Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V15_0/V15NO076.TXT

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Date: Thu,  6 Aug 92 05:03:00
From: Space Digest maintainer <[e-mail]>
Reply-To: [e-mail]
Subject: Space Digest V15 #076
To: Space Digest Readers
Precedence: bulk


Space Digest                Thu,  6 Aug 92       Volume 15 : Issue 076

Today's Topics:
              ACRV Mission Requirements, and Commentary
                      Magellan Update - 08/05/92
                   Meteor Soaks Datona FL (2 msgs)
                              NASA Tools
                   Origin of Life article (2 msgs)
                        Question about tether
                        Soyuz as ACRV (3 msgs)
     Soyuz as ACRV (Posting of previous discussion data) (2 msgs)
           TSS update (from Tuesday night press conference)
                            What is FRED?
       Whats wrong with this CIRCUIT (was: Tethered Satellites)

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Date: 5 Aug 92 13:52:20 EDT
From: "John F. Woods" <[e-mail]>
Subject: ACRV Mission Requirements, and Commentary
Newsgroups: sci.space

[e-mail] writes:
>     Again, I have a problem with this requirement.  If there was
> another Challenger-type problem, they would launch anyway to reach
> stranded folks on SSF.  Just launch when it was warm....

Actually, it is conceivable that there can exist problems that would ground
the shuttle fleet for more than 3 months, even without an actual disaster:
if a vital component that gets replaced every mission turned out to have a
manufacturing defect, and if all of the in-stock replacements had the same
defect, then you'd be looking at a delay equal to the time to analyze and
correct the problem plus the usual lead time for that part.  As I recall,
there was a bad batch of teflon seals that ended up slipping one mission
(though presumably seals aren't a long lead-time item, the diagnosis took
some time).  Perhaps someone at NASA can comment on what parts might be the
worst-case for such a scenario?

And while we're on the topic, did NASA ever get a budget for a truly complete
set of spare parts, or are they still cannibalizing Orbiters to support each
current mission?

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

Date: 6 Aug 92 02:34:09 GMT
From: Ron Baalke <[e-mail]>
Subject: Magellan Update - 08/05/92
Newsgroups: sci.space,sci.astro

Forwarded from:
PUBLIC INFORMATION OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109. TELEPHONE [phone]

                     MAGELLAN STATUS REPORT
                         August 5, 1992

     Two tests were conducted on Magellan's transmitter B last
week at its minimum temperature of 23.4 C (74 F) to see if high
rate data could be received.  Both tests showed a continuing
noise spur at various temperatures which has prevented the
transmission back to Earth of mapping data with transmitter B in
the low temperature mode.  The alternate transmitter, A, failed
last January.

     It was thought that turning the transmitter off and
permitting it to cool until needed would prevent the noise spur
from occurring.  Since it was not successful, controllers said,
the project will return to the mode of leaving the transmitter on
when it resumes testing on August 21.  That command sequence,
which runs until September 3, will be a dress rehearsal and high
temperature stabilization period for the next sequence, September
3 to 14, designed to map the last significant coverage gap, about
1.5 percent, in the global map of Venus.

     In the meantime, transmitter B has been turned off and daily
operations have been resumed on transmitter A which can be used
for gravity and engineering data.  The orbit adjustment burn to
reduce periapsis altitude to 182.5 kilometers (113.15 miles) is
still planned for September 14, marking the beginning of cycle 4.
That cycle will be dedicated to global gravity data with some
targeted mapping.  Both transmitters can be used for gravity
mission operations, but only transmitter B can be used for
mapping.
                     -------------
     ___    _____     ___
    /_ /|  /____/ \  /_ /|     Ron Baalke         | [e-mail]
    | | | |  __ \ /| | | |     Jet Propulsion Lab |
 ___| | | | |__) |/  | | |__   M/S 525-3684 Telos | You can't hide broccoli in
/___| | | |  ___/    | |/__ /| Pasadena, CA 91109 | a glass of milk -
|_____|/  |_|/       |_____|/                     | anonymous 7-year old.

