Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V13_0/V13_032.TXT

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Subject: SPACE Digest V13 #032

SPACE Digest                                      Volume 13 : Issue 32

Today's Topics:
    Re: $$/pound of Freedom vs LLNL (was: ELV Support...)
           I called the Mir 900 number ...
             Re: Interstellar Light Sails
         Re: Building a sundial, position of the sun
             Re: Interstellar Light Sails
             GUERAP III software
               Re: Hi girls... (part 2)
              Re: Interplanetary travel

Administrivia:

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Date: 3 Jan 91 22:45:05 GMT
From: csus.edu!wuarchive!usc!samsung!umich!sharkey!cfctech!teemc!fmeed1![e-mail]  (Russ Cage)
Organization: Ford Motor Co., Electronics Div., Dearborn, MI
Subject: Re: $$/pound of Freedom vs LLNL (was: ELV Support...)
References: <[e-mail]>, <[e-mail]>, <[e-mail]>
Sender: [e-mail]
To: [e-mail]

In article <[e-mail]> [e-mail] (Charles Radley) writes:
>I am astonished that you go to so much trouble to mislead the
>respected users of this net.   There is NOT an OVERALL weight saving,
>the entire analysis you presented relates only to the PRESSURIZED
>HULL which is a small part of the overall system, and has only second
>order effect on the overall weight.

Charles, your previous assertion was that artificial gravity required
a much greater mass than a non-spinning station.  I have refuted this
assertion.  For you to go and whine that this is suddenly not relevant
after making a big deal of it is immature.

>In article <[e-mail]>, [e-mail] (Russ Cage) writes:
>+Freedom will be built of aluminum.  The strongest alloy

>WRONG !! Freedom is made of a variety of materials, mostly
>graphite-epoxy composite.

That's not what you said in article <[e-mail]>.  On
November 29 1990, you posted this:

>Also, the shielding capability of LLNL's non-metallic structure is much less than
>Freedoms aluminum modules.
      ^^^^^^^^

So, which is it?  Aluminum alloy, or graphite composite?

Don't tell me that things other than the pressure hull are
the big deal.  It is the pressure hull which is the major
structural component and the bulkiest part to boot.  It is
the pressure hull, not any other part, which must be heavier
to bear additional stress from artificial gravity.  It is
the pressure hull of LLNL that you said would be too heavy.

I'm getting very tired of watching you play semantic games
and never post a number.  Getting a single unambiguous FACT
out of you seems impossible.  Be glad you don't work for me;
if you gave me any sort of report with equivocations,
half-truths and excuses in it such as I've seen in your
postings, I would fire you on the spot, for incompetence.

Before you presume to denegrate somebody else's work (such
as LLNL's), let's see you first acquire some knowledge about
it.  Get their proposal and read it.

I won't hold my breath.
--
Russ Cage    Ford Powertrain Engineering Development Department
Work:  itivax.iti.org!cfctech!fmeed1!cage   (CHATTY MAIL NOT ANSWERED HERE)
Home:  [e-mail]  (All non-business mail)
Member:  HASA, "S" division.

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

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Date: 5 Jan 91 14:40:00 PST
From: "1st Lt. Henry S. Cobb" <[e-mail]>
Subject: I called the Mir 900 number ...
To: "space+" <[e-mail]>

[Fair warning:  I know some of the people involved in the Mir lottery.
I used to live in Houston, and Houston space activists are a
surprisingly small group.  In particular, I can vouch for Jim
Davidson, the director of marketing at Space Travel Services.  I can't
believe he'd be involved in anything fraudulent.  However, I have no
connection with the company (other than as a hopeful cosmonaut).  Last
time I met Jim, he clearly had something up his sleeve, but he
wouldn't let me in on the secret.]

I called the "Fly to Mir" lottery phone line (1-900-258-2MIR) about
13:30 on 5 Jan 91.  My initial impression is that they need a lot more
explanation for both prospective and actual callers.  Here's what
happened:

There is an initial message spoken by a very fast-talking woman.  As
nearly as I can remember, it goes like this:

"This is Space Info.  You can stay on the line to register for the Mir
lottery, or send one hand-written entry per standard business-size
envelope to

   Space Travel Services
   PO Box 580249
   Houston, TX  77258

If you stay on the line, you will be charged $2.99 for this call."

