Space & Astronomy/Space and Astronomy (October 1993).iso/pc/text/spacedig/v13_2/v13_296.txt

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Subject: SPACE Digest V13 #296

SPACE Digest                                     Volume 13 : Issue 296

Today's Topics:
                Re: "Follies"
              Re: More cost/lb. follies
               Re: He3 on Moon?

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Date: Tue, 19 Mar 91 11:10:17 EST
From: John Roberts <[e-mail]>
Disclaimer: Opinions expressed are those of the sender
    and do not reflect NIST policy or agreement.
Subject: Re: "Follies"


>From: [e-mail] (Nick Szabo)
>Subject: More cost/lb. follies

>[Fraering Philip writes:]
>>Two comments:
>>
>>1. Okay, I want to see the facts on that assertion about the limiting
>>factor in chemical rocket price, and to several different decimal
>>places. To paraphrase RAH, it's math, or it's opinion.

>It is up to those requesting $billions for rocket programs to prove
>they _can_ lower launch costs.  It is not up to me, requesting no money, to
                                                     -------------------
>prove they can't.

Not quite. If you were simply *not requesting money*, I would agree. But
you are actively *requesting 'no money'*, in other words urging that advanced
chemical rocket research projects, even those that have won approval for
government funding, should have all their money taken away, so it can be spent
exclusively on the non-chemical-rocket drives you like. Some of these chemical
rocket projects have put together detailed and well thought-out descriptions of
what they hope to gain - and some have already won at least a degree of
approval from Congress. If it is your specific goal to kill off these projects,
then it is indeed up to you to demonstrate that they are no good. And merely
stating that chemical rockets are *obviously* a dead-end technology, so you
don't have to know any of the details, is no way to go about it.

Please note: I *approve* of research on the technologies you advocate, and
think that a lot more money should be spent on them than is being spent now.
But I also think it's foolish and short-sighted to throw away further progress
in what we already know works. It could well turn out that their chief
"advantage" is that they haven't yet had to prove their merit in actual
full-scale demonstrations.  We had plenty of recklessly throwing away the
old when we gave up on the Saturn V (and in fact tried to give up on all
ELVs) - let's not repeat that mistake. Sure the exotic technologies have a lot
of potential - let's sell them on their own merit.

>However, the numerical argument is
>straightforward.  The theses are:

>* We need 4 orders of magnitude drop from today's costs for space
>  colonization to be affordable.

Four orders of magnitude would be nice, but I don't see what makes it the
single "magic number". There are many types of space colonization possible,
some of which could get along with significantly higher transportation costs.
For instance, why should we wait until transportation is so cheap that everyone
could get annual visits home? Some of the serious colonization proposals would
be extremely Spartan, at least in their first decade or two.

>On the first point, divide the cost of a hypothetical Shuttle/OTV
>trip to L-5 ($40 million/person) with round trip first-class from
>Tokyo to New York ($2,000/person) to get 4 orders of magnitude.

You have previously implied that this was comparable to travel costs for early
European settlers going to North America - I suppose you could find some
item available for sale now and then from which you could reconstruct a
price index to support your point, but in general I think travel was
relatively much more expensive then than air travel is now. Remember
that many colonists were willing to obtain passage by selling themselves
into indenture - basically limited-term slavery, the usual term being seven
years. I don't know about you, but I'd be very hesitant to work for seven years
just to get a crummy plane ticket to Tokyo at current prices. Playing around
with the numbers, if we accept the premise that some people will be willing
to colonize if it costs the equivalent of seven years' labor just to get
set up, and placing a more modern US middle-class labor valuation at up
to $100000/year (salary x multiplier, where multiplier is in the neighborhood
of 3-5), then perhaps we can get viable colonies going (further assuming
the eventual utilization of local resources, of course) with only two
orders of magnitude drop in launch costs. Many people do consider two
orders of magnitude to be within the realm of possibility for chemical
rockets. And chemical rockets have the ability to perform functions some of
the other options can't - such as getting live humans into space.

The more I look at your unbending insistence on 4 orders of magnitude launch
cost drop, the less I like it. If it's a *goal*, that's fine, but you have
set it up as a *standard*, and have effectively been urging the abandonment
of work aiming toward systems that could drop costs by "only" a factor of
10 or 100. I'm sorry, but I think there would be a *lot* of benefit to
dropping costs by that amount. Maybe it wouldn't be quite enough for your
commuters' space colonies, but I think there are a lot of things that can
and should be done in space that are not 100% directed toward human
colonization. And even for human colonization - surely we can get something
done without having to cut costs to ~50 cents per pound!

>* Chemical rockets can provide less than an order of magnitude drop
>  between now and the end of the 21st century

>On the second point, several methods will derive a similar result.
>Back-of-the-envelope numbers, within +/- 50% will give sufficient
>precision to demonstrate the point.


>* Take the curve of rocket costs/lb. ($1991).  Project it into the future.
>  1960 = $12,000/lb., 1970 = $8,000/lb., 1980 = $6,000/lb.,
>  1990 = $5,000/lb, 2000 = $4,250/lb., ....2030=$3,000/lb.,...
>  2090 = $2,000/lb., ....

