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Subject: SPACE Digest V10 #426

SPACE Digest                                     Volume 10 : Issue 426

Today's Topics:
            Re: Nuclear Reactors in Space
            Re: Nuclear Reactors in Space
             Re: KSC tours (long)
       Re: Scientific value of Apollo (was Re: Motives)
            Re: Nuclear Reactors in Space
     Re: Why did Solar Max fall but space junk stays up?
               Universal units and SETI
           Re: Pioneer 12 Update - 01/12/90
          reactors in space, active control
            Re: Nuclear Reactors in Space
             Re: Airlocks & Life support
----------------------------------------------------------------------

Date: 14 Jan 90 00:03:40 GMT
From: pacific.mps.ohio-state.edu!zaphod.mps.ohio-state.edu!swrinde!cs.utexas.edu!jarvis.csri.toronto.edu!helios.physics.utoronto.ca!ists!yunexus!utzoo![e-mail]  (Henry Spencer)
Subject: Re: Nuclear Reactors in Space

In article <[e-mail]> [e-mail] (Tim Maroney) writes:
>>On another note,  how would a "cold" reactor kill thousands? My "worst
>>case" doesn't manage this much.
>
>Inhaled plutonium dust is a remarkably effective carcinogen.

Since the current space reactor designs don't use plutonium, this is
a complete non sequitur.  And the shuttle already carries several tons of
strong carcinogens on every mission.
--
1972: Saturn V #15 flight-ready|     Henry Spencer at U of Toronto Zoology
1990: birds nesting in engines | uunet!attcan!utzoo!henry [e-mail]

------------------------------

Date: 13 Jan 90 07:28:40 GMT
From: att!watmath!watserv1!utgpu!utzoo![e-mail]  (Henry Spencer)
Subject: Re: Nuclear Reactors in Space

In article <[e-mail]> [e-mail] (Tim Maroney) writes:
>>Outside of the fact that both use similar fuel I don't see much similarities.
>
>Amazing, he figured it out.

Such a pity that he's wrong, as are you, Tim.  All current RTGs use Pu238;
all current space reactors (and future ones that I know about) use U235.
Completely different isotopes with very different characteristics (and
presenting very different hazards).  They're about as similar as grease
and polyethylene (which are both petrochemicals).
--
1972: Saturn V #15 flight-ready|     Henry Spencer at U of Toronto Zoology
1990: birds nesting in engines | uunet!attcan!utzoo!henry [e-mail]

------------------------------

Date: 13 Jan 90 23:28:34 GMT
From: microsoft![e-mail]  (David LEVINE)
Subject: Re: KSC tours (long)

In article <[e-mail]> [e-mail] (John Roberts) writes:
> - For a really good look at US space hardware and information on the history
>of the space program, it's hard to beat the Air and Space Museum (part of the
>Smithsonian Institution) in Washington, DC. Unlike KSC, it's set up specifically
>for tourists. There's an amazing amount of hardware there, not just rockets
>and space probes, but also airplanes (Wright Brothers' Flyer, Spirit of St.
>Louis, Voyager, X-15, Bell X-1, many war planes), helicopters, balloons,

If you ever get to Pasadena, California check out the displays at JPL.
*Don't* go halfway around the world (or even the country) but if you are\
in Southern California it is worthwhile.  They have very close mockups of
many US probes on display (full size) including Voyager and a Viking
lander.  You can see the Deep Space Network room (usually dark -- when
its busy you won't be allowed near).  You can see the Spacecraft
Assembly Facility (less interesting with Galileo gone but if you wait
a few years you can see one of the new Mariner Mark II probes).

There is also a store that sells some good NASA related stuff.

Remember to call ahead -- I don't know what they will show to an individual
(as opposed to a group) as they are not in the tourist biz.

David Levine

=====================================================
=== The opinions expressed above are entirely mine ==
=== The facts expressed above are probably wrong   ==
=====================================================

------------------------------

Date: 14 Jan 90 00:39:15 GMT
From: zaphod.mps.ohio-state.edu!swrinde!cs.utexas.edu!jarvis.csri.toronto.edu!helios.physics.utoronto.ca!ists!yunexus!utzoo![e-mail]  (Henry Spencer)
Subject: Re: Scientific value of Apollo (was Re: Motives)

In article <[e-mail]> [e-mail] (Nick Watkins) writes:
> Anybody know anything about the TOS upper stage for Mars Observer? Is
>it the Minuteman 3rd stage referred to above?

