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Missile Defense

Technology has always found its greatest consumer in a nation's war and defense efforts. Since the last attempts at a "Star Wars" defense system, has technology changed considerably enough to make the latest Missile Defense initiatives more successful? Can such an application of science be successful? Is a militarized space inevitable, necessary or impossible?

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rshow55 - 08:29am Jan 22, 2003 EST (# 7897 of 7899)
Can we do a better job of finding truth? YES. Click "rshow55" for some things Lchic and I have done and worked for on this thread.

Even a sheaf of solutions obtained for various inputs and system parameter values, however, may not clearly show the designer how to obtain the most satisfactory behavior, and sometimes unexplored, minor changes in the inputs or the system parameters may result in very marked changes to the performance of the system.

( the bolded sentence above is an example of engineering understatement - what Graham and McRuer meant was clear to engineers. No one had any machine based nonlinear control system of the level of complexity they needed that was even remotely safe - and ones complicated enough to do the jobs they usually wanted to do were so unstable and treacherous that no one could believe it - or understand why the explosive instabilities and other perversities were as bad as they were. That remains the case, forty years later. On the other hand, everybody knew then that animals handled many such problems breathtakingly well. The military implications, and safety implications, of these facts have concerned me for a long time - and I was assigned to deal with this nexus of problems. )

" The main task of the engineering analyst is not merely to obtain "solutions" but is rather to understand the dynamic behavior of the system in such a way that the secrets of the mechanism are revealed, and that if it is built it will have no surprises left for him. Other than exhaustive physical experimentation ( note - N! increases as fast as it does ) this is the only sound basis for engineering design, and disregard of this cardinal principle has not infrequently led to disaster. In his function of understanding, the human analyst does not have any competition from the computing machinery which, if it is available, can enormously extend his power.

"Some of the most unpleasant surprises of which nonlinear control systems are capable are

1. divergent instability

2. limit cycles

3. multiple equilibrium points.

"and it needs to be continually borne in mind that, as far as nonlinear machines are concerned, the behavior is determined by the input-system combination. An understanding of the conditions under which input-system combinations may produce these surprises is facilitated by a parametric study of the system . . . .

Chapter 10 of Analysis of Nonlinear Control Systems by Dunstan Graham and Duane McRuer continues - in essence the summary is that if nonlinearities are small enough - and if the system is well understood enough, instabilities can be controlled within tolerable limits for a particular set of circumstances - limit cycles can be small enough to accept, and answers can be close enough to fit well enough defined purposes.

rshow55 - 08:30am Jan 22, 2003 EST (# 7898 of 7899)
Can we do a better job of finding truth? YES. Click "rshow55" for some things Lchic and I have done and worked for on this thread.

We haven't gotten much beyond Dunstan and McReur on these problems, as they stated them, since that time - because of the way the world unchangeably is. But we can get very good solutions, in human terms - if we're clear about what we want, have sensible priorities, and take care. For large perturbations of nonlinear systems that are not controlled at a higher level, divergent instability is the rule - multiple quasi-equilibrium points are not surprises, but the overwhelming expectation - and limit cycles are the best, as a practical matter, that anybody can actually hope for - or can actually get.

There are very good arguments for moving slowly, and taking our time. For making sure that people understand what they are doing - and do it carefully - and with appropriate fear of mistakes - and knowledge that some mistakes are available. When we do the things that we can do - that we do successfully again and again - and apply them to the problems of international conflict we can do much better than we've done. But fast, draconian moves that assume that any human organization (including the US military) can predict events, or control dangerous instabilities or costs are essentially certain to produce new problems. Problems that are now uncomfortably close to explosive instability - and huge agony and carnage. We have to do better than we've done in the past.

Situations that look stable often are not stable when you check them. Experience shows that systems that look terribly unstable usually are at least as unstable as they look - if they are not frozen, or subject to external controls.

Lighting the Fuse on Iraq http://www.nytimes.com/2003/01/22/opinion/22WED1.html

" Given the risks of military action and the widespread public opposition in the United States and abroad to acting without Security Council support, Mr. Bush should not be in a rush to go to war."

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