Radiation Shielding for Interplanetary Travel and Mars Colonization
In my previous post, I wrote about the risks of space radiation in a manned mission (If you guys want to take a look at that post, here's the link). Briefly, space radiation can pose severe health risks to the crew ranging from mild effects like disorientation and cataract to more severe effects like cancer. In this post, I will focus on how to protect our astronauts from space radiation.
RADIATION PROTECTION:
The currently used methods to protect the astronauts include 1. passive shielding (storm shelters), and 2. limiting the time they spend in space. Several active methods like using Magnetic fields to deflect the incoming radiation are also proposed. But currently, the best way is passive shielding.
PASSIVE SHIELDING:
Passive shielding is no more than keeping some material/shield surrounding the astronaut's cabin so that it can take the damage and the astronauts can be safe. An ideal shield is one in which the incident radiation deposits the maximum amount of energy, thereby losing its energy before reaching the astronauts. The next important question to ask is how to choose an effective material for radiation shielding?
SHIELDING MATERIALS:
This section is going to be a bit technical. When choosing the materials for space radiation shielding, its atomic and nuclear cross-sections should be considered. Atomic cross-section refers to the number of electrons present per unit volume and electron mean excitation energy. Materials with the most electrons per unit mass and the least mean excitation energy make the best energy absorbers. The nuclear cross-section refers to the mean-free path or the minimum average distance for a nuclear reaction to occur. More nuclear reactions mean that the incoming radiation is losing more of its energy. Generally, materials with lower atomic number elements have a higher nuclear cross-section and thus make a better shield.
Using the above reasoning along with numerous experimentation it was found that materials having higher hydrogen content or lower atomic number elements are best suited for blocking the Galactic Cosmic Rays. Currently, High-Density Polyethylene (PE) (nothing but plastic!!) is the golden standard when it comes to radiation shielding for astronauts. Research is now moving towards creating new artificial polymers which can be more effective in shielding.
Figure: Polyethylene Bricks for Radiation Shielding.
ACTIVE SHIELDING:
This type of shielding involves deflecting the radiation using electrostatic or magnetic fields. These methods are currently not feasible and are in the developmental stage. For instance, the potential required for such concepts is around 10000 million volts, and the problem of spacecraft electronics getting affected also exists. For creating magnetic fields, huge magnetic coils (more than 10 km) are required to deflect the radiation. More research is currently in progress and active shielding may become a viable option in the future.
Figure: Schematic illustration for Active Shielding.
REFERENCES:
Myung-Hee Y. K., John W. Wilson, Sheila A. Thibeault, John E. Nealy, Francis F. Badavi, and Richard L. Kiefer, Performance study of Galactic Cosmic Ray Shield materials, NASA Technical Paper 3473,1994.
Schimmerling. W, Wilson. J.W., Nealy. J.E., Thibeault. S.A , Cucinotta F.A. , Shinn J.L., et al., Shielding against Galactic Cosmic Rays, Advanced Space Research, Vol.17, 1996.
Wilson. J. W., Miller. J, Konradi. A, Cucinotta. F. A, Shielding strategies for human space exploration, NASA Conference Publication 3360.
Cucinotta F. A., Myung-Hee Y. Kim, and Lei Ren, Evaluating shielding effectiveness for reducing space radiation cancer risks, Journal of Radiation measurements, 2006.