Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V10_2/V10_245.TXT

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Date: Tue, 14 Nov 89 01:38:20 -0500 (EST)
Subject: SPACE Digest V10 #245

SPACE Digest                                     Volume 10 : Issue 245

Today's Topics:
              Re: Space Elevator
              Re: Hubble Space Telescope
              Re: Hubble Space Telescope
              Sorry, I was too fast ...
            Re: fragility of life support
             Re: Gravity inside the Earth
            RE: VEEGA stands for ?
              Re: Future Space Missions
       NASA Select TV coverage of Consort 2 launch (Forwarded)
----------------------------------------------------------------------

Date: Mon, 13 Nov 89 17:52:57
From: Michel van Roozendaal ECD <[e-mail]>
Subject: Re: Space Elevator

From: [e-mail](Betrand Michelet)
Subject: Space Elevator

Space Elevators (or: Space Tethers...)

Your article is based on the initial concept proposed by Tsiolkowsky
back in 1895; he calls is the "Equatorial Tower". I quote:

Upon ascending such a tower gravity decreases gradually; at an altitude of
34,00 werst (Russian pre SI; 1 werst=1067 meters) gravity is totally
eliminated. For that reason at a still higher altitude it is displayed
with a force directed away from the critical point; the direction is
reversed so that mans head faces the Earth.

An other Russian involved in similar work is Y.N. Arsutanov; in 1959
he proposed the Space Funicular. Other people with similar proposals are
Isaacs (1966; the sky hook), Colombo, Grossi etc (Tethered Satellite System,fro
m 1974)

In 1979 Arthur C. Clarke wrote "The fountains of paradise", in which
Dr. Morgan builds an orbital tower on the island Taprobane (=Ceylon).
The story is placed in 2142.

In all kinds of variations one can use the original concept. Most of these
concepts are referred to as to TETHERS. I will not list them all here,
because I found I never read long stories on this net myself.

One of the applications which is think is particularly nice is the
deorbit of the Space Shuttle from a Space Station using a long cable
(=tether). Rather than braking the shuttle using rocket engines,
and thus consuming propellant, we connect the station with the shuttle
on a tether. The will be given an initial displacement (Station above the
shuttle), due to gravity gradient forces they will separate; i.e. the
shuttle will go down, and the station will go up. Gravity Gradient:
In the centre there is an equilibrium between the centrifugal and the
gravity force. Closer to the Earth, the gravity force is larger, farther
away, the centrifugal force is higher.

Okay, due to the fact that both vehicles have the same initial velocity,
but are now in different orbits on different altitudes, the station
will lag behind the shuttle. Trick: the gravity gradient forces are
pointing towards/away from the centre of the Earth, they will accelerate
the station, and slow down the shuttle in such a way the shuttle and the
station are both on the same local vertical. In this process angular
momentum was transferred from the shuttle to the station. We can now
disconnect the shuttle from the tether, and start reentry, having saved
a considerable amount of fuel.

Dynamic behaviour is a big problem; can we control the (in the case above
50 km-) long Tether?? This should be demonstrated with the TSS (Tethered
Satellite System) mission in march 1991 (STS 46 with Eureca).

Coming back on an other issue you raised; the material which we can use
to build a tower/elevator/tether.

In view of our applications a nice property in order to compare materials
is the free breaking length in a 1-G environment. This is the length
of a cable of a certain material when it will collapse under its
own weight, without tapper/1G. Remember; the free breaking length
of any material is infinite when we apply tapper.

Lets list a few materials:

Steel       37 km
Glass       76 "
Nylon       92 "
Carbon     171 "
Aramide    193 "
HP-PE      336 "

So we talk about strength per density; we need in space a strong,
light weight material.

The best candidate is the High Performance Poly Ethylene fibre. This
material is very simple in structure, but all (No; many of) the molecules are
aligned in the direction of the load.

