字幕表 動画を再生する 英語字幕をプリント NASA has a mission protocol which says if a low-earth orbit mission increases the life time risk of the crew getting cancer by more than 3% then they won't go ahead with it but the upcoming Mars missions may expose the crews to levels which will be beyond that limit and two other hazards, so how dangerous is deep space travel to Mars and Beyond. With Ellen musk pushing to get men onto Mars by the mid-2020s and NASA looking to do the same for the 2013 just how much we learned since Apollo and from space stations. 50 years on from the beginning of the Apollo missions and we have yet to send any man back to the moon let alone on the much more arduous journey to our nearest viable planet Mars. Now whilst much of this as being down to the lack of political will in the face of our own man-made problems here on earth it's also down to be increasing sophistication of robotic probes and Landers that are much cheaper to make launch, can go where no man could go and continue working for years of the time. The Voyager probes for example are still going 40 years after their launch. If we relied upon man discovery only we would know a fraction of what we know now. With data from probes that we have sent around solar system since then we have built up a picture which is far from the vision of just whizzing through interplanetary space that along with the joint NASA-Russian experiment of having been in space for a year on board the International Space Station, we now have a much better understanding of what they may experience from the two-and-a-half year round trip tomorrow. We humans evolved on earth and our bodies are adapted from moving around under the effects of 1g of gravity, take that away and problem start to arise our physiology. We often forget what a sheltered life we all leave here on our little blue dot in the harshness of space. We are protected from 99.9% of harmful radiation not only from the Sun but also from other galactic sources by our atmosphere the Earth's magnetic field and the Van Allen belt, yes they make a pain for space travel but they do protect us from further radiation on earth. Get beyond the shelter of these and open space is far from empty, it's teeming with not only radiation from our Sun but also much more powerful radiation from outside our solar system in a form of galactic cosmic rays and gamma rays. Most of the hard data we have about the levels of radiation in deep space comes from the radiation assessment detector instrument which was aboard Mars rover Curiosity, part of the bar science laboratory which was launched in November 2011. The radiation assessment detector was turned on for about 220 out of 253 day journey to Mars and showed that the radiation levels were between 100 and 1000 times higher than that on the earth for an unshielded occupant but it was highly variable and depended a lot on the solar activity at the time. Experiments done on earth with Beam accelerators, computer modeling and confirmation from the cosmic-ray scope on the lunar reconnaissance orbiter as it goes around the moon has shown that plastics with a high hydrogen content are more effective than the same weight of aluminium at stopping particle radiation from both the Sun and galactic cosmic rays and this has been incorporated into the latest spacecraft design like the NASA Orion and the SpaceX Dragon 2. Galactic cosmic rays are protons and nuclei of atoms which have been expelled from supernovas and other violent cosmic events and have been accelerated to near the speed of light. Because of this they have a much greater energy level and can right through space craft and the crew. Shielding helps but it's a compromise between thickness of the shield the extra weight involved which makes it more difficult then to get into space from Earth. To contend with solar flares, a radiation shelter in the craft where there is extra shielding has been proposed with SpaceX Mars mission. Liquid hydrogen or water storage tanks around the crew areas provide a good shield against particle radiation and creating a strong magnetic shield around the crew areas are all possible but don't protect well against electromagnetic wave radiation gamma-rays. Using the curiosity data has been calculated that the radiation risk of a return journey to Mars will be about 600 millisieverts equivalent to about 50 full-body CT scans over that period or being on the International Space Station for 4 years straight. This is also about 30 times the yearly allowance for a radiation worker and that doesn't include stay on Mars itself. A dose of one sievert or 1000 millisieverts is associated with a lifetime increase in fatal cancers by about 5%, which is near the level of the whole mission including stay on Mars. This would be a career limit any of the crew and young women are at a higher risk of cancer from radiation compared to older men so that could affect the crew make up. Along with the cancer risk there's also be increased chance of developing cataracts as the radiation passes through the eye. Recent research has also suggested that the effects of galactic cosmic rays damaging brain cells at the molecular level could cause brain damage similar to the onset of dementia which could show within the duration of the journey. Away from the radiation risks they're also physiological effects of microgravity on the human body. NASA astronaut Scott Kelly spent 340 days in space on the International Space Station and even with a tough two-and-a-half-hour exercise regime each day, he still experience problems with circulation, eye sight as well as a loss of bone and muscle mass. Once in space the fluids in the body no longer have gravity to pull them into the lower extremities and are equally distributed around the body. One of the effects of this is to make the back of the eye swell up and alter their shape which effects vision. Stays on the International Space Station of about a week were quickly reversed when back on earth but lasted for much longer after several months in microgravity. On earth the heart pumps blood around the body and the veins in the legs squeeze the blood back to the heart. In space the same amount of blood is being pumped by the heart but there is much less effort required to return it to the body this allows cardio muscular system in the legs to weaken over time again. When returning to a gravity environment this can cause extreme dizziness and fainting due to the lack of blood been returned to the upper body and brain which could occur the when they reach Mars. Within five months of being in a microgravity environment, astronauts can lose up 40% of their muscle mass and 12% of bone mass, this increases the risk of bone fractures when returning to a gravity environment and it's like turning a 20 year-old into a 60-year-old in just a few months. Psychological issues are also a problem to people in isolated areas for long periods. Some scientists that worked all year round in Antarctica suffer mental health disorder called "Winter Over Syndrome" which is characterized by symptoms such as depression, irritability, aggressive behavior, insomnia and memory problems all the sort of things you don't want to happen when trying to perform mission critical tasks in space or on Mars. Humans traveling in open space is always going to be a risky business and in the end some say the risk is worth the reward of getting men to Mars and they can do much more than a robot in a short space of time and they are much better at handling unexpected situations. But dead or dying crew is something no one wants to see beamed back to earth so it's in all our interests to make sure the risks are minimized as much as possible. It will be over 50 years since the last Apollo flight by the time the earliest Mars missions come around, so even just take a little bit longer than expected, it won't make that much difference to make sure that we get it right. What do you think of the Mars mission and the risk of traveling in deep space? let me know in the comments below and don't forget to subscribe rate and share and also check out some of our other videos you may find interesting. So thanks for watching and I'll see you in the next video.