NASA has a mystery to solve: Can we send people to Mars, or not? It is a matter of radiation. We know the amount of radiation out there, waiting for us between Earth and Mars, but we are not sure how the human body will react to it.
NASA astronauts have been in space, occasionally, for 45 years. Except for a couple of quick trips to the moon, they have never stayed away from Earth for a long period of time. The deep space is full of protons caused by solar flares, gamma rays that come from newborn black holes and cosmic rays from stellar explosions. A long trip to Mars, without large planets nearby that act as shields reflecting that radiation, is going to be a new adventure.
NASA measures the danger of radiation in carcinogenic risk units. A healthy 40-year-old American, non-smoker, has a (huge) 20% chance of eventually dying from cancer. That does remain on Earth. If I traveled to Mars, the risk would increase. The question is how much?
According to a 2001 study on people exposed to large doses of radiation - p. and. Hiroshima atomic bomb survivors, and ironically, cancer patients who have undergone radiotherapy - the risk inherent in a manned mission to Mars lasting 1,000 days would fall between 1% and 19%. The most likely response is 3.4%, but the margin of error is very wide. The funny thing is that it is even worse for women. Due to the breasts and ovaries, the risk in female astronauts is almost double that of their male partners.
The researchers who conducted the study assumed that the spacecraft on Mars would be constructed primarily of aluminum, such as the Apollo capsule. The "skin" of the spacecraft would absorb almost half of the radiation that hit it.
If the percentage of the additional risk is only a little more ... it will be fine. We could build a spaceship using aluminum and head to Mars. Aluminum is the favorite material in the construction of ships due to its lightness and strength, and the long experience that engineers have had for decades in the aerospace industry. But if it were 19%, our 40-year-old astronaut would face a risk of dying from 20% cancer plus 19%, that is, 39% after his return to Earth. That is not acceptable. The margin of error is wide, for good reason. Space radiation is a unique mixture of gamma rays, highly energetic protons and cosmic rays. Bursts of atomic explosions and cancer treatments, which is what many studies are based on, are not a reliable substitute for "real" radiation.
The greatest threat to astronauts en route to Mars is that of galactic cosmic rays. These rays are made up of accelerated particles at almost the speed of light, coming from the explosions of distant supernovae. The most dangerous are heavily ionized nuclei. A surge of these rays would pierce the shell of the ship and the skin of humans like tiny cannonballs, breaking the strands of DNA molecules, damaging genes and killing cells.
Astronauts have been exposed very rarely to a full dose of these deep space rays. Consider the International Space Station (ISS): which orbits only 400 km above the Earth's surface. The body of our planet, looking large, only intercepts a third of the cosmic rays before they reach the ISS. Another third is diverted by the Earth's magnetosphere. Space shuttle astronauts benefit from similar reductions.
The Apollo project astronauts who traveled to the moon absorbed larger doses - about 3 times that of the ISS - but only for a few days during their journey from Earth to the moon. On their way to the moon, Apollo crews reported seeing flashes of cosmic rays in their retinas, and now, many years later, some of them have developed cataracts. On the other hand, they don't seem to have suffered too much. But astronauts traveling to Mars will be "out there" for a year or more. We cannot yet estimate, with reliability, what the cosmic rays will do to us when we are exposed to them for so long.
Finding out is the mission of the new NASA Space Radiation Laboratory (NSRL), based at the premises of the Brookhaven National Laboratory, located in New York, under the US Department of Energy. UU and it was inaugurated in October 2003. In the NSRL there are particle accelerators that can simulate cosmic rays. The researchers expose mammalian cells and tissues to bundles of particles, and then inspect the damage. The objective is to reduce uncertainty in risk estimates to only a small percentage for 2015.
Once we know the risk, NASA can decide what kind of spacecraft to build. It is possible that ordinary building materials, such as aluminum, are not good enough. How about making a plastic ship?
Plastics are rich in hydrogen, an element that does a great job as a cosmic ray absorber. For example, polyethylene, the same material with which garbage bags are made, absorbs 20% more cosmic rays than aluminum. Some form of reinforced polyethylene, developed by the Marshall Space Flight Center, is 10 times stronger than aluminum, and also lighter. This could become the material chosen for the construction of the spacecraft, if we can make it cheap enough.
If the plastic were not good enough, then the presence of pure hydrogen could be required. Liter to liter, liquid hydrogen blocks cosmic rays 2, 5 times better than aluminum. Some advanced spaceship designs need large tanks of liquid hydrogen as fuel, so we could protect the crew from radiation by wrapping the cabins with the tanks.
Can we go to Mars? Maybe, but first, we must solve the question of the level of radiation that our body can withstand, and what kind of spacecraft we need to build.
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