Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V13_5/V13_567.TXT

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Subject: SPACE Digest V13 #567

SPACE Digest                                     Volume 13 : Issue 567

Today's Topics:
             Re: Laser launchers
               Re: Saturn V and the ALS
          Re: SPACE STATION FREEDOM WOUNDED
       Gravity waves (was Re: LIGO (was Re: IT'S OVER))
          Re: SPACE STATION FREEDOM WOUNDED
               Re: Saturn V and the ALS
             Re: Space Station Cancelled
               Re: Saturn V and the ALS
               Re: Saturn V and the ALS
          Re: SPACE STATION FREEDOM WOUNDED

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

Date: 15 May 91 14:27:13 GMT
From: usc!samsung!emory!ox.com!fmsrl7![e-mail]  (Ron Carter)
Subject: Re: Laser launchers


In article <[e-mail]> [e-mail] (Gary Coffman) writes:
>Well we have to decide first how much power is needed at the target.
>Let's assume a payload mass of 1000 kg.

You are thinking way too big.  The proposal of which I'm aware
was for a 13.6 kg payload.  (30 pounds.)  So cut all your numbers
by 2 orders of magnitude.

(No, the purpose was NOT to orbit satellites or people.  The
purpose was to orbit bulk commodities for a space station or
other program, such as fuel, oxygen, or water.)

>.... We must attain the highest specific impulse that we can to keep
>the amount of dead weight reaction mass to a minimum. This in turn means
>that we need to deliver the same amounts of power to the payload as
>would be supplied by a chemical rocket, again, gigawatts.

There's another faulty assumption.  Chemical rockets have far more
than the amount of reaction mass required for the minimum-energy
push to orbit, and must expend more energy to lift it.  The minimum
energy mass-ratio for a rocket using a constant exhaust velocity
is about 4.  Typical rockets run 20 and up.

> To avoid
>turning the atmosphere to plasma, we need to keep beam intensity below
>about 100 Kw/m^2.

That's only 10 W/cm^2, a trifling amount of power.  You are talking out
of your hat.  Another poster mailed me information about a laser he used.
Its beam intensity was around 300 W/cm^2.  It did not ionize air, it did
not even cause thermal blooming.  Once again, you are off by at least 2
orders of magnitude.  It is not surprising that your conclusions are faulty.

>To deliver a gigawatt that requires the beam to be
>spread over 10,000 square meters. But that would require a collector
>at the payload of 10,000 square meters. Otherwise, as the beam narrowed,
>a point would be reached where the energy density per square meter would
>begin to turn the atmosphere to an optically opaque plasma.

To deliver a gigawatt at 300 W/cm^2 at the mirrors requires 333 m^2 of
mirrors.  This is a bit more than a hundred 2 m round mirrors, hardly
a difficult job to make.  At the target, where the power density would
be 1 GW/m^2, is another matter, but consider:  air is very transparent
to visible and near-IR photons, while ice (especially ice containing
dye or carbon black) can be made very, very absorptive.  It is safe
to assume that the ice would flash into steam before the air would
flash into plasma.  The ice block with the payload in front is always
moving through the air, so the air would not have a chance to become
heated by several successive shots of the laser.

>You're going to need a lot of reaction mass heated very hot and
>moving very fast to get your payload in orbit. That's going to
>require very high beam power levels from very powerful lasers
>focused on a relatively small target. The best experience in
>that field is the work of the laser fusion folks.

Laser fusion requires imploding a sub-millimeter target
symmetrically at speeds of thousands of miles a second, and
accellerating from zero to full speed in a few tens of
micrometers.  It requires precisely shaped subnanosecond
laser pulses focussed onto a microscopic target.

