Space & Astronomy/Space and Astronomy (October 1993).iso/pc/text/spacedig/v15_0/v15no087.txt

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Date: Sun,  9 Aug 92 05:00:03
From: Space Digest maintainer <[e-mail]>
Reply-To: [e-mail]
Subject: Space Digest V15 #087
To: Space Digest Readers
Precedence: bulk


Space Digest                Sun,  9 Aug 92       Volume 15 : Issue 087

Today's Topics:
                A 12 mile tether that generates 5000v?
                           Atlas and Soyuz
                        Clinton Space Position
                            Comments, Misc
                Energiya's role in Space Station assem
                       Hubble used for spying?
                Looking for information on OSC/Pegasus
Physics of shuttle & tether (LONG) (was: Re: Two questions about ...)
                    rising and setting of the Moon
                      ROCKET trajectory program
                 Russian Comment on Soyuz vs Shuttle
                                Tether
 Tether Applications (was Re: A 12 mile tether that generates 5000v?)
                        tether circuit closure

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

Date: Wed, 5 Aug 1992 20:38:37 GMT
From: Andreas Windemuth <[e-mail]>
Subject: A 12 mile tether that generates 5000v?
Newsgroups: sci.space

Greetings to all tether fans,

What has been thought or done about rotating tethers? They would still
be able to interconvert angular momentum and electrical power using the
electrodynamic effects discussed here so far. They could also
be used to slingshot payloads between low and high elliptical orbits,
acting as angular momentum banks to trade angular momentum between
spacebound and earthbound payloads. Reaction mass could be made almost
obsolete.

A payload in a low elliptical orbit would match velocities with the
lower end of a heavy, rotating tether (the lower end would lag, i.e. be
slower than the orbital velocity of the tether as a whole), dock to it,
travel half a tether revolution to the upper end and cut lose for a
high elliptical orbit (the upper end of the tether is faster than the
tether orbital velocity) The angular momentum gained by the payload is
taken from the tether, of course, but it can be regained either by
slinging another payload back to the lower orbit or, alternatively, by
using solar energy and the electrodynamic effect.

You can even imagine tethers long enough to reach a planetary surface
and act as elevators. Rotation speed would have to be such that the
tether "walks" the surface of a planet. It's lower ends would match
velocity with the planets surface and effectively dip into the
athmosphere almost vertically, leaving enough time to just hang some
payload onto a hook, to be dragged out into space as the tether rotates.
I believe that existing materials are not strong enough to support this
scheme on earth, but on the moon it might well be feasible today.

Anybody have any ideas or knowledge on this?

---
        Andreas Windemuth

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

Date: 07 Aug 92  23:31:54
From: [e-mail]
Subject: Atlas and Soyuz
Newsgroups: sci.space

Hi David!

>Several points on the issue of using Atlas as a launch vehicle for
>Soyuz:
>   The nominal SSF orbit is somewhat higher than the nominal Atlas
>orbit cited (220 nmi). However, the Centaur upper stage is very
>good at creating Delta V; it is not so good at lifting realtively
large payloads, such as a oyuz.Soiyuz

   Yes, the "nominal" SSF orbit is somewhat higher than 220 nmi I
used.  But the planned SSF rendezvous altitude for resupply is 220
nmi.
   SSF's altitude will vary (for a variety of reasons - including
atmospheric drag, which will decay the orbit over a period of
several months), with orbits from 290 nmi to about 200 nmi.
However, I looked up the planned altitudes for shuttle rendezvous,
and found it was consistently planned at 220 nmi. The plan is to let
the SSF's altitude decay to 220 nmi or so, then rendezvous with the
logistics resupply craft (Shuttle), and then reboost after resupply.
This altitude was derived from a trade study that tried to maximize
launch performance and minimize reboost propellant needed.  Since I
was trying to compare "apples to apples", I used the same rendezvous
altitude.
   To compare, I pulled the Atlas IIAS performance data off a
performance curve from the Atlas II Users Handbook and used it.
Since I'm reading off a poorly reproduced curve, my performance
numbers may easily be +/- 100 kg.
   Also, I agree that a Centaur is probably not the best designed
for lifting large payloads due to its pressure stabilzed structure.
But Centaurs have been designed for up to 6000 Kg payloads (the
Centaur G' planned and built for the shuttle was to carry over 13000
lbs into GEO), and the Centaur does lift payloads of approximately
3500 Kg into Geotransfer orbit (burning the Centaur dry inserting
the payload into GTO rather than circularizing the payload in GEO).
I figured for the ROM estimate I was making here that a Centaur
probably could handle the additional mass with a bit of care and a
hint of redesign.
     As I stated in my previous message - I THINK when everything
gets added up, a Soyuz is too heavy for a Atlas IIAS.  I haven't had
the time to dig through them in more detail as a preliminary design
study to get a more precise answer.  But the numbers are close
enough the possibility of launch of a Soyuz on a Atlas IIAS is very
interesting.
 ----------------------------------------------------------------
 Wales Larrison                         Space Technology Investor

