The concept of utilizing mined sections of asteroids as shielding material for spacecraft is an innovative approach to addressing the critical challenges of radiation exposure in deep space missions. This analysis explores the feasibility, materials, and methods involved in employing asteroid-derived materials for spacecraft shielding, emphasizing the potential benefits and challenges associated with this strategy.
Introduction
Spacecraft operating beyond Low Earth Orbit (LEO) face significant radiation hazards from cosmic rays and solar flares. Current shielding methods, predominantly using traditional materials like aluminum and titanium alloys, are costly and impractical for long-duration missions. The idea of mining asteroids for materials that can serve as effective radiation shields presents a promising alternative, particularly as advancements in space mining technology progress.
Understanding Radiation Risks
One measure of radiation is the Sievert (Sv). One Sievert is approximately equivalent to 10,000 typical chest X-rays. One millisievert (mSv) is one-thousandth of a Sievert and one microsievert (µSv) is one-millionth of a Sv. Getting 1 Sv (1000 mSv) of radiation in a short time puts you at significant risk for radiation sickness, cancer and death from damage to organs. A radiation dose of approximately 5 Sv over a short time is typically always fatal to humans.
Biological Differences in Radiation Effects
In the year 2024, established scientific truths about biology may be ignored due to ideological beliefs or psychological mechanisms that prioritize personal or collective identity over factual evidence[39][40]. Case in point, NASA has proposed a maximum career-long limit of 600 mSv (0.600 Sv) for the space radiation astronauts can receive.[24] Previously, exposure limits varied by age and gender; for instance, a 55-year-old male astronaut had a limit of 400 mSv, while a 35-year-old female astronaut was limited to 120 mSv. The new uniform limit of 600 mSv applies to all astronauts, regardless of gender or age, thus simplifying the standards and allowing for “greater inclusivity in mission assignments” and more cancer. This shift is rooted in a “commitment to equity” but the biological reality is not one of equity.
- Women generally have a higher percentage of radiosensitive tissue in their bodies, for example, breast tissue. Studies indicate that the risk of developing cancer from radiation exposure is significantly higher for women than for men receiving the same dose of radiation.[26]
- Studies in animals have furthermore clearly shown that IR exposure affects males and females differently.[27][28][29][30][31][32][33][34][35]
- The female reproductive system, including ovaries, is more sensitive to radiation damage than male reproductive organs. The ovaries are particularly vulnerable to ionizing radiation. Studies indicate that the lethal dose (LD50) for human oocytes is estimated to be below 2 Gy. This means that exposure to doses around this level can significantly impact ovarian function, potentially leading to infertility or premature ovarian failure. The effective sterilizing doses vary with age; for instance, younger women have a higher tolerance to radiation compared to older women, who may experience sterility at lower doses.[36][37][38]
Annual Radiation Dose on Earth
According to the US EPA[21] which in its February 22, 2024 update cites sources hiding behind pay walls[22], like the 2007 update from the ICRP [23], which give the average yearly dose of radiation in the body on the surface of the earth as being 0.29 mSv. Dividing this by 365 days/year, the average daily dose is 0.00079 mSv (0.79 µSv). This varies depending on location. As you move to higher elevations above sea level, galactic cosmic radiation (more about that later) increases and in some locations natural radiation in the soil changes daily dose. In low Earth orbit, for astronauts in the International Space Station (ISS), which is about 250 miles up, the estimated radiation dose is about 150 mSv per year, which is equivalent to 0.150 Sv annually.
GCR Daily Radiation Dose Calculations, UnShielded
The challenges for space radiation include passage through the Van Allen radiation belts, radiation from our sun, radiation from galactic cosmic rays (GCR) and potentially events such as gamma ray bursts.
Let’s ignore everything but CGR and calculate the radiation astronauts would be expected to get beyond low earth orbit from sources outside of our solar system.
For this calculation, will will use a male astronaut with a mass of 68 kg (149.95 lb on earth) a surface area of 1.8 m2 () and an average density of 1,000 kg/. In a ship shielded by aluminum hull of 3 millimeters thick, he would face a Galactic Cosmic Ray (GCR) flux of 3 particles/cm²/sec with average energies of 4 GeV, which comes from 7 year ISS data from the Alpha Magnetic Spectrometer (AMS-02)[41], and we will use a quality factor of 11.3. In Sv, what is the total radiation dose for the astronaut per day?
