Index
Home
About
Blog
From: Henry Spencer <henry@zoo.toronto.edu>
Newsgroups: sci.space.tech
Subject: Re: Q: Effects of solar flares on operation of Geostationary
Satellites
Date: Wed, 6 Mar 1996 23:44:16 GMT
In article <4h695g$lbq@iac2.ltec.net> "David W. Knisely" <dk84538@ltec.net> writes:
>Does anyone have any hard information concerning what effect (if any)
>solar flares (especially major: class 3 and 4) have on the general
>operations of Geostationary communications satellites? In particular,
>has one ever been temporarily (or permanently) been knocked out of
>service, and if so, for how long?
It's rare, but it happens. On 20 January 1994, Anik E1 lost its primary
momentum-wheel controller but was restabilized on the backup controller.
At the same time, Anik E2 lost both, and was essentially useless until
July, when software changes restored limited control. This wasn't a
flare per se, as I recall, but rather a surge in high-energy electron
density caused less directly by solar activity.
As others have already mentioned, some loss of solar-cell output from
radiation damage is routinely figured into the design of comsat power
systems.
>...I am aware of the increase in drag
>during high levels of solar activity, but I am more interested in whether the
>electronics have been seriously damaged (or do the on-board housekeeping computers
>just get their memories reset?).
The drag increase isn't felt at comsat altitudes; that's a LEO problem.
Occasional hiccups in onboard electronics are not uncommon at times of
high activity, but it's rare for actual damage to occur.
--
Space will not be opened by always | Henry Spencer
leaving it to another generation. --Bill Gaubatz | henry@zoo.toronto.edu
Newsgroups: sci.astro,sci.physics,sci.space.policy,sci.space.shuttle
From: Henry Spencer <henry@zoo.toronto.edu>
Subject: Re: "Space Weather Consideration During the Assembly of The
International Space Station" By Blair S. Allen
Date: Wed, 21 Feb 1996 20:48:56 GMT
>During solar maximum one can expect to observe many active regions, and
>violent space weather. Such space weather conditions can be expected to
>be a threat to astronauts, space shuttle operations and satellites
>operations...
The threat is relatively small in low Earth orbit, where the station is
going to be. "Guidance on Radiation Protection in Space Activities"
(NCRP, 1989) was prepared before the 1989 solar maximum, but had data
from earlier peaks. Its estimate was that the August 1972 flare -- the
worst on which good data was available -- would expose astronauts in a
relatively thin-skinned vehicle (1 g/cm^2 aluminum or equivalent) in
a 57deg orbit to 50mSv addition dose to blood-forming organs, 410mSv
to the eye lens, and 530mSv to the skin, assuming that magnetic-storm
effects did not modify Earth's magnetosphere enough to reduce its
shielding effect seriously. NCRP's recommended limits for 30-day
exposures are respectively 250mSv, 1000mSv, and 1500mSv. In other words,
these doses are enough to be a concern but not enough to be a hazard,
especially since I believe the station walls are better than 1g/cm^2Al.
(Oh, 1mSv = 100mREM.)
In a 90deg orbit, or on the Moon, the situation would be more serious.
For station work, the only real problem would be EVAs. The spacesuits
have little shielding. However, major flares do not strike without
warning. The delay between the flare itself (as detected in X-rays etc.)
and the arrival of the earliest particle radiation (which is the hazard)
is typically over 12 hours. Furthermore, the particle flux grows
relatively slowly, typically taking 24 hours or more to peak. With
simple precautions and a careful watch, the worst consequence of even
the quickest and worst-timed flare would be the need to terminate an EVA
abruptly and defer continuing it for several days.
I would note that the Apollo lunar exploration missions were likewise
undertaken at a solar maximum. Now *that* was taking a bit of a chance,
and in fact the August 1972 flare fell between Apollos 16 and 17. But
in a non-polar low Earth orbit the hazards are minor.
>...For example September 1989 a period of high solar wind
>existed ( 95 to 99% solar maximum period), the radiation levels would
>have been lethal to astronauts out of the space shuttle due to the solar
>flare.
This presumably refers to the 30 Sept 1989 flare. Note that Mir was
manned at the time, and although the flare caused some concern, the final
decision was that special precautions were not required.
--
Space will not be opened by always | Henry Spencer
leaving it to another generation. --Bill Gaubatz | henry@zoo.toronto.edu
Newsgroups: sci.space.history
From: Henry Spencer <henry@zoo.toronto.edu>
Subject: Re: Apollo and solar flares (was Re: Did moon landings happen ?)
Date: Sat, 1 Mar 1997 06:28:35 GMT
In article <3316AD56.76DB@CHEMISTRY.Watstar.UWaterloo.CA>,
Peter Olbach <PCOLBACH@CHEMISTRY.Watstar.UWaterloo.CA> wrote:
>> It may be a garbled version of the problem with giant solar flares, which
>> are indeed nasty but are very rare. Apollo simply took its chances...
>
>Did NASA have any contingency plans to deal with solar flares during an
>Apollo lunar mission? If a flare had occured, how much warning would
>they have had, and could they have gotten the astronauts home in time?
Some attempt was made to provide flare forecasts, but even today it's not
a very reliable process. The giant flares, in particular, are very poorly
understood, and there is little hope of reliable prediction for them. We
don't even know just how big they can get; only a few have been observed
with modern instruments, and each one is different. They tend to occur
around a maximum of the 11-year solar cycle, but the maxima are not very
sharp and this isn't a very helpful fact -- the giant flares in the
late-50s maximum were spread over about five years, and the late-40s
maximum seems to have had giant flares in 1942, 1946, and 1949.
