- 3063 - MARS - radiation doses for astronauts? Mars has virtually no atmosphere, and this means that, unlike Earth, its surface is not protected from solar and cosmic radiation. On Earth, the annual dosage on the ground is about 0.35 Rem/year, but can vary from 0.10 to 0.80 Rem/year depending on your geographic location, altitude, and lifestyle.
--------------- 3063 - MARS - radiation doses for astronauts?
- “Rem” is the units for “ Roentgen Equivalent Man” that measure the dose equivalent to the amount of energy from ionizing radiation in human tissue. About 500 Rem of radiation is considered fatal to humans. Rems are the amount of radiation energy a radioactive source deposit in living tissue.
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- “MARIE” is an instrument on the Odyssey spacecraft orbiting Mars. It shows the unshielded surface radiation dosages, ranging from a maximum of 20 Rem/year to a minimum of 10 Rem/year.
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- Astronauts landing on Mars will want to minimize their total radiation exposure during the 540 days they are expected to stay on the surface. The Apollo astronauts used spacesuits that provided 0.15 gm/cm^2 of shielding. “gm/cm^2” is grams per square centimeter of area.
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- The “Lunar Excursion Module” provided 0.2 gm/cm^2 of shielding, and the orbiting “Command Module” provided 2.4 gm/cm^2 of shielding.
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- The reduction in radiation exposure for each of these was about 1/4, 1/10 and 1/50 respectively, spacesuit, Excursion Module, and Command Module
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- The Mars astronauts using the most recent improved spacesuit technology would provide a reduction of 1/8, and that the “Mars Excursion Vehicle” provides a 1/20 radiation reduction, verses 1/4th , and 1/10th for earlier technology.
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- The Mars radiation map represent some 1,000 kilometers exploration tracks that ambitious astronauts might attempt with fast-moving rovers. Imagine a schedule where they would travel 100 kilometers each day. Suppose they spend 20 hours a day within a shielded rover, and they study their surroundings in spacesuits for 4 hours each day.
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- What is the astronauts radiation dosage per day in a region where the background is 20 Rem/year?
----------------------------- 20 Rem/year = 2.2 milliRem/hour.
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20 hours * (1/20) * 1.1 milliRem/hr + 4 hours * (1/8) * 1.1 milliRem/hr = 1.1 + 0.55 = 1.65 Rems
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- For each of the tracks on the map, calculate a dosage history timeline for the 10 days of each journey. Calculate the total dosage in milliRems to an astronaut, given the exposure times and shielding information provided.
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- The scaling relationship is that for each 20 Rems/year, the daily astronaut dosage is 0.66 milliRem/day ( e.g. 0.66/20). The factor of 2 in the answers accounts for the round-trip.
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- Track A dosage: 2*(12 Rems/yr * 10 days * (1.65 / 20)) = 2*(9.9) = 19.8 mRem.
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- Track B dosage: 2*( 16 Rems/yr * 3.3days + 18 Rems/yr * 3.3days + 20 Rems/yr * 3.3days)(1.65/20) = 2*(14.8) = 29.6 mRem
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- Track C dosage: 2*(12 Rems/yr * 5 days * (1.65/20) + 14 Rems/yr * 5 days * (1.65/20)) = 2*(5.0 + 5.8) = 21.6 mRem
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- Track D dosage: 2*(18 Rems/yr * 5 days * (1.65/20) + 20 Rems/yr * 5 days * (1.65/20)) = 2*(7.5 + 8.25) = 31.5 mRem
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- What is the annual dosage that is equivalent to these 20-day trips? How do these compare with the 350 milliRems they would receive if they remained on Earth?
- Convert 10 Rem/year into milliRem/hour.
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---------- (10 Rem/yr) * (1 year/ 365 days) * (1 day/24 hr) = 1.1 milliRem/hour
- For the 20-day excursion, Track D has the highest dosage and Track A has the lowest.
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- The equivalent annual dosage for the lowest-dosage track is 19.8 milliRem * 365 days/10 days = 722 milliRem, which is about twice the annual dosage they would receive if they remained on Earth.
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- For the highest-dosage trip, the annualized dosage is 1,150 milliRems which is about 3 times the dosage on Earth. (31.5 milliRem * 365 days/10 days = 1150 milliRems)
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February 21, 2021 MARS - radiation doses for astronauts? 3063
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