense has commissioned a nine-month study from Rice University chemists and scientists in the Texas Medical Center to determine whether a new drug based on carbon nanotubes can help prevent people from dying of acute radiation injury following radiation exposure. The new study was commissioned after preliminary tests found the drug was greater than 5,000 times more effective at reducing the effects of acute radiation injury than the most effective drugs currently available.

http://www.media.rice.edu/media/NewsBot.asp?MODE=VIEW&ID=10512&SnID=1150198771 (no update on the findings as far as I can see)

If there are effective drug treatments, then maybe massive physical shielding and/or expensive and experimental electromagnetic shielding isn't required, at least not so much at first.

[Sam Fraser]

More good news on the "radiomitigation" front:

Drug mitigates toxic effects of radiation in mice
In a study published today in the Journal of Clinical Investigation, a team led by UNC Lineberger Associate Director for Translational Research, Norman Sharpless, MD, provides a first example of successful radiomitigation in mammals. The investigators found that oral treatment of mice with a drug that inhibits enzymes involved in cell division caused certain groups of bone marrow cells to temporarily stop dividing. Several decades of work have shown that cells which are not dividing are resistant to agents that damage DNA, like radiation.

http://cancer.unc.edu/news/2010/release0623.asp

[JohnHunt]

There are superconducting magnets which are 300,000 times the strength of Earth's magnetic field. I've got to believe that the radiation problem is very solvable.

http://www.lbl.gov/Science-Articles/Archive/14-tesla-magnet.html

[Rhyshaelkan]

I wonder if these could be used for large orbital structures. Even against Mass Coronal Ejections. If so though it would go a long way toward making habitats safe.

If it is a donut ring station. I could see the dynamo at the heart. And the EM shell would pop up not unlike Earth's EM field. Could even help animals orient themselves inside the structure.

Another theoretical use. Is to repel space dust. Or perhaps funnel space dust to a collection area. Allowing for "cleaning" areas of space. Just as man has learned to alter areas of the Earth's surface(sometimes for the worse). So too man could extend its hand into space.

[joertexas]

I wonder if these could be used for large orbital structures. Even against Mass Coronal Ejections. If so though it would go a long way toward making habitats safe.

If it is a donut ring station. I could see the dynamo at the heart. And the EM shell would pop up not unlike Earth's EM field. Could even help animals orient themselves inside the structure.

Another theoretical use. Is to repel space dust. Or perhaps funnel space dust to a collection area. Allowing for "cleaning" areas of space. Just as man has learned to alter areas of the Earth's surface(sometimes for the worse). So too man could extend its hand into space.

The argument I've seen about generating magnetic fields brings up the structural strain on the station. Also, I'm not certain that a powerful magnetic field is safe for people to live in.

Most proposals for space habitats use thick shields of rock to protect the habitat areas from radiation. Water storage and possibly advanced plastics and textiles could also be used to shield spacecraft and habitats.

JR

[JohnHunt]

> the structural strain on the station
> safe for people to live in

Perhaps the powerful magnets would be placed at the end of a non-metalic boom in a tetrahedral or geodesic arrangement.

Regolith shielding for a lunar, asteroidal, or LEO location might be fine. But shielding for a craft that you have to accelerate significantly (e.g. a craft to Mars) may need something of much less mass.

[RaresH]

> the structural strain on the station
> safe for people to live in

Perhaps the powerful magnets would be placed at the end of a non-metalic boom in a tetrahedral or geodesic arrangement.

Regolith shielding for a lunar, asteroidal, or LEO location might be fine. But shielding for a craft that you have to accelerate significantly (e.g. a craft to Mars) may need something of much less mass.

Thats a solution I read about as well at one point. Keeping the magnetic barriers at a distance would certainly help.

It's reasonable to assume stations will rely more on passive barriers such as regolith and maybe water reserves with active barriers to reduce the risk in case of a solar flare. Active barriers may likely be used on vessels where weight economy is important.

[moonus111]

I tend to shy away from "new tech" as much as I can. Relying on theoretical un-tested concepts can get us into trouble. A thick regolith barrier, or some leftover slag from a post process would be much easier to impliment, as there's no new concept to develop. It also has the advantage of assureance from micrometeroids, and human mishaps. Although, it has another advantage. I was running numbers on O'Neills last week and it makes them massively heavy, to massive to move. So it may reduce perturbations effects from the gravitational feild variations, and whatnot. Also, with the mass it adds you can place power sats in orbit, for added energy intake. Making it possible to build them much furthur from the sun, where the energy density drops off. If that was necessary. Think about it though, heavy sheilding can also add a huge saftey factor to a ship, and I'd feel much better knowing there's a thick 25-100 foot plate of junk below my feet, that cannot be easily "turned-off" by some idiot/sabateur. I don't think people are going to feel safe living in something that doesn't have a huge number of redundant systems. Also, overlapping reduncancies can cause problems sometimes, but that's a long subtle subject.

Put me on the FAR conservative side on this issue. Yeah I'm the sheilding nazi!

[JohnHunt]

Agreed. There is not one solution for every situation.

On the Moon or an asteroid where there is plenty of cheap regolith available, it only makes sense to pile it up for shielding.

For a craft which needs to accelerate and/or decelerate, more mass is a real negative. In that case, the choice of shielding would probably be discovered after doing a risk-benefit analysis. My guess is that, for a mission with a small crew going to Mars, using older astronauts, orienting descension fuel and rockets between the crew and the sun, and sleeping in a water chamber may be enough.

[joertexas]

Agreed. There is not one solution for every situation.

On the Moon or an asteroid where there is plenty of cheap regolith available, it only makes sense to pile it up for shielding.

For a craft which needs to accelerate and/or decelerate, more mass is a real negative. In that case, the choice of shielding would probably be discovered after doing a risk-benefit analysis. My guess is that, for a mission with a small crew going to Mars, using older astronauts, orienting descension fuel and rockets between the crew and the sun, and sleeping in a water chamber may be enough.

Most proposals for interplanetary craft include a "storm cellar" for the crew, just as you describe.

JR

[Sam Fraser]

Latest drug mitigation research findings:

Mice can survive lethal effects of high radiation doses that are usually fatal when given a double-drug therapy – even when they get the drugs 24 hours after exposure.

A day after exposure, some mice were given the oral antibiotic fluoroquinolone while some mice were given a combination of fluoroquinolone and injections of BPI. A third group had no treatment at all.

Most of the untreated mice died within 30 days. ...survival rates jumped to almost 80 per cent in the mice given the combination therapy.

The two drugs are already known to be safe in healthy and sick humans.

Don Jones at the University of Leicester, UK, finds the study "very exciting". "The therapy looks to be very effective at mitigating the effects of total body irradiation," he says.

http://www.newscientist.com/article/dn21208-lethal-radiation-doses-can-be-treated-with-drugs.html