After a pause, the same woman delivers about a two-minute spiel on
the design and construction of the Mir space station, at the same
speed.  It seemed accurate at first listen, but you'd have to tape it
and repeat it to find out anything you didn't already know.

Why is this here?  Texas is a populist and somewhat blue-nosed place.
I assume there's a law to the effect that 900 numbers must offer
"information," not sweepstakes entries (or lascivious dialogue).  I
remember some controversy when 900 numbers were first introduced
there, but I don't specifically recall the law.

After the woman finishes, a male Texan voice (talking more slowly, but
that's redundant) says something like "You may record your lottery
entry now," and you then hear an answering-machine BEEP.

At this point, their disorganization becomes clear.  What does a
lottery entry consist of?  They don't describe that at all.  You get
about thirty seconds to record <whatever>.  It then gets played back
to you, and you can re-record by pressing 1 on a touch-tone phone.
After the third try, I wound up leaving my name, address, and phone
number, with a short comment about clarifying their entry procedure.

I have no doubt that Space Travel Services has a signed agreement to
fly someone on Mir next year.  I don't think they've really figured
out how to use it effectively.  (And I'm not entirely sure the Soviet
Union will be in shape to launch passengers by then.)  But it's a
great idea, and $3 is relatively painless even if it doesn't pan out.

Summary:  You apparently don't need to call their 900 number.
Instead, you can write to the address above.  What does a lottery
entry consist of?  Your guess is as good as mine.  Call the number if
you don't mind spending three bucks, but be sure you have a recorder
running unless you just want to leave your name and address on the
answering machine.

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

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Date: 6 Jan 91 18:26:05 GMT
From: cs.utexas.edu!swrinde!elroy.jpl.nasa.gov!euclid.jpl.nasa.gov![e-mail]  (Peter Scott)
Organization: Jet Propulsion Laboratory, NASA/Caltech
Subject: Re: Interstellar Light Sails
References: <[e-mail]>, <[e-mail]>, <[e-mail]>
Sender: [e-mail]
To: [e-mail]

In article <[e-mail]>, [e-mail] (Henry Spencer) writes:
> In article <[e-mail]> [e-mail] (Nick Szabo) writes:
> >>... If you can build the laser system
> >>on the necessary colossal scale, laser sails are workable.
> >
> >What is the spread of a laser over interstellar, or even interplanetary
> >distances?  Last I heard from the deep-space laser communications people,
> >there is large dispersion over even interplanetary distances ...
>[...]
> This says that at roughly
> optical wavelengths (a few hundred nanometers), effectiveness at interstellar
> distances (a light year is roughly 1e16 m) requires transmitters and
> receivers hundreds of kilometers across.  The receiver (sail) is not a big
> problem, since its shape is not critical.  A diffraction-limited transmitter
> lens/mirror/array that size is a challenge, to be sure, but it is not
> ridiculous.

Exactly what Forward specifies, although I think he even talks in
terms of apertures thousands of kilometers across.  He has designs,
too; I recall a lens formed by a loose mesh enclosing an aerosol,
don't remember how he handled diffusion but I assume he did.  The
man thinks *big*.  Best example of someone with their head in the
clouds but their feet on the ground that I know of.

--
This is news.  This is your       |    Peter Scott, NASA/JPL/Caltech
brain on news.  Any questions?    |    ([e-mail])

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

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Date: 6 Jan 91 17:33:58 GMT
From: isis![e-mail]  (Eric Bergman-Terrell)
Organization: Math/CS, University of Denver
Subject: Re: Building a sundial, position of the sun
References: <[e-mail]>, <[e-mail]>, <[e-mail]>
Sender: [e-mail]
To: [e-mail]

There are two books that will give you all the information about
sundial design:

1.    Albert E. Waugh, "Sundials:  Their Theory and Construction",
    published by Dover Publications

2.    R. Newton Mayall and Margaret W. Mayall, "Sundials", published
    by Sky Publishing

Both were published in 1973.


