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Subject: SPACE Digest V10 #45

SPACE Digest                                      Volume 10 : Issue 45

Today's Topics:
            Re: Lagrangian Points
        Re: Dynamics of Magnetically Driven Spacecraft
      Re: Was Voyager another damaging Apollo one-shot?
           Re: Tracking Military Satellites
         Re: Economies of Scale in Launchers
         Re: Ignorance at Christic institute
             Re: Voyager Audio/Slide Show
Re: Progress M-1 (new type of cargo craft) launched to USSR's Mir station
           Re: U.S. commemorative stamp of VOYAGER?
              Re: latest silly signature
----------------------------------------------------------------------

Date: 15 Aug 89 04:08:51 GMT
From: crdgw1!ge-dab!sunny![e-mail]  (Gregory Harrison)
Subject: Re: Lagrangian Points

In article <[e-mail]> [e-mail] (Chandrasekhara Sudhama) writes:
>Hello, this is my first posting. Would someone please explain
>(either on this network or in private email) the stability of the
>equilibrium points in the Earth - Moon system?

From my L5 days, the straight line points, on the Earth-Moon line are 2/3 stablewhich means that the satellites placed at these straight-line libration points,
L1, L2, and L3 can move in a plane that is perpendicular to the line joining theEarth and the Moon, and the libration phenonenon at these 2/3 stable points actsso as to return the satellite to the libration point.  But if the satellite moves towards the Earth or Moon, the satellite will continue approaching the Earth or Moon.  Thus the L1, L2, and L3 points are 2/3 stable, i.e. they return to the libration point from 2 of the 3 possible dimensions it can traverse away from the libration point.  On the othe










r hand, the L4 and L5 points are stable in all 3 dimensions.  The satellite can move anywhere about the point (within some kidneyshaped bounds) and still experience forces that draw it back into the libration point.

The L5 point, namesake of the pioneering space settler society, is trailing the Earth in the Earth-Moon system cyclical progression (I believe) as the Earth andMoon rotate about their combined center of rotation.  I think that was the case,and I believe the L5 Society decided on that location for settlement due to enhanced safety in case of emergency.  The Earth would be moving away from the Settlement and pose less of a danger should the satellite orbit be perturbed.

The 2/3 stable points are useful despite the instability in the 3rd dimension.  There was, and may still be, a satellite placed at the libration point between the Earth and the Sun, and set into an orbit about the line between the Earth and the Sun such that when viewed from the Earth (with appropriate equipment, not eyes, of course) the satellite would circumscribe the borders of the Sun.  NASA had redirected this satellite into that orbit after it had completed some other mission.  Perhaps it was called










Solar Max, I can't recall.  Perhaps someone else out there would know.  Maybe the L5er ==> NSS member who originally passed the news to me may be on the net and would know.

The mathematical formulations of the other postings on this subject are very interesing.  It would be interesting to know what all those numbers mean.  For instance the 24.999~, and the 27*  ... etc.  There must be a good reference?

To The Stars,

Greg Harrison
NSS member

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

Date: 6 Sep 89 01:03:09 GMT
From: cbmvax![e-mail]  (Randell Jesup)
Subject: Re: Dynamics of Magnetically Driven Spacecraft

In article <[e-mail]> [e-mail] (Jim Meritt) writes:
>In article <[e-mail]> [e-mail] (Doug Reeder) writes:
>}I will be doing my senior thesis on the dynamics of magnetically driven
>}spacecraft, working out the equations of motion and so forth.  Thus, I would
>}appreciate it if people would send me references
>}to related papers ond works.  This would include papers on the dynamics of
>}solar sails and on the magnitude and direction of the magnetic field of both
>}the Earth and Jupiter at various altitudes.
>
>See Dick Tracey, specifically the "Magnetic Space Coupe"

    Also see some of the Tom Swift, Jr novels - they had one too.

:-) :-)

    Actually, it sounds interesting.  good luck.

--
Randell Jesup, Keeper of AmigaDos, Commodore Engineering.
{uunet|rutgers}!cbmvax!jesup, [e-mail]  BIX: rjesup
Common phrase heard at Amiga Devcon '89: "It's in there!"