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

Date: 5 Aug 92 17:47:47 GMT
From: FRANK NEY <tnc!m0102>
Subject: Meteor Soaks Datona FL
Newsgroups: sci.space

-----I quote-----
A giant wave that drenched Datona FL and caused a lot of damage
in July turns out to have probably been caused by a 1 meter
meteor!

I wonder if this'll give the beancounters in Congress any
incentive to fund a near-Earth Asteroid finder program.
True, not many 1 m objects can be found, but perhaps this can
scare them enough to look for big ones on the way to turn DC
into a crater :-)
-----end quote------

There was a SF story like that written in the early '70s where the
world was held on the brink of nuclear war when a 100m rock nailed the
'zero milestone.'  Only the self-restraint of the general officer on
duty prevented a double catastrophe.

Seriously though, don't look for NASA or congress to do anything
unless they think something is in it for them.  Altruism doesn't cut
it.

Now, if we had private concerns in space (not bloody likely
considering the Commercial Space Lauch Act, which is not) we could
appeal to the profit motive.  Gee, all these rocks that come
conveniently close to earth, ready to be mined..........

Frank Ney N4ZHG EMT-P  LPVa NRA ILA GOA CCRTKBA "M-O-U-S-E"
Commandant and Acting President, Northern Virginia Free Militia
Send e-mail for an application and more information
----------------------------------------------------------------
"...I am opposed to all attempts to license or restrict the arming of
individuals...I consider such laws a violation of civil liberty,
subversive of democratic political institutions, and self-defeating
in their purpose."
        - Robert Heinlein, in a 1949 letter concerning "Red Planet"
--
The Next Challenge - Public Access Unix in Northern Va. - Washington D.C.
703-803-0391 To log in for trial and account info.

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

Date: Wed, 5 Aug 1992 18:44:53 GMT
From: Greg F Walz Chojnacki <[e-mail]>
Subject: Meteor Soaks Datona FL
Newsgroups: sci.space

From article <[e-mail]>, by [e-mail] (FRANK NEY):
>
> -----I quote-----
> A giant wave that drenched Datona FL and caused a lot of damage
> in July turns out to have probably been caused by a 1 meter
> meteor!
>
IS there any source on this <alleged> meteor event other than a TV news report?

Greg

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

Date: 5 Aug 92 12:53:48 GMT
From: John Roberts <[e-mail]>
Subject: NASA Tools
Newsgroups: sci.space

-From: [e-mail] (Bruce Dunn)
-Subject: NASA Tools
-Date: 5 Aug 92 00:27:47 GMT
-Organization: MIND LINK! - British Columbia, Canada

-> John Roberts writes:
-> No release of the TSS yet - it appears to be stuck.
->
-> Maybe they need to unpack the Ferrous Portable Leverage Application
-> Mechanism (FPLM), the Passive Maximal Kinetic Transfer Device (PMKTD),
-> and the Linear Metallic Abrasive System (LMAS), and try an EVA. :-)

-Crowbar, hammer, and file?

Very good! :-)  What I specifically had in mind was crowbar, sledgehammer,
hacksaw. That LMAS acronym needs work - I agree it's ambiguous.

The Shuttle has all sorts of nifty tools stowed away, that they never take out
unless they really need them. I don't know if they have a sledgehammer, but
I'm sure they have a hammer of some kind. To the above tools, add pliers,
a couple of screwdrivers, an adjustable wrench, and some grey tape (duct tape),
and you've got all the basic tools to demolish, er, repair just about anything.
For the ultimate in luxury, throw in an electric drill, grinder, tin snips, and
pop rivet tool. Plus assorted nuts, bolts, washers, and screws, of course.

The initial problem was that the power (/communications?) umbilical to the
Shuttle failed to unplug - it appears they finally got the actuator working.