You basically find out about these things when the X-ray flash arrives.
The good news is that the X-rays are not particularly dangerous, and the
charged particles which represent the real hazard lag well behind. The
bad news is that because the charged particles follow the interplanetary
magnetic field, which is not straight, it occasionally happens that the
flare itself is over the Sun's horizon as seen from Earth.
Disregarding the possibility of an over-the-horizon flare, and also the
related problem of deciding whether the particle cloud from a flare is
actually going to reach Earth or miss it, the time between the X-ray
emissions and the particle arrival averages about 15hr, although in
particularly unfavorable cases the fastest particles can show up in 20min
or so. Also, the larger flares usually take 24hr or more to reach peak
intensity. (But see comments above about limited data on giant flares.)
This is enough time to get abort procedures started, but not enough to get
a lunar mission home. It would probably be enough to at least get an LM
crew up off the surface and into the CM, which had better shielding.
>(How rare is "very rare", anyway? It seems unlikely that NASA would
>want to run that sort of risk without some sort of contingency plan...
There really wasn't a whole lot that could be done. (I recall some
negative comments in the early 1960s about Kennedy's schedule putting the
beginning of manned lunar exploration at a solar maximum.) Unless you've
got access to tons of shielding on maybe half an hour's notice -- which
is practical on the lunar surface but not in open space -- the worst case
simply is fatal.
As for how rare, that's kind of ill-defined. Normal flares are of no
great significance; it's the giant ones you care about. They happen maybe
a few times per solar maximum. The most recent maximum, at the beginning
of this decade, had a few (I forget, and my handy references aren't recent
enough). The previous maximum had none. The late-60s maximum had one, in
August 1972, about halfway between Apollos 16 and 17, which was big but
"soft" (few really high-energy particles); had an Apollo crew been on the
Moon at the time, they'd have gotten enough radiation to make them
somewhat ill but not enough to kill or incapacitate (James Michener
notwithstanding). The late-50s maximum had half a dozen, at least one of
which (Feb 1956) was so massive that it would probably have killed an
Apollo crew. The mid-40s maximum is poorly documented, but it appears to
have had four real monsters, possibly bigger than anything seen since.
--
Committees do harm merely by existing. | Henry Spencer
-- Freeman Dyson | henry@zoo.toronto.edu
From: Henry Spencer <henry@zoo.toronto.edu>
Newsgroups: sci.materials,sci.space.policy,sci.space.science,sci.space.tech
Subject: Re: Mars Mission - Solar Flare Question...
Date: Thu, 26 Mar 1998 14:55:26 GMT
In article <01bd55dd$a0336ca0$LocalHost@tosh>,
Jeremy Webb <jeremy.webb@jed.octacon.co.uk> wrote:
>Can anyone tell me if there is an effective technique that might be used to
>protect astronauts from the effects of radiation that would be incurred
>during a solar flare occuring during a manned mission to Mars?
Yes; the problem is manageable.
(Point of terminology: what we're worried about technically is not the
solar flares, but the "solar proton events" which are vaguely associated
with the flares... but just calling them flares is easier, so I won't be
pedantic about it.)
The normal run of solar flares, which occur constantly when the Sun is
active, actually are not a serious problem. Nor are cosmic rays. Which
is good, because shielding the whole crew quarters, especially against
cosmic rays, is an awful problem with no good solution at this time.
The problem is giant solar flares. There are typically a few of those
in each peak of the solar cycle, although the extremes are poorly known
(because we have good data for only about three peaks and poor data for
only a couple more). Giant flares are seriously dangerous, but they are
rare and do not last long. So what's needed for them is a small "storm
shelter" shielded by 20-30cm of something that's a good absorber for
particle radiation. Water actually works quite well, and since food is
mostly water, the crew's food storage can be wrapped around the shelter.
(As the food is used up, it can be replaced with the end products of the
food :-), which also have a high water content.) The crew simply retreats
into the shelter for a day or two when a giant flare occurs.
>The implications of the large density (and therefore resultant mass) of
>effective stable heavy metal radiation barriers such as lead and gold would
>tend to suggest to me that these materials would be too "expensive" in
>terms of mass to make them effective candidates to shield the entire space
>craft.
Fortunately, the real radiation problem in flares is high-energy protons,
not X-rays or gamma rays, and the protons are easier to stop. Even so,
shielding the entire crew quarters is impractical, but fortunately we
don't need shielding very often or for very long, so the "storm shelter"
approach is feasible.
(Really long-term operations outside the Earth's magnetosphere pose a
different problem: when you start spending decades in space, cosmic rays
probably have to be shielded against, and they are very penetrating. But
for relatively short expeditions, a few years maximum, the cosmic-ray dose
is a tolerable risk.)
>1) It leaves the astronauts exposed to radiation from the time between the
>detection of the radiation burst until they are shut up in the radiation
>protecton chamber. What if the flare is very large and the increase of
>radiation exposure sudden?
Only the very large flares are a problem anyway. Their risetime typically
seems to be several hours. Even the very fastest-rising flares -- which
are quite small -- have a risetime of 15-20 minutes, so the usual rule of
thumb is that you have to be able to retreat to a storm shelter in that
time.
>How large is the sample of data collected (and
>over how many years?) on the rate of increase and magnitude of the
>radiation emitted during solar flares.
