GR - a technical query (IG methods etc.)

[Michael Lee Bailey]

>. Advanced versions
> of the so-called "IG" guidance integrated twics,

that should be "twice"

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apologies if the excerpt from pg 306 constituted a spoiler

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also, I think IG was in common use as an acronym
for "Inertial Guidance" (and maybe still is,
I'm no rocket scientist)
http://en.wikipedia.org/wiki/Inertial_guidance

"Inertial guidance systems were originally developed for navigating rockets. American rocket pioneer Robert Goddard experimented with rudimentary gyroscopic systems. Dr. Goddard's systems were of great interest to contemporary German pioneers including Wernher von Braun.

"...by tracking both the current angular velocity of the system and the current linear acceleration of the system measured relative to the moving system, it is possible to determine the linear acceleration of the system in the inertial reference frame. Performing ***integration*** on the inertial accelerations (using the original velocity as the initial conditions) using the correct kinematic equations yields the inertial velocities of the system, and ***integration again*** (using the original position as the initial condition) yields the inertial position. In our example, if the blindfolded passenger knew how the car was pointed and what its velocity was before he was blindfolded, and he is able to keep track of both how the car has turned and how it has accelerated and decelerated since, he can accurately know the current orientation, position, and velocity of the car at any time."