John Roberts
[e-mail]

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

Date: Wed, 5 Aug 1992 18:35:41 GMT
From: [e-mail]
Subject: Origin of Life article
Newsgroups: sci.space

From article <[e-mail]>, by [e-mail] (Steve Troxel):
> Why is it so difficult for people who call themselves
> scientists to explore the possibility that God created the
> earth and all the creatures on it?  There is every bit as much
> scientific "proof" for the "theory" of creation as there is for
> the "theory" of evolution.  Why is everyone so set against
> acknowledging a valid alternative hypothesis?  Is there some
> prejudice against is?
>
> Steve Troxel
> [e-mail]
>
> **Save the baby humans.**

Perhaps because of all the hard physical evidence for evolution,
and the total lack of the same for creation.  Scientists work
with facts, and theories that fit them.  Hypotheses die when
not supported by evidence.

Greg Retzlaff
Saskatchewan Accelerator Laboratory

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

Date: Wed, 5 Aug 1992 18:37:14 GMT
From: Henry Spencer <[e-mail]>
Subject: Origin of Life article
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Steve Troxel) writes:
>Why is it so difficult for people who call themselves
>scientists to explore the possibility that God created the
>earth and all the creatures on it? ...

This has gotten somewhat peripheral to sci.space already, and *this* new
digression puts it over the edge.  Take it to talk.origins, please.
--
There is nothing wrong with making      | Henry Spencer @ U of Toronto Zoology
mistakes, but... make *new* ones. -D.Sim|  [e-mail]  utzoo!henry

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

Date: 5 Aug 92 17:39:18 GMT
From: Desiree Bradley <[e-mail]>
Subject: Question about tether
Newsgroups: sci.space

Thinking about the Northern Lights (aurora borealis) and the aurora australis
(near the South Pole), I was wondering if during polar winters it would be
advisable to not let down the tether anywhere near polar regions.  However, I
don't know enough to say anything about the tether and any possible effects the
auroras could have on the electricity flow in the tether.

Did somebody a while back post a message that would answer my question?  Also,
is there a good journal article (not at Ph.D. level, please) that would explain
the tether and answer my question about possible effects of auroras?  Perhaps
somebody could E-Mail the bibliographic reference (title of journal, issue date
- or volume+number).  With that much information I could find the rest.

Thanks.

Desiree Bradley

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

Date: Wed, 5 Aug 1992 17:33:27 GMT
From: "Allen W. Sherzer" <[e-mail]>
Subject: Soyuz as ACRV
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Robert A. Lentz) writes:

>Have the concerns for polluting the environment surrounding the station
>been removed? If not then would not a lot of this on-orbit processing, and
>the frequent Soyuz flights do much to polluting the environment?

Since Soyuz weighs a good deal less than Shuttle it should burn far less
fuel. Polution should therefore be lower.

>And the frequent soyuz flights would still put a cap on the duration of
>some of the microgravity experiments.

Soyuz flights wold be no more frequent than Shuttle flights.

>And last I knew, the proposal still called for refurbishment by swapping
>modules as the shuttle carried them up. I have heard how they would be
>carried up on the HLV Delta, but how would they be returned?

I envision a reusable logistics module. It is brought back using a teather
and parachute (or a small kick motor). It goes up on HL Delta and comes
down in the logistics module.

    Allen

--
+---------------------------------------------------------------------------+
| Allen W. Sherzer | "If they can put a man on the Moon, why can't they     |
|  [e-mail]     |  put a man on the Moon?"                               |
+----------------------261 DAYS TO FIRST FLIGHT OF DCX----------------------+

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

Date: Wed, 05 Aug 92 18:42:30 GMT
From: Doug Mohney <[e-mail]>
Subject: Soyuz as ACRV
Newsgroups: sci.space

In article <[e-mail]>, [e-mail] (Allen W. Sherzer) writes:
>In article <[e-mail]> [e-mail] (Robert A. Lentz) writes:
>
>>Have the concerns for polluting the environment surrounding the station
>>been removed? If not then would not a lot of this on-orbit processing, and
>>the frequent Soyuz flights do much to polluting the environment?
>
>Since Soyuz weighs a good deal less than Shuttle it should burn far less
>fuel. Polution should therefore be lower.

Oh. You left out resupply flights. Hm. You'd better go back to the drawing
board and add those up.

