Date: 8 Nov 89 04:44:28 GMT
From: mailrus!jarvis.csri.toronto.edu!utgpu!utzoo!henry@uunet.uu.net  (Henry Spencer)
Subject: Re: Radiation exposure for Apollo astronauts

In article <Added.EZITZKu00Ui3MR8U9J@andrew.cmu.edu> GILL@QUCDNAST.BITNET writes:
>... First, what is the exact range of the van Allen belts, and
>what shape are they?

Their shape and size vary somewhat with the shape of Earth's magnetic
field, which is influenced heavily by the solar wind.  The inner belt
is fairly small and sharp; things start to get warm beyond about 1000 km
up and are really hot between about 3000 and 5000.  This is at the
equator; the hot part only extends about 20 degrees north and south,
although things are still warm out to considerably greater latitudes.
The hot part of the outer belt starts at about 15000 km and ends at
about 20000, but again these numbers are at the equator; the shape in
cross-section is a crescent, with the high-latitude "horns" rather closer
to the Earth.  The warm parts extend much further; Clarke orbit is in
the outer fringes of them, and the whole area between inner and outer
belts is somewhat warm.  To avoid the belts, one must stay low, stay
a long way out, or operate only at the extreme poles (which is tricky
since polar orbits do cross the equator).

> How are they generated?

They are solar and cosmic high-energy particles trapped in the Earth's
magnetic field.

> Second, how much exposure did
>the Apollo astronauts receive (I assume the van Allen belts do not extend all
>the way to the moon)?

A quick passage in or out is not a serious problem.  I don't have numbers
ready to hand.

>Third, what are the chances of an astronaut on an
>interplanetary journey from getting nailed by a cosmic ray of sufficient
>energy to harm him/her?

A single cosmic ray is not likely to do anything serious.  There is reason
for concern about cumulative effects, once one starts talking about years
in space.

>Finally, how much are geosynchronous satellites
>affected by cosmic rays/van Allen belts?

Cosmic rays, not significant.  The fringes of the outer belt do have a
significant effect on electronics over time; in particular, the output
of solar arrays drops off as the cells accumulate radiation damage.
-- 
A bit of tolerance is worth a  |     Henry Spencer at U of Toronto Zoology
megabyte of flaming.           | uunet!attcan!utzoo!henry henry@zoo.toronto.edu

From: henry@spsystems.net (Henry Spencer)
Newsgroups: sci.space.tech
Subject: Re: Van Allen Belt Location
Date: Mon, 14 Feb 2000 22:49:24 GMT

In article <889g7u$scl$1@nnrp1.deja.com>,  <cray74@hotmail.com> wrote:
>Are the Van Allen radiation belts largely confined to
>hovering about the equator, or are they spherical shells?

Not exactly either.  Think of them as spherical shells which have slumped
a bit toward the (magnetic) equator.  They're deepest and strongest at the
equator, thin out from there, and are essentially absent at the poles.

>If they aren't shells (hell, I'll go look that up
>on the web now) can anyone tell me to what latitudes
>they extend to?

They don't have sharp boundaries, so this isn't really a very well-defined
question.  They don't stop abruptly, they just thin out.  However, a rough
rule of thumb is that they extend up to about 60deg.

>What thickness of aluminum would be necessary to
>shield against their radiation...

Depends on for how long.  The Apollo CSM had an average of circa 10g/cm^2
of shielding around its crew compartment, and was considered adequate for
a couple of quick passages through the belts.

>...and would that shielding be adequate to protect against a typical
>solar flare?

Typical solar flares are too small to worry about much.  Giant flares
(caution, I oversimplify slightly) are rare but are a serious hazard;
you need 20-40g/cm^2 for effective shelter against them.
--
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: hypothetically, what would it take for the shuttle to leave earth 
	orbit?
Date: Sun, 19 Mar 2000 04:03:23 GMT

In article <q_UA4.1340$L5.21665@newsfeed.slurp.net>,
pdc023 <pdcranz@penn.com> wrote:
>Small point here, but didn't Dr. Van Allen actually theorize their
>existence?  IIRC it wasn't until Explorer that their existence was actually
>proven.

