Space & Astronomy/Space and Astronomy (October 1993).iso/pc/text/spacedig/v16_0/v16no062.txt

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Date: Tue, 19 Jan 93 05:16:26
From: Space Digest maintainer <[e-mail]>
Reply-To: [e-mail]
Subject: Space Digest V16 #062
To: Space Digest Readers
Precedence: bulk


Space Digest                Tue, 19 Jan 93       Volume 16 : Issue 062

Today's Topics:
              "Synchronous Orbits around other planets"
                              Clementine
                        Elementary Ballistics
                         Handling Antimatter
                       Organic heat shielding.
                        Oxygen in Biosphere 2
   Silver and Liquid Hydrogen or Hydrogen Peroxide rocket engines?
                           Soyuz as an ACRV
                         US/Russian Vehicle M

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

Date: 19 Jan 93 02:40:59 GMT
From: Tom A Baker <[e-mail]>
Subject: "Synchronous Orbits around other planets"
Newsgroups: sci.astro,sci.space

In article <[e-mail]> [e-mail] (Bruce T. Harvey) writes:
>
>Understanding that for our small world, geostationary means about a score or
>so thousand miles out, are there any planets in our system where this type
>of orbit is out of the question because rotation is too fast?  I do

Oh, you mean that the planet spins so fast that anything orbiting just
above the surface can't keep up with the surface?

Think about it ... then the SURFACE would be going along at roughly
orbital velocity or better.

This argument also applies to any atmosphere you encounter.  If its going
faster than a satellite, then it's in orbit.

There is nothing substantial in the solar system that has this property,
unless you want to consider planetary rings.  However ...

Thousands of counterexamples exist if you are willing to consider SMALL
bodies.  You might find rocks, asteroids, that spin faster than their
surface's orbital velocity, and remain held together by cohesion.  A
synchronous orbit would be impossible, exactly as you are asking.

tom

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

Date: 18 Jan 93 18:06:56 GMT
From: [e-mail]
Subject: Clementine
Newsgroups: sci.space

What is the status of Clementine at this time (post-Clinton election)? I have
heard rumors that all work has stopped since Nov. 3 on the lunar mission.

I have also heard that Clementine is fully funded, and on track for a January,
1994 launch to the Moon.

--- Maximus 2.01wb

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

Date: Tue, 19 Jan 1993 02:08:38 GMT
From: Matt Healy <[e-mail]>
Subject: Elementary Ballistics
Newsgroups: sci.space

Several people pointed out that LEO takes about 8 km/sec,
minimum.  This is in the FAQ.  However, I haven't seen any
posts giving the simple math behind the 8 km/sec figure,
so I'll crack open Halliday & Resnick {Physics}:

centripetal acceleration for a body following a circular
path: a = v ** 2 /r  "v-squared-over-r".  Solve for v,
given a and r: v = square_root(a r).  I can never remember
the radius of Earth, but I recall that a meter was defined
by the 17th-century French as "one ten-millionth of the meridian
quadrant passing through Paris" so circumference is about
40000 km.  Thus r = 20000/Pi = 6366 km, assuming spherical
Earth*.  One standard "g" is 9.81 meter/second_squared.

Crunch this and you get 7901 m/s.  Of course this assumes
a spherical earth, no atmosphere, and an orbit *just* above
ground level!

Also interesting:  divide 40000 km by 7.901 km/sec, and
you get orbital period = 84 minutes, 22.4 seconds.  At
the altitudes actually used by shuttles the period is
about 1.5 hours.  This provides a nice "sanity check" on
the calculation.

But how would a *real* mass driver handle the problem of
getting up *above* the atmosphere and then circularizing
the orbit?  Theoretically I suppose one builds a *very*
tall tower.  Calculations of required tensile strengths
are left as an excercise for the reader.  I also have
not figured out how to keep satellites from hitting the
thing...


* A handbook gives 6378.2 km for equatorial radius--not enough
difference to matter given other simplifications...

Matt Healy
"I pretend to be a network administrator;
 the lab net pretends to work"

[e-mail]

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

Date: 19 Jan 93 02:43:26 GMT
From: "Kevin W. Plaxco" <[e-mail]>
Subject: Handling Antimatter
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (John Roberts) writes:
> -From: [e-mail] (Kevin W. Plaxco)

     [plan to store antimatter as trapped ion in charges fullerene omitted]

> -Proton-antiproton annihilation would convert 2/721 or 0.28%
> -of this into energy.  The energy/mass ratio of this rocket
> -fuel would, unfortunately, be no better than that of U-235.


>For launches and for interplanetary travel, such an energy density would
>be spectacularly good - in fact, you'd use many parts of normal reaction
>mass to each part of antimatter-containing material. Proposed antimatter
>rockets use a matter-antimatter ratio of millions to one.

My point remains:  This is in reality no better than a fission
reactor, and mining U-235 (or converting U-238 to Pu-238 or, I
suspect, a whole host of other transmutations to fissile material)
is enormously more energy effecient than manufacturing antimatter.
Not to mention the fact that U-235 is a hell of a lot easier to store.

Unless storage densities of greater than 1:360 are developed,
antimatter rockets will never replace nuclear-thermal.

