Difference between revisions of "Team:Stanford-Brown/SB16 BioMembrane UV"

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<div class="col-sm-7 pagetext-L"><div class="text">The high energy content of space radiation poses a severe threat to life, technology, and synthetic materials alike in an extraterrestrial context. Energized subatomic particles generated from nuclear events carry over large distances in space, and are capable of tearing through organic materials and altering molecular bonds. On Earth, the vast majority of space radiation is deflected by the magnetosphere. Much of the radiation that passes through Earth’s magnetic field is filtered out by the atmosphere, allowing only UV, visible light, and some infrared wavelengths to reach the surface. However, balloons flown in Earth’s stratosphere are offered limited UV protection due to thinning of the atmosphere with increasing altitude. Extended UV exposure can disrupt the molecular interactions within thin membranes, tearing micropores that decrease the material’s structural integrity and increase its permeability. Chief Scientist of World View Enterprises Alan Stern stated that the materials used in his near-space exploration vessels cannot be reused due to the radiation damage they sustain during flight. Representatives of other major ballooning projects such as Google X’s Project Loon and the Stanford Space Initiative’s Balloon team expressed to our team members that radiation exposure was the most significant factor in limiting the lifespans of their balloons.
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<div class="col-sm-7 pagetext-L"><div class="text">The high energy content of space radiation poses a severe threat to life, technology, and synthetic materials alike in an extraterrestrial context. Energized subatomic particles generated from nuclear events carry over large distances in space, and are capable of tearing through organic materials and altering molecular bonds. On Earth, the vast majority of space radiation is deflected by the magnetosphere. Much of the radiation that passes through Earth’s magnetic field is filtered out by the atmosphere, allowing only UV, visible light, and some infrared wavelengths to reach the surface. However, balloons flown in Earth’s stratosphere are offered limited UV protection due to thinning of the atmosphere with increasing altitude. Extended UV exposure can disrupt the molecular interactions within thin membranes, tearing micropores that decrease the material’s structural integrity and increase its permeability. </div>
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As our bioballoon is intended for planetary searching applications, it requires substantial radiation resistance capabilities. In space, particle radiation passes through membranes and damages DNA, creating significant structural weakening, particularly in biological materials. The sun constantly releases solar particles in addition to larger flares, and our balloon must be capable of physically shielding itself from this low-energy but endless source of radiation. Additionally, a more energetic type of radiation from galactic cosmic rays (GCRs) is capable of knocking apart atoms in materials upon contact, creating structural damage on the atomic and subatomic levels. [1] These particles are easily capable of wearing down our balloon membrane over time, and would drastically decrease its lifespan without adequate radiation protection. The two best ways of shielding a material from particle radiation are increasing the sheer volume of materials used to protect a structure, or use a similarly sized particle--such as hydrogen--to deflect the radiation. Unfortunately, we had neither the means nor capability to design a hydrogen-based GCR radiation shield over the summer, so we decided to create a viable means of protecting our balloon from UV radiation in light of its potential applications on Earth as a biodegradable weather balloon.</div>
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<div class="col-sm-12 pagetext"> Chief Scientist of World View Enterprises Alan Stern stated that the materials used in his near-space exploration vessels cannot be reused due to the radiation damage they sustain during flight. Representatives of other major ballooning projects such as Google X’s Project Loon and the Stanford Space Initiative’s Balloon team expressed to our team members that radiation exposure was the most significant factor in limiting the lifespans of their balloons.
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Revision as of 02:14, 17 October 2016


Stanford-Brown 2016

Why radiation resistance?