No, it was a considerable surprise when the Explorer data showed rapidly
increasing radiation levels beyond LEO, and the data was originally viewed
with some skepticism.

There *had* been a theoretical prediction of their existence, by Nicholas
Christofilos, but it was highly classified at the time, because he was
working on the idea of creating intense artificial radiation belts as an
antimissile defence.  He noticed that there was a strong possibility of
natural radiation belts, and pointed out that their intensity would have
to be measured before any useful experiments on creation of artificial
belts could be done.

(The three Argus high-altitude nuclear tests of late summer 1958, the
first nuclear explosions in space, were those experiments.  The Argus
bombs were quite small, but they explored the physics well enough to
conclusively establish that it's not feasible -- the electrons don't
persist long enough for multiple explosions to build up strong belts.)
--
Computer disaster in February?  Oh, you |  Henry Spencer   henry@spsystems.net
must mean the release of Windows 2000.  |      (aka henry@zoo.toronto.edu)

Newsgroups: sci.space.shuttle
From: henry@spsystems.net (Henry Spencer)
Subject: Re: hypothetically, what would it take for the shuttle to leave earth 
	orbit?
Date: Sun, 19 Mar 2000 20:00:57 GMT

In article <HL6B4.1913$L5.25992@newsfeed.slurp.net>,
pdc023 <pdcranz@penn.com> wrote:
>Okay, you are obviously better versed in this than me.  What was the
>chronology?  Which came first, Explorer or Dr. Van Allen's explanation?

Van Allen was the Principal Investigator for the Explorer radiation
experiment.  It had been meant for Vanguard, but a variant of the same
design was hastily built to fit in the available space in Explorer.  The
intensity of cosmic rays was known to rise as you ascended within the
atmosphere, and there was great interest in finding out whether this trend
continued.  Everyone was astonished when the instrument's electronics were
saturated by far higher intensities than it had been designed to measure,
and it took a little while for Van Allen and his group to figure out what
must be happening.
--
Computer disaster in February?  Oh, you |  Henry Spencer   henry@spsystems.net
must mean the release of Windows 2000.  |      (aka henry@zoo.toronto.edu)

Newsgroups: sci.space.shuttle
From: henry@spsystems.net (Henry Spencer)
Subject: Re: Manned lunar vehicle launching from shuttle?
Date: Sun, 10 Sep 2000 20:56:26 GMT

In article <39B87660.6956@qut.edu.au>,
John Williams  <j2.williams@qut.edu.au> wrote:
>> They are indeed called the van Allen belts, although I'm not sure about the
>> plural.
>
>Can anybody explain to me why there is a concentration of radiation in
>this region?  Is it a spherical shell around the planet, or aligned with
>the magnetic field somehow, or what?

The radiation is charged particles trapped in Earth's magnetic field, so
the belts follow the field.  The distribution and shape is somewhat
complicated, and in particular there are fairly distinct inner and outer
belts made of protons and electrons respectively, with the differences in
particle properties accounting for the difference in distribution.

The particles' precise origin is not entirely clear, and indeed there are
probably several different sources.  Some of them are probably solar-wind
particles which diffuse inward through the field.  Some of the protons are
probably decay products of neutrons emitted when cosmic rays hit the
atmosphere.
--
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.policy
From: henry@spsystems.net (Henry Spencer)
Subject: ion tugs (was Re: Loan Guarantees for Launch Vehicles)
Date: Mon, 3 Apr 2000 01:05:11 GMT

In article <slrn8efifk.ela.roystgnrNO@mycroft.jones.rice.edu>,
Roy Stogner <roystgnrNO@SPAMiname.com> wrote:
>Of course, existing ion rockets would take on the rough order of a
>month to raise that upper stage, and higher thrust models are on the
>drawing board but not the test stands.  But current launch schedules
>require months of advance notice anyway; compared to expendable
>launchers this may not be a problem...

Unfortunately, it's a problem.  One minor difficulty is that it's still an
unproven approach.  A much more major difficulty is that a good fraction
of that month is spent in the worst part of the Van Allen belts, which is
very hard on the payload (and even harder on the tug, which gets to do it
repeatedly).