This graph is where I get the average energy of galactic cosmic rays as 4 GeV. Obviously, this is more the most common energy seen, which is different from the overall average since the scale surpasses 1TeV in this graph. I’m ignoring the Dark Matter Model in this case. I just wanted the average energy for Cosmic Ray Collisions, so I used the peak value, which, if you count the tick marks, is 4 GeV.
Formula
The total energy deposited can be calculated by multiplying the flux of particles by the average energy per particle, the area of the astronaut, and the time interval. If is the flux in particles/cm²/second, A is the surface area in square centimeters cm², and is the time in seconds, we have this formula:
1 eV (electronvolt) = 1.602176634×10-19 joules, 4 GeV = 4 × 109 eV
4 GeV = 4×109eV × (1.602176634×10-19J/eV) = 6.409 × 10⁻10J
E = ( ( 3 particles cm2/sec) x 6.409×10−10 J x particle x ) / 68 kg ) x 11.3 =
Remember to follow the order of operations (PEMDAS/BODMAS: Parentheses/Brackets, Exponents/Orders, Multiplication and Division (left to right), Addition and Subtraction (left to right)), so first calculate the numerator inside the parentheses.
/ 68 kg = 0.050895= 5.0895x10-7 J/kg/sec Now multiple by 11.3
5.0895x10-7 J/kg/sec x 11.3 = 57.51135x10-7
Certain events like solar flares from our sun increase the radiation dose[17][19][20].
The Quality Factor for Protons, is it 1? 4? 20? 10? -20?
There is a difference between the amount of radiation that hits and the damage it does. The difference depends on several things. Cosmic Rays are particles, mostly protons, but not entirely. To determine the biological damage they do, scientists have a conversion factor based on the type of radiation and the observed amount of damage done or absorption in tissue. In the context of radiation physics, the Q factor (also known as the quality factor) is used to convert absorbed dose to dose equivalent, taking into account the biological effectiveness of different types of radiation. This factor is always positive and typically ranges from 1 to 20 for different types of radiation. A negative quality factor would make no sense, but what about 0? It can’t be zero either. A physical particle can’t move through a physical body without phsyical effects. Thus, the least it can be is 1, same as x-rays, but it is higher, because these particles bump others and cause cascades of ionization when they do.
For GCRs, which consist of high-energy protons (85%), alpha particles (14%), and other high-energy nuclei (HZE ions), the Q factor is actually higher than for low-energy radiation. This is because high-energy particles can cause more severe biological damage due to their increased ionizing power.
- Photons (e.g., X-rays, gamma rays): Q = 1, Alpha particles: Q = 20, Neutrons: Q can vary, often around 10, but it depends on energy. The quality factor (Q) for protons is typically considered to be 10. This value reflects the relative biological effectiveness of protons compared to low-LET (linear energy transfer) radiation like X-rays and gamma rays, which have a quality factor of 1.
So, for GCR, the quality factor should, according to the above be 20*14%+10*85% = 11.3
This is what we used and why.
Materials from Asteroids
Asteroids, particularly C-type (carbonaceous) asteroids, are rich in various elements that can be utilized for shielding. Notably, these asteroids contain clays that are rich in hydrogen, which is effective at attenuating high-energy protons and cosmic rays. Research indicates that clays extracted from asteroids can outperform aluminum in radiation shielding by up to 10% due to their hydrogen content[2].
Additionally, asteroids are known to contain significant amounts of water, carbon-rich compounds, and metals such as iron and nickel, which could also contribute to the structural integrity and effectiveness of shielding materials[4][5].
Extraction and Processing Techniques
The extraction of materials from asteroids poses unique challenges due to the zero-gravity environment. Current technologies for mining in space are still in development, with no operational machines designed for zero-gravity mining yet available. However, potential methods for material extraction include:
– Magnetic Separation: Since many asteroid materials are non-magnetic, they could be separated from other materials using powerful magnets[2].
– Robotic Mining Systems: Autonomous robotic systems could be deployed to mine and process materials on-site, minimizing the need for human presence and reducing risks associated with radiation exposure during extraction[5].