--- Maximus 2.00

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

Date: 8 Aug 92 09:24:49 GMT
From: "Frederick A. Ringwald" <[e-mail]>
Subject: Clinton Space Position
Newsgroups: sci.space

In article <[e-mail]>
[e-mail] (Greg Moore) writes:

>     (Now, the question is, does Henry have Bono's voice? :-)

Let's just hope he doesn't have his funny looks!

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

Date: 07 Aug 92  21:57:22
From: [e-mail]
Subject: Comments, Misc
Newsgroups: sci.space


Allen, this is the text of the email I have been trying to send
My apologies to the net, but my mail server (or my comm program) has
been acting up.       Hi Allen!
    Could you please stick my name and address on the space
activists mailing list, please.  I hope this email makes it through
- the net connection at this end has been pretty flaky, and my
machine has been down at home, as well.
    Been following the flame fest on sci.space regarding use of a
Soyuz.   Here's a random comment or two for you which I didn't deem
appropriate for the net.

>>No problem, if that's all you need.  Are you willing to expend the
>>logistics modules that would be brought up and down with a crew
>>rotation?
> I don't think we need to. We can stick some Shuttle tiles on it,
>put a parachute on top, and teather it down (which saves fuel and
>reduces station keeping fuel needs). It will land just like a
>capsule. ...
     Whoosh!  You're kidding, I hope.  Controlled reentry is a
tricky business, unless you're willing to take the Soviet
"hypersonic cannonball" approach by using a sphere and accepting a
dispersion (2 sigma) of about +/- 30 miles.
     To get a reasonable reentry (no fine guidance, just enough
control to maintain attitude and control to avoid tumbling or
excessive entry heating), you'll need a RCS plus some type of
aerodynamic control to maintain attitude after separating from that
tether.  [Note:  nominal reentry interface is about 400,000 feet --
about 75 miles altitude.  The tether has to be 175 miles long, or
else you'll need some attitude control after letting go.]
Mercury/Gemini didn't use aerocontrol and had an dispersion of about
+/- 20 nautical miles (2 sigma).  Apollo used active aerocontrols.
    Furthermore, a logistics module is rather unsuited for reentry -
the c.g. is way off from the c.p., which either means a ferocious
control system (huge fins or one mother of a RCS) or you'll have to
redesign to redistribute the mass.  Not cheap.
   "Sticking on shuttle tiles" probably won't work either.  There's
enough protrubrences that you'll probably have to cover large
sections with ACC or RCC, not just shuttle "tiles". Not cheap.
    The structure also isn't strong enough to take a parachute
landing impact.  The logistics module is designed to couple with the
orbiter structure, so landing it with a 30 ft/sec impact would
probably buckle the structure - at least.  You'd have to add
deployable airbags (and hope you don't have cross wind - air bags
are notorious for collapsing in a cross wind as we've found out on
the F-111 ejection capsule), or use a Russian-style retro rocket
system.  Both of these add complexity and cost and weight.

>>Again, no problem on the surface.  Although Soyuz has never had to
>>land in water, it has missed it's target area by hundreds of miles
>>on more than one occasion.
> The question here is why. It could be that Russian position
>location isn't good enough ...
  From what I've heard, the problem is timing of reentry burn and
attitude.  The Soviets didn't care about fine guidance in reentry
since they had all of Kazakahastan (sp?) to land in.  A typical
entry was +/- 30 km, if all went well.  The worst case was driven by
failure of the automatic reentry sequence.  The on-board system was
recycled, failed again, and then overridden manually and fired some
seconds late.  At orbital velocity, timing errors can really throw
the system off.  A one minute error translates into about 277 miles.