We have lots of data on small flares; they happen all the time during
active periods on the Sun. Data on giant flares is limited because we
have observed only a handful of them with good instruments. But there
comes a time when you simply have to accept the risk that Mother Nature
might still have dirty tricks in store.
>2) The team flying the vehicle are subjected to the psychological ordeal of
>sharing a very small space and performing *ALL* their duties within this
>space until the flare subsides.
Most of the duties can simply be suspended for the duration. And we have
lots of relevant experience with such situations. Not only did the Apollo
crews share a very small space (ever been in an Apollo?) for the duration,
but sailors and arctic explorers have been doing this for centuries, and
submariners for most of a century (ever been in a pre-nuclear sub?).
>3) There will be a constant fear present during the mission that a flare
>may occur with negative consequences for the crew. This may or may not be a
>good thing for crew morale.
Sailors have been living with the possibility of fatal storms for millennia.
Are today's astronauts such psychologically fragile creatures? I think not.
>Are there any better ways of protecting manned spacecraft against solar
>flares? ... Perhaps (unlikely, I
>know!) a powerful magnetic field could be employed, in the way that we are
>all protected against these stellar events.
The idea of magnetic or electrostatic shielding has been looked at often.
To date, it never seems to work out quite well enough, except perhaps when
the vehicle/habitat gets very large.
--
Being the last man on the Moon | Henry Spencer
is a very dubious honor. -- Gene Cernan | henry@zoo.toronto.edu
From: "kbm" <kbm@ix.netcom.com>
Newsgroups: sci.materials,sci.space.policy,sci.space.science,sci.space.tech
Subject: Re: Mars Mission - Solar Flare Question...
Date: Sat, 4 Apr 1998 08:48:05 -0700
George Herbert wrote in message <6g3tqs$pe8@crl3.crl.com>...
>I was simplifying a couple of logic steps.
>I know that particle acellerator grade proton beams
>and electron beams can transmute (obviously, you can't
>make neutron beams ...). I believe, from descriptions
>in NASA radiation riskpapers, that SPE protons are
>at lower energies than needed for transmuting.
>The only risks listed for transmuted materials
>that I've seen are those due to GCR heavy nucleii.
>
>If soomeone who has good SPE energy ranges would
>like to compare those with transmutation energy barrier
>levels from ordinary particle physics, it woud be
>a more useful confirmation than my sometimes poor memory.
>Or perhaps I'm wrong and SPE protons can be energetic
>enough...
>
>
>-george william herbert
>Retro Aerospace
>gherbert@crl.com
>
Measured solar proton energies range from the low energy plasma (solar wind)
to in excess of 1 GeV. The alphas have the same energies.
I have done proton testing at the cyclotron at UC Davis (Crocker Lab) and at
Harvard with protons to simulate space radiation effects. UC Davis has
energies up to 63 MeV and Harvard up to 160 MeV (University of Indiana
protons go up to 200 MeV). When testing, the materials I am irradiating get
"hot" -- although they generally decay out in several days to a week. We
put them in a box to let them decay out before we bring them home. The
threshold for inelastic scattering (i.e., transmutation) is about 20 MeV.
Above about 100 MeV, quite a bit of the proton energy loss in a material is
due to inelastic scatters.
C. Dyer at ESA has done quite a bit of analysis on activation of materials
in space. His papers are published in the IEEE Transactions on Nuclear
Science, December issues from about 1990 on. He has also written for the
RADECs conference in europe on the subject (I believe).
Kyle Miller
From: fcrary@rintintin.Colorado.EDU (Frank Crary)
Newsgroups: sci.materials,sci.space.policy,sci.space.science,sci.space.tech
Subject: Re: Mars Mission - Solar Flare Question...
Date: 6 Apr 1998 00:43:06 GMT
In article <6g5klb$5pg@sjx-ixn4.ix.netcom.com>, kbm <kbm@ix.netcom.com> wrote:
>>If soomeone who has good SPE energy ranges would
>>like to compare those with transmutation energy barrier
>>levels from ordinary particle physics, it woud be
>>a more useful confirmation than my sometimes poor memory.
>>Or perhaps I'm wrong and SPE protons can be energetic
>>enough...
>Measured solar proton energies range from the low energy plasma (solar wind)
>to in excess of 1 GeV. The alphas have the same energies.
>I have done proton testing at the cyclotron at UC Davis (Crocker Lab) and at
>Harvard with protons to simulate space radiation effects. UC Davis has
>energies up to 63 MeV and Harvard up to 160 MeV (University of Indiana
>protons go up to 200 MeV). When testing, the materials I am irradiating get
>"hot" -- although they generally decay out in several days to a week.
True, but solar particle event fluxes have a very strong energy dependence.
Only a tiny fraction of the particles have energies above 1 MeV, let
along above 50 MeV. I'd have to check, but I think the integrated
flux is proportional to 1/E^n, where n is larger than two. So the flux
of 1 keV and greater particles would be would be at least 2.5 billion
times greater than the flux of 50 MeV and greater particles. I really
don't think there would be enough > 50 MeV particles for the shielding
to become significantly radioactive.