Contrast a laser launcher.  To evaporate a layer of the ice
target at 6000 m/sec requires something like 18 KJ/gm, a far
cry from the laser fusion numbers.  The steam layer at 6000
m/sec takes 1.7 microseconds to expand to a centimeter thick;
the drive pulse could easily be several microseconds long,
with beam powers tens of thousands of times lower than
required by laser fusion even at the same total pulse energy.
These pulses are spread over an area close to a square meter,
giving a peak power/area ratio millions of times lower than
is required for laser fusion.

The two problems are not comparable.

>I have read studies, and I have done back of the envelope calculations
>myself. No chemical bond known to science has the strength to support
>a geosync to earth tether.

Knowing what you've posted in this thread, you probably ignored
the decrease in acceleration with altitude when calculating
stresses.  This throws your calculations way out of whack.

I'll see if I can find my analysis of the iron-whisker tether.
When I can post my calculations, I'll expect you to point out
exactly where they are faulty.

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

Date: 15 May 91 19:09:19 GMT
From: agate!lightning.Berkeley.EDU![e-mail]  (Frank Crary)
Subject: Re: Saturn V and the ALS

A heavy lift Titan or Delta varriant should not be needed for a capsule
type manned craft as a replacement for the Shuttle. An Apollo ASM massed
22 tonnes. This is, if memory serves me, launchable by a Titan IV.

                      Frank Crary
                      UC Berkeley

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

Date: 15 May 91 21:55:16 GMT
From: mips!zaphod.mps.ohio-state.edu!rpi!news-server.csri.toronto.edu!utzoo![e-mail]  (Henry Spencer)
Subject: Re: SPACE STATION FREEDOM WOUNDED

In article <[e-mail]> [e-mail] (Allen W. Sherzer) writes:
>... They zeroed out ALL station funding...
>
>looks like the space science people who lobbied had an effect.

Sigh, the politics of envy...  They're dreaming if they think it will have
more than a momentary effect on their own financial problems.
--
And the bean-counter replied,           | Henry Spencer @ U of Toronto Zoology
"beans are more important".             |  [e-mail]  utzoo!henry

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

Date: 16 May 91 03:54:10 GMT
From: unmvax!nmt.edu![e-mail]  (Kansas Jim)
Subject: Gravity waves (was Re: LIGO (was Re: IT'S OVER))

> [e-mail] writes:

[talks about LIGO from an episode of The Astronomers]

>
> During the making of the show, I got into a long discussion with one of
> the consultants regarding the ins and outs of inescapable gravity
> fields, gravity propagation possibly exceeding the speed of light, etc. I
> wound up making a rather large cash bet that, once we are able to detect
> gravity waves, we would discover that they make a far less cluttered
> means of interplanatary communications ( and that we are more likely to
> detect another civilization using gravity wave communications than radio).
>
> Comments? Ideas? Speculations?
>
Someone has probably already mentioned this, but I haven't seen it so here
goes...

The idea of using gravity waves as a means of communicating through
space was proposed by Larry Niven in a short story some time ago.  I
don't remember the name of the story but it is included in the book
"N-Space".

It is an interesting idea but aside from the problem of detecting
gravity waves, how would we (or anyone 'out there') generate them in
an organized manner?  (Niven's story uses a primordial black hole
contained in a magnetic bottle.)

(If this has been already brought up, I must have missed it - sorry.)

Jim
--
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------------------------------

Date: 16 May 91 01:36:28 GMT
From: media-lab.media.mit.edu![e-mail]  (Marvin Minsky)
Subject: Re: SPACE STATION FREEDOM WOUNDED

In article <[e-mail]> [e-mail] (Allen W. Sherzer) writes:

>The next step however, is to turn this into an advantage. If Freedom
>is killed we need to push for a real station. This would be a good time
>to tell your Congresscritters about projects like the Commercially
>Developed Space Facility or ideas from the SSI External Tank Study.
>Push to get them funded.
>
>This vote is a good thing for space. The Freedom station just wasn't
>panning out. It was getting smaller and smaller with no reductions in
>cost.