The high energy content of space radiation poses a severe threat to life, technology, and synthetic materials alike in an extraterrestrial context. Energized subatomic particles generated from nuclear events carry over large distances in space, and are capable of tearing through organic materials and altering molecular bonds. On Earth, the vast majority of space radiation is deflected by the magnetosphere. Much of the radiation that passes through Earth’s magnetic field is filtered out by the atmosphere, allowing only UV, visible light, and some infrared wavelengths to reach the surface. However, balloons flown in Earth’s stratosphere are offered limited UV protection due to thinning of the atmosphere with increasing altitude. Extended UV exposure can disrupt the molecular interactions within thin membranes, tearing micropores that decrease the material’s structural integrity and increase its permeability.
Chief Scientist of World View Enterprises Alan Stern stated that the materials used in his near-space exploration vessels cannot be reused due to the radiation damage they sustain during flight. Representatives of other major ballooning projects such as Google X’s Project Loon and the Stanford Space Initiative’s Balloon team expressed to our team members that radiation exposure was the most significant factor in limiting the lifespans of their balloons.
On Earth, the main source of concern for radiation damage is ultraviolet radiation (UVR). These wavelengths are between 290 and 400 nm when they hit the Earth’s surface, and do more damage the shorter they get. UV wavelengths between 320 and 400 nm are called UV-A, and are the culprits behind sunburns and cataract formation. UV-A radiation creates indirect DNA damage through the generation of reactive oxygen species (ROS), forming strand breaks in DNA and DNA-protein crosslinks. [2] Shorter wavelengths from 290 to 320 nm are called UV-B wavelengths. UV-B is absorbed directly into DNA and causes damage to DNA at the molecular level. [3] Excessive UV-B exposure can induce significant DNA mutation and cell death, and our bioballoon will be exposed to dangerous amounts of radiation due to its high elevation during flight. Ideally, our balloon coating would have included an interweaving of zinc oxide, a white pigment that excels at blocking and reflecting UV-A and UV-B rays. [4] Zinc oxide is used in many commercial sunscreens, as a solution with as low as 25% zinc oxide content results in protection of at least SPF 20. [5] However, we wanted to produce our UV protector entirely biologically rather than attempting to incorporate an inorganic compound into our membrane. As such, we decided to focus on creating a method of UV protection for our balloon that utilises a melanin coating attached to the balloon’s outer membrane.

References
1. How to Protect Astronauts from Space Radiation on Mars. (2016). NASA. Retrieved 9 October 2016, from http://www.nasa.gov/feature/goddard/real-martians-how-to-protect-astronauts-from-space-radiation-on-mars
2. Brenner, M. & Hearing, V. (2007). The Protective Role of Melanin Against UV Damage in Human Skin†. Photochemistry And Photobiology, 84(3), 539-549. http://dx.doi.org/10.1111/j.1751-1097.2007.00226.x
3. Ultraviolet Radiation: How It Affects Life on Earth : Feature Articles. (2016). Earthobservatory.nasa.gov. Retrieved 9 July 2016, from http://earthobservatory.nasa.gov/Features/UVB/
4. Soni, R. & Toetia, M. (2016). Impact of Zinc Oxide on the UV Absorbance and Mechanical Properties of UV cured films. Presentation, Department of Chemistry, C.C.S. University of Meerut.
5. ZINC OXIDE | ZnO - PubChem. (2016). Pubchem.ncbi.nlm.nih.gov. Retrieved 9 July 2016, from https://pubchem.ncbi.nlm.nih.gov/compound/zinc_oxide#section=Therapeutic-Uses

Melanin-based protection

Melanin is the primary source of naturally-occurring UV protection for human skin. Darker skin pigmentation resulting from melanin production functions as a UV absorbent, and melanin when used as a sunscreen has been shown to absorb between 50-75% of UVR. [1] Two main types of melanin exist: eumelanin and pheomelanin, with eumelanin being darker and browner in colour and more effective at photoprotection. After significant UV-A absorbance, melanin tends to produce ROS and create single-strand DNA breaks, with pheomelanin being significantly more susceptible to photodegradation than eumelanin. Thus, brown eumelanin was chosen as a good candidate for our balloon’s UV protection.

References
1. Brenner, M. & Hearing, V. (2007). The Protective Role of Melanin Against UV Damage in Human Skin†. Photochemistry And Photobiology, 84(3), 539-549. http://dx.doi.org/10.1111/j.1751-1097.2007.00226.x
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