Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V13_4/V13_470.TXT

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Subject: SPACE Digest V13 #470

SPACE Digest                                     Volume 13 : Issue 470

Today's Topics:
         Re: Underground tests, now targeting
    Re: SPACE Digest V13 #364 now life on Jupiter, reprise
               Re: Saturn V and the ALS
             Re: Laser launchers
            Re: tabloids and moon landings
         Re: "Bussard Ramjets" AKA duct space drives
              Buckyballs and ion engines
                  Re: (none)
       Corrected phone number for Mazatlan eclipse trip
         Re: Dan Quayle on Mars (was: "Face" on Mars)
               Re: Saturn V and the ALS

Administrivia:

    Submissions to the SPACE Digest/sci.space should be mailed to
  [e-mail].  Other mail, esp. [un]subscription requests,
  should be sent to [e-mail], or, if urgent, to
             [e-mail]

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

Date: 26 Apr 91 00:26:29 GMT
From: agate!bionet!uwm.edu!spool.mu.edu!cs.umn.edu!quest!orbit!pnet51![e-mail]  (S Schaper)
Subject: Re: Underground tests, now targeting

I rather imagine that we _do_ have China targeted, after all, I think it is
well-known that the French have _us_ targeted.
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------------------------------

Date: 26 Apr 91 00:26:30 GMT
From: usc!sdd.hp.com!spool.mu.edu!cs.umn.edu!quest!orbit!pnet51![e-mail]  (S Schaper)
Subject: Re: SPACE Digest V13 #364 now life on Jupiter, reprise


  There may well be life on Jupiter, and on Mars. Earth life, from impact
induced panspermia.  The big problem with Mars is the UV and lack of currently
easily available water. On Jupiter it may very well be that convection would
take microbes and spores into uninhabitable regions before a life-cycle could
start or at a higher rate than reproduction could conteract. Those are _big_
storms.

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           Aslan is on the move!
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------------------------------

Date: 26 Apr 91 13:55:52 GMT
From: usc!samsung!news.cs.indiana.edu!noose.ecn.purdue.edu!en.ecn.purdue.edu![e-mail]  (/dev/null)
Subject: Re: Saturn V and the ALS

In article <[e-mail]>, [e-mail] (Henry Spencer) writes:
> In article <[e-mail]> [e-mail] (/dev/null) writes:
> If that's what you were trying to say, I suggest thinking a bit harder
> about Congress's reaction to this idea.  "You took umpty-zillion dollars
> to build this operational launcher -- which you assured us was going to
> be the best thing around -- and now you want to scrap it?"  Fat chance.
> You can't scrap multi-billion-dollar failures.  Example:  the shuttle.
> The only way to build something you can scrap if it doesn't meet specs
> is to make it explicitly an experimental program, and not try to sell
> it as God's gift to payload owners.
>

I agree with you on what is likely to happen.  I was stating what *should*
happen.  Take lessons learned and move on.  Maybe disguising it as a
'strictly experimental' program may work, but congress could then use
that as an excuse for cutting funding "We need this money for other things,
we don't need it to try something that's not going to be used directly
as product!"  I know its a poor attitude for Congress to take, but
they seem to be masters of that king of Catc-22 logic:  You don't get $$
for experiments until you show us some launchers....

>
> By trying to build production launchers with experimental technology,
> you are making sure that your launchers will never be cheap.  The whole
> approach does not work.  What works is what you do in aviation, to the
> enormous benefit of aviation in general and US aircraft builders in
> particular:  build X-planes for experiments, 747s for production, and
> don't forget that there is a difference.

Yes, there is a difference, I agree.  As far as cheapness, well, a
technology demonstrator is probably not going to be as cheap as
NASA expects, in that I agree.  However, I feel the ALS should NOT
be a gadget-mobile, but an exercise in cheap launchers.  If they
can aim towards THAT, then the first one will be an expensive
protoype, and the rest, cheap launchers (like what car makers do
before releasing a new model.

