GR - a technical query (IG methods etc.)

[Monte Davis]

 > Struggling through the scene where Katje educates Slothrop in
rocket-lore, I was terminally baffled by this clause: "methods of computing
Brennschluss by IG and radio methods" (V223.11). 
 
   
IG = INERTIAL guidance, i.e. guidance derived from inertia (Newton's first
law)... measuring the forces on a gyroscope, which attempts to maintain the
spin and orientation it had before the rocket's flight started. Put those
forces (and the time during which they are sensed) through some arithmetic,
and you get the current position and velocity of the rocket... leading to
the right moment to shut down the engine (Brennschluss).
 
Alternately, the guidance system can receive signals from two or more radio
sources (a la GPS, today's Global Positioning System) and use trigonometry
to calculate its position. This was planned for the V2 and tested, but never
became operational AFAIK. Used extensively by bombers. 
 
Either way, the transition from *powered* and *controlled* flight to
*ballistic* trajectory -- governed only by gravity, all its future implicit
in this moment,  fated and irreversible -- is a central metaphor, arguably
*the* central metaphor, of the book. Or at least that's the subtle hint *I*
take from the title :-)
 
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