Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V10_2/V10_201.TXT

Internet Message Format | 1991-07-08 | 17KB

Return-path: <[e-mail]>
X-Andrew-Authenticated-as: 7997;andrew.cmu.edu;Ted Anderson
Received: from beak.andrew.cmu.edu via trymail for +dist+/afs/andrew.cmu.edu/usr11/tm2b/space/[e-mail] (->+dist+/afs/andrew.cmu.edu/usr11/tm2b/space/space.dl) (->ota+space.digests)
          ID </afs/andrew.cmu.edu/usr1/ota/Mailbox/oZIcSTi00VcJ4DKU4E>;
          Sat,  4 Nov 89 01:54:24 -0500 (EST)
Message-ID: <[e-mail]>
Reply-To: [e-mail]
From: [e-mail]
To: [e-mail]
Date: Sat,  4 Nov 89 01:53:20 -0500 (EST)
Subject: SPACE Digest V10 #201

SPACE Digest                                     Volume 10 : Issue 201

Today's Topics:
              Re: Fragile Space Shuttle
         Re: Galileo and the proposed asteroid flybys
             Re: PowerSat Options
          RE: Payload Canister Investigation... ;-)
            Advice?? (asking for)
         Re: Powersat options II: Magnetism?
             Re: PowerSat Options
               Venus atmosphere
            Re: Moon Colonies / Ant Tanks?
    Re: Balloon Launch attempt of a High Power Rocket (40 Miles).
----------------------------------------------------------------------

Date: 2 Nov 89 05:58:47 GMT
From: bfmny0![e-mail]  (Tom Neff)
Subject: Re: Fragile Space Shuttle

In article <[e-mail]> [e-mail] (Nutsy Fagen) writes:
>        Okay, another question for you.  Every time the shuttle goes up or
>comes down, I read about how just about every system is checked, removed,
>replaced, etc.  I can understand a thorough checkout, and the fact that
>space travel is, to say the least, a risky business, but how much of what
>NASA does for turnaround would be considered unneccesary in 10-15 years
>(Provided the same shuttle design is still running).
>        Few of us have a problem with a commercial plane ride in bad weather,
>yet we read that they can't even roll the shuttle to the pad because of rain!
>This also reminds me of just about every nut and fastener being traceable to
>who installed it, when, where it came from, etc.

Even commercial transport requires thorough checkout.  There just aren't
any Public Affairs Offices keeping you informed on the maintenance being
done on the 747 you'll be flying later in the week.

The only time you hear about aircraft checkout and maintenance is when
someone FORGETS or slacks off, and then it's a sidebar to the body count.

The shuttle is more fragile than an airliner, of course, but that's
because we ask it to do much more violent things.  An airliner's metal
skin may laugh at raindrops, but reentry heat would vaporize it.

My prediction is that we will never be allowed to stop checking spacecraft
with a fine toothed comb.  What we can hope to do is make components
more reliable, so they require less swapping out; and to budget a stack
of hot spares for the cases where they still must be swapped, rather than
have to cannibalize other spacecraft.
--
Knowing *when* to optimize is just   >>>/     Tom Neff
  as important as knowing *how*.       /<<<   [e-mail]

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

Date: Thu,  2 Nov 89 00:05:15 PST
From: Peter Scott <[e-mail]>
Subject:  Re: Galileo and the proposed asteroid flybys
X-Vms-Mail-To: EXOS%"[e-mail]"

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

Date: 2 Nov 89 14:28:55 GMT
From: rochester![e-mail]  (Paul Dietz)
Subject: Re: PowerSat Options

In article <[e-mail]> [e-mail] (Leonard Erickson) writes:

>My comment re the 15 Gigawatts was because I was amazed that anyone would
>think a 15 *megawatt* satellite would be of any use. Density beamed to
>Earth is low.

>Would it be possible to refocus the beam to something tighter at "short"
>ranges? I agree that a several mile dai. atenna is a wee bit vulnerable.

Simple physics lesson...