--
+-----------------------------------------------------------------------+
| Brent L. Irvine     |            These are MY opinions   |
| Malt Beverage Analyst     |            As if they counted...:) |
+-----------------------------------------------------------------------+

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

Date: 26 Apr 91 17:16:09 GMT
From: usc!rpi!news-server.csri.toronto.edu!utzoo![e-mail]  (Henry Spencer)
Subject: Re: Laser launchers

In article <[e-mail]> [e-mail]-mrc (Paul Johnson) writes:
>Errm, 'scuse me.  Dumb question time.  How does a laser launcher actually
>work?

From an old posting of mine:

There are a variety of schemes using lasers to transmit power from big
fixed power plants to spacecraft (and aircraft).  One problem that does
appear is that rocket engines are ferociously powerful, and really
enormous lasers are needed to transmit enough power to run a big one.
(The Saturn V first stage power output at launch was circa 35 gigawatts.)
Another difficulty is building a "combustion" chamber with a very highly
transparent window in it.  (It is possible to transmit the beam up the
nozzle, but this has its own problems.)

Both of these problems can be minimized if you are using the system for
satellite maneuvering rather than boost to orbit, since you can then use
a small, low-thrust engine which doesn't put massive demands on chamber
materials.  This is a very promising idea.

However, Earth-to-orbit is what we'd really like to do.  And it looks
viable, if you change some of the assumptions.  The power needs can be
brought within reason simply by scaling down the size of the payload,
on the assumption that higher launch rates will make up for small size.
You can do a useful launcher with a few megawatts per kilogram, if I've
remembered the numbers correctly.

As for the chamber problem... one scheme for a solid-fueled laser rocket
was basically just a stick of propellant with a nozzle around one end,
with the nozzle sliding up the stick as the laser wore away the end.
You can go one better, if your laser can generate a pair of closely-spaced
short pulses.  The first pulse vaporizes a thin layer of the surface.  The
second starts a "laser-supported detonation wave" in the vapor, heating it
to very high temperatures.  Put the two pulses close together, and the
vapor is still a thin layer on the surface of the propellant when the
second pulse arrives.  Now you don't need a nozzle, because the vapor
expands mostly at right angles to the surface.  So your spacecraft is
very close to the ideal: a block of propellant with a payload glued on top.

There are several other advantages to this approach.  For one thing, the
thrust is perpendicular to the surface, not the beam, so the beam can be
coming in at almost any angle.  This also means you can steer the thing
with the beam, varying the power distribution across the beam to rotate
the spacecraft.  It is probably possible to literally have nothing but
"propellant, payload, and photons", although in fact a bit of cooperation
from the spacecraft makes things like beam pointing rather easier.  If
you are concerned about effects on the ozone layer, or whatever, you
can just turn off the beam and let the spacecraft coast while it passes
through sensitive regions.  Range safety is easy, because the spacecraft
has no independent maneuvering ability and its trajectory is very
predictable.  The accelerations are a few gees, low enough that a big
system could probably be man-rated.

Could you use air as propellant?  Maybe.  A reflective plate with parabolic
hollows carved in it will focus an incoming pulse (provided it's pretty much
perpendicular) to a set of hot spots near the plate, where the air will
break down and absorb the beam, producing miniature thermal explosions
that will push on the plate.  It's been tried in the lab; it works.

Could you build one today?  Maybe a small one.  Both lasers and optics are
beyond the off-the-shelf range, but there are contractors who could build
the laser as a routine custom engineering job.  It helps that this system
works fine, in fact better, at relatively long wavelengths, where almost
everything is easier.  The right thing to do would be to build one with
a payload of, say, one kilogram, as a test system.  There are still a lot
of unknowns in the detailed engineering.  Once the test system proved
feasibility, a few hundred million dollars could build one with a yearly
payload to orbit equalling the (theoretical!) payload of the entire
shuttle fleet.  Costs depend on how intensively you use it, because the
capital costs of construction tend to dominate the power bill.  A man-rated
system would be really huge because of the sheer mass needed; better stick
to sending up cargo in small pieces for now.  You can do an awful lot with
20kg pieces delivered cheaply to orbit in large numbers.