The only HP-PE fibre soon in production is DYNEEMA SK-60 from the Dutch
firm DSM-Stamicarbon. (Pilot plant in the Netherlands)

An aramid fibre will be used in the TSS mission (in this case Kevlar).
This material is as strong but weighs more:

                Strength          Density

Aramid Fibre      2  GPa/density    1.44  kg/dm3
HP-PE             3    "            0.97    "

Drawbacks are for a HP-PE; exposure to atomic oxygen/high temperatures.

Other hazards for all possible materials and applications: Debris and
micrometeoroids, which can cut the tether.

That's it for the moment; I realise this posting is to long, sorry
for that.

I did my thesis work on tethers, so if somenbody wants extra info
(and you think I might be able to help you), ask
me. I can also send long lists with references.

One example: Guidebook for analysis of Tether applications, Joseph A. Carrol,
Martin Marietta corp, march 1985. (Contract RH4-394049O)


^-----------------------------------------^----------------------------------^
^ Michel van Roozendaal                   ^  EARN: ESC1759 at ESOC           ^
^ c.o. European Space Operations Centre   ^                                  ^
^ Robert Bosch strasse 5                  ^  valid till 20 december 1989     ^
^ 6100 Darmstadt  FRG                     ^                                  ^
^ tel. [phone]                     ^                                  ^
^      (0)6151-595725                     ^                                  ^
-------------------------------------------------------------------------------
-> ESA does very little work on TETHERS, they certainly don't pay me for it <-
*******************************************************************************

End of Message

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

Date: 13 Nov 89 01:26:41 GMT
From: cs.utexas.edu!samsung!aplcen!haven!uvaarpa!hudson!astsun9.astro.Virginia.EDU![e-mail]  (Greg S. Hennessy)
Subject: Re: Hubble Space Telescope

In article <590B0C11140C02E7-MTABWIDENER*DXANDY@widener> [e-mail] writes:
#
#  I recall reading somewhere that the Hubble Space Telescope would be able
#to resolve continents on planets orbiting distant stars.  Is this a piece of
#fanciful reporting, as it would seem, or is there actually some basis in
#truth?

The resolution of HST is [roughly] 20 milliarcseconds. Let us consider
Alpha centuri. It is about 1.3 parsecs away, this 1 arcsecond will be
1.3 AU or about 130 million miles. 20 mas will be about 26 million
miles. This is about 100 times the earth moon distance. I would
consider it rather awful reporting myself.

-Greg Hennessy, University of Virginia
 USPS Mail:     Astronomy Department, Charlottesville, VA 22903-2475 USA
 Internet:      [e-mail]
 UUCP:        ...!uunet!virginia!gsh7w

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

Date: 12 Nov 89 23:07:15 GMT
From: uhccux![e-mail]  (Jeff Goldader)
Subject: Re: Hubble Space Telescope

In article <590B0C11140C02E7-MTABWIDENER*DXANDY@widener> [e-mail] writes:
>
>  I recall reading somewhere that the Hubble Space Telescope would be able
>to resolve continents on planets orbiting distant stars.  Is this a piece of
>fanciful reporting, as it would seem, or is there actually some basis in
>truth?

*Very* fanciful reporting.  Originally, it was hoped that HST would be
able to resolve a planet from its parent star (i.e. see them as two separate
points of light rather than one) but that's now been shown to be very
unlikely, if not impossible.

I know there are some searches planned, including one by an amateur, Ana
Larson, a student/mother/homemaker at the University of Washington; her
observations will look for astrometric wobbles in the motions of T Tauri
stars (very young stars).  She was one of the winners of the amateur
proposal program.

Jeff Goldader                        University of Hawaii
[e-mail]      Institute for Astronomy

"Bill, strange things are afoot at the Circle-K..."
-Ted, "Bill and Ted's Excellent Adventure"

Disclaimer: The University of Hawaii and the Institute for Astronomy neither
support nor are in *any way* responsible for these opinions.

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

Date: Mon, 13 Nov 89 09:25:06
From: Lutz Massonne <ESC1325@ESOC> ([phone]) <[e-mail]>
Subject: Sorry, I was too fast ...