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

Date: 5 Sep 89 13:33:05 GMT
From: bfmny0![e-mail]  (Tom Neff)
Subject: Re: Was Voyager another damaging Apollo one-shot?

In article <[e-mail]> [e-mail] (Andy Clews) writes:
>From article <[e-mail]>, by [e-mail] (Tom Neff):
>| I mean after all, think about it -- NOW what can JPL do that will grab
>| the attention of the man in the street ...
>
>Why is it so important that space exploration projects become part of
>the big media circus?

Because when it comes time to fund space exploration projects, NASA has
to go to the Congress.  Much-hated and much-misunderstood by many space
nuts, Congress is several hundred legislators all of whom are answerable
to the voters and their home interests.  In order to be willing to go
out on a limb and spend the public's monies on a space project, enough
Congresspeople have to be convinced that there's either (a) public
support for it, or (b) economic benefits for the home district.  The
latter equation has been in place a long time -- obviously the House
reps from many districts in California, Florida, Utah, Texas etc. are
boosters.  But they alone can't make it happen; to get the support of
the remaining majority of Congresspeople you need public support.  In
this country, the continuum of public interest is the commercial media.
But media coverage can be supportive or skeptical, so you need to do the
little (and big) things that put the media on your side.  NASA's manned
program has basically blown it in this regard (nothing like a siege
mentality to make enemies), but JPL still has a cachet of wonderfulness.

>                       The man in the street couldn't care less about the
>achievements of Voyager, and never could.  OK, a few people might say
>"Cor, ain't that clever.  Isn't science wonderful" but they'll forget
>all about it by the following day.

Listen, the man in the street couldn't care about SDI either, and yet we
expend gigabucks on it -- UNTIL it becomes clear that SDI has lost its
marketing clout, so that Congresspeople no longer feel compelled to
crawl out on that spending limb for it.  It's a wonderful dynamic; what
the space program needs is to surf it properly.

>                                    How many people have *you* counted
>today in the street, chatting eagerly about Voyager's latest
>discoveries?

I live in NYC so my sample is biased (tugged both ways, since we read
more but watch TV less) but I have been surprised at the non-space
friends who have volunteered the question "have you been following this
Voyager thing?" which of course I answer in the enthusiastic
affirmative.  I think there's more interest, at least in this country,
than Andy assumes.  What the interest level is in Oceania I don't know.

>                                                      Space exploration
>must be in a pretty parlous state if it has to rely on media-hype to
>keep it going.

I shouldn't think so.  As has been discussed here often, once there's a
clear profit motive out there, the spacefaring Vanderbilts will bull
their way into space and the public be d____d.  Until then, as long as
it's the public purse at stake, traditional politicking is needed to
keep space exploration alive, and that means media("-hype" if you
will).
--
Annex Canada now!  We need the room,    \)    Tom Neff
    and who's going to stop us.        (\    [e-mail]

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

Date: 5 Sep 89 14:38:36 GMT
From: frooz!cfa250![e-mail]  (Jonathan McDowell)
Subject: Re: Tracking Military Satellites

From article <[e-mail]>, by [e-mail] (Nick Watkins):
> According to several reports this was a pair of SDS satellites launched
> on a Titan 34D.

However, only two objects were cataloged with this launch.  Unless NORAD
are deliberately screwing us around (possible), this would suggest one
payload and one rocket body.  Similar confusion with the Titan 2 launch
on Sep 5, 1988 claimed to be a NOSS but only three objects cataloged.  I
want to see the orbital elements they release to the UN - which they
have not yet done in direct violation of international treaty.

Jonathan

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

Date: 5 Sep 89 21:48:44 GMT
From: swrinde!cs.utexas.edu!csd4.csd.uwm.edu!mailrus!jarvis.csri.toronto.edu!utgpu!utzoo![e-mail]  (Henry Spencer)
Subject: Re: Economies of Scale in Launchers

In article <[e-mail]> [e-mail] (Bob Pendleton) writes:
>> Are we confusing high thrust with efficiency?
>
>Could be. I don't claim to be an expert...
>As I remember it, I don't have the articles with me, The effective
>back pressure is lower for a high molecular weight exhaust. I could
>have this wrong. But, "Aerospace America" is the journal of the
>American Insitute for Aeronautics and Astronautics and they did say
>that high molecular weight exhaust is preffered in the lower
>atmosphere.

