new NASA Administrator Jim Bridenstine has announced that he wants to make sure
there is never another day when humans are not present in space. "In
fact," he said, "we want lots of humans in space."
But is the present version of humanity really up to the job?
humans, space is a very hostile environment.
There's no air to breathe, and "no one can hear you scream".
There's also no gravity, the lack of which over a few months will cause
your muscles to degenerate and your bones to lose mass.
Further, outside the Earth's protective geomagnetic field and
atmosphere, your body will be irradiated by much more ionizing radiation, which
will damage or kill the cells of your body, will produce dangerous mutations in
your future children, and will increase your chances of developing cancer in a
decade or so.
Charles Stross in his novels in the Saturn's Children
universe and particularly in his short story "Bit Rot", has envisioned a
race of radiation-resistant android servants that had been engineered by
humanity to better withstand the hostile environment of space, including working
in vacuum without a spacesuit and enduring long periods of zero gravity without
degenerating. According to Stross'
scenario, sometime in the twenty-third century humanity will go extinct and our
former humanoid servants will take over jobs for which they are better equipped:
exploring space and populating the stars of our galaxy.
Reengineered humanoids might be a nice solution to the man-in-space
problems described above, but we must work with the humans that are presently
available. This raises the question
of whether there are technological work-arounds for the space-related frailties
First, let's consider the problem of human degeneration in low
gravity. Despite what you may have
been led to believe by science fiction, there's no plausible way of creating a
local gravitational field except with a planetary mass.
It takes a lot of mass to bend space enough to make a gee-level field,
and there does not seem to be any field-based alternative.
Fortunately, Einstein's equivalence principle leads us to another
alternative: an accelerated reference frame is equivalent to a gravitational
field. The acceleration can either
be linear acceleration, as in a
spaceship accelerating forward, or angular
acceleration as in the rotating space station in the film 2001.
With our present technology, gee-level linear acceleration can't be
maintained for very long without running out of fuel, but rotation, once
started, requires no fuel to continue.
Therefore, the human need for gravity can be accommodated by providing
rotating vehicles and habitats in space to produce centripetal acceleration.
The pseudo-gravitational force provided in a rotating habitat is
proportional to R, the distance to the
axis of rotation, and is inversely proportional to the square of
the frequency (or angular velocity) of rotation of the habitat.
For example, the wheel-like space station in the film 2001
had a distance from the habitable region to the rotation axis of about R
= 160 m. To produce 1 gee of
artificial gravity, that habitat would have to rotate at an angular speed
= 2.36 revolutions per minute, a bit more than twice the rotation rate of the
second hand of a wall clock.
The problem with such a rotating habitat is that centrifugal gravity is
accompanied by the Coriolis force, a velocity-dependent "sideways" force
that is proportional to the "vector cross product" of the speed v of an object in the
local rotating environment and the rotational speed f, where the direction of f
is along the axis of rotation. One
of my early Alternate View columns for Analog
(AV-18 in the
February-1987 issue) goes into considerable detail about Coriolis effects in
a rotating space station. Here let
us just say that the Coriolis force will produce stomach-wrenching annoyances
that tilt the floor when you turn or nod your head and make thrown objects veer
off in unexpected directions. In a
small habitat or ship where R
is small and f must
be large, it would be troublesome, disorienting, and difficult to adapt to.
The Coriolis effects could be made almost unnoticeable, however, by
making the habitat's R
The moral here is that long-term off-planet human existence in space
will probably require a considerable investment in rotating ships and habitats.
The problem of space radiation does not have a well-known techno-fix.
The Sun, particularly at times of solar flares, spews out floods of fast
electrons and protons that make the Northern Lights on Earth and represent
radiation hazard for space travelers. Moreover,
galactic and extra-galactic cosmic rays include a population of very energetic
highly-charged atomic nuclei, frequently iron nuclei, that create a radiation
shower in shielding. These
bare nuclei ionize so strongly that, if they encounter the DNA of a cell, will
almost always break both bonds of the double helix, making natural DNA repair
The standard international unit of radiation dosage is the sievert (or
Sv), defined as one joule of ionizing radiation energy deposited in one kilogram
of mass. A sievert represents a
seriously large exposure to radiation. A
dose of about 4.5 Sv is enough to kill about half of a population of humans in
30 days. More typical exposures are
measured in millisieverts (or mSv), one thousandth of a sievert.
For example, the average human living on the Earth's surface will
receive a yearly dose of about 3.6 mSv, a CAT-scan delivers a dose of about 8.5
mSv, a Department of Energy radiation worker is allowed a yearly dose of 20 mSv,
and a Mars colonist would receive a yearly dose of about 234 mSv on the surface
of that planet. A 234 mSv dose is
not lethal, but it greatly increases the likelihood of mutations in children
produced by colonists and the incidence of cancer in later life.
To put it another way, unshielded life on Mars will deliver a dose of
ionizing radiation that is 65 times larger than that of the average Earth
resident and 12 times larger than that allowed for a DOE radiation worker.
That is enough for a great deal of concern about the health of Mars
The cells of a living organism damaged by radiation take three paths:
cell repair, cell senescence, and cell death.