The next step however should be to think again.  Several small
remotely manned space stations would develop the technology for a
more plausible manned one later.  Repeating Skylab makes little sense;
telepresence in the natural next step.  It could produce so many
wonders in LEO, GEO and on the moon that the public will DEMAND larger
manned projects soon.  But if the reduced Fred were to proceed, the
public will only quit a little later, setting everything back even
more.  C'mon guys, you're all living in 1970.

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

Date: 16 May 91 17:07:19 GMT
From: sdd.hp.com!wuarchive!rex!rouge![e-mail]  (Fraering Philip)
Subject: Re: Saturn V and the ALS

In article <[e-mail]> [e-mail] (Doug Mohney) writes:

>Perhaps you really don't care about sacrificing ESA/NASA joint ventures, but
>I think ESA has been screwed enough already.


It'll be easier to just reconpensate ESA and NASDA for what they have
already done than to go ahead in the fashion that NASA is.

--
Phil Fraering || Usenet (?):[e-mail] || YellNet: 318/365-5418
''It hardly mattered now; it was, in fact, a fine and enviable
madness, this delusion that all questions have answers, and nothing is
beyond the reach of a strong left arm.`` - Larry Niven and Jerry
Pournelle, _The Mote in God's Eye_

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

Date: 16 May 91 23:02:09 GMT
From: epic![e-mail]  (Phil R. Karn)
Subject: Re: Space Station Cancelled

In article <[e-mail]>, [e-mail] (Reg Clemens) writes:
|> Lets hope they have the courage to keep it cancled.. Then we can get
|> on with doing some REAL Space Science.

Reg,

I'm sure you'll get soundly flamed in this newsgroup, so I thought I
would lend you some support (and I know I'll get flamed for it too).

If cost were absolutely no object, I'd be all in favor of a space
station.  Heck, I thoroughly enjoy the 2001 space station scene and
the shuttle IMAX movies as much as anyone, and I've certainly had my
share of personal spaceflight fantasies.

But there's simply no way I can rationalize such an expensive project
with such vague goals, no matter how "neat" and emotionally appealing
it might seem. When you start talking about such large pricetags, it
is as vital to apply the notion of "cost effectiveness" to space as to
anything else.  And the space station just isn't cost effective, no
matter how you look at it. It's been years since it was first
proposed, and STILL nobody really has a clue as to what the damn thing
will be useful for.

The many space cadets who seem to inhabit this newsgroup would do well
to stop sounding like members of a religious cult purging heretics.
They should take the time to study the actual history of NASA during
the shuttle program. Lots of small space science programs got axed to
cover shuttle overruns.  Despite Henry Spencer's emotional
protestations to the contrary, history clearly shows that manned space
flight budgets are NOT independent of space science funding.

True, cancelling the Space Station will probably not make equal funds
available for space science. But it is an egregious fallacy to assert
that going ahead with Space Station funding would not negatively
affect space science. If the history of the Shuttle is any guide, it
would utterly devastate it. In other words, the question is *not*
whether cancelling Space Station would help space science, the
question is whether *going ahead* with Space Station would *hurt* space
science.  And the lesson of history is crystal clear.

The only way I could see the proposed Space Station as being worthy of
funding is if it were to be used to send Dan Quayle to Mars without a
spacesuit, since he obviously feels he wouldn't need one. :-)

Phil

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

Date: 16 May 91 14:00:44 GMT
From: agate!linus!linus!cyclone![e-mail]  (S. J. Okay)
Subject: Re: Saturn V and the ALS

In article <[e-mail]> [e-mail] (Frank Crary) writes:
>A heavy lift Titan or Delta varriant should not be needed for a capsule
>type manned craft as a replacement for the Shuttle. An Apollo ASM massed
>22 tonnes. This is, if memory serves me, launchable by a Titan IV.


Speaking of which, whats wrong with using this as a crew transport vehicle?
If we're going to revive the Saturn V and spend all those $$$ on retooling,
why not spend an extra few to revive the Apollo CM?.