>>Your point about the single point failure is well taken, however,
>>four crewmembers simply cannot fit inside a Soyuz return module.
> They can for the short time needed to get to the other one.
   Errr.... beg to differ here.  I've been inside an early-model
Soyuz (circa 1978) and have examined the interior of a Soyuz TM at
close range (couldn't get into that one - had a plexiglas cover over
the hatch area).  The three people inside have to be very good
friends, as the inside of a Soyuz is about the size of a large phone
booth.  If I remember correctly on Soyuz 11, they launched 3 crew
without suits becuase they couldn't fit three suited cosmonauts into
the interior volume.  After the deaths on Soyuz 11, the Soviets
launched 2 man Soyuzes with suited crews.  Only after the Soyuz TM
did they return to 3 man crews (in suits) - achieving the additional
internal volume through repacking upgraded avionics.
  You MIGHT get 4 persons in (very doubtful), but I doubt you could
get the hatch shut (and there is only one hatch).  And if you could
the 4th person couldn't get turned around and would have to shimmy
out the way he got in.

>We use some of the savings to fund the hard suit (which they should
>have done in the first place). Pre-breath won't be needed. This
>gives us two ways to get the crew to the vehicle.
   Difficult to don a hard suit in a Soyuz.  You need at least 3
times the volume of a person.  1 for the person, 1 for the suit, and
1 for maneuvering the suit and the person around to don it.  That
type of delta volume in just not available in a Soyuz.  And what
happens when you open the hatch? Where are the other 3 suits stored?

>We use the Russian automatic docking system to dock the two Soyuz's
>together.
   The automatic docking system is currently running about 50%
reliability - the past 2 Progress missions have failed on at least 1
attempt each (although they succeeded on subsequent trys with a lot
of ground intervention), and the latest Soyuz mission had to abort
its automatic dock and come in on manual.   Not really a
trustworthy system if it's the only way to get to your ride home...
                                     Cheers!    - Wales -

--- Maximus 2.00

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

Date: 6 Aug 92 23:15:59 GMT
From: Charles Frank Radley <[e-mail]>
Subject: Energiya's role in Space Station assem
Newsgroups: sci.space

SSF is in 28.5 deg orbit because congress limited the number of
Shuttle flights, and NASA wants to squeeze as much mass as it can
into each Shuttle.
  Launching into 55 deg orbit is a mass payload penalty of
about 15 %

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

Date: 8 Aug 92 16:12:28 GMT
From: John Roberts <[e-mail]>
Subject: Hubble used for spying?
Newsgroups: sci.space

-From: [e-mail] (Hoyt A. Stearns jr.)
-Subject: Re: Hubble used for spying?
-Date: 5 Aug 92 00:56:16 GMT
-Organization: International Society of Unified Science

-A PBS broadcast on spying a couple of years ago described the KH11 and KH12
-spy satellites.  They seemed remarkably similar in size and shape to the
-Hubble telescope. Are you sure they're not related? :-)

The *mirrors* are related. Hughes Danbury also makes spy satellite mirrors,
and the HST primary mirror was made at the spy telescope mirror facility,
though to different specifications than the spy telescope mirrors.

This was a contributing factor to the mirror aberration - DoD essentially
told NASA to keep their noses out of the fabrication process, because they
were uncomfortable about having civilians knowing about the classified
portions of the process. As a result, NASA didn't have enough supervisory
presence to catch the errors Hughes Danbury made.

There's no reason to believe there's any close relation between the
*instruments* of the two systems. FOC, for instance, was made by ESA,
which probably doesn't make US spy satellite instruments. :-)

I'm not sure, but when HST is pointed at the Earth for half of each orbit,
I think the door in front of the telescope aperture is kept closed until
Earth is out of the way. There must be a reaction wheel routine programmed
to compensate for the opening and closing of this door.

John Roberts
[e-mail]

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

Date: Sat, 8 Aug 1992 16:40:31 GMT
From: Brian Reynolds <[e-mail]>
Subject: Looking for information on OSC/Pegasus
Newsgroups: sci.space,rec.models.rockets

I would like to build a model of the OSC/Pegasus, but I have no scale
information.  The sci.space FAQ doesn't really provide much
information.  Can anyone give me the address or phone number for OSC
so that I can request some information?  Does anyone know of a model
of the Pegasus?  I recall that Monogram re-released their B-52 carrier
aircraft / X-15 model substituting a Pegasus for the X-15, but I
really don't want to build the B-52.  Did Monogram ever release the
Pegasus as a separate kit the way they issued the desktop version of
the X-15?

Thanks in advance.