Frank Crary
CU Boulder
From: gherbert@crl3.crl.com (George Herbert)
Newsgroups: sci.space.policy
Subject: Re: Lunacorp and Apollo
Date: 3 Aug 1999 23:27:57 -0700
<corncrate@my-deja.com> wrote:
>Well, at last we get to the crux of the matter! So NASA was perfectly
>willing to risk the lives of the astronots because there was no way of
>predicting if a major solar flare would happen at any stage while
>outside the earth's magnetic field! And they were out of low earth
>orbit for at least eight days (I think it was that long, if not longer.)
Yes. That risk was openly discussed in the press, bought into by
the astronauts, etc. This is not news. It's well known.
>So to put it simply... at *any* time during the alleged lunar landings,
>a major solar flare *could* have occurred and this would have at least
>made the astronauts physically sick (which could have killed them if
>they were wearing their spacesuits and were on an EVA, and unable to
>get back into the LEM) or would have killed them outright. End of
>story. And that is exactly what happened. Go and find out how often
>solar flares strong enough to induce vomiting in deep space occur.
>
>So NASA had to fake it. Imagine seeing Neil Armstrong collapsing after
>an hour's EVA and then being sick inside his helmet. And Buzz Aldrin so
>sick he can't even help his partner back into the LEM. Sounds pretty
>bad, huh? But of course, that's no reason to fake it. Oh no.
Please reference the following convenient websites:
http://www.windows.umich.edu/spaceweather/images/proton_events_ron_turner_gif_image.html
http://umbra.nascom.nasa.gov/SEP/
http://www.fas.org/nuke/hew/Nwfaq/Nfaq5.html
The detailed event history for 1969-72 isn't online anywhere I can
find it, it starts with 1976.
One significant event happened in 1976. Two in 1977. Nine in 1978.
Seven in 1979. Two in 1980. Ten in 1981. Twelve in 1982. Two in 1983,
seven in 1984, four in 1986, one in 1987, nine in 1988, 23 in 1989,
twelve in 1990, 17 in 1991, six in 1992, two in 1993, two in 1994,
none in 1995, two in 1996, eight in 1997, and five so far in 1999.
The low end of those listed events wouldn't have necessarily
made the astronauts sick. The high end would have killed them
(the peak 1989 and 1990 events at over 40,000 pfu for energies >= 10 MeV).
"pfu" is defined as: 1 pfu = 1 p cm-2 sr-1 s-1
If we assume an average energy of 35 MeV for those particles (high),
and assume a Q factor for protons of 10 (this is a guess, but it's
not likely to be much factor) then you get roughly the following
dose rate per pfu:
1 pfu = 1 proton/steradian/cm^2/sec
est 3 steradian exposure
est human body surface area is 1 m^2
= 10,000 cm^2
= 30,000 protons/body/sec
conversion MeV->Joules is *1.602192e-13
35 MeV ~= 6E-12 J
One rad = 0.01J/kg; for a 100kg human,
~= 1.7E-7 rad/sec, or 1.7E-6 rem/sec/pfu
The first event in 1978 was a 24.5 hr, average 850 pfu event.
88,200 sec, about 75 million pfu-seconds worth, which works out
to 127 rems. Enough for nausea, but not serious short term illness.
From Carey Sublette's Nuclear Weapons FAQ:
>100-200 REMS
>Mild acute symptoms occur in this range. Tissues primarily affected are
>the hematopoietic (blood forming) tissues, sperm forming tissues are
>also vulnerable. Symptoms begin to appear at 100 rems, and become common
>at 200 rems. Typical effects are mild to moderate nausea (50% probability
>at 200 rems) , with occasional vomiting, setting in within 3-6 hours
>after exposure, and lasting several hours to a day. This is followed by
>a latent period during which symptoms disappear. Blood changes set in
>and increase steadily during the latency period as blood cells die
>naturally and are not replaced. Mild clinical symptoms return in 10-14
>days. These symptoms include loss of appetite (50% probability at 150
>rems), malaise, and fatigue (50% probability at 200 rems), and last up
>to 4 weeks. Recovery from other injuries is impaired and there is enhanced
>risk of infection. Temporary male sterility is universal. The higher
>the dosage in this range, the more likely the effects, the faster
>symptoms appear, the shorter the latency period, and the longer the
>duration of illness.
The times and average rates for the 1978 events are:
Event Duration pfu rem
-------------- --- ---
24:30 850 127
1:00 65 4
39:15 1000 240
0:05 100 0.5
2:05 19 2.4
17:30 25 27
7:00 20 10
17:30 2,200 235
0:10 38 0.4
Note that only three events in 1978 are enough to make an
astronaut ill, and two which were enough to have serious long
lasting health effects. Lifetime dosage limits are 200 rem.
You can work these numbers out for the other years and events.
Solar flares large enough to have serious health effects are not
that common. The numbers speak for themselves. A serious ongoing
lunar program would eventually probably over-irradiate some astronauts
if you didn't have proper shielding, but Apollo played a mild gamble
with relatively rare events and won, as the numbers indicate is
likely given how rare SPEs are.
Now I am going to conclude with a free hint. If you knew enough
to be making serious claims regarding space travel and safety,
you both could and should have done this research yourself.
If you want anyone to take you seriously when you post here,
you have to put some effort in. So do some research next time.
-george william herbert
gherbert@crl.com
Newsgroups: sci.space.history
From: henry@spsystems.net (Henry Spencer)
Subject: Re: Space radiation
Date: Mon, 9 Aug 1999 14:53:04 GMT
In article <379aad80.16436021@news.btinternet.com>,
billo bear <billo@isee.com> wrote:
>New to this group but would like a question answered. Is the Earths
>atmosphere protecting us from harmful radiation from the sun.