– In-Situ Resource Utilization (ISRU): This approach involves using the materials found on asteroids directly in space, reducing the need to transport heavy shielding materials from Earth[3].
Towing Repair Mass
When propulsion technologies allow, large asteroid fragments could be brought in tow, making a wagon train where lost or damaged ship shielding mass could be repaired. This would not arouse suspicion of possible hostile alien forces, since this configuration is often seen after the break up of a large mass.
Advantages of Asteroid Shielding
1. Cost-Effectiveness: Utilizing materials found in space could significantly reduce the costs associated with launching heavy shielding from Earth. With launch costs estimated at around $30,000 per kilogram to LEO, sourcing materials in situ could provide substantial economic benefits[4].
2. Enhanced Protection: The hydrogen-rich clays from asteroids not only offer better radiation protection but also contribute to the overall structural integrity of spacecraft, potentially allowing for lighter designs without compromising safety[2].
3. Sustainability: Mining asteroids for resources can alleviate some of the environmental impacts associated with terrestrial mining, as it reduces the extraction pressure on Earth’s resources and minimizes ecological damage[3].
Radiation Shielding Requirements
Cosmic Rays and High-Energy Particles: Spacecraft traveling through interstellar space are exposed to cosmic rays, which consist of high-energy protons and heavier nuclei. These particles can penetrate conventional materials and pose significant health risks to astronauts. Effective shielding against cosmic rays typically requires materials that can attenuate high-energy radiation, with hydrogen-rich materials being particularly effective due to their ability to slow down and scatter protons.
Material Thickness: Estimates for the thickness of shielding necessary to protect against cosmic radiation vary. Some studies suggest that a thickness of one to two meters of hydrogen-rich materials or equivalent shielding (such as lead or polyethylene composites) may be required to provide adequate protection over long durations in space. More conservatively, two (2) meters of lead equivalent is a starting point from various research. However, this thickness could increase depending on the mission duration and the specific radiation environment encountered.
3mm Aluminum Shields
The effectiveness of 3mm aluminum shields against Galactic Cosmic Rays (GCR), which primarily consist of protons and alpha particles, is limited. GCR are high-energy particles, often with energies reaching millions to billions of electron volts, making them challenging to shield effectively.
1. Energy Levels: GCR can penetrate significant amounts of material. For instance, a proton or alpha particle in the upper energy range can pass through more than a meter of aluminum without being stopped, indicating that 3mm of aluminum would be insufficient to stop these particles effectively[13][14].
2. Material Properties: While aluminum is a common shielding material, it is not the most effective against GCR. Materials rich in hydrogen, such as polyethylene or water, are more effective because they produce less secondary radiation when impacted by high-energy particles. This is crucial since secondary radiation can contribute to overall radiation exposure[13][15].
3. Monte Carlo Simulations: Studies using Monte Carlo simulations have shown that thicker shields are required to significantly attenuate GCR. For example, while 0.32 cm (approximately 3.2mm) of aluminum can stop protons with energies up to about 10 MeV, this is far below the energy levels typical of GCR, which necessitate much thicker barriers for effective protection[11]1[4].
In summary, a 3mm aluminum shield would provide minimal protection against Galactic Cosmic Rays, particularly at the higher energy levels typical of these particles. More substantial and hydrogen-rich materials would be required for effective shielding in space environments.
Two (2) Meters of Lead Shields
While 2 meters of lead will effectively stop nearly all alpha particles, it will also significantly reduce the intensity of protons, especially at lower energies. However, for high-energy protons, some may still penetrate, albeit at a greatly reduced flux. The exact fraction of cosmic rays stopped would depend on their energy distribution and the specific interactions with the lead material. Overall, lead shielding is a practical choice for mitigating exposure to GCRs in space environments.
