- 2834 - COSMIC RAYS - The Risks of Space Travel. The scariest menace for space travelers are Cosmic Rays. They are not “rays” at all. They are charged particles that are everywhere in space hurtling at near light speed. Most are positive ions of hydrogen nuclei ( a proton, H+1 ) but some are the nuclei of the heavier elements, even iron ( Fe +26 ).
--------------------------- 2834 - COSMIC RAYS - The Risks of Space Travel.
- Cosmic Rays represent an irreducible risk for space travelers and could likely prevent man’s journey to Mars altogether.
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- Cosmic Rays are created in the cosmos when supernova explosions slam into interstellar gas. Electrons are stripped from atoms and the positive nuclei get accelerated by intergalactic and galactic magnetic fields.
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- The Milky Way has a magnetic field strength of 10^-10 Tesla. The radius of the Milky Way is 5 * 10^21 meters. The charge on a proton, a hydrogen nucleus, is 1.6 * 10^-19 Coulombs.
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- The momentum of a proton traveling along this galactic magnetic field is equal to , = (Electron Charge of a Proton ) * ( Magnetic Field Density ) * ( Radius of Milky Way ) = (1.6 *10^-19 ) * ( 10^-10 ) * (5*10^21) = 8*10^-8 kilogram*meters/second.
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- This is the momentum of a proton which has a mass of 1.67*10^-27 kilograms. Momentum is mass * velocity. If we divide by the mass we get a velocity that is much greater than the speed of light. When you approach the speed of light you must us equations of relativity, not simple algebra.
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- So, we leave the answer in Momentum. For comparison the electron in the old fashion TV cathode “ray” tube has a momentum of 10^-22 kg*m/s. A proton in our best particle accelerator has a momentum of 6*10^-16 kg*m/s, which is 10,000 times more momentum. Compare that with the Cosmic Ray, 8*10^-8 kg*m/s, is still another 100,000,000 times greater momentum.
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- Why aren’t Cosmic Rays harmful to us on Earth?
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- Two reasons: Earth’s magnetic field and Earth’s atmosphere. Earth’s magnetic field provides some shielding because Cosmic Rays are charged particles and they will be flung at right angles to the magnetic field lines that they cross. So, this may change the trajectory of the particle but it is the depth of the atmosphere that really saves us.
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- Every square centimeter of Earth’s surface has a vertical column of 1000 grams of air pressing down from above. About 70 grams of atmospheric gas is needed for the incoming Cosmic Rays to hit an atomic nucleus and explode into smaller, elementary particles. The collision creates a shower of shrapnel that the rest of the atmosphere continues to absorb with repeated atomic collisions. High energy Gamma Rays and Pi Mesons ( Pions ) are created amongst the shrapnel.
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- Each Gamma Ray that propagates produces an electron and positron pair. These are matter and anti-matter and the two particles will annihilate each other creating another Gamma Ray of less energy. This cycle continues until the Gamma Ray becomes too weak to produce electron/positron pairs.
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- At the same time Pions are decaying into Mu Mesons ( Muons ) which reach the surface and penetrate the ground. Muons pass though our bodies producing ions, braking chemical bonds but not seriously enough to cause bodily harm.
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- Cosmic radiation reaching the surface of the earth amounts to 0.03 rems per year. This is equivalent to 2 chest X-rays each year.
- Space travelers above the Earth’s atmosphere experience intense cosmic radiation , 5,000 ions pass through their bodies every second. Every trajectory through their body would have a trail of broken chemical bonds.
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- The same shrapnel shower that occurred in the atmosphere would occur inside their much denser human flesh and organs. Heavier nuclei, such as a iron nucleus , would do 675 times more damage that a proton ion. In one year 1/3 of an astronaut’s body DNA would be cut by cosmic radiation.
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- Natural biological repair mechanisms would not keep up with this damage level. A Mar’s astronaut would receive 80 rems a year. By comparison, the legal limit for a nuclear power plant worker is 5 rems per year. The Mar’s astronaut is getting 16 times more radiation.
