Re: go interceptors!

From: James Rogers (
Date: Fri Jul 20 2001 - 11:48:25 MDT

On 7/19/01 9:17 PM, "John Clark" <> wrote:
> Then why did the military insist that the test decoy by round and not cone
> shaped
> like the real warhead and like any self respecting enemy decoy would? And why
> did they insist there be only one decoy?

I wasn't going to explain it in detail, but why not. Inflatable decoys have
a number of bang-for-the-buck issues that make spherical decoys the obvious
choice. Note that these days balloon decoys primarily serve to generate an
illusion for optical sensors.

The reason spherical decoys work is that from many aspects, the cone shaped
warhead looks essentially identical to the spherical decoy to the optical
sensor. Therefore, a sphere always takes on a theoretically valid profile
of a real warhead, thereby serving its purpose.

A cone shaped decoy balloon *could* work, but there are a lot of practical
reasons why it doesn't. The biggest reason is that it is difficult to make
a cone-shaped decoy balloon act like a real warhead on the sensors without
it becoming heavy and expensive. A real warhead has a stable aspect with
respect to its trajectory. With a cone-shaped decoy, a sensor can detect
any rotation of the decoy that is inconsistent with a real warhead because
the asymmetry of the shape makes it possible to do this optically. Not so
with a sphere. Since the balloons are released and then inflate while
floating freely, it would require the addition of an inertial guidance
package to the cone-shaped balloon to make sure that it was actually stably
oriented in the right direction to fool the sensors.

Of course, if your sensor systems can discriminate between balloons and
warheads regardless of shape, then it doesn't really matter what you do with
the balloons. This is frequently the case with current technology, so in
that respect the decoy WAS a dog and pony show for the most part.

In any case, the decoy was largely irrelevant to the test. The
discrimination and sensor technologies are well-proven and most are
deployed, at least in part, in other military systems. The decoy was
probably added to make the test look spiffier than it was. What they are
really testing is the physical engineering of the vehicle, as that is the
unproven part.

I'm not a big cheerleader for SDI, but you are grossly mischaracterizing the
technology. Let us at least keep that part of the discussion reasonably

-James Rogers

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