ARMS-D-Request@MIT-MC.ARPA (Moderator) (01/11/86)
Arms-Discussion Digest Friday, January 10, 1986 8:06PM
Volume 6, Issue 17.3
Today's Topics:
See 17.1
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Date: Thu 9 Jan 86 22:20:28-PST
From: Jim McGrath <J.JPM@Epic>
Subject: Complexity measures
Reply-to: mcgrath%mit-oz@mit-mc.arpa
From: Jim McGrath <Mcgrath%mit-oz@mit-mc.arpa>
5. If you answered no to question 1, or hold SDI to
a substantially higher degree of reliability than existing
systems, then the logic fails. The problem I have with
this debate is that the anti-SDI people are not addressing
either of these two points adequately. On the former,
people have been concentrating on size of code for SDI.
From: Herb Lin <LIN@MC.LCS.MIT.EDU>
I haven't been. Parnas hasn't been. Who has been?
I would not blame people if they did however. Big things are
more complex than little things.
By far the most common measure of complexity that has been offered in
these discussion (whenerver a metric has been provided - often
complexity is simply claimed), it has been code size. You made a
point of that yourself in your Scientific American article (although
in that context you were concentrating specifically on the software
complexity issue, so there was no confusion). I have not read
Parnas's arguments yet, so refrain from comment, but almost every
computer science critic of SDI has concentrated on code to the
exclusion of other elements, proceding to generalize there (often
valid) concerns about software performance to system performance.
I can think of many programs that are large and LESS complex than
smaller programs (although they are exceptions). And I can thing of
many physical systems that are quite complex, but have quite simple
software. Until recently the phone network was almost entirely
implemented in hardware. Although people may dispute whether it is as
complex as SDI, surely you would not dispute that it is very complex
in some absolute sense?
Thus I think your statement is clearly wrong. Big things (in a
software complexity sence) are NOT necessarily more complex than
little things (if the little refers to software and the complexity
measure is system complexity). Until critics of SDI stop pretending
that software is everything, and concentrate on the system, they are
not going to be able to sell people their arguments.
Besides, AEGIS is enormously easier to test. Remember, it is a
real-time system. SDI will have to handle 10^6 potential targets
in 30 minutes. AEGIS is designed to keep track of 200 targets
within ~ a half hour flight time.
Aegis being a real time system (as opposed to SDI, which is a batch
system?) makes it ENORMOUSLY EASIER to test? Anyway, you are using
simple complexity measures again. First, an ocean environemnt (or a
land environment) is FAR more unpredictable than a space environment.
Thus realistic testing (i.e. testing under a good sample of
environmental responses) is, alone at least one dimension, far harder.
Second, I anticipate that the hardware involved in Aegis is far more
unreliable than hardware commonly used in space right now. While some
of that may be due to a trade off (Aegis hardware is designed to
survive battle conditions), a lot of it is due to either a sense that
the hardware can always be replaced (a mistaken sense, given the time
you would have under an attack to do so) or to the simple fact than an
ocean environment is pure hell on machines. Thus Aegis loses on that
dimension.
On the statistic you cite, the times involved are the same (which
makes it nice - no one can repair/reprogram either system (although it
makes me wonder more why people are resisting human involvement in
SDI, when it is clearly done in Aegis)). But the projectile numbers
are a bit misleading. First, Aegis is covering a limited zone. If
the SDI system was set up in a similar zone pattern, the number of
projectiles per subsystem would drop accordingly. Second, and far
more seriously, you are underestimating the role of the environment.
An ocean environment is bound to generate more false signals (birds,
etc...) from nature than a space environment. Finally, while we all
anticipate countermeasures in space, the environment hampers such
attempts (to give one example, maneuvering in space is very difficult
and expensive compared to doing so in the atmosphere), so the objects
that are there should be, individually, easier to track.
Jim
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Date: Thu 9 Jan 86 22:44:06-PST
From: Jim McGrath <J.JPM@Epic>
Subject: Summing up on SDI
Reply-to: mcgrath%mit-oz@mit-mc.arpa
From all these messages, I've come to two conclusions. First, that on
the whole, I tend to feel that SDI is a more complex system (mainly
because of its mission size) than existing ones, such as Aegis. But I
could be wrong (either way). And I do not believe that it is "orders
of magnitude" more complex than existing systems. Thus it would seem
that it could be built to existing system performance standards.
The second question is whether these standards are "adequate," and if
not can we improve upon them? It is clear that existing systems are
not being tested as fully as possible (Herb Lin's report on the Aegis
tests makes them appear to be a joke). I've already pointed out that
substantial testing of mid-course and terminal phases, far more
extensive testing than any of our other systems have received, can be
carried out. Thus, provided we have a proper commitment, even our
current testing technology can be better applied (with better results)
than we have done up until now.
To a large extent the standard you require depends upon your
definition of the mission of the system. Clearly the system was never
designed to make OUR nuclear weapons obsolete (just the Soviet's). So
under any mission we would probably retain a force sufficient to
destroy the USSR, and so can always fall back on MAD. Any reasonable
performance level would protect our weapons to a significant extent
(and if not, you can always keep a sub force). So the real question
is whether it can protect cities.
I would tend to doubt it, under a full and unimpeded Soviet attack.
But there are many scenarios (from accidental launch to a limited
(decapitation or counterforce) strike to a second strike (the first
perhaps going to Europe and/or China)) where it quite possibly could.
In any event, I am certainly not sure enough to either commit to SDI
deployment nor to terminate research. Since all SDI is at the moment
is research, I have no problem with the existing program. Still,
knowing how programs have a tendency to outlive their usefulness, I
think strong scrutiny is appropriate. But not mindless opposition.
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End of Arms-Discussion Digest
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