I don't *think* so; TOS is a commercial development, Orbital Sciences'
original product.  (The market fell out from under them when the shuttle
got out of the commercial-launch business, although there are still a few
customers who want to use TOS on expendables.)

>>... (I'll post more on the
>>Voyager/Viking launcher history when I have a bit more time.)  ...
>Please do post, I for one would be interested ...

I'll try to do this soon.

>Exactly how much can a Titan IV with Centaur send to Mars, then?

I'd have to look up the numbers, but it's something not a whole lot bigger
than Viking.  The sample-return missions I've seen schemes for end up
having to coordinate 3 or 4 TIV/C launches, ugh.
--
1972: Saturn V #15 flight-ready|     Henry Spencer at U of Toronto Zoology
1990: birds nesting in engines | uunet!attcan!utzoo!henry [e-mail]

------------------------------

Date: 13 Jan 90 23:48:19 GMT
From: microsoft![e-mail]  (David LEVINE)
Subject: Re: Nuclear Reactors in Space

>that it uses heavy water as a coolant and moderator to slow the neutrons down,
>increasing the likelyhood of them colliding with the fuel and sustaining the chain
>reaction.  Loss of the coolant results in the neutrons escaping the core
>and the chain reaction stops on its own.  I am not a nuclear expert, and I am
>sure that there are other control systems which regulate the rate of the reaction.
>I am fairly sure that this type of reactor is operational in canada, and that canada
>sells such reactors to other countries.

Last I heard (8 years ago) reactors based on the CANDU  (short for
Canadian Deuterium) design were operating in Canada and actually making
a *PROFIT* (unusual in the commercial nuclear power biz.)

David Levine
=====================================================
=== The opinions expressed above are entirely mine ==
=== The facts expressed above are probably wrong   ==
=====================================================

------------------------------

Date: 13 Jan 90 23:25:06 GMT
From: bfmny0![e-mail]  (Tom Neff)
Subject: Re: Why did Solar Max fall but space junk stays up?

In article <[e-mail]> [e-mail] (Henry Spencer) writes:
>[why do big satellites re-enter but space junk 'stays up'?]
>
>You're assuming that the big birds are high up.  Not always.  Remember,
>Solar Max got a shuttle visit several years ago (the same mission that
>deployed LDEF), and the shuttle just can't get very high.  Space debris
>also lacks big air brakes, aka solar arrays, which most satellites have.

But not LDEF!  Also, LDEF was deployed higher than the shuttle
usually goes, as was Max.

I think the original question was interesting and the answer somewhat
more complex.

A paint flake *is* inherently readier to re-enter than a satellite at
the same altitude.  But there are a couple of special factors.

One (most important), debris is constantly resupplied.  Nearly every
unmanned launch we, the Euros or the Soviets perform (remember the USSR
does the lion's share) is a potential source for debris.  Most booster
separations are done pyrotechnically, which means multiple clouds of
particles exploding outward in space.  When staging is performed
rapidly, the interstage covering of the expended stage is often shredded
by rocket exhaust.  And every so often the Soviets render a dying
military satellite worthless to scavengers by simply exploding it!

Two, many satellites have lots of reboost capability in their
maneuvering rockets.  Their orbits are periodically adjusted to
compensate for drag and tidal effects; you just don't hear about it.
When a satellite has no propulsion (like LDEF) or runs out of fuel (like
Skylab or LDEF) its days are numbered.  Skylab, Max and LDEF all started
out pretty high by manned space standards, which is why they lasted as
long as they did when the fuel ran out.  Unpowered expended stages in
low orbit may only last a few months.

Three, drag is NOT an unchanging force up there!  When the Sun is in the
active part of its cycle the exoatmosphere expands drastically, and
everything -- spacecraft and debris alike -- is swept more intensely by
its tenuous scouring.

>1972: Saturn V #15 flight-ready
>1990: birds nesting in engines

1972: armchair critics scorn NASA
1990: Canada bravely follows :-)

--
The real problem with SDI is     %/    Tom Neff
that it doesn't kill anybody.    /%    [e-mail]

------------------------------

Date: 12 Jan 90 06:22:05 GMT
From: zaphod.mps.ohio-state.edu!samsung!munnari.oz.au!cluster!metro!pta!teti!teslab![e-mail]  (Andrew Phillips 289 8712)
Subject: Universal units and SETI

The following simple idea occurred to me when I was doing Physics II
at Sydney Uni in '78.  I thought that it must also have occurred to
someone else but have never seen it mentioned in any literature
(though I haven't made an exhaustive search).  At first I thought it
was just a curiosity but then I realised that it may be of use in the
search for extraterrestrial intelligence (SETI).