--
Brian Reynolds
[e-mail]
NAR# 54438
IPMS# 30162

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

Date: 7 Aug 92 16:40:29
From: Craig Powderkeg DeForest <[e-mail]>
Subject: Physics of shuttle & tether (LONG) (was: Re: Two questions about ...)
Newsgroups: sci.space,sci.space.shuttle

[e-mail] (Alan Kilian) writes:
   1) The shuttle is at one end of a conductive wire. The satellite is at
      the other. If the wire moves through a magnetic field you can generate
      an electric potential. Now how do you measure the potential?
      They were hoping for 5000 Volts on a 12 Mile tether but got 40 Volts
      on a 750 Feet tether.

The potential is an emf around a conductive loop.  More explanation under
(3), below.


   2) Why does the ball (It's easier than satellite) keep moving away from
      the shuttle as you unwind the tehter?

This is a pretty cool effect, and it can be explained in two equivalent
ways.

First, one can say that the ball, being at a different altitude than the
shuttle, `wants' to orbit with a different period, so will pull `ahead'
(if, as on this flight, it's lower than the shuttle), or `behind' of the
shuttle.  The tether pulls it back against this tendency, so is kept taut.

Alternatively (and perhaps better), the space around the shuttle is
subjected to a gravitational gradient.  That is to say, the gravitational
field (due to the Earth) in the vicinity of the shuttle, changes with
altitude above the Earth.  The ball, being closer (farther) to (from) the
earth than is the shuttle, is pulled more strongly (weakly) by the earth
than is the shuttle.

The result is that things in orbit about one another, tend to want to
stretch along the axis between the things.  This is the effect that
creates tides on the Earth (and Moon too!), aligns the LDEF experiment,
and (in an extreme and hypothetical case) would hold up the Space
Elevator[1].


   3) (I know I said two but what the heck) How can you use the potential
      from the one wire tether?

This is a really cool effect, and uses the plasma around the earth.

You can make an electromotive force around a loop of wire by cutting magnetic
field lines with the wire, by the Maxwell equation relating curl of V to
dB/dt.  In fact, the emf exists around any closed loop of space, whose flux
linkage is changing, regardless of whether there's a wire there or not.

The tether experiment uses the conductive properties of the plasma around
the earth, to make a *really* *large* loop of conductor using just the
tether.

The (very tenuous) atmosphere at Shuttle orbital height is a plasma, ie a
gas that is mostly ionized, and thus conducts electricity.  (You have
probably seen electrically conductive plasmas -- you need only look as far
as the nearest neon light -- but that's a different story.)  The shuttle
used the plasma surrounding it as the return wire for the tether experiment.

There's one more effect we need to describe.  That's the reason why the
conductive loop was *really* *large*, instead of just (more-or-less)
shuttle-sized.

When a charged particle moves at right angles to a magnetic field, it
`feels' a force at right angles to the motion and to the field.  The result
is that its motion (if there's no electric field) is circular.  But *any*
motion can be resolved into a component at right angles to the field, and
one along the field.  So any charged particle travelling through a magnetic
field (in the absence of collisions and electric field) will spiral around
the field lines themselves.

If you stand far back and squint (ie you care only about really long
distances), this means that electrons travel *only* along magnetic field
lines.  The only ways to conduct across the field lines involve a high
electric field, or collisions between charge carriers. So it's really easy
to conduct electricity along magnetic field lines and hard to conduct it
across them.  The magnetic field lines act almost like wires!

The conductive loop in the tether experiment consists of (a) the tether
between the shuttle and the ball; (b) the (REALLY LONG!) field line
extending from the shuttle to the nearest magnetic pole of the Earth; (c)
some small resistive elements between nearby field lines (which get really
close as you get closer to the poles); and (d) the field line extending
back to the ball from the magnetic pole.

The ball is, well, a conductive ball, so it has a lot of surface area to
collect electrons from the surrounding space.

The shuttle has an electron gun mounted on it (in the nose? the bay?  I
forget.) to expell electrons out into the surrounding plasma.  If there
were enough emf, a simple (lightning-rod type) needle point would do the
trick, concentrating the electric field enough to rip electrons out of
the metal.

There's one catch: In order for the separation of field lines to work, the
two magnetic field lines that you use have to be much farther apart than
the diameter of the spiral made by each electron around its `home' field
line.  When the field lines get that close, then a single collision can
cause an electron to skip from one to the other, so there isn't much
electrical isolation between the field lines.