Similarly, for linear launchers and laser launchers -
* Take the curve of costs/lb. to LEO ($1991).  Project it into the future.
  1960 = infinite, 1970 = infinite, 1980 = infinite,
  1990 = infinite, 2000 = infinite, ....2030=infinite,
  2090 = infinite, ....

This is not to say that I feel such launchers will always be infinitely
expensive, but that I think extrapolating curves from the past is generally
a very poor way to predict future costs, given continual advances in
technology and shifts in design goals and investment patterns. You may
protest that the reason the ground-powered launch techniques are not
currently available (and thus of finite price) is that nobody has yet
worked really hard and invested a lot of money in accomplishing this goal.
My reply would be that nobody has yet worked really hard or invested a lot
of money in greatly reducing per-pound chemical rocket launch costs either.
Quite a few people have pointed this out to you, and you have ignored it.
(The Shuttle started out largely as such an effort, but was subverted by its
DoD sponsors into stressing performance over price, which as we know painfully
well is no way to minimize price.) There *is* increased interest now in
reducing per-pound chemical rocket launch costs - for instance the expanded
Delta and Titan designs described by Allen Sherzer (with hope for up to 2-3X
drop in cost/pound, and availability in perhaps only a few years), and ALS
or the new technology launcher system (with development expected to take about
a decade, and perhaps as much as 10X reduction in launch costs). So if you're
going to extrapolate costs from the past, and yet allow that future trends
will permit the current curve for exotic launchers (flat at infinity) to
change, you must also allow that future trends may allow the curve for
chemical rocket launchers to change too.

>* For similar payload sizes, the cost of building an internal-chemical-powered
>  air vehicle is roughly a function of the vehicle mass/payload
>  ratio.  For example, we can derive the cost of a reusable rocket, with 1/3
>  the payload and 10 times mass, from the cost a 747:
>  ($100 million)*(30/1) = $3,000 million
>  which is about the actual cost of building a Shuttle.  Due to
>  the scientific limits in the exhaust velocity (and thus energy
>  efficiency) of chemical rockets, the payload/mass ratio cannot
>  be significantly increased.
>* The cost of an internal-chemical-powered land or air vehicle is
>  typically 3 orders of magnitude higher than the cost of its fuel load
>  (**2 orders of magnitude for expendable vehicles).
>  eg:
>    car: $10,000     <=>    tankfull of gas $10
>    747: $100 million <=>    full load of jet fuel $50,000
>    reusable rocket: $3,000 million <=> rocket fuel $3,000,000
>    ** expendable rocket: $100 million <=> rocket fuel $1,000,000
>  Use-once-and-discard forms of transportation have to break
>  the curve to be competitive with reusables.

These last two arguments are an attempt to eliminate technical details,
find a few regularities in existing systems, deduce that these regularities
must be natural economic laws, then apply them to future systems. Max Hunter
uses this line in some of his arguments, and I don't care for it when he does
either. I just don't see a benefit from deliberately avoiding the technical
details in order to obtain some high level of abstraction, other than the
ability to quickly and easily spew out great quantities of numbers of dubious
value. And economic theory is far less solid than models of technical
advances - as someone once pointed out, the US is full of stock market analysts
who demonstrably have no idea what the market is going to do next, though
they can all confidently explain why it did what it just did.

For the idea of vehicle cost being a function of the cost of a tank of fuel,
if there's any validity to it at all, then it must be a function of underlying
factors, such as design constraints, intended use, and the physical properties
of the medium through which it travels. It would be foolish to ignore these
details, for if you just assume it to be a universal principle, then you must
fit in all vehicles, such as boats, horses, etc. Looking at the details, it
could well be that the apparent identical multiplier for cars and airplanes
is just a coincidence, or that a comparable multiplier for advanced chemical
rockets should be very different. In any event, trying to apply such a number
to a future system is of very limited value, especially if you try to use it
as a guide for design. Imagine using this formula as an explanation for why
cars that use premium gasoline cost more than cars that use regular gas,
or designing a new car with a gas tank only half normal size, on the grounds
that this should cut total vehicle cost by around 50%.

>Until we develop a method much better than chemical rockets, we must
>be damned smart about what we launch, and search for all opportunities
>to let the solar system do the work for us.

>Nick Szabo            [e-mail]
               John Roberts
               [e-mail]

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

Date: 20 Mar 91 00:20:28 GMT
From: orca!oscar![e-mail]  (Bob Pendleton)
Subject: Re: More cost/lb. follies

Path: oscar!bpendlet
Newsgroups: sci.space
Distribution: world
Followup-To:
References: <[e-mail]> <[e-mail]>
From: [e-mail] (Bob Pendleton)
Reply-To: [e-mail]
Organization: Evans & Sutherland Design Systems
Subject: Re: More cost/lb. follies
Keywords:

Knowing full well that posting into a flame fest is a good way to get
burned he still feels this overwhelming urge to post. Oh my.

I'd like to say I agree with some points posted by most everybody.
Nick Szabo has pointed out that all our current rockets are right at
their technical limits. He's right, they are. He then uses that fact
to support his argument that chemical powered rockets cannot become
cheap enough to make space travel economically possible. Well, at
least not in his life time.

