Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V16_4/V16NO467.TXT

Internet Message Format | 1993-07-13 | 15KB

Date: Sat, 17 Apr 93 05:21:52
From: Space Digest maintainer <[e-mail]>
Reply-To: [e-mail]
Subject: Space Digest V16 #467
To: Space Digest Readers
Precedence: bulk


Space Digest                Sat, 17 Apr 93       Volume 16 : Issue 467

Today's Topics:
                      Elevator to the top floor
                         End of the Space Age
                            Guns for Space
                    Orion drive in vacuum -- how?

    Welcome to the Space Digest!!  Please send your messages to
    "[e-mail]", and (un)subscription requests of the form
    "Subscribe Space <your name>" to one of these addresses: listserv@uga
    (BITNET), rice::boyle (SPAN/NSInet), utadnx::utspan::rice::boyle
    (THENET), or [e-mail] (Internet).
----------------------------------------------------------------------

Date: 5 Apr 93 18:58:33 GMT
From: Dani Eder <[e-mail]>
Subject: Elevator to the top floor
Newsgroups: sci.space

Reading from a Amoco Performance Products data sheet, their
ERL-1906 resin with T40 carbon fiber reinforcement has a compressive
strength of 280,000 psi.  It has a density of 0.058 lb/cu in,
therefore the theoretical height for a constant section column
that can just support itself is 4.8 million inches, or 400,000 ft,
or 75 Statute miles.

Now, a real structure will have horizontal bracing (either a truss
type, or guy wires, or both) and will be used below the crush strength.
Let us assume that we will operate at 40% of the theoretical
strength.  This gives a working height of 30 miles for a constant
section column.

A constant section column is not the limit on how high you can
build something if you allow a tapering of the cross section
as you go up.  For example, let us say you have a 280,000 pound
load to support at the top of the tower (for simplicity in
calculation).  This requires 2.5 square inches of column cross
sectional area to support the weight.  The mile of structure
below the payload will itself weigh 9,200 lb, so at 1 mile
below the payload, the total load is now 289,200 lb, a 3.3% increase.

The next mile of structure must be 3.3% thicker in cross section
to support the top mile of tower plus the payload.  Each mile
of structure must increase in area by the same ratio all the way
to the bottom.  We can see from this that there is no theoretical
limit on area, although there will be practical limits based
on how much composites we can afford to by at $40/lb, and how
much load you need to support on the ground (for which you need
a foundation that the bedrock can support.

Let us arbitrarily choose $1 billion as the limit in costruction
cost.  With this we can afford perhaps 10,000,000 lb of composites,
assuming our finished structure costs $100/lb.  The $40/lb figure
is just for materials cost.  Then we have a tower/payload mass
ratio of 35.7:1.  At a 3.3% mass ratio per mile, the tower
height becomes 111 miles.  This is clearly above the significant
atmosphere.  A rocket launched from the top of the tower will still
have to provide orbital velocity, but atmospheric drag and g-losses
will be almost eliminated.  G-losses are the component of
rocket thrust in the vertical direction to counter gravity,
but which do not contribute to horizontal orbital velocity.  Thus
they represent wasted thrust.  Together with drag, rockets starting
from the ground have a 15% velocity penalty to contend with.

This analysis is simplified, in that it does not consider wind
loads.  These will require more structural support over the first
15 miles of height.  Above that, the air pressure drops to a low
enough value for it not to be a big factor.

Dani Eder

--
Dani Eder/Meridian Investment Company/[phone](w)/232-7467(h)/
Rt.1, Box 188-2, Athens AL 35611/Location: 34deg 37' N 86deg 43' W +100m alt.

Reading from a Amoco Performance Products data sheet, their
ERL-1906 resin with T40 carbon fiber reinforcement has a compressive
strength of 280,000 psi.  It has a density of 0.058 lb/cu in,
therefore the theoretical height for a constant section column
that can just support itself is 4.8 million inches, or 400,000 ft,
or 75 Statute miles.

Now, a real structure will have horizontal bracing (either a truss
type, or guy wires, or both) and will be used below the crush strength.
Let us assume that we will operate at 40% of the theoretical
strength.  This gives a working height of 30 miles for a constant
section column.

A constant section column is not the limit on how high you can
build something if you allow a tapering of the cross section
as you go up.  For example, let us say you have a 280,000 pound
load to support at the top of the tower (for simplicity in
calculation).  This requires 2.5 square inches of column cross
sectional area to support the weight.  The mile of structure
below the payload will itself weigh 9,200 lb, so at 1 mile
below the payload, the total load is now 289,200 lb, a 3.3% increase.

