Acceleration Environment Coordinate System Used in NASA-STD-3000

This system is based on the direction a body organ (e.g., the heart) would be displaced by acceleration. Table II in this figure (and in particular, system 4, which is based on displacement of body fluids) explains the most commonly employed terms.

Figure 5.3.1-1 (Part 1 of 2) Acceleration Environment Coordinate System Used in MSIS

Acceleration Environment Coordinate System in picture format

Reference: 101, NASA-STD-3000 436

Figure 5.3.1-1(Part 2 of 2) Acceleration Environment Coordinate System Used in MSIS

LINEAR MOTION Direction of Acceleration Inertial Resultant of Body Acceleration
Acting Force Acceleration Description Reaction Force Verticular Description
  Forward +ax Forward accel. +Gx Eye Balls In
  Backward -ax Backward accel. -Gx Eye Balls Out
  Upward -az Headward accel. -Gz Eye Balls Down
  Downward +az Foorward accel. +Gz Eye Balls Up
  To Right +ay R. Lateral accel. +Gy Eye Balls Left
  To Left -ay L. Lateral accel. -Gy Eye Balls Right
ANGULAR MOTION
  Roll Right +p   -Rx Cartwheel
  Roll Left -p   +Rx  
  Pitch Up +q   -Ry Somersault
  Pitch Down -q   +Ry  
  Yaw Right +r   +Rz Pirouette
  Yaw Left -r   -Rz  

Reference: 380; NASA-STD-3000 435

Footnotes:
Large letter, G, used as unit to express inertial resultant to whole body acceleration in multiples of the magnitude of the acceleration of gravity.
Acceleration of gravity, g, = 980,665 cm/sec2 or 32.1739 ft/sec2.