Ignoring for the moment all forces except gravity there are three
units of measurement.  These are usually described as mass, length
and time but any orthogonal set of three would do (such as mass,
speed and time).

I found it intriguing that there are also three dimensioned constants
that depend on the three units.  These are Newton's gravitational
constant (G), Planck's constant (h) and Einstein's speed constant
(c), often referred to as the speed of light.  If you choose values
for the units so that all three constants have the value one in these
units then you have a system of units far more universal than grams,
meters and seconds.

In a book by Carl Sagan, I read that there was some debate as to what
frequencies of radio waves should be scanned in the SETI.  It seems
to me that the best frequencies would be those which have a frequency
(and wavelength) of one in these universal units or a binary multiple
thereof.

The latest theories on the formation of the solar system seem to
indicate that most star systems should have planets.  And most second
generation single stars should have small rocky inner planets and
lots of organic compounds around.  Given this it seems extraordinary
to me that we have not detected other intelligence somewhere nearby
even in this unfashionable western spiral arm of the galaxy. (Maybe we
should ban the playing of cricket :-).  I hope this idea can be of use.

Andrew.

P.S. it is also interesting that this idea can be extended to other
areas of physics.  For example, in electromagnetism you have the unit
of charge and the constants mu-zero and epsilon-zero (which along
with c are mutually dependent).  Units of charge can be chosen so
that mu-zero and epsilon-zero are one.
--
Andrew Phillips ([e-mail]{.au}) Ph. +61 (Aust) 2 (Sydney) 289 8712

------------------------------

Date: 13 Jan 90 07:53:19 GMT
From: att!watmath!watserv1!utgpu!utzoo![e-mail]  (Henry Spencer)
Subject: Re: Pioneer 12 Update - 01/12/90

In article <[e-mail]> [e-mail] (Lord Snooty @ The Giant Poisoned Electric Head       ) writes:
>interesting data - ditto giotto.
>trouble is, i have no idea at all where these two craft are located!

Pioneer 12 is also known as the Pioneer Venus Orbiter, in orbit around Venus.
Giotto is loose in the inner solar system, in an orbit which will bring it
fairly close to Earth this summer.  (Serious consideration is being given
to retargeting it for another comet flyby, assuming its instruments are in
sufficiently good shape to make this worthwhile.)
--
1972: Saturn V #15 flight-ready|     Henry Spencer at U of Toronto Zoology
1990: birds nesting in engines | uunet!attcan!utzoo!henry [e-mail]

------------------------------

Date:         Sat, 13 Jan 90 15:39:11 EST
From: Kenneth Ng <[e-mail]>
Subject:      reactors in space, active control


:Received: by ORION (Mailer R2.04) id 4812; Sat, 13 Jan 90 06:38:01 EST
:Comments: To: [e-mail]
:
:A nuclear reactor does not need active reaction damping controls. In fact
:this is a poor design decision and is responsible for many of the problems
:nuclear reactors have. Sweden is implementing reactors with active controls
:which sustain the reaction. In the absense of such controls the reaction
:passively stops. The US is studying such reactor designs.
:
:John L. McKernan.                                                  [e-mail]

Um, most nuclear reactors in the United States have passive controls.
For example, if the temperature rises, the reaction rate slows due to
the laws of physics, not an active control mechanism.  In BWR reactors
when more steam is generated, the lower density of water lowers the
effectiveness of the water slowing down the neutrons, thus lowering
the number of neutrons that can substain the reaction, thus slowing
the reaction down.

The only reactor design I know of that has positive feedback is the
Chernobyl reactor.  Note: my reactor design books dated from the
early 80's, so my comments may be out of date.

------------------------------

Date: 14 Jan 90 00:13:30 GMT
From: microsoft![e-mail]  (David LEVINE)
Subject: Re: Nuclear Reactors in Space

In article <[e-mail]> [e-mail] (Andrew J Hasara) writes:
>Keywords:
>
>a few small calories of heat added.  The processing for this fuel produces
>toxic wastes, and improper handeling has caused millions in damage, and
>widespread ecological damage is caused every year because of limited
>releases of this substance.