C-Type Asteroid Shields
Given their relative densities, a shield thickness of approximately 13.34 meters of C-type asteroid material would be required to match the protective capability of 2 meters of lead.
| Material | Density (g/cm³) | Stopping Power for Alpha Particles (MeV/cm) | Stopping Power for Protons (MeV/cm) | Energy Blocked by 2m (MeV) |
|---|---|---|---|---|
| C-type Asteroid | 1.7 | 0.1 | 0.02 | Alpha: 200, Protons: 40 |
| Aluminum | 2.7 | 0.2 | 0.03 | Alpha: 400, Protons: 60 |
| Lead | 11.3 | 0.5 | 0.1 | Alpha: 1000, Protons: 200 |
16 Meter (48 ft) Thick Asteroid Shields
Galactic Cosmic Rays (GCRs)
A shield of 16 meters thickness would provide significant attenuation of GCRs. The effectiveness of shielding against GCRs is generally quantified by the concept of “stopping power,” which indicates how much energy is lost by the particles as they pass through a material. C-type asteroids, composed mainly of carbonaceous materials, can absorb a substantial amount of radiation due to their density and thickness. Studies suggest that materials with high hydrogen content, such as water or polyethylene, are particularly effective against GCRs, but a thick C-type shield would also offer considerable protection by scattering and absorbing the particles.
Van Allen Belts
The Van Allen radiation belts are zones of charged particles trapped by Earth’s magnetic field. While these belts are a concern for spacecraft in low Earth orbit, a 16-meter thick shield would provide substantial protection against the radiation emitted from these belts. The thickness would significantly reduce the exposure to harmful radiation, making it safer for occupants inside.
Coronal Mass Ejections (CMEs)
CMEs are significant bursts of solar wind and magnetic fields rising above the solar corona or being released into space. The charged particles from CMEs can be harmful to both astronauts and electronic equipment. A thick asteroid shield would help mitigate the effects of these solar particle events by absorbing and deflecting a portion of the incoming particles.
Gamma Ray Burst Within Milky Way
The Milky Way galaxy is approximately 100,000 light-years across. This measurement refers to the diameter of the galaxy’s disk, which is about 1,000 light-years thick. Additionally, recent studies suggest that the Milky Way’s dark matter halo may extend its effective size to nearly 2 million light-years across, significantly larger than the luminous part of the galaxy itself. As previously noted, a typical GRB can release energy on the order of joules to ergs (approximately 1044 joules). For a GRB within the Milky Way, let’s consider a distance of 1,000 light-years (a reasonable estimate for a nearby GRB). At that distance, a GRB would reach us with an intensity of . Gamma rays from this event would be effectively reduced to near zero after passing through 16 meters of rock.
Gamma Ray Burst at 650Ly
A 16-meter thick asteroid could potentially shield against a gamma-ray burst (GRB) originating 650 light-years away. Gamma-ray bursts are among the most powerful explosions in the universe, releasing immense energy that can have devastating effects on any nearby celestial bodies. The intensity of a GRB diminishes with distance due to the inverse-square law, meaning that as the distance from the source increases, the energy received per unit area decreases significantly. At 650ly, a burst with an energy of joules would be attenuated down to .
Gamma rays interact with matter primarily through photoelectric absorption, Compton scattering, and pair production. The attenuation length () for gamma rays in rock (which is a common composition for asteroids) is typically around 10 cm (0.1 m) for high-energy gamma rays. Gamma rays would be effectively reduced to near zero after passing through 16 meters of rock.
Challenges and Considerations
Despite the potential advantages, several challenges must be addressed:
– Technological Development: The lack of current mining technology for zero-gravity environments necessitates significant investment in research and development to create effective mining and processing systems[2][4].
– Logistical Complexity: Transporting mined materials back to spacecraft or habitats poses logistical challenges, including the need for efficient transportation systems in space[3].
– Regulatory and Environmental Concerns: As with any mining operation, space mining will require careful consideration of environmental impacts, including the potential for space debris and the management of waste materials generated during extraction[3].
Conclusion
The concept of using mined sections of asteroids as shielding material for spacecraft presents a groundbreaking opportunity to enhance astronaut safety during deep space missions. With the right technological advancements and strategic planning, asteroid-derived materials could revolutionize spacecraft design and significantly mitigate the risks associated with space radiation. Yes, future space ships may look suspiciously like asteroids that can change course on their own. You may recall the claim that Oumuamua changed course as it passed through our solar system. NASA, using observations from the Hubble Space Telescope and ground-based observatories, concluded that ‘Oumuamua accelerated and changed its course as it passed through the inner solar system in 2017.[42] Scientists attribute this change in trajectory to jets of gaseous material expelled from the object’s surface, similar to the off-gassing that affects the motion of many comets in our solar system.[43] A one time course correction written off a comet off-gassing does not pass the smell test. Rather, it stands to reason that asteroid material as ship protection would be a logical solution throughout the cosmos. Continued research and investment in asteroid mining technology will be crucial to realizing this vision and ensuring the sustainability of future space exploration efforts.