>>And the frequent soyuz flights would still put a cap on the duration of
>>some of the microgravity experiments.
>
>Soyuz flights wold be no more frequent than Shuttle flights.

Oh. Neet. Resupply occurs by magik. Nifty. Oh. or HLV Delta flights. But, like
sand, it slips out of your overall fiction, er picture.


                 Support U.N. military force against Serbia

  -- >                  [e-mail]                        < --

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

Date: Wed, 5 Aug 1992 19:55:38 GMT
From: "Allen W. Sherzer" <[e-mail]>
Subject: Soyuz as ACRV
Newsgroups: sci.space

In article <[e-mail]> [e-mail] writes:

>>Since Soyuz weighs a good deal less than Shuttle it should burn far less
>>fuel. Polution should therefore be lower.

>Oh. You left out resupply flights. Hm. You'd better go back to the drawing
>board and add those up.

OK. Since Soyuz and the resuply modules weigh less than the equivalent
Shuttle flights, polution should be lower.

Polution is furthur reduced since logistic modules are teathered down
which means both fewer burns for logistics AND fewer burns for Freedom
stationkeeping. This also saves additional $$ since less fuel is needed.

How's that?

   Allen
--
+---------------------------------------------------------------------------+
| Allen W. Sherzer | "If they can put a man on the Moon, why can't they     |
|  [e-mail]     |  put a man on the Moon?"                               |
+----------------------261 DAYS TO FIRST FLIGHT OF DCX----------------------+

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

Date: Wed, 5 Aug 1992 17:13:45 GMT
From: Mark Littlefield <[e-mail]>
Subject: Soyuz as ACRV (Posting of previous discussion data)
Newsgroups: sci.space

In article <[e-mail]>, [e-mail] (Allen W. Sherzer) writes:
|> In article <[e-mail]> [e-mail] writes:
|> >Allen and I did a significant thrash of this topic in January on
|> >talk.politics.space....
|>
|> I'm deleting most of this and just want to comment on a few points.
|>
|> >   However, we still haven't resolved the issue of return cargos.
|> >To return 80,000 lbs per year is not trivial.
|>
|> Since January I have spoken with an engineer who works on Freedom. He says
|> that very little will be brought back and that the biggest single object
|> is a stationkeeping engine which weighs about 15K pounds. Aside from that
|> vast majority of what will be returned is trash which we can simply teather
|> down and let it burn up. It sounds like Dale's comment about putting the
|> stuff in a shoe box is about right.

Like so many of Allen's postings, this one suffers from selective
blindness (is that flame-bate or what ;-).  True, the single largest
object to be returned from Freedom is a station keeping engine pallet.
However, the engine pallets are not the only massive objects to be
returned (besides, sets of two pallets are changed out and returned at
one time, doubling the mass).  Experiment racks are returned during
each utility flight and are refurbished and re-used.  Also, the
logistics modules are returned and re-used on many of these flights.

Now, granted, you could simply destroy all of these by dumping them
overboard, building new ones, and launching them on expendables and
probably do it cheaper than using the shuttle to launch, recover, and
re-launch.  HOWEVER, the shuttle will also be performing crew
rotations at that time (1 to 2 more launches), the shuttle provides
support for Freedom while on station (shuttle RMS is used along with
SSRMS, shuttle is available for crew and equipment retrieval, etc)
PLUS, the shuttle provides a low-G return capability that is not
available on your "slapping some Shuttle tiles on a logistics
module and adding a parachute" scheme.

Next, watch for Allen to pull some more numbers out of his hat to show
that you could actually get a fully functional moonbase from materials
bought at K-mart and have change left over for a movie.....

--
=====================================================================
Mark L. Littlefield              Intelligent Systems Department
internet: [e-mail]
USsnail:  Lockheed Engineering and Sciences
          2400 Nasa Rd 1 / MC C-19
          Houston, TX 77058-3711
====================================================================

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

Date: Wed, 5 Aug 1992 18:16:45 GMT
From: "Allen W. Sherzer" <[e-mail]>
Subject: Soyuz as ACRV (Posting of previous discussion data)
Newsgroups: sci.space

In article <[e-mail]> [e-mail] writes:

>Like so many of Allen's postings, this one suffers from selective
>blindness (is that flame-bate or what ;-).