>Once a craft gets 650 miles out into space is it bombarded with
>harmful radiation.
No, not to any great extent.
The main harmful radiation from the Sun is that produced by the occasional
giant solar flares. Normal solar flares are too small to be important.
In the absence of flares, the Sun doesn't produce any significant amount
of highly penetrating radiation. (Note, I'm being a trifle sloppy about
terminology here, for simplicity and clarity -- flares are not the actual
problem, but events closely associated with them are.)
The radiation from solar flares, normal and giant, is mostly stopped by
Earth's magnetic field, not Earth's atmosphere. That's why spacecraft in
low Earth orbit -- which puts them above 99.9%+ of the atmosphere -- are
still relatively safe against flares.
(The atmosphere does stop cosmic rays, which are too energetic for the
magnetic field to stop them. But they are not a significant health
problem unless you are spending years in space.)
The Earth's magnetic field also traps particle radiation, forming the Van
Allen belts. These are zones of high radiation not far above low Earth
orbit; in fact, they set the effective upper limit for LEO, 1000km or so.
They are the main radiation problem for Apollo-style missions, but they
can be dealt with by modest amounts of shielding and use of a trajectory
which passes through the belts rapidly.
Brief deep-space missions can just take their chances with giant flares
to some extent; that's what Apollo did. A worst-case giant flare might
have killed an Apollo crew, and certainly would have made them sick, but
the odds of having one happen during an Apollo flight were small.
Longer flights would need a "storm shelter" to which the crew could
retreat when a giant flare occurred.
--
The good old days | Henry Spencer henry@spsystems.net
weren't. | (aka henry@zoo.toronto.edu)
Newsgroups: sci.space.history
From: henry@spsystems.net (Henry Spencer)
Subject: Re: Space radiation
Date: Mon, 9 Aug 1999 21:01:38 GMT
In article <37af2a8a@news.uk.ibm.net>,
Alejandro Zuzek <az9k AT dc DOT uba DOT ar> wrote:
>> Longer flights would need a "storm shelter" ...
>
>How long does a typical giant flare last? how much time would the crew have
>to retreat to the shelter?
They generally last a day or two. The onset is typically fairly slow,
taking hours to build up to a dangerous level, but more rapid onset has
been observed once or twice, and a common rule of thumb is that shelter
must be accessible within 30 minutes. (Not an issue in a spacecraft, but
potentially a problem on the surface of the Moon, Mars, or an asteroid.)
A certain amount of caution is desirable, because we have good data on
only a handful of giant flares. There simply haven't *been* very many
since good data started to be available in the late 1950s; typically there
are only one or two giant flares in each sunspot cycle. Possibly we have
not seen them at their very worst. (There is limited historical data a
bit farther back, from things like radio-propagation disturbances, which
suggest that some of the flares of the 1940s may have been larger than any
since.)
--
The good old days | Henry Spencer henry@spsystems.net
weren't. | (aka henry@zoo.toronto.edu)
From: henry@spsystems.net (Henry Spencer)
Newsgroups: sci.space.tech
Subject: Re: Cosmic Rays, Van Allen Belt, and Radiation Shielding
Date: Thu, 18 Nov 1999 23:02:03 GMT
In article <38343E25.9D5A553A@sig.net>,
George Edward Purdy <slogan@sig.net> wrote:
>How and when did these "cosmic rays" and dangerous particles
>in the Van Allen Belt get discovered?
Cosmic rays are not in the Van Allen belts; they are a different matter,
and a much less serious one unless you're talking about years of exposure.
(Oh yes, and despite their name, which is historical, they too are
high-energy particles, not rays.) They were known well before spaceflight,
since the particle showers from high-energy cosmic rays hitting Earth's
atmosphere are detectable at ground level.
The Van Allen belts were discovered and mapped by the early satellites,
with the initial discovery made by Explorer 1 in early 1958.
>What kinds of radiation are threats to astronauts in space?
One minor subtype of cosmic rays is thought likely to slowly damage living
cells, possibly leading to excessive nerve damage and substantial risks of
cancer if exposure lasts several years.
Giant solar flares (warning, I oversimplify slightly), which happen a few
times per 11-year solar cycle, produce a lot of high-energy radiation in a
short burst. The biggest would be certain death to unshielded astronauts,
and serious even in a thick-skinned spacecraft like the Apollo CSM.
Neither is generally very significant unless you are outside Earth's
magnetosphere. The Apollo crews were out too briefly for cosmic rays to
be a real problem, and they took their chances with giant flares.
The trapped particles in the Van Allen belts are a serious problem for
long exposure or in the absence of significant shielding, but are not
serious for relatively brief exposure in a thick-skinned spacecraft.
>How did our researchers find materials to shield the capsule
>and astronauts from these dangerous elements?
>How did our scientists test these materials? What are they?
>Special alloys? Single crystal metals?
Nothing magic is required. Simple *mass* is all it takes, although some
kinds are a bit better than others. The Apollo CSM used its heatshield
and other equipment -- the crew were basically in the center of the CSM,
with everything else around them, and essentially no mass had to be added
specifically as shielding. The Apollo 4 and 6 unmanned tests went out
through the belts and then came back in, carrying radiation instruments in
the cabin to confirm this:
These missions show that there will be no biological hazard
associated with passage through the trapped radiation belts
during the translunar and trans-Earth phase of Apollo lunar
missions, providing that there are no further high-altitude
nuclear tests and that astronaut activity is confined to the
command module during belt passage.