The belts are bad enough that there have been serious suggestions to use a
rad-hardened ion tug to carry fuel to refuel a chemical tug up above the
worst of the belts.  That way at least the payload gets a quick trip
through the nasty area.
--
"Be careful not to step                 |  Henry Spencer   henry@spsystems.net
in the Microsoft."  -- John Denker      |      (aka henry@zoo.toronto.edu)

Newsgroups: sci.space.policy
From: henry@spsystems.net (Henry Spencer)
Subject: Re: ion tugs (was Re: Loan Guarantees for Launch Vehicles)
Date: Mon, 3 Apr 2000 15:31:28 GMT

In article <slrn8eg8t3.ela.roystgnrNO@mycroft.jones.rice.edu>,
Roy Stogner <roystgnrNO@SPAMiname.com> wrote:
>>The belts are bad enough that there have been serious suggestions to use a
>>rad-hardened ion tug to carry fuel to refuel a chemical tug up above the
>>worst of the belts...
>
>How high up is the worst of the belts?  This seems like even more
>complexity for less return.

The belts start getting serious at about 1000km up, and the next few
thousand km are the bad part.  I forget just how high the refueling was
supposed to be -- ten thousand?  The system was intended to be reusable,
so the chemical tug needed fuel to come back down too.

>Although, Scientific American claimed that NASA has a 1 megawatt MPD
>thruster developed, and implied that it was more than three times the
>thrust of an ion rocket.  Given a large enough tug, that could get up
>to GEO in a week, and surely there's room for improvement.

Another approach, if you're willing to build a fairly heavy tug, is to
build an ion tug with a shielded cargo bay.  It's not like cosmic rays,
you don't need a lot of shielding to cut the intensity down greatly.

>...One 10 ton stage solely for the LEO burn, attached to a
>second stage (brought up in a separate RLV flight) with the payload
>and rocket for the GEO burn.  A slight adjustment to the Hohmann
>trajectory could reduce it's perigee and burn up the LEO stage
>afterwards.

There is some price for that, in that the stage has to stay alive and
under attitude control until apogee (to do the adjustment cheaply).
Apparently it's possible to pick a transfer orbit such that lunar and
solar perturbations will drive its perigee down into the atmosphere,
although I don't remember details.
--
"Be careful not to step                 |  Henry Spencer   henry@spsystems.net
in the Microsoft."  -- John Denker      |      (aka henry@zoo.toronto.edu)

Newsgroups: sci.space.policy
From: henry@spsystems.net (Henry Spencer)
Subject: Re: ion tugs (was Re: Loan Guarantees for Launch Vehicles)
Date: Mon, 3 Apr 2000 16:33:37 GMT

In article <38E89F4C.E1B34510@ibm.net>, David Cornell  <corne29@ibm.net> wrote:
>How about a hybrid tug that used chemical engines to push itself and its
>payload on the upward leg and used ion engines to return just itself to
>a lower orbit for refueling and a new payload.

Hmm, some merit in that.  Also, you could probably use the ion engines for
the later part of the trip up, after clearing the bad part of the belts.
(This also uses the ion engines to better advantage -- maneuvering with
low-thrust engines in strong gravity fields is wasteful of fuel.)

>I am assuming that the
>tug would mostly be used to move payloads to a higher orbit and only
>rarely to bring payloads down.

A safe assumption.  There's little requirement for payload return from
GSO, at least until launch costs come down a lot.  (At some point it will
become reasonable to bring a satellite down for repair and take it back
up -- or send a repair crew up -- but costs have to come down a lot first.)

>By the way, exactly what damage would the belts do to the tug?  I can
>see that the electronics would suffer, but what else?

The electronics are the main issue, but that's a broad category.  Notably,
if it's solar-powered, the solar arrays will suffer badly.  Control and
power-handling electronics could probably be shielded well enough, but
it's just not practical to shield the big solar arrays, and they are
probably too heavy to replace on every flight.
--
"Be careful not to step                 |  Henry Spencer   henry@spsystems.net
in the Microsoft."  -- John Denker      |      (aka henry@zoo.toronto.edu)