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Subject: SPACE Digest V10 #192

SPACE Digest                                     Volume 10 : Issue 192

Today's Topics:
 Re: Manned Jupiter Mission (was Re: Condensed CANOPUS - August 1989)
             Re: PowerSat Options
         Units of Measure (was fluxgate magnetometer)
 more on the dreaded vcr in space (and can they get dallas up there?)
               Re: PowerSats as Weapons
             Re: PowerSat Options
               Re: Terraforming
                Mass drivers?
       Re: Units of Measure (was fluxgate magnetometer)
             Re: PowerSat Options
----------------------------------------------------------------------

Date: 30 Oct 89 01:55:51 GMT
From: mailrus!jarvis.csri.toronto.edu!utgpu!utzoo![e-mail]  (Henry Spencer)
Subject: Re: Manned Jupiter Mission (was Re: Condensed CANOPUS - August 1989)

In article <[e-mail]> [e-mail] (Brian Yamauchi) writes:
>Are there any technical obstacles to a Jovian mission other than the
>longer flight time (requiring more supplies, larger ships, etc.) and
>the radiation around Jupiter?

Manned Jupiter missions could *really* *really* use better propulsion
than chemical rockets.  Otherwise the travel times start getting really
troublesome.  This gets still worse farther out.

Long travel times magnify supply problems and increase the advantages of
closed-cycle life-support.

Power will also be somewhat of an issue, as a manned mission will probably
want more than RTGs can conveniently supply.  Either a reactor or an
advanced high-concentration solar-array system would be needed, I think.

However, I'd say that the limitations imposed by Jupiter's Van Allen belts
are the only technical problems that couldn't be solved with reasonable
effort.  Progress in advanced propulsion has been largely stalled for two
decades, and isn't showing any signs of unstalling, but there are several
concepts that could be practical relatively soon with a vigorous development
effort.  Full-recycling life-support would take longer, but interim systems
good enough for a relatively quick trip should not be too hard.  And space-
qualified reactor systems are commercially available, although admittedly
there is only one supplier and there are political problems with buying
from him.  These issues all strike me as manageable with effort.
--
A bit of tolerance is worth a  |     Henry Spencer at U of Toronto Zoology
megabyte of flaming.           | uunet!attcan!utzoo!henry [e-mail]

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

Date: 30 Oct 89 04:20:28 GMT
From: munnari.oz.au!murtoa.cs.mu.oz.au![e-mail]  (John Keong-Jin Lim)
Subject: Re: PowerSat Options

in article <[e-mail]>, [e-mail] (Leonard Erickson) says:
> I'd expect the beam to be more like 15 *giga*watts! And one thing you'd
> have to worry about if powersats were "common" is what happens if your
> friendly neighborhood military types get the beam redirected to power a
> space based weapon of some sort? What kind of FEL (Free Electron Laser)

C'mon, have you looked at the specs for SPS transmission ?

The transmission area is about 1km x 1km so any receiver would have to be
on that sort of scale to receive your 15 GW (actually all the proposals
that I've studied are in the order of 1 - 8 GW).
Such an antenna would be incredibly vulnerable to physical damage
by projectiles etc.

> possibilities. Is it possible to use a maser to "pump" a laser directly?

Yes a laser can be  excited by microwave.

Why is there all this talk of masers, by the way?
The current SPS studies assume the use of magnetrons (yes those oven thingys)
to produce the microwave power from the dc supplied by the photoconverters.
Magnetrons can easily be built to an efficiency of 90%+.
I doubt that masers would be any more efficient than lasers.

> Leonard Erickson        ...!tektronix!reed!percival!bucket!leonard
> CIS: [70465,203]

Greg Kaan (using anothers account).

"It does not take 'good old American know-how' to build a city in space.
 The laws of physics work just as well for others as they do for us." - R.A.H.