("Apollo 4 and 6 Radiation Analysis", White&Hardy, J. Spacecraft 7.7, July
1970, originally presented at a conference in January 1969.)
Early high-altitude nuclear tests dumped a lot of particles into the
belts, considerably increasing radiation intensities. Spacesuits provide
little shielding, as did the fairly thin-skinned Lunar Module, hence the
restriction to the Command Module.
>What materials do our space missions use today?
Today's missions have little radiation problem, since none go beyond low
Earth orbit. Radiation exposure might be slightly increased at times of
giant flares, but otherwise is no great concern. For shielding, they rely
on the same approach used by Apollo, putting the crew in the middle of a
thick-skinned spacecraft. When giant flares seem likely, spacewalks are
avoided and preparations are made to bring crews down quickly if it turns
out to be necessary (which has never happened).
--
The space program reminds me | Henry Spencer henry@spsystems.net
of a government agency. -Jim Baen | (aka henry@zoo.toronto.edu)
From: henry@spsystems.net (Henry Spencer)
Newsgroups: sci.space.tech
Subject: Re: Cosmic Rays, Van Allen Belt, and Radiation Shielding
Date: Thu, 25 Nov 1999 04:20:11 GMT
In article <81hf5j$9c4$1@nnrp1.deja.com>, <wmook@my-deja.com> wrote:
>We did not shield the Apollo astronauts in any meaningful way.
>The Apollo flight occurred during the famous Maunder Minimum in sunspot
>cycles BECAUSE we didn't have sheilding and we knew it.
Uh, no, I'm afraid this is not right.
First, the Maunder Minimum was from 1645 to 1715, somewhat before Apollo.
Second, solar cycle 20 *peaked* in 1968-69, just when Apollo did. There
was some early criticism of Apollo, in fact, for planning to have crews
outside the magnetosphere at a time when a solar maximum could reasonably
be expected. There was a giant solar flare between Apollos 16 and 17.
>The CM offerred some scant sheilding, true. But not enough. Any
>shielding offerred was not by design!
Yes and no -- while it wasn't specifically meant as radiation shielding,
it was most definitely and deliberately used for that. That is, the
designers knew they didn't have to add shielding because they already
had quite a bit of it. If memory serves, the CSM averaged about 8g/cm^2
of shielding, which is quite significant. (Remember that the SM helped!)
>...Many of the moonmen have already died of diseases that is
>likely related to their radiation exposure received during their travels
>in space.
I'm sorry, Bill, but this is utter nonsense. Most of the lunar astronauts
are still alive and in good health. (Indeed, John Young flew two lunar
missions and is still nominally an active astronaut.) Out of twenty-odd
lunar astronauts (not all of them moonwalkers, by the way, which is why
the count may sound high), I count six dead, including two heart attacks
and one motorcycle crash... and those guys are almost all in their sixties
and seventies now.
>Most of those spent around 8 days above the Earth's radiation
>sheild. A mission to mars will expose crews to hundreds of times more
>radiation than that received by the moon men.
There are only two real problems here. One is the occasional giant solar
flare; a "storm shelter" area will handle that. The other is the
long-term exposure to heavy cosmic rays, which over a period of *years*
may damage enough nerve cells and cause enough increase in cancer chances
to be worrisome.
>The problem is a serious one. On the surface of the moon you'd need
>about 10 feet of dirt above each square foot of moonbase to reduce the
>AVERAGE radiation levels on the moon to Earth background levels.
Note that the thickness doesn't indicate that the radiation level is
actually particularly high. Something close to that depth is needed for
long-stay bases because the heavy cosmic rays are hellishly penetrating
and tend to throw off showers of secondary radiation when you do stop
them, so bringing the radiation level all the way down is difficult. For
periods of weeks or months, though, you can simply accept the dose; the
rate is not all that high, it's just that it keeps on accumulating.
--
The space program reminds me | Henry Spencer henry@spsystems.net
of a government agency. -Jim Baen | (aka henry@zoo.toronto.edu)
From: henry@spsystems.net (Henry Spencer)
Newsgroups: sci.space.tech
Subject: Re: Cosmic Rays, Van Allen Belt, and Radiation Shielding
Date: Fri, 26 Nov 1999 02:40:02 GMT
In article <383D3B70.E7DD55DF@NOSPAM.erols.com>,
rk <stellare@NOSPAM.erols.com> wrote:
>...flying through the south atlantic anomaly doesn't help. for gemini,
>where they had some experiments (like a cosmic ray experiment) that were
>sensitive to radiation, they would choose a different path, so that the
>background wouldn't be too high.
Also, the one or two Geminis which used the Agena engine to boost the
capsule to a higher altitude chose the timing of this carefully so that
the high apogee avoided the SAA.
>as far as the shielding not being enough, there were radiation detectors and
>the dose would be known. i have the reports for gemini, not apollo, perhaps
>h.s. has that.
I don't have the actual reports, but I do have the total-dose data, from
the 1989 NCRP report on space-radiation guidelines. The numbers weren't
particularly high; if I'm converting the numbers right, the worst Apollo
crew took about 1 REM... and there have been a couple of high-altitude
shuttle flights which took nearly as much.
--
The space program reminds me | Henry Spencer henry@spsystems.net
of a government agency. -Jim Baen | (aka henry@zoo.toronto.edu)
Newsgroups: sci.space.shuttle
From: henry@spsystems.net (Henry Spencer)
Subject: Re: Manned lunar vehicle launching from shuttle?