Even the test system would be useful, actually, since it could vaporize
small pieces of space debris and de-orbit larger ones, if it were equipped
to deal with completely uncooperative targets.

Would it be useful as a weapon?  Against satellites, maybe, depending
on how much cooperation it needs from the target.  Against smaller and
faster targets, not very.  The long wavelength works against it in a
weapons application, where doing maximum damage quickly is essential.

Is it being worked on?  Yes, in a minor way.  There is a small group at
Lawrence Livermore that is looking into things like the laser-propellant
interactions.  They are assuming that SDI will push laser and optics
technology far enough, and are working on the non-weapon-relevant aspects.

What's the holdup?  Money.
--
And the bean-counter replied,           | Henry Spencer @ U of Toronto Zoology
"beans are more important".             |  [e-mail]  utzoo!henry

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

Date: 26 Apr 91 20:22:49 GMT
From: news-server.csri.toronto.edu!utzoo![e-mail]  (Henry Spencer)
Subject: Re: tabloids and moon landings

In article <[e-mail]> [e-mail] (Matthew DeLuca) writes:
>>The people using the retroreflectors for precise lunar distance
>>measurements typically get one or two photons back per laser pulse.
>
>The bare surface of the moon, on average, is 11% reflective; the laser
>reflectors must be much more, at least 70%-80% reflective.  How could they
>only get one or two photons, then?

The retroreflectors are only half a meter or so across.  Even a telescope
gives you a beamwidth of a kilometer or two at lunar distances.  The
retroreflectors get more than just one or two photons, but they don't get
the whole beam by any means, and diffraction and the inverse-square law
get you on the way back too, so only one or two end up being detected.
--
And the bean-counter replied,           | Henry Spencer @ U of Toronto Zoology
"beans are more important".             |  [e-mail]  utzoo!henry

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

Date: 26 Apr 91 00:26:30 GMT
From: usc!sdd.hp.com!spool.mu.edu!cs.umn.edu!quest!orbit!pnet51![e-mail]  (S Schaper)
Subject: Re: "Bussard Ramjets" AKA duct space drives

Interestingly, local space seems fairly depleated of hydrogen.

**************************************************************************
Zeitgeist Busters!
UUCP: {crash tcnet}!orbit!pnet51!schaper
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           Aslan is on the move!
****************************************************************************

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

Date: 26 Apr 91 15:50:31 GMT
From: rochester![e-mail]  (Paul Dietz)
Subject: Buckyballs and ion engines

I read with interest that some researchers are investigating
"buckyballs" (buckminsterfullerenes, soccer-ball shaped molecules
consisting of 60 carbon atoms) for use as reaction mass in ion
engines.  Recently, a simple and potentially low cost means of making
buckyballs was discovered; Smalley is projecting the cost should drop
to a few dollars per pound.

The reason why you might want to use C60 in an ion engine can be seen
from the physics of these engines.  In an ion engine, a material is
ionized, and positive ions are accelerated across a gap between two
grids.  The current is limited by space charge effects.  The ion space
charge limit is:

    5.402E-8 ( v / M )^(1/2) E^(3/2) d^-2  amps/cm^2

where v is the valence of the ion, M the mass of the ion in AMU, E the
potential (in volts) across the gap, and d the gap (in cm).

At constant exhaust velocity and electrode spacing, the thrust density
of an ion engine scales as M^2 (for univalent ions).  An ion engine
can therefore be made much more compact if it accelerates ion with a
large mass/charge ratio.  (Ultimately, the voltage required would be
too large, however, and the electrode spacing d would have to be
increased.)  Also, for some applications (for example, earth orbital
transfer) one would like exhaust velocities lower than are practical
with existing ion engines (which are around 30 km/s).  Higher mass
ions could do this.

C60 has a mass of 720 AMU, vs. ~130 for cesium or xenon.  The
advantage of C60 over other molecules would be that C60 appears to be
very rugged, yet easily ionized, so it should be possible to ionize it
without generating large numbers of low mass fragments, which would
degrade engine efficiency (ion engines are most efficient when all the
ions have about the same mass/charge ratio).  I read that buckyball
ions accelerated to 15,000 mph have been observed to survive impact
with metal surfaces, which illustrates how resilient they are.