Since it is obviously not true, I'll simply ignore it. :-)

In case I have missed something, I have doubled the cost of everything. If
you want, we can triple the cost of everything and STILL save $2 billion
per year.

>True, the single largest
>object to be returned from Freedom is a station keeping engine pallet.
>However, the engine pallets are not the only massive objects to be
>returned (besides, sets of two pallets are changed out and returned at
>one time, doubling the mass).

As long as it fits into the logistics module. Since I propose to use
the same one going down as up, it should fit OK.

>Now, granted, you could simply destroy all of these by dumping them
>overboard, building new ones, and launching them on expendables and
>probably do it cheaper than using the shuttle to launch, recover, and
>re-launch.

Well then that's what you should do. Only NASA could make wasting money
a virtue.

>HOWEVER, the shuttle will also be performing crew
>rotations at that time (1 to 2 more launches),
                        ^^^^^^^^^^^^^^^^^^^^^^^
I don't understand what you mean here.

If somebody else can provide the same service for half the cost then I
don't care what the Shuttle does.

>the shuttle provides
>support for Freedom while on station (shuttle RMS is used along with
>SSRMS, shuttle is available for crew and equipment retrieval, etc)

Is this capability worth the billions it costs? for a fraction of this
cost we could add an extra arm to Freedom and have it available ALL the
time.

>PLUS, the shuttle provides a low-G return capability that is not
>available on your "slapping some Shuttle tiles on a logistics
>module and adding a parachute" scheme.

How do you know? We can base it on the DC-Y vehicle without the engines,
tanks, ect. Such a vehicle would be reusable with very little if any
maintenance. Offer significant crossrange capability AND return with
lower Gs than Shuttle.

>Next, watch for Allen to pull some more numbers out of his hat to show
>that you could actually get a fully functional moonbase from materials
>bought at K-mart and have change left over for a movie.....

Which numbers do you think I have pulled out of my hat? All my launch
costs are list prices generally available today. HLV costs are based
on offers made to the government.

As to K-mart and the moon base, I'll bet I could find a lot of stuff
there which would work just fine on the moon. Maybe not but until you
look with an open mind, you will never know.

  Allen

--
+---------------------------------------------------------------------------+
| Allen W. Sherzer | "If they can put a man on the Moon, why can't they     |
|  [e-mail]     |  put a man on the Moon?"                               |
+----------------------261 DAYS TO FIRST FLIGHT OF DCX----------------------+

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

Date: 5 Aug 92 13:50:49 GMT
From: John Roberts <[e-mail]>
Subject: TSS update (from Tuesday night press conference)
Newsgroups: sci.space

-From: [e-mail] (John Roberts)
-Subject: Another TSS update
-Date: 5 Aug 92 05:04:39 GMT

-I got most of the post-midnight press conference on videotape. It's too
-much to type in at 1 AM. Maybe in the morning I can post some of the
-highlights (and of course we can hope for official releases from the
-NASA people).

-Basically, it got stuck several times, and didn't deploy as far as planned
-for the first day. It's thought that the main problem at the moment is
-that high tension in the earlier maneuvers has caused some of the loops of
-tether on the reel to slip down beneath the outer layer of loops, causing
-them to have much higher friction in deployment. There's considerable
-hope that getting a "running start" and deploying faster than originally
-planned will get them past the points where it sticks.

-There's still some hope for a deployment of the originally planned length,
-but consumables on the satellite are a concern. The mission has been extended
-one day to increase the amount they can accomplish. Currently the satellite
-is in a stable mode 870 feet from the Shuttle, with minimum power consumption.
-All the scientific instruments appear to be working correctly. The Shuttle
-team that works with the tether has gone to bed, and they plan to get up
-in seven hours and continue work.

Additional notes:

 - Initial cause of umbilical disconnect failure was probably moisture.
   They did a "soak" in sunlight to heat the mechanism, and it worked.