Terrell

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

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Date: 6 Jan 91 02:09:54 GMT
From: usc!cs.utexas.edu!news-server.csri.toronto.edu!utzoo![e-mail]  (Henry Spencer)
Organization: U of Toronto Zoology
Subject: Re: Interstellar Light Sails
References: <[e-mail]>, <[e-mail]>, <[e-mail]>
Sender: [e-mail]
To: [e-mail]

In article <[e-mail]> [e-mail] (Nick Szabo) writes:
>>... If you can build the laser system
>>on the necessary colossal scale, laser sails are workable.
>
>What is the spread of a laser over interstellar, or even interplanetary
>distances?  Last I heard from the deep-space laser communications people,
>there is large dispersion over even interplanetary distances ...

Different assumptions about the optics involved.  You cannot do useful
power transmission over interstellar distances if you insist on building
optics only centimeters, or even meters, across.  If I am remembering it
correctly (this is not an area I'm intimate with), the basic rule of thumb
for diffraction-limited optics is that most of the power of a beam of
wavelength lambda from a transmitter of radius Rt will end up in a receiver
of radius Rr at distance D if

    Rt * Rr > D * lambda

(it is just possible that those radii should be diameters, but in any case
this gives us an order-of-magnitude answer).  This says that at roughly
optical wavelengths (a few hundred nanometers), effectiveness at interstellar
distances (a light year is roughly 1e16 m) requires transmitters and
receivers hundreds of kilometers across.  The receiver (sail) is not a big
problem, since its shape is not critical.  A diffraction-limited transmitter
lens/mirror/array that size is a challenge, to be sure, but it is not
ridiculous.
--
"The average pointer, statistically,    |Henry Spencer at U of Toronto Zoology
points somewhere in X." -Hugh Redelmeier| [e-mail]   utzoo!henry

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

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Date: 6 Jan 91 02:24:54 GMT
From: zaphod.mps.ohio-state.edu!ceres.physics.uiowa.edu!iowasp.physics.uiowa.edu![e-mail]  (John B. Sigwarth)
Organization: Department of Physics and Astronomy, University of Iowa
Subject: GUERAP III software
Sender: [e-mail]
To: [e-mail]

I am looking for sources for the software GUERAP III.  This software
calculates the stray radiation scattered through an optical system
defined by the user.  I know of a commercially available source that
wants $1500. for their "improved" version.  They also told me that the
orginal software is in the public domain.  Does anybody know where a
public domain copy might be available?  E-mail to me directly and I will
summarize any responses to the NET if there is interest.  Thank you for
your help.
                               John Sigwarth
--
John B. Sigwarth               INTERNET:  [e-mail]
The University of Iowa              NSI:  IOWASP::SIGWARTH
Department of Physics and Astronomy
403 Van Allen Hall
Iowa City, IA 52242-1479                  [phone]

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

Date: 4 Jan 91 00:13:18 GMT
From: hpda!hpcuhb!hpihoah![e-mail]  (Jon Watts)
Subject: Re: Hi girls... (part 2)

I really shouldn't lower myself to responding to this kind of drivel, but
sometimes you just can't resist.
From: [e-mail] (Avery Colter)
>[e-mail] (Mark SOKOLOWSKI) writes:
>
>>    - Maximum speed: 750 mph (that's 1250 km/h) (around 2 gallons per
>>      mile at that speed, after rough calculations)
>
>And what do you do if you need to put on the brakes? Common wisdom is that
>a normal human's reaction time needs a sighting of danger at least 2 seconds
>before impact. To decelerate from 750mph in 2 seconds would be more Gs than
>the most air-hardened test pilot could handle.

About 17g, near the death limit.  Not to mention how you achieve it.  I don't
know where you get the 2 sec. from though,  I think human reaction time is
around 0.2 sec but that has nothing to do with how fast you slow down.  If you
do go from 750 mph to 0 in 2 sec. that gives you a stopping distance of ~1100
ft. not counting reaction time, you'd better be far sighted.