The next mile of structure must be 3.3% thicker in cross section
to support the top mile of tower plus the payload.  Each mile
of structure must increase in area by the same ratio all the way
to the bottom.  We can see from this that there is no theoretical
limit on area, although there will be practical limits based
on how much composites we can afford to by at $40/lb, and how
much load you need to support on the ground (for which you need
a foundation that the bedrock can support.

Let us arbitrarily choose $1 billion as the limit in costruction
cost.  With this we can afford perhaps 10,000,000 lb of composites,
assuming our finished structure costs $100/lb.  The $40/lb figure
is just for materials cost.  Then we have a tower/payload mass
ratio of 35.7:1.  At a 3.3% mass ratio per mile, the tower
height becomes 111 miles.  This is clearly above the significant
atmosphere.  A rocket launched from the top of the tower will still
have to provide orbital velocity, but atmospheric drag and g-losses
will be almost eliminated.  G-losses are the component of
rocket thrust in the vertical direction to counter gravity,
but which do not contribute to horizontal orbital velocity.  Thus
they represent wasted thrust.  Together with drag, rockets starting
from the ground have a 15% velocity penalty to contend with.

This analysis is simplified, in that it does not consider wind

loads.  These will require more structural support over the first
15 miles of height.  Above that, the air pressure drops to a low
enough value for it not to be a big factor.

Dani Eder

--
Dani Eder/Meridian Investment Company/[phone](w)/232-7467(h)/
Rt.1, Box 188-2, Athens AL 35611/Location: 34deg 37' N 86deg 43' W +100m alt.

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

Date: 16 Apr 93 06:41:04 GMT
From: john baez <[e-mail]>
Subject: End of the Space Age
Newsgroups: sci.physics,sci.space,sci.astro

There is an interesting opinion piece in the business section of today's
LA Times (Thursday April 15, 1993, p. D1).  I thought I'd post it to
stir up some flame wars - I mean reasoned debate.  Let me preface it by
saying that I largely agree that the "Space Age" in the romantic sense
of several decades ago is over, and that projects like the space station
miss the point at this time.  Reading, for example, "What's New" -
the weekly physics update we get here on the net - it's clear that the
romance of the day lies in the ever more fine-grained manipulation of
matter: by which I include biotechnology, condensed matter physics (with
its spinoffs in computer hardware and elsewhere), and the amazing things
people are doing with individual atoms these days.  To a large extent, I
think, the romance some people still have with space is a matter of
nostalgia.  I feel sure that someday we - or more precisely, our "mind
children" - will spread across space (unless we wipe ourselves out); but
I think that *manned* space exploration is not what is exciting about
what we can do *now*.

Anyway, let me quote some of this article, but not all...


SPACE AGE GLORY FADES FROM VIEW

Micheal Schrage (writer, consultant, and research associate at MIT)

At 35, America's Space Age won't have to suffer through the angst of a
midlife crisis.

The reason is that the Space Age is already dead.  The technologies no
longer define our times, and the public has grown weary of the multibillion
-dollar celestial investments that yield minimal psychic or economic
rewards.

Space exploration has mutated from a central focuse of America's science
and technology debate into a peripheral issue.  Speace is not a
meaningful part of the ongoing industrial competitiveness debate, our
technology infrastructure discussions or even our defense conversion
policy.

To be sure, America should continue to invest in satellite technologies
for telecommunications and remote sensing - cheap deep-space probes
would be nice too - but the ideal of space as a meaningful driver of
scientific and industrial innovation is now dead.

.....

Before the change in administrations, it would have been foolish to
write an obituary for the Space Age.  The Bush White House aggressively
supported the space program and proposed spending well over $30 billion
to build space station Freedom alone.

Even as he proposed budget cuts in other science and technology domains,
Office of Management and Budget Director Richard Darman was an outspoken
public champion of big-ticket space expenditures.  The reality that much
of the civilian space program - from the shuttle to the Hubble telescope
to the space station - was poorly conceived and unimpressively
implemented did not seem to matter much.

Political inertia and a nostalgic sense of futurism - not a coherent
vision or cost-effective sensibilities - determined multibillion-dollar
space budgets.

Indeed, with few notable exceptions, such as Voyager, the post-Apollo
era is the story of the gold-plated porkification of space exploration
with programs and promises that delivered less for more and more.

......

While the Clinton Administration has kept on the highly regarded Daniel
Goldin as administrator of the National Aeronautics and Space
Administration, it seems clear that space exploration is not being
positioned as either a symbolic or substantive centerpiece of America's
technological prowess.  The space station budget has - rightly - been
slashed.  Space is virtually ignored when the Administration champions
its competitiveness agenda.

