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From: jon@cs.washington.edu (Jon Jacky)
Newsgroups: sci.military
Subject: Re: Some comments and questions on SDI
Summary: "Brilliant Pebbles" are currently 100 pounds, not grams
Message-ID: <10745@cbnews.ATT.COM>
Date: 30 Oct 89 02:51:26 GMT
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From: jon@cs.washington.edu (Jon Jacky)

> Henry Spencer (henry@utzoo.toronto.edu) writes of the "Brilliant Pebbles"
> scheme to orbit up to 100,000 100-pound antimissile satellites,
> "Correction, not 100 pounds, more like 100 *grams* ("pebbles", not "rocks")"

In the "Brilliant Pebbles" plan currently being studied by the SDIO, the 
pebbles are 100 *pounds*, not grams.  Or at least that's how they were 
described in the flurry of news stories that appeared last spring.  A NEW
YORK TIMES story ("What's next for `Star Wars'? `Brilliant Pebbles'", William
J. Broad, Tuesday April 25 1989, p. 19) includes an artist's 
conception of a "pebble", which the caption explains is about three feet long
and weighs 100 pounds.  The picture shows a torpedo-like object, which is 
mostly a tank of rocket fuel, with the sensor and "brilliant" computer stuck 
on the front.  The picture is captioned, "Source: Strategic Defense 
Initiative."  I think I recall seeing a photo of a model of that thing in
AVIATION WEEK about the same time.

Perhaps Henry is thinking of an earlier pebbles incarnation.  At the 
SDI "fifth birthday party" in March 1988, Livermore weapons scientist
(of X-ray laser fame) Lowell Wood rhapsodized about a pebbles scheme in 
which the satellites wieghed (or "massed") about 1.5 to 2.5 kilograms.
However, when the pebbles scheme surfaced again, in former SDIO director
James Abrahamson's "End of Tour" memo, they had become a lot bigger, and
there were a lot fewer of them (from "100,000" in Wood's scheme to "thousands"
in Abrahamson's memo).   Then there is the version in the NEW YORK TIMES
story, which probably represents someone's engineering judgment about what
it would actually take to implement the proposed pebbles functionality with
technology that is likely to appear in the next five or ten years.

With "pebbles" as with other SDI schemes, it is quite 
difficult to distinguish the actual projects that the SDIO is 
devoting significant money and effort to from the many
concepts, ideas and notions that are floated about, which are hardly more than
people speculating out loud.  It is not unusual for different versions of a
scheme referred to by a single name to differ by several orders of magnitude
in important technical characteristics.  

> (Henry notes that the launch requirements for orbiting large numbers of
> the larger-version pebbles are prodigious)

Indeed, that is a problem.

> Many of SDI's problems diminish greatly if interceptors are plentiful and
> need not be conserved

But others do not, and additional problems are implied by filling low earth 
orbit with huge numbers of very highly automated rocket-smashing machines.
The October, 1989 issue of TECHNOLOGY REVIEW and the current (I think 
November) issue of BULLETIN OF THE ATOMIC SCIENTISTS both contain articles 
critical of "brilliant pebbles", which include histories of the program.

- Jon Jacky, University of Washington, jon@gaffer.rad.washington.edu