Date: Tue, 12 Sep 2000 02:54:40 GMT
In article <39BD08DC.AF8D7DD4@videotron.ca>,
JF Mezei <jfmezei.spamnot@videotron.ca> wrote:
>At what altitude is the protective magnetosphere in normal regions ? I assume
>that over the south atlantic, is it somewhat lower than the ~350km (~200nm) ?
There is no sharp lower boundary. A reasonable rule of thumb is that in
most areas, it gets serious around 800-1000km. The South Atlantic Anomaly
is noticeable even at normal orbital altitudes, though.
>In Apollo 13 (the movie), there is mention of how unshielded the LEM is. Since
>it would be outside of the earth's protective magnetosphere, wouldn't the
>astronauts not have been serously irradiated then ?
For normal LM operations, yes, barring giant solar flares (the emergency
procedure for which was to return to the CM as quickly as possible).
>(and how about the CM ?
>Did it have shielding to protect occupents while it was outside of the earth's
>magnetosphere ?
No deliberately added shielding, but since the crew was more or less in
the middle of a massive collection of heatshield and equipment, there was
quite a bit of shielding provided. (The emergency procedure for a giant
flare, once everybody was back in the CM, was to point the CM down at the
lunar surface, and wait it out. There was rather less radiation coming
from below, due to the Moon getting in the way. The SM, the main CM
heatshield, and various layers of structure and storage provided
considerable extra shielding rearward, so one pointed that end at the sky,
where the radiation was worst.)
--
Microsoft shouldn't be broken up. | Henry Spencer henry@spsystems.net
It should be shut down. -- Phil Agre | (aka henry@zoo.toronto.edu)
Newsgroups: sci.space.shuttle
From: henry@spsystems.net (Henry Spencer)
Subject: Re: EVAs and flares
Date: Wed, 18 Oct 2000 14:51:30 GMT
In article <Vg9H5.951$h77.516551@news.uswest.net>,
Doug... <dvandorn@uswest.net> wrote:
>...If I recall properly, in the event of a major
>solar flare while a LM was landed, the drill was to get the LM crew back
>into orbit ASAP and into the CSM, and then position the CSM with the bulk of
>the SM between the CM and the sun. And to maintain that attitude for as
>long as the radiation flux continued at dangerous levels.
Almost exactly right. The one small error is that the particle radiation
is not very directional -- think cloud, not hailstorm -- so pointing the
SM at the Sun isn't useful. However, in low lunar orbit you've got the
bulk of the Moon blocking off almost half the sky. So you point the least
shielded side of the CSM *down*. The least-shielded side turns out to be
some sort of compromise between the nose and the windows: the SM
contributes some shielding (although its tanks are nearly empty), the
heatshield is thicker on the base, and there is more equipment inside the
CM on the non-window side of the cone.
>What keeps occurring to me is that the Earth's magnetic field changes
>polarity every 70,000 to 100,000 years... I just wonder what
>will happen to the objects (and people) in LEO when this happens?
It's a slow process, so there will be plenty of time to prepare. There
may still be some shielding during the transition, too, because the field
probably doesn't die out -- rather, it becomes weak and confused, and
gradually re-establishes itself pointing the other way.
>And consider, since we don't have exact timing on these polarity
>reversals, and because the last one happened sometime roughly 60,000 to
>70,000 years ago, we might be due for one any time now...
Actually, there is speculation that Earth may be in the early stages of a
field reversal now. But accurate knowledge of the details of the field is
too recent to get a good sense of the trends, and for that matter we don't
understand the reversals well enough to know exactly what to look for.
--
Microsoft shouldn't be broken up. | Henry Spencer henry@spsystems.net
It should be shut down. -- Phil Agre | (aka henry@zoo.toronto.edu)
Newsgroups: sci.astro,alt.sci.planetary,alt.astronomy
From: henry@spsystems.net (Henry Spencer)
Subject: Re: STARDUST Spacecraft Encounters Solar Flare
Date: Wed, 22 Nov 2000 23:28:04 GMT
In article <n0BsiGAxgDH6EwfK@brox1.demon.co.uk>,
Eric Crew <eric@brox1.demon.co.uk> wrote:
>>STARDUST SPACECRAFT ENCOUNTERS SOLAR FLARE
>
>Please note, Henry (Spencer) and others there can be large flows of
>positive (protons) from the Sun, as well as negative. Not just a plasma
>containing equal numbers of positive and negative particles.
And your evidence for this is...? Quite apart from the perils of trying
to use press releases (!) as scientific evidence, they mention the protons
(as do the scientific papers about solar proton events) simply because the
protons have far more significant effects than the electrons. It doesn't
mean the protons are coming out unaccompanied by electrons.
--
When failure is not an option, success | Henry Spencer henry@spsystems.net
can get expensive. -- Peter Stibrany | (aka henry@zoo.toronto.edu)
Newsgroups: sci.space.history
From: henry@spsystems.net (Henry Spencer)
Subject: Re: Radiation Exposure
Date: Thu, 8 Feb 2001 17:01:37 GMT
In article <sol38t83h7rg0k8gsc2lp57s1h07nmrhu0@4ax.com>, Graham <-> wrote:
>>Correct... but note that those are *extremely* rare, only a few per
>>11-year solar cycle.
>
>I think a big class X event like this is about 1% of all flares.
