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From: henry@utzoo.UUCP (Henry Spencer)
Newsgroups: net.space
Subject: SETI vs. starflight
Message-ID: <6315@utzoo.UUCP>
Date: Wed, 22-Jan-86 20:35:05 EST
Article-I.D.: utzoo.6315
Posted: Wed Jan 22 20:35:05 1986
Date-Received: Wed, 22-Jan-86 20:35:05 EST
Organization: U of Toronto Zoology
Lines: 69

In the recent joint issue of Communications of the ACM and IEEE Computer
(Nov 1985, both) appears a paper on the search for extraterrestrial
intelligence (SETI):  "Signal Processing in SETI", by D.K. Cullers,
Ivan R. Linscott, and Bernard M. Oliver, of NASA Ames, Stanford, and
Hewlett-Packard respectively.  By and large it's pretty good, and worth
reading, which is half the reason why I bring it up.

The other reason is one paragraph of incredible nonsense, near the
beginning:

	At present spacecraft speeds (circa 1e-4 c), a round-trip to
	the nearest star would take about 80,000 years.  At 0.32c the
	trip could be made in 30 years, but even with a 100 percent
	efficient drive, the energy required is the annihilation
	energy, mc^2, of the payload.  For a thousand-ton ship, this
	is enough to supply all US energy needs for a millenium.  The
	extreme cost of interstellar travel, even with no technological
	limitations save those imposed by natural law, probably explains
	"their" absence here and casts grave doubt on our ever reaching
	the stars ourselves...

This is either political propaganda -- which I had thought beneath such
eminent authors in a technical publication -- or appalling ignorance.
The numbers are probably correct (I have not checked them, but they sound
about right), but the conclusions drawn from them are total bullshit.
An hour's browse through back Interstellar Studies issues of JBIS, or ten
minutes' inspection of the Project Daedalus report, or attending just one
of Robert Forward's talks on advanced propulsion, would reveal this at once.

"All US energy needs for a millenium", at *what* demand?  Today's demand?
1940's demand?  985 AD's demand?  If it's 1940's demand, then the total
energy requirement is *one* large modern power plant running for a decade
or so.  Hardly an exorbitant investment.  Obviously they mean today's demand,
but it is worth emphasizing that the energy resources at our command have
grown TEN-THOUSANDFOLD in less than fifty years.  One large modern power
plant, *idling*, puts out more power than the entire US did in 1940.  If
this trend, or anything remotely resembling it, continues, then the energy
resources needed for starflight will pose little problem soon.

Furthermore, the authors don't seem to appreciate the power levels involved
in even today's primitive rocketry.  A single Space Shuttle Main Engine puts
out 5-7 gigawatts of power.  A Saturn V at takeoff was FORTY gigawatts of
useful output -- over a tenth of the entire power production of the US.
Handling enormous energies is nothing new in space propulsion.

Robert Forward, who has studied the matter professionally as a USAF
consultant on advanced space propulsion, says that antimatter propulsion
is within our reach with today's technology.  Antimatter production would
be extremely expensive, but you don't need much.  At $50M/mg (yes, that's
millions per milligram), antimatter is competitive with Earth-launched
hydrogen/oxygen mix for in-space propulsion.  At $20M/mg, it's competitive
with fission rockets.  At $10M/mg, it's competitive with fusion rockets.
Forward indicated that at least the first of these numbers, and possibly
all three, look possible with current accelerator technology.  Antimatter
handling needs work, but doesn't appear to need breakthroughs.  (Really
large-scale production would be simpler and safer in space, mind you.)

And if we are on the brink of starflight -- reading JBIS will tell you
that there are *dozens* of different schemes for interstellar propulsion
that look viable -- what about civilizations millenia older than ours?
"Their" absence here is a considerable mystery, which has occasioned much
debate in recent years, but the "extreme cost" of interstellar travel just
does not suffice as an explanation.

"Antimatter rockets will take us to the stars.  *This is no longer
science fiction*." -- Forward
-- 
				Henry Spencer @ U of Toronto Zoology
				{allegra,ihnp4,linus,decvax}!utzoo!henry