beowulf in space
Gerry Creager N5JXS
gerry.creager at tamu.edu
Fri Apr 25 08:16:38 EDT 2003
The Van Allen belts are not a continuum of radiation that you see as a
"shell", but rather, are modulated by the solar environment and the
earth's own geomagnetic environment. One might look at the variations
in geomagnetic potential and gravetic potential for the earth at its
surface, and some projections (and measurements) in low earth orbit.
The possibility of an increased ion/particle based event is higher when
passing through the "belts" than when outside of them. Thus, there is
concern. There tends to be a higher concentration of radiation
environments ("belts") in the mid-earth-orbit range (1500-5000km) than
at lower altitudes, but the concentration of particles is higher in the
lower orbits within the belts. So, it's a catch-22.
I might add, it's hard to explain this, as there's not a board handy I
can drawon, and I can't be seen waving my hands. Then there's the issue
of adequate coffee levels...
In the ISS, there are "safe haven" areas with more shielding than other
parts of the station. In the event of a strong solar event, the crew
could be ordered into the safe haven area for a period of time. Or,
they could be ordered to prepare for evacuation via Soyuz.
Medical planning for a Mars mission was problemmatic when I was at NASA.
The concept of a safe haven has to be considered as the potential for
a solar storm is non-trivial during a mission transit of the necessary
duration, and theweight penalty for such a safe haven area is very
great. Addition of multiple layers of heavy metal, which might mitigate
some of the ion transitions has its own drawbacks, as mentioned
earlier. Layering of heavy metals and differing dense materials is one
path that's been evaluated.
Let's add to the discussion: There are conditions where the human
machine will self-repair better than silicon or germanium... or
silicon-on-saphire, or, pick your substrate. In these cases, we have to
protect the computers more. However, the reverse can also be true, if
the hit is a soft, but fairly frequent set of radiation hits: The
machine sees these as single event upsets, while the human could well
see them as enough ionizing radiation to modify the immune system, the
neurological system or synapses. So protecting hardware _and_ liveware
becomes an important, and difficult task.
And there should be no separation of NASA and follow-on commercial
concerns: These concerns should be echoed all down the chain, because
the concept of protecting the hardware and the liveware isn't something
NASA does to ramp up the costs.
I feel obligated to note that there was a Shuttle mission several years
ago, where the crew were exposed to a sudden and unanticipated solar
event. They were placed in safe-haven in the airlock for a period of a
couple of hours until the majority of the event had passed. THere was
inadequate time to de-orbet and protect them via the atmosphere. All
dosimeters were over normal exposure limits. Certain post-flight
medical recommendations were made with regard to the potential for
reproductive health, and they were subjected to more, and longer
follow-up medically than other crews. I'm not aware of any lasting
consequences... but then, if I were, I'd probably have violated some of
the confidentiality tenets. The story here is simple, though: Solar
events happen, sometimes unexpectedly. When they do, some contingency
planning must be on hand to rapidly (or by design) protect the liveware
and hardware, or something may get damaged. It's really hard to make a
service call to a broken device when it's vertical offset is 250 or so
km, and its delta-V is over 10m/s...
Jim Ahia wrote:
> So the radiation concerns with rad-hardened computer equipment are not
> as much of a problem once clear of the Van Allen Radiation Belt? How
> does this affect the space station and the planned missions to mars?
> What about the lunar environment? I admit to having a lot of ignorance
> on this subject, but I am concerned because part of my college project
> is for robotic teams to do excavation / mining using a "hive" concept.
> The end result is to get more information on the challenges that will be
> faced by the robotic workers that are eventually sent to the moon first,
> and to mars second.
> I am not speaking about the exploration missions by NASA, but rather
> the much-farther-down-the-road commercial mining interests that will
> want to build a foundry on the moon and a spacedock in earth orbit prior
> to the big colonization push into our solar system. I believe it is
> going to happen someday, because we already know that eventually our sun
> will go nova and earth will be no longer habitable. Sooner or later
> mankind, if it is to survive, will need to undergo some kind of diaspora
> and migrate out into space.
Gerry Creager -- gerry.creager at tamu.edu
Network Engineering -- AATLT, Texas A&M University
Cell: 979.229.5301 Office: 979.458.4020 FAX: 979.847.8578
Office: 903A Eller Bldg, TAMU, College Station, TX 77843
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