......

"I wish this had happened 10 years ago instead of starting to happen
now," says Bruce Murray, a Caltech professor who ran NASA's Jet
Propulsion Lab in Pasadena.  "We've put off a lot of things we shouldn't
have.... I would rather see a $10-billion NASA doing well than a
$40-billion one filled with white elephants."

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

Date: 5 Apr 93 17:35:23 GMT
From: Dani Eder <[e-mail]>
Subject: Guns for Space
Newsgroups: sci.space

Okay, lets get the record straight on the Livermore gas gun.
The project manager is Dr. John Hunter, and he works for the
Laser group at Livermore.  What, you may ask, does gas guns
have to do with lasers? Nothing, really, but the gun is physically
located across the road from the Free Electron Laser building,
and the FEL building has a heavily shielded control room (thick walls)
from which the gun firings are controlled.  So I suspect that the
office he works for is an administrative convenience.

I visited Hunter at the beginning of Feb. and we toured the gun.
At the time I was working on gas gun R&D at Boeing, where I work,
but I am now doing other things (helping to save the space station),

The gun uses a methane-air mixture, which is burned in a chamber
about 200 ft long by 16 inch ID (i.e. it looks like a pipe).
The chamber holds a 1 ton piston which is propelled at several
hundred m/s down the chamber.  On the other side of the piston
is hudrogen gas, initially at room temperature andsome tens
of atmospheres.

The piston compresses and heats the hydrogen ahead of it until
a stainless steel burst diaphragm ruptures, at around 50,000 psi.
The barrel of the gun is about 100 feet long and has a 4 inch
bore.  It is mounted at right angles to the chamber (i.e. they
intersect).  This was done so that in the future, the barrel
could be raised and the gun fired into the air without having to
move the larger and heavier chamber.  The projectile being used
in testing is a 5 kg cylinder of Lexan plastic, 4 in in diameter
and about 50 cm long.

All of the acceleration comes from the expansion of the hydrogen
gas from 50,000 psi downwards until the projectile leaves the
barrel.  The barrel is evacuated, and the end is sealed with a
sheet of plastic film (a little thicker than Saran wrap).  The
plastic is blown off by the small amount of residual air trapped
in the barrel ahead of the projectile.

The gun is fired into a bunker filled with sandbags and plastic
water jugs.  In the early testing fragments of the plastic
projectile were found.  At the higher speeds in later testing,
the projectile vaporizes.

The testing is into a bunker because the Livermore test range is
about 3 miles across, and the projectile would go 100-200 km
if fired for maximum range.  The intent is to move the whole gun
to Vandenberg AFB after the testing is complete, where they can
fire into the Pacific Ocean, and use the tracking radar at VAFB
to follow the projectiles.

The design goal of the gun is to throw a 5 kg projectile at 4
km/s (half of orbital speed).  So far they have reached 2 km/s,
and the gun is currently down for repairs, as on the last test
they blew a seal and damaged some of the hardware (I think it
had to do with the methane-air more detonating than burning, but
I haven't had a chance to talk to Hunter directly on this).

There are people waiting to test scramjet components in this
gun by firing then out of the gun into the air (at Mach 12=
4 km/s), since the most you can get in wind tunnels is Mach 8.

This gun cost about 4 million to develop, and is basically
a proof-of-concept for a bigger gun capable of firing useful-
sized payloads into space.  This would require on the order of
100 kg projectiles, which deliver on the order of 20 kg
useful payload to orbit.

Dani Eder

--
Dani Eder/Meridian Investment Company/[phone](w)/232-7467(h)/
Rt.1, Box 188-2, Athens AL 35611/Location: 34deg 37' N 86deg 43' W +100m alt.

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

Date: Sat, 17 Apr 1993 05:33:33 GMT
From: Leigh Palmer <[e-mail]>
Subject: Orion drive in vacuum -- how?
Newsgroups: rec.arts.sf.science,sci.space

In article <[e-mail]> James P. Goltz, [e-mail]
writes:
>  Background: The Orion spacedrive was a theoretical concept.

It was more than a theoretical concept; it was seriously pursued by
Freeman Dyson et al many years ago. I don't know how well-known this is,
but a high explosive Orion prototype flew (in the atmosphere) in San
Diego back in 1957 or 1958. I was working at General Atomic at the time,
but I didn't learn about the experiment until almost thirty years later,
when
Ted Taylor visited us and revealed that it had been done. I feel sure
that someone must have film of that experiment, and I'd really like to
see it. Has anyone out there seen it?

Leigh

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

End of Space Digest Volume 16 : Issue 467
------------------------------