Now, if only we had nuclear-thermal...

-Kevin

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

Date: Tue, 19 Jan 1993 01:45:36 GMT
From: Bruce Dunn <[e-mail]>
Subject: Organic heat shielding.
Newsgroups: sci.space

> Dave Michelson writes:
> As a point of interest, the original plan for the Saturn S-IVB stage
> was to use balsa wood for insulating the LH2 tank.  (The details
> are discussed in Stages to Saturn, an often quoted source in this
> group :-)  Only after determining that they would need far more balsa
> than the world could every hope to supply (!) did they switch to a
> synthetic material...


        The liquid hydrogen tank of the DC-X currently being built is
insulated with balsa wood.  I saw a photo over the weekend - the speaker
noted that they had to bring a worker out of retirement who had the necessary
skills for bonding it to the metal.  Unless my eyes pulled a perspective
trick, the photo showed the balsa on the ***inside*** of the tank.


--
Bruce Dunn    Vancouver, Canada   [e-mail]

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

Date: Mon, 18 Jan 1993 23:58:40 GMT
From: Carl Hage <[e-mail]>
Subject: Oxygen in Biosphere 2
Newsgroups: sci.space

The relatively small atmosphere of Bioshpere or a space colony would
seem to have a number of problems which would not be significant in the
large atmosphere of Earth. This brings to mind several questions. Does
methane production from the waste processing marsh or in soil composting
become a problem? Closed sewage treatment plants and landfills often
have burners, but it seemed from the description, that an enclosed digester
was not used in Biosphere. Also, it would seem that odor might be a problem
in such a small enclosed space.

How is the CO2 removed? Is a chemical method used like in the Shuttle, or
is it condensed out with chillers?

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

Date: 19 Jan 1993 02:52:10 GMT
From: "Kevin W. Plaxco" <[e-mail]>
Subject: Silver and Liquid Hydrogen or Hydrogen Peroxide rocket engines?
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Jon Marshall) writes:

>rocket engine made of silver. I'm not sure if it used Liquid Hydrogen
>or Hydrogen Peroxide for fuel(probably peroxide for a catalyst reaction?).

"Land speed record" (quotes because it's invariably set with the
equivalent of a rocket that just happens to be in contact with the
ground, rather than, as it should be, with a souped-up '57 Chevy
driven, as God intended, through it's wheels) attempts have been
made with H2O2 powered rockets.

H2O2 (about 50% in H2O) is passed over silver mesh which catalyzes
the breakdown of peroxide into O2 and superheated steam.  I've heard
that plastic garbage bag strips will do a pretty good job too.

-Kevin

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

Date: 18 Jan 93 16:51:04 GMT
From: [e-mail]
Subject: Soyuz as an ACRV
Newsgroups: sci.space

AW>>And Alan thinks you'll see a Soyuz sitting on top of a U.S. booster l
AW>>from a U.S. facility....
AW>
AW>Oh, that's a given. The booster may be the Shuttle but we will see Soy
AW>being launched for (at the very least) ACRV on US launchers.

Under the terms of the Launch Services Purchase Act, NASA is prohibited
from orbiting non-shuttle-specific payloads. Therefore,

using the shuttle to orbit Soyuz spacecraft contravenes the LSPA.

However, several U.S. commercial vendors can supply launchers that
can easily orbit a Soyuz for a more reasonable price than the shuttle. As
a nice side benefit, this would create a second means of access to space
in the US, in case the shuttle fleet is grounded.


AW>+----------------------990 DAYS TO FIRST FLIGHT OF DCX----------------


Does this mean that you are now a Delta Clipper pessimist?

___ WinQwk 2.0b#0

--- Maximus 2.01wb

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

Date: 18 Jan 93 17:01:06 GMT
From: [e-mail]
Subject: US/Russian Vehicle M
Newsgroups: sci.space

BH>Remember the NASA group that studied the Soyuz as Assured Crew Return
BH>Vehicle (space station lifeboat)?  They learned that the limitaion of
BH>famous three-month lifetime on Soyuz/Mir is that there are some seals
BH>that dry out or outgas or something.
BH>
BH>If you launch Soyuz inside a Shuttle orbiter instead of atop a
BH>Semyorka, with the seals covered, they'll last a *long* time in space.
BH>
BH>NASA would find replacing the Soyuz every few months unacceptable.
BH>With a long lifetime, Soyuz becomes a much more attractive
BH>candidate.

1) The 90 day limit existed in the 1970's and early 1980's. It has since
been exceeded.

2) The seals fail because of thermal cycles inherent in low earth orbit.
Launching them in a shuttle will not prevent the Soyuz from exposure
to thermal extremes, unless the Soyuz is kept inside the Shuttle for the
entire stay in orbit.

3) The principal seal that the Russians worry about is the liner
of the fuel tank, which is deep inside the Soyuz.

4) Even if the Soyuz has to be replaced, say every six months or so,
that's great, because it can be flown to the station by real live human
beings, giving us a significant increase in human traffic in space, and a
second means of access to space (after the shuttle). And Soyuz is *cheap*.




___ WinQwk 2.0b#0

--- Maximus 2.01wb

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End of Space Digest Volume 16 : Issue 062
------------------------------