Sorry for my incorrect answer to the COBE question - I did not read
the original question correctly (and received the COBE article
much later - the SPACE distribution over here has a rather
strange time correlation :-) ).
For a *sun*-synchronous orbit there are a lot of observational
arguments - in fact I work on ERS-1, the European Earth observation
sat which is also in sun-synchronous orbit mainly for attitude control
reasons. We have sun sensors fixed at certain angles which correspond
to the chosen orbit.
If you do optical observations of the Earth's surface you are normally
interested in equal lighting conditions - hence also a sun-sync orbit.

Regards, Lutz

(Usual disclaimer applies)

|                                                      |
| Dr. Lutz Massonne, mbp Software & Systems GmbH, OAD, |
| European Space Operations Centre, Robert-Bosch-Str.5 |
| D-6100 Darmstadt, FRG  <[e-mail]>         |

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

Date: 13 Nov 89 20:05:49 GMT
From: datapg!com50!questar![e-mail]  (Al Viall)
Subject: Re: fragility of life support

In article <[e-mail]>, [e-mail] (Henry Spencer) writes:
> The answer to this is obvious:  systems which can suddenly "fail hard"
> must be fixed to either fail more slowly or fail soft.  (Just hoping
> they won't fail is not acceptable for long-term habitation; they will.)
        [ some text deleted ]
>   It should be possible to handle most everything
> else with the same approach used on Earth, i.e. repair of broken systems
> plus sufficient reserves to survive transient failures.

I agree. The way many systems are scrutinized by NASA, it is doubtful that
they will use "fail hard" systems.

But, then again, many, even to this day, still feel that the shuttle system
we have now is a testament to a more slow failing system, but we all know that
many areas of the shuttle can go just like 'flick', that.

Having multiple systems and/or backup reserves for life support is great,
but when does the line get crossed between original and backup. I could
probably last in Alaska with a backup wood stove, or better yet, pop a hole
in the roof and build a fire in the kitchen. One couldn't be as resourceful
on the moon.

--
| INTERNET: [e-mail]      |    NEW PRODUCT ON THE MARKET     |
|     UUCP: ..!amdahl!tcnet!questar!al     |        "Flame in a Can"          |
|  FIDONET: 1/282:2,3 (Al Viall)           | Just tear off the protective     |
| "MMMMMMM. And so good for you!"          | seal, point and shoot. Great fun!|

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

Date: 13 Nov 89 18:14:04 GMT
From: pur-phy![e-mail]  (Carrick Talmadge)
Subject: Re: Gravity inside the Earth

In article <Added.MZJO0BK00Ui388kE8=@andrew.cmu.edu> [e-mail] writes:
>                                 Inside the Earth, gravity varies
>approximately linearly, from 0 at the centre to g on the surface.
>Density variations and non-sphericity of the Earth account for the
>approximately.

I'm afraid that this is not even approximately true.  A typical Earth
model has the net gravitational acceleration g starting at 9.8 m/s^2 at the
surface, increasing to a maximum of 10.7 m/s^2 at a distance from the
center of ~ 0.55 R (R = Earth radii), and only then decreasing
approximately linearly to zero.  It can be shown that for bodies such
as the Earth, g will increase with depth until the local density
approaches ~ 2/3 the average density of the body, and this occurs near
the depth 0.55 R [at least in the Preliminary Reference Earth Model].

Carrick Talmadge                [e-mail]
-------

References:

A. M. Dziewonski and D. L. Anderson, Phys. Earth Planet. Inter. 25,
    297-356, 1981.

F. D. Stacey, Sci. Prog., Oxf. 69, 1-17, 1984.

C. Talmadge and E. Fischbach, in _Fifth Marcel Grossmann Meeting_,
    Perth, Australia, 8-13 August, 1988, edited by D. G. Blair
    and M. J. Buckingham (World Scientific, to be published).

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

Date: Mon, 13 Nov 89 10:02:39 CST
From: [e-mail] (When in fear, or in doubt, run around, scream and shout)
Subject: RE: VEEGA stands for ?