>
>Also, you must be Richie Rich to be able to afford a car which gets a half-mile
>per gallon.

Not that bad for someone who can afford a $10,000,000 car.

>
>>    - 0-60 in 0.5 sec (aspiration system on the tires to keep it glued..)
>
>120 miles per second squared. Again, this much acceleration would likely
>leave you crushed.
>

It's really not that bad, about 5.5g - nasty but indurable (with a gee suit and
proper training).

- Jon Watts

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

Date: Sun, 6 Jan 91 19:41:40 EST
From: John Roberts <[e-mail]>
Disclaimer: Opinions expressed are those of the sender
    and do not reflect NIST policy or agreement.
Subject: Re: Interplanetary travel


>From: John Roberts <roberts>
>Subject: Re: Interplanetary travel

>>From: cs.utexas.edu!news-server.csri.toronto.edu!utgpu!cunews!cognos!geovision![e-mail]  (Gord Deinstadt)

>>Fusion engines are just the thing for travelling about in the solar
>>system.  Since the ideal reaction mass is 4 times the (payload+
>                ------------------------------------------------
>>structure) mass, there is no point in having a higher-density fuel.
> ---------------
>>You just have to carry more reaction mass to compensate for the
>>reduction in mass of the fuel.  Consequently, for efficient (minimum-
>>energy) operation, fusion is just as good as antimatter, provided
>>the fusion reactor can be made light enough.

>>Gord Deinstadt  [e-mail]

>I don't understand why that should be considered an ideal ratio. By the
>classic equations, this should allow a total change in velocity of about
>1.6 times the exhaust velocity, but why is that a particularly good number?

After I posted that, it occurred to me that the concept of an ideal reaction
mass ratio might have some significance for a specialized type of problem.
Assuming a fixed mass for the rocket (minus reaction mass) and a fixed
amount of energy to drive the reaction mass, what amount of reaction mass
will result in the greatest total change in velocity for the rocket? I
don't believe there's a straightforward answer unless a further constraint
is added that the rocket operate with a fixed exhaust velocity.
It is also assumed that all the energy used is converted to kinetic energy.

Variables:    m1 = mass of rocket (not counting reaction mass)
              E1 = total energy available for rocket drive
              x  = reaction mass
              r  = mass ratio = x / m1
              Ve = exhaust velocity
              dV = total velocity change of rocket


Initial formulae:
   dV = Ve * ln((m1 + x) / m1)  (classical rocket equation)

   E1 = 0.5 * x * Ve^2          (total kinetic energy of exhaust)

Derived equations:
   Ve = sqrt(2 * E1 / x)

   dV = sqrt(2 * E1 / x) * ln(1 + (x / m1))

      = sqrt(1 / x) * ln(1 + (x / m1)) * sqrt (2 * E1)

      = sqrt(E1 / m1) * sqrt(2 / r) * ln(1 + r)        <-- useful form

It is possible to solve for r by finding the value that produces the
greatest dV, or by differentiating one of these forms and finding the
point where the slope equals zero, for example:

dV/dx = sqrt(2 * E1) * ((1 / ((m1 + x) * sqrt(x))) - (ln(1 + x / m1) /
           (2 * x^(3/2))))  (set m1 = 1, dV/dx = 0, solve for x).

By either method, I calculate that the ideal mass ratio r is 3.9215536345,
which I suppose is pretty close to 4.                   -----------------

With this ratio, and within the described constraints, you can hope for
a total change in velocity of  dV = 1.1380775 * sqrt (E1 / m1).
                               ------------------------------

While this math is very interesting, I'm not sure how applicable it is
to interplanetary travel. The underlying assumption of this approach seems
to be that energy is the most expensive resource in space travel, to the
extent that the relative availability of reaction mass is not a factor.
I suspect in many cases, the availability and expense of energy will be
less of a problem than that of reaction mass.

Does anyone know whether the math (and the conclusion) are correct?
Note that I did not include relativistic terms, so this applies only to
"low" velocities. Good luck to anyone wishing to include relativity. :-)
           John Roberts
           [e-mail]

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

End of SPACE Digest V13 #032
*******************