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.
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
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:
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
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
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.
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.
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.
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.
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
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
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.
Here for Today's Blog
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and exploration policy, but I'll try very hard to skip by the politics
and mostly counter productive harassment of God and everyone else.The almost-daily
QuantumLimit blog is found by clicking on the button above or by clicking
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