Class X flares and giant flares are different things. The giant ones
don't have a specific designation, as far as I know.
>For 250 flares, that is 2.5 class X's, 25 to 50 class Ms.
>According to NOAA figures, there were 713 in July 1971, and 673 in
>August 1971. This seems like more than a few to me.
You're still confusing giant flares with the larger of the more ordinary
ones. Also, do note that despite sloppy terminology, the real issue is
not the *flares* but the solar proton events, which tend to occur together
with the flares but not always. The X/M/etc. classification of flares is
based (as I recall) on their X-ray emission, which does not tell you a lot
about the size of any associated proton event. It's the protons that
matter most.
There was *one* giant flare during the entire operational period of
Apollo, the one in August 1972, between Apollos 16 and 17. The two next
largest, one in early 1971 and another in mid 1972, were more than an
order of magnitude smaller by the measure that counts (highly-energetic
particle output).
>>This is an interesting fantasy, but the numbers have no relation to
>>reality. Only the rare giant flares involve significant radiation dose.
>>Normal-sized flares cause insignificant radiation exposure.
>
>To reach your 11rem that you mention below, with 250 flares, you are
>looking at an average of 0.044 rem per event.
>In my view, am SPE (Solar Particle event) of 0.044rem is a fantasy.
It's reality. Deal with it. Do remember that it's only the fairly
energetic particles that matter, especially with the crew inside the
CSM (which actually had quite a bit of shielding, equivalent to about
8g/cm^2 for typical flare spectra).
>If we are generous, and say that each flare on average was 1/1000th of
>the power of the 1972 event...
You apparently have no concept of the range of sizes involved. The
difference between giant flares and ordinary ones is *much* larger than
that. There were only about a dozen flares in that whole solar cycle
which were as *big* as 1/1000th of the August 1972 flare (by energetic
particle output).
>>And small radiation exposures. The highest actual dose taken by an Apollo
>>crew was about 11rem, on Apollo 14.
>
>These small radiation exposures are interesting. I suppose that you
>remember Sputnik 2 in Nov 1957 going off the scale with radiation??
The early spacecraft instruments were designed to measure the quite small
amounts of radiation expected, and were often swamped by the unforeseen
effects of the Van Allen belts. The Soviets got only a few days of
radiation data from Sputnik 2; are you sure you aren't confusing this with
later events?
That aside... There were half a dozen giant flares in solar cycle 19
(peaking in the late 50s), and a couple of dozen near-giants. This did
worry Apollo's planners, but cycle 20 unexpectedly turned out to be much
less violent -- the difference is quite striking on a plot (see, e.g.,
page 50 of "Lunar Sourcebook", ed. Heiken et al).
>Dr. James Van Allen himself commented in 1959 that "Our planet is
>encircled by two zones of high energy particles, against which space
>travellers will have to be shielded".
He was right, and this was a significant design issue for the Apollo CM,
but the combination of the heatshield, the masses of equipment around
the interior, and the SM covering the rear, provided adequate shielding.
Inside dose rate in the worst region, 800-2400 nmi, was a bit over 1rad/hr
according to the radiation instruments on the Apollo 4 and Apollo 6 unmanned
test flights. This was deemed acceptable, given that the spacecraft went
through that region very quickly, provided the crew remained in the CM and
there were no more high-altitude nuclear tests. (See the paper on this in
the July 1970 Journal of Spacecraft and Rockets.)
>In fact, this wasn't enough for the US, for after three attempts in
>1958 with operation Argus, the US tried doing Starfish Prime.
Those were two completely different programs. The "attempts" of Operation
Argus were all successful, using quite small bombs to explore the physics
of the belts. Starfish Prime was a repetition of Starfish (which was a
launch failure) as part of Operation Dominic, which did much larger tests
to assess the general effects of nuclear explosions in space.
>8th July 1962 at 9:00gmt a megaton device was exploded at 248miles up
>near Johnston Island in the Pacific, which created a totally new
>radiation belt at about 4,500 miles up. This belt is 25 to 50 times
>stronger than the other belts.
It *was*. It isn't any more. The high-energy electron flux in the inner
belt was up about 100x immediately thereafter, and the Starfish electrons
dominated the natural inner-belt electrons for about five years, were
easily detectable for ten years, and could be noticed by careful data
analysis for about fifteen years.
>You may have seem on TV documentaries, that sometimes the laptops in
>MIR would crash, as the station brushed up near the inside ring, or a
>solar event got through.
Minor hiccups in computer operation are routine during passage through the
South Atlantic Anomaly, the region where the inner Van Allen belt dips
down closest to Earth. (In fact, errors detected in satellite computer
memories have been used to map the SAA.) And a high-inclination satellite
like Mir does see some solar effects, since the natural shielding of the
magnetosphere gets weaker toward the (magnetic) poles.
>1957 was the watershed year, when NASA realised that space travel
>would be rather more of a problem than they had thought.
The problem wasn't actually known until 1958 and wasn't really well
understood for another year or so, as data trickled in from infrequent
satellite launches. After which, it was just another engineering problem,
and not a severe one.
>How do you think that the astronauts got such a small exposure,
>consistent with the level of radiation present in LEO? I would be
>interested in any explanations..
The level of radiation simply isn't as high as you think, even in
deep space.
--
When failure is not an option, success | Henry Spencer henry@spsystems.net
can get expensive. -- Peter Stibrany | (aka henry@zoo.toronto.edu)
Index
Home
About
Blog