The gyroradius (as it's called) increases linearly with the velocity of
the electron, and decreases as the magnetic field strength increases.
I can't remember offhand a `typical' gyroradius for electrons at that
height, but I imagine it's on the order of 100m -- which would mean that
electrons can easily `hop' about 100m across the magnetic field.

So the shuttle-and-ball system wasn't very effective at all, as a
dynamo -- if the tether had unreeled more than a few hundred feet, there
would've been much better electrical isolation between the ball and the
shuttle, and the conductive loop for the experiment would've been
vastly, mind-bogglingly more huge.  Considering that most of the electrons
probably stayed in the near vicinity of the shuttle/tether system, rather
than wandering out on the magnetic field, it's amazing it worked at all!

[1] as described in _The_Fountains_of_Paradise_, another one of Arthur
Clarke's self-important novels.
--
Craig DeForest:  [e-mail]  *or*  [e-mail]

"So, if you guys make a living looking at the SUN, why do you spend so much
        time at the SYNCHROTRON, working UNDERGROUND at NIGHT?"

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

Date: Sat, 8 Aug 1992 9:31:17 -0500 (CDT)
From: [e-mail] (Patricia Reiff [phone])
Subject: rising and setting of the Moon

To the person interested in times of moonrise and moonset:
A great piece of software is "Voyager" for the Mac - it can give
altitudes, azimuths, etc, for stars and planets, any day, any location -
in fact, you have to be careful - if you put in the year as "92" you
get the result for 1900 years ago!  Similar software exists for pc's, and
shareware versions are probably available.

Many people aren't aware of the basics of moonrise and moonset - that it's
linked to the phase of the moon.  A first quarter moon rises at noon and
sets at midnight, a full moon rises at sunset, etc.  (draw a simple diagram
of the sun- earth - moon from above the ecliptic plane (look down from the
north), and recall that the earth spins, and the moon orbits, counter-
clockwise).

Another lkf (little-known fact):  a full moon in summer is low in the sky
(like a winter sun, and for the same reasons), and high in the sky in
winter.  That, plus the deviation of +/- 5 degrees from the eclipic, can
make a full moon in summer not last very long in the sky.  There is a
fascinating legal case that Abe Lincoln won that concerns the rising and
setting of the full moon.

------
From the First Space Science Department in the World:
                                                    :      _^ ^_    ____
     Patricia H. Reiff                              :     / O O \   |GO \
     Department of Space Physics and Astronomy      :     \  V  /   |OWLS\
     Rice University, Houston, TX 77251-1892        :    / ""R"" \__/
     internet:  [e-mail]  (128.42.10.3)    \ ""U"" /
     SPAN:      RICE::REIFF                         :    _/|\ /|\_

"Why does man want to go to the Moon? ...  Why does Rice play Texas?"
   ....JFK, Rice Stadium, 1962

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

Date: 6 Aug 92 23:13:32 GMT
From: Charles Frank Radley <[e-mail]>
Subject: ROCKET trajectory program
Newsgroups: sci.space

Has anybody heard of an old public domain NASA trajectory analysis
program called (I think)    ROCKET   or something like that ?

Would appreciate it if anybody has heard of it, or preferably
knows where I can get a copy.

Please e-mail to my other address which is :-


Thanks

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

Date: 07 Aug 92  21:45:44
From: [e-mail]
Subject: Russian Comment on Soyuz vs Shuttle
Newsgroups: sci.space

    Just thought I'd add this to the discussion going on about Soyuz
and shuttle for space station operations....

    According to the trade press, cosmonaut Anatoly Artsebarsky
stated at a press conference in Chicago last Tuesday, regarding the
Buran:
    "We need it (Buran) to bring back (to Earth) materials and
experiments from the station... When using the Soyuz spaceship, we
have to abandon some experiments and materials due to its limited
(return) capability."

    Artsebarsky is on a visit to Chicago to promote a Russian space
exhibition.

    Since the Russians have some years of space station operating
experience, and their space station configuration is somewhat
smaller than the planned SSF configuration, and Artsebarsky has
recently returned from a Soyuz/Mir mission, I thought this was an
interesting comment, re the current continuing discussion  |-).

