Hmm, well the TOS writer's guide might not support my theory:
The writer's guide is posted here:
http://captainrobertapril.angelfire.com/Star_Trek_Writers_Guide.pdf
DEFLECTORS
The primary "defensive shield" of the U.S.S. Enterprise.
It is, in effect, an invisible force barrier around the
Enterprise which protects the vessel from anything but
the most sophisticated and powerful weapons. It is
automatically activated by the ship's sensors when an
unknown danger approaches. Note: The ship's Transporter
cannot be used while the deflector screen is operating.
If the vessel should be under attack, the power of the
deflector shield can be considerably increased, but at
a commensurate loss in ship's power and at maximum
shielding can only be maintained for a limited time.
The ship also has "navigational deflector beams" which,
guided by "navigational scanners", sweep out far ahead
of the vessel's path through space, deflecting from the
ship's course meteoroids, asteroids, or space debris
and ether objects which would cause damage should the
vessel strike them at this enormous speed. These are
all fully automated, operated by the vessel's computers.
The writer's guide is posted here:
http://captainrobertapril.angelfire.com/Star_Trek_Writers_Guide.pdf