Read More
[1] https://www.reddit.com/r/SpaceXLounge/comments/189d05l/how_viable_does_asteroid_mining_become_once/
[2] https://www.newscientist.com/article/2124676-asteroid-clay-is-a-better-space-radiation-shield-than-aluminium/
[3] https://undark.org/2024/05/08/asteroid-mining-space-metals/
[4] https://mipse.umich.edu/files/Goebel_presentation.pdf
[5] https://2016.spaceappschallenge.org/challenges/solar-system/asteroid-mining/projects/astro-shield-for-earth-mars-cycler
[6] https://www.sciencedirect.com/science/article/abs/pii/S0146645303000241
[7] https://pubmed.ncbi.nlm.nih.gov/26432594/
[8] https://en.wikipedia.org/wiki/Health_threat_from_cosmic_rays
[9] https://www.radiationanswers.org/radiation-and-me/effects-of-radiation.html
[10] https://www.epa.gov/radiation/radiation-terms-and-units
[11] https://www.sciencedirect.com/science/article/abs/pii/S2214552422000141
[12] https://www.reddit.com/r/askscience/comments/24604a/can_someone_explain_cosmic_radiation_and_why_its/
[13] https://forum.nasaspaceflight.com/index.php?topic=30480.240
[14] https://ntrs.nasa.gov/api/citations/20130001610/downloads/20130001610.pdf
[15] https://marspedia.org/Radiation_shielding
[16] https://www.radiologyinfo.org/en/info/safety-xray
[17] https://www.health.harvard.edu/cancer/radiation-risk-from-medical-imaging
[18] https://www.moffitt.org/diagnostic-services/radiology-diagnostic-imaging-and-interventional-radiology/safety-in-radiology/x-ray-safety/
[19] https://www.cdc.gov/radiation-emergencies/php/ph-professionals/measuring-radiation.html
[20] https://www.nuffieldhealth.com/article/radiation-exposure-from-medical-scans
[21] https://www.epa.gov/radiation/radiation-sources-and-doses
[22] https://ncrponline.org/publications/reports/ncrp-report-160-2/
[23] https://www.icrp.org/docs/ICRP_Publication_103-Annals_of_the_ICRP_37(2-4)-Free_extract.pdf
[24] https://www.nationalacademies.org/news/2021/06/nasa-should-update-astronaut-radiation-exposure-limits-improve-communication-of-cancer-risks
[25] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6509159/
[26] https://www.iaea.org/resources/rpop/health-professionals/radiology/mammography/screening
[27] https://pubmed.ncbi.nlm.nih.gov/15063138
[28] https://pubmed.ncbi.nlm.nih.gov/15249225
[29] https://pubmed.ncbi.nlm.nih.gov/15555557
[30] https://pubmed.ncbi.nlm.nih.gov/16019925
[31] https://pubmed.ncbi.nlm.nih.gov/16272168
[32] https://pubmed.ncbi.nlm.nih.gov/18823940
[33] https://pubmed.ncbi.nlm.nih.gov/18508093
[34] https://pubmed.ncbi.nlm.nih.gov/20478395
[35] https://pubmed.ncbi.nlm.nih.gov/27375442
[36] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1519954/
[37] https://www.aaem.pl/Effect-of-ionizing-radiation-on-the-female-reproductive-system,112837,0,2.html
[38] https://www.aaem.pl/pdf-112837-47014?filename=Effect+of+ionizing.pdf
[39] https://en.wikipedia.org/wiki/Denialism
[40] https://cmm.ucsd.edu/research/labs/varki/denial/index.html
[41] https://pdf.sciencedirectassets.com/271542/1-s2.0-S0370157321X0004X/1-s2.0-S0370157320303434/main.pdf
[42] https://www.autoevolution.com/news/oumuamua-interstellar-object-accelerated-and-changed-course-in-our-solar-system-126694.html
[43] https://www.space.com/oumuamua-discovery-solar-system-implications