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

Date: 30 Oct 89 00:13:03 GMT
From: vsi1!wyse!mips![e-mail]  (Vaso Bovan)
Subject: Units of Measure (was fluxgate magnetometer)

In article <[e-mail]> [e-mail] (Doug McDonald) writes:
>>>
>>>I would like to measure changes at least as small as
>>>10 gammas (.001 Gauss), and if possible, even smaller.
>>>
>>
>>?  You mean of course, nanotesla (nT), since 1954.  :-)
>
>I have been in the science business for over 20 years and have
>never heard anyone refer to magnetic fields in Tesla - everyone
>uses gauss. It is true that people know that someone somewhere
>created a unit of magnetic field called a Tesla, but no one
>remembers how many gauss are in one Tesla, and no one uses it.
>Sometimes it might appear in a textbook (usually directed at
>freshmen or sophmores - more advanced books use gauss).
>
>There are lots of names of units out there that are simply not used.
>

There are too many units out there that ARE being used. That is the reason
various international technical standardization organizations has strived
for a minimal set of clearly defined units. Unfortunately, there are many
authors who insist on dragging their feet on the changeover, so that one often
sees, for instance cgs and SI metric units intermingled, even within the same
equation !  I note that refereed journals usually require SI metric, but allow
obsolete cgs units "where traditional." This is an unfortunate loophole. I'm
an electrical engineer. I have to deal today with gauss, tesla, and microns,
all to describe the same parameter. (I won't even mention the profusion of
inch-based electro-magnetic units which are STILL found in new textbooks).

Let's not even start on the disgraceful reluctance of certain sectors of
U.S.A. engineering, mechanical engineers in particular, to expedite conversion
to metric measure.

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

Date: 30 Oct 89 06:12:54 GMT
From: milton!maven![e-mail]  (Games Wizard)
Subject: more on the dreaded vcr in space (and can they get dallas up there?)

Just thinking briefly along the lines of the tape recorder/VCR? on board
some of the things we fly...

How long before someone replaces those with DAT tapes, or rewritable
optical disks, or even large ( data volume, not size ) hard drives,
or even an 8mm type drive.

Part of the above statement will show ignorance on my part.
It seems that the last I read ( somewhere official-like ) the
tape in voyager used DAT type techniques...  But the discussion
seems to lead me to believe that it is the same old helical-scan
adapted video casette tape type thing. ( I assume that it is at
least a 3/4" or 1" commercial tape as opposed to a Beta or VHS
tape?)

Seems to me that even though the capacity of an erasable optical disk
is far smaller than what say an 8mm tape can provide, however the tape
is prone to a lot of radiation damage ( magnetic tape an all ), but the
optical disk is more secure.  is this an advantage, or is the smaller
size too much of a drawback. ( 600meg as opposed to say 2 or 3 gig )

Just random thoughts...
-------------------------------------------------------------------------------
Trendy footer by:
            John Stevens-Schlick
            Internet?: [e-mail]
            7720 35'th Ave S.W. Seattle, Wa. 98126
            (206) 935 - 4384
-------------------------------------------------------------------------------
My boss dosen't know what I do.

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

Date: 30 Oct 89 17:47:43 GMT
From: jumbo![e-mail]  (Bob Ayers)
Subject: Re: PowerSats as Weapons

Wm E Davidsen Jr writes

    Instead of evil military types, picture a fanatic who would redirect
    and intensify the beam if it were possible to do so, and who was
    willing to die to do it. Guess what, he may not be the typical
    terrorist, he may be a fundementalist, creationist, environmentalist,
    whatever. He may be any of the engineering types who would be needed
    to keep such a power plant working.
    I think some good protection against misuse is smart, I don't think
    that the issue is a canard, and I don't believe that dismissing people
    who have legitimate concerns is going to help advance technology.
    Better to be a bit paranoid about misuse than to have it happen.

First, I'll let others discuss the physics, and why an transmitting
antenna of diameter D cannot focus a beam of wavelength W into a
ground-patch smaller than P.