In a diffraction limited system, the product of the diameters of the
transmitter & receiver is proportional to the product of the length of
the beam times the wavelength of the radiation.  For 10 cm microwaves,
this product is .1 m x 4e7 m = 4e6 m^2.  If the transmitter is maybe
a km across, the beam at the earth will be several km across.  There
is no way to avoid this.

If you go from 10 cm to 1 micron radiation, the product goes down
by a factor of 10,000 to 400 m^2.  The diameter of the transmitter
and receiver can be reduced by factors of 100, so, at constant power
density, the beam power goes down by a factor of 10,000.  If the original
microwave system had a power of 15 gigawatts, the laser system has
a power of 1.5 megawatts.  However, the power density is still < sunlight,
so a weapons system powered by such a beam would be as vulnerable as
a solar-cell powered weapons system (which is to say, very vulnerable).

You could gang the beams from N independent solar-pumped lasers together;
even if they add incoherently it would make the beam N times more intense.

About using power from powersats to energize weapons: wouldn't it be
easier to generate the power *on the ground* and beam it up?  The
transmitter is much easier to build and maintain, and we have hundreds
of gigawatts of generating capacity already available.  Indeed, I've
sometimes thought that the best way to power a lunar base is to use a
large earth-based laser and a series of mirrors in orbit.

    Paul F. Dietz
    [e-mail]

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

Date: Thu, 2 Nov 89 11:28:22 edt
From: Thomas Lapp <[e-mail]>
Subject: RE: Payload Canister Investigation... ;-)

> Date: 26 Oct 89 22:51:20 GMT
> From: trident.arc.nasa.gov![e-mail]  (Peter E. Yee)
> Subject: Payload Canister Investigation Update (Forwarded)
> [...]
>           There is minimal damage to the test weight.

Well, I for one am glad to hear that the 20-ton slab of concrete used
as the test weight did not undergo any serious damage.  I know that
the expense of repairing (or, horrors, replacing) the slab would have
been enourmous ;-)

(tongue firmly in cheek)

                         - tom
--
internet     : mvac23![e-mail]  or  [e-mail]
uucp         : {ucbvax,mcvax,psuvax1,uunet}!udel!mvac23!thomas
Europe Bitnet: THOMAS1@GRATHUN1
Location: Newark, DE, USA
Quote   : Virtual Address eXtension.  Is that like a 9-digit zip code?

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

Date: 3 Nov 89 00:22:49 GMT
From: psuvm![e-mail]  (Amy Antonucci)
Subject: Advice?? (asking for)

I was wondering if anyone out there could give me advice on how
to get on the right track so that I may be involved in the space
program as a career.  I'm not sure what I want to do, but I don't
expect to make it in the astronaut program.

I'm a freshman at Penn State, and I've chosen an astronomy-physics
double major.  I don't particularly care to go into engineering, but
I will if it means more of a chance with NASA. (I'd like *some*
electives).  I've also considered AFROTC.

Comments? Advice? Any would be greatly appriciated. Thanks.
-------
"You know, MacGyver, that's why you're so hard to beat.
Nobody knows what you're doing next, including YOU"- Murdoc

Amy Antonucci [e-mail]

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

Date: 1 Nov 89 19:32:31 GMT
From: hpfcso!hpfcdj![e-mail]  (Bob Myers)
Subject: Re: Powersat options II: Magnetism?


So far I've seen four responses here that didn't have diddly to do with
the original idea - namely, magnetism used to deliver power from powersats.
(Yes, we're running "notes" here - howdjaguess?)  At any rate, it's time
for SOMEBODY to respond to this idea.  Being a former inmate at the Red Brick
Home For Engineers-to-be, here goes:


Assuming that you're in the EE program there, may I ask if you've taken
EE311 yet?  If so, please haul out your text and check your proposal against
the laws of electromagnetism.  There are some very good reasons why EM
radiation - in this specific case, microwaves - is the only available means
for "wireless" power transmission.  Your proposal is certainly a creative
idea, but it simply isn't workable.