>This substance is crude oil.  Without it, most people couldn't get to work each
>day.  Most people use petrolium distilants like methane (a natural distalant)
>to heat thier homes.  Jet-A is a type of Kerosene.  Carbon Monoxide is a
>mutagen (I'm unsure on this, but I seem to remember something like that from
>High School Biology), and I at the least destroys the usefulness of hemoglobin.
>
>People doen't listen about the danger of petrolium because they see more good
>than bad.  Think about it, WHAT DOESN'T HAVE A DOWN SIDE?  Everything has some
>problem, and the potential for better things outweighs many of those problems.
>Even in the use of nuclear power sources.

I agree that everything has a down side.  (In fact, the energy technology
that may have the worst DIRECT impact on the enviornment is hydroelectric).
However, the down sides of fossil fuels and of nuclear-type fuels are
a bit different.  The mortality and morbidity of fossil fuels are mostly
very widespread but incremental.  For nuclear energy related processes,
single point failures are a much bigger concern.

Sure, the Alaska oil spill was terrible, but it will not result in the
death of many *people*.  A serious nuclear accident *could* result in
the deaths of many more people than the worst fossil fuel disaster
(even an LPG laden tanker running into the dock in Long Beach -- BIG
EXPLOSION!).  I'm not saying that the potential for such nuclear
accidents makes it a more dangerous technology overall, just that the
risk analyses of nuclear vs. fossil fuel cycles are different.

This is a big reason (IMHO) why the anti-nuclear forces are much more
hysterical and outspoken than anti-fossil fuel forces.

David Levine

=====================================================
=== The opinions expressed above are entirely mine ==
=== The facts expressed above are probably wrong   ==
=====================================================

------------------------------

Date: 13 Jan 90 07:59:41 GMT
From: swrinde!cs.utexas.edu!wuarchive!texbell!nuchat![e-mail]  (Steve Nuchia)
Subject: Re: Airlocks & Life support

In article <[e-mail]> [e-mail] (John Kallen) writes:
>see how it would work. Is air sucked out of the airlock prior to the
>opening of the outer hatch before EVA exit, or is it dumped in space when
>the hatch opens?

Probably dumped, since large (fast) effective vacuum pumps are heavy,
but I don't know for sure.  The weight of volatiles lost for a bunch
of EVA cycles would not equal the weight of the pump plus the fuel
to run it.

>In the former case, what kind of mechanism would be required? Is the
>evacuation of the airlock the activity that makes EVAs so lengthy timewise?

No.  The atmosphere in most spacecraft is an O2 N2 mix, approximating
normal air in composition and pressure.  This is done for a combination
of physiological and safety reasons -- most notably, the flamability
of most materials increases rapidly with increasing percentage oxygen.

(This surprised me, but in fact over the familiar temperature/
pressure/composition regime the oxygen/nitrogen ratio seems to be
more important than the partial pressure of oxygen in determining
flamability)

The EVA suits are designed to use a low-pressure oxygen atmosphere.
The low pressure so the joints can me moved by a mortal human, and
pure oxygen so the lucky stiff gets enough.  (Physiological oxygen
requirments are satisfied by partial pressure.)

You've probably heard of the "bends" -- decompression sickness --
in the context of SCUBA diving.  What happens is that gasses,
mostly nitrogen, disolve in your blood and body tissues in proportion
to their partial pressure in the stuff you are breathing.  If the
absolute pressure drops below the vapor pressure of the disolved
gasses they "fizz" in the blood and tissues.  If an astronaut
went directly from 14 PSI 80% N2 mix to 3 PSI 100% O2 too quickly
he would get bent.

So the EVA preparation includes a long "pre-breathe" period in
which the EVA personnel breathe pure oxygen at cabin pressure.
This used to be done in the EVA suit, but recent tests have been
conducted using the escape suit helmet, allowing them to be both
comfortable and useful.  The pre-breathing allows
the nitrogen to dissipate to a safe level before the decompression
in the air lock.  This is what makes spur-of-the-moment EVAs
impossible.

>with air when it is manned? How long can they survive only by recycling with
>LiOH(I think?) before they absolutely need more oxygen (disregarding food

Lithium Hydroxide is used to "scrub" the air, along with activated
charcoal.  It does not "recycle" anything, it *removes* CO and
maybe CO2 and some other light organics that the charcoal doesn't
get.  I'm a little light on the exact capabilities of these systems,
but I do know that the day I spent on a sub with one (out of three)
scrubbers down wasn't real pleasant, so they seem to do something :-)
--
Steve Nuchia          South Coast Computing Services      [phone]
"If the conjecture `You would rather I had not disturbed you
 by sending you this.' is correct, you may add it to the list of
 uncomfortable truths."   - Edsgar Dijkstra

------------------------------

End of SPACE Digest V10 #426
*******************