 - The running start method has already been successful at least once.
   It is expected that it will be needed several times, probably at intervals
   of several hundred meters. They think they can get it "as far as needed".
   18-20 km may be practical.

 - All the scientific instruments have been successfully activated.
   The cargo bay electron guns have been fired.

 - They probably will not be able to have the full set of scientific
   instruments activated until they get up to 6 km, and during retrieval
   after it gets closer than 6 km, due to battery constraints. (Some of the
   power has already been used.)

 - 20kg of nitrogen remaining - ~60% has been used so far. With 20km deploy,
   expect to need ~12kg of nitrogen.

 - Stops at a few cm and at 180m are thought to be related. Deploying the
   boom may have been what pulled the tether tight enough to jam up the loops
   of tether on the spool. It may be a specific point along the length of
   the spool that has the problem. Next expected stick point if this assumption
   is valid is 1000-1100 meters. Increasing the rate of deploy is expected
   to help.

 - They stopped for the night instead of letting the other crew shift continue
   operations because it's a very complex activity, and just the one crew has
   received TSS training.

 - Minimum deploy for fully satisfactory results would be 10 km.

 - The satellite flies very well, and the dynamic interaction between the
   satellite and the Shuttle has been easy to control. (It remained stable
   overnight.)

 - The satellite battery has a capacity of 9000 watt-hours. A delay of 24
   hours would still have allowed nominal energy for the whole mission.

 - Beyond 1200 meters, the gravity-gradient pull should be sufficient to
   help considerably with the deployment.

 - Tentative schedule: Resume deploy ~10AM EDT Wednesday. ~6 hours for
   deploy to 12.5 miles (3:30 PM EDT). 8 hours science mission at full
   deploy, ending at 11:30 PM EDT. Retrieval sequence - 6.5 hours for
   first stage, ending at 6AM EDT Thursday, final phase 4.5 hours, until
   10:30 AM EDT, then dock to boom at 12:30 PM EDT Thursday. (There may
   have been a half hour slip thus far.) About a day later, lower orbit to
   128 nautical mile orbit, to support the other experiments. Landing on
   Saturday morning.

 - Wednesday morning - they've just reeled in 88.5 feet of tether. It's
   hoped that unreeling over that distance will get speed up to about
   2 feet per second before it reaches the 850 foot stick point.

Comments: It would be nice if there were provisions to use some of the
tether-generated power to recharge the satellite batteries. It also appears
that it might be a good idea to develop some sort of "tension regulator"
(analogous to a SCUBA pressure regulator) to go between the tether reel and
the satellite, so the tension on the reel is never allowed to go above a
certain level. Tension should also be carefully regulated in the initial
winding of the spool, and on rewind. I'm sure they took this into account on
this mission, but perhaps they didn't do enough. :-)

John Roberts
[e-mail]

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

Date: Wed, 5 Aug 1992 16:55:10 GMT
From: "Robert A. Lentz" <[e-mail]>
Subject: What is FRED?
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (John Roberts) writes:
>
>-From: [e-mail] (Henry Spencer)
>-Subject: Re: What is FRED??
>-Date: 4 Aug 92 22:34:02 GMT
>
>-In article <[e-mail]> [e-mail] (Michael Corvin) writes:
>->What program does "fred" refer to?  I've seen it mentioned quite
>->a bit but have never come across what it actually is...
>
>-It's a cynical nickname for Space Station Freedom, coined when the thing

>-shrunk yet again a couple of years ago.
>
>Actually, somebody on sci.space suggested "Fred" even before Reagan announced
>the name "Freedom".

As I recall it was proposed back during a discussion about naming the new
shuttle. It was pointed out that we have Atlantis, Colubia, and Discovery,
so the new shuttle name should begin with a "B". Someone then suggested the
pair of Fred and Barney for the station and shuttle. Someone else suggested
Darwin' ship "Beagle", commenting that it sort of even looks like one :-)

As I like telling my friends, the station started out as "Freedom", and
through the cutbacks/redesigns is now "Fred", and anymore cutbacks will
make it "dead".

