[ODE] Quaternion Integration

[John Lagerquist]

It appears that NASA has a quaternion integration method that does not
require normalization between integration steps.  Does anyone have any
information on this technique?  Their webpage
(http://ettc.usc.edu/dryden/tos/closedform.html) states:

"NASA's technology represents a substantial improvement over traditional
methods of integrating 4-D kinematics equations. Those methods solve the
quaternion kinematic equations in a way that does not automatically preserve
the unit normalization of the quaternion. These methods are therefore
inherently prone to error and difficult to correct. Such traditional methods
are computation-intensive because of the substantial amount of error
correction needed to compensate for analytical drift. NASA's integration
method preserves the mathematics of the quaternion space that it creates and
therefore introduces no error associated specifically with non-preservation
of the quaternion norm. As a result, error correction associated with
normalization is not needed in the NASA method"

John