(And if you haven't had 311 yet, MAKE SURE you get it on your schedule
as SOON as possible!  Is Prof. Bill Hayt still teaching this class?  If so,
make EVERY EFFORT to get into HIS class - accept no substitutes!!!)

Some specific questions for you to consider:

How does the strength of a magnetic field vary with distance?

Is it possible to vary a magnetic field without producing a varying electric
field (and so actually using EM radiation)? Can a magenitic field *by itself*
transmit power over a distance (without magnetic coupling as in a
transformer, which isn't really "over a distance" anyway)?

What would the "transmitter" of such a field look like?  What would the
"receiver" look like?  How closely coupled would they be?  What would the
efficiency of such a system be?  (Specifically, what physical dimensions
would be required for this to be usable?)

Why are microwaves the best choice for power transmission?  Why not lower
frequencies?  (For example, why isn't the AM radio band being considered
for power transmission?)  Why did you choose "50-120Hz" for the frequency of
your "varying magnetic field"?


Bob Myers  KC0EW   HP Graphics Tech. Div.|  Opinions expressed here are not
                   Ft. Collins, Colorado |  those of my employer or any other
[e-mail]               |  sentient life-form on this planet.

(BSEE Purdue '79)

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

X-Delivery-Notice:  SMTP MAIL FROM does not correspond to sender.
Date: Thu, 2 Nov 89 16:09:30 CST
From: scott <@GACVAX1.BITNET:scott@mcs-server>
Subject: Re: PowerSat Options
Cc: [e-mail]

>Please forgive a novice's ignorance on this subject but I thought I read
>somewhere about a powersatellite collecting solar power and passing it
>down to receiving stations either as microwave or even as a laser beam.  I
>knew that microwave energy was a viable option but what about laser energy?

Mayhaps the Cristics and their friends can get in on this one, also.  Rather tha
   n
doing it directly like this (with [lm]asers), one could charge up large fuel
cells, and drop them, and then those planetbound could catch them and
extract the charge there.  Since it is so obvious that we could have used
15 year fuel cells for the Galileo mission (snort, snort) rather than
psuedo-nuclear power, we should be able to put up very efficient fuel
cells for this.  Of course, after getting this ball rolling, they could come
back three-five years later and scream about these people dropping these large,
energy-filled objects from space, and how if all of the energy was spread out an
   d
released within the nostrils of all of the people on Earth, everyone's nose coul
   d
possibly be blown, thereby causing tremendous misfortune everywhere, and possibl
   y
the collapse of civilization as we know it.


:-):-):-):-):-):-):-):-):-):-):-):-)

Scott

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

Date: 3 Nov 89 02:33:58 GMT
From: cs.utexas.edu!uwm.edu!mailrus!jarvis.csri.toronto.edu!utgpu!utzoo![e-mail]  (Henry Spencer)
Subject: Venus atmosphere

In article <8911022149.AA00914@.next-2.> scott@mcs-server (scott) writes:
>I believe that the reason the Earth has lost much of its heavier elements is
>related to why the gas giants still have most of theirs.  We are lucky enough to
>have a huge moon which is one quarter the Earth's size (1/6 the mass), which
>strips away much of our atmosphere...

This was a popular theory for some years.  Of late it has been "kept alive"
by virtue of featuring prominently in one of Larry Niven's SF short stories.
It is no longer taken very seriously in the scientific community, however.
Earth's atmosphere was not stripped off by the Moon; it was absorbed by
reaction with the rocks and the oceans.
--
A bit of tolerance is worth a  |     Henry Spencer at U of Toronto Zoology
megabyte of flaming.           | uunet!attcan!utzoo!henry [e-mail]

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

Date: 2 Nov 89 18:42:34 GMT
From: uceng![e-mail]  (daniel mocsny)
Subject: Re: Moon Colonies / Ant Tanks?