 ------------------------------------------------------------------
 Wales Larrison                         Space Technology Investor

--- Maximus 2.00

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

Date: 8 Aug 92 16:44:31 GMT
From: John Roberts <[e-mail]>
Subject: Tether
Newsgroups: sci.space

-From: [e-mail] (Andrew Haveland-Robinson)
-Date: 6 Aug 92 20:32:01 GMT
-Organization: Haveland-Robinson Associates

-In article <[e-mail]> [e-mail] writes:
->On the contrary, if energy is extracted from an orbiting body, its kinetic
->energy *increases* by this exact amount.  All this additional energy is
->provided by the gravitational binding energy.  A very useful use of a tethered
->loop could be not to extract electric energy at the expense of gravitational
->energy, but the  contrary: electric energy, coming from solar cells for
->instance, can then be used in the opposite way to lift up the satellite orbit.
->
->        Daniel Pfenniger

-You make some interesting though to my mind, rather curious assertions.
-How does it gain kinetic energy if you take energy out of it?

Drawing power from the tether takes away from the kinetic energy of the
Shuttle. This in turn causes it to drop to a lower orbit. The drop in
orbit causes some of the gravitational potential energy of the Shuttle to be
converted into Shuttle kinetic energy. Thus the net effect is that the change
in gravitational potential energy goes partly into the power drawn from the
tether, and partly into increased kinetic energy for the Shuttle. Whether
the two amounts are equal takes a little more math.

-As I understand it, if you take energy out of an orbiting body, it moves
-into a higher orbit at a slower velocity. If you take more out then it
-ceases to orbit and starts falling to earth.  If there is still an angular
-moment then it will stabilise in an orbit (if the Earth doesn't get in
-the way of the trajectory!).

That's backwards. Centripetal force on the Shuttle from its orbit equals
v^2 / r, where v is the orbital velocity of the Shuttle, and r is the distance
from the Shuttle to the center of the Earth. The gravitational attraction
between the Shuttle and the Earth is essentially GmM / r^2, where G is the
gravitational constant, M is the mass of the Earth, and m is the mass of the
Shuttle. (Note that if the tether is very long, and if the mass of the
satellite is nearly the mass of the Shuttle, then the calculation of r is
a little more complicated.) Kinetic energy equals 0.5 * m * v^2. So a high
circular orbit has less kinetic energy but more gravitational potential
energy than a low circular orbit. The high orbit has greater (kinetic plus
gravitational potential) energy than the low orbit.

-I suppose the current will alternate during the orbit too, depending on which
-orbit was chosen (I guess a polar one would be most productive).

If the plane of the orbit is exactly perpendicular to the axis of the
magnetic poles (not sustainable because this axis wobbles with the rotation
of the Earth), then you would get DC out. For a Shuttle orbit, you get DC
with a slight AC ripple superimposed. If you move parallel to the lines of
magnetic force, you don't get any voltage out.

John Roberts
[e-mail]

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

Date: Sat, 8 Aug 1992 18:02:00 GMT
From: [e-mail]
Subject: Tether Applications (was Re: A 12 mile tether that generates 5000v?)
Newsgroups: sci.space

In article <[e-mail]>, [e-mail] (Andreas
Windemuth) writes...
>
>Greetings to all tether fans,
>
>What has been thought or done about rotating tethers?

>You can even imagine tethers long enough to reach a planetary surface
>and act as elevators. Rotation speed would have to be such that the
>tether "walks" the surface of a planet. It's lower ends would match
>velocity with the planets surface and effectively dip into the
>athmosphere almost vertically, leaving enough time to just hang some
>payload onto a hook, to be dragged out into space as the tether rotates.
>I believe that existing materials are not strong enough to support this
>scheme on earth, but on the moon it might well be feasible today.
>
>Anybody have any ideas or knowledge of this?

Great set of questions there. The formost person that I know working on tethers
right now is Dr. Robert Forward.  He is the guy who was working with the U.S.
Air Force on antimatter research.  He has guggested that a lunar transportation
system could be set up with tether of a length of about 1000 km.  The center
would be in a stable lunar orbit at 500 km and would rotate. The lower end of
this rotation would be at the lunar surface and of course the higher end
would be in a pretty high lunar orbit. The only problem with a rotating
tether transportation system is that the mass that you pick up and or leave
either on the moon or in orbit about the earth must be balanced with picking
up or dropping an equivalent weight on the other end.  If you are very good
with your transportation logistics this would work but scheduling would be
a major pain.