Others, Henry especially, have argued that Nick is wrong. They've
pointed out the work of Max Hunter and others that indicate that
chemical rockets can be made cheap enough to make space travel
economically possible in our life times. I happen agree with Henry on
this.

Look at where our rockets come from. They are mostly military rockets.
Military rockets are built on the hairy edge of the possible because
of outside constraints. Not because of anything having to do with the
technical limits of rockets.

Take a look at MX. When the MX was being designed they had a set of
constraints they had to live with. It had to fit in a mobile
transporter and be tube launched.  That meant that it had to be
designed to get the absolute most performance out of a fixed weight
and size.

Why did they have to get the most performance? Because political
decisions could wind up putting MX anywhere inside the continental US
and it still had to beable to reach it's targets.

So they went all out with high tech filament wound cases and
carbon-carbon nozzles, and extendable exit cones, and high energy
fuels to get the most out of the weight and size budget. They produced
a very high tech rocket designed right on the hairy edge of the
possible.

This is true of Atlas, Titan, and Delta (aka Thor). Every other US,
and I dare say European, rocket has it's roots in the same engineering
culture that designed all our war rockets. They only really know how
to design this way. Even the people running the ALS program realize
that the "hairy edge" design culture is so prevalent that it endangers
the project. They say they are taking special precausions to avoid its
influence. I don't think they're succeeding.

Hairy edge engineering is expensive, and it's prone to failure. So I
understand where Nick gets his ideas.  But that's not what the Max
hunters of the world are talking about.

Throw away the "hairy edge" mentality. Think about ocean liners
instead of airplanes.

Think about the problem of building a lighter than air ship out of
stainless steel. Could you do it? Could you do it if it had to fit
inside a Titan II silo? No I don't think you could.  If you did the
walls would be so thin you could see through them. The Titan rockets
use chemical etching to get their tank walls thin enough.

What if you could build it any size you want? Could you do it then?
Maybe you could.  Maybe this is a rediculous example. :-) Think about
the cube-square law. If you can build any size you want then the cube
square law can give you an enormous volume to structure ratio. Maybe
good enough to build a stainless steel balloon.

Rockets are a lot like stainless steel balloons. The dominant factors
in rocket design are exhaust velocity and mass ratio. There are lots
of other factors and I'm ignoring them deliberately. So flame me:-)

Exhaust velocity is pretty much a given if you are talking about
chemical fueled rockets. There isn't much you can do to increase it
without going out on the hairy edge where things like the SSME live.
But there have been postings to this group about the $50,000 5,000,000
pound thrust motor developed by Boeing back in the late '60s. I'll bet
it's ISP wasn't great compared to a SSME. But I'll bet it's margins
were a lot better and the price is right. We can build cheap motors
with enormous thrusts.

So the only thing you can do is improve the mass ratio. Remember the
stainless steel airship and the cube-square law? Think big. Think
about dry docks instead of hangers. If you build big enough you can
build rugged structures with very high mass ratios and payloads to
match. If you want to build space ships, build space SHIPS. Huge sea
launched vehicles built with ship building techniques. Single stage
resuable vehicles that burn lots of fuel to make up for their rugged
structure and huge size. Reusable vehicles that land on the ocean.
Ships whose density is so low after their fuel is spent that they can
reenter slowly so their steal hulls can stand the reentry heating.

Reusable, rugged, and low tech rockets should give a low cost per
pound to orbit.  From what I've read I'm convinced that this approach
can work.

        Yours in Murphy

            Bob P.

--
              Bob Pendleton, speaking only for myself.
   [e-mail] or decwrl!esunix!bpendlet or utah-cs!esunix!bpendlet

                         Tools, not rules.

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

Date: 20 Mar 91 02:52:03 GMT
From: stanford.edu!unixhub!slacvm![e-mail]  (Jon J Thaler)
Subject: Re: He3 on Moon?

In article <[e-mail]>,
[e-mail] (Horowitz, Irwin Kenneth) says:

>>I'd like to do that exercise, but I don't know:
>>1: The flux of He3 in the solar wind,
>>2: The residence time for He3 in the lunar soil.
>>
>>Please supply us eager NetNews fans with these numbers.
>When I said it was left as an exercise for the reader, I meant it was left as
>an exercise for the reader.  Get up from that computer terminal and walk to
>the local science library (or better yet, an astronomy library) and look up
>those values for yourself! :-)  Shouldn't be too difficult...just need the
>total flux of the solar wind, and the percentage of He3 in the solar wind.
>As for the "lifetime" of He3 in the lunar soil, I can't think of any loss
>mechanisms that would necessarily apply (except perhaps evaporation and
>thermal escape from the "lunar atmosphere").  He3 is a stable isotope, so
>it won't decay radioactively.

That's the crux of the problem.  Since the He3 in the solar wind will only
penetrate a few microns into the lunar surface, it is probably going to
escape (due to thermal effects) very quickly.  Thus, I'd expect only
microscopic amounts of He3 to be present at any time.  (It sounds to me like
you don't know the answer either...)

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

End of SPACE Digest V13 #296
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