-Robert
--
[e-mail]      "We're a rock-and-roll band and we'll bring down the house
                   the way Bill is going to bring down the country."
                       -Roger Clinton, on his band's plans to play at the
                        Inauguration if his half brother, Bill, wins.

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

Date: 5 Aug 92 18:57:22 GMT
From: "John W. Cobb" <[e-mail]>
Subject: Whats wrong with this CIRCUIT (was: Tethered Satellites)
Newsgroups: sci.physics,sci.space

I'm cross-posting to sci.space. Scott said that they were having a
similar discussion. I haven't been keeping track there. I hope this
is a help and not a hindrance there.

In article <[e-mail]>, [e-mail]
(Steven Robiner) writes:
|>
|>Excuse me, but isn't something missing from this "Tethered Satellite"
|>experiment?  The shuttle is at one end, and the satellite is at the
|>other, right?  But that's an open circuit, so where's the load
|>joining the ends of this 'generator.'?
|>

Why should this bother you anymore than seeing something like:
                    -----------|

                             -----
                              ---
                               -
On a circuit diagram? Where's the load for a grounded circuit?
How do you get a power supply that guarentees you the input is at
+9V?

The difference here is that we appeal to a novel source of EMF rather
than something more standard like a battery or a power supply.

Now if you want to get to the nitty gritty, you should ask, well lets
follow the electrons and see what happens. So lets try that. The tether
will soak up electrons (I'm assuming a polarity here, I may have it reversed)
then transports it to the shuttle. Since the shuttle will have an excess
of electrons, it will shed them when its potential compared to the
local plasma is higher than the work function for the shuttle surfaces.
So now you have the "infused" electrons into the flux tube that contains
the shuttle. Eventually normal plasma-plasma and plasma-neutral interactions
will allow the electron to move back to its original flux tube. This however
may take some time. So the circuit is really completed in the same sense
that grounded circuits are completed, except here we don't have a good ground
because of magnetic insulation. The critical question becomes, what is
the maximum current I can pull off of this circuit. That is the voltage is
fixed, so the power output depends on the maximum current. Well if you
pull enough current fast enough, you will create a charge imbalance between
the flux-tubes and shut down the circuit. Two things will determine this
limit. The first is the relaxation time mentioned above and the second is
the motion of the shuttle itself. The shuttle is moving across the magnetic
field, so if it saturates the local flux-tube with excess electrons then
it cannot draw extra current until its orbital motion takes it to another
flux tube. Now I am not sure whether natural relaxation time or orbital
motion sets the limit on power extracted.

Now for some numbers (order of magnitude only). Suppose the spacecraft has
an orbital velocity of ~10,000 meters/sec and the geomagnetic field is
~10 Gauss. The relevant expression(cgs) is E = V X B / C = 333E-6 statvolt/cm
= 10 Volt/meter = 16,000 Volt/mile of tether. This is pretty close to the
quoted numbers. The actual orbital velocty is probably closer to 5000m/s.

Now lets talk about how the tether might affect the orbit of the satellite.
Imagine a local coordinate system where: V = - |v| \hat{y} ; B = |B| \hat{z}
and the tether is extended in the -x direction. In this cooridnate system,
an equatorial satelite is moving east-to-west (pardon the heresy), the
magnetic field points from the south to the north and the tether is lowered
earthward. The electric field is VXB/c. Therefore it points earthward (-x
direction). E is parallel to J by Ohm's law. The force on the tether is
JXB/c therefore it points in the + y direction. It acts to slow down the
spacecraft. Now the thing to ask is how large. Well that depends on the
resistivity in the tether, since that will determine J. It don't have that
number in my head. Perhaps someone else will comment.

|>Conspiracy Theory:
|>------------------
|>The whole thing is Top-Secret high-tech fishing trip: just stick
|>a satellite out on a long string and see if any 'UFO's bite.  ;)

Be careful what you wish for, you may get it. :>

john w. cobb
[e-mail]

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End of Space Digest Volume 15 : Issue 076
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