Also a non rotating tether transportation system has been proposed for Martian
operations, I beleive by Paul Penzo of JPL.  His system would have payloads
in LMO catch the bottom end of a Phobos anchored tether where a simple
elevator would move the payload up to phobos, then upwards on another tether
where it would be released.  The length of this upper tether would be such that
the orbital altitude gained would place it in a position that would allow it
to be caught by a tether on the low side of Deimos.  Again by a simple elevator
the payload would be moved up to Deimos then outward from Deimos to a point
to where the delta V from the tether gravity gradient would propel the
payload into an interplanetary trajectory. Neat huh!

The only problem with electrodynamic power generation in LEO is that you do
not get something for nothing. If you take power from the Earth's magnetic
field you lose orbital momentum.  If you have extra power and put it into the
tether you gain orbital momentum, which increases your orbital altitude.
Someone on here posted that if you decrease orbital energy you gain altitude,
this is wrong.

The applications of tethers are so rich that it should be one of the two
or three critical technologies to pursue in truly opening up the solar
system to development.  That is the underlying reasons that we are doing
our satellite deployment via a tether. If our scenario works out it will help
all of our scenarios, even Allen's to become faster cheaper and better.

Dennis, University of Alabama in Huntsville.

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

Date: Sat, 8 Aug 1992 9:05:35 -0500 (CDT)
From: [e-mail] (Patricia Reiff [phone])
Subject: tether circuit closure

re closure of tether circuit:  This closure is, as has been mentioned,
effected by collection of charge on the shuttle surface.  Since the surface
is covered mostly by non-conducting tiles, this is rather poor and the
effective collecting area is small.  Thus, when the shuttle "Atlas" program
a few months ago flew an artificial aurora experiment, putting out a ~kV
electron beam with ~0.5 amps merely just makes the shuttle charge up to
~kV with respect to the local plasma, shutting the beam off.  To get a full
current circuit, they turned on a plasma gun (yes, ions and electrons).
The ions would then escape to close the circuit and the electrons return to
the shuttle, effectively replacing the electrons emitted (it's a bit more
complicated than that, but you get the idea).

The video is really impressive - only when the *plasma* gun is on can you
see the effects of the *electron* gun, because only then is the circuit
closed effectively.  The aurora experiment was a tremendous success, and
posed new questions (as every really good experiment does) - the beam
spread was larger than expected, etc.  Because it was such a success, it
didn't get the press it deserved, and despite pleas, is probably not going
to be reflown.  Note that the PIs for the artificial aurora experiment are
very close colleagues with the TSS PIs (lots of overlapping Co-I's, very
similar instrumentation and plasma gun, etc.), and, had the tether itself
not failed, the odds of tether science success would have been nearly
unity.  Another fact possibly not generally known is that this is the
second tether reel system.  The first was recognized to be bad, and was
replaced by the Italians, and this one had been the cause of a great deal
of worry by the scientists as well.

   One would hope that both the artificial aurora AND the tether systems
can be reflown, but with the shuttle politics, it is probably unlikely that
they will be.  It is this kind of thing that makes the "small" scientist
really get fed up with the manned program, that absorbs such a great
fraction of the dollars for such a relatively small science payoff, and why
so many space scientists fear Fred.  (No flames, please, just stating the
facts - we don't need another several megabytes of discussion there).

   These kinds of delays and frustrations have really plagued the
scientific community for the last decade or two, and make our graduate
students wonder whether it's worth all the effort to get a degree.  My
reply is, yes, it's not the field for everyone - if you want safety in
funding and assurance of results, it's better to go into high energy
physics, fusion research, or work at a federally funded lab   ;)     !  But
when things *do* work, and you learn something that noone has ever seen
before, or prove something that people had always suspected, then it seems
more worthwhile.  It's just sad to have to put in 10 days of paper-pushing
for 1 day of research!

   As Charles Darwin said:  "A naturalist's life would be a happy one if he
had only to observe and never to write".

------
From the First Space Science Department in the World:
                                                    :      _^ ^_    ____
     Patricia H. Reiff                              :     / O O \   |GO \
     Department of Space Physics and Astronomy      :     \  V  /   |OWLS\
     Rice University, Houston, TX 77251-1892        :    / ""R"" \__/
     internet:  [e-mail]  (128.42.10.3)    \ ""U"" /
     SPAN:      RICE::REIFF                         :    _/|\ /|\_

"Why does man want to go to the Moon? ...  Why does Rice play Texas?"
   ....JFK, Rice Stadium, 1962

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End of Space Digest Volume 15 : Issue 087
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