But second, keep things in perspective. We, today, have power generating
facilities that can have their power turned loose to kill at least
thousands, perhaps millions, of people. They are called "dams." Many
cities in the world are downhill from large hydro installations. These
installations are not in earth orbit: you can get to them with a Chevy,
not a Shuttle.

The world's already built like that.  Terrorists misuse plastic explosive
over and over. It would be trivial for one person to "take over" a gasoline
(or chlorine!) tank truck most anywhere.

I won't worry about super-terrorists 'taking over' a Clarke-orbit powersat
and re-engineering it (remotely or not) to do things it wasn't designed to
do -- not when there ar so many easier targets around. That's like
worrying about alar while smoking.

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

Date: 30 Oct 89 17:13:51 GMT
From: bfmny0![e-mail]  (Tom Neff)
Subject: Re: PowerSat Options

In article <[e-mail]> [e-mail] (bill davidsen) writes:
>In article <[e-mail]>, [e-mail] (Paul Dietz) writes:
>|  Sigh, yet another canard.  This person has beam-o-phobia.
>
>       I can see that the Christics have won an important victory...
>anyone who questions the safty of any technology is dismissed with no
>thought that they might have a valid point.

It's true that these discussions are becoming too polarized, not just
here but in the general discourse.  I noticed it happening before anyone
knew what a "Christic" was, and I don't really think it's part of their
agenda (or within their power) to do so anyway, but that's not important.

What is important is that BOTH sides, or *all* sides if (as I suspect)
there are more than two, take the extra moment to consider objections
*seriously* rather than rushing to find an appropriately contemptuous
pigeonhole for the person raising the objection.  I can see where
personal animus and ad hominem sidetracking is a temptation when two
people square off in a convention hall somewhere -- one with a Jerry
Garcia haircut, crystal rainbow T shirt and No Nukes buttons, the other
in short sleeved polyester shirt with pocket pen protector, American
flag lapel pin and Ben Bova's latest paperback tucked under the arm --
but these here computer nets are supposed to insulate us from such
things.  (Silly "I'm the NRA" sigs aside.)  If we can't communicate
here, we're in trouble.

The fault lies on both sides.  But only individuals can fix it, and that
means starting with one's OWN side.

OK, smoke em if you got em. :-)
--
 1955-1975: 36 Elvis movies.  |  Tom Neff
 1975-1989: nothing.          |  [e-mail]

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

Date: Mon, 30 Oct 89 22:16:55 EST
From: John Roberts <[e-mail]>
Disclaimer: Opinions expressed are those of the sender
    and do not reflect NIST policy or agreement.
Subject: Re: Terraforming


>From: crdgw1!crdos1![e-mail]  (Wm E Davidsen Jr)
>Subject: Re: "Terraforming", so-called...

>  I think that "terraforming" is an ambitious concept.
Agreed. However, it is probably not necessary for the spread of humanity
from the earth. I think that a few trillion dollars and 50 years of work
would probably be sufficient to establish a self-sufficient colony on Mars.
(More optimistic estimates call for less money and a shorter time.) Other
sites are promising given continued interplanetary commerce, including
the moon and asteroids. (Old question repeated: if Mars or the moon were
given an atmosphere of the same composition and surface density as the earth's,
how long would it stick around?)

>  The stars: hell, let's just find one with some nice planets and move
>there. Leave terraforming to fiction.
Colonization of bodies in the solar system has one main advantage: it is
almost certain that it can be accomplished, given sufficient time and effort.
For settlement of other star systems, there are several unknowns:
  - It is not *known* that we will ever develop a practical means of human
    travel over interstellar distances.
  - It is not known whether any star systems within reach have planets with
    size and chemical composition similar to earth.
  - It is thought that the current "livable" conditions on the earth are
    largely a result of changes brought about by the presence of life. Thus
    if we are to find "livable" planets (as opposed to planets to terraform),
    there is a good chance that they will have to have life already present.
    This is not certain. Even if such a planet is found, we will have to
    determine whether this life is compatible with earth life. (It would be
    a shame to land on a newly-discovered planet, then suddenly die from a
    local infection.)
                                  John Roberts
                                  [e-mail]

