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Dennis Chamberland's
Science and Exploration
Today

 

(The following is a compilation of a series of blogs published in June 2006)
 
The Great Unknown of Space Radiation 
 
     Humanity has announced its full intentions to go to Mars. With our current technology, such a trip will require about 1000 days. But, that is an audacious announcement, considering very few men have ascended above the protective environment of the Van Allen Radiation belts for any significant length of time. Even the US and Russian space stations have all orbited beneath that protection, so there is not much information on what happens when a human exposes their brain and body to raw, unfiltered space radiation. 
     Now, it is true that the Apollo Astronauts all traveled well out of the belts to the Moon and back for periods of more than a week. But how does 10 days compare to 1000? How much damage can 1000 days exposure to raw space radiation do to the soft human tissues and especially to difficult to regenerate brain neurons? 
     The answer is – no one knows. 
     Radiation is not radiation is not radiation. A medical or dental x-ray will penetrate your flesh with a photon – electron particle zipping along at nearly light speed. But it is quite small – say 1/1836 of a single atomic mass unit. So when the x-ray is over, so what? It hurts far less than paying the bill. And if you could look deep into your cells, you almost certainly would notice nothing amiss. It is theoretically possible that the tiny particle traveling with an energy of kilo-volts may have detached one or two DNA bonds, but they probably repaired themselves immediately or they were in non-reproducing cells and it did not matter. The end result is the same billions of times every day – no harm no foul. 
     But in space, the monsters are MUCH bigger. Obviously the earth is “in space” but we don’t get visited by many of the big monsters. Most of them strike the Van Allen radiation belts and the big guys are shunted up and reflected/deflected away from us. Thanks to the earth’s natural magnetic fields, we don’t get hit very much. 
     But let’s compare cosmic radiation with x-rays or natural occurring radiation sources such as radium or uranium. Again, they are small – in the thousands of electron volt ranges. But space radiation sources were generated in the heart of stars and supernovas. These particles are NOT lowly electrons of the 1/1836 AMU variety – they are of 1 or greater AMU masses (nearly two thousand times more massive) and they are also traveling at relativistic velocities near the speed of light. The end result is, instead of a momentum of a few thousand electron volts, the monster carries an energy measured in the billions of electron volts for each one. Further, instead of sub-sub-microscopic effects, its linear energy transfer trail (LET) is so large it can actually be viewed with a microscope where it passed thorugh the cell's tissues!
     What happens when one of these monsters strikes your cells or your neurons? Well, the answer is relatively simple: its’ lights out. 
 
Space Radiation's Imminent Threat 
     There is a position in low earth orbital space over the South Atlantic Ocean and most of South America where the magnetosphere of the earth takes a dip toward the surface of the earth. Into this region is part of the nominal orbits of the space shuttle and the International Space Station. When these manned spacecraft enter this region called the South Atlantic Anomaly (SAA), they fly below a part of the natural space radiation shield and they are exposed to increased levels of space radiation. During these times, astronauts noticed what they first called retinal flashes. 
     A retinal flash is a streak of light “seen” inside the brain. They are probably erroneously called retinal flashes, because some brain scientists now think they are probably caused by a high energy particle of space radiation streaking through the brain’s neural cortex and killing an optic neuron. A true retinal flash can be caused by mechanical stimulation of the retinal neurons, but these are something else altogether. They were first reported by the astronauts of Apollo 14 on their way to the moon. The flashes were so problematic to astronaut Jerry Linenger on the MIR space station in 1996 that he slept with his head between two lead batteries because the troublesome lights kept his awake when the station orbited though the SAA. He reported that the batteries actually did very little good.
     The problem is obvious. If each flash of light represents the death of an optic neuron, then how many other brain cells were killed as the massive, high energy object made its way through the brain to the optic neuron? How many brain cells will be killed in a 1000 day Mars expedition? (Mars has no effective magnetosphere.)
     And if all that were not enough worry, we cannot duplicate space radiation on earth. We can only use our most massive particle accelerators to duplicate one to several energetic particles at a time, but nothing like the rich diversity of space born particles. We can only experiment on this with any validity in deep space (outside the influence of the magnetosphere). 
     The question is obvious: how much is bad and how much is really bad? No one knows. But before we commit astronauts to 1000 days in the celestial shooting gallery, we have to know for sure! We can go ahead and spend our billions inventing space machines to take them there, but until we get a handle on the key question, we will have to know the answer for sure. 
     Oh, by the way. Since the term retinal flash is not entirely accurate, let me suggest a new name for the flashes caused by space radiation. I suggest we call them the “Tobias Effect”, named after the scientist who first discovered them in 1951 after he placed his head in the beam of the Berkeley particle accelerator. Upon doing so, he reported that his “head was filled with brilliant light flashes” and thought he was seeing into the heart of the universe. 
 