Higher fullerenes (C70, etc.) have also been made and purified, and
may make even better fuels.  Also, large buckyballs could be made
containing multiple heavy atoms trapped inside.

    Paul F. Dietz
    [e-mail]

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

Date: 26 Apr 91 20:37:49 GMT
From: usc!zaphod.mps.ohio-state.edu!rpi![e-mail]  (Michael V. Kent)
Subject: Re: (none)

In article <[e-mail]> [e-mail] ("Wm. L. Ranck") writes:
>   First I find Michael Kent's signature line especially ironic.  Here is
>a person saying how the old technology of Saturn V is not worth reviving
>and new is better, with a signature line that says 'Apple II forever!'.
>Am I the only one that finds this funny?

There are two reasons why these opinions are compatible.

1) Today's Apple II bears little resemblence to the one that was released in
1977.  Although it can run the same software as the 1977 model, the new ones
have much new equipment built-in.  It is much like a Delta II, which bears
little resemblence to the first Delta that was launched in the early 1960's.

2) IThe Apple II has been in continueous production for these last 14 years.
The Saturn rocket hasn't been built in 20 years.  Going back to my previous
example, the flight test equipment I was working on was such a pain because
it had been out of production for 7 years, thus leading to the problems I was
having.  The airplane it was to fly on -- the F/A-18 -- had been in continuous
production since then, and can be produced today with relatively little diff-
iculty.

Using modern technology and production techniques, Apple can today produce an
Apple IIGS which is ten times as powerful as the original Apple II and do it
for half the cost.  If we were to startup the Saturn production line again, go
with a Saturn VI.  It will be more reliable, less expensive, and more powerful
(if we want it to be).

Apple II follow-ups to comp.sys.apple2 please.

Mike

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

Date:    Fri, 26 Apr 1991 23:16:52 CDT
From: [e-mail] (Pat Reiff [phone]-2650)
Subject: Corrected phone number for Mazatlan eclipse trip
X-Vmsmail-To: SMTP%"[e-mail]"

OOOPS!!!
  I accidentally mistyped the phone number for information on the eclipse
trip to Mazatlan. The correct number is [phone].  The Houston number
was right - [phone] or 480-1988.

------
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: 26 Apr 91 00:26:30 GMT
From: usc!wuarchive!sdd.hp.com!spool.mu.edu!cs.umn.edu!quest!orbit!pnet51![e-mail]  (S Schaper)
Subject: Re: Dan Quayle on Mars (was: "Face" on Mars)

I believe that the evidence is that Quayle is actually quite intelligent, the
respected senator, and all that. He had a good reputation. When he hit the
national scene, the Politically Correct crowd, hating his views, concocted
this whole image for him, which he does help out with his gaffes and slips of
the tongue.
**************************************************************************
Zeitgeist Busters!
UUCP: {crash tcnet}!orbit!pnet51!schaper
INET: [e-mail]
           Aslan is on the move!
****************************************************************************

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

Date: 26 Apr 91 17:29:12 GMT
From: swrinde!zaphod.mps.ohio-state.edu!rpi!news-server.csri.toronto.edu!utzoo![e-mail]  (Henry Spencer)
Subject: Re: Saturn V and the ALS

In article <[e-mail]> [e-mail] (/dev/null) writes:
>BUT, engines could be made that burn less fuel and therefore lift
>even more to orbit.  Maybe rocketdyne could modify the F-1 to
>bring it up to date.

Why bother?  It works fine as it is.  Fuel costs are a negligible fraction
of launch costs, and the Saturn V's payload to orbit is adequate for most
any foreseeable project.

If you insist on "improving" half the subystems, *then*, yes, reviving the
Saturn V will be extremely expensive.  The way to do it cheaply is to
firmly refuse to redevelop anything unnecessarily.
--
And the bean-counter replied,           | Henry Spencer @ U of Toronto Zoology
"beans are more important".             |  [e-mail]  utzoo!henry

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

End of SPACE Digest V13 #470
*******************