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

Date: 30 Oct 89 19:38:03 GMT
From: milton!maven![e-mail]  (Games Wizard)
Subject: Mass drivers?

yet another FAQ?  ( Only I haven't seen it for real for a while... )

What is the current status of Mass Drivers. ( or that genre of technology )

Yes, I read "The moon is a Harsh Mistress" By Robert A Heinlein and I saw
the twenty year old movie of a guy with some rings shoot a chunk of steel
out the other end but...

What if anything is happening today.  Where do I find details on this topic.
Are any of these types of beasts built for industrial applications ( I.E.
designed to do other than put something into space?)  Who builds them...
Ant good references to theoretical work in the area.

Obviously some of the same stuff is used in accelleration of very small
particles to very high speeds so people can smash them together, and wear
great silly grins afterwards, but I am looking for something designed for
appreciable mass ( I.E. a couple of lbs ( Oops Kgs, forgot the metric rage )
or bigger ).

-------------------------------------------------------------------------------
Trendy footer by:
            John Stevens-Schlick
            Internet?: [e-mail]
            7720 35'th Ave S.W. Seattle, Wa. 98126
            (206) 935 - 4384
-------------------------------------------------------------------------------
My boss dosen't know what I do.

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

Date: 30 Oct 89 13:50:42 GMT
From: deimos.cis.ksu.edu!harris.cis.ksu.edu![e-mail]  (Myron A. Calhoun)
Subject: Re: Units of Measure (was fluxgate magnetometer)

In article <[e-mail]> [e-mail] (Vaso Bovan) writes:

[many lines deleted]

>.... I have to deal today with gauss, tesla, and microns,....

Someone once referred to the USA's "solution" to this problem as
  "INCHING OUR WAY TO THE METRIC SYSTEM"!

--Myron
--
Myron A. Calhoun, PhD EE, W0PBV, [phone] (work), 539-4448 (home).
INTERNET: [e-mail]
BITNET:   [e-mail]
UUCP:  ...{rutgers, texbell}!ksuvax1!harry!mac

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

Date: 30 Oct 89 14:42:06 GMT
From: crdgw1!crdos1![e-mail]  (Wm E Davidsen Jr)
Subject: Re: PowerSat Options

In article <[e-mail]>, [e-mail] (Paul Dietz) writes:
|  Sigh, yet another canard.  This person has beam-o-phobia.

       I can see that the Christics have won an important victory...
anyone who questions the safty of any technology is dismissed with no
thought that they might have a valid point.
|
|  The power density of a powersat beam is low.  A space-based weapon with
|  a rectenna several miles across would be absurdly vulnerable.

  An the atom will only be used for peaceful uses... Sure the density is
*intended* to be low, but I would want a good failsafe system in place.
Who cares if it's vulnerable, if you have to destroy your investment to
control it?

  Instead of evil military types, picture a fanatic who would redirect
and intensify the beam if it were possible to do so, and who was willing
to die to do it. Guess what, he may not be the typical terrorist, he may
be a fundementalist, creationist, environmentalist, whatever. He may be
any of the engineering types who would be needed to keep such a power
plant working.

  I think some good protection against misuse is smart, I don't think
that the issue is a canard, and I don't believe that dismissing people
who have legitimate concerns is going to help advance technology. Better
to be a bit paranoid about misuse than to have it happen. One real
disaster involving civilians could be used to halt our space program for
decades.
--
bill davidsen    ([e-mail] -or- uunet!crdgw1!crdos1!davidsen)
"The world is filled with fools. They blindly follow their so-called
'reason' in the face of the church and common sense. Any fool can see
that the world is flat!" - anon

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

End of SPACE Digest V10 #192
*******************