I had cause to review this recently for the talk I gave on Earth-to-orbit
propulsion at the BIS party at the Worldcon.  Unless there's something I
missed, back pressure is not an issue.  The reason high molecular weight
is preferred at low altitudes is not that it maximizes exhaust velocity,
but that it maximizes thrust.  Other things (many other things...) being
equal, the volume flow rate of an engine is independent of gas composition.
But thrust is exhaust velocity times *mass* flow rate.  The relation between
volume and mass basically boils down to molecular weight:  heavier molecules
make denser gases.  So an engine of a given size has highest thrust with
highest molecular weight.  (The reduction in exhaust velocity hurts thrust,
but not as much as the increase in density helps.)

At low altitude, the crucial item on the agenda is getting up out of the
atmosphere, so that serious acceleration towards orbital velocity can start.
(Actually the transition between climb and acceleration is gradual, with
the path following an optimized curve, and wings or air-breathing engines
add further complications, but seperate climb and acceleration phases is
a useful model for thinking about it all.)  For the climb, high thrust
is the priority, to minimize gravity losses.
--
V7 /bin/mail source: 554 lines.|     Henry Spencer at U of Toronto Zoology
1989 X.400 specs: 2200+ pages. | uunet!attcan!utzoo!henry [e-mail]

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

Date: 6 Sep 89 01:19:34 GMT
From: bfmny0![e-mail]  (Tom Neff)
Subject: Re: Ignorance at Christic institute

In article <[e-mail]> [e-mail] (Tim Shimeall x2509) writes:
>The recent posting by the Christic Institute was (to put it
>charitably) a work of ignorance ...
>
>>The probe's
>>unsterilized parachute will probably carry billions of live
>>microbes. ...
>
>Note the nested probabilities inherent in this argument:
>  1) Terrestrial microbes survive the trip to Jupiter
>  2) The microbes are not eliminated by the strong radiation found in
>     and around Jupiter
>  3) The microbes survive the trip through jupiter's caustic atmosphere
>  4) The microbes end up in a region of appropriate chemistry,
>     pressure, and temperature to permit survival
>  5) The microbes find native organisms (OK, let's be charitable and
>     just say organic matter) of sufficient volume and similarity in
>     chemistry to serve as a food source
>  6) The microbes find some mechanism to remain in the life-permitting
>     areas -- which I would suspect are very transient, given
>     Jupiter's turbulent atmosphere.

Not really taking Christic's side -- in fact I posted my own skeptical
followup for different reasons -- but I believe their full article
indicated that the primary danger was from microbes INSIDE the probe,
not those on the surface.  There's a re-entry shell which will be
charred quite thoroughly thank you :-), then this drops away and the
cone descends for some time, then the drogues are deployed and the main
chute, and I *think* instruments are extended at that time although I'm
away from my pretty picture.  This presents some opportunity for
microbes to be protected through the horrendous phases yet exposed
during the interesting ones.  And I believe the layers passed through
before Earthlike temperatures are reached are not so "caustic," the
really terrible stuff lies deeper.  Hydrogen wind isn't going to kill
sporulated microbes.

Now organic matter *does* exist down there, we know that from our little
metal buddies and Earth based observations.  How useful and at what
temperatures I don't know, but we are at least in the realm of
discussion here, it's not TOTALLY out of hand.  And while convection may
flush most of the temperate zone periodically, we also know from the
existence of things like the Red Spot that chaotic fluid systems tend to
produce semi permanent eddies.  If an Earth spore found the most
evanescent of whirlpools on the Jovian scale -- say, one with no more
than a fifty thousand year lifespan -- it could still get some work done
(by the time it blew away, it would have a few quadrillion kids to take
up the baton).