For very large doses the dominant effect is cell death, bringing with it
the symptoms of acute radiation poisoning: immediate hair loss and low blood
pressure, nausea and bloody vomiting in 10 minutes, bloody diarrhea and fever in
1 hour, headache in 2 hours, and ultimately death.
For milder exposures the outcome depends on the character of the
radiation. Electrons, muons, x-rays,
and gamma rays tend to produce single breaks in DNA strands that, if they
don't pile up, can be fixed by the ever-present internal cell repair
mechanisms. Protons and
heavier nuclei have high ionization densities that produce more damaging double
DNA breaks. The radiation damage
might be in a "junk" DNA region where it would have little effect, but some
of the double-break radiation damage will inevitably render the cell
non-functional. Then the cell will
either die or go senescent.
In the average human intestinal cells die and are replaced every 10
days, skin cells are replaced every month, red blood cells are replaced every 4
months, and liver cells are replaced every year.
In case of mild radiation exposure, cell death is preferable to cell
senescence, as long as it does not add too much to the normal rate of cell
When cells do go senescent, there is a problem.
They shut down their normal functions and express the protein p16,
thereby warning cell-reproduction machinery not to cause this cell to divide and
reproduce. However, because of their
internal malfunctioning they also become "zombie cells", sending out harmful
chemical messages to their cellular neighbors that create inflammation and
In a recent test with mice, a quantity of fat cells were withdrawn from
test-subject mice and externally exposed to x-ray radiation until the fat-cell
population became about 80% senescent. Then
the treated cells were re-injected into the test subjects.
The effect of the presence of senescent cells was compared with a control
group that had the same treatment without the radiation exposure and induced
senesce. It was found that when as
little as 0.1% of the mouse fat cells were made senescent, this produced
observable degradation of the motor-activity and fitness of the test subjects.
The conclusion was that even a small fraction of senescent cells present
in living organisms degrades health and fitness.
At present the only remedy for space radiation exposure that has been
seriously considered is the use of shielding, which requires lots of mass to be
transported into space. It's
envisioned, for example, that if a Mars mission carries with it a large quantity
of water for consumption and propulsion reaction mass, the crew must be housed
behind water-filled walls to reduce space radiation exposure, and there may also
be smaller extra shielded regions to which the crew can retreat in the event of
a major solar flare. Such shielding
requirements greatly complicate manned-mission design.
Therefore, I have a suggestion for an alternate and complementary way of
dealing with the problem of space radiation.
In my Alternate
View column "Can We Cure Aging?", published in the May-June 2018 issue
I described a radical new DNA-based technique developed by the Seattle-based
startup Oisin Biotechnologies for reducing the effects of human aging and for
treating cancer. Oisin has sequenced
a plasmid DNA-ring that, when deposited inside a cell wall by a bubble-like
liposome, detects whether the cell has become senescent and is expressing the
protein p16, and if so triggers a suicide gene that causes the senescent cell to
neatly disassemble itself and go away. Oisin
has also developed an alternate plasmid that detects the expression of protein
p53, which is a signal that a cell has become malignant and cancerous.
Ionizing space radiation is normally not so intense as to produce
massive cell death in exposed humans in space.
Rather, cell damage accumulates over a period of time, with the rate of
damage accumulation much larger than in environments on Earth.
That accumulated damage mainly takes the form of senescent and
pre-cancerous cells. With the added
body-burden of senescent cells, the space-traveling humans will have reduced
fitness, premature aging, and a much greater cancer risk.
The good news is that by applying the Oisin treatment, damage from space
radiation at moderate exposure levels producing senescent and pre-malignant
cells can fixed. The damaged cells
will be swept away, to be replaced by healthy ones, potentially restoring space
traveling humans to optimum fitness and providing the ability to better
withstand the effects of space radiation.
I should also mention a slight downside to the Oisin treatment.
It has been discovered that senescent cells play an valuable role in the
healing of wounds, by sending out chemical signals that promote the wound
closure and healing. Therefore,
an astronaut in a hypothetical situation in which he is both wounded and exposed
to radiation should be treated for the wounds first and for the radiation
exposure only after the wounds have healed.
NASA Space Radiation ebook: https://www.nasa.gov/sites/default/files/atoms/files/nasa_space_radiation_ebook_0.pdf
Cell Clearance in Transgenetic Mice:
"Clearance of p16Ink4a-positive senescent cells delays ageing-associated disorders", Darren J. Baker, et al, Nature 479, 232-236 (10 November 2011); see also
"Ageing: Old cells under attack", Daniel S. Peeper, Nature 479, 186-187 (10 November 2011)
Biotechnologies web site:
John Cramer's book on Quantum Mechanics: a non-fiction work describing his Transactional Interpretation of quantum mechanics, The Quantum Handshake - Entanglement, Nonlocality, and Transactions, (Springer, January-2016) is available for purchase online as a printed or eBook at: http://www.springer.com/gp/book/9783319246406 or https://www.amazon.com/dp/3319246402.
SF Novels by John Cramer: my two hard SF novels, Twistor and Einstein's Bridge, are available as eBooks by Book View Cafe and are available at : http://bookviewcafe.com/bookstore/?s=Cramer .
Columns Online: Electronic
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