In article <[e-mail]>, [e-mail] (Dave Burton) writes:
> In article <[e-mail]> [e-mail] (Tom Neff) writes:
> |Oh by the way, if you have to burrow underground to survive in a
> |Moon colony, why bother to go?  Why not just build underground
> |colonies here? ...
>
> That is a rather silly argument for staying home. Similar
> rationale could be used to justify never leaving the country,
> state/province, city, or neighborhood! I mean, I live here,
> why would I want to go anywhere else?

Previous emigrations from one part of the earth to another are nothing
at all like potential emigrations to the Moon. Consider the European
colonization waves to the Americas. Europeans left reasonably
well-developed, but over-crowded areas that lacked in opportunities
compared to the vast stretches of fertile, under-populated (from a
European viewpoint, not necessarily from an Amerind viewpoint),
resource-rich land. While the European pioneers were entering a rather
hostile environment, they certainly did not face any fundamental
environmental obstacles compared to living in Europe. The only
difference was that the Americas lacked infrastructure. European
technology (agriculture, sailing ships, firearms, etc.) obviously
worked as well here as it did there. In many ways life in America
was easier, because of inexpensive land and bountiful resources.
If you had a gun, you had a hard time starving.

Going to the Moon, on the other hand, will be incomparably harder.
The profound lack of resources, especially air and liquid water, means
that life on the Moon will be several orders of magnitude less
convenient than life on the Earth. (And as every marketer knows,
consumers demand convenience over almost anything else.) The closest
terrestrial comparison is probably living in Antarctica, or perhaps on
the ocean floor.  We do not see many people finding this to be
attractive economically or aesthetically.

I do not oppose attempts to establish bases and/or colonies on the
Moon, or in Antarctica or under the oceans. Indeed, I would like to
see more efforts in these directions, though I suspect that our
information and manufacturing technologies must improve labor
productivity by several orders of magnitude before Moon colonies
become feasible. (I expect this improvement to occur, perhaps within
my lifetime.) Only then will people become materially productive
enough to meet the massive overhead required to sustain life on
an airless ball of rock without massive terrestrial subsidies.

Dan Mocsny
[e-mail]

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

X-Delivery-Notice:  SMTP MAIL FROM does not correspond to sender.
Date: Thu, 2 Nov 89 15:49:32 CST
From: scott <@GACVAX1.BITNET:scott@mcs-server>
Subject: Re: Balloon Launch attempt of a High Power Rocket (40 Miles).
Cc: [e-mail]

>But what good is a baloon rocket launch?  When it comes to getting into
>orbit, 90% of the problem is gaining horizontal velocity, not going through
>the atmosphere or gaining altitude.
>--
>Brad Templeton, ClariNet Communications Corp. -- Waterloo, Ontario 519/884-7473

Sorry, they aren't launching anything into orbit.  They just want to go high up
and get some nice pictures.

In another area:

>Can anyone explain why Venus, which is smaller and with weaker gravity
>than Earth, has an atmosphere 100x more dense?  Why didn't it just
>escape?  (Conversly, why is Earth's atmosphere so thin?)
>Greg.
>--
>Gregory Bond, Burdett Buckeridge & Young Ltd, Melbourne, Australia
>Internet: [e-mail]    non-MX: [e-mail]
>Uucp: {uunet,pyramid,ubc-cs,ukc,mcvax,prlb2,nttlab...}!munnari!melba.bby.oz!gnb

I believe that the reason the Earth has lost much of its heavier elements is
related to why the gas giants still have most of theirs.  We are lucky enough to
have a huge moon which is one quarter the Earth's size (1/6 the mass), which
strips away much of our atmosphere.  The gas giants have no comparably sized moo
   n
(think of how big Jupiter's would have to be!), so they get to hold onto most of
their gasses.  Of course, they can hold on much better, and keep lots of hydroge
   n
around, which Venus isn't nearly large enough to accomplish.  Maybe we could gra
   b
a moon for Venus, and orbit it for a couple hundred (thousand) years :-)  How ma
   ny
Energias would this take? :-)

Scott

I don't know where any replies to this would go (if replying directly to me, tha
   t
is).  Please use [e-mail].

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

End of SPACE Digest V10 #201
*******************