BTW, were Fred to ever have a lifeboat capability, why not use the CM capsule?
If I recall correctly, there was some extra space in the capsule itself that
might provide room for the 4th seat.

Comments?

---Steve

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

Date: 16 May 91 16:33:40 GMT
From: theory.tn.cornell.edu![e-mail]  (Bill Newman)
Subject: Re: Saturn V and the ALS

In article <[e-mail]> [e-mail] (Doug Mohney) writes:
>In article <[e-mail]>, [e-mail] (Allen W. Sherzer) writes:
>>Yep. Costs are:
>>
>>1. Develop two HLV's:                $1 billion
>>2. Integrate Soyuz with new
>>   vehicle:                          $1 billion (should be less than this)
>>3. Build econo-lodge station:        $2 billion (I'm splurging here as well)
>>                              total: $4 billion
>>
>>Which is a lot less than a years Shuttle costs.
>
>Glad to see you can be as creative at math as the 70s NASA managers. The only
>thing which might be close is the Soyuz intergration.

Well, I am certainly not an aerospace expert, but I
don't think it's clear that Allen's HLV numbers are out of line.  Consider:

First, the development proposals Allen is referring to do not seem to
require developing sophisticated new hardware: they can use parts of
known design, cost, and performance for the engines and control systems.
They will design new tanks, structures, plumbing, and so forth, but
this kind of engineering is well understood enough that the contractors
can make a fairly good idea how much it will cost to develop and
manufacture.  Therefore, there is a real chance that the contractors
can make a realistic offer.  Why not take the $500M offer for a heavy-lift
booster seriously, by offering to fund it?  If the contractors back out
when time comes to close the contract, then nothing is lost, except
maybe a bit of Allen's optimism.

Second, $500M for a HLV is not obviously
out of line with the costs for Pegasus.  Pegasus probably
didn't need to generate truckloads of procedures and reports for launching
from the Cape, and it was undoubtedly cheaper to build and test prototypes
for the smaller Pegasus hardware, but Pegasus was also a more unorthodox
design: the carrier aircraft can't baby Pegasus as much as a ground launch
complex could, Pegasus needs to separate from the carrier aircraft
reliably and controllably, and Pegasus needs to get the hypersonic
aerodynamics right enough to generate significant lift and control,
instead of just punching a cylindrical hole in the atmosphere.  It was
my understanding that Pegasus' development costs were comfortably under $100M.
Why should the development part of the HLV contract (as opposed to
production and operation costs) have to be substantially more?  Or is the
$500M figure unrealistic because the production and
operation costs will necessarily be much greater than $300M?  (I don't have
any handy figures for comparison here, except maybe the cost of airliners.)

What do you think would happen if Allen's proposal were followed?  Would the
HLV contractors back down and refuse to hold to their $500M bid?  Would they
hold to it, demand prepayment, and then stiff the government?  Would they
hold to their bid and then lose a huge amount of money or fail to deliver?
What is the worst outcome for the taxpayer/voter that you can imagine?

  Bill Newman
  [e-mail]

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

Date: 16 May 91 20:04:58 GMT
From: rochester!sol![e-mail]  (Brian Yamauchi)
Subject: Re: SPACE STATION FREEDOM WOUNDED

In article <[e-mail]> [e-mail] (Herman Rubin) writes:

>What we need is for the government to allow those who want to do it to
>do so without restriction from government restrictions.

>This is the thing to lobby for.  Then those who believe in space science
>can raise money from various sources for it, and those who believe in
>man in space can do likewise, and the various profit and nonprofit
>organizations can cooperate to get the job done.

Sounds good to me -- what *specific* restrictions are currently
preventing private and non-profit organizations from pursuing space
exploration and development?

--
_______________________________________________________________________________

Brian Yamauchi                University of Rochester
[e-mail]        Department of Computer Science
_______________________________________________________________________________

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

End of SPACE Digest V13 #567
*******************