My primary objection to the Christic infection scenario is that if this
sort of thing CAN happen, it probably already HAS, given that Jupiter is
an absolute monster gravity well and things fly all over the darn solar
system as it now seems.  If we inadvertently release anything into a
survivable layer of the Jovian atmosphere, it will be the first takeout
meal Earth ever delivered.  (Next time we should ask Frank Drake to etch
a menu!)
--
Annex Canada now!  We need the room,    \)    Tom Neff
    and who's going to stop us.        (\    [e-mail]

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

Date: 5 Sep 89 22:42:41 GMT
From: agate!sandstorm.Berkeley.EDU![e-mail]  (George William Herbert)
Subject: Re: Voyager Audio/Slide Show

In article <[e-mail]> [e-mail] (John) writes:
>
>Does anyone know voyager's email address? I tried [e-mail], but it
>bounced. Why didn't anyone think of including a gateway to USENET in the
>voyager software? That would give the space aliens a far more comprehensive
>view of life on earth. And we could look forward to some interesting postings
>too, if they are advanced enough to be able to type.

Someone tried to install one, but the other machines couldn't deal with the
long and ever-increasing time delay in transmission...;)

Pingings it took too long, too.  And someone complained that it took forever to
route mail through it...

george william herbert
[e-mail], [e-mail]

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

Date: 4 Sep 89 04:37:53 GMT
From: zephyr.ens.tek.com!tektronix!psueea!parsely!bucket![e-mail]  (Leonard Erickson)
Subject: Re: Progress M-1 (new type of cargo craft) launched to USSR's Mir station

[e-mail] (nick szabo) writes:

<      (if technology permits) Mercury orbiter/lander.

Actually, I'm not sure that *physics* will permit a Mercury orbiter.
I seem to recall seeing some figures that showed that the Sun's
attraction of anything in Mercury orbit is almost as great as that of
Mercury. At least at reasonable altitudes. Anybody else have figures?
If not I guess I'll have to calculate them myself and post.

I am pretty sure that in any case an orbit around Mercury would be
highly perturbed!
--
Leonard Erickson        ...!tektronix!reed!percival!bucket!leonard
CIS: [70465,203]
"I'm all in favor of keeping dangerous weapons out of the hands of fools.
Let's start with typewriters." -- Solomon Short

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

Date: 5 Sep 89 13:14:07 GMT
From: ncspm![e-mail]  (Jay C. Smith)
Subject: Re: U.S. commemorative stamp of VOYAGER?


Voyager has already been featured on a stamp.

There was a space achievements issue in 1981 that highlighted the new space
shuttle, but the block of eight stamps (which featured the shuttle in the
middle four) also depicted Skylab, a communications (or weather?) satellite,
Apollo (man on the moon), and Voyager.  The stamps were designed by Robert
McCall, a noted space artist who is responsible for other stamps as well as
those publicity paintings for "2001: A Space Odyssey."

--
"Good.  For a minute I thought we were in trouble."
---------------------------------------------------------------------
Jay C. Smith                      uucp:     ...!mcnc!ncsuvx!ncspm!jay
Domain: [e-mail]        internet: [e-mail]

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

Date: 6 Sep 89 00:30:13 GMT
From: concertina![e-mail]  (Steve Hix)
Subject: Re: latest silly signature

In article <[e-mail]>, [e-mail] (Henry Spencer) writes:
> In article <[e-mail]> [e-mail] (Tom Neff) writes:
> >Annex Canada now!  We need the room,    \)    Tom Neff
> >    and who's going to stop us.        (\    [e-mail]
>
> Heh heh.  You folks said roughly that early in 1812, just before you
> invaded us last time.  By the end of that invasion, the only US soldiers
> still in Canada were POWs, three US armies had surrendered, and we had
> occupied Michigan and most of Indiana and Ohio.  (The war went back and
> forth in various silly ways for a couple of years after, and ended up
> settling in at more or less the previous status quo.)  The invasion of
> Canada was the most spectacular US military disaster in history, dwarfing
> Vietnam etc.  Wanna try again? :-) :-) :-)

Why??!  You guys banning us from Banff/Jasper/??  (Spending money in Canada
the current way is sure cheaper than than paying for sending tourists in
poorly-tailored, drab suits...)

'sides, who else would keep away the polar bears?

( :} just joking, there...really...put down that poker...please?...)

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

End of SPACE Digest V10 #45
*******************