Your Brain And Space Radiation 

     The most damaging effect of the massive, energetic particles that make up the most dangerous component of space radiation targets the brain. To be most specific, the radiation will initially target the sensitive inner brain regions where it may do its most severe damage. 
     Recent studies have shown that what we were taught in school is wrong. We were taught that “brain cells cannot regenerate – that what you were born with is all you will ever have.” That is wrong. The innermost chambers of the brain in the limbic region are lined with a layer of adult stem cells. This region has become known as “brain marrow”. Just as the bone marrow generates and replaces blood cells through adult stem cell regeneration, so does the brain marrow. It is a process that was heretofore thought impossible: neurogenesis. 
     Space radiation will probably target these brain marrow cells first. Research is now underway using the crude approximation of space radiation from high energy particle accelerators. Initial but still inconclusive data has demonstrated these areas are highly sensitive to acute doses of space radiation. Beyond a certain range of damage – and no one knows that that means exactly – the organism will die. 
     The questions are important and on them depend the future of human space exploration. The questions are: how much is bad? How does time and radiation exposure together effect the body’s natural ability to heal itself? How is the normally slow process of neurogenesis affected by the onslaught? What exposure (what combination of energy and time) is the point of no return for the brain marrow? At what dose and conditions will symptoms emerge in the organism? What will those symptoms be? ALL of these questions MUST be answered before the first astronaut is committed to a Mars expedition.
 
The Gamble of Space Radiation 
 
     If you venture into space, you are going to get zapped by increased radiation. For those of us who live on the earth’s surface, we are protected by the earth’s relatively thick atmosphere and by the ever-present magnetosphere which both shields and redirects radiation away from us. All around us beneath our feet and drifting about in the air are natural sources of radiation and we certainly take a dose from those sources, but nothing like the radiation in space. 
     For example, if you are an astronaut in the International Space Station, you will receive over 365 times the radiation in one day as those on the earth’s surface get from natural sources. In other words, spending one day on the ISS is equivalent to one year exposure to natural background sources of radiation walking about on planet earth. And if you launch yourself away from the low earth orbit of the space station, which generally speaking, orbits beneath the protection of the magnetosphere, the exposure jumps four times that. Further, the difference between the lower energy radiation in low earth orbit is much better understood than the high energy-high mass radiation of interplanetary space. 
     The key question from all this is: so what? 
     Cancer is the answer, of course. Yesterday we discussed the massive particles of deep space and their potential destruciton of the sentitive regions of the inner brain. Today we will discuss a better understood risk. An increased exposure to ionizing radiation subsequently increases cancer risk. But what kind of risks are we talking about? On this question there is a wide range of disagreement. 
     NASA’s position is that it is well within acceptable limits. To a government agency, that means that it is within acceptable legal limits of exposing the work force to ionizing radiation. The EPA has set the limit on that: no one is legally permitted to receive a dose of radiation on the job that would increase their risk of death by cancer by greater than 15%. NASA has determined that a stint of duty on the ISS increases the cancer death risk by less than 5%. 
     But along comes Dr. Marco Durante of the Federico II University in Naples. He has conducted a lengthy study on MIR astronauts for the ESA. He has determined in a study of eight astronauts who had spent 70 days or longer on Mir, he found three with chromosomal abnormalities that might be precancerous. From this he calculates that there is a 20 per cent higher risk of dying from cancer. This, of course, is above US government limits of acceptable risk, and that is only 70 days below the protective layer of the magnetosphere compared to a 1000 days Mars trip - all of it in deep, unprotected space. 
     Further, Dr. Durante has also determined than on any Mars mission, half of the crew would die of radiation induced cancer upon return from the mission. As far as I can determine, no US Government source has made any comments on this as of this writing. 
     I have made a dedicated effort to keep this blog readable, and I have been promising for the last three entries to discuss what we may be able to do about the space radiation. So, unless I run into some more irresistible data, I will bring that long promised essay on those countermeasures to you tomorrow! Be patient – and stop smoking! 
     (Why? Cancer is the answer. If you smoke, you increase your cancer rate to ten times that of the astronaut corps! Why? Naturally occurring radioactive polonium bioaccumulates in the tobacco plant leaves and the smoker bathes his lungs in it each and every day. Not a good idea.)