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Below is a table of relative comparisons of the amount of cosmic radiation received at different elevations and different distances into outer space:
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------------------- Sea level -------------------------------------------- 0.03 rems per year
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------------------- 5,000 feet ------------ ------------------------------- 0.05
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------------------- 10,000 feet ---------- ------------------------------- 0.10
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------------------- 40,000 feet in an airplane ----------------------- 2.80
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------------------- Low Earth orbit in the Shuttle ----------------- 10 .
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------------------- Van Allen Belt surrounding Earth -------- 1,500 .
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------------------- Moon’s surface --------------------------------- 10 .
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------------------- Interplanetary Space --------------------------- 20 .
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------------------- Interstellar Space -------------------------------- 50.
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- You can see that once we get outside the Earth’s atmosphere we need shielding to protect astronauts from cosmic radiation. The Shuttle, International Space Station, and Moon astronauts get the equivalent of 666 X-rays a year.
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- Even flying on airplanes 60 days out of the year would equate to 30 X-rays. Fortunately for the Shuttle and Moon astronauts they have the Earth and the Moon to hide behind. That protects them from 33% of the Rays. The Earth’s Magnetic field provides another 33% protection.
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- The Van Allen belts are the worst. They are 2,000 and 9,000 miles up. The lower belt are protons and the upper belt electrons that are bouncing back and forth between the poles trapped by the Earth’s magnetic field. The poles are magnetic mirrors ( auroras ) to these charged particles. The radiation is 1,500 rems/year, equivalent to 100,000 X-rays. Ouch!
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- Moon astronauts were only exposed for a few days and they saw flashes of light in their retinas and in their brains as Cosmic Rays came through. Today many have developed cataracts as a result of this radiation damage. But, Mar’s astronauts would be exposed for over 400 days.
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- Space Travelers need shielding If we took along some atmosphere we would need 500 grams of air per cm^2. Or, 5 vertical meters of water. The problem is the shield would weigh 500 tons. The space shuttle can only carry 30 tons.
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- Using a material shield seems impractical. The best we have found so far is polyethylene plastic which is good at absorbing Cosmic Rays because it is rich in hydrogen. It is also lighter than aluminum and 10 times stronger, and , being used on the International Space Station.
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- How about using a magnetic shield? Positive ions would be hurled at right angles to the lines of force in a magnetic field shield. But, the strength of the magnet would have to be on the order of 600,000 the strength of the magnetic field on Earth. The electromagnet designed to do this would weigh 9 tons.
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- Magnetic fields provide little magnetic shielding near their magnetic poles. Therefore, the living quarters of the spacecraft would need to be a donut shape and the astronauts would live in a constant 20 Teslas. We do not know what long term exposure to 20 Teslas magnetic field would do to body chemistry.
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- Well if magnets won’t work how about using electrostatics? Simply charge up the space ship with a positive charge of 2,000,000,000 volts that would repel Cosmic Ray protons that approached the ship. This would work, except that space is not empty and there are free negative electrons out there along with positive Cosmic Rays.
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- The negative electrons would be accelerated by the electrostatic field and would behave just like Cosmic Rays having as much energy as protons. In addition, accelerating electrons would produce Gamma Rays. In short, the electrostatic solution would defeat the purpose trying to solve the original problem.
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- An obvious answer to limit astronaut’s exposure is to make the trip in a shorter time. Faster rockets may be a partial answer. Once on Mars the atmosphere is only 10 grams per cm^2. Remember, we need 70 grams to stop a Cosmic Ray. Therefore living quarters on Mars would have to be underground using layers of soil to shield the astronauts. And , they would have to limit their exposure time working on the Martian surface.
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- All this says we do not yet have an answer to Cosmic Rays. This alone could prevent humans from making the trip to Mars. There are many problems to solve. In the meantime robots like Rover and Sojourner and Spirit and Opportunity and Curiosity are sent to do the work on Mars for us. Perseverance Rover is next to arrive in February, 2021.
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- Humans have millions of years of evolution designed to live on a well protected Earth. Robots can be designed for the hazards without the time delays. The more you learn the greener the grass looks here at home.
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- September 14, 2020 709 2834
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--------------------- --- September 19, 2020 --------------------------------------
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