My thanks to everyone (and I do mean everyone) on the net for answering this
one.  And to a number of you who pointed out that I had guessed the correct
number of letters for each word.

Oh well, I have asked dumber questions.

Dillon Pyron                         | The opinions are mine, the facts
TI/DSEG VAX Systems Support          | probably belong to the company.
[e-mail]                  |
[phone]                        | Professional assassination
                                     | The highest form of public service

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

Date: 13 Nov 89 18:30:18 GMT
From: gem.mps.ohio-state.edu!samsung!cs.utexas.edu!ut-emx![e-mail]  (Anita Cochran)
Subject: Re: Future Space Missions

In article <[e-mail]>, [e-mail] (lawrence.m.geary) writes:
> In article <[e-mail]> [e-mail] (Ron Baalke) writes:
> >                         Future Space Missions
> >
> >   o Cassini
> >       Possible launch in 1996, orbiter would spend 4 years studying Saturn and
> >       send an atmospheric probe into the moon Titan.
>
> I have heard that Cassini will also use an Earth flyby to gain speed.
> I assume this means that these probes are using underpowered boosters
> and launching from the shuttle, as was the case with Galileo. This was
> done with Galileo because it was too late - or would cost too much, or
> the probe was too heavy - to refit the probe for launch on an ELV with
> a Centaur upper stage. But WHY in heavens name is JPL sticking to this
> method for probes planned for far in the future?
> Why aren't there plans to use appropriate boosters?
>

You are wrong in what you heard about the launch method for Cassini.  Both
CRAF and Cassini are NOT shuttle launches. Since they were being planned
around the time of the Challenger explosion, NASA realized relying totally
on the Shuttle was not a good idea.  Instead, both of these missions
will launch on a Titan IV with Centaur upper stage.  This is not
the most powerful combination we have ever had but it will work.
And yes, there will be an earth flyby to gain velocity.

Galileo would have been fine with a shuttle launch as originally planned.
However, when the Challenger blew, it was decided that the IUS was
potentially too dangerous.  Thus, they went to the Centaur.  That is why
they had the earth flyby on Galileo.  Cassini has another very important
constraint on launch characteristics.  If it launches much later than
scheduled, it will not be able to use the Jupiter gravity assist which
is so important to getting to Saturn since Jupiter will move out of
position with respect to Saturn.


--
 Anita Cochran  uucp:  {noao, ut-sally, ut-emx}!utastro!anita
                arpa:  [e-mail]
                snail: Astronomy Dept., The Univ. of Texas, Austin, TX, 78712
                at&t:  [phone]

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

Date: 13 Nov 89 21:30:38 GMT
From: trident.arc.nasa.gov![e-mail]  (Peter E. Yee)
Subject: NASA Select TV coverage of Consort 2 launch (Forwarded)

Barbara Selby
Headquarters, Washington, D.C.                  November 13, 1989

N89-75
NOTE TO EDITORS:  NASA SELECT TV COVERAGE OF CONSORT 2 LAUNCH

     The launch of Consort 2/Starfire 1, scheduled for 10:45 a.m.
EST, Nov. 15, from the Naval Ordnance Missile Test Station at
White Sands Missile Range, N.M., will be carried live on NASA
Select television beginning at 10:15 a.m. EST.  NASA Select TV is
available via Satcom F-2R, transponder 13, 72 degrees W.
longitude, 39.60 MHz, audio monaural 6.8 MHz.

     Consort 2, a suborbital rocket flight sponsored by the
Consortium for Materials Development in Space at the University
of Alabama, Huntsville (UAH CMDS), is designed to provide 7 to 8
minutes of microgravity for 12 materials and biotechnology
experiments.  The entire mission, from launch to touchdown, is
expected to last approximately 15 minutes.

     The UAH CMDS is one of 16 of NASA's Centers for Commercial
Development of Space.  Following the successful Consort 1 flight
on March 29, 1989, NASA decided to extend funding support for a
series of similar flights.

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

End of SPACE Digest V10 #245
*******************