The Long Pole

     Space Radiation, in space agency parlance – is the “long pole in the tent”. In other words, if we can’t first understand it then solve it, mankind will never get beyond low earth orbit. If we do not fully understand and solve this problem starting now, there will never be a moon base and there will never be a Mars expedition of off earth settlements – ever. That makes the solution very important! 
     And what are those solutions? Here are five that have been suggested.

 USE NUCLEAR ROCKETS: If we can speed up our space voyages, it exposes our crews to less radiation while in space. The less time spent on getting from point A to point B means less risk. Then we can use the methods below on the surface of the planets to mitigate the on site exploration risk.

 SPACE VEHICLE SHIELDING: This is actually the least practical of all the suggestions. If one can put enough shielding around a spacecraft, one can shield out much of the space radiation. However, in the case of the “heavy primaries”, it would require one massive shield. Mass in space is always a significant problem: how does one get it there and then, once the spacecraft is shielded, then where does one get all the energy to accelerate and then decelerate it? It is possible to employ a small asteroid and burrow down to its core, using the asteroid as a shield, then propel the asteroid like a spacecraft – but, the energy required to do this is well beyond our technology.

 REGOLIOTH SHIELDING: If one can pile up enough in situ shielding atop a planetary base, it is possible to shield the offending energies out. On the surface of the Moon or Mars, this is not a serious problem. One simply piles up enough regolith (the off-earth word for ‘soil’ or ‘dirt’ – which have different meanings off-earth) on top of the habitat to shield it out. It is the least expensive and most (pardon the pun) down-to-earth method. Unfortunately, the Hollywood image of the domed colony is out.

THE HIGH VOLTAGE SHIELD: It may be possible to duplicate a mini-magnetosphere by arranging a series of spherical balloons over and around the colony structures as shown in the illustration above. These spheres are then charged with very high voltage – on the order of 50 million volts. This voltage would then – like the earth’s own shielding mechanism – direct the high energy particles away and to ground. Such a system is in the planning stages now.
     But what about those long space voyages between planets? There are concept drawings for this kind of shielding as well. But, any high voltage shield comes with its own pre-packaged demons.
     There is also a well known risk associated with exposing living cells to high voltage fields. There are cancer risks and others suggested by the anecdotal evidence. I did a study at Oklahoma State University where I indirectly exposed mouse epithelial cells to a coil that was transmitting only 110V 60HZ wall current. The cells did very poorly. After the experiment, the cells also showed distinct chromosomal aberrations. If we expose our crews to fields of an energy many times that, there is a suggestion that it may actually be worse for them than the space radiation. It is important to point out, however, that this idea is only conjecture and needs much study before these high energy shields are actually employed and crews exposed. 

 STEM CELL REPLACEMENT THERAPY: I have heard a suggestion that one could conceivably actually replace the stem cells of the inner brain if they are killed en-route, caused either by a solar storm or just from day-to-day chronic space radiation exposure. In this scenario, astronauts would give medical scientists a sample of their own stem cells from their inner brain before launch. The scientists would then culture them and grow up several batches. They would then launch these brain stem cells along with the crew. A port would be fitted in the astronaut’s skull and if necessary, they could inject themselves with new brain stem cells. In this way, they could look the universe in the eye and say, “Bring on your worst!” and still survive in a relatively healthy condition. What this therapy does not address is the other myriad cancers in the body that will invariably be triggered by the radiation exposure.
 
     The bottom line question is simple: can we go to the moon and mars and build bases there and live without being killed or badly injured by space radiation? The answer is: no one knows the answer to that question today. However, it is a near certainty that we will figure it out. I would guess that a combination of several or even all the above methods will eventually be employed in a kind of hybrid strategy to defeat this problem.
 
Dennis Chamberland


 
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